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BULLETIN
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PIIBMCATION TRIMESTRIELLE
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4® SÉRIE, T. 17, 1995, (1-4)
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VIP Symposium international, Parc de Miguasha, Québec
Études sur les Vertébrés inférieurs
Coordonné par Marins Arsenault, Hervé Lelièvre et Philippe Janvier
Reconstitution de deux
Dunkleosteus terelli,
Placodermes géants
poursuivant
un Cladoselache.
Dessin de
© Joseph WINANS
BULLETIN DU MUSÉUM NATIONAL D 'HISTOIRE NATURELLE, Paris
4® sér., 17. 1995, n° 1-4, section C, (Sciences de la Terre : Paléontologie, Minéralogie, Géologie)
Vlith International Symposium
Studies on Early Vertebrates
9-22 June 1991, Miguasha Parc, Québec
Marius ARSENAULT, Hervé LELIÈVRE and Philippe JANVIER
(Editors)
CONTENTS
M. Arsenault, h. Lelièvre & Ph. Janvier. — Forewords . . . . . . VII
P- Y. Gagnier. — Ordovician Vertebrates and Agnathan phylogeny . 1
V. Karatajute-Talimaa & N. Predtechenskyj. — The distribution of the Vertebrates
in the Late Ordovician and Early Silurian palaeobasins of the Siberian Platform . . 39
N. -Z. Wang. — Silurian and Devonian jawless craniates (Galeaspida, Thelodonti) and
their habitats in China . 57
R. K. Carr. — Placoderm diversity and évolution . 85
K. Dennis-Bryan. — Some comments on the Placoderm parasphenoid . 127
Ph. Janvier. — The brachial articulation and pectoral fin in Antiarchs (Placodermi) . . . 143
H. Lelièvre. — Description of Maideria falipoui n. g., n. sp., a long snouted brachy-
thoracid (Veriebrata, Placodenrii, Arthrodira) from the Givetian of Maider (South
Morocco), with a phylogenetic analysis of primitive brachythoracids . . 163
O. Hampe. — Plicatodus jordemi n. g., n. sp., a new xenacanthid shark from the Lower
Permian of Europe (Saar-Nahe Basin, Gemiany) . 209
D. Esin. — Ontogenetic development of the squamation in some Palaeoniscoid fishes . 227
M.-M. ChanG. — Diabolepis and its bearing on the relationships between porolepiforms
and dipnoans . . . . . 235
E. -C. Hitchcock. — A functional interprétation of the anteriormost vertebrae and skull
of Eusthenopteron . 269
O. A. Lebedev. — Morphology of a new osteolepidid fish from Russia . 287
A. Kemp. — On the neural crest cells of the Australian lungfish . 343
J. A. Clack & M.I. COATES. — Acanthostega gunnari, a primitive, aquatic tetrapod ? . . 359
— IV —
M.I. COATES & J. A. Clack. — Romer’s gap: tetrapod origins and terrestriality . 373
R. L. Carroll. — Problems of the phylogenetic analysis of paleozoic choanates . 389
A. Blieck, D. Goujet, Ph. Janvier & F. Meilliez. — Revised Upper Silurian-Lower
Devonian ichthyostratigraphy of northem France and Southern Belgium (Artois-
Ardenne) . 447
C. Derycke, A. Blieck & S. Turner. — Vertebrate microfauna from the Devonian/Car-
boniferous boundary stratotype at La Serre, Montagne Noire (Hérault, France) .... 461
C. Derycke, D. Brice, A. Blieck & N. Mouravieff. — Upper Givetian and Frasnian
ichthyoliths from Bas-Boulonnais (Pas-de-Calais, France): preliminary records . 487
S. Turner & G. -S. Nowlan. — Early Silurian microvertebrates of Eastern Canada ... 513
The articles of the présent volume must be cited as follows:
Gagnier, P- y., 1995. — Ordovician Vertebrates and Agnathan phylogeny. /n: Studies on Early
Vertebrates (Vlith International Symposium, 1991, Miguasha Parc, Quebec), M. Arsenault,
H. Lelièvre & Ph. Janvier (eds). Bull. Mus. natl. Hist. nat., Paris, 17 (C) 1-4: 1-37.
BULLETIN DU MUSÉUM NATIONAL D'HISTOIRE NATURELLE, Paris
4' sér., 17, 1995, n" 1-4, section C. (Sciences de la Terre: Paléontologie, Minéralogie, Géologie)
VIF Symposium international
Études sur les Vertébrés inférieurs
9-22 juin 1991, Parc de Miguasha, Québec
Coordonné par Marins ARSENAULT, Hervé LELIÈVRE et Philippe JANVIER
SOMMAIRE
M. Arsenault, h. Lelièvre & Ph, Janvier. — Avant-propos . VII
P.-Y. GagNIER. — Les Vertébrés ordoviciens et la phylogénie des Agnathes . 1
V. Karatajute-Talimaa & N. Predtechenskyj. — La répartition des Vertébrés dans
l'Ordovicien terminal et le Silurien inférieur des paléobassins de la Plateforme
sibérienne . 39
N. -Z. Wang. — Les Crâniates sans mâchoires du Si luro- Dévonien (Galeaspida et Thelo-
donti) et leurs habitats en Chine . . . 57
R. K. Carr. — Diversité et évolution des Placodermes . 85
K. Dennis-Bryan. — Remarques sur le parasphénoïde des Placodermes . 127
Ph. Janvier. — L’articulation brachiale et la nageoire pectorale chez les Antiarches (Pla-
codermi) 143
H. Lelièvre. — Description de Maideria faliptnti n. g., n. sp., un brachythoraci à museau
long (Vertebrata, Placodermi, Arthrodira) du Givétien du Maider (sud marocain) et
analyse phylogénétique des brachyhtoraci primitifs . 163
O. Hampe. — Plkatodus jordani n. g., n. sp., un nouveau requin xénacanthe du Permien
inférieur d’Europe (bassin de la Sarre, Allemagne) . . . . . 209
D. EsiN. — Développement ontogénétique de la squamation chez quelques poissons
paléoniscides . 227
M.-M. Chang — Diabnlepis et sa signification quant aux relations de parenté entre les
Porolépiformes et les Dipneustes . 235
E. -C. Hitchcock. — Interprétation fonctionnelle des vertèbres les plus antérieures et du
crâne d' Eusthenoptewn , . * . 269
O. A. LEBEDEV. — Morphologie d’un nouvel Ostolepididae de Russie . 287
-VI-
A. Kemp. — À propos des cellules de la crête neurale chez le dipneuste d’Australie . . . 343
J. A. Clack & M.I. COATES. — Acanthostega gunnari, est-il un tétrapode aquatique pri¬
mitif? . 359
M.I. COATES & J. A. Clack. — La lacune de Romer : les origines des tétrapodes et
l’adaptation à la vie terrestre . 373
R. L. Carroll. — Les problèmes de l’analyse phylogénétique des choanates du Paléozoïque 389
A. Blieck, D. Goujet, Ph. Janvier & F. Meilliez. — Révision de l’ichthyostratigraphie
du Silurien supérieur-Dévonien inférieur du nord de la France et du sud de la Belgique
(Artois-Ardenne) . . . . 447
C. Derycke, A. Blieck & S. Turner. — La microfaune de Vertébrés du stratotype de
la limite Dévonien-Carbonifère à La Serre, Montagne Noire (Hérault, France) . 461
C. Derycke, D. Brice, A. Blieck & N. Mouravieff. — Ichthyolithes du Givétien su¬
périeur et du Frasnien du Bas-Boulonnais (Pas-de-Calais, France) : données prélimi¬
naires . 487
S. Turner & G. S. Nowlan. — Microvertébrés du Silurien inférieur du Canada oriental. 513
Les articles de ce fascicule doivent être cités de la façon suivante:
Gagnier, P- y., 1995. — Ordovician Vertebrates and Agnathan phylogeny. In : Studies on Early
Vertebrates (Vlith International Symposium, Parc de Miguasha, Québec), M. Arsenault,
H. Lelièvre & Ph. Janvier, (eds). Bull. Mus. natl. Hist. nat., Paris, 17 (C) 1-4: 1-37.
Études sur les Vertébrés inférieurs
Studies on Early Vertebrates
Coordonné par Marins ARSENAULT, Hervé LELIÈVRE et Philippe JANVIER
(Publié avec le concours du Ministère de l’Environnement et de la Faune, Gouvernement du Québec)
Avant-propos
Depuis le symposium international de Miguasha sur les Vertébrés inférieurs quatre années
se sont écoulées. Ce n’est en effet qu’après un rude combat contre l’adversité économique que
les contributions des participants à cette réunion peuvent enfin être publiées, grâce au Bulletin
du Muséum national d'Histoire naturelle, Paris, et au soutien du Ministère de l’Environnement
du Gouvernement du Québec : qu'ils soient ici remerciés.
On pourrait penser qu’un tel délai de parution rendrait désuets les articles présentés. Cela
serait peut-être vrai dans d’autres disciplines, mais dans ce cas précis il n’en est rien. La plupart
des contributions réunies dans ce volume sont des articles de fond, des descriptions anatomiques
de base qui n'ont pratiquement pas pris une ride en quatre ans. Cette pérennité est. du reste,
l’une des qualités des volumes issus de cette série de rencontres sur les Vertébrés inférieurs qui
commença à Stockliolm en 1967, puis se poursuivit par les symposiums de Londres (1973),
Tallinn (1976), Canberra (1983). Pékin (1987), Tallinn (1989), Miguasha (1991) et cette année
à Paris (1995). Ils restent toujours à portée de main des chercheurs qui travaillent soit sur les
Vertébrés paléozoïques, soit sur les Vertébrés dits «inférieurs» actuels (globalement les poissons
et les amphibiens). Les pages qui suivent contiennent par exemple la première description du
squelette de l’un des plus anciens tétrapodes connus, Acanthostega, la description détaillée de
l’anatomie de l'osiéolépiforme le mieux conservé connu à ce jour, Medoevia, ou encore la
première description des Vertébrés ordoviciens et siluriens de Sibérie. D’autres articles proposent
soit des analyses phylogénétiques de groupes, soit des analyses de la biodiversité d’environne¬
ments paléozoïques, soit encore des données d’ordre biologique sur les Vertébrés primitifs actuels.
Le site de Miguasha, qui a accueilli ce symposium, est l’un des plus riches gisements de
Vertébrés dévoniens ; c’est à René BUREAU qu’il doit son statut actuel de parc protégé. Ce gise¬
ment a en outre livré les spécimens du poisson ostéolépiforme Eustlienopteron foordi, dont l’étude
par le Professeur E. Jarvik, du Musée Suédois d’Histoire naturelle de Stockholm, a été la clé
de la compréhension du passage de la vie aquatique à la vie terrestre chez les Vertébrés. C’est
pour celte raison que le Professeur E. JARVIK, effectuant ainsi sa première visite sur ce site
après un demi-siècle de recherches sur Eustlienopteron, était Président d’Honneur de ce sym¬
posium ouvert par le Professeur Pageau, autre pionnier auquel nous souhaitons rendre hommage.
-VIII-
Mais n’oublions pas tous ceux, nombreux, qui contribuèrent au succès de cette rencontre,
par des «affiches» ou des communications publiées séparément (leur impatience ne peut certes
être blâmée !).
Pour la postérité, ajoutons que lors de ces journées de juin 1991, sur le rivage de la baie
des Chaleurs, le soleil était radieux et les homards succulents. L’accueil des habitants de
Miguasha, dans la langue de Molière comme dans celle de Shakespeare, restera longtemps dans
la mémoires des participants.
M. Arsenault, Parc de Miguasha, C.P. 183, Nouvelle, Québec GOC 2EO, Canada.
Ph. Janvier & H. Lelièvre, Muséum national d’Histoire naturelle, Laboratoire de Paléontologie et URA 12 du CNRS, 8 rue
Buffon, 75005 Paris, France.
Bull. Mus. natl. Hisî. naî., Paris, 4® sér., 17, 1995
Section C, n" M : 1-37.
Ordovician Vertebrates and Agnathan phylogeny
(A contribution to IGCP 328-Palaeozoie Microvertebrates)
by Pierre- Yves Gagnier
Abstract. — The most coniplele Ordovician vertebrate known to date is Sacahamhaspis janvien This
jawless Rsh, like heterostracans, possesses dorsal and ventral shields rnadc up of large médian plate». Anteriorly,
the dorsal shield delimits an elliptical spuce thaï eontains lhe eyeball.s with their dermal sclerotic and scierai
ossification.», and the paired olfaciory capsules. The anierior part of the ventral shield is composed of square-
shaped platelets aligned in row.s to form an exoskeictal mouth apparatus resembling ihat of heterostracans. S.
janvien may hâve a latéral .sériés of 20 branchial plates and ils bone is cellular. Ail the Ordovician venebrates
were previousiy classified with the heterostracans Our présent knowledge of the anatomy of the Ordovician
vertebrates indicates thaï the Auslralian and Bolivian forms are more closely related to each other, forming a
monophyletic gropp (Arandaspidiformes), than to the Nonh American généra which are more closely related to
the heterostracans. The Ordovician vertebrates may thu» be United with the heterostracans into a monophyletic
group, the Pteraspidotnorphi. This does not invalidate lhe myopterygian concept, bul reduces the importance of
the involved characterislics. The analysis suggests ihat lhe presence of two oJfactory capsules is primitive for
vertebrates, as is also a single médian narial opening.
Keywords. — Vertebrata, Agnatha, Ordovician, anatomy, relationships.
Les Vertébrés ordoviciens et la phylogénie des Agnathes
Résumé. — La morphologie la mieux documentée de Vertébrés ordoviciens est celle de Sacabambaspis
Janvier!. Elle montre la présence de deux boucliers médians couvrant le dessus et le de.ssous de la tête, d’une
vingtaine de plaquettes marginales disposées en rangées obliques, de globes oculaires antérieurs, de deux dépres¬
sions Juxtaposées en position pinéale et parapinéale, de hautes et fines écailles disposées en 4 rangs sur le pourtour
du corps, d'une nageoire caudale diphycerque et d’un système de la ligne latérale bien développé. Ces données
montrent que les formes australiennes et boliviennes ont entre elle.» des relations de parenté piu.s étroites qu’avec
les genres nord-américains. Astraspis et Eripiychius. Une nouvelle définition des Heterostraci est avancée : elle
exclut les ia,\a ordoviciens qui tous possèdent plusieurs orifices branchiaux externes. Le taxon Pteraspidotnorphi
est proposé pour l’ensemble des Vertébré.» ordoviciens et des Heterostraci. Les Pteraspidomorphi sont caractérisés
par une cuirasse externe composée d’au moins deux plaques os.scuses médianes, à croissance concentrique. Enfin,
les résultats de l’analyse phylogénétique produite n’invalident pas le concept de Myoptérygien, mais en réduisent
de beaucoup .son importance. La présence de deux capsules nasales semble être un caractère primitif pour Ten-
semble des Vertébrés, au même titre que la présence d'un orifice nasal impair et médian.
Mots-clés. — Vertebrata. Agnatha. Ordovicien, anatomie, phylogénie.
P.-Y. Gagnier, Redpath Muséum, McGill University, 859 Sherbrooke Street West, Montréal, P. Québec, Canada, H3A-2K6.
Introduction
Recent analyses suggest a doser relationship between the petromyzontids and gnathostomes
than between the petromyzontids and myxinoids (L0VTRUP, 1977; JANVIER & BLIECK, 1979;
Janvier, 1981; Forey, 1984). Historically, Cope (1889). Goodrich (1930), Stensiô (1927),
Jarvik (1964), or more recently Yalden (1985) regarded agnathans as monophyletic. Cope
— 2
(1889) United the Heterostraci and Osteostraci, together with the Antiarchi (Placoderms) under
the name Agnatha. Most recent and current phylogenetic reflections on vertebrates consider that
the gnathostomes descend from a group of agnathan (L0VTRUP, 1977; Janvier, 1978, 1981;
Janvier & Blieck, 1979; Hardisty, 1979; FOREY, 1984). The taxon Agnatha thus represents
a paraphyleiic group, contrary to the opinion of Jarvik (1967, 1968) or STENSlô (1964).
Nevertheless, 1 shall use here this naine for practical reasons, since it is well known, though
referring to a grade.
The Heterostraci (pteraspids) and Osteostraci (cephalaspids) were formerly grouped with
the Antiarchi in lhe “ostracoderms” because of their dermal bony armour, as opposed to the
Cyclostomata. lampreys and hagfishes, which are boneless. Later the Antiarchi were recognized
as gnathostomes and removed from the Agnatha. Because of iheir dermal armour, ostracoderms
hâve been mainly ckcssified on the basis of their type of armour growth.
Since Sten-SIO (1927) iried to demonstrate a relationship belween cephalaspids and lampreys,
the term “ostracoderm” refer.s to a paraphyletic group, and is no longer retained as a taxon.
Neverthele.ss, it emphasizes on lhe problem of comparisons between boneless extani agnathans
and armoured fossil agnathans. Ali phylogenetic schemes reflect this problem. The idea of a
cephalaspid-lamprey sister-group relationship was long maintained and developed (Janvier &
BLIECK, 1979; JANVIER, 1980, 1981; Hai.STEAD, 1982; Bl.lECK, 1982).
The inclusion of fossil taxa by Stensio (1927) lias reorganized agnathan phylogenetic to¬
pologies, with the Cephalaspidomorphi. which include the petromyzontids (lampreys). Osteostraci
and Anaspidu, as opposed to the Pteraspidomorphi, which include the myxinoids (hagfishes) and
Heterostraci (STENSlO, 1927, 1964, 1968; JARVIK. 1964. 1968; ROMER, 1968; J.-\N VIER. 1975b).
The Cephalaspidomorphi are characterized by a nasal sac and a nosiril opening that arc médian
in position and confluent with the hypophyseal duct. They also possess muscularized fins and
extrinsic eye musculature. The Pteraspidomorphi retain what is considered as a more primitive
condition in which the nasal sacs and lhe external narinal openings are paired, as in the gnathos-
tomes.
Halstead (1973a, 1982) and NOVITSKAYA (1975. 1983) made restorations of the hetero-
stracan olfactory organ, based on the gnathostome modcl. The suggestion of a paired olfactory
organ did not receivc great acclaim. Then, myxinoids and hetcrostracans where treated inde-
pendently and Pteraspidomorphi became a synonym of Heterostraci. The term Pteraspidomorphi
has thus been discarded. fn contrast. Janvier & BUECK (1979) adopt a phylogcny where petro¬
myzontids and gnathostomes are sister-groups. Janvier (1981, 1984) included the Cephalaspido¬
morphi in the myopterygians and suggested a possible sister-group relationship between
osteostracans and gnathostomes. One of their main ideas was a progressive development of
muscular fins, from unpaired to paired.
The three-taxon phylogcny of extant craniates, including hagfishes, lampreys and gnatho¬
stomes, is not yel resolved. The addition of fossil agnathans does not increase the resolution.
Moreover, as pointed out by Schaeffer & Thomson (1980), lhe outgroup is uncertain. Cephalo-
chordates, with their notochord, epichordal nervous System, metameric musculature, and branchial
région, are convenient outgroups but are far from providing a suitablc list of homologous
characters. In this paper I do not intend to reconsider lhese problems. I shall instead focus on
the implication of Ordovician vertebrates to our understanding of primitive vertebrate (agnathan)
— 3 —
relationships. A character analysis using PAUP software 2. 4. 1. for IBM compatible (Swofford,
1985) was performed using a matrix (table 1) that includes different taxonomie levels. Cephalo-
chordates were used as outgroup.
The fosxil record of jawlcss fishcs began when they evolved the ability to produce a bony
armour. The following extinct taxa are recognized as Paleozoic agnathans; Helerostraci,
Galeaspida, Osleosiraci. Anaspida, Thclodonti. In addition the two exlatil agnathan taxa, my-
xinoids and petromyzontids. are known as early as the Carboniferous. Agnathans with dermal
skeleton are known from the Ordovician to the Upper Devonian. Their greatesl diversity was
reached between the mid-Silurian and the late Devonian (Fig. I), and they become extinct at
the end of the Frasnian, in the late Devonian.
Thrce different epochs may be defined in agnathan history:
1. The Ordovician period, with the earliest known forms (Fig. 1), which is the main subject
discussed here;
2. The Si lu ri an- Devonian is the Golden Age of agnathans, which reached their highest di¬
versity during this period. At the beginning of the Devonian, during the diversification of the
gnathostome.s. heterostracans almost disappear and are followed by the olher groups of bony
agnathans. One of lhese groups is the anaspids, but somc authors consider anaspids as being
more closely relaled to the Recent petromyzontids (Stf.nSIÔ, 1927; WÀNGSJO, 1952; Janvier,
1981; Janvier & BeiECK, 1979; Forey, 1984). This relationship is likely, but still supported
by tenuous evidence.
3. Finally, the Carboniferous period provides the first record of the Myxinoidea, or Hyper-
otreti, and the Petromyzontida. or Hyperoartia (Bardack, 1986, 1991; BardacK & RICHARDSON,
1977; Bardack & Zangere. 1971; Janvier & Lund, 1983; Lund & Janvier, 1986). These
two groups are the only agnathans known from post-Devonian times.
Extant agnathans, lampreys and hagfishcs, neither possess a dermal skeleton. nor paired
fins. Their first appearance in the fossil record is aiso problematical. The resemblance of the
SERIES
I PTERASPIDOMORPHES
! Pteraspidiformes
I* • I â
OSTEpSTRACANS « T ' I
A ANASPIDS Cyathaspidiformes
Mi 1 1
THELODONTS GALEASPIDS "
Famennian
Frasnian
Giveliün
lEifeilan
En'stan
Pragian
Lochkovian
Prldoli
Ludlow
[Weniock
Llondovery
|Ashgill
Corcxjoc
Llondeilo
Uonvirn
Arenig
îremodoc
Astraspidiformes
• I
Arandaspidifofmes
Fig. 1. — Stratigraphie distribution of the agnathans in Paleozoic limes. A, possible osteostracans (SMITH, 1991); B, possible
thelodonts (Spjri.DNAF.S, 1979); C, tesseraspids.
Répartition stnttigraphiqt4e des Agnathes au Paléozoïque. A, Ostéostracés possibles: B. Thélodontes possibles: C, Tesseraspides.
— 4 —
mouth parts of hagfishes and conodonts suggests the later as possible relatives of the former.
Recent studies hâve focused on these problems and the implications they hâve to phylogeny
(Krejsa et al., 1990a, b; Smith & Hall, 1990; Brtggs, 1992). The Silurian form Jamoytius
mighl be related to the petromyzontids (Bardack & Zangerl, 1971; LUND & Janvier, 1986),
but it is Hardistiella, from the Lower Carboniferous, which is the earliest accepted record of a
fossil lamprey.
Abbreviations
bo branchial opening, ouverture branchiale -,
bp marginal (branchial) plate, plaque marginale (branchiale) -,
bs body scale, écaille du corps -,
en nasal sac, sac nasal ;
dr dorsal crest, crête dorsale -,
drs dorsal rigde scale, écaille de la crête dorsale -,
ds dorsal shield, bouclier dorsal ;
gr dorsal shield and nasal bone (nb) groove,
bouclier dorsal et sillon pour l'os nasal (nb)-,
iol infraorbital sensory line groove, sillon sensoriel infra-orbitaire-,
k branchial pit, dépression branchiale -,
m medio-ventral sensory groove, sillon sensoriel ventro-médial-,
mds dorso-medial sensory groove, sillon sensoriel dorso-médial ;
n nare, narine-,
nb nasal bone, os nasal -,
or orbit, orbite -,
pi pineal and parapineal dépréssions, dépressions pinéale et parapinéale -,
s sclerotic ossification, ossification sclérotique ;
sbp supramarginal plate, plaque supra-marginale •,
sol supraorbital sensory line groove, ligne sensorielle supra-orbitaire-,
tz transition zone between the dorsal shield and body scales,
zone de transition entre le bouclier dorsal et les écailles du corps-,
vlp antero-ventrolateral projection of dorsal shield,
projection antérovenirale du bouclier dorsal-,
VS ventral shield. bouclier ventral-,
MHNC Museo Historia Natural de Cochabamba;
MNHN Muséum national d’Histoire naturelle de Paris;
YPFB PAL Yacimientos Petrolera y Fiscales de Bolivia, Paleontological collection.
ORDOVICIAN VERTEBRATES
Leaving aside the question of the craniate affinities of the conodonts, recently propo.sed by
Briggs (1992) and Sansom et al. (1992), the earliest known vertebrates are from the Ordovician
period. Records of Ordovician vertebrates consist of agnathan remains from the Stairway Sand-
stone in Australia (Ritchie & Gilbert-Tomlinson, 1977; Ritchie. 1985), which are of Lower
— 5 —
Ordovician âge (Early Llanvim; Fig. I). The vertebrate fauna from the Stairway Sandstone is
represented by two agnathan species; Arandaspis prionotolepis and Porophoraspis crenulata.
Some microremains, such as Anatolepis from Spitsbergen (BOCKELIE & Fortey, 1976) which
hâve been considered as vertebrate, arc aiso known from the Upper Cambrian and Early Or¬
dovician. but their vertebrate affînity is questionable (Peel & Hjggins, 1977).
The first described Ordovician veitebrates are from the Upper Ordovician in central North
America (WaLCOTI. 1892; Denison, 1967: Lehtoi.A, 1973; El.EIOTT. 1987; 0RVIG, 1989;
Elliott et al.. 1991). Axiraspix desiderata and Eriplychins americanus are ail of Caradoc âge
(Fig. I). Other Ordovician veitebrates are known from North America such as Astraspis or Pye-
naspis splendens, specifically differentiated by histologie charaders of bony fragments, ofien of
unknown anatomical position. DENISON (1967) described E. oervigi from Wyoming as having
thicker dermal plaies, with a more massive ornamentation than E. americanus. E. leipnitzae
(SCHALLREtJTER, 1983), is in fact an inarticulatc brachiopod (BLIECK, 1992).
Astraspis is frequently recovered as isolated tesserae, ornamented with stellate tubercles.
Elliott (1987) reassessed Astraspis on the basis of new specimens collecled in 1968, which
had been misinterpreted by LEHTOLA (1983). Elliott (1987) provided evidence for the presence
of the dorsal shield. first thought to be a mass of poorly preserved scales, with part of the orbit
and eighl latéral branchial openings. The dorsal shield was previousiy known from the specimen
recorded by WALCorr (1892) and described by EASTMAN (1917: 238-239) in a footnote. It shows
a shield made up of tesserae that bear small tubercles. 0RVIG (1958) idenlified the position of
sensory line Systems (see also STENSIO, 1964: 344-346) and pointed out the lack of a rostral
région. The shield surface of A. desiderata shows a médian crest (dt, Fig. 2B) and a pair of
latéral crests along the edges of the shield. A group of elevated tubercles in anteromedian position
might indicatc the pineal organ (Stensiô, 1964). The remainder of the body is covered with
triangle-shaped to rhombic scales. Contrary to ELLIOTT, after examination of a cast of the speci¬
men I do not believe the caudal fin to he complété (Fig, 2B).
The second Harding Sandslone vertebrate. Eriptychius americanus (Denison, 1967, Fig. 2),
is generally found as isolated tesserae. These are ornamented with massive crests (0RVIG, 1958,
Fig. 5) and are easily distinguished from Astraspis.
Only one partially articulatcd specimen of Eriptychius is known to date (Denison, 1967,
Fig. 2). U .shows the probable rostral part of a possible dorsal shield. Sawin (1959) illu.strated
a group of scales of Eriptychius, similar to those described by Denison (1967). They are thin
and deep, rather than rhombic.
Arandaspis prionotolepis, from the Srairway Sandstone in Aiistralia, as redescribed by
Ritchie (1985. Fig. 3 A), has a dorsal and a ventral shield, separated by a slanting row of dia-
mond-shaped platelets (Fig. 2A). Ritchie (pers. comm.) found that each platelet bears a tiny
hole and must thus represent branchial covers. The ornamentation is formed by rhombic tubercles.
The dorsal shield shows parallel grooves interpreted as sensory Unes. Ritchie (1985) illustrâtes
a paired pineal-parapineal opening. The rostral région is still not clear but one specimen shows
a notch on the side of the dorsal shield that might represent the orbit (Fig. 2A). No bone is
preserved in the Stairway Sandstone and therefore the histologie structure is unknown.
— 6 —
Fig. 2. — A, Arandaspis prionotolepis, reconstruction in right latéral view (modifled front Ritchif. & Gilbert-Tomlinson, 1977.
Fig. 8; lhe anterior portion of the donnai shield is reconstructed from RlTCHlE, 1985 and unpublished material). B, Astraspis
desiderata, reconstruction of an articulated specimen showing the orhit, cight branchial opcnings, body scales and incomplète
caudal fin (modil'ied from ElXlOTT. 1987, Fig, 3).
A, Arandaspis prionotolcpi.s. reconstitution en vue latérale dmite (modifié d'après RrrcH/E Gilbert-Tomunson, 1977,
fig. fi, la partie antérieure du bouclier dorsal est reconstituée d'après HtTCHfE, 1985 et du matériel non publié). B, Astraspis
desiderata, reconstitution d'un spécimen articulé, montrant l’ orbite, huit ouvertures branchiales, tes écailles du corps et la
nageoire caudale incomplète (modifié d'après ElUOTT, 1987, fig. 5).
The body is covered by deep, thin scales with parallel ornamentation (Fig. 2A), arranged
in chevrons on each side. No detail of the caudal fin is known.
The second species from the Stairway Sandstone, Powphoraspis crenulata is based on plate
fragments which differ from the former species by the perforation of the diamond-shaped
tubercles. These perforations, grade into scalloped margins of the tubercles, thereby making them
re.semble the oak leaf-shaped tubercules of various Silurian and Devonian heterostracans such
as Traquairaspis plana and Weigeltaspis alla (RiTCHiE & Gilbert-Tomlinson, 1977).
The Australian généra were referred to the heterostracans on the basis of the presence of
two large shields covering the cephalobranchial région and the shape of the ornamentation.
The latest discovered Ordovician vertebrate is Sacabambaspis janvieri (Gagnier et al,
1986), from the Anzaldo Formation of Bolivia (Llanvirn-Caradoc, Ordovician). It represents the
first record of an Ordovician vertebrate showing most of the dermal skeleton (Gagnier, 1987,
1988, 1989a, b, 1991, 1993; Gagnier & Blieck, 1992; Blieck et ai, 1991; Elliott et al,
1991), and allows comparisons with other agnathans. More recently, Andinaspis suarezorum was
described (Gagnier, 1991) from supposedly Ordovician rocks of Bolivia. This form will not be
discussed here, since its âge remains uncertain.
DESCRIPTION OF Sacabambaspis
An extensive description of S. janvieri is provided in Gagnier (1993a, b) but since it rep¬
resents the best known Ordovician vertebrate, I shall give here a succinct description. Its average
length (Fig. 3) is about 35 cm, of which the head shield represents more than a third. The shield
is about 8 cm wide. The overall morphology is quite similar to that of Arandaspis from Australia,
with two large bony units covering the head, and rows of latéral platelets. The body shape
vaguely resembles that of a tadpole.
The head shield is formed by two large bone units composed of tiny platelets (tesserae)
fused at the level of thcir basal layer. These platelets are roughly hexagonal in shape and hâve
Fig. 3. — Sacabambaspis janvieri. reconstruction of an articulated specimen in right latéral view (modified from Gagnier, 1989).
Sacabambaspis janvieri, reconsfitution d’un spécimen articulé en vue latérale droite (modifié d'après GagnieR, 1989).
— 8 —
an average size of 2 mm. Their external surface is omamented with an oak leaf-shaped tubercle.
The bone in the médian part of the tesserae is enclosed by individual walls and the inner part
is filled with spongious bone. No trace of discontinuity in the basal layer of the shield is visible,
but it shows small nutrient foramina which may hâve served the irrigation of the bone.
The dermal bone tissue of Sacabamhaspis Janvieri is highly recrystalized, but nevertheless
shows a mesostructure. Il is made up of a ihin laminar basal layer and a more important cancellons
layer made up of polygonal chambers. Even if the bone of Sacabamhaspis is highly recrystallized,
there is no reason to believe thaï denline or a hypermincralLzcd cnameloid tissue was covering
the tubercles. At this .structural level, certain vacuities are still présent in the bone and are of
the right size (2 lo 5 pm) for cell spaces. The vacuities do nol show any prolongation or smaller
ramification. There is no indication that these vacuities are due to either recrystallisation, or a
posi-nioriem decay such as fungic action.
The dorsal shield of the head (ds, Figs. 3, 4) has antérolatéral projections which delimit an
elliptical space containing the cyeballs and nostrils (or, Figs. 3, 4). Thèse eyeballs are preserved
as scierai and sclerotic (s. Fig. 4) ossifications. There is a médian T-.shaped bone (nb. Fig. 4),
articulated with the dorsal shield and which séparâtes two openings that may be interpreted as
nostrils. The posterior end of the dorsal shield is transitional with the body scales. On the dorsal
shield, there arc paired dépréssions in the anterior médian part of the shield (pi, Figs. 3, 4).
Postenor to this paired dépréssion, the tubercles of the dermal units are smaller and their orien¬
tation gives a false impression that there is a separate plate. This dépréssion is interpreted as a
paired pineal-parapineal aperture, because of the modified ornamentation of the surrounding plate-
lets (GaGNIER, 1989a, b, 1991, 1993; Gagnier & Blieck, 19921.
The anterior part of the ventral shield is made up of .square-shaped platelets aligned in
rows to form the e.xoskeletal mouth apparatus. A little lump makes the transition between the
mouth and the ventral shield. The ventral shield is deep and convex. and oval in shape in ventral
view. It is strongly convex anteriorly and become.s fiattened posteriorly, so that, in latéral view,
it appears higher anteriorly and gently sloping posteriorly. Its posterior end is produced into a
médian, rounded, and convex lobe onto which are attached body scales forming a ventral médian
ridge.
On cach side, the ventral shield is lined by a .sériés of marginal plates (Fig. 3). There is a
single dorsal one contacting with the dorsal shield on each side and a sériés of 18 to 20 smaller
ones articulated between the supramarginal (sbp, Fig. 4) and the ventral shield on each side.
They are diamond-shaped and some show a small posterior knob at midheight. They extend
from approximatcly the level of the pineal openings to the posterior end of the ventral shield.
They probably are covers for the external branchial openings.
The rcmainder of lhe body is covered with rows of thin, deep scales (bs. Fig. 3) omamented
with oak leaf-shaped tubercles similar to tho.se of the shields. but arranged in parallel rows.
There are four main scale rows covering ihc flanks, plus two small ones that form the dorsal
(drs, Fig. 3) and ventral médian scale ridges. The four main rows are arranged two-by-two in
chevrons. There are more than a hundred scales along the axis of the chevrons. The scaled part
of the body is about 25 cm long, of which 5 represent the tail. The ventral médian ridge scales
seem to end before the tail.
Fig. 4. — Sacahambuspîs janvieri, cast of the nalura! inould in dorsal view, specimen MHNC 1005 b.
Sacabamba.spts janvieri, moulage du moule naturel en vue dorsale, spécimen MHNC 1005 b.
The sensory line System consists of paired, longitudinal and transverse grooves. The dorsal
shield also possesses two anterolaterally curved grooves that had been previously described on
the holotype and specimen YPFB PAL-62()6 (Gagnier, 1987). There is also a discontinuous,
paired, médial sensory line groove (mds, Fig. 3). On the ventral shield the sensory line pattern
consists of a paired, médial, discontinuous line turning latéral !y near the mouth plates. In the
latéral part of the shield is another discontinuous groove which runs posteriorly from the oral
— 10 —
région on thc posterior Iwo thirds of lhe shield and then turns ventromedially. A sériés of 18
to 20, laterally placed. transversal commissures is situated ventrally to each marginal plate row.
There is a pair of vcntrolateral lines on the body seules, running from the ventral shield on the
two thirds of the body length. They are marked by a continuons and straight groove on the
surface of the seules.
PHYLOGENETIC RELATIONSHIPS OE AGNATHANS
As gcncrally accepted, craniates are characterized by the présence of a cranium, sensory
capsules, and the neural crest and its dérivatives (character 1). Vertebrates are characterized by
such neontological fealures as the nervous régulation of lhe lieart. or arcualia (characlers 2, 3;
see JANViiiR, 1980: 381, 1981: 121). As FOREY (1984. 333) pointed out, lhe relalionships of
hagfi.shes and lampreys is nol yel clear. 1 do nol intend here to review the monophyly of the
major agnathan groups. However. lhe relalionships of lhe so called Ordovician heterostracans
are reconsidered. I shall thus consider the taxa already defined and use their most recent défi¬
nition, as proposed by Forev (1984), Janvier (1980, 1981, 1984). Janvier & Blieck (1979),
and Turner (198.5, 1991).
Blieck et ai. (1991) reviscd lhe définition of heterostracans. It includes the distinction
made by LANKESTER (1868-1870). who separated the Heterostraci from thc Osteosiraci by lheir
histology. lu thc Heterostraci the bone is composed of aspidin. an accllular bone (Lankester’s
“bonc without bone-lacunae”), The bone mesostructure consisis of an internai lamellar layer, a
thicker médian cancellous layer, and an external layer of dentine ridges, A second character
pointed out by LANKESTER (1870) is the presence of a single pair of dorsolateral branchial open-
ings. l'OREY (1984) metitioned a third beterostnacan character: lhe présence of at least one médian
plate growing above and below the head. Blieck et al. (1991) added a fourih hcicrostracan
character: lhe laleral-line System enclosed in canals within thc cancellons layer of the exoskeleton.
Récent sludies on Ordovician vertebrates (BLIECK et al., 1991; Elliott, 1987; Ellioti et
ai. 1991; Gagnier, 1988, 1989, 1991; GagNIER et al.. 1986; GagnieR & BLIECK. 1992; 0RVIG.
1989; Ritchie, 1985; RiTCltIE & GlLBERT-TfLMliNSON, 1977), hâve .shown that they are ail more
closcly related to heterostracans than to any olher craniaie group. The main feature ihat unités
the Ordovician vertebrates wiih heieroslracans is lhe structure of the head armour, which consists
of large médian dorsal and ventral shields. ELLIOTT (1987), as previousiy noied. suggesls that
Astntspis shovild bc cxcluded from heterostracans because of the présence of numerous pairs of
branchial openings. 0RviG (1989) arrivcd ai lhe .samc conclusion on the basis of thc histologie
structure. GAGNIER (1988. 1989, 1991. 1993), Gagnier & Blieck (1992), Blieck et al. (1991),
Et.LiOTT et ai (1991) aiso pointed out thaï Sacahamha.spLs and Anmdaxpis raised lhe same prob-
lem as to thc presence of numerous pairs of branchial openings. The Ordovician vertebrates will
be ircated separetly, and lhe heterostracans will bc represcnicd in thc analysis by the cyathaspids.
The characters used in the présent phylogenetic analysis hâve been assessed as follows:
1. Neural crest and dérivatives absent (0); présent ( I).
2. Neural arches absent (0); présent (1).
3. Nervous régulation of heart absent (0); présent ( I ).
4. General morphology. (0), head as broad as the body (burrowing habits at one stage of their
development): (1), head dorsally flattened. ventrally bulged. and slightly larger than the body;
(2), head dorsoventrally depressed. larger than the body.
Rrmarks: Overali morphology is used here as an indicator of ecological trends. A similar
elongated shape was pointed out by JANVIER (1981) in Amphioxiis, myxinoids and petromyzon-
tids. This shape is associated with a benthic or burrowing mode of life, at least during part of
the life (larval stage of petromÿzontid). The elongated morphology, with a head rounded in .section
and as broad as the body, associated with a benthic or burrowing mode of life could be considered
as plesiomorphic.
Ordovician vcrtebrates and hctcrostracans hâve a head larger than the rest of the body, with
the dorsal shield more or less flattened but the ventral shield bulged. In osteostracans and
galeaspids il is the ventral part of the head that is flattened.
5. Head length/total length ratio. (0), 50% to 41%, stocky animal; (1), 40% to 3I%>; (2), less
than 31%, animal elongated in shape.
Remarks; The ratio of the head length to the total length gives an idea of the degree of
stretching of the body. This ratio was obtained by measuring the current reconstructions. Astraspis
hâve a ratio of about 50%, a value close to the one obtained for certain heterostracans, such as
psammoslcid. In pteraspidiform hetero.stracans this ratio is tluctuating around the 40%, but an¬
imais with a longer rostrum givc an over-rated value. The cyathaspidiform value of 30% would
be a better approximation.
Anaspids hâve a ratio of 25 to 30%, except for animais likc Euphanernpx, where it reaches
up to 50%. This is linked to the development of numerous branchial pouches that could reach
the anal région (Arsenault 8l Janvier, 1991). Numerous branchial pouches is considered as
a derived character in galeaspids (JANVIER. 1984: 349).
This ratio is about 17 to 25% in osteostracans and adult petromyzontids. In the former
group, it reflects a .shortcning of the cranium (neurocranium -t splanchnocranium). In pelromy-
zontids where the splanchnocranium extends behind the neurocranium (rather than below as in
osteostracans). it indicates an élongation of the body (compared to its larval stage).
6. Dermal bonc absent (0); présent ( I ).
Remarks; The First question to answer is whether bone is présent or absent in the common
ancestor to ail craniates. There .seems to be a thcorctical con.sensus on ils présence, if we consider
dermal bone as a dérivative of the neural crest (ectome.scnchymc), which is an apomorphy of
the craniates (.see SCIIAEFEER, 1987). There is, however, no dcirnal bonc in myxinoids, exçept
if the conodonts are related to them, The conodcmts hâve rcccntly been shown as possibly pos-
sessing cellular bone and enameloid tissues (San.som et al., 1992). Even if conodonts arc not
related to myxinoids, the presence of bone could be a derived character of the vcrtebrates (petro¬
myzontids + gnathostomes) if it were présent in petromyzontids, but it is not. However, some
authors hâve produced analyses suggesting that the dermal bone might hâve been secondary lost
in petromyzontids (JANVIER, 1981, Hardisti', 1982; Maesey, 1986), The rest of the vcrtebrates
share the presence of a dermal skeleton..
— 12 —
As mentioned above, the comparison between lampreys (petromyzontids) and the other verté¬
brales is problematic because the majority of the characters of the fossil forms is of histological
nature and concerns the dermal skeleton.
7. Bone cellular (0); acellular (aspidin) (1).
RiiMARKS: The primitive (Denison, 1963; Halstead, 1987) or dcrived (0RVIG, 1958, 1967,
1989) State of the acellular bone lissue (aspidin) is still debated (see Blieck, 1992). Histology
does not provide any answer to this problem, but 0RV1G (1958), showed that acellular bone is
more frequent iii the latest forms of the vertebrate groups, such as acanthodians. actinopterygians,
or osteostracans (0RV(O, 1968), and tins suggests that the primitive State wou|d be cellular. In
this scope, il is not surprising to tlnd cellular bone in lhe Ordovician (Blieck, 1992; Denisün,
1967; 0RVIG. 1965; Smith, 1991; SpjELDNAES, 1979), This leads to the conclusion thaï acellular
bone has a parallel history in the vertébrales as suggcsied by Halstead (1982). The occurence
of cellular bone as early as the Ordovician does not necessarily support lhe hypolhesis of lhe
pre.scnce of cellular bone in Sacabumbaspis, but réfutés primary objections.
8. Dentinc absent (0); présent (1).
Remarks: Saeuhambaspis displays a mesostructure, and the absence of a dentine layer re-
calls the hcterostracan Ctenaspis (Denison. 1964. Fig. lOlC). Such an absence of dentine cover-
ing is not unique among lhe vertébrales. Il was described in anaspids (Gross. 1958) and
galeaspids (Janvier, 1990). In general, thelodont scales possess an orlhodcntinc covering
(Kar.atajute-Talimaa, 1978) or '‘multitubaie” dentinc (Smith & Hall. 1990). Such dentine
occurs in Eriptychius and hcierostracans. Dentinc is nol very clear in Asiraspis, but well-
devclopcd in ihc related genus Pyenaspis. 0rvig 1 1989) notes that the Nonh American Ordovician
vertebrates are conform. in histologie structure, to hcierostracans. I am inclined to agréé that
the orlhodcntinc of Eriptychius rescmbics more thaï of the heicroslrueans than anything else
(Denison, 1967; Halstead, 1987; 0rvig, 1989; Blieck, 1992).
In addition, Sacabainbeispis has a bone mesostructure of cyathaspid type and Asrraspis of
pteraspid type. In Eriptyi hius. il is more of a psammosteid type (0RVIG, 1989).
The polygonal tesserac of Sacahamhaspis reeall lhe Icsserac of Astra^ipis, .somc heterostra-
cans and even to somc extern, osteostracans. This probably represents a primitive condition. In
ternis of shared characters, a basal layer that unités the eniire shield inio a large growing plate,
is only prescrit in Sacahambuspis and non-lessellate heterostracans. A cancellar acellular bone
layer covered wilh denline is shared by Astraspis {Pyenaspis), Eriptychius and hcierostracans.
9. Ventral shield absent (0); or présent (1).
Remarks: The Ordovician vertebrates Arandaspis and Sacabambaspis possess two médian
shields, one dorsal and one ventral, as in heterostracans. Heterostracans possess additional plates,
branchial, rostral, or cornual, that are unknown in the Ordovician vertebrates. Astraspis and
Eriptychius might hâve possessed a ventral shield, but only the dorsal one is known. Material
of the Wyoming Eriplychiidae could potentially relate that group to the heterostracans. A plate
was interpreted as orbital by DENISON (1967) and branchio-cornual by 0RVIG (1989). These
plates are only known in heterostracans.
— 13 —
10. Growth of the dermal shield cyclomorial (0); areal (synchronomorial) (1); or micromeric (2).
Remarks: Sacabamhaspis and Arandaspis share with the majority of heterostracans the
presence of a macromeric cephalic shield. Astraspis possesses a mesomeric shield, as certain
forms of les.sellate heterostracans (Teuxenmpis for example), Eripivclnux also possesses a mesom¬
eric shield, but its tesserae are of a different type (Bryant. 1936: 0rvig, 1958, 1967, 1989;
Denison, 1967; Hal.STEAD. 1969, 1973a, b. 1974).
The relationships between the- various agnathan forms are mainly dépendent on hypothèses
about the proees.s of formation of the shield, i.e. whether it grows from a primîbve tessellate
stage U) a complclcly fuscd shield, or from a large unit that evolves toward a fragmented stage.
This question is still debated.
Historieally, ROHON (1892) suggested that a macromeric stage could be a primitive State
relatively to the large shields made up of small units. Jaekel (1911) sces cyathaspids as an
idéal primitive model from which ail other forms could be derived. This point of view was
discussed and followed by niany authors such as STEN.Slô (1927), Tarlü (1962, 1965). Denison
( 1970). Ri'ICHje & Gilbert-Tomlinson (1977; 365), followiiig Lhc samc idea saw in the tessellate
dermal skeleton of Eripivchiiis or Astnispis a condition derived front lhc dissociation of large,
single-unit shields, like that of Arandaspis. They also suggested that lhc Ihclodonl seules might
hâve developed by a similar régression, from a macromeric stage.
Thelodonls difler from the other agnathans because of their seules, which are practically
uniform ail over the head and body. Their variations in scale pattern are limited to size and
distribution. Contrary to the opinion of RlTCHlE & Giebert-TomlINSON (1977), this uniformity
suggests that it is primitive (0RVIG, 1968, 1989; JANVIER, 1981). The Ordovician vertebrates
from the Southern Hcmi.sphcre, .Arandaspis and Sacabamhaspis, share vvilh heterostracans a mac¬
romeric State.
0RVIG (1989: 430) poinled out the w'eakness in the reasoning which considers macromery
as primitive. It rests on the assumption of a sudden appearance of a complété shield al the
initial Icvel of exoskeletal development. .Such an armour (shield) certainly requires the interaction
of a variety of mechanism and different histologie material. The complété sequence of events
must hâve taken place by degrees of skeletal assimilation over a long period of lime (0RVIG,
1968: 374-388. 1975: 51-52, 1977: 69-72). The absence of dentine in some groups probably
represenis one particular degree of this sequence.
The idea of a primitive micromeric stage was defended by numerous authors (e.g. 0RVIG,
1951, 1989; .StensiÔ, 1958,, TRAQlfAIR, 1899, 1900; Obruchev, I944;Tareo. 196(1; Hae.STEAD,
1973a, b). Stensio (1961, 1962, 1964) suggested a growth pattern thaï progressively organized
cyclomorial units into larger unit or small plates in a synchronomorial way. He also suggested
(1964) that the honeycomb-like middle layer of the exoskeleton in certain heterostracans, such
as the Cyathaspidiformes, derived from the coale.scence of cyclomorial units into a single mac¬
rostructure. In this case the dermal skeleton of Astraspis or Eriptychius represents. as HalsiTad
stated ( 1973b: 281 ), "the siariing point for a subséquent évolution of the heterostracans carapace”.
Such a level of organization is also encountered in somc heterostracans like Tesseraspis.
As to growth, 0RViG (1989: 430) pointed out that if macromery is primitive, then large
shields should not show any character considered as derived, such as concentric growth zone
14 —
or an association with separale tesserae (see also Halstead, 1987: 344-345). Shields with con-
centric growth zones are well known in heterostracans (Denison, 1964; White, 1973; DiNELEY
& Loeffler, 1976; Halstead, 1987) and présent in Sacabambaspis, at leasl on the latéral margin
ot the shield (MHNC 1005 b, Fig. 4). The marginal plates 2 to 3 show rows of smaller tubercles
along the margins than in the re^sl on the shield. It seems thus that macromery should not be
retained as a primitive condition.
The armour of the Cyathaspidiformes (sensu "CA group", Blieck et «/.. 1991) is made up
of dorsal and ventral shields, separated by a branchial plate. The cephalic shield of Arandaspis
and Saiabcimbcispis is reminisccnt of that of the Cyathaspidiformes.
Blieck ( 1984) and Blieck et ai {1991) think that the tesserae of such Ordovician taxa as
Asinispis (Fig. 2B) or Eripnchius (DENISON, 1967, Fig. 2) are primitive, and that those of psam-
mosteids are sccondarily derived. Against Ihis idea is the study by 0RVUj { 1989) which highlights
the similarity between the histology of the dcrmal bone of Eriptychius and psammosieids.
11. Différentiation of the dermal skeleton. No différentiation into cephalic and post-cephalic
parts (0); mesomeric shield with post-cephalic tesseriform scales (1); mesomeric or macromeric
shield with differentiated post-cephalic scales (2).
Remarks: If we can reject the primitiveness of macromery, our présent knowledge makes
it difficult 10 décidé which of the varions types of me.somery and the micromery of the ihelodonls
could be primitive. Rather than theorising on the nature of the histologie developmeiiL I prefer
to consider the skclctal macrostructural différentiation. 0RVia (1989) pointed ont ihe uniformity
of the squamaiion of the thelodonts, where the only différences are the size and distribution
patterns. Thelodonts do not show cephalic and posicephalic skeletal différentiation, contrary to
the Ordovician verlebiates, hetero.slracans, anasp/td.s and osteostracans. The tessellate heterostra-
can taxa, the cyathaspid Atbenae^is, Eriptychius and Astraspis could be considered as showing
an inteDiiediate condition between non-differentiated and differentiated cephalic and postcephalic
exoskelelon. The cyclomorial polygonal te.sserae of the .shield arc ail of ihe same size as the
proximal trunk scales and grade into them (sec StenSIO. 1964: 182, for the psammosteids; and
Elliott, 1987: 191, for Asimspis desiderata). If the donnai skeleton is originally mesomeric,
then il is the scaled post-cephalic skeleton that is derived.
12. Exoskeletal mesostructure. Lamellar bone (0); bone with a lamellar base (1); bone without
a lamellar base (2).
Remarks: Like heterostracans, Sacabambaspis has a lamellar base covered by a spongy
layer. It differs front the compact lamellar bone of anaspids or galeaspids. The histology of
Eriptychius differs front that of A.straspis in that the mesostructure coniains large ascending canals
in the aspidin basal layer and clongated pulp canals beneath the dentinc cresls. However, there
is an enameloid cap on the surface of certain crests (DENISON, 1967).
13. Perichondral bone, absent (0); présent ( I ).
Perichondral bone in the endoskeleton occurs in osteostracans, galeaspids and the gnathos-
tomes. This is regardcd as a derived condition, relatively to hyaline cartilage alone.
14. Scales deep and narrow (0); rhombic (I); sntall, massive, micromeric (2).
— 15 —
Remarks; Seule morphology is a character associated svith the macrostmeture of ihe dermal
shield (see characier 11). The thelodont scales resemble Ihus those of chondrichthyans in being
of micromeric type. The .scales of Astraspis are rhombic in shape (Fig. 2B), like these of Tes-
seraspis (WiLLS, 1935) or Aihi-iuiegis (SOEiiN & Wit.sON. 1990). The scales of Asiraspis and
Eriptychius seem to hâve an originally mesomeric structure and are considered as primitive by
0RVIG tl989). Pteraspid scales could be derived from an Asiraspis type of seule, i.c. thick and
rhombic in shape (WHITE. 19.35' Gross, 1963). Wilhin the pteraspids there is an e.xception;
Doryuspis which has deep. almost rectangle-shaped scales (STF.NSIÔ, 1968. Fig. 18A). but this
is contradicted by Benoix-Almgreen (1986: 95). This type of scales is of a cyalhaspids type
(Kiaer & HElNr/t, 1935; DiNEi.EV & Loefu.hr, 1976; Broad & DiNF.LEV. 1973; Blifck &
Heintz. 1983). Among the cyalhaspids, Alheiuit'gis cluUertoni has rhombic scales.
Sacahamhu'ipis -And Aranikispis hâve very deep and nararw scales, like those of some anas-
pids and oslcoslracans. SAWIN (1959. PI. 2: 3) illusirated deep and narrow scales in Eriptychius,
thus different from those of Denison (1967) which are more ma.ssive and rectangular in shape.
Deep and narrow' scales certainly represent a primitive type, as their arrangement matches the
axial musculature (Traqdair, 1905; Simpson, 1926; Kiaer, 1924; Pearson, 1980).
15. Shape of myosepta (myocommata). > -shaped (0); S -shaped (1).
Remarks; If the scales. as .suggested. reflect the arrangement of the myomeres. the trunk
musculature most hâve been separated into two main parts which givc the seules an anleriorly
pointed chevron shape in Sacahamhaspis and Anmdaspis. Simpson (1926) supposed a possible
concordance in the latéral musculature of anaspids and Cephaloc bordâtes. However. the concor¬
dance would be more accurale belween Sacahumhaspis and Ampbiuxus, where there is no ventral
process. In anaspids. the position of ventral scales (characier 15) clcarly shows thaï the post¬
branchial myomeres had a ventral process. This ventral process is cranially directed, like in the
osteostracans, petromyzoniids or gnathostomes.
16. Caudal Un. Paddle-shaped (0); with horizontal chordal lobe (1); or slrengthened with radiais (2).
Remarks; The caudal structure of the cephalochordates and myxinoids forms a paddle in
which ray s are not associated w'ith the inuscular System (regarded as a primitive condition for
the craniates by JANVIER, 1981). Drdovician vertébrales do not hâve any fin other lhan the caudal.
Heterostracans were believed to hâve a simple natatory paddle, like myxinoids. but the caudal
fin of some heterostracans siich as Cordipeltis or Drepanaspis, displays dermal ray-like lobes.
Such '‘dermal rays" are aiso visible in Atlienaegis (SoEHN & Wit.sON, 1990, Fig. 5C). A fin
could hâve aIso existed in the "pteraspid indet. CusmuspisT' of Denison (1971. Fig. 9). Soehn
& Wilson (1990) suggested that il would be a functional convergence with bony fishcs. However,
Janvier (1981; 144) argued thaï the présence of normal seule on the paddle and of dorsal and
ventral ridge scales would not permit the présence of a fin with radiais and radial muscles.
The homology of the caudal fin in the gnathostomes and osteostracans is based on the
presence of radiais which could hâve possessed a musculature (Janvier, 1981). Forey (1984)
supported this interprétation in various fossil groups by the change in .scale orienialion on the
caudal fin (“hinge line”). Sacahamhaspis janvieri does not clearly show a change in the orien¬
tation of the scales in the caudal fin.
— 16 —
17. Caudal fin diphycercal (0); hypocercal (1); epicercal (heterocercal ) (2).
Remarks; Only the osteostracans and gnathostomcs possess an epicercal (heterocercal)
caudal fin, and the anaspids and thelodonts hâve a hypocercal caudal fin (i.e. the chordal lobe
turns downwards). A divergent évolution may thus hâve a risen front the primitive diphycercal
condition.
Diverse arguments hâve heen raised about the structure of the caudal fin, Saccibombaspis
and the petromyzontids both show a diphycercal tail. Sacabuntbaspis has large webs, dorsally
and ventrally lo the chordal lobe. Although the caudal fin of petromyzontids looks slightly hy¬
pocercal, Forf:v ( 1984) pointed out that it possesses radiais around the posterior tip of the no-
tochord. The diphycercal tail of Sacabambaspis and petromyzontids may hâve had different
historiés of the lobe structure. Nevertheless, hypocercal and epicercal tails represent different
trends in évolution, and there is no reason to consider one of them as primitive.
18. Anal fin absent (0); présent (1).
Remarks: .An anal fin is known in the thelodonts, anaspids, and gnathostomes, where there
is no médian ventral scale ridge.
19. Ventral médian preanal scale ridge scale présent (0); absent (1).
20. Dorsal médian scale ridge absent (0); présent (1).
Remarks: Sacabambaspis, like other Ordovician taxa, heterostracans and myxinoids which
do not hâve any fin other thaï the caudal, hâve médian, dorsal and ventral, preanal scale crest
or skin ridge. These ridges are certainly plesiomorphic for the craniates, présent in the outgroup,
the cephalochordates.
A dorsal persists in osteostracans, although they possess one or two dorsal fins, and in
anaspids.
21. Dorsal fin absent (0); présent (1).
Remarks: The petromyzontids and gnathostomes are the only groups to hâve dorsal and
caudal fin radiais associatcd witli radial musculature (FüREY, 1984; Hardisty. 1982; Janvier,
1981; Maisey, 1986). J.ANVIKR (1981) suggests a pos.sible relationship between the absence of
other fins (paired and unpaired) and the présence of médian ridge seules, but osteostracans and
anaspids reiain siich .seules. At Icast the dorsal ridge seules could persist along with the presence
of dorsal fin. In the thelodonts. where médian dorsal riiJge sçales are lacking (c.g. Phlebolepis),
the dorsal fin docs not show any character that suggests the presence of radiais.
22. Pectoral fin absent (ü); présent in pectoral position (1); in epibranchial position (2).
Remarks: Pectoral fins, when they exist in agnalhans, are either in postbranchial position
(anaspids) or in epibranchial position (osteostracans and thelodonts; M. Wilson, pers. comm.).
They are a.ssociated with folds in ventrolateral position. The gnathostome pectoral fins are charac-
terized by an endoskeletal structure and associated pectoral girdie musculature {jimircu tor pec¬
toral is', Greenwood & LaudeR, 1981). Osteostracans possess a fenestra pecloralis in the
cephalic armuur and their pectoral fins arc narrow-based (Stensiô, 1927, 1968; Janvier, 1978,
1981; Janvier & Blieck. 1979), but Ateleaspis, considered as primitive (JANVIER, 1984), has
— 17 —
broad-based paired fins, and tremataspids do not possess any. Homology is less than évident,
the positive points being Janvier’s (1985) observations on the attachment area for the pectoral
fin skeleton of a single specimen, and Belles-Isles (1987, 1989) black spots in the pectoral
fin of Alospis macrotuherculata. whicli coiild represent endoskelelal structures. Anaspids are
known to possess dermal pectoral structure (spines) and fins wilh endoskeleton where aiso de-
scribed (RiTCHIE, 1964, 1968b, 1980, 1984), The flaps of thelodonts shows .some siniilarity with
the pectoral fins of skales. but is hardly comparable lo a ime pectoral fin. The sole common
feature is that they are in a pectoral position.
23. Latéral fin fold présent (0); absent (1).
Remarks: Sacabambaspis, rnyxinoids, heterostracans, and possibly the petromyzontids [see,
however, discussion in Janvier (1981) suggesting that pectoral fins in lampreys could hâve
been secondarily lost] might be considered as primitive because of the absence of latéral fin
folds (see RiTCHiE, 1964, 1968a, b, 1980, 1984; or Janvier, 1981, 1987).
24. Horny teeth absent (0); présent (1).
Remarks: Myxinoids and petromyzontids share a simple mouth bearing horny teeth, which
are unknown in other groups of craniates. Moreover. Yalden (1985) considers the muscle-car¬
tilage complex of the pseudolingual apparatus, as homologous in the myxinoids and petromy¬
zontids. The pre.sence of a lingual piston cartilage lias never been clearly demontrated in other
groups of craniates. It has no homologue in the gnathostomes. It was once supposcd to be présent
in anaspids {Phanmgolepis: KlAER, 1924; SMITH. 1957, STENSiù, 1958, 1964). Later. RlTCHlE
(1964, 1980) revised lhe material used to support this idea and concluded that the structure
referred to a “rasping tongue” was in fact a dermal bone and has nothing to do with the pseu¬
dolingual structure. A peculiar dumbell-shaped endoskeletal élément was found in one specimen
of Sacabambaspis janvieri. that may be associated with a pseudolingual apparatus. This remains,
however, highiy spéculative.
25. Mouih funclional structure. Annulât cartilage (0); lower lips covered with scales, tesserae,
or articulalcd plates disposed in a fan-like manner (1).
Remarks. An annular cartilage has been claimed to be présent in anaspids, this could be
true if Jamaytiiis is regarded as an ana.spid (Ritchie, 1984). The annular cartilage could represent
a unique shared character of petromyzonlids and anaspids. The mouth is very poorly known in
fossil agnathans except in heterostracans and osteostracans. The mouth is in a subterminal position
in ail agnathans except for the osteostracans and the galeaspids, where it is ventral, due to the
shape of the animal.
It is only in the heterostracans that the mouth if fairly well described with its fan-shaped
assemblage of more or less rectangular platelets (KlAER, 1928; White, 1935; Stensiô, 1958,
1964; Dentson. 1960. 1961; Janvier. 1981; Soehn & Wilson, 1990, Fig, 6). The arrangement
of the tesserae in the mouth région of Sacabambaspis rccalls the condition in heterostracans. It
represents a primitive condition from which the oral platelets of heterostracans may hâve evolved.
The mouth of the anaspids and thelodonts is poorly known, though surrounded by scales.
In osteostracans [HirclUr, HeinTZ, 1939), the lower lip. or postoral field, is compo.sed of non-
organized tesserae. This condition is structurally - but probably not functionally - close to the
tessellate “fan” of Sacabambaspis.
26. Branchial cover. No bony cover (0); bony cover présent (1).
REMARKS: The specimen MHNC 1(H)9 qï Sacabambaspis janvien shows a sériés of paired,
transversal undulaiions on the dorsal shield placed in conjunction wilh thc marginal plates. These
undulations probably correspond to underlying branchial pouches (Fig. 5). The marginal plates
can certainly be considered as branchial plates, Arundaspis prionntolepis also has the same margi¬
nal platelets (RITCHIE & Gu.BERT-TOMl.lN.SON. 1977). The marginal and .supramarginal plates in
Sacabambaspis (Fig. 3) and Arandaspis (Fig. 2A) are thus a .synapomoiphy of arandaspids. No
other agnathan group posses&es ossified branchial covers. The osteosiracan branchial openings,
8 to HJ in numbers. might hâve been protecled by a small skin tbid covered by dermal cléments
(Heintz, 1939; Janvier. 1985). probably like in thelodonts (S. Turner In Hout,. 1990). In
thelodonts, the demial éléments would he sniall scales, like on lhe body. The osteichthyans aiso
possess an exiernal branchial cover. the operculum, but the hyoidean cover (opercular) is certainly
not homologous to the dermal covers of lhe agnathan, nor is the structural organization of the
branchial System (Mai.I.ATT. 1984).
27. Number of pairs of branchial openings or arches. Belween 5 and 7 (0); between 8 and 10
(I); more than 10 (2).
Remarks; In anaspids, 8 to 18 pairs of openings are présent as holes in a latéral plate and
fomi a slanling row in lhe branchial région (STENStô, 1964). Galea.spids could hâve to 24 pairs
of branchial openings. but the galeaspids which are considered as primitive (Janvier, 1984:
349) hâve between 7 and 10 pairs of branchial openings. Like in osteostracans, they are located
on the margin of the oralobranchial cavity. Thelodonts hâve 8 to 10 pairs of independent branchial
openings which seem to open on the ventral side of the animal (Turner & In Hout, 1990).
Thelodonts from the Canadian Arctic hâve their branchial openings arranged in a slanting row,
like anaspids, lampreys, Arandaspis and Sacabambaspis. The Carhoni ferons lamprcy Hardistiella
does not seem to possess more than 6 pairs of branchial pouches, cunirary to thc modem forms
which possess 7 (H.iND & JANVIER, 1986). Myxinoids hâve from 6 to 15 pairs of branchial
pouches (Brodai. & Fange, 1963). Finally this number is fixed at 5 in the gnalhostomes, except
some elasiTiobranchs where it can reach 6 or 7, but this condition is considered as derived
(Maisey & Wolfram, 1984). In the majority of the agnathan groups, a large number of gill
pouches is considered as derived. and a low number (5 to 7) plesiomorphic for the craniates.
Arandaspis and Sacabambaspis, wilh their twenty pairs of branchial pouches are convergent
with certain galeaspids and ana.spids. Another possibility is that a large number is primitive and
a low number deribed but homoplasic.
28. Morphology of branchial chambers. Pouch-shaped (0); transversally elongated (1).
Remarks; The branchial pouches of myxinoids are in direct communications with the
pharynx (AVERS & JACKSON, 1901), like in the ccphalochordates, thc larval of lampreys (Am-
mocetes) and thc gnalhostomes. The name Marsipobranchii. formerly used for the extant cylos-
tomes refers to the pouch-like structure of their gill chambers, which differ from those of the
gnalhostomes. Forey (1984: 338) mentioned that the branchial chambers of fossil agnathans
— 19 —
(heterostracans, osteostracans, galeaspids, lhelodonts and here Sacabambaspis) are transversally
stretched rather than forming small, rounded pouches, like in the myxinoids and petromyzontids.
The gill lamellae are homologous in hagfishes, lampreys and the gnathostomes, but not the en-
doskeletal arches (JouLllî, 1968; Mallatt, 1984).
An interprétation of the heterostracan branchial apparatus based on a gnathostomes model
has been proposed by Tarlo & Whiting (1965), Halstead {1973a, b) and Novitskaya (1983),
but it is rejected by Janvier (1981: 143). It is more simple to consider the branchial apparatus
of the heterostracans as similar to that of osteostracans.
The myxinoids branchial apparatus is located far behind the braincase. The right and left
pouches are disposed alternatively. This condition repre.sents a parallel with the position of the
lungs in snakes, where the secondarily elongated shape induces a shift of the internai organs.
Branchial openings arranged in slanting row hâve been suggested to be a derived condition
shared by anaspids and lampreys (FoREY, 1984, Fig. 5). This character is linked with the forward
Fig. 5. — Sacabambaspis janvieri, hypothetical reconstruction in dorsal view, showing the approximate shape of the brain based
on the size and position of cycball.s, pinçai and parapincnl fossac. ihc bcginning of the dorsal shicld crcst, and the nasal
bone suggesting the presence of two nasal sacs. The branchial fossae arc reconstructed from the undulations observed on
ihc dorsal shield of the specimen MHNC-I0Ü9 and the immber and position of the marginal (branchial) plates.
Sacabambaspis janvieri, reamstitutum hypothétique en vue dorsale, nwntrant la forme approximative de l'encéphale sur la
base de la taille et de la position des yeux, des fos,ses pinéate et parapinêale, de l’extension de la crête dorsale, du bouclier
et de l ’o.s nasal qui suggère la presence de Jeu t sacs nasau s. Les fos.trs bronrhiulrs sont reconstituées à partir des ondulations
obserx'ées sur le bouclier dorsal du spécimen MHNC-Ji)()9 et le nombre et la position des plaques marginales (branchiales).
— 20 —
extention of lhe trunk musculature above and below the branchial apparatus. Also, the branchials
opening sériés disposed in posteroventral slanting row in the anaspids, could hâve indicated the
presence of an oesophagobranchial duct, like in lampreys (Janvier, 1981).
29. Position of the external branchial openings. Latéral and arranged in a slanting row (0); ventral
and arranged in a circle (1); dorsolateral (2).
Remarks: Fossil agnathans show three tendencies for the position of the external branchial
openings: a dorsolateral position (Astraspis and the heterostracans); a ventral position (osteos-
tracans, galeaspids and some thelodonts), and arranged in a latéral, slanting row (Arandaspis,
Sacabambaspis. petromyzontids, anaspids, and some thelodonts)
Heterostracans possess only one pair of dorsolateral branchial openings in the posterior part
of the head shield (Fig. 6A). Astraspis. hâve a horizontal rows of 8 pairs (Fig. 6B). placed in a
dorsolateral position on the head shield (Elliott, 1987). Heterostracans also probably possessed
Fig. 6. — Right latéral view of the cephalic shield showing the position of the branchial openings. Dashed line (passing through
the orbit) indicates the presumed base of the nciirocraninm. A, Pornspis representing heterostracans. B, Astraspis shares with
heterostracans a reduced number and a dorsolateral position of the branchial openings. C, Sacabarnhaspis janvieri displays
quitc a different condition, with the large number of external branchial openings arranged in slanting row.
Vue latérale ânnïe du bouclier céphaliiiue montrant la position des ouvertures branchiales. Lu /igné en pointillé indique te
niveau présumé de la base du neurocrâne. A, Poraspis, représentant tes Hétérnstracés. B. Astraspis partage avec les hété-
rostracés un nombre réduit et une position dorsodatérale des ouvertures branchiales. C. Sacabambaspis janvier! présente
une .strurtun' bien différente, tîVe’r un grand nombre dduverturv.s branchiales disposées en rangée oblique.
— 21 —
8 pairs of branchial arches as suggested by undulation on the natural mould of certain forms
such as Seretaspis (Stensiô, 1958, Fig. 204) or Anglaspis, Tire low number of branchial arches
and the dorsolateral position of the extemal branchial openings on the head shield seem to be
shared by Astraspis and heterostracans. A morphocline is possible front a condition like that in
Sacabambaspis, where the branchial openings are in sianting row (Fig. 6C) to a dorsolateral
position, like in Astraspis and heterostracans. The réduction to a single pair of common extemal
branchial openings is unique to heterostracans.
30. Number of extemal branchial openings equal to that of branchial pouches (0); or single
common extemal branchial opening (1).
Remarks: A single pair of extemal branchial openings is regarded as a unique hetcrostracan
characlcr (Lankester. 1870; Janvier & Blieck, 1979; Janvier, 1981; Forey, 1984). Such a
condition is not unique in craniate history because it also occurs in Myxine, osteichthyans and
holoccphalans. In myxinoids, the number of the extemal branchial openings varies l'rom a single
one to 15 pairs. The embryology of the Myxine (Hoi.mgREN, 1946) shows that the presence of
multiples extemal branchial openings is plesiomorphic for the group. So, the acquisition of a
single pair must be a parallelism. contrary to what was suggested by Stensiô (1927, 1958,
1964, 1968) or Jarvik (1965).
31. Nasal sac single and bilobate in shape (0). paired (1).
Remarks: The development of the olfactory organ was a subject of controversy. In this
controversy, two different questions are to be considered: the condition of the nostrils and the
structure of the olfactory organ proper. Monorhiny and Diplorhiny where often confused by the
interprétations made on the basis of the nostrils. One of the main point is to know whether the
primitive condition of the olfactory organ is paired, because of the basic bilateral symmetry of
the craniates. or unpaired because of the location of the organ in the terminal .segment. The
Kôlliker organ of the ccphalochordatcs fails to prove to hâve any homology with the craniate
olfactory organ. Thus, there is no possible outgroup comparison. Two patterns are known in
extant craniates; a single, unpaired, bilobate capsule (myxinoids) which can be divided by a
médian septum (petromyzontids); or two independent capsule in the gnathostomes. The myxinoids
and petromyzontids pattern may bc the conséquence of an overall elongated shape, but embry¬
ology is inconclusive and, therefore, it may also be considered as a shared derived condition
termed as “monorhiny”.
The anterior position of two nostrils in heterostracans, supposed by NovitSKAYA (1975),
réfutés the hypothesis of a prenasal sinus, like in myxinoids, as suggested by STENSlÔ (1927,
1968) and JANVIER (1975b, 1981).
The impression of two olfactory tracts on the internai surface of dorsal shield in hetero-
stracans Icads some authors (Hai.STËAD, 1973a. b; NOVITSKAYA. 1975) to the conclusion of the
presence of two independent olfactory capsules. Opponents argue that a single, médian nostril
is known in heterostracans. From that point, the argumentation bccomes confused in assimilating
two characters: the nostrils and the olfactory organs. In Sacabambaspis the paired nostril is
shown by the anterior T-shaped bone forming a dermal septum (Fig. 4). It suggests the presence
of two separate nasal capsules (Fig. 5).
— 22 —
32. Nostrils. Monorhiny (single médian opening) (0); diplorhiny (paired of nostrils) (I).
33. Nasohypophysial duct absent (0); présent (1).
Rkmarks: Galeaspids hâve a large médian dorsal opening thaï recall ihe nasohypophysial
opening of osteostracans, but morphologically and striicturally dilïcrent, as it communicates ven-
trally with the oralobranchial chamber.. This opening lias been interpreted as a nasopharyngeal
duct [exhalent by Beli.ES-Isles (1986) and inhalent by Janvier (1981, I984)|. Rcccntly, Wang
(1991a. h) described two independent olfaciory capsules in ihe anterior part of a galeaspid skull.
This discovery shows the coexistence of paired olfactory capsules and a single médian dorsal
opening. The galeaspids Ihus display a perfectly iniermediaie condition between diplorhiny and
monorhiny. Anaspids possess a médian dorsal opening which looks like a na.sohypophyscal open¬
ing, but the internai structure of these forms is still unknown. On the coiitrary. osteostracans
hâve an endoskcleton which shows ihat the médian dorsal opening is a blind nasohypophyseal
opening, much like that of petromy/'ontids (Kiaer, 1924; STENSiÔ, 1927, 1964, 1968; WÀNGSJÔ,
1952; .lANVtER, 1975b, 1981; FORHY, 1984). A blind nasohypophysial opening, that does not
communicate with the pharynx is restricted to the petromyzontids and o.steostracans.
34. Position of nostrils anterior (0); dorsal (1).
Remarks: The development of lamprey shows a nasohypophysial opening which is first
ventral, in communication with a bilobatc capsule, and then migrâtes dorsally. Thus, it is rea-
sonable to accept that a ventral or terminal opening. associated with two olfactory sacs is a
primitive condition for the vertebrates. Secondary fusion of the olfactory sacs is suggested by
the presence of two olfactory nerves.
35. Nasopharyngeal duct présent (0) or absent (1).
Remarks: Janvier (1981, 1984) considered the nasopharyngeal duct (i.e. communicating
with the pharynx) as primitive for the craniates, since it is the condition in myxinoids. Such an
inhalent duct is présent in galeaspids. The condition in heterostracans and thelodonts is unknown,
despite Janvier’s (1981) daim that these taxa possessed a nasopharyngeal duct.
36. Semsory Unes absent (0), présent but superficial (1). or deepiy sunken in the dermis (2).
Remarks: Among estant craniates, ony the petromyzontids and gnathostomes possess a
sensory line System on the head. The condition in myxinoids is unclear, Kupefer (1900) and
Ayers & WORTilINGTON (1907) showed that grooves on the head of Bdellostoina originated
from the same embryonic territory as the latéral line System, but failcd to demonsirate a con¬
nection with the sensory System. FERNHOLM (1985) considered that these Unes most probably
correspond to the sensory Unes in Epiatrenis.
Sacubtimbaiplx (Fig. 3), osteostracans, galeaspids, and the gnathostomes possess a single
pair of longitudinal dorsal sensory Unes on the head shield. Heterostracans always hâve two
pairs of longitudinal dorsal sensory Unes, which might represent an autapomorphy.
37. Ventral sensory line ab.sent (()), présent as a single pair (I), or présent as two pairs (2)
— 23 —
38. Distribution of trunk latéral Unes. Single pair of horizontal segments, never reaching the
caudal fin (0); three pairs of horizontal segments, never reaching the caudal fin (1); three pairs
of horizontal segments of which one reaches the caudal fin (2).
RemarKvS; Thelodonts and certain acanihodians show three segments of the latéral line Sys¬
tem on the trunk, of which the middie one reaches the caudal fin. The homology of the trunk
segments is unccrtain. Nevertheless. the thelodonts show a typical gnathoslome pattern, contrary
to other agnathans which possess a pair of ventral Unes that do not extend to the caudal fin.
39. Trunk latéral line.s absent (0); présent as free neuromasts in grooves (I); or présent as canals (2).
Remarks: the trunk .sensory lines of the gnathostomes are enclosed in modified scales
(Avers & WorthingtüN, 1907). Groove-like sensory lines are pre.scnt in Sacahiimbcispis and
Arandaspis. Il was previously recorded Iront anaspids, galeaspids, and some heterostracans such
as the amphiaspids. Certain aulhors (Pehrson, 1922; STEN,SIô. 1921) suggcsl that sensory line
probably originale ITom induction of latéral componenls of the dermal skelelon. Since the neu¬
romasts originale from placodes. thus. sensory lines in grooves could be easily regarded as primi¬
tive and those enclosed in canals as derived. Thus the sensory groove in Sacahambiispis could
bc regarded as a starting point from which could independcntly evolvc the gnathoslome and
heteroslracan trunk lines.
40. Scierai (perichondral) ossification. Absent (0); présent in eyeball (1).
RHMakks: The anlcrior position of the eye of Sacabambaspis (Figs. S-."») certainly represents
an autapomorphy because il is unknown in ail other craniales, even in the early embryonic
development. In ail other agnathans, the eyes arc in latéral position except in galeaspids and
osteostracans w'here they are in a dorsal position due to the shape of the animal. The primitive
galeaspids. such as Hanyangnspis, hâve iheir eyes in latéral position rather than dorsal, as in
the supposedly more derived. This suggesls a piirallel évolution in galeaspids and osteostracans.
Elliott (1987) dc.scribed a circumorbital bone in Axlraspis (Fig. 2B). .Such a botte is known in
the Cyalhaspidifonnes, Athenuegis vhtnerwni (SOhllN & WiLSON, 1990, Figs. 2F, 3. 4, .SE). A
perichondrally ossified sciera is known only in osteostracans and the gnathostomes (placoderms).
It may, however, exist also in Sacabambaspis
41. Sclerotic (dermal) ossification. Absent (0); présent (I).
RHMARKS: a dermal sclerotic ossification is known in Sacabambaspis, osteostracans, and
the gnathostomes.
42. Oculomotor musculature absent, with conical eyeball (0); prc.senl (1).
Remarks: Myxinoid eyes hâve classically be considered as primitive (Stensiô, 1927),
simple, w'ithout crystalline and conical in shape. The heteroslracan eyes hâve been compared
with those of myxinoid because of the impression left in the dorsal shield of the former. This
was to support an inierrelationship (.IanviER, 1975a) and implicilly refuie the presence of an
oculomotor musculature. The simple myxinoid eye structure could also be due to degeneracy,
in turn linked with iheir mode of life.
The eyes of lampreys hâve an exlrinsic musculature attached to the orbital cavity (Hardisty,
1982), like in the gnathostomes. The eyeball of Sacabambaspis with both scierai and sclerotic
— 24 —
ossifications, suggest lhe existence of an oculomotor musculature. The oculomotor musculature
seems to be more widespread in vertebrates than previously thought.
43. Comeal musculature. Absent (0); présent (1)
Remarks; A comeal musculature has been also suggested to exist in ana.spids (Janvier,
1981), like in lampreys, due to scàle arrangement around the orbit. The comeal musculature is
innervated by the oculomotor nerve (III) and seems to be homologous to the oculomotor muscu¬
lature (Nicol, 1989). The inferior reclus muscle is innervated by the abducens nerve (VI) in
lampreys, and by the oculomotor nerve (III) in the gnathostomes (Rovainen 1979). This muscle
may not be homologous in the two groups.
44. Pineal and parapineal organs in a single médian cavity (0), or side by side (1).
Remarks:. In vertebrates. lhe pineal and parapineal organs are respectively in relation with
the right and leR halwnula, suggesting a primitive symmetry. However, Bjerring (1975) sug-
gesied a possible homology of the pineal with the médian eye of larval ascidian lunicatcs, which
develops in relation with the unterior cérébral vesicle. BJERRlNCfs suggestion thus implies that
the pineal organ was primitively single and médian. Even if Ihere is no homology belween the
médian eye of the lunicates and the pineal organs, developmental studies fail in linking funclion-
ally the pineal and parapineal organs (Wingstrand, 1966), and thus gives no support to an
original symmetry.
Some heterostracans, osteoslracans, galeaspids. anaspids hâve only one pineal foramen.
AranJttspis (RlTCtllH, 1985) shares with Sacahambaspis a double dépréssion, pineal and para¬
pineal, where the two organs are side by side (Figs. 3-5). This character is not shared with any
other agnalhan and is considered here as a synapomorphy.
45. Nerves IX and X issuing behind the braincase (0); front the braincase (1).
Remarks: This character, taken front Forey (1984). concems the position of the two last
cranial nerves, inside or oulside the brain case. In lhe galeaspids. osteoslracans, and gnathostomes
the nerves IX and X are issued from the braincase, whereas they are issued behind the braincase
in petromyzontids and myxinoids.
CONCLUSIONS
The rrlationships oe the ordüvician vertebrates
Character analysis using PAUP .software 2.4.1 for IBM compatible (SWOFFORD, 1985) was
performed. A single matrix was buill, iitcluding different taxonomie levels. Cyathaspids were
used to code for lhe Heterostraci. Cephalochordates were used as an outgroup. The character
matrix shown in table 1 was also sintpiified. A first analysis was produced. with cyathaspids
represenling the heterostracans, and Eripiychius being removed. The 12 taxa and 45 unordered
characiers Icfl gave a single trec of 11)2 steps, with a consistency index of 0.578. In a .second
analysis anaspids, galeaspids, osteoslracans, thelodonts, and chondrichthyans were removed as
well as ail lhe characters thaï became useless.
— 25 —
PTERASPIDOMORPHI 3
Cephalochordates
HETEROSTRACI
7
ASTRASPIDIFORMES
6
ARANDASPIDIFORMES
4
Pteraspidiformes
Cydthaspidiformes
Eriptychius amencanus
Astraspis desiderata
Arandaspis prionotolepis
Sacabambaspis janvieri
Petromyzontids
Myxinoids
Fio. 7. — Hypothesis of lhe phylogenelic relationships in thc Pteraspidoniorphi. For node I and 2, the reader is referred (o figure
8. 3, médian dorsal and veiural growing plates coveriiig head; denual bone witli lamcilar base and spongy middic layer; two
anterior nostrils (diplorhiny). 4. more ihan H) pairs of branchial arches with individuni branchial covers; pinçai and parapineal
organs placed sidc by sidc. 5, lesseriform posicephalic scales and rhombic body seules: branchial openings in dorsolateral
position; dernial hone covered wilh dentinc. 6. animal short and robust. wilh a mcsomeric shield; acelltilar dermal bone with
basal layer non-lamellar but cancellar or pierced by pulp cavity openings; bone covered wilh superficial deniine layer. 7,
single pair of branchial o|>enings-
Hypoilié>t‘ di- n'Itillons de parenie un .tciii des Purasfiidimiiiiplil. Pour les noeuds / et 2. se reporter à la pgiirr 8. J, plaques
médianes dorsale et etnarole enrissrintes et couerani In tête, os dermique ù eouihe hasnie lamellaire et l ouvhe moyenne
sponnifuse: drus narines anlerieures Idtpiarhinirl- 4. plus de II) paires d'arcs hranchiaux avec opercules individuels: organes
pinétd et purupoiéal silaés làte-à'eôte. 5, éeililles posUréphaliques tessèrifarmes ci ernitles du ei>rps rhombiques; ouirrtures
branchiales en posilion dnrsolnicrale: os dermique couvert de deniine. 6. animal Irappu, avec un bouclier mésomérique; os
dermique acellulaire à couche hasale non lamellaire mais rancellaire ou percée de foramens pour les cavités pulpaires. 7,
une .seule paire d'ouvertures branchiales.
Using previous phylogenelic sludies by Janvier & Blieck (1979), JANVIER (1981, 1984),
Forey (1984), Elliott (1987) and Wang (199lb), Gagnier (1987, 1989), Gagnier ei al.
(1986). and considérations of Ordovician vertébrales by BLIECK et al. (1991) and ELLIOTT et
al. (1991), Gagnier & Blieck (1992) suggesied a pattern of interrclaiionships in which Sa-
cabambaspis shares only one synapomorphy sviih hcteroslracans: the large ventral and dorsal
shields covering the head. It was also pointed ouf that the sculpture of the shield ornamentation
shows a gradation from Aranda.vpis to Pompharaspi.s and Sacabambaspis. starting from diamond-
shaped lubercles which would beconie sculplured inio an oak leaf-shaped tubercle (G.C. Yoling,
pers. comm.). The elongaied luhercles of Eriptychius seem doser to this pattern lhan lhe stellate
ornamentation of Astraspis. Sacabambaspis shares with Arandaspis the branchial openings ar-
ranged in a slanling row. each one being covered by a platelet, whereas lhese seem to form a
horizontal row in Asira.spis (ElI.IOTT, 1987). The double pineal dépréssion in Sacabambaspis
and Arandaspis is nol présent in Astraspis. The elongated shape of the body .scales is also known
in Eriptychius (Sawin, 1959, plate 2: 3), but these are doser to the rhombic scales of Astraspis
(Elliott, 1987). These considérations supposed that Sacabambaspis would he the sister group
of A.dra.ipis and hcteroslracans (Fig. 7).
— 26 —
The phylogenetic analysis of the craniates characters highiights the close relalionship be-
tween Ordovician vertebrates and the heterostracans. The Northern Hemisphere Ordovician taxon
are the sister-group (Astraspidiformes) of heterostracans and the Southern Hemisphere Ordovician
taxon (Arandaspidiformes) is the sister-group of the former assemblage, i.e. heterostracans plus
Astraspidiformes. I suggest to name the ensemble of Arandaspidiformes, Astraspidiformes and
Heterostraci, as the Pteraspidomorphi.
This analysis leads to the following définition of the higher taxa.
Class PTERASPIDOMORPHI Goodrich, 1909
The Pteraspidomorphi include the Ordovician vertebrates and heterostracans. It would thus
include the Arandaspidiformes, Astraspidiformes. Cyathaspidiformes. Pteraspidiformes and prob-
ably varions tessellated taxa. These four major groups share the presence of an armour made
of two large médian plates, one dorsal and onc ventral (character 9; one of the characters in:
Blihck et ctl.. 1991; FoRliV, 1984; Janvier, 1981; Janvier & Blirck, 1979). These plates hâve
a concentric growth (character 10). The mouth apparatus is made up of an inferior lip covered
with scales, tesserae or mobile and articulated plates arranged in a fan-shaped pattern (character
25), and a diplorhinal State (characters 31, 32). This new définition may change when more is
known of the Astraspidiformes.
The Astraspidiformes and Heterostraci (Cyathaspidiformes and Pteraspidiformes) are united
principally by the shape of the scales (character 14), a tessellate armour (characters 10. Il ), and
the histologie structure, made up of acellular bone with a similar structure in Astraspidiformes
and certain psammosteids (0RViCi, 1989). The rhombic scale shape and the tessellate structure
of the armour existed in such Cyatha.spidiformes as Arhenaegis.
In arandaspidiforms and cyathaspidiforms. the middie layer is divided into small chambers
and the plates hâve concentric growth (character 10).
Order ARANDASPIDIFORMES Ritchie and Gilbert-Tomlinsson, 1977
The Ordovician vertebrates, Aranclaspis and Scicabambaspi.'! form the family Arandaspididae
in their own order. the Arandaspidiformes. They are characterized by a bony branchial cover
(marginal plate) on each external branchial opening (character 26) and a long and narrow su-
pramarginal plate. Trunk scales are deep and siender (character 14), and a ventral sensory line
runs on ihcm (character 35). Pineal and parapineal organs are placed side by side (character 44).
Bcside the omanienialion of their dermal skelelon. Annulaspis and Savabciinbcispis, differ
by the division of the supramarginal plate. There is a single supramarginal plate in Saccihambaspis
raiher than individual platelets dorsally to each marginal plate in Arandusph. Pomphoraspis is
provisionally included here because of the ornamentation and the presence of large plates.
The Arandaspidiformes share with the Heterostraci (Fig. 7) the presence of médian plates
with concentric growth. covering the head dorsally and ventrally (characters 9, 10), and a di¬
plorhinal condition (character 32).
— 27 —
Superorder ASTRASPIDA Stensid, 1958 (= Berg, I9.'?7)
The Astraspidiformes and Heterostraci (Cyathaspidiformes and Pteraspidiformes) share the
presence of dentinoiis tissue (charactcr 8) and the bonc madc up of aspidin (character 7). They
aiso share a low number of gill chambers (character 27). branchial opcnings. and lheir dorsolateral
position (character 29; Fig. 6). Othcr characters may support this grouping. but arc poorly docu-
mented, such as the possible réduction of the eyc musculature (character 42), or the réduction
of the caudal fin to a simple paddie (character 16). The North American Ordovician vertebrates
share more derived characters with the Heterostraci than arandaspids.
Order ASTRASPIDIFORMES Berg, 1937
The Astraspidiformes arc known cssentially by the family Astraspididae which comprises
the généra Axtru.spis and Pycnaspis (HaI.STEAD. 1973b). For convcnience. the Hriptychiidac are
here included in the same order, Astraspidifonnes. The name Astraspidiformes lias been used
by HAI..STEAD (1973b), but no définition was given. This author placed Eriptychius in its own
order thaï contains the Eripyehiida and Tesseraspida. I do not relain thèse taxa, owing to the
lack of data on lhese groups. The Astraspidiformes are characterized by a tessellate cephalic
shield (characters 10, II) and by the mesostructure of the dermal bone, with a non-lamellar
base that could cither bc cancellar or notched by pulp cavitics, and covered with a superficial
hypermincrali/.ed tissue (character 12).
Certain tessellate taxa classically placed in the Heterostraci seem to share some characters
with the Aslraspidiformc.s. The synchronomorial growth of the plates and the type of ornamen¬
tation that form the dorsal shield (tessellate structure, characters K), II) suggest a relationship
between Eriptychius and Tesseraspis (Obruchev, 1964; HA1..STEAD, 1973b). The two dorsal and
latéral crests of Tesseraspis might represent a shared character with Astraspis.
Order HETEROSTRACI Lankester. 1868-70
The Heterostraci include two major taxa, the Cyathaspidiformes and Pteraspidiformes. They
form a monophyletic group, characterized by a single pair of branchial openings in dorsolateral
position (character 30).
Suborder CYATHASPIDIFORMES Berg, 1937
The Cyathaspidiformes (sensu “CA group” in Blieck et al., 1991) include cyathaspids and
amphiaspids, and are defined by an armoiir madc up of médian dorsal and ventral plates, separated
by branchial plates (fused in amphiaspids); the lateral-line System is composed of two pairs of
longitudinal lincs, with al Icast threc trun.sver.se commissures on the dorsal shield. The pineal
branches of supraorbital canal do not Join to form a V; the dentine cresLs are longitudinal and
laterally crenulaie; the hody seules are deep and rectangular in shape (Blieck et al., 1991).
— 28 —
Suborder PTERASPIDIFORMES Goodrich, 1909
The Pteraspidiformes {sensu “APP group” Blieck et al. 1991), including anchipteraspids,
pteraspids, and psammosteids. are defined by cephalic armour formed by dorsal and ventral mé¬
dian plates, pineal and rostral plates, a pair of orbital plates (two pairs in psammosteids), and
branchial and cormial plates (branchiocorrutal in anchipteraspids); the sensory-line System of the
dorsal shield is the same as in Cyathaspidiformes. except for the pineal segment, vvhich forms
a V-shaped commissure; the ornamentation consists of concentric ridges with serrated margins;
the body seules are thick and rhombic in shape (BlieCK et al., 1991).
The RELATIONSHtPS OF THE PTERASPIDOMORPHt
Authors like SXENSIÔ (1927, 1964) or JANVIER (1975a, b) proposed a relationship between
myxinoids and the Pteraspidomorphi. Morphological characters of Sacahumbaspis janvieri, such
as those of the eyes, nostrils, dermal skeleton. lateral-line system or trunk musculature réfuté
this hypothesis.
In the prévient hypothesis (Fig. 8). petromyzontid.s are the mo.st primitive vertebrates. Beside
the absence of a dermal skeleton (characters 6-12, 14. 26), the petromyzontids and myxinoids
hâve a branchial apparatus with individualized pouches in relation with the pharynx (characters
28, 35), a mouth armed with homy teeih, and a pseudolingual apparatus like (character 24, 25).
These characters were considered as homologues by Yalden (1985), which used them in the
justification of the monophyly of the cyclostomes. However, even if the homology of these
characters is not disputed, they are here regarded as craniate characters. and the cyclostomes
remain paraphyletic in this analysis.
The présent analysis suggests that the dermal bone is a derived character wiihin ihe verte¬
brates. This is not surprising since this study is largely bascd on fossils. Placing petromyzontids
as the mosl primitive vertebrates poses certain problems in particular with the médian fins. The
plesiomorphic State would be the lack of médian fins and the prcscticc of a médian dorsal scale
ridge. One of the solution is, as suggested by Janvier (1981 ), to consider the absence of dermal
skeleton and anal fin as secondary and thus to put the petromyzontids higher in the classification.
The narne Myopterygii (Janvier. 1978) may be considered as synonym of Vertebrata. The
presence of two individualized nasal sacs (character 31) and the letention of a médian external
opening (character 32) in galeaspids légitimâtes the assumpiion thaï Diplorhiny is derived. It
should be noted that the presence of two nasal sacs is attested only in animais with a broad
head (character 4, 31). Two individual nasal sacs may be primitive for the vertebrates as sugge.sted
by the double olfactory tractus in petiomyzontids.
The presumed relationship between galea.spid.s and osteoslracans (Hal.stead, 1982; Janvier
& Blieck, 1979; Janvier, 1984), scems to be duc. in a large part, to homoplasics in the mor-
phology of these animais: the dorsovcntral llattening. the mouth in a ventral position (character
25), the branchial openings arranged into a ventral circle (character 29), and the trend toward
a dorsalisalion of the eyes and nasal opening (character 34). The histologie structure of the bone
in galeaspids and the morphology of the olfactory system suggest that galeaspids are primitive
bony vertebrates.
— 29 —
3
2
1
Cephalochordates
4
Pteraspidomorphs
Galedspids
Chondrichthydns
Thelodonts
Osteostracans
Anaspids
Petromyzontids
Myxinoids
Fig. 8. — Hvpolhesis of phylogenclic relalionships among craniates. 1. neural crest and ils dérivative; horny teeth. 2, nervous
régulation of the heart; arcualia: oculomotor musculature; caudal fin with rays. 3, branchial chambers transversally elongated;
(phosphalic) acellular bone. 4. mouth wilh inferior lip covcred by articulatcd scales or tesserae; sensory-line System enclosed
in canals. 5. ventral shicid. 6, branchial opening.s covcred with individual gill covers; heteroceral caudal fin; pectoral fin;
cellulat demial bone wilh non-lamellar but cancellnr base or with pulp cavily upcnings; bone covered with siiperficial dentinous
tissue (mc.sodenline, iitcladenline or orihodcniine). 7, microineric dcrmal skelclon without différentiation beiween cranial and
postcranial skelclon; Iwo uniertor nosirils (diplorhiny); anal Tin.
HypttihÈsf de relulioits phyUifiètiètiifiies entre tes eraniates, I. erêle rieurnie et ses d^nv^s. dents rorn^es, 2, réf^utoUon nerveuse
du i<rur. an-mdiu. niuieulaiure nrulomnirire. nofteoire rdudate armée de rayons. J. chambres bmnehfales allongées trans¬
versalement. ns aeellulaire H’Iw.sphaièl. 4. lèvre injèrietire de la bouche couverte d'écailles articulées ou de te.s.séres, .système
de lu ligne .sen.uirielle rnclos dan.s de.s vunoux. 5, bouclier ventral. (S, ouvertures branchiales inunie.y d'opercules individuels,
nageoire caudale hétéroverque, nageoires pectorales, os dermique cellulaire à couche basale non-lamellaire mais cancellaire
ou percée de foramens pour les cavités pulpaires. os couvert d'un tissu dentineux superficiel Imésodenüne, métadentine ou
orthodenlinel. 7, squelette dermique inicromérique sans différenciation entre squelette crânien et postcrânien, deux narines
antérieures (diplorhinie). nageoire anale.
The distribution of such characters as the presence of a nasopharyngeal or a nasohypophysial
duct suggests lhat they are présent in the pteraspidomorphs, since they occur in the petromy¬
zontids and the osteostracans. The other solution is that it was lost more than once.
A relationship between anaspids and petromyzontids was suggested and it is still considered
as a valid hypothesis (STBNSlô, 1927; WÀNGSJÔ, 1952; JANVIER, 1981; JANVIER & BUECK, 1979;
Forey. 1984). Characters, such as the branchial openings arranged in slanting row (character
29) or the presence of an annular cartilage (character 25) are here considered as primitive for
the vertebrates. The présent hypothesis rather suggests that anaspids are more derived because
of their bony dermal skeleton and pectoral appendages.
One stable point of the analysis is the interrelationship of thelodonts and gnathostomes.
They share a micromeric exoskeleton, without any anteroposterior différentiation (characters 10,
11). One may argue that micromery is a primitive State, but the PAUP analysis suggests the
contrary, Micromery would be derived from a dermal skeleton with a cyclomorial growth pattern
(mesomeric dermal skeleton).
— 30 —
The new thelodont morphology revealed by the Arctic forms (WiLSON & Caldwell, 1993)
was not included in the présent analysis. It is certain that these forms will hâve a great importance
in our understanding of the agnathan évolution. From the présent phylogenetic analysis, I predict
that the pectoral appendages will lose of their significance as a character and that the olfactory
apparatus and bone mesostructure will be more significant features.
Acknowledgments
The fieltlwork was niude possible by a granl from the National Géographie -Society (.^3.34-87 and
4394-90), the Muséum national d'Histoire naturelle (MNHN), Paris, and the kind help of the Gerencia de
Exploracion de Cochabamba of YPFB. The fossils of Sacabanibttspi,\ are the propeny of the Paleontological
A.ssociation of Bolivia. Spécial lhanks to Ramiro SuARt-/ SoklCO, Carlos Molina MONTES, and Mario
Suarez Riolos for iheir collaboration and logislic support during the 1985. 1986, 1987 and 1988 field
seasons. G. Rodrigo de Walker. M. Toro, A. Blieck, R. RaLSCHER, and C. Emig kindly provided up-
dated informations. Ph. Janvier read and constructively criticized early drafts of this paper.
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— 37 —
Table 1. Characttr matrix uæiI in thc PAUP 2.4.1 program analysi.s (SWOFFORD. 1985). The N values (irrelevant) are replaced
in analy.sis by ? (unknown). Ail characters are unordered, and the option .swap=global and multipars was set on. The resuit
is illustrated in figures 7 and 8.
Motrice de caractères ulUisée dans l'analyse à l’aide du logiciel PAUP 2.4.1 (SwotFORD, 1985}. Les valeurs N (non pertinent)
sont remplacées par ? (inconnu}. Tous les caractères sont non ordonnés et l'option '‘swap=global’' et "multipars" a été
appliquée. Le résidât est illustré par lc.\ figures 1 et 8.
Bull. Mus. natl. Hist. nat., Paris, 4'"’ sér., 17. 1995
Section C, n" 1-4 : 39-55.
The distribution of the vertebrates in the Late Ordovician and
Early Silurian palaeobasins of the Siberian Platform
by Valentina KARATAJUTE-Talimaa and Nikolaj Predtechonskyj
(A contribution to IGCP 328-Palaeozoic Microvertebrates)
Abstract. — Scattered vertebrate exoskeletal éléments occur in the faciès of bar belt, restricted shallow
shelf, lagoon bcir, coastal beli and undcrwater part of alluvial plain.s of the Ordovician and Silurian of the Siberian
Platfomi. During Laie Ordovician tunes and ni Ihc bcginning of the Early Llandovcry. llic Astraspidida played
a significant rôle in vertebrate faunas. On the small territory of lhe Niuya-Beresovo area, Ihelodonls and the
oldest known Gnalhostomata -acunlhtxlians and chondrichthyans- were found in Lower Llandovenan rocks. Rich
vertebrate assemblages distribuled on large areas of Ihc Southern part of the Siberian Platform are characteristic
for Middle Llandovery beds. A considérable Uirn in veinebrate assemblages U>ok place during lhe Late LIaiidovery,
when mongolepidids (Chondrichthyans) and several new généra of acanthudians appeared. The generic composi¬
tion of Wenlockian vcrtchrate as.semblages is slil! unclear. The occurrence of new thelodonls is established. The
aniseed-ojl method of ideniifiealion for vertebrate rnieroremains is deserihed. Il is concltided thaï in the first
half of the Early Palaeozoic, lhe major morphogenelic types of lhe dermal skeleton, lhe main modes of growth
and aiso variou.s types of tissues were already présent.
Keyword.s. — Vertebrata, Agnaiha, Chondriththyes, Acanthodii, Ordovician, Silurian, Siberia, palaeoeco-
logy, biosiratigraphy.
La répartition des Vertébrés dans l'Ordovicien terminal et le Silurien inférieur
des palénbassins de la Plateforme Sibérienne
Résumé. — Des restes d’éléments exosquelettiques isolés se rencontrent dans les faciès de lagons, de
barrière côtière, et de plaine alluviale sous-marine de l'Ordovicien et du Silurien de Sibérie. Pendant l’Ordovicien
supérieur, et au début du Llandovcry inléricur, les Asiraspida occupèrent une place importante dan.s les faunes
de vertébrés .Sur le territoire restreint de la région de Niuya-Beresnvo. des thélodontes et les plus anciens Gna-
thotomata connus (Acanthodiens et Chondrichthyens) ont été trouvé.s dans le Llandovcry inférieur. De riches
assemblages de Vertébrés, distribués sur de vastes régions de la pailic Sud de la Plateforme Sibcricmie. sont
caractéristiques des niveaux du LIaiidovery moyen Un cbangemem considéiable dams la composition des faunes
de Vertébrés .s'est produit au LIaiidovery .supérieur, quand les mongole'pidides (Chondnchihyens) et plusieurs
nouveaux genres d'acanthodiens apparurent La compo.silion générique des faunes de Vertébré.s wenlockieiines
n'est toujours pas claire, mais l’apparition de nouveaux ’lliélodomes est établie. La méthode d’identification des
microresles de Vertébrés par immersion dans l’essence d’anis e.sl exposée. Enfin, il est conlu que dans la première
moitié du Paléozoïque inférieur, les principaux lypies morphogénétiqiies de .squeleile dermique, les principaux
modes de croissance, ainsi que divers types de tissus durs étaient déjà présents.
Mots-clés. — Venébrés, Agnatha, Chondrichthyes, Acantliodii, Ordovicien, Silurien, Sibérie, paléoécologie,
biostratigraphie.
V. Karatajute-Talimaa. Lithuanian Geoingical tnsntute, Seveenkos 13, Vilnius, LR 2600 Lithuanie,
N. Predtechenskyj, All-Russian Scientific Research Geulogical Institule, Srednij prosp, 74, St, Pelersbiirg, 199026 Russie,
Introduction
The Siberian Platform is one of the larges! areas where Silurian deposits are exposed. These
deposits cover more than two million square kilométrés and form an enormous Middle Siberian
sedimcmary basin. In 1972 the research program on Silurian deposits started on ihis terrilory,
in Ihc l'ramcwork of the project ‘‘Ecostratigraphy’'. This program was headed by N. Prf.dtR-
CHENSKY.r (St. Pclersburg) and Y. TiiSS.<\Kov (Novosibirsk). Early results hâve heen published.
but the publications do not contain data on the vertebrates. The field-work diiring which the
vertebrates were collected started in 1982 and was carried on in 1984 and 1986. The rock sumples
containing vertebrates w'ere collected in outcrop.s and later proccssed with acid. They corne from
the following sections: Tchuna-Biriussa (6), Angara-llim (7), Niuya-Beresovo (8) and Maimetcha
(12) (Fig. 1). The material from the Turukhansk t4), Tunguska (5). Viliiij (9) and Moyero (11)
areas was sampled when looking for other taxa and therefore does not yield extensive data.
VERTEBRATE OCCURRENCES
Discrète éléments of vertebrate exoskeleton in the Late Ordovician and Early Silurian are
bound to the following faciès in the paleobasin: the bar belt, restricted shallow shelf, lagoon
belt (saline and brackish lagoons), Coastal belt and underwater part of alluvial plains (Fig. 2).
The sedimcntological pattern of the Silurian basin of the Siberian Platform has been published
by PRli.DTliCtIbNSKY.i (1989).
In the upper parts of the Ordovician, tesscrae of astraspidids ( Astraspididae n. g., n. sp. I)
were found. along with conodonts, pelccypods, gastropods and brachiopods, in borehole cores
from drillings through the marine shallow water deposits in a small area of the Viliuj région
(9. Fig. I). In the same area, at the base of the Silurian, occur conglomérâtes in which tesserae
of Astraspididae n. g,, ii- sp. 2 were found togeiher with Silurian conodonts. The Astraspididae
n. g. (Tesaküviusijis conci'ntniu Karatajute-Talimaa noinen iituititii. KARATAJUTE-Talimaa, 1978,
PI- 32. Figs 4-7) is characteristic of the basal part of the Silurian section to the West, in the
Tunguska area (5), on the Lower Tchunku (Ni/hniaya Tchunku) River. The same species has
been discovered in a sandstone layer of the bed 42 of the Old Balturino outerop in the Tchuna-
Biriussa area (6). logether with a .shelly fauna (Fig. 3).
It can bc concluded that in the Late Ordovician and at the beginning of the Early Llatidovery
astraspidids arc prevailing (Figs. 4. 5) among vertebrates. Some acanthodian scales found in the
supposcdlv Ordovici.an part of the Balturino Formation (Fig. 3) could eventually occur in the
samples.
A section on the river Niuya (8) in South Yakutya (Fig. 6) is of particular interest. In the
Melitchan Formation (Lower Llandovery) were found the oldest knowri gnathostome scales. They
belong to a new chondrichthyan gémis and a new acanthodian genus, and occur with thelodont
scales. Those minute verlebrale remains conte from the opeii shallow shelf faciès, and the outer
and inner zones of the shoal. The rocks which yield these remains are metasomatic dolomites
and dolomitized limestones containing relies of a primary nodular texture, diagenetic llint con¬
crétions together with conodonts, cephalopods, solitary tetracorals, brachiopods and traces of
— 41 —
Fig. 1. — Stratigraphical subdivision of the Siberlaii Platform for the Silurian .System, and geographical position of ihe sections.
1, boundary of the basins (stratigraphie region.s); 2. boundarics of ihc sub-regions: 3. boundaries of the areas; 4, Lower
Silurian vertébrale localilies; 5, upland arais; 6, sub*regions; 7. rvference sectioas; K, areas ( 1 - Norilsk, 2 - Igarka, 3 - Kureika,
4 - Turukhansk, 5 - Tunguska, 6 - Tchuna-Biriussa. 7 - Angara-llim, 8 - Niuya-Beresovo, 9 - Viliuj, 10 - Morkoka. Il -
Moyero. 12 - Maimetcha); 9, référencé sections with Lower Silurian vertebr3te.s; 10. Upper Ordovician vertébrale localities.
Subdivisions strati.qraphîques du Silurien de la l^latefornw Sibérienne et positbm géographique des sections, l. limite des
bassins {régions straligraphiques) : 2. limites des sous-régions : 3. limite des zones: 4, localités d’âge silurien inférieur: 5,
zones vmergees: 6, sous-régions : 7. sections de référence: 6’. zones il - Norilsk, 2 - Igarka, 3 - Kureika, 4 -Turukhansk,
5 - Tunguskxi^ 6 - Tchuna-Biriussa. 7 - .Angara-IUm, 8 - Niuya-Beresovo. 9 — Viliuj, 10 - Morkoka. lî -Moyero. 12 -
Maimetcluri : 9, sections de léférence pour les Vertébrés du Silurien inférieur: 10, gisements à Vertébrés de l'Ordovicien
inférieur.
i*— *
Oo — Qu
28
7
iS
29
p:;pq„.
> isia
5 lia
•fQ
2-(
32
-d
22
— 43 —
“mud-eaters”. Bionomie peculiarilies of the basal member of Melitchan Formation show that it
has been formed in the upper, wavy zone of the open shelf and in a near-shore shallow water
environment.
In the outerop near Old Balturino village (bed 42), in the Tchuna-Biriussa area (6), verte-
brates of Lower LIandovery âge were found in the cross-bedded, poorly sorted quartzitic sand-
stones. rhytmically intercalated wilh .siltstones and silty sandstoncs, rich in traces of “mud-eaters”.
They were deposited on ihc margins of the basin, most probably in an underwater delta environ¬
ment.
The Middie LIandovery beds arc charaeterized hy eomparatively rich vertebrate assemblage
with LoganelHa? moskulenkoae Karatajute-Talimaa, /,. sihiriva Karatajute Talimaa, Elegesutlepis
conica Karatajute-Talimaa and Acanthodii n, g. A (Figs. 4, 5, 6). Tesserae with areal growth,
probably belonging to the Astraspidida, are aiso présent (Fig. 7E. F). This assemblage cornes
from the near-shore and lagoonal faciès and is distributed over a significantly large territory
(Fig. 4).
Fig. 2. — Faciès mode! of lhe Silurian paieobasin of lhe Siberian Platform (after Predtechenskyj, 1989). l. argillites: black,
carbonaceous (up to 12%), containing pyrite, horizontally laminated; 2, argillites: dark-grey, weakly carbonaceoiis (2-5%),
with nuerlayers of grey ntarU. .sonieiitncs coMUtining tulcareous concreiions and dispersed pyrite, hori/onlally and wavy
beddctl; 3. argilliic.s; grcaiisb-grey, cjlcufcou^c bmiiuied. coiUaiiting pyrite: 4, gre\; arcillaccous. pcitiomorphic
lime.sioiiev. containing pyrite 5. muddy. pcliunnorphic hmcsinncv. hillocky bedded wilh diu.tlcm.v: h. argillites; piiiple lo red,
horiZi>nially bcnklcd: 7, mails containing Cuncrctioilx and Ivniicnlur inlcrluycrs of niudd} limcsloiies, abundanl Iraces of "mud-
eaters”. lunucN of biomorphit aulhigenous bieccîae; argillaceous limcsloiiPK, nodular, widi (racc< of “mud-catçrs'*; 9. ar-
gülaceous üniestoncs: nodular, dcmioas, with lenliçular iiUçrlayçrs of maris, traces of ' mud-eaters''. someiimcs containing
siliceou.s conctetions; 10. hioheiras; coral sinim4iopoml. dilopholdal; IK nodular limesiones and deiritic maris with
ienscs uf musMVc dcirilic Innesumes; 12. nodular liine.stone.s; detritou.s, conialniug flinisionc foucrctions: l.V large massive
brachiopod and/or peleuypod-hearinB bariks: 14. vifomaioporid coraJ and .dgaJ biosiroms with traces of iheii Jc.vtrüctiuri; 15.
bedded and bun-shaped sifomatolUes w'iili aulhigcnou.s valcBrcon&''dülorMitic brcccuie: 16, ooliiic JirrieHlones. 17. limesiones:
black odorouN uiiculilic. oflen doloinrnzed; IH. dolomitic Ijme.'ilones: black witli gastropods; (9. argillaccous-siliy dolomites
and dolumilic nutrU: 20. dolonsites: iiiaKsive. f'elid; 21. tlolortnlic îtiarK tdomerrtcsi; 22. argjllaceotts dolomites wilh traces
of “mud-calcr-i": 23, microphytulitic hmesiones, 24. argillites: daik grey hon/oiiiallv bedded. containing py lilc: 25. calcareous-
doloniitic, atilhigcnouv hmedae. 26. frtnyi'/iVMi-dolomiies and domcriies; 27 argillites and silismnes with shrinkage cracks
and cjvcrna duc lü dissolution of halile: 2K gypsum-heaiing dolomites dn«i gypsUm; 29. vandsioncs: mj^sne, cross-bedded;
30, wdnegjted sihstoncs: 31. .32, sandsioncs: massive, cross-bedded. coniaining, pebbles. with intercalations of ihin-laminated
argillacc’ouN dolomites, domcril&s and gypsum wjlh wide shrlnkugc cracks.
Modelé de ftitiês du piiîçfthus.'^tu Silun'eti de lu Plutcfinmv Ülhcrieuue {d'opiTs PHUJlHCHENHKYi, /P.fV). /, argîUn's: noir,
avec des fnu'e.v de charhon (juuiu'a 72%), pyrifeu.'ies, teiminccs fwrizontak’nu'm . 2, orgitiies: gm soinhre faihicnient char-
botmeuxfs {2-5 ‘15 ). inter\truttfu‘e\ de.i t/tarnes ^rhe.i. comenaut parfois des conrréthn.y calraira et des traces de pyrite,
en slmtei hoiic^yntalcs et ondulées. ar^iHitt.'i : ^riso,frdiUrc. carbonutées, laminées, contenant parfnh de ta pyrite; 4,
calca'ues Rrls. ar^OtuÂ, t>éliUniunphcs. pyriieux 5. cahsiues argileux, pelitomorphcs. lité\ en hifincks avec des diitstèmes :
6. arffitiU'.s. rnupex n viidetiex. linUx hta i:yntt/dement ; 7, nwives contenant des iovcrénon.s et des hutUlcs de cuit aires
argileux, civçc de ncwtbtvuses traces d‘orgaui.snu‘s Iftnivotvs et des lentilles de brèche, s auihigenii^ues bioinotphcs ; 6', calcaires
argileux, avec tnices d'orgunf.smes limnttnw; 9, valcnftrs or}iileit.v • iwduleu.v. dètntitiues. avec des {entillex de niante, conte¬
nant des Pores d'orgimismex limivans et parfois des concreftu/ts sihctiises: W. biohentUi: à loroiix. siromatoporides et
algues, ditaphoides: If Cidcaires nodnieux et marnes dêtn'tii^ucs mec ienlilles de cuUuire déiritiifuv masd}'; J 2, calcaires
nodulcüx ' dérrifu^ues. à l'imcrciiotts de silex; IJ. grands bancs massifs riches en Brntfiwpode.K ct/ou fiivûU'Cs: /«/, hiohcrmes
à cornus sfnnmiloporides et hioslwmes algatres avec des traces dt: Uur destruction; IS. siwtriutolifv.s lilè.'! et en forme de
beignet avec des hrcthes auilugènex calcairex à doInmitUptes ; 16. eukotre oolishkpie . 17. ade aires: noirs, fétides, uncho-
lithupies, vr»Hiv/fi rA>/iU/7i7rc/Mc.>'.‘ /■‘f. latcitiris diflontirittuc.s . lunt, m ci r/e.> gu.ytrropodes ; 10. dolomie, s o/gflcuses d siiteuses
et marnes dolomitiipics : 20, dolomies: massives, félidés; 2f marnes dolomtticptes (doméniesk 22. dolomites argileuses
avec traces d'organtsmex limivores ; 23. calcaires microphyioliniiues : 24. argUites: grh-sonihir. litces hoh.’ontakrnent. py-
riteuses: 25. bivches tUithigênes cdlcaire.\ doUmàtUpics : 26. dolomies à Eurypicrus et domêtilcs ; 27. argtti(e\- ci silts à
fentes de dessication et Uicunes dues à la dissolution de cristaux de sei gemme ; dolomies gvpseitscs et .gvpse; 29. grès :
massifs, à xirafifirafionx entrecroisées ; .h), stlts bariolés; 3/. 32. grès . mu.ssits, 4 .ura!irwution.\ enincroi.stvs, contenant
des galets, t^vre des intercalations de dobnnivs finement litces, de domériîes et de gypse, et avec des , fentes de dessication.
WENLDCK
— 44 —
— 45 —
In lhe Niuya River outcrops. the most abundant vertebrate remains of Middie LIandovery
âge are mcl wilh at the base of thc Utakan Formation (see Fig. 6, outcrop 156, beds 37, 38;
outcrop 157, beds 26-42). Here they occur in clayey, silty. dolomitic limestones containing rare,
small tahiilaïc corals, brachiopods, gastropods atid ostracods. Obviously the deposits weie formed
in a shallow watcr environment with an abnormal salinity. This vertebrate assemblage, together
with oslracodes and traces of '‘mud-eateTs" is less frequent in limcstone layers. among the varie-
gated siltstoncs and dolomitic argillites which were evidently fonned m lagoonal conditions.
The riehcst vertebrate samples of this level were colleetcd in the viciniiy of lhe Tushama
station (7. Figs. 1, 4). They corne from variegated (green with reddish, brown spots) and red
siltstones containing quailz grains, as well as from poorly soUed, grey quailzitic quartz sandstones
with a calcareous cernent. Numerous lingulids and pelecypods were found along with the verte¬
brate remains. These beds were probably formed in lagoons with a low salinity, in an underwater
delta région.
In the Laie LIandovery beds occur remains of numerous and various acanthodians (at least
two new gênera and 4-5 new species). mongolepidid chotidrichlhyans (two new généra), a new
species of thelodonts (Luganellia e.x gr. svoiica n. sp. 1), minute scalcs oï Ele^estolepis cnnica
Karatajute-Talimaa and numerous tesserae of a new genus, possiby belonging to a lower chordate?
(Figs. 4, 5). The most complété as.semblagc occurs in ihc Tchuna-Biriussa (6) area. In the Old
Balturino outcrop (Fig. 3) occur some layers intercalated with ■‘bone-beds". Vertebrates corne
from brackish lagoonal deposits and underwater delta sédiments. Horizontally laminaicd, varie¬
gated and greyish green siltstoncs and maris, and horizontally bedded sandstones wilh calcareous
concrétions are considered as brackish lagoonal deposits. Un.sorted, cross-bedded, or massive
and indislinctiy horizontally bedded. quartz-bearing quartzitic sandstones with “bone-bed" inter-
layers represent underwater delta deposits.
In other areas of the paleobasin poorer vertebrate assemblages were found in the near-shore
marine deposits of the Upper LIandovery (Fig. 4).
Fig. 3. — Di.suibution of thc vertebnues in ihu Old Balturino outcrop (upper pari). I, quarts Siindstonc. fine and iiicdium-grained
(a), wilh quart/ and quurUilic pcbbics (H); 11. sundy sdlstone; III sillslone: IV. mnrl'- calcnrenuR (a), dolomitic (b); V, calcareous
cemeni. VI. lirncsionc intcrlaycr and separatc calcareous concrclions: VU. undulating ripplcs marks; VIII. traces of 'mud-
ealers“: IX. i.io!i.s-bcdding (a), hori/onlal bcddirig (bl: X, mud-crucks; XI, érosion surface. Colüur Of lhe rocks. XII, green;
Xm. red; XIV, vuriegulcd, spoUed. XV, neutral; XVI. from lalus- Taxa-. I. TtsükmUi.yfiis rontentriio Kiu^ata-jute-Talimaa; 2,
Loganclliü ex gr ^cntico (n. sp. ! ); .3, cf. iisioiico (Karalajuic-Talimiia); 4. fiefennlt'ptK'^ n. sp.; 5. H<*hnolepis?
sp.; b. EU’gesrolcpis contra Karatajutc-lalimaa; 7, E^lcgvstolepisy .sp.. H, Mongolepididac n. g. A; 9, Mtmgolepididac n. g.
B; 10. Acanihodii n. g. B, sp. !• Il, Aciiiiihodii n. g. U. 12. Acanthodii n. g. C. 13, Acjiiiihüdii indei. tiesscrae). 14, Acanihodii
indel- 15. acanihodii n. g.?; 16. A.slraspidida? indci.; 17. cf Osicostraci indcl.; 18. lower ChordaUi? n. g.; 19. gastropods;
20. conodonls; 21. nauiiloids: 22. linguhds a. bed: b. thicknc.ss: c. coloui of the rocks: d, position of thc sampling.
Répartition c/ev Vtrtéhrts tJuns ghftmtnl tlu Vieux Ballurinn {patlû- supèrieun-f. J. grex t^uuitzetLi: grain Jîn à mnyin (a),
avec galct\ de ipwrtz ou de tptortM (b) : I sût sableux: IR, xih : IV. nwme: calvaire (a), dolotninguc (b): V ciment
calciàtY ; VI. inter^traîcs citivctires et loncrcthns cuU ainx sepotées.- VII, rippU nutrks andulcex ; VIII, trnee.^ d’organismes
limivorcA , IX, Mmtiftcatwns enirdcroiséex (aj, couches honz.tmUtU's (hi; X. femex de dcsxicaiiim : XI, xurthee J'érosion.
Couleur da roches: Xfl. verte: XIH. rouffc : A7V! htuiolées, tachetées: .VK neutre: XVI. du talus. Taxons: l. Tesakoviaspis
conccninca Karaii{Jute-Talimao : 2. Loganclliü ex gr. scotica (/i. sp. !) : J. Loganellia </. asiaticû {Kanttaj^lte^T<^timua) ; 4,
Heleilolepis ' n. sp. ; .5, Kolenolepis / sp : 6, Hlescxlolcpis conica Karalujuie-Tulinuia : 7, Elegestolepis 7 sp. ; A. Mongole-
pididoc U. g. A : d. Mongohpuiidae n. g, B: RK Aranrhodii n. g B. sp, I : //, AeanthodU n. g. B; 12, Acanthodü n g. C:
13. Acanrhodii indet ite.'isén’s) , H. .Acanrhodii inder. : /5. Araniliodti n. g. '! : 16, A.straspidida ? indet. : 17, cf. Ostcostraci
indel.: IB. Chonlata infcrieur.s ? n,g,i 19, CüSlcropadcs : 20, Conodontes: 21. NautHotde.s : 22, Lingulides. a. couche; h,
épai.\seur: r, couleur Je la roche: d. posttiou de rérhantillonnage.
Fig. 4. — Vertebrate assemblages in lhe Lower Silurian of the Siberian Platform.
Assemblages de Vertébrés dans le Silurien inférieur de la Plateforme Sibérienne.
03 LLANDOVERY |weN-
^sh L. I M. I U. LOCK
^^0^ WM*'
— y class
- Prder
FamiLu
^ J&enus
Species
Astraspididae g.n.,sp.n. 1
Astraspididae g.n.,sp.n. 2
Tesakoviaspls concentrica
Astraspidida ? indet
Elûsmobranchii g.n.
Eiegestolepis conica
ElegestoLepis ? sp.
Mongolepididae g.n. A.
Mongolepididae g.n. B.
LoganelLia sibirica
Logûnellia ex gn scotica
LogoneliLa ex gr. scotica 1
ioganeuLa ex gr. scotica 2
LoganetlLa ? moskalenkoae
LoganelLia cf. osiatica
NeLenolepis ? sp.n.1
Acanthodii g. n. A.
Acanthodii g. n. B ,sp. 1
Acanthodii g.n. B
Acanthodii g.n. B ?
Acanthodii g.n. C
Acanthodii ind. _
Lower Chordata 2 g.n.
phosphatic nodules
Fig. 5. — Distribution of the vertebrates in the Upper Ordovician and Lower Silurian of the Siberian Platform.
Répartition des Vertébrés dans l'Otriovicien supérieur et le Silurien inférieur de la Phuefonne Sibérienne.
subcllss HETEROSTRAÜ CHONDRICHTHYES THELODONTI ACANTHODI
— 48 —
Fig. 6. — Distribution of the vertebrates in the outcrops of the Niuya and Lena rivers (outcrop 163). For explanation of liihological
composition of the rocks in the sections, sce Figure.s2 and 3.
Répartition des Vertébrés dans les gisements des rivières Niuya et Lena (gisement 163}. Pour les explications concernant la
composition UthologUfue des sections, voir figures 2 et 3.
— 49 —
The generic and spécifie content of lhe vertebrates in Wenlock beds is not yet fuily studied.
According to the data frotn three areas, 4, 5 and 6 (Fig. 4), the Wenlock assemblage includes
new species of thelodonts - Luganeüia ex gr. scotica n. sp. 2, L. cf. Asiatica Karatajute-Talimaa
and HeleiwU’ijis? n. sp. 1, and the saine acanthodian and chondrichthyan généra (6) as in the
Late Llandovery beds. The Wenlock vertebrate assemblage is most complété in the Old Balturino
outerop (Fig. 3).
Out-side the Siberian Platform similar vertebrate assemblages bave been discovered at the
top of the Ordovician and in the Llandovery of Tuva, as well as in the Upper Llandovery of
northwestern Mongolia.
Astrapidid tesserac oecur in the Upper Ordovician of Tuva. In the Llandovery of this région,
there arc frequently thelodonts. acanthodians and chondrichthyans (mongolepidids included),
which resembic those from the Siberian Platform. In the Upper Llandovery assemblage of Mon-
golia, the mongolcpidid chondrichthyans (three généra) arc abundant, and acanthodians are rep-
resented by the same Acanthodii n. g. B.
METHODS OF STUDY
The studied collection of early vertebrate remains consi.sts exclusively of micro- and mesom-
eric tesserae and seules obtained by rock dissolution. As there is a very large number of discrète
exoskeletal éléments which var>' in shape and structure, a spécifie method should be applied to
define their systematic position. Recently the interesl in vertebrates micro-remains has largely
increased, and it would be reasonable to consider in detail the methods for their identification.
The monographie description of the malerial is, however. planned to be prepared for publication
in 1998.
Al first, the remains should be visually identified according to their morphological features.
Such a rough sorting of the malerial allows to establish lhe vertebrate group contents in respective
samples. Later, such work should be made on samples of one and the same geological unit of
uniform or almosl uniform lithological composition. Le. of a bed. a number of beds, or a member
of a formation. Il is recommended to study very large samples to avoid including into the hy-
podigm of a species éléments belonging to another closely related species. It is necessary to
establish the limits of the morphological variabilily in sets of tesserae and seules, i.e. to get and
idea of the set of exoskeletal éléments forming the squamation. In the exoskeleton of varions
early vertebrates which consist of micro- and mesomeric ossifications, the degree of variabilily
of the éléments may be different.
Then should follow the study of the inner structure of the romains and the définition of
the mode of growih of the micro- and mesomeric exoskeleton éléments. Investigating the inner
structure of the dermal éléments of a vertebrate is quite necessary for the identification of its
systematic position, as lhe extemal aspect does not aiways permit to assign the remains to a
particular group. Usually, sections should be made, i.e. some vertical and horizontal sections of
tesserae or seules coming from different parts of the animal. If the skeletal élément is light in
colour and comparatively thin, it may be placed into aniseed oil, and studied under the micro¬
scope. llluminated from behind it is partiy transparent and many details of the inner structure
— 50 —
become visible. In this way, it is possible, without sectioning, to get an idea on the presence
of canals, thinner tubuli and cavities, and to identify the presence and length of pulp cavities,
osteocyte lacunae and type of dentine. The retnains which are black in colour, recry.stallized or
with heavy iron content, as weJl as thicker scales and tesserae with superpositional growth cannot
be studied in (bis way. Therefore, thin sections should be inade.
Most microremains from the LIandovery and Wenlock rocks of the Southern part of the
Siberian Platform (Old Baltiirino and Tusharna outcrops and those alotig the river Niuya) are
suitable for histologie studies. Since the remains are white, yellowish and brownish in colour,
numerous sections were made, whereas very fine scales and tesserae (0.2-1. 2 mm in diamètre)
of astraspidids, ihelodonts and chondrichthyans with comparatively ihin base were studied under
a microscope in aniseed oil. In the latter case one can observe a cavity or a canal at different
levels and along its entire length. by changing the locus, which is not possible in sections. It
is aiso important thaï such studies can be repeated. However, il musi bc pointed out that a
skeletal élément should not be kept in aniseed oil for a long lime. Aller skciching or photo-
graphying, it should be carefully washed in alcohol. In order to hâve a full picture of the mi¬
crostructure, a sériés of photographs made at different locus levels is needed. The sketch can
be donc in such a way that the cavity or canal can be shown in its total extern. The method is
illiistrated by sketches in figures 7 and 8, i.e. sketches of tesserae and scales immersed in aniseed
oil during drawing.
GROWTH AND STRUCTURE OF THE SKELETAL ELEMENTS
The available material of Astraspididae allowed us to establish the growth pattern of tesserae
during ontogeny, starting from a single primordial tubcrclc, almost undisiinguishablc from thelo-
dont scales, and ending with complelely formed, complex tesserae. Tesserae of different species
of a new genus of Astraspididae (n. sp. 1, n. sp. 2 and Tesukoviaspis conventrica) differ from
one another in shape and size, as well as in the number and density of the tubercles.
Figure 7A shows a tessera of Astraspididae g. n., sp. n. I in an early stage of development,
revealing a big primordial tubercle with dentine tabules which resemble those of orthodenline.
Fig 7. — Tesserae of Aslraspidida. A. Aslraspididae n. g-, n. sp. I. Nrl 0-098, Middle Morkoka area (9 in Figure 1), hore-holc
151. depth 65.7 m.. Upper Ordovician. Bura horixon: B. Tesakoviasfûs concentrica Kardtajure-Talimaa. Nr 10-099, Tchuna-
Biriussa area (6 in Rgiuru I ). outcrop Old Baliurino, bed 42, Lower Silurian, I.owcr IJandovcry. I.ower Baltminif Subformaiion;
C, D. Astraspididae n. g., n. sp. 2. NrlO-KM) and lü-IOl, area between Markhu und Morkoka rivers (9 in Fic:ufv I). bore-holc
412. depth 315 m.. Lower Silurian. Lower LIandovery: E. F. Asirci.'jpidida? n. g.. Nr ïO-102 and 10-103. Niuya-Bcresovo
arc'û (K in Figure I). Niuya River, ouicrop 157. bed 37. Lower Silurian. Middle LIandovery. Lower Utakan Subformation.
AH illuslralionH uf tesserae bascd on spécimens immersed in aniseed oil.
Abbr.: pL primordial luberclc; l, lubercleA of areal xones of growth: dl, luhules in orthodenline: pc, pulp cavities filled by
osieodeniine (?>.
Tessèri'.s J‘Aslra.spidida. A. Axtraspididae n. g.. « sp. k Nri()~09S. région du Morkoku Moyen {9 dans figure I). somiage
J5J. profondeur 63. 7 m.. Ordovicien supérieuK horizi>n de Bura : B. TVsaktniaspis concentrica Karatajute Taiinwa. Nr /0-099.
région de Teiiuiuj Biriusra f6 danr figure IK gisement du ^ieux Baltunno, rouche 42. .Silurien inférieur. LIandovery inferieur,
sousfornurtion de Bü(lt4rino inferitun : C, O, Asira.spididae n. g., n. sp. 2. NrJB-IOO et lO-lOl. région entre les rivières
Markha et Morkoka (9 dans ftguiv /}. sondage 4/2. profondeur 3/5 m.. Silurien inféneur. LIandoverv inferieur: E, F. /\5-
traspididti? n. g., Nr 10~I02 et J0-/03. région de Niuya-Beresovo (d dans figurv />. rivière Niuya. gisement 157, couche
57, Silurien inférieur. LlonJnveiy moyen, sous-forniaiiott de Utakan inférieure. Toutes les il/uslrations des te.s.Kères sont basées
sur des specimens immergés dans l'essence d'anis.
Ahrév.: pt. tubercule primordud : t. tubetvules des cônes de civis.samc concentriques : dt. mbules dans Forthodentine : pc,
cavité pulpaire remptic d'osttodenfinc (?}.
Figure 7B illustrâtes a completely formed tessera of Astraspididae (Tesakoviaspis concentrica
Karalajute-Talimaa, 1978), with the central, rounded tubercle. and four zones of areal growth
consisting of rounded, very closely packed, tubercles. Clear growth Unes and thin dentine tubules
are visible in tubercles. The tesserae of Astraspididae n. g., n. sp. 2 (Fig. 7C, D) are characterized
by large, rounded and flattened central tubercles (Fig. 7D). or more frequently. high, thom-like
ones (Fig. 7C), with comparatively small, scattered sharp-topped tubercles on the areal growth
zones. In ail astraspidids of this type, the pulp cavities of the tubercles are well developed, even
in the smallcst oncs.
The structure found in the small tesserae of Astraspidida? n. g. (Fig. 7E, F) is entirely
different. Thèse éléments show a central part, stirrounded by concentric growth zones which
generally do not form a full circle. The nature of the dentinous tissuc which forms the crown
of the tesserae is not very clear (it resembles somewhal osteodentine); it is a comparatively
dense tissue. without distinct pulp cavities.
The thelodontid scale in Figure 8A bas a high neck and a small, anteriorly protruding base;
it resembles the seules Apalolepis (Kar.atajute-Talimaa, 1978). The crown has one large
pulp cavily with dentine lubuli branching off from it; ihc crown structure is characteristic of
orthodentine. Thi.s seule belongs to the oldesi repre.sentatives of the Thelodontidu. Up to now,
seules of a member of this order (Thelodus sp.) were known from the Upper Llandovery (Turner,
1973; Marss, 1986; TURNER. 1986). The majority of the thelodont seules fourni in tlie Lower
Silurian of the Siberian Platform bclong to the Loganiidae, but their generic and spécifie as-
signment deserves further clarification.
Chondrichthyans are an important component of the vertebrate assemblages of the Lower
Silurian of the Central A.sian région. At least three orders are represented, with forms which are
differentiated mainly by their cxoskeleton.
The body of elegestolepidids was covered with simple, non-growing shedding scales.
Figure 8B-F shows the scales of Elegestniepis conico KAR.ATAJtiTE-TAldMAA (1986) to illustrate
the variability of the seule morphology. There are rounded head scales with a low, flattened
crown (Fig. 8B), and body seules, which are either single-topped with a high, conîcal crown
and a unique pulp cavity (Fig. 8D, F) or three-topped with three pulp cavities (Fig. 8C, F). The
dentinous tissue of the scale crowns is spécifie, whereas the dentine tubules in the superficial
layers of the crown are characteristic of orthodentine.
Fig 8. — Thelodontid and ela«mohranch .'urnles. A, Thelodontida gen indet., Nr 10-104. .Niuya-Bercsovo area (8 in Figure I ),
Niuya Hiver, üU(cf>>p 157. Lower Silurian, Mnidie Llandovery. Lower l'takan Suhformation; B-F, Iiie^esiolepis conU a
Kariittijiitc Taliman Nr.slO-105 to 10 109. Niuya-Bcro.sovo area iS [n Figure 1). Niuya River, ouicrop 157, bed k). Lower
Silurian, Middle Llundovery. Lower Utiikûn SubJ'ormaiion; G-L, Elithcnobranchii n g , Nrs lO-IIOlo 10-115. Niuya Beresovo
area l8 in Figure U, Ninya River, otilcrops 156 bed 57 (J. K. Li and 157 bed M (G. H. 1), Lower Silurian. Middic Llandovery,
Lower IJlakan Subformalion. AU ilUuirationîi are ba^ed on .sentes Inunerscd in amsecd oil.
Abbr.: pu, pulp opening; pc. pulp eavHy; dl denOnal tubules; os< osleodentine?
ÈcatHes de ThêtoiJ(?nutIi=s t'f A. Thclodofnida ifiJvt,. Ar de S'iuyii-Iivfv4ovo (8 dans
flfiurc I ). nvivrv Niuva, lifsetnrnt 157, vont he Mï, SHurien tfifcrii'ur, UonJuvery mo\rn, sott,\--fonrmliifn Je Ulukun inférieure :
B-F. Flegcsiolepis conica KanpajiJe-TfJinma. Nrs I0 f05 J réf(ion Je Niuyu Heiv.sovo (H dans fiaure I), rivière
Niuya. gisemenr iS7. couehe MK SUurûm inférieur. UanJover» moy'en. .<ini.s-fonthinon Je Uuikan inférieure: (!-L Elusmo-
hnUh'tJt n. g.. Nrs 10-110 û I0-U5. régum de Niu\o-Btreyt>vii (8 dtins figure fi. riviéir Ninya. gi.srmenl 156. couche 37
{1. K. /.J el gisemenf 157, couche 37 {(7, H. h, Sifurien ittférirnr, fJonJovery moyen. inuiS’formanon de Utukan inférieure.
Toutes les if/usmuhn.s sont basées sur de.s éciiftle.s immergées dons d'ani.s.
Ahrev. . y»f», ouverture pulpüitv : pc. cavité pidpaire: dt. tuhule.s de ia dentine, ns. o.\'té(fdeniine
mi:-
— 54 —
A completely different dentine type has been found in the scale crowns of the Elasmobranchii
n. g. (Fig. 8G-L). It may rcsemble osteodentine by the arrangement of the short dentine tubules
and the presence of small cavities between them. In some cases the bicuspidate crowns of these
scales hâve a single pulpar opening (Fig. 8H. J), whcrca.s in the olher cases every crown cusp
has its individual pulpar opening Evidently, this type of scale is représentative of a new elasmo-
branch genus characterized by a synchronomorial type of growth.
The scale structure in mongolepidid chondrichthyans is ralher complcx (Karatajute-Tali-
MAA ei £//., 1990). The odonlodes forniing the scale crowns are an'anged into longitudinal rows
and are fused into complicated odontocomplexes. The odontodcs consi.st of a spécifie atubular
dentine referred to as lame Mine. The scale crowns had a synchronomorial mode of growth.
Acanthodians are abondant in the biocoenoses of the Early Silurian paleobasin of the Si-
bcriaii Platform. beginning with the Late Llandovery. In the Upper l.landovery. the scales of
Acanthodîi n. g. B predominate among mteroremains in almosi every sample. The head scales
of this form resemble the elasmobranchs scales of the Holmesella type by their more of growth.
The layers of bone tissue grow supcrpositionally only on the sides and downwards around the
primordial scale. and do not cover the upper parts of the crown. Some of the transitional and
body scales hâve a superpositional growth, as usual in acanihodian scales. Ail Early Silurian
acanthodian of this région hâve a well developed bone tissue nol only in the base, but also in
the crown of the scales (mésodentine).
The study of the structure of the most common exoskeletal éléments in the Upper Ordovician
and Lower Silurian of the Siberian Platform leads to the conclusion that various types of ossi¬
fication. growth. and hard tissues werc présent already at the beginning of the Early Palaeozoic.
• Accordingly the types of ossification are:
Tw'o kinds of simple, non-growing monodontodia. respectively: 1) with one basal pulpar
opening (Thelodonlida); 2) with basal and neek pulpar openings (Elegestolepidida).
The polyodontodia. represented by: 1) simple scales formed by incrément (adding) of new-
odontodes to the pre-existing ones (Elasmobranchii, n. g.); 2) scales consisting of a System of
longitudinal odontocomplexes (Mongolepidida) and 3) odontocomplexes with concentric growth
zones around the embryonic scale primordium (AcanthodÜ, lower Chordata?).
The te.ssei'ae (Astraspididae, Astraspidida?).
• The modes of growth include:
The cyclomorial areal growth (Astraspididae, Astraspidida?);
The areal superpositional growth directed toward the epithelium ( Acanthodii);
The areal superpositional growth directed toward the korium (Acanthodii, lower Chordata?);
The synchronomorial growth (Elasmobranchii n. g., Mongolepidida).
• The types of tissues are:
Aspidin (acellular bone tissue; Astraspidida, Thelodonti, Elasmobranchii, lower Chordata?),
Bone with cell-spaces (Acanthodii);
Orthodentine (Astraspididae ?, Thelodontida, Elegestolepidida);
— 55 —
Osteodentine ? - (Astraspidida? n. g., Elasmobranchii n. g.);
Mesodentine-like ? tissue (Thelodonti, Loganiida);
Lamelline or atubular dentine (Mongolepidida).
Taking into account an enormous variety in the structure of the exoskeleton of the earliest
vertebrates, it is difficult to consider one of the tissue or growth types mentioned above as
primitive. Evidently, the skin différentiation took place before the hard tissues appeared in them.
Addendum
The three thinsections of Tesakoviaspis concentrica tesserae hâve been studied by help of the excellent
microscope at the Department of Anatomy UM/DS Guy’.s Hospital, in London. It has turned ont, that the tubercles
of tesserae do not consist of orthodentine, as il has been assumed earlier, but of unusual atubular tissue, which
has been called by u.s with Dr Moya M. Smith as “conical lamelline”. Hence. the ail tesserae, attributed by us
to Astraspididae, Astraspidida or Astraspidida? (Figs. 3, 7), really are not Astraspides, but represent a new group
of lower vertebrates with cyclomorial type of tesserae growth.
Literature cited
Karatajute-Talimaa. V.N., 1978. — [Silurian and Devonian thelodonts of the USSR and Spitsbergen]. Vilnius:
Mokslas. [In Russian],
Karatajute-Talimaa. V.N., L.I. Novitskaya, K.S. Rozman & J. Sodov. 1990. — Mon^olepis, a new genus
of Elasmobranchii from the Lower Silurian of Mongolia. Paleonr. Zh., 1: 76-86. [In Russian].
MÀRSS, T., 1986. — Silurian vertebrates of Estonia and West Latvia. Tallinn: Valgus. [In Russian].
Predtechenskyj, N.N., 1989. — Lithologie-facies criteria for définition of local and régional stratigraphie sub¬
divisions. lii: Geology and paleontology (to 100“ anniversary of D.V. NALtVKIN), B. S. SOKOLOV & V.D.
Nalivkin. eds, Leningrad: Naiika. [In Russian]: 122-134.
Turner, S,, 1973. — Siluro-Devonian thelodonts from the Weish Borderland. J. geol. Soc. London. 129: 557-584.
— 1986. — Thelodus macintosbi Stetson. 1928. the largest known thelodont (Agnatha: Thelodonti). Breviora,
486: 1-18.
Bull. Mus. natl. Hist. nat., Paris, 4' sér., 17, 1995
Section C, n“ 1-4 ; 57-84.
Silurian and Devonian jawless craniates
(Galeaspida, Thelodonti)
and their habitats in China
by Nian-Zhong WANG
(A contribution to IGCP 328-Palaeozoic Micro vertebrates and The National Science Foundation of China)
Abstract. — A review of fo.ssil jawless traniaie siudies in China concerns mainly galeaspids and thelodonts.
The pattern and structure of the sensory line System in galeaspids differs gready (rom lhat of osteostracans or
heterostracans. The ordcr Macrothyraspidida is a monopliylctie group within ihe Galeaspida, defined by an im¬
portant synapomorphy, i.e. the eephalic shield with a pair of latero- or médial dorsal fenestrue. The habitat of
fossil jaw'le.ss craniates in China might hâve been littoral to neritic, on the basis of associated marine fo.ssils and
the analysis of fish-bearing sedimentary faciès. They are coasidered to be euryhaline animais and not solely
fresh water.
Keywords. — Galeaspida, Thelodonti, Silurian, Devonian, China, morphology, phylogeny, habitat.
Les Craniates sans mâchoires du Siluro-Dévonien (Galeaspida, Thelodonti)
et leurs habitats en Chine
Résumé. — Les recherches sur les Craniates fossiles sans mâchoire en Chine concernent essentiellement
les Galéaspides et les Tliélodontes. Le trajet et la structure des lignes sensorielles chez les Galêaspides diffèrent
remarquablement de ceux des 0,stéostracé.s ou des Héiérostracés. L'ordre de Mactothyraspidida est un groupe
monophylétiquc de Galeaspida caractérisé par une importante synapomoiphie : le bouclier dorsal avec une paire
des fenêtres laléro- ou mesio-dor.sales. L'habitat des Galéaspides et des Thélodontes en Chine était principalement
littoral à néritique. comme en témoignent les fossiles marins associés et l’analyse du faciès .sédi mental re. Ils
peuvent être considérés comme des animaux curyhalins et non pas uniquement d'eau douce
Mots-clés. — Galeaspida, Thelodonti, Silurien, Dévonien, Chine, morphologie, phylogénie, habitai.
N. -Z. Wang, Insîitute of Vertebrate Paleontology and Paleoanthropology, Academia Sinica, P. O. Box 643, Beijing 100044, China.
Introduction
The studies of fossil jawless craniates (Agnatha) in China can be divided into four periods:
the 1930-1940S, 1960s, 1970s and the lasl ten years.
Agnathans were first reported from Soutit China in 1937 by Ting V.K. & Wang Y.L. At
the 18th International Geological Congress, YOUNG C.C. (1951) recorded the Devonian verte¬
brates including “Ceplialaspis". This material was never described. However, in the same area
(Qujing, Yunnan Province) and .same horizons wilhin the Cuifengshan Group, several peculiar
agnathans were discovered during the early 1960s. The new généra Eugaleaspis (Galeaspis) and
Nanpanaspis were assigned to the Osteostraci (Cephaiaspjdes), while Polybnmchiaspis was
— 58 —
placée! in the Heterostraci (Pteraspides) (Liu, 1965). These fossils were unlike any previously
described jawless craniates and their relationship to the known major groups became a subject
of controversy. Tarlo (1967) suggested that eugaleaspids (galeaspids) and polybranchiaspids
should be United into a higher category, the Galeaspida. on the basis of the shape of the dorsal
shield, and classified among the Cephalaspidomorphi. with the same rank as the Osteostraci,
Anaspida, and Petromyzontida. This view was supported by Janvier (1975) but was rejected
by MOY-TltOMAS & Miles (1971). This view received the support from Chinese paleontologists
in the early 1980s (WANG & Wang, 1982a; ZtlANG et al., 1986).
In the 197()s many new galeaspid généra of Early Devonian âge from Yunnan. Guangxi,
Sichuan and Guizhou provinces were described (Liu, 1975; Pan et al.. 1975; Pan & Wang,
1978) and were cla-ssified with the hetcrostracans. By that time it was clear that South China
was a unique vertebrate province whcre fossil jawless craniates underweni a great radiation.
In the last decade, rcscarch work has greatly expanded and previous work on jawless crani¬
ates has been confronted by a serions challenge in several aspects.
Abbreviations
bo buccal opening, ouverture buccale ',
bro branchial opening, ouverture branchiale -,
dbo “dorso-branchial openings”, "ouvertures branchiales dorsales"',
Ido latero-dorsal fenestrae, /'enétreA' latéro-dorsales',
no e,xonasal openings, ouvertures nasales e.xternes',
orb orbital openings. orbites",
pdo médial dorsal fenestrae, /tfnê/ré'A mésio-dorsales',
pi pineal opening, ouverture pinéale -,
scs sensory canal sy.stem. sy.stème des canaux sensoriels;
sis sensory line System, système de la ligne sensorielle ;
Vp ventral plate, plaque ventrale;
IVPP Institute of Vertebrate Paleontology and Paleoanthropology, Academia Sinica ;
MGB Muséum of Geology, Beijing.
REVIEW OF THE FOSSIL JAWLESS CRANIATE STUDIES IN CHINA
First many new galeaspid généra hâve been described not only from the Early Devonian
strata of the southwestern provinces but also the Early Silurian strata in the région of the middle
and lower reaches of the Yanglze River (Pan & Wang, 1981; Wang & Wang. 1982a, 1982b;
Wang, 1984, 1986b, 1991; Llü, 1985; Pan & DlNEl.EY, 1988; Zhu, 1992; WANG & Wang,
1992; Pan & CheN, 1993). The new fossils of Early Silurian galeaspids found in Northwest
China (Kalpin District, Xinjiang) are very similar to those of Hanyanguspis from Hubei Province
of South China. This has important biogeographic significance because it suggests that the Tarim
Block and the South China Block hâve a more close relationship than other blocks in the Early
Silurian period (Fig. I).
Second, the data on the external charaders of the Galeaspida are fairly complété. The
Galeaspida possess a bony cephalic shield, varying both in shape and size and covering the
— 59 —
O Changxing
/
Shidian
Yiliang
Zhaotong* •'
Wudang 0 ^Duyun
'Xinshan q
Hgzhang
Xiushu
.Zhanyi
1
/
Wuting»
• vilang
Yilang
Wenshan 09'
^•^,1
lOD
,Guangnan
•Guiping _ —
Liujing
® Lofe Dev,
I^MIddl© Dev,
|EartyOev.
^EarlyDev.
@Lafe Siluflon
QjEorfy SIluflon
OEoMy Slurlon
Fig. 1. — Localities of Silurian and Devonian Galeaspida and Thelodonti in China. Round marks: Galeaspida, square marks:
Thelodonti.
Localités à Galéaspides et Thélodontes siluriens en Chine. Marques rondes : Galéaspides, carrés : Thélodontes.
anterior part of the body. In some forms there is a cephalic shield with a long rostral process,
and long latéral or posterior. cornual processes (Fig. 2H. I). The dorsal part of the cephalic
shield consists of a single exoskeletal plate, commonly with a large opening for the exonasal
openings, paired orbital openings, a single pineal opening and in some forms even paired latero-
or medio dorsal fenestrae (Fig. 21 ) and with a galeaspid-type sensory canal sysiem. The ornament
consists of snowflake-shaped tubercles.
There are two types of ventral part of cephalic shield ; one is found in Hanyangaspis
(Fig. 2B) and Pentathyra.ipi.i, the former with both anteroventral and posteroventral plates and
the latter with only one ventral plate covering completely the orobranchial chamber, and with
a buccal opening and paired, separate, pore-like branchial openings. The other type is that of
— 60 —
Polybranchiaspis (Fig. 2F), wilh a médian ventral plate and peripheral tesserae, a buccal opening,
and many, paired, individual branchial openings.
There are narrow and deep latéral scales. In some forms there are dorsal ridge scales, and
small diamond-shaped scales on the ventral surface of ihe tail. There is no evidence of movable
paired fins and Sanqiaspis rosi rata hud a hypocercal tail (Hai.sTRAD et al., 1979).
Third. several specimens of Galeaspida from both the Lower Devonian and Lower Silurian
of China show internai anatomy, including the central nervous System, vascular System and
varions sensory organs, preserved as iiltenial ca.sts. E.vaniples include Duyunolepis iDiivunaspis)
and Paraduyunaspis (Pan & Wancî, 1978); in particular, the internai anatomy ol' Chang.Kingaspis
(Wang, 1991) is e.xtremely well preserved. A summary of the internai anatomical characters of
the Galeaspida hased mainly on specimens of Chiing.xingaspis gui is given in Figure 3, (aiso
see Wang, 1991, pis IC, D, 2B. 3. 4. 5B).
Five divisions of the cranial cavity can be recognized: telencephalic. diencephalic, mesen-
cephalic. metencephalic and myelencephalic. Nine pairs of cranial nerve canals hâve heen iden-
tilted: terminal, olfactory, optic, oculomotor, trochlear, trigeminal, facial, glossopharyngeal and
vagus neiA’es. Of these. the structure of the telencephalic portion and the long terminal and
olfactory nerves are very important for deciding the phylogenetic relationship of the Galeaspida.
The most prominent feature of the vascular System is the paired latéral head veins, a large
dorsal aorta, paired extrabranchial arleries and a subaponeurotic plexus in the cephalic shield.
The major features of galeaspid sensory organs w'ere the separate, paired nasal sacs that
lack an ossified tloor; the single pineal and parapineal organ; the anlcrior and poslerior vertical
semicircular canals of the labyrinth cavity with ampullac, sacculus and endolymphatic duct open¬
ing e.xternally. Among them, the structure of the separate. paired nasal sacs is important for
deciding the phylogenetic relationship of the Galeaspida. In addition, six to more lhan twenty
pairs of branchial pouches hâve separate openings to the exlerior. A detailed hislological study
of tlie exoskelelon in the Galeaspida remains to be unraveled dnough good material (Reif, 1982;
Janvier, 1990; Wang, 1991).
Following on from the discovery of new forms and new' characters of the Galeaspida, the
discussion of the relationship between Jawless craniales and the Gnathostomata lias bccome fo-
cused on the position of the Galeaspida, which has changed sub.stantially. HalSTEad (1982)
stiggested a sister-group relationship between the Galeaspida and the Osteostraci, and aIso be¬
tween the Heterostraci and the Gnathostomata. Janvier (1984) showed a sister-group relationship
between the Osteostraci and the Gnathostomata, while the Galeaspida were placed as the sister-
group of the Osteostraci plus Gnathostomata. The author iWanG, 1991) pointed oui a sister-group
relationship between the Galeaspida and the Gnathostomata; in ihis case the Osteostraci should
be placed as the sister-group of the Galeaspida plus Gnathostomata. A close relationship between
osteostracans, galeaspids and gnathostomes has been propo.sed by Young (1991. Fig. 8a). yet
in an unresolved trichotomy. One functional interprétation of the galeaspid médian dorsal opening
has been given by Belles-ISLES (1985), who regarded the opening as an exhalant one that
permitted water to flow through the gills by the mechanism of fluid induction. In addition, the
mould of four row^s of high, narrow trunk scales has been fotind in China, and regarded as
anaspid scales in China (Liu, 1983), but there is not the slightest evidence for the existence of
either the Osteostraci or the Heterostraci in Silurian and Devonian strata of China (Wang, 1986b).
— 61 —
Fig. 2. — Main extemal characters of the Galeaspida. A, B, Hanyangaspis guodingshanensis (from Wang, 1986, Figs. 1,3). C,
D, Changxingaspis gui (from Wang, 1991, Figs. 1,2). E, F, Polybranrhiaspis liaojiaoshanensis (t'rom LlU, 1975, Fig. 5A,
B). G, Éitgaleaspis xujiachongensis (from Liu, 1975. Fig. 2). H, Sanqiaspis rostrata (from Liu, 1975, Fig. 12). I, Lung-
menshatwxpix kîangynuensi.s (from WANG, 1991, Fig. 14). A. C, E. G-l. dorsal aspect; B, F, ventral aspect; D, extent of the
endoskeleton (stipple).
Principaux coroctères externes des Galeaspida. A. B, Hanyanga.spis guodingshanensis (d’après W/t/vc. 1986, figs J. Si C,
D, Changxinga.spis gui (d’après WANG, 1991. figs /, 2). E, E Polybranchiaspis liaojiaoshanensis (d'après Uv, 1975, fig. 5
A. B). G. Eugalea.spjs xuJiachongensi.s (d'après Liu, 1975, fig. 2). H. Sanqiitspis rostrata (d'après LiU, Î975, fig. 12). 1. Lung-
menshanaspis kiangyouensis (d'après Wang. 1991, fig. 14). A. C E, G-l, face dorsale: B. F, face ventrale: D, distribution
de l’endnsquelette (gnsé).
— 62 —
Fig. 3. — Changxingaspis gui (from Wang, 1991, PI. 3) showing the neurocranium and viscéral endoskeleton. IVPP V8297, 2.
(Scale bar: 1 mm.)
Changxingaspis gui (d’après WANG, 1991, pl. 3), montrant le neurocrâne et l’endosquelette viscéral. IVPP V8297, 2. (Échelle :
l mm.)
— 63 —
Fourth, Silurian and Devonian lhelodonts hâve been recorded from China (Wang, 1984;
Wang et al., 1986; Wang & DONG, 1989; Wang, 1992) (Fig. 4). The diversity of the chinese
fossil jawless craniates has been increased, since the group contains not only the endemic
galeaspids, but also both cosniopolilan and endemic thelodonts (GrOSS. 1967; KaraTAJUTE-Tali-
MAA, 1978; Turner, 1991; Wang, 1993). The thelodont from China currently con.sisis of i.sulated
scales from ihe Ludlow, Gedinnian, Emsian, Eifelian and Givetian of ,southwestern China. They
are very u.seful for dating fish-bearing strata.
Turinia asiatica from the Xilun Fonnation of the Cuifengshan Group, Qujing District, Yunnan
Province, Is the first report of Üielodonts in China (Wanc;, 1984). A nevv cornbined programme to
recollect fossils bed by bed from the Cuifengshan Group was madc in 1991, in which abundant
thelodont scales were extracted by treatment with dilute acetic acid from the sample-s of 14 layers
(YDC.59, YDC.145) in both the Xishancun and Xitun Formations of the Cuifengshan Group. A new
genus, wliich consists of five species including four new ones and Turinia asiarica, will be erected,
along with thelodontidae gen, indet. on the basis mainly of new material (Wang, MS.).
The lower part of the Cuifengshan Group was placed in the Early Devonian by many workers
because of its endemic vertebrate content and its plant fossils. It wus placed in the Pridolian
by Mu ei al. (1986) although il does not hâve any fossils of proven Pridolian âge, but only
because it gradationally overlies Late Ludlow conodonts, the crispu.'i zone (W.\NG, 1981) in the
upper part of the Yulongsi (Yulungssu) Formation. I place the thclodont-bearing strata (the lower
part of the Cuifengshan Group) in the Late Pridolian to Early Lochkovian on the basis of the
new thelodont genus with the eharacters of both Silurian Thelodus and Devonian Turinia and
the following arguments. The brachiopods fossils of the Miaogao (Miaokao) Formation, which
conformably underlies the Yulongsi Formation, were regarded as Late Ludlovian to Early
Pridolian âge and ihosc of the Yulongsi Fonnation as Pridolian (RoNG & Yano, 1981). Recently,
new conodont and chitinozoan a.ssemblage.s were found in the uppennost part of the Yulongsi
Formation in the Qujing area. The former includes Ozarkodina excava/a. Deutacadina sp., and
cf. Ligonodina elegans detorta overlying the crispas zone, in which Ligimudina elegans deiorta
is the uppennost zone fossil of the Pridolian. The lattcr includes Eisenackilina, Lagenomorpha
and Margachilina sp. bclonging to the Margachitma elegans zone of Middle Pridolian âge (CAI
et al., 1994). A more important argument is that a species of the new thelodont genus in the
Cuifenshan Formation, in conjunciion with conadonl lcriodus wnschmidti, was found in the lower
Putonggou Formation of Early I.ochkovian âge in the West Qinling Mountains, Gansu Province,
North China (WANG et al., MS ).
Thelodus sinensis from the Guandi (Kuanti) Formation and Kawalepis comptas from the
Miaogao Formation of Qujing. Yunnan, were regarded originally as two Ludlovian lhelodonts
(WANG & Dong, 1989), but the latter may be a palaeoniscoid scale (EsiN & Talimaa. pers.
comm.).
Turinia sp. and Nicoliviidae gen. indet. are two isolated thelodont scales from the Emsian
Yukiang Formation, Liujing area, central Guangxi (Wang, 1992).
Turinia pagoda from the Givetian Heyuanzhai Formation, Turinia n. sp.? A and Turinia n.
sp.? B from the Eifelian Maluiang Fonnation were discovered in Shidian County, West Yunnan
(Wang et al., 1986). The former may be regarded as a new genus within thelodontidae (Talimaa
pers. comm ).
— 64 —
Fie. 4. — A, B. Thelodus .siiten.sis. a thelndoiM scalc (rom Ihc Gu;m(ii Formation (Lutllow-Pndoli) of the Qujmg area. Yunnan
Province (Crom WANG & DON’G. 1989. Pl.lF. G). IVPP V7225. 1 (x50). C. D. Tuhniu sp.. a ihclodnni stale IVom the Yujiang
Formation tlower F.msjan) of the Liiijing arva. Guang.xi Province (trom Wang, 1992, PI. l A-B). îVpp V974.^ (x50). E. F.
Turinin ^p. nov.? B. a thelodonl .scale frotn the VtaUMang Fonnulioit (Middie Devonian) of the Shidian County, We.si Yunnan
(from Wang ef (j/-, 198(>, Fig. 6G-H). (0-VF357 (x60). G. H. Turiniü pagoda, a iheUHlont scalc from the Heyuanzhai
Formation (Middie Devonlan.i of ihc Shidiun County, West Yunnan (from Wang i'i ai,. 1986. Fig. 6A-B). 1G-VF356 (x42).
A. C. E. G. exiemal view; B. D. F, H. ba>>al view.
Thelodus sinensi.s. uac vcailtv de thélodontf dt la Formalion dt Guandi ILudlow-Fridoli) de la pégUm de Qajhig. Yunnan
ld'tiprè.s Wang et Donc. pl. IF, C), IVPP V7225. 7 fx 50} : C. D. Turinia sp.. une émille de dietthionte de ta Fonnation
de yujiang (Einsien inférieur) de la région de lÀujing, Guangxi (d'apréx Wang, 7992. pi JA, P), IVpp V97d3 ix50). E. F.
Turinia .vp. nov. ‘J B. une éciitUe de ihélodonic de la Formation de Mulutang (Dévonien moyen) du district de Shidian, Yunnan
occidental (d'après Wang et a].. lhH6, fig. 6G-H), JGAF357 (x60). G. H. Turinia pagoda. une éraillé de tliélodonte de la
Formation de Heyuanzhai (Dévonien moyen) du district de Shidian, Yunnan accidentai (d'après fPA.va et al.. J9H6, fig. 6A B).
IC'VFSSh (x42) A. C, E. G. e.iterne : B. L). F H. \ue bu.udr.
THE SENSORY LINE SYSTEM IN THE GALEASPIDA
The dorsal part of the galeaspid cephalic shield displays the typical galeaspid pattern of
the sensory line System. This pattern consists of threc main éléments: the supraorbital line, in-
fraorbital line (latero-longitudinal line and latero-transversal lines), and one or two medio-trans-
versal commissures. There are three major types of pattern:
1) supraorbital sensory-iines undeveloped or absent, two medio-transversal commissures,
as in Hanyanga.spis (Fig. 2A) and Changxingaspts (Fig. 2C);
2) a V-shaped pineal line and one medio-transversal commissure such as Huananaspiformes
and Polybranchia.'ipi.'i-VAs forms (Fig. 2E);
3) the pineal line extending backwards to contact with the medio-transversal commissure
such as in Eugaleaspii (Fig. 2G). This sensory line pattern differs greatly from that of the Osteos-
traci or the Heterostraci (Fig. 5).
— 65 —
Fig. 5. — Paitern of sensory-line sysleni in The dorsal shield. A, ihe osieosiracan Cephalaapis pagei (slightly modified Irom
Stensiô, 1932. Fig. 33A). B. The hetecostracan Pomspis sp. (slightiy modified from DENlSox. 1964. Fig. 91 A). C. the galeaspid
Damasph vortus (from WANG & WANG, 1982b, Fig. l).
Répartition üu système sensoriel de lu ligne latérale sur le bouclier dorsal. A, rOstéostracé Cephalaspis pagei (d'après
Stensiô, 1932. fig. 33A. légèrement modifie). H, VHctérostrucé Poi'a>pi.s .\p, (d'après OENISON, 1964. fig. 91 A. légèrement
modifié). C. le GaJéaspide Dama.spj.s vartus (d'après Wang U'aA'C. 1982h, flg. /, légèrement modifié).
Generally, the Osteostraci lack the supraorbital line and has an infraorbital Une without
latero-transversal Unes. The Heterostraci hâve two paired, dorsal longitudinal Unes joined into
a separate dorsal network by transverse commissures (latero-transversal line).
The sensoJ7-Une System in lhe dorsal shield of the Galeaspida is well developed in the
form of canais in the bony ex.o.skeleton and superficial grooves (Fig. 6). It is connected with
the lateralis nerve canais in the carapace by the pores situated in the lower part of the sensory
canal. The pattern of the galeaspid sensory Unes differs thiis from that of the Osteostraci or the
Heterostraci.
The sensory-line system of the Osteostraci is nol embedded in the bony exoskeleton. but
merely leaves a feu- fragmentary interrupted superficial grooves lo indicate its course. The
sensory-line system of Ihc Heterostraci is well developed in the fomt of canais in the middle
layer of the e.xoskeleton. which open to the exterior by a sériés of pores (Stensiô. 1932; Denison,
1964; Stensiô, 1964; Moy-Thomas & Miles, 1971; Ritchie & Gilbert-Tomlinson, 1977;
Jarvik, 1980; Novitskaya, 1983; Blieck, 1984; Janvier, 1985a). The Galeaspida resemble
more the Heterostraci than the Osteostraci in the structure of sensory Une system of the dorsal
shield. This is probably a symplesiomoiphy.
GALEASPIDS WITH THE PAIRED LATERAL OR MEDIAL DORSAL FENESTRAE
The plates and figures of three formerly described galeaspid généra attracted my attention.
These are Lungmenshanaspis and Sinoszechuanaspis, both from the middle part of the Pingyipu
— 66 —
Frc. 6 - Hnfvhmnfhtaspn' sp.. IVPP VIÜ33!. A, aspect of lhe canab and of the sensory-line syslem ot ihe dorsal shield
(scale bar: î cm). B, vertical section ot iwo canais (scale har: lü pm arrows). C. venicat thin section showing details of a
. canal (.scale bai; 10 pm). D. vertical thin section shovi ing the structure ol ihc sensory canal wall and a passage between lhe
sensory-line in lhe e^oskeleton and the underlying cartilage (scalc bar: 10 Mm),
Polybranchiaspis sp.. IVPP VJÜJ3I A. ospect des canaux et sillons du sysrèntn de la ligne luiénilc sur le bouclier dorsal
icvhelle: I cm). B, section verticale de deity canaux iéchelfe : 10 flèchesh C. section verticale d'un canal, montrant les
flétaif.s (le la urucmre {.echelh' : 10 pmi. O, section verticale d'un canal montnwt tes détails de la structure des parois, ainsi
qtt'un passage entre le canal et l'endosquelette sous-jacent (échelle : 10 pm).
Group, Lower Devonian, Jiangyou District of Sichuan Province (Pan et ai, 1975), and Qing-
menaspis from the upperpan of the “Cuifengsban" Group of Early Devonian âge in the Qingmen
area. Zhaotong District of Yunnan Province (Pan & Wang, 1981 and also see Fig. 7).
Previousiy, lhe author provided a new interprétation and a new illustration of the dorsal
surface of a cephalic shield of Lungmenshatwspis (Fig. 8B ) and considered Uiiigmenshanaspis
to hâve paired laiero-dorsal fcnestrac (openings) of unkiiown funclion, judging by its plates
(Wang, 1991).
In the original illustration of Qingmenaspis, a pair of openings in the dorsal shield was
interpreted as “dorso-branchial openings" (PAN & Wang, 1981, Fig. 3 and also see Fig. 8F),
which, in my opinion, is a pair of médial dorsal fenestrae (postero-dorsal openings) (Fig. 8G),
and is a synapomorphy shared by Qingmenaspis and Liingmenshanaspis (Wang, 1991. Fig. 14).
— 67 —
Fig. 7. — A. Qingmcnaspix microculus (fmm Pan & Wang, 19K1, PI. 1, Fig. 3^ dorsal shield. MGB V1745. B, Lungmenshanaspis
kiangyouensis (from PAN et al., 1975. PI. 17, Fig. l), dorsal shield, MGB V1513. C. Sinoszevhuanaspix yanmenpaensis, (from
Pan et al. 1975. PI. 2, Fig. 1). posterior paît of the dorsal .shield, MGB VI514. Scale har: 1 cm.
A, Qingména.spis microculus (li'après Pan Wang, 1981, pl. /. /ig. 3), bouclier dormi, MGB VI745. B. Lungmenshanaspis
kiangyouensis (d'après P.AN ei al., 1975, pi 17,Jtg. J), bouclier dorsai MGB VJ5IJ. C, Sinoszechuanaspis yanmenpaensis,
(d’apt'ès Pan et al.. 1975. pi 2. ftg. l). partie postérieure du bouclier dorsal, MGB VI514. Échelle ■ / cm.
— 68 —
In the original description of Sinaszechuanaspis (Szechiianaspis), a peculiar sensory line
canal System in the dorsal shield was noted by Pan & Wang (1975, Fig. 3 and also see Fig. 8C).
In the second illustration of the same specimen, the .sensory line canal System was changed into
a pattern wiih a pair of elliptic circles (PAN & DtNELEY, 1988, Fig. 9, and also see Fig. 8D).
Recently. PAN (1992) accepted the interprétation that the paired elliptical “sensory line System”
are a pair of dor.sal fenestrae (médial dorsal fenestrae in this paper) as true (Fig. 8E). I agréé
with this. A new genus, Macrothyraspis, described by Pan proved that the paired dorsal fenestrae
exist in galeaspids.
n
II
II
II
II
Fig. 8. — Different restorations of the dorsal shield in three généra of the Macrothyraspidida. A, B, Lungmenshanaspis kiangy-
ouensùr, C-E, Sinoszechuanaspis yanmenpaensis: F, G, Qingmenaspis microculus. A, C, from PAN et ai, 1975, Figs. 1, 4;
B, from Wang, 1991, Fig. 14; D, from Pan & Dinbley, 1988, Fig. 9; E, G. slighlly modified fmm PaN, 1992, Figs. 29.
50: F, from PAN & WANG, 1981. Fig. 3.
Différentes reconstitutions du houvïier dorsal chez trois genres de Macrothyraspidida. A. B. Lungmenshanaspis kiangyouensis :
C~E> Sinoszechuanaspis yanmenpuensis ; F, G. Qingmenaspis microculus. A. C, d‘après Pan aL. 1975. figs /. 4 : B, d'après
Wang. 1991, fig. 14: O, d'aprè.\ Pan & Dineley, 19S8, fig. 9: E, G, légèrement modifié d'après Pan, 1992, figs 29. 30:
F. d'après Pan tS Wang, 19SI. fig. 3.
— 69 —
There are therefore four généra; Limgmenshanaspis, Q'mgmenaspis, Sinoszechuanaspis and
Macrothyraspis ail having paired latéral or médial dorsal fenestrae of unknown function, and a
long rostral process, as well as a pair of long transverse comual processes.
Pan (1992) described two other new généra: Pentathyraspis and MicrohopUmaspis, bearing
latero-dorsal fenestrae, but neither with a long rosirai process nor a pair of long transversal
cornual processes.
Liu (1993) compared the latéral fields of osteostracans with the latéral fenestrae (the latéral
or médial dorsal fenestrae in this paper) of galeaspids. He thinks that “the latéral fenestrae of
galeaspids are not only morphologically comparable with, but aiso phyletically homologous to
the latéral fields of osteostracans, and the feature is shared only by osteostracans and galeaspids
within agnathans”.
The homology of the paired latéral or médial dorsal fenestrae in .some galeaspids is a very
inlcresting problem, I shall give my interprétation below.
First, the ccphalic shield of osteostracans hâve one or more pairs of latéral fields and a
single médian field. but those of galeaspids possess only a pair of either latero-dorsal fenestrae
or médial dorsal fenestrae.
Second, the paired latéral fields of osteostracans are situated laterally, in front of, and behind
the orbital plane. On the conlrary, a pair of latero-dorsal fenestrae as well as médial dorsal
fenestrae of galeaspids are always situated always behind the orbital Icvel. Moreover, the paired
médial dorsal fenestrae of galeaspids are so large that they occupy most of the postero-dorsal
part of the cephalic shield.
Fig. 9. — Phylogenelic interrelationships among the Macrothyraspidida.
Relations phylogénétiques entre les Macrothyraspidida.
— 70 —
Third, the latéral fields of osteostracans are covered with dermal platelets and are connected
by canals to the capsule, whereas the latero- or médial dorsal fenestrae of galeaspids are devoid
of any similar dermal platelets and canals.
Under such circumstances. it is difficult to say that the latero- or médial dorsal fenestrae
of galeaspids are comparable both morphologically and homologically with the latéral fields of
osteostracans. I think that the fenestrae are a synapomorphy of the fenestrate galeaspids and the
order Macrothyraspidida is a monophyletic group within the Galeaspida. Six généra possessing
the latero- or médial dorsal fenestrae can be referred to two families, the Macrothyraspididae
and Pemathyraspididae, within the order Macrothyrasidida. The Macrothyraspididae includes four
généra: Lungmanshanaspis, Qingmenaspis, Sinnszechuanaspis and Macmthyraspis, and the Pen-
talhyraspididae includes two généra: Pentathyraspis and Microhoplonaspis. Their phylogenetic
relationships are shown in the cladogram in Figure 9. The numbered .synapomorphies are:
1. Dorsal shield with a pair of latéral or médial dorsal fenestrae placed behind the orbital level.
2. Cephalic shield with a pair of broad inner cornua.
3. Cephalic shield with a rostral process and a pair of long latéral comual processes.
4. Dorsal shield with paired médial dorsal fenestrae.
5. A heart-shapcd exonasal opening. orbital openings placed laterally.
It is interesting that the combination of a longitudinal slit-shaped exonasal opening and the eu-
galeaspid pattern of the sensory-line System used previously as the apomorphic characters for
the Eugaleaspidiformes actually appear in the huananaspidid-like forms such as Pterogonaspis
Fig. 10. — Cladogram showing the relationships betwecn the Eugaleaspidiformes, Huananaspidiformes, and Pterogonaspis.
Cladogramme montrant les relations phylogénétiques entre les Eugaleaspidiformes, Huananaspidiformes, et Pterogonaspis.
— 71 —
(Zhu, 1992) and Tridensaspis (Liu, 1986). Similarly, the feature of the paired latéral or médial
dorsal fenestrae is reported from the fenestrate huananaspidid-like forms (Macrothyraspididae)
and in the polybranchiaspidid-like forms (Pentathyraspididae).
On account of the reason statcd above, I consider thaï boih the Huananaspidiforme.s and
Eugaleaspidifomies. regarded previously as two monophyletic groups within the Galcaspida. are
confronted by a .serions challenge. I provide a cladogram showing ihis relalionship (Fig. 10);
the numbered synapomorphies are:
1. Longitudinal slit-shuped exonasal opening and supraorbital seosory Unes in contact with the
médial transversal commissure.
2. Cephalic shield with a long rostral process and a pair of long latéral comual processes.
HABITAT OF THE FOSSIL JAWLESS CRANIATES
(GALEASPIDS, THELODONTS) fN CHINA
The habitat of the fossil jawless craniates is a very interesting problem (Robertson, 1957;
Allen & Tarlo, 1963; Boucot & JANts. 1983; Goujet, 1984; Wang, 1984, 1986b; Hal.stead,
1985; Janvier, 1985b; Mârss, 1991). The fos.sil jawless craniates found in China are represented
by two groups: the Galeaspida and Thelodonii.
Mo.st thelodonts hâve been extracted from Silurian and Devonian carbonates, particularly
from bioclastic limestone. non-bioherm limestone and pseudo-oolitic limesione in China.
Thelodus simnsis from the Late Ltidlow lo Pridoli Miaogao and Guandi Formations of Qujing
District, Yunnan Province (Wang & Dong. 1989); Tiirinia sp. and Nikoliviidae gen. et sp. indet.
from the Early Emsian Yujiang Formation of Liujing village, Guangxi Province (Wang, 1992);
Turinia sp. nov.? A and Turinia sp. nov.? B from the Eifelian Malutang Formation and Turinia
pagoda from the Laie Givelian Heyuanzhai Formation of Shidian District of west Yunnan (Wang
ex ai, 1986). Associated fossils are conodonts, and other microfossils found mainly in shallow
marine environment. The thelodonts were extracted from a mari and calcareous sandstone in the
Xitun Formation of the Cuifengshan Group (WANG, 1984; WANG, MS). Other associaled verté¬
brales are galeaspids, acanthodians. sarcopterygians. placoderms, chondrichthyans (Wang. 1984;
Zhang et al., 1986) and marine bivalve.s, chitinozoans, acritarchs, inarticulate hrachiopods, lin-
gulids etc. (Pan et al., 1978; Fang et al., 1985). The thelodont-bearing strata indicaie a littoral
environment, judging from abundanl chondrichthyan remains, marine invertebrates, and even
other marine microfossils. Conscquently, the thelodonts found in Silurian and Devonian strata
of China occupied a littoral or neritic depositional environment.
The major question to be answered is: did the Galeaspida inhabit a marine or fresh water
environment? The question can be answered on the basis of three sets of evidence.
1) Other fossils found with lhem in the Cuifeng.shan Group of Qujing, Yunnan;
2) the sedimentological analysis of galeaspid-bearing environments of the Lower Devonian
in Sichuan, Guangxi and Guizhou Provinces;
3) the data of the Silurian galeaspids and galeaspid-bearing red clastic rocks.
— 72 —
The name of the Cuifengshan Group was derived from Mount Cuifeng located U) km west
of Qujing City, eastern Yunnan. According to the paleomagnetic data studied by C. LiU & Q.-Z.
Liang (in Fang et al, 1985), the Qujing région was situated slightly north to the equator in
Early Devonian timc.s, The Lower Dcs'onian section extends approximatcly 7 km from Xi.shancun
village ihrough the Xilun, Guijiatun to Xujiachong villages. Its thickness is 2100 m. It has good
e.Kpo.sure. with abundani early vertcbraie fossil.s, tlic First galeaspid fossil was recordcd in this
section. The Cuifengshan Group was regarded as continental for a long time bccause of its fresh
water fishes and plants. The author suggests a new analysis for the habitat of the Lower Devonian
galeaspids in Qujing on the basis of data provided by geologists and paleoniologists in the last
decade. particularly in 1991. including new collections of fossils and observations in the field.
The Lower Devonian stratigraphie sequence in the Cuifengshan area of Qujing is, in as-
cending order: the .Xishancun, Xitun, Guijiatun and Xujiachong Formations.
In the Xishancun Formation of the Cuifengshan Group, the main éléments of vertebrate
fossils are the Galeaspida (Agnatha) and Yunnanolepilbrme.s (Anliarch). The former includes
Polybntnehiaspis minai; P. yulon^^xsus, P. miandkmiunensis, P. liaajki.shanensix, Diandangaspis
xishancunensis, Dcmgfangaspis qujingensis. and Dcimctspis vartiix; the latter includes Yiiniuinolepis
chii, and Qujinalepis grucilis. Other fossils are marine bivalves: Madimarplui yunnanensis; M.
cf. hrevis. Dysodaïua depniti. D. luevix, D. arbila, and D. pUinidcnlafa: acritarchs: Leiofusa sp.
and Leiosphaerkiia sp.; chitinozoans; Aiiyravhiiinci sp. and Angochiiina sp.; inarticulate bra-
chiopods; lingulids; eurypterids and spores. It is interesting lhat our research group found a
complété articulated branchiopod fossil in a saine horizon together with Pidybranchkixpis liao-
jiuüshanenxis in 1991.
lu the Xitun Formation of the Cuifengshan Group, the vertebrate fossils are very abiindant
Galeaspida; Engaleaspis changi, Ncinpaiwspis nncwculus, Laxaspis qujingensis, and Dongfan-
gaspis major. Thelodonti: the new genus and Thelodontidae gen. indet. Acanthodii: Yaimgacan-
thus gracilis, Noslolepis sp. and Ischnacanlhidae indet. Sarcopterygii; Youngolepis praecursor
Flü. 11. ^ — Trace lossil Chondrites in a.ssociation with many fi.sh scales in a bone bed of the Xitun Formation, Qujing area,
Yunnan Province. IVPP VlOT^l (Xl).
Trace fossile du genre Chondrites, cissociée à de nombreuses écailles de poissons dans la Formation de Xitun, région de
Qujing. Yunnan. IVPP VJ033I {xJ).
— 13 —
and Diabdlepis speratus. Placodermi: Yunnanolepis chii, Y. parvus, Qujinolepis gracilis, Phy-
molepis cuifengshanensis, and Szelepis yunnanensis. Chondrichthyes; Guolepis elegans, Chan-
golepis tncuspidus. Peilepis soUda. and Ohiolepis xitunensis. Other fossils are marine bivalves:
Modiomorplia hicosiata, M. yunnanensis, Dysodonta deprali, D arbilii, and D. kievis: sonie
complété lingulids or numerous fragmenls of lingulid shells in association with vertébrale mi-
crofossils were exiracled from calcarcous rocks by Ircalment with acetic or fonnic acids, and
cven many trace fossils were Ibund (Fig. 11). I waiii to empliasizc l'oilowing facts: the marine
bivalves that occur în the Xitun Foimation, are oflen associaled with vertebrate fos.sils. either
in the samc layer or in an overlying or underlying layer. Many chondrichthyan .scales can be
extracted both from the calcareous sandstone and the argillaccous limestone. in which some
complété cranial roofs of sarcopterygians, and complété head-sliield and trunk-armour of the
Yunnanolepiformcs were also found. The rich calcareous material indicates a transgression. The
pre.sence of chondrichthyans supports the view thaï the Xitun Formation was a marine deposit
(Wang, 1984, 1986b) and thaï the vertébrales in the Xitun Formation were not of fresh water
origin.
While the view of the marine condition of the Xishancun and Xitun Formations is accepted,
to the conlrary. the sedimentaiy environment of the Guijiatun and Xujiachong Formations has
aiways been regarded as continental, primarily because the Guijiatun Formation is a red clasiic
rock sequence with "fresh water fish fossils” and the .Xujiachong Formation has “fresh water
fish fossils” and plant fossils. However, I found many layers together with vertébrales, bivalves
and lingulids both in the Guijiatun and Xujiachong Formations in 1991. The same bivalves are
also found in marine deposits (Fang Z.-J. pers. comm.). In the upper part of ihc Xujiachong
Formation, there is a layer with galeaspids; Etigalea.':pis xujiaelumgensis. quite similar to E.
chungi from the Xitun Formation, and a new form, associaled with lingulids and marine bivalves
and many plant fragments, such as Drepanophycus spinaejormis and Zostewphylluni yuiuutiücum
(Li & Cai, 1978), Both vertebrate and invertebrate fossils are aulochlhonous. On the contrary,
the plant fragments were clearly iransported over a long distance (LlG Z. -H. pers. comm.).
Undor such circumstances, there are reasons to believe that galeaspids, Ihelodonls. and other
fishes foupd in the Cuifengshan Group once livcd mainly in a littoral habitat. There are also
other evidence in The Bac Bun Formation of northern Vietnam (corresponding to the Cuifengshan
Group of East Yunnan); the layers conlain a vertebrate fauna including galeaspids. and the Howit-
tia wangi brachiopod fauna (Tong-Dzuy & Janvier. 1990).
Lower Devonian galeaspid-bcaring strata are distributed through the Cuifengshan Group of
Yunnan Province, the Pingyipu Group of Sichuan Province, the fàanhuashan and Nakaoling For¬
mations of Guangxi Province, the Danlin, Shujiaping and Wudang Formations of Guizhou Pro¬
vince, and are even found in the Norlhca.sl of Vietnam.
The problem of marine versus freshwater environment can bc further addressed through the
analysis of the sedimentary environment in the Pingyipu Group (Lungmenshan area, Sichuan
Province); the Lianhuashan and Nakaoling Formations (Liujing area. Guangxi Province), and
the Danlin. Shujiaping and Wudang Formations (Guizhou Province).
A sludy of the sedimentary environment in the early Lower Devonian Pingyipu Group was
donc by Tang D.-Z., Liang Q.-J. & Du Z.- Y. (1988). The Pingyipu Group (from the Guixi
Formation up to the Guanshanpo Formation) was previousiy regarded as a continental deposit.
< — yxtjuoApo- -y^A^ 07
— 75 —
Tang, Liang and Du’s work bolh in the field and in the laboralory on the lilhology, biola and
sedimentary structure, resulted in an important conclusion: the sedimentary environments during
the early lower Devonian Pingyipu Group are, respectively, the fore littoral zone (foreshore),
near-littoral zone (nearshore), and shallow-water shelf (shelf) with clear beach characters from
the Southwest lo the northeast (Fig. 12). The Group consists of terrestrial clastic rock, mainly
light grey, médial and fine-grained quartz sandstone, with some fine-grained quartz greywacke,
siltstone and mudstone. and a few grey, silty mudstones. Sedimentary structures are well preserved
in this set of strata, and cross-bedding is vcry clear. Many trace fossil faciès are aiso well pre¬
served, such as Skolithos faciès, Cniziaiui faciès and Zoophycus faciès. Fossils include hra-
chiopods: Hcnvellella sp., Setophochanetes pinf’yipuensis, S. cnnvexa, Humiiffia cf. wungi, and
lingulids, oslracods; Guaiigxinkt heichuancnsis. Beyrkhia guixinenxix, and Birdxallella xi-
chuanenxix: bivalves, spores, chitinozoans. echinoderms. some fragments of plants and vertebrate
fossil galeaspids: Dimgfangaspix major, Sanqiaxpix xichtuinenxix, S. roxtrata. Sinoxzecluianensix
yunmenpuenxts, and Litngmenxhanaspix kUingyotiensix can be found in the middie and upper
parts of the Pingyipu Group in the Yanmenpao area of Jiangyou District. Therefore. the author
believes that the galeaspids in the Early Devonian Pingyipu Group lived in nearshore, foreshore,
and shelf manine environments.
The f.iujing Devonian section in Hengxian District. Guangxi Province, is one of the most
famous Devonian sections in South China. The sedimentary environments were from the front
margin of the platform, then open platform to tidal Hat, on a limiied platform. The sédiments
are mainly various carbonates with few terrigenous clastic constituants (Kuang et al., 1989,
Fig. 3, and also see Fig. 13).
The eaily Lower Devonian Lianhuashan Formation and the lower part of the Nakaoling
Formation were previousiy regarded as continental deposits by virlue of purple-red and greyish
green clastic rocks and fresh water fish fossils. New works of Wu Y. et al. ( 1987 1 and Klang G.-
D. et al. (1989) both in the field and in laboralory on the lithology, biota, sedimentary structure,
sedimentary faciès, and palaeoecology, provided a new conclusion: the sedimentary environment
of the Lianhuashan Formation was littoral, with shallow. low energy, slightiy-moving w'ater in
a basin which was locally closed. It changed from littoral to neritic in the early Nakaolian period
(Kuang et ai, 1989, Fig. 19, and also see Fig. 14).
Fig. 1 2. — InicrpreUilion of sçdinicntary environmeni in lhe curly Lower Uovonian ot Lun^menshan area. .Sithuan Pri'vince, islighily
moditied from Tang ei ni., ItlXX, Fig. .t|). FOS, foreshore; ItWL, high water mark; LG. lagoon; l.o, lower part; Nfm, inud
moumJ; NES. nearshore. Sb. sand bar: Sc. sand cre.sr: SHE. shelt; Up. upper part. I. macroemss-slnilificalion. 2. rriugh
eross-slralirie.iliott: 3. cross-bedrling; 4. ininot sand luminule bedding: 5. orthngrain seqiienee bedding: 6. hori/onlal bedding;
7, articulale brachiopod; K. chitrnozoa; d, irilobites; 11), lishes (Agnatha and llshest; 11. bivalve.s; 12. plants: 13. ostracods:
14, lingulids; 15. Fftvi<it/tv; 16, PUinolilex, |7. Slmlillinr, 18, Arv'itcnlhrs-, l‘). Chnndnicx: 20 C'rit.^irrnrr; 21, rhukisoiwides.
tnrerpréiaiion de l 'eiivimnnemciir sddimeiiiuire dtiri.t le t>é\omtn iiilérieur hti.^al de la réMion de l.iaigmeiuhaii, priniiu v de
Sichuan, {d'apri^ lAUr, étal.. IVtlS, fig. it, légéremeni mndijlé). lOX, marge: HWU maiyue des houles eaui; LC,, lagune
: La. parlie inférieure Mm. manik ule de trise ; NfîS. proche rivage : Sh. heirre s,rhleiisc : Sc. crête de .vahle : SHE. plateau
: Up. partie .supérieure. I. n ratification à grands entrectioisemeni.s ; 2. stratiju ation entrecroisée grossière . J. stratification
entrecmiséc fine : 4. stmlifiratinn de .sable fin : 5. séquence siraifiée grannclasxée : 6. stnilftralinn bnrigonlale : 7. tira-
chiopodes articulés: fl. Chitinazouires : d, Trilohiles ; 10. pai.ssans !,\gnaihes et poissons): H. Hivalves ; 12. Plantes: 13.
Ostracsides : 14. Lingulides : 15, Phycodes .• 16, Planolites . 17, Skolithos; Id, Arenicolite.s .■ 10. Chondrites .• 20. Crur.iana ;
27, Thulii.s.sinoidcs.
— 76 —
w. .. 0 zoom , , ,
siùtîorv
FiO, 13, — Stratjgiai)liic section of Lower Dcvoman in ihc üiijing area, Guangxi Province, {slighily modifieü from Kuang et
al.,, 1989, Fig. 3). l, conglomeraïc; 2. sandstone; 3, pelilic sand.stone; 4, pelilic siltstone; 5, sill dolomite: 6. mudstone; 7,
argilloccous limesione; 8. mari; 9. limestone; 10, siliceous dolomile.
Coupe stratigraphitiue du Dévonien inférieur dans la région de Liujing. pixnince de Guangxi. {d’après Kjang et al., J989.
fig d. légètvmenr modifiél /. (ongfomerat ; 2. grès ; J. grès pélitique : 4, silt péUtique ; 5. xih dolomifufue ; 6. argilite : 7.
calcaire argileuL, 8, inurne . 9,. luicaln' : 10. dolomie siliceuse.
Fig. 14. — Sketch showing the sedimentary tacies of the Lianhuashan-Nakaoling stages in the Llujing area, Guangxi Province,
(slightly raodified from KLtANG et al., 1989, Fig. 19).
Schéma montrant les faciès sédimentaires des étages Lianhuashanien-Nakaolingien dans la région de Liujing, Guangxi Pro¬
vince. (d’après Kuang et al., J9S9. fig. 19. légèrement modifié).
In the Lianhuashan Formation of Liujing area there are Ymnanolepis sp. and Qitjinolepis
sp. In the lowermost part of Nakaoling Formation there are the galeaspids Asiaspis expansa,
Antiquisagittaspis cornuta, and the arthrodiran Szelepis sp.; and in the middle and upper parts
of the Nakaoling Formation there are fishes such as acanthodians: Gomphonchus liujingensis,
Machaeracunthns? bohemicus, and a sarcopterygian. Onychodus sp. (Wang, 1992).
The transgression sédiments from littoral faciès to neritic organic bank faciès took place
during the Yujiang period. The substrate was mainly a soft, sandy, and limy mud on a gentle
slope (Kuang et al., 1989, Fig. 22, and also see Fig. 15).
— 77 —
"I Lin^uHa.*
BsheU
lii^’extone
Srlittausitlt *7?
lirnett»^ Ammo^d
Fig. 15. — Sketch showing the .sedimenlary faciès in the Yujiang Formation and the unnamed formation of late Early Devonian
âge in the Ltujing area, Guangxi Province, (slighrly modified from Kuasg et ai, 1989, Fig. 22).
Schéma montrant le a furies sédimentaires dans la F'onnation de Yujiang et dans la Jnrmalinn non nommée, d’âge dévonien
inférieur basal, dans la région de Liujing. province de Gunng.d (d'après KuanC et ai., I9S9, fig. 22. légèrement modifié).
Many microremains of vertebrate fossils hâve been described from the Yujiang Formation
of the Liujing area, including thelodonts: Turinia sp., Nikoliviidae gen. indet.; acanthodians:
Cheiracantlioicles complus, Gomphnnehus liujingensis\ sarcopterygians; Onychodus sp.; and chon-
drichthyans: Ohiolepis newberryi, Wuxuanivhthys warigi, Guedepis sp., and Hercynolepis sp.
(Wang, 1992).
The sedimenlary environment of the Lower Devonian Danlin and Shujiaping Formations
of Guizhou Province are respectively littoral or epicontinental littoral to nerilic, judging from
chitinozoans. spores and saline or brachish water algae in the Danlin Formation and by bra-
chiopods such as Euryspirifer paradoxus shujiapingensis, Oiospirifer dedeensis in the Shujiaping
Formation (Hou et ai, 1988).
The galeaspid Duyunolepis paoyangensis occurs in the lowermost part of the Shujiaping
Formation of Paoyang District, Paraduyunaspis hezhangensis in the uppermost part of the Danlin
Formation of Hezhang District, and Neoduyiinaspis minuta in the middle part of the Wudang
Formation of Wudang District, Guizhou Province. The Wudang Formation corresponds to the
middle and upper parts of the Danlin Formation and the lower part of the Shujiaping Formation
(Fig. 16).
With respect to the lower Devonian galeaspid-bearing sedimentary environments in Yunnan,
Sichuan, Guangxi and Guizhou Provinces, the above data lead to the conclusion that the
galeaspids lived completely in marine (littoral to neritic) environments. They were possibly eury-
haline agnatlians but no fresh water ones.
The problem can be also re.solved from the analysis of the Silurian galeaspid environments
and Silurian and Lower Devonian red clastic rocks.
Silurian galeaspids hâve been mainly reported from the région of the middle and lower
reaches of the Yangtze River. The oldest reported galeaspid-bearing stratum is the Rongxi For¬
mation of Dayong District. Hunan Province, with the galeaspid Dayongaspis hunanensis. The
formation is mainly composed of red, yellow or greyish green silty mudstone and contains bra-
chiopods: Nalivkinia. Nucleospira, Isorthis, Striispirifer, trilobites; Logiashunia\ graptolites:
Hunanodendriim; and crinoids; Pisocrinus (Fig. 17).
— 78 —
East Yunnan
Central Guangxi
North Sichuan
South Guizhou
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Ertaizi Fm.
Ertang Fm.
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Ganxi Fm.
Guijiatun Fm.
Nakaoling Fm.
Bailiuping Fm.
Xitun Fm.
^anylnmlao Fm.
Lianhuashan Fm.
Xishancun Fm.
Guanshanpo Fm.
Muerchang Fm.
Gulxi Fm.
Shujinping Fm.
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Pre Devonian
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Silurian
Silurian
Ficî. 16. — Cla.ssical corrélation of the galeaspid and thelodont l>earing strata of the Lower Devonian in China. Round marks,
galeaspid.s: square marks, thelodonts.
Tablfcm des afrrvlalhns classiques entres les niveaux ù Goléaspides et à Thélodontes dons le Dévonien inférieur de Chine.
Marques rondes, Galéaspides ; carrées, Thélodontes.
The overlying upper Xiushan Formation contains a diverse shell fauna of mostly bra-
chiopods: Salapinellci. Xinancispiiifer, Nalivkina, Atrypoidea, and Atrypopsis'. irilobites;
Carana.ipi.'i. Comnocephalus rex. Kailia, and Rongxielhv. naiitiloids: Sichuanocerax; graptolites;
Stomatograptiis sinensis\ conodonl.s: Pternspathodus telloni; and chitinozoans; Angochitina lon-
gicollis (Rong & Chen, 1990). The Xiushan fauna has bcen widely encouniered in the Late
LIandovery Goudingshan Formation of Wuhan city, Hubei Province with the galeaspid Hanyan-
gaspi.'i giiodingslianensi.'!, and in the Fentou Formation of Chaoxian District. Anhui Province,
with the galeaspid Latirnstraspis chaohuensis.
The so-called Upper Red Beds of the Silurian contain the galeaspid-bearing formations;
Hui.xingshao. Xikeng, and Maoshan formations, ail overlying the Xiushan Formation. The
— 79 —
a b
Fig. 17. — Different opinions on the âge of the Lower Silurian galeaspid and ihelodont-bearing strata in China. A, after N.-Z.
Mu et al.„ 1982; B, by RONG & Chen, 1990. l, Huixingshao Formation; 2, Majiachong Formation; 3, Maoshan Formation;
4, Xikeng Formafion; 5. Giiodingshan Formation. Round marks. galea.spids; square marks, thelodonts.
Différentes opinions sur l'âge des niveaux à Caléaspides et Thélodontes dans le Silurien inférieur de Chine. A, selon N.-Z.
Mu et al., 1982 ; B. selon Royc &. CheN, 1990. I. Fortnation de HuLxing.shcw ; 2. Formation de Majiachong : 3. Formation
de Maoshan : 4, Formation de Xikeng ; 5. Formation de Gttodingshan. Marques rondes. Caléaspides ; carrés. Thélodontes.
Huixingshao Formation of Xiushan District of Sichuan Province includes the galeaspid Eu-
galeaspis xiushanensis (LlU, 1983). The Xikeng Formation of Xiushui District, Jiangxi Province,
includes galeaspids: Sinogaleaspis shankanensis, S. xikengensis, Xiushuiaspis juvigxiensis, and
X. ganbeiensis (P' AN &. DlNELEY, 1988). Tlie Maoshan Formation of Changxing District. Zhejiang
Province includes galeaspids: Sinogaleaspis zhejiangensis (P' AN & Wang, 1981), Changxingaspis
gui, and Meishanaspis lelunani (WANG, 1991). Other fossils in the Upper Red Beds are
gastropods: Discodichilus sp., bivalves: Modiolopsis sp. and microfossils: Leiosphaerida eisena-
chia, L. laeviguta, L. pilonim, L citrintts, Trachysphaeridium sp., Lophosphaeridium cf. parver-
arus, and Macrohystridium nainacanthus. In addition, the Wujialie Formation of Ziyang District,
— 80 —
Shaanxi Province includes Galeaspida gen. et sp. indet. in conjunction with graptolites in the
same horizon. It should be évident from the above data that the Silurian galeaspids lived in a
marine environment.
It is interesting that agnathan (galeaspid and thelodont) bearing strata arc moslly purple,
red clastic rocks both in Silurian and l.ower Devonian; such as the so-cailcd Lovver Red Beds.
the Lower Silurian marine Rongxi Formation: the so-called Uppcr Red Beds, the Lower Silurian
marine Xikeng, Maoshan and Huixingshao formations; the Upper Silurian Guandi Formation;
the Lovver Devonian Lianhuashan Formation; the Guijiatun Formation and the Wudang Formation.
The data from the Lianhuashan Formation can help us to understand the marine clastic rock
séquences. There arc somc vertical U-shapcd dwelling trails, many lingulids in their living con¬
dition with muscle scars, as well as some Skolitho'! in the lower part of the Lianhuashan For¬
mation, which indicate typical tidal fiat, .sandy to muddy sédiments.
The features of the sédiments in the middle and upper parts of the Lianhuashan Formation
are line-grained clasts with much mud, mainly purfile-rcd in culour. .small to medium-sized wave-
generated cross beddings, and oblique cross beddings in the sandstone or siltstone. The amount
of B-elements exceeds 120 ppm. In addition, therc are somc fossils. such as ostracods, bivalves,
brachiopods and gastropods. and particularly trace fossils. such as Cruzimia. Clinndriiex, Zoophy-
cuü. SIcolithns. Phyendes, Plannlires, Arenirolites, and Thdiassinakies. It is clear that the sedi-
menlary environment in ihc middle and upper parts of the Lianhuashan Formation indicates a
sublittoral zone condition with shallow, lower energy, slightiy moving water bodies, in a locally
closed area. The purple colour of the strata is to be expected in the presence of iron (Fe, 3-
valences), and even biotite and illite in weathering conditions (Kuang et al., 1989).
CONCLUSIONS
1) The Chinese fossil jawless craniates contain the endemic Galeaspida and cosmopolitan
as well as endemic Thelodonti. No fossil of both the Osteostraci and Heterostraci has been dis-
covered in China. Galeaspids are found mainly in the Early Silurian and Early Devonian of
South China, and ihelodonts in ihe Late Ludlovian to Givetian of southwestern China.
2) The data from the external morphological characters of the Galeaspida are fairly
complété, Here a important character is defined: a pair of latéral or médial dorsal fenestrae in
the dorsal shield in certain forms. Many internai anatomical characters are extremely well pre-
served, particularly the structure in front of the telenccphalic portion in Cluingxingaspi.s gui
Wang, 1991, such as long, paired terminal and olfactory nerve canals. a pair of separate nasal
sacs lacking an ossified floor, and joining outwards and forwards with a large exonasal opening
in the dorsal shield.
3) The pattern and structure of the sensory line system in the dorsal shield of the Galeaspida
differs greatly from that of the Osteostraci or the Fleterostraci. The sensory line System in the
dorsal shield of the Galeaspida is well developed both in the form of canals in the bony ex-
oskeleton and in the form of superficial grooves.
4) The feature of a pair of latéral or médial dorsal fenestrae is a synapomorphy of the
fenestrate galespids, and the order Macrothyraspidida, which display this feature, are a mono-
— 81 —
phyletic groiip. The orders Eugaleaspidifornies and Huananaspidiformes, previously regarded as
two monophyletic groups within lhe Galeaspida. are conf'ronled to a serious challenge.
5) Silurian and Devonian jawless craniates (Galeaspida and Thelodonli) in China had a
littoral or neritic habitat, judging from the data on the associated marine fossils and from the
analysis of the fish-bearing sedimentary faciès. They were euryhaline agnathans, not fresh water
ones.
Acknowledgetnents
It is a pleasure to record my lhanks lo The National Science Foundation of China for the financial
support and to the Government of Quebec, Drs M. ArsKNault and D. Vbzina, and the Parc de Miguasha
for a favourable opportunity of presenling my work at the 7th International Symposium on Studies of
Early Vertebrates in Miguasha. Canada. 1991. Spécial thanks arc due to IGCP project .^28 co-leaders Drs
S. Turnbk and G.C. Young, and the UNESCO-IUGS for a financial support which enabled me to attend
the Symposium. 1 would like to thank Pr M.M. Cuanc for lier continuous encouragement and Drs S.
Turner, Ph. J.a.nvier, H. Lelièvre, M, ArsenaULè and G O. Johnson for reading my manuscript and
providing valuable coniments. 1 iim indebted to Drs Cai C,-Y., Lit) Z. -H. and F,\NG Z.-J. for helpfui dis¬
cussion on the sedimentary environment of the Cuifengshan Group al Ouj'ng. Yunnan Province during the
field work 1991; 1 thank Mr Pu Z- and ^Il• Zhong J. for opiical pbotography. Mr Zhang w.-D. for SEM
photography. and Mr Hou J. -F. for the drawings. 1 aiso thank Ms Shen M., Mr Zhu M., Mr Jin F., and
Mr Fan J. -H. for their help in using the computer.
Literature CITED
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A/rtg,, 100: 129-155.
Belles-Isles, m., 1985. — Nouvelle interprétation de l'orifice médio-dorsal des Galéaspidomorphes ("Agnatha”,
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Section C. n" 1-4 : 85-125.
Placoderm diversity and évolution
by Robert K. CARR
Abstract. — Stratigraphie ranges for 720 placoderm la\a are presented and diversity patterns arc charac-
terized for six nionopliyletic placoderm orders a.s well as for other Devonian and Mtssissippian gnatliostome.s.
Analysi.s al the leve) of sub.stagc is critical for the récognition of placoderm subclade diversity patterns. The
carrent temporal and taxonomie résolution of mdividual placoderm taxa is sufficient to providc a clcar picture
of diversity independent of the level of resolution selecled for screening data. Analysi.s of ail availabic data
provides tlic hest picture of placoderm diversity. Current hypothèses of arihrodiran compétitive displaccment
represent gltibal patterns and rcquirc carcfitl considération of patterns ofphylogeny. géographie distribution, and
ecological synipatry. The.se considérations proviile alternative interprétations of tinting of events and influence
the analyses of alternative hypothèses of biological mtemctinns (compétitive or opporiunistic replacements or
chance). Pachyoslcomorph arthrodiran diversity niay be correlated with morphological évolution related to adap¬
tations associated with feeding and locomotion, Gnalhostoine diversity siiggesls thaï Devonian extinction épisodes
are not uhiquitous events widi clades .showing different respon.ses It.t ihree putative lipper Devonian extinctions
(Givetian-Hrasnian, f rasiiian-Famcnnian. and Famennian Tournaisian). The Frasnian-Faineuman extinction evetit
had a significanl effect on phicoderms. This event may hâve reduced the nuinhcrs of placudcrms siifficiently to
providc a '‘window of opportiiiiity” for the early radiation of actinopterygians and chomlrichlhyans. During the
Famennian there is evidence for predatnr-prey relationships and potential compétition for resoiirces aiiiong sur-
vivmg placoderms and other gnathostoincs Thc.se biological interactions are coincident with an inverse relalion-
ship between placoderm diversity patterns and those for actinopterygians and chondrichthyans. Thi.s coincidcnce
suggests that the extinction of placoderms may be attributed to compétitive displacemcnt although opportunisiic
replacement following the putative Famennian-Tournaisian extinction event remains as an alternative explanation.
Keywords. — Placoderms. évolution, diversity. monophyletic orders, Devonian extinctions.
Diversité et évolution des Placodermes
Résumé. — Les répartitions straligraphiques de 720 taxons de Placodermes sont présentées et leur diversité
est définie pour six ordres de Placodermes ainsi que pour d'autres Gnathosioines dévoniens et mississippieiis.
L'analyse au niveau du sous-ctage est cruciale pour la connaissance de la structure de la diversàlé des sous-clades
de Placodermes. L'ticiiiel degré de résolution temporelle ei raxonomique de chaque taxon de Plaeoderine est
suffisant pour donner iiiie image nette de leur diversité, indépendamment du niveau de ré.solution choisi pour
l’examen des données. L'analyse de toutes les données di.sponibles fournil la meilleure image de la diversité des
Placodermes. Les hypothèses actuelles sur les déplacements liés ii la compétition chez les luthrodires produisent
des structures de répariihon globales et demandent une attention pantculière ii fcgaid de la phylogénie, de la
distribution géographique et de la synipalne. Ces considérations conduisent à des interprétations alleniafivcs des
évènements cbronologiqiies et influencent l'analyse des hypothèses possibles sur les interactions biologiques (rem¬
placement compétitif ou opporluni.ste. ou hasard). La diversité des urthrodties pachyosléomorphes peut être cor¬
rélée avec une évolution moiphologique lice à des adaptations du régime alimentaire ou de la locomotion. La
diversité des Gnaihosiomes suggère que les épisodes d'extinction au Dévonien ne sont pas des évènements ubi-
quistes, car des clades montrent différentes réponses aux eAlinclioiis présumées du Dévoiuen supérieur (Oivé-
tien-Frasnien. frasnicn-l amcnnien et Famennien-Tournaisieii). L'e.xlinclion du Frasnien-Famennien a eu un effet
significatif sur les Placodermes. Cet évènement peut avoir réduit leur nombre suffisamment pour offrir une chance
à la première radiation des Aetiniplérygiens et Chondrichthyens. Pendant le Famennien. on a la preuve d’une
relation prédateur-proie et d'une compétition polentielle pour les rcsource.s entre les Placodermes et les Gnatho-
slomes survivanls. Ces interactions biologiques coïncident avec une relation inverse entre la diversité des Pla¬
codermes et celle des Aciinopiérygrens et Chondrichthyens. Celte coïncidence suggère que l’extinction des
— 86 —
Placodermesi peut êlre attribuée à une compétition, bien que des remplacement opportunistes à la suite de l’ex¬
tinction présumée du Famennien-Tournaisien restent une explication alternative.
Mots-clés. — Placodermes. évolution, diversité, groupes monophylétiques. extinctions dévoniennes.
Robert K. Carr. Muséum of Paleontology, 1109 Geddes Rd., The UniverstTy of Michigan, Ann Arbor, Michigan 48109-1079,
USA.
Introduction
Placoderms. known from thc late.si Silurian to the earliest Mississippian, offer an excellent
mode] for the analysis of evolulionary patterns and mechanisms at a lime early in gnathostome
history. .Not only do placoderms a'pre.sent a morphologically and ecologically diverse group, the
most speciose gnathostome clade présent from the earliest Devonian until the latest Frasnian.
but their extinction was associaied with several putative global extinctions and the radiation of
other gnathostomes. AlThough placoderms hâve been studied for many years, a number of fun-
damental questions remains. Early attemprs to undersiand the biology of placoderms were
hindered hy numerous misconceptions about their evolutionary history. This has required re-
analysis of anatomy, taxonomy and systemalics (e.g. Mii.es, 1969; Mii.es & YOUNG, 1977: Mil.ES
& Dennis, 1979; Goujet. I984a. b; Lelièvre et ai. I9S1; Young. 1981; FORRY & Gardiner,
1986; IVANOV. 1988; Leijèvre, 1988; Long, 1990a; Vézina, 1990; Gardiner, 1990; Carr,
1991). From this new foundation, a better understanding of placoderms is emerging along with
important information concerning other vertebrates, This sludy provides a currenl summary of
placodcrm species, along with their .stratigraphie ranges, and an analysis of placoderm diversity
patterns for species- and genus-Ievels (number of taxa per stage or subsuige).
A number of hypothèses hâve been put forth concerning the nature and number of global
extinctions during ihe Devonian (HOUSE, 1985, Sepkoskj, 1986; McMillan et al.. 1988).
Gnathostome diversity patterns are evaluated in light of these hypothèses and hypothèses of
biological interactions among gnathostomes. Ecological replacement (opportunisric replacement),
compétitive displaccmctu, and chance hâve been proposed to explain patterns of teniporal re¬
placement of One group or clade by another. M1L.E.S (1969) and Gardiner (1990) provided a
hypoihcsis for the succession of competitively superior levels among arthrodiran placoderms.
Their assumptions are subjectively evaluated. based on curreut phylogcnctic and diversity pat¬
terns. Additionally, other comparisons among placoderm cladcs are evaluated along with neces-
sary précautions rclatcd to assumptions of biological interactions. A number of morphological
changes hâve been documented among brachythoracid arthrodires with pachyosteomorph ar-
throdircs .showing a significant diversity increa.se. Evaluation of adaptive aspects of these changes
suggest a corrélation between pachyosteomorph diversity and improvements in feeding and loco¬
motion.
Abbreviations
Aup autopalatine ossification of the palatoquadrate, ossification autopalatine
du palatocarré\
cr.art articular crest of the scapulocoracoid, crête articulaire du scapulocoracoïde \
Hm hyomandibula, hyornandihutaire ;
— ST¬
IC infei ognathal plate, infémgnathale ;
MD médian dorsal plate, plaque médiane dorsale',
Mk Meckel’s cartilage, cartilage de Meckel;
PVL posterior ventrolateral plaie, plaque ventrolatérale postérieure ',
Qu quadrate ossification of the palatoquadrate, ossification carrée du palatocarré ;
SO suborbital plate, plaque subarbitaire ',
scier sclerolic plate, anneaux sclérotiques.
MATKRIAL AND METHODS
Appendix 1 provides a species level compilation of stratigraphie ranges for ail placoderms
(Denison, 1978; placoderm référencés from the Zoological Record, 1975-1991). It includes tax-
onomically and temporally ambiguous taxa (e.g. indeterminate material, unresolved synonyms,
species bascd on fragmentary material, incertae sedis). Indeterminate taxa are inciuded whenever
they provide temporal range information or represent forms from distinct géographie régions.
Temporal résolution for taxa ranges from indeterminate to substage (50 species without strati¬
graphie résolution lo .sériés are recorded in Appendix 1, but are not included in diversity analyses).
A range through method is used for taxa with poor stratigraphie resolutimi (e.g. a Frasnian oc¬
currence is recorded as a Low'er to Upper Frasnian presence at the subslage level). Also included
is unpubiished data from research in progress (indicated in Appendix I as “n. sp.”, Carr &
Hlavin, in press, Dunkleosletts n. sp. |, D. n. sp. 2; Carr. MS. Stenasteus n. sp. -pers. comm.-
Lelièvrb, Maideriu fulipuui, this volume). A total of 720 taxa are recorded with diversity patterns
(number of taxa per unit of time) analyzed at different levels of temporal and taxonomie resolution
(among the 720 taxa lhere are 267 recognized généra and 591 recogmzed species. Thirty-three
forms are indeterminate to a generic level w-ith an additional 41 species having questioiiable
assignments to generic level. Seventy-five taxa assigned to a genus lack assignment of a species
name; recorded as "sp.". Eight taxa represent species provisionally assignable to other recognized
species; recorded as “cf.”. One conferrable genus is recorded. Seven qiiestionable species as¬
signments are recorded wûth onc spécifie variety noled.j. Extinction levels for the Frasnian-
Famennian boundary are recorded for both species- and genus-levels and at stage- and
substage-levels of analysis (table 1 ).
It is important to consider the level and units of analysis to be used in the study of diversity.
Placoderm data suggest substage-level analyses are necessary to clearly evaluate suhclade pat¬
terns. The resolution of the individual data is Ics.s critical; however, this may be due solely to
the relatively low level of indeterminate taxa (4.6% indeterminate to genus and 5.7% w-ith
questionable generic assignments) and taxa with poor stratigraphie résolution (6.8% not resolved
to sériés (epoch) and 11.9% resolved to scries). Stage names follow those of Denison (1978)
which are used in his compendium. No effort has been made to convert DenisoN's Early Devonian
stage names (Gedinnian and Siegenian) to current formai names (Lochkovian and Pragian) sinee
exact stratigraphie data is not available for an aceurate conversion (refer to Harland et al.,
1989, for a discussion of the relationship between formai names and those used by DENtsON,
1978). Stage names for the last appearance data taken from Sepkoski (1992) follow those of
Harland et al. (1989).
— 88 —
From these data, the diversity patterns for a number of monophyletic placoderm groups are
described and conipared. Additionally. the generic diversity for ail remaining Devonian and Early
Mississippian gnathostomes is evaluated to document patterns of change during this critical time
in vertebrate history. Data for chondrichthyans (Zanoeri,. 1981, CaRROLL. 1988). and acan-
thodians (Df.nison, 1979) are recorded at stage Icvel; howcvcr. ostcichthyan data (taxonomy
and range data from CarROI.L, 1988) are recorded using sériés, Mii.fs’ (1969; see aiso Gardinf.R.
1990) characterization of arthrodiran évolution as a succession of competitively superior grades
is specifically considered by subjectively comparing his and current estimâtes of arthrodiran
clades against predicted patterns for compétitive and opportunistic replacements. l'he radiation
of pachyosteomorph, or morc specifically aspinothoracid. arthrodires in the Laie Devonian is
evaluated. Morphological changes within this cladc are compared Ihrough analogy with extant
fishes and mechanical aspects of these changes are evaluated in terms of biological rôles and
mechanical effectiveness.
The specimen number prefix CMNH dénotés the Cleveland Muséum of Natural History.
The suffix "id” when used to form taxonomie adjectives does not refer to family-level Linnean
classification and is u.sed as a convenience for discussing informai taxonomie units. Abbreviations
for stage names used in figures and Appendix 1 follow that of Hari.and et al. (1989).
RESULTS
Patterns of diversity for Placoderms
Placoderm global diversity rose at a nearly steady rate from the Silurian to the Frasnian-
Famennian boundary reaching both generic and spécifie peaks within the Frasnian (Fig. 1; see
also Gardinf.R. 1990). At the FrasnianT-amennian boundary current data .suggest an overall pla-
coderm species extinction of 48-51% and a generic extinction of 52-53% (table I).
The genus- and species-lcvcl diversity patterns for placoderms are équivalent for both sub¬
stage and stage-level analyses- of ail avnilable data, only minor fluctuations are noted at substage
levels (Fig. 1). Figure 2 demonstrates similar generic patterns for:
1) .stage-level analysis of ail available data;
2) data with a temporal résolution to stage level or finer;
3) taxonomically resolved data (indeterminate forms and doubtful generic assignments are
excluded);
4) and data resolved both temporally and taxonomically.
The orders Rhenanida {sensu s'iricia, i.t., excluding palaeacanthaspids) and Petalichthyida
(Figs. 3A, B, 4-5) showed low spécifie diversity from their first appearance in the Gedinnian
to their final appearance in the Upper 1-rasnian (Upper Devonian records are represented by
single species). Both orders wcrc marine and hâve bcen characterized as being dorsoventrally
compressed (Denison, 1978). This characterization is seen in Genniendina siuertzi (a rhenanid,
Fig. 3B) with ils dorsally placed orbits and enlarged ray-like pectoral fins; however, little is
known concerning the body form aniong petalichthyids. Lunaspis hroilii (Fig. 3A), one of the
better known petalichthyids from tlie Hunsriickschiefer of Gemiany, has been secondarily com-
— 89 —
Fig. 1. — Placocicrm divcrsily uiilizing ail available data dcmonstrating équivalent patterns among differing levels of analysis.
A, stage-level analysis of spécifie (squares! and generic (circles) diversity. B. substage-level analy.sis.
Analyse de la diversité des Placodermes utilisant les données disponibles et montrant les modèles éift4ivalents à différents
niveaux. A, données sur les espèces (carré) et sur les genres (cercle) en fonction des étages géologiques. B, mêmes données
en fonction des sous-étages.
Fig. 2. — An analysis iising alicrnative screening criieria for placoderm data. Results of ihe analysis dcmonsiralc équivalent
diversity patterns for cach screening criterion, Placoderm generic diversity (squares) utilizing ail data: data taxonomically
resolved to genus wiih indeiemtinuic form.s omiiied (circles); temporally resolved taxa to stage level or finer (triangles): and
both taAononiicully and temporally resoivctl daui (diamoiids). A, siiigc-lcvcl analysis. B, substage-lcvcl analysis.
Analyse utilisant les critères alternatifs sur les données des Placodermes. Ia's résultats de cette analyse mettent en évidence
des modèles de divetsitê équivalents pour chaque critète. Piversiié générique de.s PUicodcrmcs (carrés) : donnée taxtmonii-
quement ré.snlue au niveau du genre avec le.s formes indéterminées nmi.ses (cercles): taxons résolus au niveau de l'étage
géologique ou plus (triangles) : ilonnées rtUolurs laxonomiquement et fempnrellement (losanges). A. analyse par étage géo¬
logique. B. analyse par sans-étage géologique.
— 90 —
presscd during préservation. Little information is obtainable front other petalichthyids, concerning
body form, other than the partial shift of the orbits onto the head shield. Rhenanids disappeared
from the North American craton during the Frasnian-Famennian extinction épisode (Upper
Frasnian last appearance) wel) after the Middle-Upper Devonian faciès transition from shallow
water carbonates to anoxie clastic deposits. Petalichthyids survived into the Famennian. However,
petalichthyid and rhenanid low global diversities argue against the attachment of any particular
significance to their final disappearancc.
The order Phyllolepida (Fig.s, 3C, 4-5) was clearly présent in the Frasnian and survived
until the end of ihe Devonian. They reached their highest spécifie diversity after the Frasnian-
Famennian extinction epi.sode. An earlier Eifelian First appearance may be indicated if Antim-
taspis (whose stratigraphie range is unclear, i.c. Middie or LIpper Devonian) is eonsidered as a
member of Phyllolepida (family Antarclaspidae is consîdered here Arthrodira inceriae sedis).
Phyllolepida were ihoughl to be restrieted to freshwater by Df.nison (1978; BENDIX-Almgreen,
1976), although LKRICHE (1931) concurred.. he noled the latéral association between Belgian
marine Schistes de la Famenne and Psammiles et Schistes d’Fvieux which now suggests the
possibility that these latter pbyllolepid deposits are polentially marginal marine. Recent analyses
aiso hâve ealled into question a non-marine interprétation for .some Old Red Sandstone style
sédiments (see discussion below). Phyllolcpids survived lhe Frasnian-Famennian extinction
(table I) with a .spécifie incrcasc. but a without gcneric change; however. low spécifie diversity
limits analysis.
The order Antiarcha (Figs. 3D, 4-5) first appeared in the Silurian of China and possibly
survived lo the Lower Carboniferous (seven of the eight species recorded from the Carboniferous
are resolved temporally to serie.s-ievel. i.e. Lower Carboniferous, suggesting that diversity plots
for antiarchs, figures 1. 2, 5, and 10, may artificially exlcnd their range through the Visean).
Diversity during the Lower Devonian remained stable with successive incrcases seen in the
Eifelian, Givetian, and Frasnian when they finally reached their peak. Again. many species are
known from Old Red .Sandstone faciès. Antiarch extinction across the Frasnian-Famennian bound-
ary was between 30-58% (table 1).
The order Ptyctodontida (Figs. 3E, 4-5) first appeared in the Siegenian with their last ap-
pearuncc in the Famennian {Tollodus brcvispinii.'i is recorded from the Siegenian of the Soviet
Arctic. 0RVIG, 1980b, with other généra first appearing in the Eifelian). After lhe Eifelian, spécifie
diversity continued to incrcasc until lhe Frasnian-Famennian extinction épisode when 75-77%
of ptyctodont species went cxtinct (table I). Gencric diversity remained level from lhe Eifelian
through the Frasnian w'ilh a 71% décliné of known généra ai the Frasnian-Famennian boundary.
Fig. 3. — Représentative reconstructions for members of the placoderm orders discussed in the text. A, Lunaspis hroilii, dorsal
view. A. a petalichthyid B. Gtniucndim stuertzi. dorsal view, a rhenanid. C. Phylhlepis nnini, dorsal view of head and
ihoracic shield.v. a phyllolcpid; D. Ctvnmvllu jilthihüdifH.us. a ptyctodont. latcraJ vicw. H. HoüuioU’pis citniulensts. an antiarch.
latéral view. F, Ctfnip.\h‘u\ ruspufaïus. a brachythoracid, latéral view. A F taken Iront STENSIO, l%3.
Rcronfilituliatu de dtven laxons d'oidres de Ptumdermex présentés dans le texte. A, un pêtulichlhyide. l.unaspis broilii,
dorsate. B. un rhenttnide. Gemundina slucr/i ai V'Mt» dorsale. C. ttn phyUolépidt\ Phyllolcpis orvini. vue dorsale des cuirasses
crânienne et thoraciquê'. Ü, un ptyi ttulonlc, Cicnurclla ^hidbuchcnsiv »•« me latérale. F., un untiatrhc. Bolhriolcpis canaden.sis
ai me kttvntle. F. un hntchylhoracidr. C(k:co81cus cuspidülu.\ en eue laténde Fifiurcs A^F reprises de SfhMSiù. J963.
— 92 —
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FlG. 4. — Cladogram indicating generalized phylogeny within Placodermi. Modll'ied from GOUJKT (1984b), Gardiner (1990),
and Carr (1991).
Ctaàogramnie des Placodermes modifié d'après GOUJET (I^H4b), Gardinf.K (1990). et Carr (1991).
The order Arthrodira (Figs. 3F, 4-5) has been reported from the Wenlockian (Pan & Dine-
LEY, 1988), although, GoUJET (pers. comm.) suggests these Chinese forms arc not Irue arthrodircs.
Arlhrodires are known with ceitainty from the Ludlovian to pcissibly Toumaisian and showed
an increase in diversity from first appearance to the Siegenian, from which point they maintained
— 93
stable levels until the Fra.snian. Peak diversily was achieved in the Upper Frasnian followed by
a dramatic drop at the Frasnian-Famennian boundary (57-62%, table I). Figure 6 présents generic
diversities for Actinolepidoidei, Phlyctaenii. coccostcomorph, and pachyosteomorph arthrodires
based on both Miles' (1969) and current classifications (see discussion below).
Patterns of Diversity for other Gnathostomes
Chondrichlhyans are first recorded from the Lower Silurian (Novitskaya & Karatayute-
TALtMAA, 1986; KARATAYUTE-Tai.i.VIAA. 1992) with a significant increase in diversity ai the
Devonian-Mississippian boundary (Fig. 7A). Approximately 50% of this increase is accounted
for by isolated teeth. denticles (dermal and mucus membrane), and other ichthyodorulites. Among
chondrichthyans, the Suhterbrancbialia (Zangerl, 1981) and elasmobranchs hâve similar patterns
with elasmobranchs possessing greater numbers,
Acanthüdians (f-Tg 7B). with bimodal peak generic diversities in the Siegenian and Eifelian,
demonstratcd a relatively graduai décliné throughout the Devonian and Carbonifcrous until their
extinction in the Permian. A moderate increase in the rate of décliné is noted at the Frasnian-
Famennian boundary, Among the three recogni^ed orders of acanlhodians (Denlson, 1979), the
climatiids and ischnacanthids appear to account for the earlierpeak in diversity while climatiids
and indelerminatc spécimens account for ihe latter acanthodian peak. Low diversity among these
orders hinders further analysis.
Among sarcopterygians (taxonomy after Carroi.i., 1988), Onychodontiformes, Holopty-
choidea, and Dipnoi first appear in the Lower Devonian (Carroll, 1988; Fig. 8). Osteolepidoidea
first appear in the Middie Devonian (Carroll, 1988) and are followed in the Frasnian by
coelacanthiformes and Telrapoda. Sarcopterygians. recorded here at an epoch level of resolution,
demonstratcd an increase in generic diversity frora the Givetian to Frasnian. Diver.sity changes
during the Frasnian-Famennian extinction épisode cannot be evaluated due to the lack of reso¬
lution. In contrast, actinopterygians (Fig. 8B) showed little or no increase from first appearance
in the Middie Devonian (CARROLL. 1988) until the Tournaisian. During the final décliné of pla-
coderms we see a similar décliné in rhipidistians and dipnoans, although, noi to complété ex¬
tinction with the exception of onychodonts, Coelacanth diversity remained relatively stable during
the Late Devonian and Early Mississippian, but again, this may reflect a lack of resolution.
DISCUSSION
Diversity Patterns
Although the fossil record is a filtered view of “true” diversity (Raup, 1979, notes biases
due to taxonomie level, géographie distribution, taphonomy, sampling, and rock availability),
this record represents the only source of information for extincl taxa like placoderms. In con-
sidering évolution and extinction, it is important to recognize that diversity patterns reflect out-
comes of both physical and biological interactions. Additionally, in evaluating global diversity
it is important to consider paltems of phylogeny and géographie distribution. With the above
— 94
information, one can begin to evaluate spécifie hypothèses of extinction effects, biological in¬
teractions, and morphological évolution.
During the Devonian there was a major radiation within gnathostomes. The water column,
in which these fishes livcd, was not devoid of other predators; however, the history of early
vertebrates sliows the origin and évolution of organisms wiih spécialisations in locomotion, feed-
ing structures, and sensory organs, as well as central processing and coordination of sensory
and motor sysicms (NORTHCUTT &■ Gan.s, 1983). The appearance of these new morphologies
are suggestive of an adaptive radiation.
Devonian sédiments potentially offer an unique and impt)rtant view of early gnathostome
history since they represent the largest estimated volume and geological map area for Paleozoic
Systems (Dinkley, 1984). The globally di.siributed Old Red Sandstonc developed during this
period and was associated with a number of lectonic events. A major faciès shift occurred within
the séries of North American Carbonate basins at the beginning of the LIpper Devonian. charac-
teriz.ed by the widespread déposition of anoxie black shales. The LIpper Devonian further rep-
resents a lime of complex biotic and abiotic events which inelude numerous orogenies putatively
associated with the sururing of Pangaea (McMillan et al., 1988). Johnson (1970) noted shifts
among brachiopods from earlier provincialisin lo cosmopolitanism associated with Upper Givetian
onlap. eft'eclivcly lowering the North American continental arch. HOUSE (1985) described eight
separate extinction events among Devonian amrnonoids of which six range from Upper Givetian
to Lower Tournaisian (Taghanic, Frasnes, Keliwasser, Enkeberg, Annulata, and Hangenberg
Events ). Of these events, SepküSKI ( 1986) con.sidered Ihrcc to be significant (Frasnes or Givetian-
Frasnian. Keliwasser or Frasnian-Famennian, Hangenberg or Famennian-Tournaisian; Fig. 9).
McGhee (1982, 1990) repoited 65% extinction among manne placoderm species and 23% among
putative freshwater forms during the Frasnian-Famennian extinction épisode, ihough current data
suggest an overall placoderm species extinction of 48-51% and a generie extinction of 52-53%
(table I); fîve out of six placodenn orders survived (Antiarcha, Arthrodira. Petalichthyida, Phyl-
lolepida, Plyctodonlida). McGhee commented upon the potential significance of différences in
freshwater antl marine extinction to the évaluation of causal mcchanisms, however, freshwater
interprétations for many Old Red .Sandstone style sediments hâve been called into question (e.g.
SpiLsbergen. GouJLT, 1984a; Escuminac Formation, CltiniAC. 1989 and Viy.INA. 1991; Easl Ballic
and Podolia, Mxrk-KuRIK, 1991). The Frasnian-Famennian décliné was possibly associated with
a global eveni that affected bolh invertebrate and vertebrate benthic and pelagic communities
(McLaren, 1988). Causes and timing of this event are currently under debate (for a discussion
see McMillan et al. 1988; H0U.SE. 1985; SEPKOSKl. 1986). The final décliné of placoderms
occurred in another association wiih a major event (Fig. 9). Despite the possibility of a physical
cause, it is worlhwhile afso to evaluate potential biological factors for this final décliné. To this
end, gnathostome diversity patterns are evaluated.
In the absence of an established phylogeny, Miles (1969) characterized placoderm évolution
in ternis of specializaiions related lo their life on or just off the hottom. Within arthrodires, he
described a succession of compelitively superior grades related lo improvements in feeding and
locomotion. GardineR (1990) further noted a number of morphological innovations associated
with feeding and locomotion. LONG (1990a: 255) evaluated aspects of placodenn évolution in
terms of “guiding factors" related to evolutionary trends, although. it should be noted that his
— 95 —
dichotomy of intrinsic (“genetic drift, heterochrony, biophysical constraints”) and extrinsic (“en¬
vironment, abundance of food, predator pressure”) factors represents a potential continuum of
both proximate and ultimate causal factors.
Placoderms and other Gnathostomes
In one instance among placoderms, choice of taxonomie level (genus versus species) is
critical. Ptyctodont generic diversity may represent a misleading indicator of “true” diversity
since most members of Ihis taxon are form-genera based on gnalhal plates (Miles & YOUNG,
1977). Spécifie analy.sis (Fig. 5) provides a more accurate estimate of ptyctodont diversity with
22 out of 31 species in lhe Frasnian represented by form-genera (Paleomylus, Plyciodus, and
Rhynchodus).
Biological interactions can take several forms including direct compétition for resources
(e.g, food and nesling sites) and predator-prey relationships. Underlying the potential for inter¬
action are assumpiions of géographie overlap and ecological sympatry. The necessity to consider
thèse assumptions is demonstrated below by example. Phyllolepids and rhenanids hâve a similar
dorsoventrally compressed body form suggesting specialization for bottom living. Addilionally,
petalichthyids hâve been inteipreted as possibly bottom living (DENISON, 1978). The phyllolepids
appear as a temporal replacement for the rhenanid and petalichthyid clades (Figs. 4-5); however,
if truly marine, it is unlikely that phyllolepids (restricted to Old Red Sandstone marginal marine
or estuarine clastic habitats) competitively displaced rhenanids and petalichthyids which inhabited
Fio. 5. — Species-level diversity patterns for nioiiophyletic pliii.oderm pruiips. A, arihrodires tlriungles), anüurclis (filled .squares),
rhenanids (diainunds), pciûlichfhyidîi (filled drdçjiK phyllolepids (open squares), and piyctodonls (open circles). B, arihrodires
and anliarchs omilled lo bcHer deinoiistrate paderns for low divcrsiiy clades.
Courbe des fnoJèles de diversilv des espèces pour tics gntupes inonophylétit^ues lU- Ptacodennvs. A. nrthnjditvs llnanylcs),
antiarches (carrés pleins/, rhénunides (losanges/, prudivhthsides (cercles pleins), phyllntépules (carrés), et ptyvtndontes (cer¬
cles). H, mêrtuj courbe sans les arihrodires et les antiarches pfin de meure en evhienee les modèles de diversité pour des
ckides peu diversifies
— 96 —
distinct environmenls (carbonate and basinal habitats). A globally distributed taxon may interact
with other pandémie taxa or regionally with a number of endemic forms. Pan & DiNELEY (1988)
noted a high level of endemism among placoderms and antiarchs, in particular, suggesting that
régional or basinal patterns may repre.sent an appropriate limit of résolution for que.stions con-
cerning ecological interactions.
Patterson & Smith (1987) demonstrated the potential for pseudo-extinctions with use of
paraphylelic groups. Additionally, they noted the potential élongation or truncation of temporal
ranges for taxa and possible différences in the timing of peak diversitics (contrast Sepkoski.
1987). Once a phylogenetic study has been completed. evolutionary irends can be compared and
evaliialed tising monophylelic taxa. Analyses in this study are resirictcd primarily to monophyletic
uttits as cunently understood. The systematics of placoderms is often based on a limited knowl¬
edge of morphology and variahility, These limits suggest that rclationships among placoderms.
in contrast to better documented groups. are more susceptible to change with the discovery of
new or better material. At présent, no higher level monophyletic groups (strict consensus sensu
SOKAE & Roule, 1981) are held in common among the alternative published hypotbeses for
the relationships of placoderm orders (analy.sis based on Miles & YOUNG, 1977: DenLSON, 1978;
Gardiner, 1984; GoUiET, 1984b; FOREY & Gardiner, 1986). Within Placodermi, Denison
(1978) recognized nine orders, with Arthrodira, Phyllolcpida, Pclalichthyida, Ptyelodontida, An-
tiarcha, and Rhenanida generally considered to be monophyletic (.Miles & Yül’NG. 1977; DENI-
SON. 1978; Gol jet, 1984b). The relationships of Stensioellida and P.scudopetalichthyida remain
obscure while Acanthothoraci appear to be paraphyletic (GOLTEl. 1984b: .see YoUNO, 1980, who
includes palaeacanthaspids within rhenanids). Figure 4 is a hypothc.sis of relationships for the
majority of taxa addressed here and is based on a number of cladistic arialy.ses (order relationships
after GouJUT. 1984b; arthrodiran relationships modified front Gardiner. 1990; Carr, 1991).
Among the ailhrodires, the Actinolepidoidei (Fig. 6). a monophyletic group representing
Miles’ (1969; 144) "actinolepid level of organization,” include the Actinolepididae and Wut-
tagoonaspididae (Fig. 4; Mll.ES & YouNG. 1977; DenisüN, 1978; Goluet, 1984a). Phlyctaenii
(Fig, 6; “phlyctaenaspid level” in part. Miles, 1969; 143) were considered paraphyletic by Miles
& Dennis (1979) and Gardiner (1990), but monophyletic by GOUJE'I' (1984). Included in this
clade are Arctaspididae, Arctolepididae, Groenlandaspididae, Phlyctaeniidae, and Tiaraspididae
(Fig. 4; Goluet, 1984a, includes Tiuruspis among the Groenlandaspididae). Miles (1969) addi¬
tionally included Williamsaspididae among the Phlyctaenii, but williamsaspids are here con¬
sidered basal brachythoracids (Fig. 4; GoLUET, 1984a). Coccosteomorph and pachyosteomorph
subgroups (Fig. 6) are considered lo be monophyletic Coccosteomorph arthrodires include
Camuropiscidae, Coccosteidae, Pholidosteidae. Plourdosteidae in part. Rhachiosteidae, and
Torosteidae (Fig. 4; DENNIS & MILES. 1979; GARDINER. 1990), The “coccosteomorith level" of
Miles (1969; 147) furiher included Buchanosteidae. Euleptaspididac. Gemuendenaspididae. and
Ilolonematidae. These familles represent either basal brachythoracid clades or members of basal
clades (Fig. 4; "primitive" brachythoracids of Lelièvre. 1988; Carr. 1991), Finally. pachyostco-
morph arthrodires include the aspinothoracid arthrodires and the Dunkleosteidae (used here as
équivalent to the Dinichthyidae sensu Denison, 1978, but excluding Dinicltrliys herzeri, Gorgon-
ichthys clarki, Heintzichthys gouldii. and Hnldenius hiildenr, contrast StensiO, 1963, and VÉZINA,
1990). Miles (1969) additionally considered Rhachiosteidae (here considered a coccosteomorph)
— 97
Fig. 6. — A comparison bclween the generic-leveî Uiversily palicms associulcd wiih Mil.l-.S (1969) hypothcMs of replaccmeni
and the paUcrns aittong inonophyldic placoderm groups. Note difterences in timing of oiiginaiions and ihc poicnlial for
interactions betwcen croups. A. arlhrodiran Jiversiiy afier Mii.E\S <I%9); aciinolcpid Icvcl (squares), phlyctacniid level (iri-
angles), coccostcomorph level (dituiionds), and pachyosleomoiph level (circles). B. nionophyletic groups; Actinolepidoidei
(squares). Phlyciaenii (uiangles), coccostcomorph arihwdircs (duimonds). and pachyosleomorph arihiodircs (circles).
Comparaixon entre iex modêle.s de la dixerxite des genres de Harodennes selon l'hypothèse de Mjlks et les modèles
de groupes numophyléUtpies de Placodennes. Hemarifuez les différences entre le temps de l'ongine des groupes et leurs
relations mutuelles. A. diversité des otyhrodites selon Mn.hs 11969): aviinolépides (carrés): phlyctaeniides (triangles) : coc-
costéomorphes (losanges) et p<ichyitstéonwrphes (vercles). B, groupes mnnophylétiques : Actinolepidoidei (carrés). Phlyciaenii
(triangles). coccosléomorphe.s (lnsange.\) et pachyosiéomorphes (cercles).
and Homosteidae ( •'primitive” braL'hythoracid, I.ELifevRb,. 1988) to be pachyostcomorph ar-
throdires. Aspinothoracid arthrodircs are considered to be monophyletic (Miles & Dennis, 1979;
Carr, 1991; but conirast Denison, 1984) and here incliide: Brachydeiridae. Bungartiidae,
Leiosteidae, Leplostcidae, Mylostomatidae, Selenosteidae, Tilaniehlhyidac. Trematosteidae,
Gorgonichthys clarki, Heintzichthys goiildii. HoUhniiis holdcni (pers. observ.). and Dinklttliys
herzeri (CARR & Hlavin. MS).
A generalized sequence of temporal replacement can be seen aniong the four arlhrodiran
clades as noted by Miles ( 1969) and Gardiner ( 1990); however. a compétitive causal relation-
ship is nol certain .sincc these patterns represenl global data. The pairwise patterns in each case
of putative compétitive displacement do not demonslrale a clear pattern of ecological replacement
(■‘double-wedge pattern,” Benton. 1987). Additionally, a causal relalionship between Mll.ES’
(1969) levels should bc cvalualcd in the light of other placoderm and gnuihostome taxa con-
sidering alternative bioiic or abiolic interactions. Actinolepid and pblyctaeniid patterns are not
consistent with compétitive di,splaccmcnl (Fig. 6) with both groups sharing a similar hisiory of
first appearance and peak diversily (Gedinnian and Siegenian respcctively). Substage-levcl analy¬
sis demonstrates a possible delay in the liming of pblyctaeniid peak diversity (Llppcr Siegenian
versus Lower Siegenian for the aclinolepids). AJso. il should be remembered thaï phlyctaeniids
may represenl a paraphyletic assemblage needing further évaluation. Coincideni with the décliné
of phlyctaeniids and inerease among coccosteomorphs was an increasc among antiarebs, ptyc-
todonts, pachyosieomorphs, and osiciçhthyans (Figs. 5, lOA). Wheii using monophyletic groups
— 98 —
FiCi. 7. — ChondrichÜiyan and acanihodian Hiage-level generic diversilv pallcroH Noie lhe end Devonian diversiiy increase among
chondrichihyans and ihe Middie and l-aie Devonian décliné vif acaïuhodian.s. A, chtindrichihyan diversiiy: Chondrichihyes
(squares). Elasmobranchii ilriangles). und Suhierbranchialia (circlcn). B. acanihodian diversiiy: Acanlhodii (tillcd squares),
order Acanihodida (circles). order Clinialiidac ((rianclcs). order Iivchnacanthida (diumonds). and incertae sedis (open squares).
Courbes de modèle.'» de diversité de.\ genres d'Arurilhodirns et de Clumdrù hthyem en fonction des éhiffes .^êologiifues. Re-
mon/uez fa croissance de la diversité des Chondnchthyen.<! à la fin du Dévonien et le déclin des Acanthodiens pendant le
Dévonien moyen et terminal. A. diversité des Chondrichthyens : Chondricluhyes (carrés}. t'Uismohrancliii (triani^les). Subter-
hranchialia (ceirles). B. diversité de.s Acant/wdiens : Acanthodii (carrés pleiin}. ordre des Acanthodida (ren ies), ordre des
Climatiidae ffrian^hs), ordn' des fschnacaïuhida (losanges) et inccriae sedis (carrés).
(Fig. 6B), the décliné of phlyctaeniids begins prior to the origin of coccosteomorph arthrodires;
however, a comparison of phlyciaeniids and brachythoracid arihrodires is suggestive nf a pattern
of compétitive displacement in analyses carried oui at both stage- and substage-level resolution.
Generic patterns for pachyosteomorph and coccosteomorph arthrodires are roughiy parai lel
(Fig. 6) and suggest a single pattern differing only in levels of diversiiy with pachyosleomorphs
reaching a higher maximum diversiiy. In contrasl, a substage-level analysis (Fig. lOB) shows
the peak diversities of the two clades to be offset which accounts for the bimodal maxima seen
in lhe species- and genus-level Frasnian diversities for placoderms (Fig. IB), Coccosteomorph
arthrodires reached maximum diversiiy in the Lower Frasnian (which includes the well docu-
mented Gogo Formation fauna) with their grealesi décliné in the Middie Frasnian prior to the
Frasnian-Famennian extinction event. This décliné does not coincide with known extinctions and
suggests a possible hiolic cause, although, il is not clear as to which taxa are interacting during
this short interval. Pachyosteomorph arthrodires reached peak diversiiy in the Upper Frasnian
prior to lhe Frasnian-Famennian extinction épisode. The conclusions of Mii.ES (1969) and
Gardinf.R (1990). concerning biological interactions among arthrodires, provide a basis for a
number of hypothèses that siill necd régional évaluation and analysis at a finer lime seule.
Most placoderms were cxtinci by lhe end of lhe Devonian with antiarchs possibly surviving
until the Lower Carboniferous and some arthrodires surviving into lhe Toumaisian; however,
patterns for placoderms and other gnalhostomes do not support an ubiquitous cffect for lhe numer-
ous extinction evenls reporied from lhe Middie and Upper Devonian (HOUSE. 1985; Sepkoski,
1986). Al the Givetian-Frasnian boundary (Figs. 5-8, 10) few of the major gnathoslome clades
— 99 —
SIlI DEV I CARB DEV I CARB
FiG. 8. — Osteichihyan stage-level generic diversiiy. Note sarcopterygian increasing, stable, and declining diversities associated
with the GIV-FRS. FRS-FAM, and FAM-TOU extinction events respectively. A, sarcopterygian diversity: Osicolcpidoidca
(filled squares). Holoplychoidea (filled circles). Onychodonliformes (triangles). Coelacanthiformes (diamonds), Teirapoda (open
squares), and Dipnoi (open circles). B, actinopterygian generic diversity which parallel.s the pattern seen among chondrichlhyans
(Fig. 7A).
Courbe de diversité des Ostéichlhyens en fonction des étapes géologiques. Remarquez les diversités croissante, stable puis
décroissante associées respectivement au.x événements d'extinction du Givétien-Frasnien, du Frasnien-Famennien et du Fa-
mennien-Toumaisien. A, diversité des Sarcoprérygiens : Osteolepidoidea (carrés pleins), Holoptychoidea (cercles pleins). Ony-
chodonîiformes (triangles), Cœlacanthifortnes (lo.sanges). Teirapoda (carrés), Dipnoï (cercles). B. courbe de diversité des
genres d'Actinoptérygiens ; elle présente des similitudes avec celle des Chondrichthyens {ftg JA).
Fig. 9. — Family-level lasl appearances for ail marine animal families taken from Sepkoski, 1992.
Courbe de la dernière présence signalée au niveau de la famille des animau.x marins, d’après Sepkoski, 1992.
demonstrate a generic décliné except petalichthyids, whose low diversity prevents meaningful
analysis, and acanthodians. Several clades demonstrate increases in the number of généra (acti-
nopterygians, sarcopterygians, chondrichthyans, arthrodires, and phyllolepids) while remaining
— 100 —
clades of gnathostomes maintain stable levels. The Frasnian-Famennian boundary euincides with
déclinés in ail placoderm orders discussed here, but one (low diversity phyllolepids), and a con-
tinuing décliné in acanthodians. At the Famennian-Tournaisian boundary, there was a major di¬
versity increase for chondrichthyans and actinoptcrygians. Coincident wiih this increase was a
décliné among rhipidistians, dipnoans. and remaining placoderms. McGhee (IOSSj noted the
importance of temporal résolution in cvaluating the timing ofevents in the fossil record; hovvever,
resolution problems still cxisl and the relative timing of the osteichthyan radiation and placoderm
décliné is not clear, This is dcmonstrated by the epoch level resolution for sarcoplerygian diversity
which limits any analysis of the Frasnian-Famennian extinction eveni for this clade.
Wtt.LtAMS (1990) providcd direct evidence for the interaction among Late Famennian
gnathostomes within the Cleveland Shale fauna. He documenied évidence for predatur-prey rc-
lationships among piscivorous members of the fauna concluding (p. 287) simpiy that “the big
fish ate the little ones.” suggesting a general absence of prey sclectivity. Additionally, there W'as
potenlial compétition among durophages with independent évolution of durophagous feeding
structures in placoderms (c.g. Ptyctodontida. Mylostomatidae), dipnoans, and chondrichthyajis
(e.g. Orodiis). By the end of the Mississippian, a number of holocephalan and clasmobranch
durophages had cvolved (Zangerl. 1981; CarroLL, 1988), Additionally, Vermeu (1987) noted
a doubling of marine durophagous families of eurypterid and crustacean arthropods, cephalopod
molluscs, and vertebrates belween the Middle and Upper Devonian.
The above findings suggest that the Frasnian-Famennian extinction épisode was critical in
the initial évolution of actinopterygians and chondrichthyans providing a so-called “opportunity
FlG. 10. — A. a comparison of slage-level generic diversity for major gnathoslome clades: placoderms (squares), acanthodians
(circlcs), osleichihyaiis (dimnonds). and chondrichthyans (triangles). B. cuhrachyihoracid subsiage-level generic diversity: coc-
cosieomorph arlhrodircs (squares) and pachyosieomorph arlhriulire.x (circles). Noie ihc décline of coccustcomorph arihrodires
prior lo the FRS-PAM e.stiiiction eveiu.
A, Courbe fh' rontfuiraisnn Je la divrrsili' des majeure dr Coathi/suunes en Jof^i'îion des éki^es fiéologU/ues : Pla-
rodrntir.s i{urn\si. luunthadietts (cen lesl osudchrhyens tlosongys) et chondrif luhyens llrianglest. B. même courbe pour les
Eubrachyllwraa en fonctit/n des unt.\-êluges . Anhrodires eorcostétmotplH'S icüvtvs}, Anhrodires pachyostêomorphes icer-
des). Remanfuez le déclin des cficcostétnnnrpbes ù partir de l'rvénemenl Fnisnlvn Fnmennten.
— 101 —
or opcn window" for tiieir early radialion. Within the Famennian there is clear evidence of direct
predator-prey interactions and apparent compétition for other resources. Much of placoderm évo¬
lution revolved around specializations on a basic plan with rétention of a rclatively primitive
placoderm suspensorium and veriebraie loconiotor pattern (see discussion bclow). In contrast,
chondrichthyans and uctinopterygians evolved a number of innovations associatcd with fecding
and locomotion vvhich hâve been vvell documented (c g. ScHAr.FFER, 1975: Zangerl. 19X1;
Lae'DER, 1982; Webb. 1982; LUND cl al.. 1984). With ihc rapid increa.se in diversity among
actinopterygiaiis and chondrichthyans aftcr lhe Frasnian-Famennian extinction event. it is pro-
posed that thc>e forms may hâve competilivcly displaced contemporaneous placoderms; however,
the suggested présence of a major Famennian-Tournaisiaii extinction event is consistetit with a
model of opportunistic replacement by surviving actinopterygiaiis and chondrichthyans. Tests of
this hypolhesis musl await dctailed basimd and régional faunal analyses, Current field work and
review of lhe open basin faunas as.sociated wilh the Catskill Oelta and Michigan Basin may
shed light on lhe history and extinction of placoderms in lhe LIpper Devonian.
PACtlYO.STF;OMORPH DIVF.RSITY PATTERNS
Among pachyosleomorph arthrodires, lhe aspinothoracid subclade accounts for 50% of ail
described pachyosleomorph species. Remaining pachyosteomorphs comprise the Dunkleosteidae
(and possibly Panxiosleidae). Aspinothoracid aithrodires firsi appeared in the Upper Givetian
with un apparent increase in species diversiiy uniil lhe Frasnian-Famennian extinction épisode.
The Laurasian record for aspinothoracids includes LagerstMiten on boih sides of the extinction
épisode suggesling lhe Frasnian peak does not represent a sarnpling bias. Each Lagerslatten
(Upper Frasnian Keliwasserkalk of the Muiinciiccni.\ beds of Bad Wildungen. Germany, and
Laie Famennian Clevelanci Shale. norihern Ühio, U.S.A) represents similar deep water sedimentary
environments which suggesi polentially similar taphonomic processes. There is no data available
for Devonian slage level sechment volumes and surface exposures RONOV (1980) provides ser-
ies-level global data which indicales équivalent sédiment volumes and areas for the Middie and
Upper Devonian. However. différences iit eslimaied duration (Harland et al., 1989) suggcsl a
poiential sarnpling bias in favor of Frasnian sedimenis, but Sefkosisi (1991) has pointed out
that âges for lhe Devonian stage boimdaries arc poorly constrained and lime averaging may be
omitted until bctter e.stimates are available (Haki.a.no ci al.. 1989. note a high level of uncertainty
for e.stimaling the louer boundary date for each Upper Devonian stage. They note an error of
plus or minus an amounl equal lo or greater than the duration of the stage). During lhe Famennian,
there was lillle if any numencal recovery of diversity at the species level following the Frasnian-
Famennian extinction event. However, among arthrodires there was a secondary radialion as-
socialed wiih habitat utilizalion, feeding slrticliires, food acquisition, and loconiotor patterns.
Aspects of this radiation are seeii clearly in lhe Laie Faiiiennian Clevelaiid .Shale fauna of North
America with its morphologically diverse as.semblage of aspinolhoracid arthrodires. The question
then arises: whai iiiight accounl for this apparent increase in pachyosteoniorph diversity? Two
major adaplive aspects of the phenotype are associaled with feeding and locomotion. Il is difficult
to déterminé the prey of iiiost placoderms. but the biological rôle, in niechanical ternis, of the
structures associatcd with feeding and locomotion can be evaluulcd. An analysis of polential
funclional conséquences of evoliitionary changes in feeding morphologies must consider both
— 102 —
architectural and physiological aspects of muscle. Recent advances in the understanding of feed-
ing mechanics necessitate a more thorough considération of the components involved and the
potential trade-offs associated with evolutionary modification.
Feeding
Miles (1969) and Schaeffer (1975) discussed major trends in feeding mechanisms within
placoderms and gnathostomes respectively. Placoderms possess an autostylic jaw suspensorium
(Fig. 11; Miles, 1969) with the hyomandibula (Hm) supporting the submarginal plate (GOUJET,
1984a, b; contrast YOUNG, 1980, 1986). The palatoquadrate is fused to the dermal cheek (sub¬
orbital, SO, and postsuborbital plates, Fig. 11) providing support for the jaw articulation. An
adductor mandibulae muscle originales from the palatoquadrate and the médial surface of the
suborbital plate (Goujet, 1984b) and inscris along the latéral surface of the lower jaw (IG, Fig.
Il), attaching either to the non-masticatory portion of the inferognathal plate, when présent,
and/or to Meckel's cartilage (Mk, Fig. 1 1). The dermal inferognathal plate (Figs. 11, 12) consists
of an anterior occlusal région and posterior non-masticatory or “blade” portion. The non-mas-
ticatory ossified portion varies in arthrodires (Carr, 1991) from a short ventrally grooved struc¬
ture capping Meckel's cartilage (Fig. I2A) to a single enlarged lamina médial to Meckel’s
cartilage (Fig. 12B-G).
Miles (1969; 149) considered main brachythoracid trends to hâve been associated with
increasing the gape and “effective use” of gnathal éléments (incrca.sed inferognathal length, large
nuchal gap, functional articulation of the head). What constitutes “effective use” dépends upon
the rôle required of tlie gnathal éléments (e.g. durophages increase crushing forces while some
piscivores increa.se closing velocity to let the strike facilitate prey capture). MILES ( 1969) charac-
terized the inferognathal as a third class lever, arguing thaï évolution of the brachythoracid feeding
Fig. 11. — Latéral view of Coccosteus sp„ showing autostylic jaw suspension of arthrodires. from Gardiner, 1984. Structures
deep to dermal bones are drawn with a dashed oiilline. Cartilaginous structures arc siippled.
Vue latérale de Coccosteus sp.. montrant la supension autostylique des mâchoires, d'après Caroiner, 1984. Les structures
périchondrales profondes sont indiquées par une trame. U\s structures cartilagineu.ses sont en pointillé.
— 103 —
mechanism balanced an anterior muscular inseriion (improved in-force) with improved gape. For
a given mass of muscle, a more distal placement and increased velocity associatcd with enlarged
gape are potentially in contlict (inferognathal velocity is dépendent in part on the foree available
for mandibular accélération which rellects muscle fiber organization and rotational inertial ef-
fects). Il is noi clear what consliuues MlLE-S* (1969) concept of élongation for the lower jaw.
The ossified “blade” does noi extend from the articular lo the occlusal surface in ail arthrodires.
Elongation may be liscd tn describe the lengthening of the '‘blade" to reach the articular or to
describe the relative increase in length for the entirc lower jaw (articular to syrnphysis). It appears
thaï bolh forms of élongation hâve occurred among arthrodires. A complété ‘■‘blade". présent
from the articular to the occlusal région, appears lo be a synapomorpby of eiibrachythoracid
arthrodires and llomastius (CARR. 1991). A visitai inspection of the relative lengths between the
lower Jaw (or the length between the quadrale on the postsuborbital plate and the position of
the posterior supcrognalhal on the suborbital) and a longitudinal measure for the head shield
(e.g. orbit to glenoid condyle) suggests that pachyosteomorph arthrodires huve developcd an
elongated lower Jaw. Finally, Miles’ summary does noi explain the presence of forms with a
reduced blade restricting muscular insertion posteriorly (e.g. Hiuirosteus, Fig. 12F).
In a rotational gnathal .System (Eq. 1; ALEXANDER, 1968), the out-moment is equal to the
in-momenl.
F„ L„ = Fl Lj (Eq. I)
F„ = ( Fi Li ) / (Eq. 2)
More effective out-force application (Eq. 2) can be achieved in a number of ways.
(1) The out-force moment arm (L„) can be reduced either by applying forces only to post¬
erior aspects of the occlusal surface or by shortening the inferognathal (as seen in Mylostoma,
Denison. 1978, Fig. 79. or in Oxyostinm. Stensiü. 1963. PI. 55, Figs. 4, 5).
(2) Muscle force (/■',) can be increased by increasing the mass of the muscle (Gans & DE
Vree, 1987; Gans & Gaunt, 1991). Addition of muscle mass is constrained by restrictions on
muscle packing (i.e. available space and liber orientation) and mclabolic cosis.
(3) Fmally. out-forces can be affecled through modification of inferognathal shape with
development of a coronoid process (as noted by Miles. 1969, and among placoderms seen only
in Brachyasteus dietrichi, Fig. I2D). ’fhis either accommodâtes phylogenelic shifls in the angle
between Unes of mu.scle action and lever action or sirnply provides increased area for the insertion
surface. MILE.S' (1969) proposai - à simple anterior shifl of muscle insertion (increased £,) -
fails to rccognize that an increase in moment arm is paid for by a réduction in muscle force
(Gans, 1988; Gans & Gaunt, 1991 ). Placement of the adductor muscle clo.ser to the Joint does
minimize the rotational inerlia (GanS, 1988).
An alternative lo MlLES’ hypothesis (élongation of inferognathals to increase in-force mo¬
ment arm and gape) includes (I) inferognathal élongation to increa.se gape, (2) élongation and
réduction of inertial effecls lo increase closure velocity (note that power increascs with increased
muscle force, but not with changes of in-force moment arm), and (3) ossification of the inferog¬
nathal plate, from the articular to the symphysi.s, lo stabilize and .strengthen the lower Jaw. Since
power does not increase and out-forces decrease with the increase of Jaw length (out-force mo¬
ment arm), other mechanisms for enhanccmcnt of the bile might be predicted based on feeding
strategy. Development of an ossified blade provides a strengthened and stable in.sertion for a
— 104 —
Fig. 12. — Inferognathal piales in latéral view. A-G redrawn l'rom Gross, 1967. A, indeterminate dolichothoracid. x 0.96. B.
Pholidosteus friedeli. x 1.16. C. Dunkleosteiis terreUi. X 0.24. D, Brochyosteus dietrichi, x 1.48. E. Rhinosteus îuberculatus,
X 1.6. F. Hadrosreus rapax. x 0.44. G. Diph^inathiis mirabilis, x 0.38.
Plaque gnathale inférieure en vue latérale. A-G d'après Gross, 1967. A. dolichoihoracide indet.. x 0.96. B. Pholidosteus
friedeli, x I.J6. C. DunkJeosieus terrelli, x 0,24. P. Brachyo.sieus dielrichi, x 1.48. E, Rhinosteu.s îuberculatus, x 1.6. F. Ha-
drosleus rapax. x 0.44. G. Diplognathus mirabilis, x 0.38.
— 105 —
potentially larger adciiictor muscle mass wilh a resulting Increase in in-force. Hlongation of the
blade in placoderms may hâve represented a conséquence of the relationship between the sus-
pensorium and dermal cheek in placoderms. Fusion of the palatoquadratc and dermal skcleton
along with limited check mobility or fusion of the cheek to the head shicld restricted expansion
of the muscles upon contraction. An elongatcd blade provides a polential attachmcnl for a larger
anterior-posterior muscle mass, although. changes in liber orientation may provide similar rcsults
(équivalence, Gan.s & CiAuNi, 1001). In contrasi, the proporlionally short blade fhuiroxieiis
(Fig. 12F) and Üiiilo^iuiilitis (Fig. 12G) suggests spécial ization for rapid closure. The presence
of elongaied deniicles along the occlusal surface in these généra, especially l)if>li>f;naihns, ïs
con.sistent with a siralegy of taking whole prey with liltle or no buccal réduction after capture.
A common pattern among pachyosieoiriorph piscivores (e.g. Dnnkleosieii\, Fig. I2C, Heint-
zichthys. and Gurymiklithys) was development of an anterior ctisp maximi/.ing the stress (force
per unit area) imposeil upon prey and proviiling .sufficient shear forces to piercc dermal bone
or the exoskeletun of invenebrates. The piesence of a single infei'ognathal ossifreation provided
résistance lo bending forces gencrated by an impal ing action of the anterior cusps. Seleno.steids
(0RVIG. lOHOa. Figs. 52-56) a)id liuiiyiiriius (DfnisùN. 1978. Fig. 81 ) similarly developcd a prominent
denticle along the occlusal surface. Long occlusal suifaces (e.g, up to 66% of inferognathal lenglh
in Hadrasteiis) provided postcriorly displaccd occlusal suifaces with an incteased range of out-foix:es
for crushing, partiltoning. or grasping- while mainlaining an enlarged gape (occlusal surfaces are
close to 50% among dtinkleosteids. selenosleids. Heùiizichihys. and HoUleniur, similar proportions
are fotind in eubrachythoracids in general). Development of large oibiLs. seen in a number of
aspinothoracid and coccosicomorph arthrodires. would nol hâve been a limiting factor in development
of an enlarged gape and muscle inseriion as suggested by Mil. HS' (1969).
Within pachyosteumorph arthrodires there was a morphologieal diversification of occlusal
surfaces. In this group were speciali/alions for dtirophagy (e.g. Mylostoma, Panimylostoma),
piscivory (e.g. Dunkleosreiis, Goryoïtivluliys, Heintzichihy.s), and possibly planktivory {Ti-
timichthys, DtNl.sON. 1978), Occlusal divers! Heation aiso occurred independently within the coc-
costeomorph arthrodires. although. to a lesser degree.
Locomotion
Several trends within eubrachythoracid (pachyosteomorph) évolution appear to involve
aspects of locomotion. The post-thoracic région is known only for a few placodemis. In ail these
cases and those in which there is partial préservation of the vertébral column. the notochord is
unrcstrictcd. The shapc of the caudal fin can be described as hcteroccrcal but, uniike sharks,
there is no direct evidence for an enlarged dorsal lobe and the ventral lobe is small and supported
only by elongatcd haemal arches. Wit.i.iA.MS (pers. comm.) has reported the presence of cera-
totrichia in the pectoral fin of an unidentified aspinothoracid and a spccimen of Dunkleosteiis
suggesting the possibility of expandcd arthrodiran fin profiles beyond their currently known
limits. Flydrodynamically. the caudal fin has a low aspect ratio (span/chord), resulting in relative
decreased thrust. The mode of locomotion was most likely anguilliform or eel-like undulation.
Associated with this type of locomotion in extant fishes are:
(1) slow speed;
(2) a lack of rapid accélération;
— 106 —
(3) and decreased agility (referring to the rate of movement).
Unlike extant anguilliform swimmers and suggestive, in part, of subcarangiform locomotion
(Lindsey, 1978) was the inflexibility of the anterior third of the body along with a concentration
of mass antcriorly (Lindsey 1978, table 2, characterizes subcarangiform mode as; similar lo
anguilliform with reduced anterior ondulations; fusiform body; “body tends to be heavier and
more roundcd anteriorly": deep caudal peduncle; low aspect ratio caudal fin: llexible caudal fin
with straighl posterior margin or indented margin and intrinsic musculature). Effecis of these
Iwo parameters (flexibility, mass), concentrated undulations to the posterior two thirds of the
body and limited anterior yaw. Extant subcarangiform fishes often reduce the effect of yaw
through an enhancemeni of lhe latéral profile, which additionally shifts the center of gravity
forward (similar latéral compression is seen in Brachydeiridae). To go beyond these simple ob¬
servations is difficull silice the hydrodynamics and range of responses in extant anguilliform
swimmers are still poorly understood, Associated with changes in arihrodiran caudal locomotion
were modifications in the pectoral fins improving maneuverability.
Pectoral fins are diflicult to evaluate in placoderins, but there are some basic principles
that can be assessed (for a review of hydrodynamics see BonE and MaKSHALL, 1982). In fishes,
fins can be oriented in any position from horizontal to vertical with the latter case operating in
a drag régime, analogous lo using a boat oar. Horizontal fins can be either passive or active
lift structures with the amount of lift varied by shifting the angle of attack. An active lift System
is one in which lift is used to generate forward thrust. e.g. as seen in extant holocephalans
(Lindsey. 1978) and possibly among ptyctodonts and rhenanids (Miles, 1969, argued that the
heavily scaled and narrow based fins of gemuendinids were incapable of generating forward
thrust. but were used in burying the animal in sédiment, however, these two functions are not
mutually exclusive). In pachyosteomorph arthrodires, the fin was a nearly horizontal lift structure
in which the fin base was lengthencd with a concurrent incrcase in the number of fin basais
(cr.art, Fig. 13; Westoll, 1958; SlENSlO, 1959). Outgroups had a narrow based fin with fewer
basais (Fig. 13 A; Stensiô, 1959; GoUJET, 1984a, YOUNG & Zhang, 1992). Fin basais articulated
Fig. 13. — A comparison of narrow and broad based pectoral fins. A, Pholidosteus sp.: B. Rhhiosteus pan ulus, redrawn from
Stf.NSIô, 1959.
Comparaison entre des nageoires pectorales étroites et larges. A. Pholidosteus sp. ; B. Rhinosleus parvulus. d’après STENStô,
1959.
— 107 —
individually with the pectoral girdle, typically without fusion of these structures into more com-
plex pro-, meso-, or metapterygia. A simple metapterygium is known in severai forms. In Heint-
zichthys gouldii, the metapterygium has a posteriorly placed flange (Carr, 1991, Fig. 16), which
may hâve functioned as a site for muscle attachment for use in fin rétraction or in altering fin
camber (anteropo.sterior curvature). Retraction allows for changes in geomelry of the fin with
differing velociiies (rétraction is not secn in extant sharks with a broad based fin). Additionally,
there was increased surface area on the scapulocoracoid for both dorsal and ventral mu.scle at-
tachments (Fig. I3B). This type of fin potentially could increase maneuverability through the
use of differential lift or to reduce surface friction ai faster swimming speed.s for which less lift
is required. Another possibility is that seen in extant holocephalans where forward thru.st is pro-
vided by pectoral Fin undulalions. In these forms, a forward ihrusl equal or grcaier ihan caudal
thrust can be generatcd (LiNDSEY. 1978). In aspinothoracids, choice between these iwo options
would be purely .spéculative. Decision requires infoimalion about the fin span; however, increased
musculature and lack of fusion might suggest the possibility of active lift in some forms. On
the other hand. distally tapered basais in Heinizichihys gouldii (CARR, 1991, Fig. I6A, B) would
suggest passive lift in this form.
Shortening of the thoracic shield represents another trend potentially associated with loco¬
motion (Fig. 14). An enclo.sed irunk was a primitive characteristic of placoderms (Miles &
Young, 1977; GOUJET, 19S4h), with antiarchs and arthrodires possessing a relaiively elongated
thoracic shield posterior |o the pectoral fenestra. Early évolution of head and thoracic shields,
as noted above. may hâve been associated with modification ol primitive anguilliform swimming
to minimi^e yaw associated wilh undulatory locomotion iheieby limiiing energy loss (Webb,
1982). Arthrodires eventually lost body scales increasing flexibility, In Coccosleus cuspidcitus
(Fig. 3F), nearly 38% of the total body length is inflexible to latéral bending. The starting point
for the génération of a propulsive boily wave to accelerale a body of water was therefore displaced
posteriorly. Wf.STOLI. (1958) and M11.F.S (1969) separately suggested shortening of the thoracic
shield and recruitmem of addilional body segments to increase. propulsive capability through the
development of large amplitude waves; however, it is the rate lhat the water is slied which is
proportional to thrust. Most bony fishes and lammd sharks, in contrasl. increase the propulsive
effect by shortening the length of the body involved in the propulsive wave and increase the
aspect ratio or latéral profile of the tail along with oscillaiory rate. In many cases among ar¬
throdires, the shortening of the thoracic shield is restricted to the latéral pectoral cmbayments
and médian dorsal plate (MD. Fig. 14). The posterior ventrolaleral plates (PVL, Fig. 14) extend
posteriorly to a position equal to that in forms with a closed pectoral fenestra. This would limit
undulations to rcgion.s équivalent to forms without réduction. In forms with shortening of the
latéral and midline portions of the thoracic shield (e.g. Homoxtius, Hetewsteus, rhenanids, and
ptyctodonts which arc interpreied a.s botlom dwcllers). the réduction may hâve been a.ssociated
with improved maneuverability in tuming. Overlap and interdigitation between plates of the der-
mal head shield aiso providcd a stable platform as.sociated with development of the cranio-
thoracic articulation, although. the articulation is lost in brachydeirids and of questionable
fonction in Holonema (LELIÈVRE ei al.. 1990). The articulation was furlher modified in brachy-
ihoracid arthrodires by transverse occipital thickening of the head shield (GoUJET, 1984b). Short¬
ening of thoracic shield rcduces anlerior body ma.ss. Wiihin aspinolhoracid arthrodires this was
— 108 —
Fig. 14. — Latéral view of three arthrodiran thoracic shiclds showing the shortetiing of latéral and dorsal portions: A. Dicksonosteus
arcticus, a phlyctaeniid redrawn from Goujet, 1984a. B. Coccosteus cuspidatus, a coccosteomorph arthrodirc redrawn from
Miles & Westoll. 1968; C, Heintzichthys gouldii. an aspinothoracid arthrodire redrawn from CaRR, 1991.
Vue latérale de trois cuirasses thoraciques d'arthrodire montrant le raccourcissement des régions dorsales et latérales: A,
Dicksonosteus arcticus. un phlyctaeniide d’après Goujet. 1984a. B. Coccosleus cuspidatus. un coccostéomorphe d’après
Miles & Westoll, 1968: C. Heintzichthys gouldii, un Arthrodire aspinothoracide d’après Carr. 1991.
paralleled by a réduction in the head shield and may be related to changes in static buoyancy
associated with sustained or prolonged swimming (Hoar & Randall, 1978; xiii).
Orbits
Many extant mesopelagic fish, which live between 200 to 1000 m, and benthic fishes living
above 1000 m hâve large eyes (NiKOLSKY, 1978; NICOL, 1989). Large eyes are correlated with
increased visual acuity in diurnal fishes or increased sensitivity in crepuscular and nocturnal
— 109 —
fishes (Walls, 1942; NICOL, 1989). Associated with this increase in both relative and absolute
sizes is a concordant change in pupil size (NicOL, 1989). Since the intensity of light varies as
the square of the distance traveled, an increase in eye diameter would require an enlargement
of the aperture to maintain image intensity on the relina. This relationship is found within both
elasmobranchs and osteichthyans (NICOL.. 1989) suggesting a common, although independently
derived (Gruber & CotlEN. 1978), pattern among gnathostomes.
Within aspinothoracids, large eyes developed independently .several limes (Figs. I5B, I6A).
This independencc is supported, in part, by différences in the head shield to accommodate in-
creased orbit size (e.g. trematosteids show an élongation of the prcorbilal plates with increased
orbit size Whereas Luropean selenosteids, Fig. I5B, hâve elongated central plates with marginals
incorporated into the orbital border). Heinizichibys ÿouldii (Fig. 16A), in conirasi to Dunkleosteus
terrelli (Figs. 15A. IfiB-C), shows ail increase in relative and absolute orbit size. The internai
curvature on the sclerotic of Heinizichihyx guuldii furlher supports this différence in size. Ad-
ditionally. the diameter of the aperture has increased, so thaï the pupil could hâve been bigger.
Large orbils may suggesl adaptation for improved visual acuily or low light intensity (Miles,
1969) either al nighl or deeper in the océan. A similar pattern of orbit size is seen within coc-
costeomorph arlhrodires (compare Pholidosteus with Lalocamurus).
In summary. the pallem of species diversity for aspinolhoracid arthrodires suggests an ap¬
parent increase for this group in the late Middle and early Late Devonian. Coincident with this
increase are a number of morphological changes relaled to feeding. locomotion, and food ac¬
quisition. In cvaluating thcse changes relative to other gnathostomes, the placoderms in general
hâve retained their primitive suspcnsorium and locomotor pattern; however, the eubrachythoracid
and in particular the aspinolhoracid arthrodires demonstrate a number of speeialized modifications
on this basic pattern.
Fig. 15. — A coniparison of ihe relative size for sclerotic rings redrawn from STENSIÔ, 1963. A, Dunkleosteus terrelli. x 0.07.
B, Mirrosteus anfiusriceps, x 1.1.
Comparaison de la taille relative des anneaux sclérotiques, d’après Stensiô, 1963. A, Dunkleosteus terrelli, x0,07. B, Micro-
steus angusticeps, x /./.
Fig. 16. — Heintztchfhys gouldii. A. righ( sclerotic ring and inferognaihal (CMNH 7308). Dunkleosteus terrelli. B, partialiy
reconstructed and mounted left sclerotic ring (CMNH 6090). C, incomplète sclerotic ring (CMNH 8800). The above sclerotics
are reproduccd to ihc same .scalc. Note ihc ab.soluic and relative increase in orbit .size for Heintzichthys a much smaller
arlhrodire, Scale bar: I cm.
Heintzichthy.s gouldii. A, anneau sclérotique droit et inférognathal {CMNH 7}08}. Dunkleosteus terrelli, B. anneau sclérotique
gauche reconstruit (CMNH 6090). C. anneau sclérotique incomplet (CMNH 8800). Les figures A-C sont à la même échelle.
Remarquez la croissance absolue et relative de la taille de Corbite pour Heintzichthys, le plus petit urthrodire des deicx.
Echelle : / cm.
CONCLUSION
The pattern of placoderm global diversity suggests a number of hypothèses conceming their
ecology and évolution (see above; Miles, 1969; Long, 1990a; Gardiner, 1990) however, tests
of these hypothe.se.s should additionally consider both basinal and régional patterns. Existing
data, allow détermination of critical times of origination and extinction and potential causal in¬
teractions which suggest areas for additional study (e.g. diversity shifts at the Middle-Upper
Devonian transition associalcd with major faciès changes suggesting questions of émigration
versus extinction). The current study .sugge.sts thaï stratigraphie analysis down to substage level
is required for the récognition of patterns among placoderm subclades. At présent, taxonomie
and temporal resolution for individual taxa is less critical with utilization of ail available data
providing the best picture. To address remaining questions, much work is needed exploring west¬
ern North American cratonic deposits. Recent field work in Indochina (e.g. Blieck er al., 1984;
Janvier et al.. 1987; Thanh & Janvier, 1987: Long ci al., 1990), Africa and Middie East
(e.g. Lelièvre, 1984a, b; 1988; Lelièvre et al.. 1981), Australia (e.g. Miles & Dennis, 1979;
Young, 1988a; Long, 1990b), Antarctica (e.g. Young, 1988b) and South America (e.g. GOUJET
et ai, 1985) hâve added significantly to our understanding of diversity and biogeography among
gnathostomes. Addiiionally, spécifie critical periods in gnathosiome évolution (e.g. Famennian-
Toumai-sian) requirc active exploration with known Devonian localities needing renewed interest.
A number of Middle and Upper Devonian Michigan Basin invertebrale localities hâve been
collected exiensively (Ehlers & Ki-SLING, 1970) with few or no records of fossil fishes. In a
two week lïcld period (Antrim Shale Formation and Traverse Group. Summer 1991 ), 1 collected
remains belonging to 12 généra of gnathostomes, new to the basin, along with Ihrce généra
which repre.scnt extensions of known ranges. The Middle to Late Paleozoic represents a key
period in the evolutionary history of gnatho.stomes and a renewed interest in field work offers
much potenlial.
The early placoderms show a trend toward solidification of the head and thoracic shields
associated with the origin and cnhanccmcnt of the cran io- thoracic articulation and possible mod¬
ification of anguilliforin locomotion. Arthrodires redticed body .scales, perhaps increasing maneu-
verabilit>', Within aspinothoracid arthrodires, secondary locomotor (rends included further
development of pectoral fin maneuverability and lift along with mass réduction through latéral
shortening of the thoracic shield and thinning of the dcrmal bone. If initial gains in rnass were
associated with inertial stabilization in a modification of anguilliform locomotion, secondary
loss would suggest fuilher modifications away from a purely anguilliform style of locomotion.
However, there is no préservation of post-thoracic anatomy among aspinothoracid arthrodires to
confirm this relaiionship. Several fomis (brachydeirids) showed latéral compression which would
minimize yaw associated with loss of anterior mass. Pachyosteomorph arthrodires developed the
widest range of feeding modifications on the unique placodcrm patlcrri of fixing the susperisorium
to the dermal skeleton. This pattern may hâve been a limiting factor in their évolution and
compétition with other evolving gnathostomes, despitc the évolution of a widc diversity of gnathal
morphologies among pachyosteomorph arthrodires along with mechanical specializations. Ossi¬
fication of the inferognathal blade (a brachythoracid character) provided atiachment for enlarged
adductor musculature. A number of taxa developed elongated inferognathals charactcrizcd by
increased hite velocity and modification of the anterior cu.sp to impale prey. Large occlusal sur¬
faces permitted a widc range of potential out-forcc for crushing or partitioning of food. Special-
ized durophages (e.g. Myln.'itümu) reduccd the occlusal portion of the inferognathal concentrating
crushing surfaces posteriorly. Enlarged orbits were achieved independcntly in a number of ar-
throdire groups and are correlated with either increased acuity or specialization for low light
intensity.
In contrast to the generalized perception of placoderms as sluggish modified bcnthic fishes,
the diversity of morphological .specializations suggest that these fishes were ecologically diverse
with some being active predators capable of effective locomotion (Fig. 17). Placoderm extinction
cannot be attributed to any single cause, During the Upper Devonian their décliné at the Frasnian-
Famennian boundary can be attributed to a global extinction event (Sepkoski, 1986; McMillan
et al., 1988); however. the event did not equally affect each of the gnathostome clades présent
at that time. After a réduction in diversity of over 57% (table I ) there is evidence for a partial
recovery among arthrodires during the Upper Famennian where they were competing with rapidiy
Fig. 17. — A life reconsiruclion üf iwo Dunkleosteiis ierrelli with the right individual in active pursuil of Cladoselache sp. Drawn
by Joseph Winans, © 1992.
Rei'onstiiuùon dr deux Dunkleostcus terrelli, l'individu de droite poursuivant un Cladoselache sp. Dessin de Joseph Winans,
© 1992.
evolving chondrichthyans and actinopterygians. The Frasnian-Famennian extinclion épisode, by
reducing placoderm diversity, may hâve providcd a “window of opporlunity” for early radiation
of chondrichthyans and actinopterygians. Placoderm évolution had centered on diverse, but
limitcd modifications of primitive patterns of locomotion and suspensorium. Thç évolution of
specializcd actinoptcrygian subcarangiform and carangiform locomotion provided cost effective
improvemcnls uvcr primitive anguilliform or modified anguilliform patterns (Wrbb. 1982). Ac¬
tinopterygians and chondrichthyans aiso demonstrated a grcatcr plasticity in development of struc¬
tural modifications for feeding. The Early Mississippian extinction of placoderrns is consistent
either with compétitive displacement or with opportunistic replacement following the global
Famennian-Tournaisian extinction event. It is possible, even likely^ that both factors may play
a rôle. Distinguishing betwccn thc.se two models rcquires a more complété understanding of
early osteichthyun diversity. Due to the high reported levels of endemism among placoderrns,
the interrclationships among gnatho.stomes should be verified regionally as well.
Finally, additional study is needed to evaluate these and other hypothèses of placoderm
évolution. An intégrative approach considering environmental, géographie, and biological inter¬
actions with a renewed emphasis on field work will shed new light on placoderm, as well as
overall gnathostome. évolution.
Acknowledgments
1 would like to thank Dr Hervé LELtÈVRE and the inembers of my dissertation committee (Drs Daniel
Fisher. Cari Gans, Daniel Goujet. Philip Gingerich. and Gerald R. Smith) for their reviews of ihis
manuscript and for Daniel Goujet’s assistance in tracking dowii a number of difficulties to find référencés.
I arn greally indebted to Shen Mai for her as.sistance in iranslating stratigraphie data front niimerous Chinese
référencés. Also. l would like to thank Rob Cox for our many discussions; Dr Michael FooTH for discussions
on diversity; and Dr Cari Gans for disttissioiis on muscle funclion and architecture. I want to thank Dr
Michael WILLIAMS for his lime in showing me the material used in his 1990 paper and the placoderm
pectoral fin material with preserved ceratotrichia. Finally, the life leconstructions of üiinkleustcus lerrelli
and Cltulosvlache sp. were drawn by Joseph C. Win.ans, 1992. His work has helped to bring to life an
inierpreiation of placoderrns as active piedators in the Devonian seas. Field work. referred to in Ihis paper,
was supporlcd in part by grants froin the Geological Society of America and Scott TURNER Awards in
Earth Science. The University of Michigan. This report was siibniiitcd in partial fulfillment of the require-
ments for a Doctor of Philosophy in Geological Sciences in the Horace H. Rackham School of Graduate
Studies at The University of Michigan.
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Table I. Species- and genus level Frasnian-Famennian extinctions (percent réduction) for substage and stage. (*) indicatcs an
increase across the F-F boundary. The number of taxa présent before and after the extinction event are recorded in parenthèses.
Pourcentages, par sous-étages et étages, des espèces et genres présents après lé.xtinction du Frasnien-Famennien. L'astérisque
* indique une augmentation des taxons après la crise du Frasnien-Famennien. l-e nombre de taxons présents avant et après
l'extinction est indiqué entre paranthèses.
— 118 —
Appendix I
Stratigraphie ranges for placoderm species compilée! from Denison (19781 and ihe Zoological Record (1975-
1991». Range through melhod is employed for taxa known from disjuncl stages or substages (e.g. GED-EMS or
L. GED-U. GED). Taxa known from distinct stages are fully recorded (e.g. GED. SIG. EMS). Ranges with poor
stratigraphie résolution are recorded to (he level known (e.g. L. DEV or DEV). Tuxonomy, in ihe rnosl pan,
follows thaï of Denison iI978); phlyctaeniid and aciinolepid laxonomy after Goi jet (1984a) and "primitive"
brachythoracids after Lei.irvre (1988). Dinichthya herzeri (Carr and Hi.avtn. MS) along wilh Gorgonichthys clarki
and Heintzichlhyx goiiUlii (Carr. 1991) are assigned to Aspinothoracidi iiicertae sedh. * - Tomsteus. a nomen
nudtim, is replaced by GoujcUiaU'us by Kim Dennis-Bryan in tins volume (p. 133).
Rdixirtithiis atniligraptnqiws des espèces de Plucadermes d'après les données de Denison (1978) et le
Zoological Record (1975-1991). U‘s répartitions de ta.sa dans des étages ou des sous-étages disjoints .sont indiquées
(par es.: CED-EMS ou L GF.D-U. GED). luis ta.xons présents dans des étages distinctes sont notés (par ex. :
GED, SIG, EMS), Les répartitions stradgraphiques imprécises .sont indiquées pur référence au système ou sous
système (par ex.: L. DEV nu DEV). La systématique utilisée suit celle de Denkon (1978); la systématique des
phlyctaeniides et des actinolépides est celle de Goiuet tl984u), celle des "Brachyhtoraci primitifs" est celle de
Lelièvre (1988). Dinichthys herzeri (Carr & Hlavi.n. MS) de même Gorgonichthys clarki et Heintzichthys gouldii
(Carr, 1991) sont rapportées aux aspinothoracides incertae sedis. Torosteus. considéré comme un nomen nudum
est remplacé par le nouveau nom de genre Goujetosteus créé par Kim Dennis-Bryan dans ce volume (p. 133).
— 120 —
Family Buchanosteidae
Buchanosteus confenituherculutus EMS
Kuekhovdepis sinensia SIG?
Barabuchanosteus murrumhidgeensis
EMS
Buchanosteidae? gen. et sp. indet. EIF or GIV
Family Bunoartiidae
Bimgartius perissus U. FAM
Family Camuropiscidap.
Catiuiri’pisch concinniis
Cümiiropisrix tuidinwi
Faliaciisivus uinu'rt
Latocannirus cotiUhurdi
Rolfostcm Ciinningvnxi.K
Tiihimasus leniutrdi‘ii.\ îx
Family CorrosTr.iDAr-
Belgidsleiis nuirlelmunxi GIV
Clarkeosieus hulmodeux EIF or L. GIV
Clarkeomeus sp. GIV
CoccosH'ux nispidaiiis EIF
Coccnslt'iis grossi EIF
Coccosttiis nitirktiv GIV
Coccosteiis.’ iigusiir.i ?
Coccostfiis'.' t'uyahogtif FAM (U, FAM?)
Coccosifus}' friliihi ?
Coccoslctis? Iien ynius ?
Coccostt'iis? tihmsiis ?
CoccosU'ii.s'.' occidanndis EIF
Cociostrus.’ terniiioyae U. DEV
Coixoslfii\? sp. L. FRS
DU'kosteus Ihrt-iphmdi U. EIF, L. GIV
Dickostrus sp. EIF
Eldeiufsiriis iirizoïiriisis FRS
Janioslt'iis liiiiaiiiciis FRS
Jiiichengiit Uingoct ipiiii M. DEV
Milleroslt'iis ininor L. GIV
Milterostfus orvikui EIF
Millerosteiis sp. GIV
Millerosieiis? iH iiiiiituirus EIF
Plotiidnsli’us miuidi'nsis L. FRS
Ploindimeiis gnissi M. FRS
Plourdosleus liriinicus L. FRS
Plourdosieus miroitori M. FRS
Plourdosleus Iriiutsiliiildi FRS
Plourdosleus sp. GIV
Plourdosieus sp. L. FRS
Plourdosleus sp. FRS
Plourdosieus? inugnus L. FRS
Plourdosleus? ponderi L. FRS
Prolilcmu hlhys fossuius EIF
ProlllauiehlIiYS roekporlensis L. GIV
Protitaiiif hihys cf. roekporlensis GIV
Walsonosleus Jlelli U. GIV
Walsonosieiis ef. /lent GIV
Woodwiirdosleiis spatidatus EIF
Coecosteidae gen. et sp. indet. L. or M. EIF
Super Family CoccdSltuiDEi
Pinguosleiis llnilhoriii L. FRS
L. FRS
L. FRS
L. FRS
L. FRS
L. FRS
L. FRS
— 121 —
— 122 —
Holonema westolli
Holonema sp.
Holonema sp.
Holonema sp.
Holonema sp.
Holonema sp.
Holonema sp.
Holonema .sp.
Megaloplax marginalis
Rhenonema eifeliense
Tropuiosteus curx’atus
Family Leiosieidae
Rrromenosieiis hrachyrnstri.i
Ermmenosteus concaviis
Erromenostens diensti
Errotnenoslens inflatus
Erromenostens koeneni
Erromenostens lucifer
Erromenostens platycephalus
Family Lehtosteidae
Leptostens hkkensis
Leptostens involutns
Family Myio.stomatidak
Dinomylostoma heecheri
Dinomylostoma bnffaloensis
Dinomylostoma eastmani
Dinomylostoma sp.
Dinomylostoma? sp.
Dinomylostoma? sp.
Mylostoma eurhinus
Mylostoma newherry
Mylostoma variahile
TajilalUiitliys la voca ti
Family Panxiosteidae
Panxiosteiis ocullus
Family Phlyctaeniidae
Aggeraspis heintzi
Cartieraspis nigra
Diadsomaspis elongata
Diadsomaspis remscheidensis
Elegantaspis reticornis
Esutaspis megista
Ciaspeaspis c assivii
Heterogaspis acuticornis
Heterogaspis horealis
Heterogaspis gigantea
Heterogaspis hornsundi
Heterogaspis minuta
Huginaspis hroeggeri
Hnginaspis vogti
Kolpuspis heaudryi
Knnmingotepis tucaowanensis
Laurentaspis splendida
— 123 —
Family Tiaraspididae
Dichotiaraspis barbarae
Tiaraspis subrilis
Tiaraspis sp.
Tiaraspis sp.
Family Titanichthyidap
Tilanichlhys agassizi
Tilanit htbys attenuaws
Tilanichlhys clarkii
Tilanichlhys hussakofî
Tilanichlhys reclus
Tilanichlhys lermieri
Tilanichlhys sp.
Tilanichlhys? koziowskii
Family Torüsteidae
Torosieus* pulchellus L. FRS
Torosteus* luberciiUilus L. FRS
DOLICHOTHORACI indeierminant FAM
Dolicholhoiaci gen. et sp. indet. FAM
ART>IR0DIRA inceriae sedis
— 124 —
— 125 —
Bothriolepis sineitsis
Bothriolepis stevensoni
Bothriolepis laslenica
Bothriolepis tatongensis
Bothriolepis tayhiri
Bothriolepis tnic/uairi
Bothriolepis rungseni
Bothriolepis turaniiv
Bothriolepis virginiensis
Bothriolepis vuwae
Bothriolepis wilsotii
Bothriolepis yimnanensis
Bothriolepis zadonica
Bothriolepis sp.
Bothriolepis sp
Bothriolepis sp.
Bothriolepis sp,
Bothriolepis sp.
Bothriolepis sp.
Bothriolepis ,sp.
Bothriolepis sp.
Briagalepis warreni
Dianolepis Hui
Crossilepis brandi
Grossilepis spinosa
Grossilepis luherculata
Monarolepis verrucosa
Vietnamaspis trii
Wudinolepis weni
Xichonolepis tpdjingensis
GIV
U. DEV
FRS
U. GIV or L. FRS
FRS
FRS
GIV
FRS
7
GIV, FRS
U. DEV
GIV
?
FRS
FRS
FRS
FRS
FRS
L. FRS
FAM
FAM
FRS
M. DEV
FRS
FRS
FRS (U. DEV?)
7
GIV, FRS
M. DEV
GIV
Family Sinolepididae
Sinolepis macrocephala FAM
Sinolepis szei FAM
Sinolepis wutungensis FAM
Vanchienolepis langsonensis ?
Family Wedinolepididae
Hohsienolepis hsintuensis M. DEV
Family Yünnanolepididae
Phymolepis citifengshanensis L. DEV
Yunnanolepis hachoensis ?
Yunnunulepis ihii L. DEV?
Yunnanolepis départi ?
Yunnanolepis parvus L. DEV
PTERICHTlIYODOIDhA
Wuruiigiilepis denisoni EIF
ANTIARCHA ineertae sedis
Eoantiarchilepis xitunensis L. DEV
Grossuspis carinata GIV
Hillsaspis gippslandiensis U. DEV
Itunanolepis heni GIV
Lepadolepis stensiaei U. FRS
Lianhuashaiiolepis liukiangensis L. DEV
Orieniolepis neokwangsiensis GED or SIG
Taeniolepis speciosa FRS
Tsuifengshanolepis diantungensis L, DEV
Zhanjilepis aspratilis L. DEV
Bothriolepidoidei
Bull. Mus. natl. Hist. nat.. Paris, 4^ sér., 17, 1995
Section C. n“ 1-4 : 127-142.
Some comments on the Placoderm parasphenoid
by Kim DENNIS-BRYAN
Abstract. — Fara.sphenoids hâve or are being describcd iii thirly-nine généra oC ilie Placodermi. AU but
three of the gênera are arthrodires, The aciiial number of parasphenoids preserved is very sinall. A review of
the literature reveals that inany que.slions regarding this bone reniain unanswered e.g. its nrigin. whal is the
primitive and advanced condition, what change.s occur during growlh? Thnugh used by some authors as a character
that is diagnostic of partieular grotips of arthrodire. it seems on existing evidence that the parasphenoid is speeies
spécifie. There are few indications, at the présent tinte, thaï lhe bone is iisefui in working ont plactxierm rela-
tionships.
Keywords. — Placodermi. parasphenoid.
Remarques sur le parashénoïde des Placodermes
Résumé. — Le parasphénoïde est connu chez trente-neuf genres de Placodermes, parmi ceux-ci trois ne
sont pas des Arthrodires. Ainsi le nombre de genres où le parasphénoïde est connu est-il très restreint. Une
analyse des ouvrage.s où cet os dermique a été décrit, révèle que bon nombre de questions reste en suspens,
ainsi son ongine; quels sont les états primitifs et dérivés des caractères que Ton peut définir ? Quels sont les
changements qui l'affeclenl pendant la croissance? Bien que des auteurs aient utilisé le parasphénoïde dans la
définition de certains grrpupcs d' Arthrodires, il semble n'être seulement Caractéristique qu'au niveau spécifique.
Aujourd’hui, seuls quelques traits apparaissent utiles dans l'analyse des relations de parenté des Placodermes
Mots-clés. — • Placodermes, parasphénoïde.
K. Dennis-Bryan, 29 Easî End Road, Finchley N3 2TA London, United Kingdom.
Introduction
Among placoderm.s the parasphenoid is preserved in only a few arthrodires, the acanthothor-
acid Kosoraspis, the phyllolepid Austrophyllolepis and an undescribed Bothriolepis from Gogo,
Western Australia (table 1). In most cases only the ventral surface is known. The Gogo arthrodires
hâve provided a number of complété parasphenoids, but the significance of this bone in working
out relationships remains uncertain.
BM(NH) Natural History Muséum, London, United Kingdom.
WAM The Western Australian Muséum, Perth, Australia.
HISTORICAL BACKGROUND
Placoderm fossils hâve been recognized for over a century (McCOY, 1848), but the para¬
sphenoid was unknown until 1936 when Edwin Sherborn Hills, in describing the skull roof of
128 —
Buchanosleus (Coccosteus) osseus, also provided the first description of a placoderm parasphe-
noid. According to YOUNG (1979), the specimen described by Hills is ‘now in a poor State of
repair.’ However, his figures 4 and 5 show the bone to hâve a denticulated ventral surface and
a paired buccohypophysial foramen with an incomplète ventral iransverse groove posterior to
il. The restored bone is shown as being longer lhan it is broad. WttITE & TOOMBS ( 1972) described
three funher parasphenoids of Budumosieus. They too are denticulated but in these specimens
the buccohypophysial foramen is sited in the ventral transverse groove. Furthermore, White &
Too.mbs describe the bone as ‘broadly spade-shaped, about a.s long as wide’. YouNG (1979)
described anorher three parasphenoids muking a total of seven. These specimens show an increase
in breadth with increasing size which YoUNG interprets as an allometric growth feature.
In 1942, STENStÔ described the parasphenoid of the actinolepid Kujdanowiaspis (Fig. lA).
As in Buchanosleus. the dorsal surface is unknown. The ventral surface is entirely covered with
tubercles and is perforated by a large, undivided médian buccohypophysial foramen. The outline
of the bone is uncertain as there is considérable variation between Stensiô’s (1963) figures lOA
and 14. There are also différences in the shape of the buccohypophysial foramen and its spatial
relationship with the foramina for the hypophysial vein.
It is in the addendum to STENSlô's 1945 paper on the cranium and cervical joint of the
Dolichothoraci that the parasphenoid of eubrachythoracid arthrodires is first mentioned. StensIÔ
States that the bone is preserved in three généra - Erromenosteus (Fig. 2E), Trematosteus (Fig. 2F)
and Bnwhyosteus - from Wildungen in Germany. There are no descriptions, only the comment
that it is a 'powerful bone' extending backwards, as it does in crossoplerygians and palae-
onisciforms, to the transitional part between the orbito-temporal and otic régions of the en-
doc ranium.
Two eubrachythoracid parasphenoids were briefly described the following year by Dunkle
& Bungart (1946). However, the authors considered the bone to be homologous with the anterior
basal element of acanlhodians and so it is labelled as such in their drawings (Ab. Dunkle &
Bungart, 1946, Fig. 3). Among eubrachythoracid arthrodires there are a number of subdivisions,
two of which hâve been adopted here (coccosteomorph and pachyosteomorph, see table 1). Both
of the arthrodires described here are considered to be pachyosteomorph (for charactcrs, see Carr,
1991). The parasphenoid of Dunkleosieus (Dinichthys) rerrelli (Fig. 3 A) is described as being
’thickened anterornesially' and with two overlap areas on its anterior margin for the posterior
processes of the left and right anterior superognathals. In conlrast the parasphenoid of Heint-
zichthys gouldii is said to be ’a proportionally much narrower, thin lamina of bone, strongly
arched dorsally' that has no contact with the toothplates. A more detailed account of the former
is mentioned by the authors to be forthcoming but has not been traced. The latter was redescribed
by Carr in 1991.
Jarvik (1954) did not describe any arthrodire parasphenoids. However, in his discussion
of the évolution of the parasphenoid in fishes he concluded that, in arthrodires, ‘it is a thin
tooth-bearing plate atlached to the médian parts of the ventral faces of the ethmoidal and orbito-
temporal régions of the neurocranium, but is of varying shape and size and it may extend behind
the ventral opening of the fossa hypophyseos, thus being pierced by a hypophysial canal, or
end in front of that opening.' He considered the arthrodire parasphenoid primitive and charac-
terized by disintergration and réduction.
— 129
Fie. 1, — Piirasphcnouls in ventral view. A, Knjdanowiospis sp. (front STENSlô. 1963. Fig. lOA), B. Anlineosteits lehmani (from
Lelièvre, I98S, Fig. 2A). C. Anrolepis decipietis (from Coiijet, 1984, Fig, 81), D. Hamiixmibxiu elegans (from MILES &
Dennis, 1979. Fig. 13A). E. Coccosteus nispidatus (from Mills & Wf.stoll. 1968. Fig. 18u)
Parasphénoldes en vue ventrale. A, Kujdanowiaspis .\p. (d'aprèi STENSIt). 1963, fîg. lOA). B. Aniineosteus lehmani (d'après
Lelièvre, I9NS, fig. 2A). C, Aretolepis dccipiens (ddprès CouJfi, I9d4, flg. Si). D. Harrytoombsia elegan.s (d'après Miles
& Dennis, 1979, fig. I3.AI. E. Coccosteus euspidatus (d'après Miles <{ Wesivll, (966, fig. ISal.
Much of the above bas already been summarized by Kulczycki (1956). It was lie who,
in addition to providing the first detailed description of the eubrachythoracid parasphenoid, also
divided the bone into anterior (prehypophysial) and posterior (posthypophysial) divisions. The
three parasphenoids he described are referred to Dinichthy.s cf. piistulosus, Malerosteus gorizdmae
(Kulczycki, 1957), and brachythoracid indet. (Fig. 3E). It is interesting to note that in the latter
case the bone margin has been restored (Kulczycki, 1956, PI. IH) with the same ‘feathered
edge’ as is seen in Heinizichlhys (Carr, 1991, Fig. 8A).
KULCiZYCKI also considered the origin of the placoderm parasphenoid. He claimed that it
was a dermal bone on évidence of its histological structure and the presence of ornamentation
on the ventral surface. He rejected the suggested homology (DUNKLE &, BUNGART. 1946) with
the anterior-basal élément of acanthodians because of its perichondral origin and the ab.sence of
foramina and grooves for the internai carotids on the ventral surface.
In 1957, Kulczycki also described the parasphenoid of the pachyosteomorph Pachyosteus
bulla (Fig. 3B). He considered il more primitive lhan tho.se he had described previously despite
— 130 —
the lack of ornamentation on the ventral surface. His account of the bone is as follows: ‘25 mm
in length and 14mm in maximum width. Us smooth and plane ventral surface bas the outline
of a somewhat elongate and rounded hexagon. Anteriorly it is provided with a process whose
latéral margins first run parallel and lhen converge al a nearly right angle. Dorsally^ in the hind
part of the parasphenoid is a raised area with an extensive bowl-like, pituitary dépréssion. On
both latéral sides the margin of the dépréssion is parlicularly raised. To the front of this déprés¬
sion, on ils outer embankmeni extends a transverse groove whose latéral ends are directed ar-
cuately backward, Medially this groove branches off inio an unpaired ramification directed
straight forward, along the central line, over the dorsal surface of the anterior process, which
is here somewhat raised. These grooves probably contained internai carotids fusing here into
one unpaired canal entering the cranial cavity.*
There were now seven descriptions of different arihrodire parasphenoids |and mention by
Stbnsiô ( 1945) of at least Ihree more). It therefore seemed reasonable for Kulczycki ( 1957; 346)
to assume that eventually the diversity in shape and structure of the ailhrodire parasphenoid would
provide.. .‘additional evidence for the différentiation of separate evolutionary lines within this stock.’
The parasphenoid of Kianf^yousteiis (I.,IU, 1955) is omilted from KULCZYCKt's discussion
possibly because it had been misidentified by I.IÜ as a pineal plate. The bone is incomplète but
can be .seen to hâve the more complex structure of the previously mentioned eubrachythoracid
arthrodires. It bas a prehypophysial région and a thickened posterior part that houses the bucco-
bypophysial dépréssion and paired foramen. Using four characters. three of which refer to the
unusual form of the 'pineal', LIU concluded that Kiangynusieus was related lo the ancestral form
of either Tiiunkhthys or Dinichibys. Denison (1978) supported the latfer relationship and des-
ignated the genus to his family Dmichthyidae based in part on the similarity of the parasphenoid
(and the anterior latéral) with that of Dunkleosieits.
Lehman (1956: 38-54) discusses some incomplète parasphenoids in his account of ar-
throdire.s from the Upper Devonian of Tafilalet. ‘Only the central part of the parasphenoid can
be observed in my material. of a Dmkleosleus indéterminable at the species level; the préparation
of this central part shows that the dorsal face of Ihc parasphenoid plate was excavated and in
part occupied by a hypophysial fossa; at its lowest point it is pierced by two canals that open
in doser proximity to one another on the lower face of the bone...'
’I add to this description two photographs of parasphenoids of american brachythoracids
from the Nalural Hislory Muséum atiribuled respectively to Titmiichihys (P9384) and ?Proti-
tanichlhys Jossatus (P9368). These pièces seem lo he genencally indéterminable; it is not likely
that we are dealing with Tiranichihyi for which the parasphenoid must bave been larger than in
the Dmichthyidae. These pièces are nonetheless interesting as examples of parasphenoids of large
Brachythoraci.’
‘The parasphenoids each comprise an anterior and a posterior part; the two parts being
separated from one another by two symmetrical notches at the latéral edges of the bone situated
level to the centre of radiation; near to the radiation centre there opens one (?) or two canals.
The anterior border of the bone shows two concavities in which the anterior superognathals
inserted. At either side of these concavities towards the edges of the bone, the parasphenoid has
very thin expansions. The posterior border of the bone is transversely truncated between two
lobes, one to the right and one to the left.'
— 131 —
Fig. 2. — Parssphcnoids in ventral view. A, Gn^upiirh ffram GaBPINPR A Miie-S, 1994, Fig, 17B). B, Gnnjeto^fetis
[Torosteus) (ihUheUus (froni G^Rt'lNtR & MILES. 1990, Fig 24A| C, BuDerichthys facstdens (Iront DENNIS & Miles. I9S0,
Fig, 9B). D. £ü.irmti«fu/<'u.t caUiùipia (trom DRNNIS-BRVAN.I9S7. Fig, 17B). E. Émmvno.\teu.\ lucifer (front Strn.siô. I9fi3,
Fig. II5F1, F, Tremiÿlostnus fotUanellu.y (front STENSIÔ* I96.S, Fig. 92A)-
Parasphenoides en eue Ycnrrale. A. Gogopiscis gracilis d'après OAROINtH & MlLtS, l9<J4.fig. 17B^. B. Goujctosteus Crorosleus)
pulchellu-s (i/'aprf.t Gauoiukk Si Milks, 1990, fig. 24AI. C. Btillerichlhyii facsiden» (d'après Densis Sl Milhü. l9S0,fig. 90).
D. EastntanosifiLs calliaspis (d'après P£.\dlS-BuyAN. 1987. fig. I7B), f. Erromenosteus lucifcr (d'après SruNSId. I96J,
fig. 1I5EI f. Tiemaiosleu.s foniaiielius (d'après Sre-NSip. I96S. fig. 92A).
In addition it should be noted that the parasphenoid of P9368 bas the same ‘feathered edge’
as that described by Carr (1991) for Heintzichlhys but has a posterior configuration similar to
that of Dunkleosteus. The so-called ‘anterior concavities’ for overlap with the anterior superog-
nathals are unclear in this specimen compared with P9384. The parasphenoid of P9384 is also
less robust than in P9368.
In 1959 Gross described a non-arthrodiran parasphenoid - that of the acanthothoracid Ko-
soraspis. It most closely resembles the parasphenoid of Kujdanowiüspis in having a simple struc¬
ture with a denticulated ventral surface bearing a single buccohypophysial foramen. However,
in contrast to Kujdanowiaspis, the parasphenoid of Kosora.spis is long and narrow. The anterior
margin is unclear on the figured specimen.
Another review of arthrodire parasphenoids appeared in 1963 with the publication of
StensiÔ’s authoritative work on the arthrodire head. He included descriptions of four new par¬
asphenoids and mentioned the existence of a fifth, that of the trematosteid Brachyosteus. Stensiô
— 132 —
divided the parasphenoids of the pachyosteomorph arthrodires into five types: trematosteid, er-
romenosteid, dunkleosteid, heinlzichthyoid and pachyosteoid.
The trematosteid type of parasphenoid is long and narrow and has a conspicuous downward
bend in ils mid-region. The parasphenoids of both Trenuitosleus (Fig. 2F) and Brachyosteus are
said to be of this type but only that of the former is described and only the ventral surface is
known. The prchypophysial région is ‘veiy long and strelches forw'ards between the vomers’
(anterior superognathals). StensIÔ postulâtes that the bones were in contact with one another
but ihere are no overlap areas for the toothpiates on the parasphenoid as there are în Dunkleosleus.
The buccohypophysial foramen is unpaired and there is no ventral transverse groove or ornamen¬
tation.
The erromanosteid type is known only in Erromenosteus (Fig. 2E). Il is similar to the tre¬
matosteid type in ail the above features bar one, it lacks a buccohypophysial foramen. However,
according to Stensiô it is ‘very likely pierced by an unpaired buccohypophysial foramen.’.
These two types of parasphenoid along with the pachyosteoid type, which is known only
by thaï described for Pachyosteus by KULCZYCKI (1957). are suggested by STENSIÔ to be charac-
teristic of the familics Trernalostcidac, Leiosteidae and Pachyosieidae respectively. For example,
he says of the pachyosteoid parasphenoid thaï ‘there is strong reason to believe that a parasphe¬
noid of this type aiso exi.sted in Ensensleus, Ottnnosleiis, Wa Items te us and Parawaltemsteus.’
However, this inferencc is ruade withoul any direct évidence thaï this is the case. It lherefore
seems equally reasonable to assume thaï the parasphenoids described are species spécifie and
not as stated by Stensiô until further material becomes available for siudy.
The dunkleosteid and heinlzichthyoid types of parasphenoid are, according to Stensiô, rep-
resented respectively only by the généra Dunkleosleus (Fig. 3A) and Heinzichlhys both of which
hâve aiready been mentioned. It should, however, be noted that Heintzifhthys, having been cited
as a pachyosteomorph arthrodire with a characleristic type of parasphenoid, is omitted from
Stensiô's (1963: 387) familial listing of the group because, at that time, it was ‘so slightly
known’.
The parasphenoids of Pholidosteus and Tapinosteus are also described by Stensiô. That of
Pholuhsteus is long and narrow and is without notches, foramina or grooves. It is known only
from the ventral surface which is covered with small tubercles. The parasphenoid of Tapinosteus
(Stensiô, 1963, Fig. 7 IA) is of similar length, but is expanded laterally in the midregion. Again
only the ventral surface is known. In contrast to Pholidosteus, the Tapinosteus parasphenoid
lacks ornament and is pierced by a paired buccohypophysial foramen. At either side of the fora¬
men there is a short transverse groove that ends in a foramen presumably for a branch of the
internai carotid ariery. Posteriorly there is another unpaired foramen for the médian hypophysial
vein. Neither parasphenoid extends far enough anteriorly to overlap with the toothpiates. Despite
the very different form of the parasphenoid in these two généra, they are both considered to be
members of the family Pholidosteidae. As 1 hâve not been able to examine this material, 1 am
unable to comment further,
In 1968, Miles & Westoll de.scribed the parasphenoid of Coccosteus cuspidalus (Fig, lE).
The bone is roughiy circular in shape with a fiat ventral surface, There is a transverse groove
which is discontinuons and fades out medially at either side well short of the central région.
Tubercles are restricied to this central région which is pierced by a paired buccohypophysial
— 133 —
foramen. The médian septum thaï divides lhe foramen also divides the ill-defined buccohypophy-
sial dépréssion in half. Posteriorly there is a foramen for the médian hypophysial vein. The
posterior groove recorded by Miles & Westoll is re-assessed by Gardiner & Miles (1990)
as ‘no more than a step in the bone surface.’
In 1975, another non-brachythnrucid parasphenoid, that of the phlyctaeniid Dicksonosteus
arciicus, was described by GOUJEl as a ‘short tuberculated' bone with a single buccohypophysial
foramen at its centre He redescribed the bone in 1984 together with ihose of two other phlyc-
taeniids, Arctolepis decipiens (Fig. IC) and Heinizosteiis brevis (GOUJET, 1984, Figs. 91, 98),
and the actinolepid Lehmanosteus hyperborcus (GouJET, 1984, Fig. 107). The three phlyctaeniid
parasphenoids are similar in being broader than they are long, and in haviiig reduced prehy-
pophysial régions and anteriorly situated buccohypophysial foramina (revised by GouJET for D.
arciicus). Ail hâve dcnticulaled ventral surfaces. In contrast. in D. arciicus and H. bn’vi.<i the
buccohypophysial foramen is undivided whereas in A. decipiens it is a paired structure similar
to thaï of certain brachylhoracid arlhrodires. Transverse sections of lhe parasphenoid in D. arc-
licus suggest a bone of mixed origin as ‘the edges of the bone merge into the perichondral bone
enveloping the endocranium’ but ‘there is also fusion between the dermal bone and the internai
perichondral bone covering lhe hypophysial fossa,’
The parasphenoid of the actinolepid L. hyperboreus is most clo.sely similar to that described
by Stensiô for Kujdaïu/wiaspis in that the ventral surface is featureless except for the ornament
and a single buccohypophysial foramen at its centre. In shape, however, it is more like the
above phlyctaeniids in that if is broader than it is long.
Wang (1979) figures the anterior ventral part of a parasphenoid in his accouni of Panx-
iosteus occullus. He describes the bone as being without either a hypophysial foramen or surface
ornamentation but there dites appear to be a transverse ventral groove. His figure 2 shows the
parasphenoid with a substaniial overlap for lhe anterior superognathals. However, it is possible
that the bone has bcen displaccd forwards ihcreby suggcsting an unusually large overlap area.
Wang condudes that ‘the .strucliire and form of the parasphenoid are similar to thaï of
Dinichihys- but is distinguished |from it| by such as lhe central not bordering on the margin
and the dermal plate with tubercles.' Wang also writes that P. occullus is very similar to Pholidos-
leus except for the parasphenoid in which it differs distinclly,"
Between 1979 and 1994, MILES, Dennis-Bryan (also see Dennis), and Gardiner described
parasphenoids from len different généra of alhrodirc i.e. Harryioomhsia (Fig. ID; Miles & DEN¬
NIS, 1979), Brunlonichlbys (Fig. 3G) and Bullerichlhy.s {Fig. 2C; Dennis & Miles, 1980). Inci-
soscuium (Dennis & Miles. 1981). Simosteu.'i (Dennis & Miles, 1982). Kimberleyiclnhys
(Dennis-Bryan & Miles, 1983), Easimanosieus (Fig, 2D; Dennis-Bryan, 1987). Gnujetosieus
(Torosleus) (Fig. 2B; GARDINER & MILES. 1990; Vezina. in press) and Compagopiscin and
Gogopiscis (Fig. 2A; Gardiner & Miles, 1994). In all. except Brunlonichlbys, the bone is
detached from the endocranium and can be viewed from both dorsal and ventral aspects. Each
parasphenoid is spccics spécifie ihough they do hâve certain featnre.s in common. These simi-
larilies represenl a rétention of primitive features rather than the presence of shared derived
fealures. For example, in none of the Gogo arthrodires does the parasphenoid overlap the looth-
plates; all hâve a paired buccohypophysial foramen. Only in Easimanosieus calliaspis are there
134 —
a number of parasphenoids preserved and some variation in the bone bas been noted e.g., the
ventral groove is roofed over laterally in Iwo of the eleven specimens.
Two other parasphenoids from Gogo arthrodires hâve been described by Long (1988a, b)
for the eamuropiscids Tuhcmasus (Fig. 3C) and Latocamurus (Fig. 3D). Both bones are long and
rather narrow. a feature that Long suggests may be characteristic of the family Camuropiscididae.
However, the parasphenoid i.s not yet known in the camuropiscid Camurupiscis (Dennis & MILES,
1979a), and il is also elongaled in Bruntonichthys which is not a member of the that family.
Long (1988a) suggests that the similarity in the Bruntonichthys- parasphenoid i.s due to convergent
évolution. Long (in iilC.) has also described the parasphenoid of a plourdosteïd arthrodire (WAM
86.9.676) from Gogo. Its basic structure is much like that of other arthrodires from that locality.
In 1984, Long described the parasphenoids of two phyllolepids, Ausirophyllolepis ritchiei
and Austrophyllolepis youngi, though only that of A. ritchiei is illustrated in any detail. Both
appear to be very similar in structure for Long does not distinguish between them, The ventral
surface has a tuberculated central région in which there lies a paired buccohypophysial foramen.
Fig. 3. — Parasphenoids in dorsal view. A, Dunkleosteus ^Dinich1hys) terrelli (from DUNKLE & BUNGART, 1946, Fig. 3A). B,
Pachyosteus huila (from Kluzicki, 1957, Fig 13A). C, Tubonasus lennanit'n.m (from Long. 1988, Fig. 3B revcrsed). D,
l^rncamurus ioulthanli (fioin LONrt,l98K, Fig- MB)- F. Brachythoradd iiidel. ((rom KOLCZYC'KI, 1956, PI. IH). F, Ta-
ftluliirhthys lavocttti (from Lei.IF.vre, 1991, Fig. 4B). G, Brunjonkbthys multitUns (from DenNIS & MiLES. 1980, Fig. 3C).
Parasphénoïdes en vue dorsale. A, Dunkleosteus (Dirhehthys) terrelli (d’après DuNKLh dt Pl'NGARl, 1^46, Itg. JA). B, Pa-
fhyosteus bulla {d'après KOLtZiCKI. 1957. fig. IJA). C. Tuixnuisus lennardcnsi.s (d'après UiNO, l9fiK ftn- JB inversée). D,
Latocamurus coulthardi (d après Lofso. I9S8. fig JIB). L Brachyrltoradd auiet. (d'après KuiCZKKl. 1956. pi JH). F. Ta-
filalichthys lavocati (d'après LEUtVRE, J99I. fig. 4B) C, Brunloniehlhv>* multidens (d’après JC \tllMS. J9SI}, fig. JC).
— 135 —
The surrounding area which is only seen in the larger specimens (mature individuals) is ‘incised
with radial striae.’ The absence of this ouler région in juvéniles suggests that, for this group at
least, the growth of the parasphenoid is not by enlargement of the whole structure, but by addition
to the periphery (Long, 1984, Figs. 5, 6) The ventral groove is only évident at the latéral margins
of the ventral surface, as it is in Coccosieus cuspidtmis, but in shape the parasphenoid of a
mature individual is most similar to that of Biichanosteus. The bone is situated in the centre of
the head in a more posterior position lhan in other placoderms.
The First description of the homosteid arthrodire, Antineosleus lehmcmi (LiillÈVRE, 1984),
was confined to head and trunk armour plates. However, a further publication by LuliÙVRE
(1988: 289-29(1) describes an isolated parasphenoid, associated wilh typical Antineosteus dernaal
bones, showlng both dorsal and ventral surfaces. The dorsal surface has a broad transverse de-
pression at the centre of which ihcre i.s a clearly divided hypophy.sial fo.ssa. The ventral surface
(Fig. IB) has a large tuberculated area and is perforated by a paired buccohypophysial foramen.
The general shape of the para.sphenoid and the extent of ihe ornamented région i.s, according
to Lelièvre, unique to this arthrodire and probably aiso to ‘primitive brachythoracids' (see
table 1).
In 1987 Lelièvre ei al. described the parasphenoid of a selenosteid, MelaHosteus occitanus.
It has a very long, naiTow prehypophysial process which has a groove of unknown function
running along its dorsal surface. There i.s a paired hypophysial foramen on the main body of
the dorsal surface but, having merged within the bone, it opens on the ventral side as a single
opening. Again the form of the para.sphenoid is characteristic of tlie brachyihoracid arthrodire
in which it occiirs.
The parasphenoid of the type specimen of TafilaUchihys lavocati was described by LelIÈVRE
in 1991. Both dorsal (Fig. 3F) and ventral aspects of the bone are preserved. It is rounded in
shape with a paired buccohypophysial foramen. The ventral surface has a transverse ventral
groove but lacks ornamentation. The dorsal surface shows moderate development of the post¬
érolatéral processes.
The parasphenoid of Bothriolepis sp. is currently being described by YOUNG, Long,
Gardiner and Dennis-Bryan. The description is based on a single example of the bone
(BM(NH) P5(J898) from Gogo, Western Au.stralia. There is a well developed but narrow prehy¬
pophysial process below which is an expanded région with a convex posterior margin. The latéral
edges are notched as in some arthrodires but tbere is no buccohypophysial dépréssion or foramen.
Other placodenns with parasphenoids preserved thaï are currently being described include:
Gyinnotrachelui by CARR and two .species of Dunkleosteus aIso by Carr (pers. comm)
DISCUSSION
There are now many varied accounts of the parasphenoid in placoderms. Thirty-six généra
are represented of which ail but three are arthrodires. Despite this fairly extensive range of
material, the number of parasphenoids on which the descriptions are based is small with perhaps
only one or two of the bones being preserved for each species e.g. Harryioombxm ( I ), Tubonasus
(1), Melanosteus (I), Antineosteus (1). As a resull of this, apart from a description, information
— 136 —
about the placoderm parasphenoid is somewhat limited. Origin, variations, changes during growth
and sexual dimorphism ail require a larger sample size than is presently available. More recently,
however, characteristic features of the parasphenoid hâve been used by varions workers in an
attempt to work ont phylogenetic relationships (GARDlNliR & MILES, 1990, 1994; Carr, 1991).
The origin of the parasphenoid remains an open question. A number of sources hâve been
suggested, some based on analogy (Dl'NKLE & BengART, 1946) and others on histological évi¬
dence (KulczVCKI, 1957). More recently Goujet (1984) has pre.sentcd evidence from tran.sverse
sections of Dicksnrwsteiis thaï the parasphenoid has a mixed origin. This view supports Stensiô's
(1963: 228) suggestion for the origin of the parasphenoid in pholidosteids. However. in both of
these fomts the parasphenoid is closely asÿociated with the endocranium. This is noi the case
with. for example, the arthrodires from Gogo where the parasphenoid is easily isolated and both
dorsal and ventral surfaces of the bone are available for study. The endocranium is rarely pre-
served. The origin of the parasphenoid in these latter forms remains uncertain.
With such a small sample size, it is particularly difficuli to assess changes ihai occur during
growth or to know whether or not sexual dimorphism, the ageing of mature individuals and/or
normal variation are contributing to the différences observed. The parasphenoids of both Inci-
soscutuni (9 examples) and E. calliaspis (II) vary but. the specimens in which the différences
occur, are of very similar size. YOUNG ( 1979) attributes changes in the shape of the parasphenoid
of Buchanosteui (7) to growth and variation in the omamenl to postmortem damage. In contrast.
the parasphenoid of E. calliuspls allers very liltle in shape from the smallest (prepineal length
50.6 mm) to the largest specimen (prepineal length 196.0 mm) (Dennis, 1984 Ph. D. thesis).
Long (1984) suggests that in Austwphyllulepis, juvénile (small) specimens lack ihe edenticulate
région found in the parasphenoid of adults (large). However, this bone is preserved in only two
juvéniles of eaeh species. As 1 hâve not examined this material. and as LONG’s ( 1984. Figs. 5-6)
figures are unclear with regard to this feature, [ cannot comment further on this matter.
Prior to the uiilization of paiasphenoid characters for phylogentic analyses, parasphenoids
were discussed more in terms of which were primitive Types’ and which were advanced or
derived (Dennis, 1984, Ph. D thesis; Gardinlr & Miles, 1990). The primitive parasphenoid
is usually fiat and without notches or grooves. The ventral surface is covered with tubercles
and there is a large médian huccohypophysial foramen which may be single or paired. The ad¬
vanced Type' is thicker and more structured bearing notches, grooves and foramina. Tubercles
are reduccd in number and extent or absent. There is usually a well developed médian ventral
cresi, There are two notable exceptions to the above - Phohdosteus and the two species of
Austmphyllolepis. The former is considered to be an advanced arthrodire, but has the so-called
primitive parasphenoid and in the latter case the reverse is irue. It is perhaps possible that the
dorsoventrally flattened phyllolepids are in fact more advanced among placoderms than was first
thought.
The parasphenoid appears to be species spécifie in ail placoderms except the phyllolepids
which Long (1984) describes wjthout noting any significant différences. The question therefore
rcmains as to whether any character of this bone can be established that defines a larger phy¬
logenetic group. Goujet (1984: 237) stales that a small, subcircular or triangular parasphenoid
pierced by either a single or paired huccohypophysial foramen is a character shared by acti-
nolcpids, phlyctaeniids and brachythoracid arthrodires. There are, however. wilhin this group of
— 137 —
arthrodires, parasphenoids of very different shapes and which lack a buccohypophysial foramen
e.g. Pholidosteus. Pachyosteus.
Gardiner & Miles (1990; 197) suggest that parasphenoids possessing (a), a posterior di¬
vision of lhe fossa hypophyseos housjng lhe foramen for the médian vein and (b), postérolatéral
processes are characteristic of Cocensteus. Harrytuomhsia, Gaiijetosteus (Torosieus). Kimberley-
ichthys. Incisoxcitlum and Tiihonaxus (see character 22.7 of their ‘cladogram.’ Fig. 30). These
are the only forms in which the parasphenoid is prcseived, though olher arthrodires are included
in the groiip. However, lhe parasphenoids of Coccoxteiis, Harrytoombsia and Incisoscuium lack
postérolatéral processes and thaï of Tuhonasus (Long, 1988a, Fig. 3) lacks both featurcs (a) and
(b). Converseiy, Eastmanosteus which is not included in lhe group has a parasphenoid with bolh
a posterior division of the fossa hypophyseos and postérolatéral processes (Dennis-Bryan, 1987,
Fig. 17A).
Gardiner Sl Miles (1990) also use the presence of a médian crest on the ventral surface
of the parasphenoid as pari of ihcir characler 22.27 (characler 58. Gardiner & .Miles. 1994).
However, Ihis crest is clearly évident on the parasphenoid of a number of other arthrodires e.g.
BuUerichthys. E. cotliaspis, Dunkleosteus. that are excluded from the group. CarR (1991) aiso
uses this character in his data matrix (number 74) but it should be noled lhat he has scored the
crest as being présent in bolh Rolfosteus and Camuropixcis though the bone is not preserved in
these forms.
Gardiner & Miles (1990: 198-199) use a third parasphenoid characler in their cladogram
to unité among others the arthrodires BuUerichthys. Brimlonichlhys. Errometiosteiis. Brachyasteus,
Trematosteus and Pachyosteus. The character employed is as follows: ‘parasphenoid with strongly
developed postérolatéral processes which give it great depth and a buccohypophysial dépréssion
with both anterior and posterior divisions... paired buccohypophysial dépression... well developed
posterior shelf. This shelf is found in those forms above Pholidosteus in our cladogram.' Only
the parasphenoid of BuUerichthys conforms with every feature mentioned ahove. Even Bntnian-
ichthys. lo which it is choughl to be closely related. has a parasphenoid that lacks postérolatéral
processes. Of the other parasphenoids, thaï of Brachyo.steus has not bcen de.scribed. those of
Erromenosteus and Trematosteus are only known in ventral aspect and thaï of Pachyosteus con¬
forms on only one point - it has a posterior shelf, Il seems, therefore, that this parasphenoid
character is also invalid in the GARDINER and Miles phylogenetic scheme, though it is retained
in their 1994 paper (character 67).
Gardiner ( 1990: 313, character 59) uses part of the above character i.e. strongly developed
postérolatéral processes and a hypophysial dépréssion with anterior and posterior divisions, to
define a group of arthrodires lhat includes BuUerichthys. Bruntouichthys, Brachyosteus. Simos-
teus, Trematosteus, Erromenosteus and Pachyosteus and others in w'hich the parasphenoid has
not yet been dcscribed. The reasons for its removal at this level hâve aiready been discussed.
Carr (1991) uses four parasphenoid characters in his data matrix. One, number 74, has
aiready been mentioned, lhe others are as follows;
— character 71, width to length ratio for the parasphenoid pre- and posthypophysial shelf;
— character 72, parasphenoid postérolatéral processes;
— characler 73, the presence of a foramen for the médian hypophysial vein on the parasphenoid.
— 138 —
The lalter characler is ciled wilh five others as defining the monophyly of coccosteomoiph
arthrodires. However, thi.s foramen is présent in some parasphenoids of the pachyosteomorph
Eastmanosteus callia.ipis e.g. BM(NH) P51I40 and P51229. Other specimens of E. calliaspis
e.g, BM(NH) P50877 and PSOSSS, hâve only a groove which passes back on the posterior face
of the bone without disappearing from the surface. The variation of ihis charactcr within a species
makes it uniikely to be usefui in defining a higher taxonomie level. Such characters should.
however. continue to be included in analyses as it is important to présent and evaluate ail the
information that is available. Furthermore, the inclusion of new data could alter the significance
of such characters.
Despite the number of parasphenoids currenlly available for study, it seems that we are
still unable to satisfactorily explain its structure in ternis of placoderm phylogeny. Each, with
the exception of AitstrophyUolepis appears to be species spécifie e.g. character 14 in the Lelièvre
et al. (1987) cladogram, parasphenoid with long prehypophysial process, refers only to Mela-
nosleus. Carr (pers. comm) is currently describing two species of Dunkleosteus based on différ¬
ences in the parasphenoid.
CONCLUSION
On présent evidence it seems that the parasphenoid of placoderms is species spécifie and
no feature/character has yet been established that is exclusive to a higher taxonomie level. Another
group in which the parasphenoid is being studied in detail is the dipnoans (CLOLTtER. pers.
comm). Initial findings indicate that here too there is a high degree of species specificity.
Acknowlcdgements
I wish to thank Dr. Marius Arsenault for his exlreme patience in waiting for my manuscript; Dr.
Richard Cloutier for his encouragement, discussion and help wilh French translations. I am also most
gratefui to Drs John Long. Daniel Goujet. Hervé Lelièvre, Bob Carr and Brian Gardiner for their
comments and discussion throughout the production of this paper. Spécial thanks go to staff of the Natural
History Muséum, London for their continuing help and for allowing me to work in the research collections.
LITER.ATURE CITED
Carr. R. K.. 199L — Reanalysis of Heinnichthys eoutdii (Newberry), an uspinothoracid arthrodire (Placodermi)
from the Famennian of norlhern Ohio, with a review of brachvlhoracid systemalics. Zwil. J. Linn. Soc.
Lomlon.Mi: 349-390.
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— 140 —
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Appendix I
PLACODERMI
antiarcha
BOTHRIOLEPIDIDAE
PHYLLOLEPIDA
PHYLLOLEPIDIDAE
acanthothoraci
PALAEACANTHASPIDAE
ARTHRODIRA
ACTINOLEPID ARTHRODIRES
ACriNOLEPiDiDAE Kujdanowuispls rectiformis
Stensio, 1963, Figs. 14, 41.
Kujdanowiaspis huezaeziensis (Brotzen)
Stensio. 1942, Figs. 4. 5.
Kujdanowiaspis sp.
Stensio, 1963, Figs. 20A-D, G, 36; p. 57, 93, 95-97,
108. 119-121.
Lehmanosteus hyperhoreus
Goujet. 1984, Fig. 107; p. 227.
A Listing of Placoderm parasphenoids described to date.
Bothrioiepis sp. (from Gogo Western, Australia)
Yoüng, 1986: 47.
AustrallophvHolepis youngi
Long, 1983, Figs. IID, I2C, 16, I8B, 20; p. 282.
Austrophyllolepis ritchiei
Long, 1983, Figs. 4A, 5, 6, I4B, 17; p. 282.
Kosoraspis peckai
Gross, 1959, Figs. 6A, C. 7; PI. 6.1; p. 24.
Stensio. 1963, Fig. 12B.
PHLYCTAENIID ARTHRODIRES
PHLYCTAENiiDAE Arctolepis decipiens (Woodward) 1891
Goujet, 1984, Figs. 74, 81; p. 171,
Heintzosteus brevis (Heintz) 1929
Goujet. 1984, Figs. 91, 98; p. 198.
— 141 —
Dicksonosteus arcticus
Goujet, 1975, Fig, 4; p. 92.
Goujet, 1984, Figs. 6, 34-38; p, 107-109.
BRACHYTHORACID ARTHRODIRES
'PRIMITIVE' BRACHYTHORACIDS
BUCHANOSTEiDAE Buchanosteus confertituberculatus (Chapman)
Hills, 1936, Figs. 4. 5; p. 221-222;
White & Toombs, 1972, Figs. 4-11, PI. 3; p. 385-388;
Stensiù, 1963, Figs. 37A, 44A-B; p. 95-100, 108,
121-123, 274;
Yolinc, 1979, Figs. 5, 7A, 12, 17, Pis 4-5; p. 336-340.
HOMosTEiDAE Atitineosteus lehmani Lelièvre 1984
Lelièvre, 1988, Figs. 2, 3A-C; p. 289-290.
EUBRACHYTHORACID ARTHRODIRES - COCCOSTEOMORPHS
coccosTEiDAE Coccosteus cuspidatus Miller ex Agassi?
Miles cfe Westoll. 1968, Figs. 17A, I8A-B,
PI. 2E; p. 405-408.
CAMUROPisciDiDAE Tubonasus lennardensis Dennis & Miles 1979a
Long. 1988, Fig. 3; p. 83-84.
Latocarnurus coulthurdi
Long, 1988, Figs. 5. lOB-D, PI. 2; p. 250-251.
PLOURDOSTEiDAE HarrytoombsUi elegans
Miles & Dennis. 1979. Fig. 13; p. 50-51.
Goujetosteus (Torosieusj luberculalus
Gardiner & Miles, 1990, Fig, 9; p. 186, 193-194.
Goujetosteus (Tomsieus) pukhellus
Gardiner & Miles, 1990, Fig. 24; p. 186, 194.
Kimberleyichthys whyhrowi
Dennis-Bryan & Miles, 1983. Fig. 4; p. 160-161.
Kimberleyichthys bispicatus
Dennis-Bryan & Miles, 1983, Fig. 13; p, 166.
Panxiosteus ocullus
Wang. 1979, Fig. 2; p. 183, 186, 188.
Compagopiscis croucheri
Gardiner & Miles. 1994, Figs. 7, lOD-7; p. 143.
Gogopiscis gracilis
Gardiner & Miles, 1994, Fig. 17; p. 462-465.
PHOLiDOSTEiDAE PhoUdosteus bidorsatus (v. Koenen)
Stensiô, 1963. Figs. 49B-C, 5IC, 75; p. 172-173, 211,
228, 302.
Tapinosteus heintzi Stensiô 1959
Stensiô. 1963, Figs. 48, 50A, D. E. 53 A, 55C, D, 56B-
D, 58, 63, 71; p. 169-173, 211, 228, 302.
Malerosteus gorizdroae
Kulczycki. 1956, Pis IH, 2, Figs. 1-2; p. 104-106.
Klilczycki, 1957; 297.
EUBRACHTYTHORACID ARTHRODIRES - PACHYOSTEOMORPHS
DiNicHTHYiDAE Dutikleosteus terrelli (Newberry)
Dunkle & Bungart, 1946, fig. 3A, B; p. 6.
Stensiô, 1963, Figs. 114A-C, 115A; p. 271-272,
354-356.
— 142 —
SELENOSTEIDAE
LEIOSTEIDAE
TREMATOSTEIDAE
Family indet.
Kendrickichthyid arthrodires
Dunkleosteus? sp.
Lehman, 1956, PI. 10, fig. 3; p. 38.
Eastmanosteus calliaspis
Dennis-Bryan, 1987, Figs. 9A, 17; p. 27-28.
Heintzichthys gouldii (Newberry)
Dunkle & Bungart, 1946, Fig. 3C, D; p, 6.
Stensiô, 1963, Figs. I I4D-F; p. 271- 272, 356.
Carr, 1991, Fig. 8A-C; p. 361.
Kiangyousteus yohii
Liu, 1955, Fig. I, PI. 2; p. 3 described as a pineal.
Denison, 1978, Fig. 71; p. 91.
Melanosteus occitanus Lelièvre & Goujet, 1987
Lelièvre, Feist, Goujet & Blieck, 1987, PI. 2 C-E;
p. 13.
Pachyosteus bulla Jaekel, 1927
Kulczycki, 1957, Fig. 13; p. 326.
Stensiô, 1963, Fig. 1I5H-J; p. 271, 274, 302,
356-357.
Erromenosteus lucifer Jaekel, 1927
Stensiô, 1945: 67.
Stensiô, 1963, Fig. 115E-G; p. 272, 354.
Trematosteus fontanellus Gross, 1932
Stensiô, 1945: 67.
Stensiô, 1963, Figs. 87A, D, 91D, 92A, B; p. 271-
272, 352-353.
Brachyosteus dietrichi Gross, 1932
Stensiô, 1945: 67.
Stensiô, 1963: 354-356.
Incisoscutum ritchei
Dennis & Miles, 1981, Figs. 14-15; p. 235.
Tafüalichthys lavocati Lehman, 1956
Lelièvre, 1991, Fig. 4; p. 124.
Simosteus tuberculatus
Dennis & Miles, 1982, Fig. 5C; p. 163.
Bruntonichthys mullidens
Dennis & Miles, 1980, Figs, 1, 2, 3C-D; p. 51.
Bullerichthys fascidens
Dennis & Miles, 1980, Fig. 9; p. 58-59.
Bull. Mus. natl. Hist. not., Paris, 4^ sér., 17, 1995
Section C, n" 1-4 : 143-161.
The brachial articulation and pectoral fin
in Antiarchs (Placodermi)
by Philippe JANVIER
Abstract. — The structure of the arliculation for the pectoral fin in thc Antiarcha is reviewed, with particular
reference to the Early Devonian taxa front China, Vietnam and Australia: the Yunnanolepiformes, Procondy-
lolepiformes and Sinolepidae. The Sinolepidae display an amazing diversity of structure of the brachial articulation
area of the antorior ventrolateral plate, raiigmg front a very simple structure. Iike that of the Yunnanolepifonnes,
to more complex ones resembhng quiie closely thaï of the Êuantiarchi. This suggests thaï the Sinolepidae may
not be monophyletic, and that their presumed auiapomorphy (the large ventral fenestration of lire thoracic armotir)
could be either ple.siomorphous for (lie Antiarcha or for lhe ensemble Sinolepidae + Euantiarchi, or also homo-
plastic in Vanchienolepis, Xicliniiolepis and Sinoleph. The pectoral fin exoskeleton is deseribed in a
Vanchienolepis-liVe specimen from Yiinnan. and a possible pectoral fin, paitly covered with seales or minute
platelets is deseribed in a specimen of Yummnolepis from Vietnam.
Keywords. — Antiarcha, Yunnanolepiformes. Procondylolepiformes, Sinolepidae, brachial articulation.
L’articulation brachiale et la nageoire pectorale
chez les Antiarches (Placodermi)
Résumé. — La structure de l'articulation brachiale des Antiarches est décrite, en particulier chez des formes
du Dévonien inférieur de Chine, du Viêt-Nam et d'Australie : les Yimnunolépiformes. Procondytolépifomies et
sinolépidés. Les sinolépidés présentent une étonnante diversité dans la structure de la zone d'articulation brachiale
portée par la plaque venlrolalérale antérieure. Celle-ci va d'une structure très simple, assez comparable à celle
des Yunnanoiépiformes, ju.squ'à une .structure beaucoup plus complexe et très voisine de celle des Euaiitiarches,
suggérant ainsi que les sinolépidés. définis par la présence d'une large feneslration ventrale de la cuirasse tho¬
racique, ne sont peul-ètre pas monophylétiques. Dans ce cas. leur autapomorphie présumée pouiTuii être soit un
caractère plésiomorphc pour les antiarchcs ou pour Tcnscmblc sinolépidés + euanliarches, soit une homoplasie
chez Vanchienotepis, Xichonolepis et Sinolepis.
Mots-clés. — Antiarcha, Yunnanoiépiformes, Procondylolépiformes, Sinolepidae, articulation brachiale.
Ph. Janvier, Laboratoire de Paléonlulogie dit Muséum national d'Hisinire naturelle, et URA 12 du CNRS, R, rue Buffon, 75005
Paris, France.
Introduction
The Antiarcha is a monophyletic group of placotierms characterized by e.g. a derived struc¬
ture of the pectoral fins, which consists of generally jointed appendages enclosed in a rigid
sheath of dermal platelels, and which articulâtes directiy with the anterior ventrolateral plate
(thereafter called AVL) of lhe thoracic armour. Since Hugh Mii.ler (1841), and until the 196nies,
the antiarchs had been recorded from many Middie and Lato Devonian localities of Europe,
— 144 —
North America, Asia, Australia and Antarctica, but were shown to be quite homogeneous in
structure. Two major groups, the Bothriolepidoidei and Asterolepidoidei, were distinguished, both
possessing jointed pectoral appendages, with one exception: the Late Devonian asterolepidoid
genus Remigolepis whose appendages are unjointed. Also, in both groups, the exoskeletal com-
ponent of the pectoral fin articulâtes on the AVL plate by the means of a ball-and-socket device,
the bail being an helmet-shaped brachial process (brp. Fig. ID) of the AVL plate. The vascu-
larization and innervation of the fin was effected through a large axillary foramen (axf, Fig. ID)
Fig. 1. — The brachial articulalion area of the anierior veniroIateraJ plaie (AVL) in Lhc Aniiarcha. A, Chuchinoiepis dongmoensis
Tong Dzuy & Janvier, Early Devonian of Vietnam, poslerïor view (from TonG DZUY & Janvier. 1990, modified afier further
préparation of UHDü-VND27d), B, Vanchienolepis Umgsonensis Tong Dzuy & Janvier, Early Devonian of Vietnam, latéral
view (based mainly on .spccirnen UHDC'VND47 in Figure 5C). C. Grenfellaspis, Laïc Devonian of Australia (from Young
& Zhang, 1992). D, Bothriolcpis maephersoni Young, Devonian of Antarctica (from YOUNG 1988). Scale bar 1 mm for A,
B, and 5 mm for D.
RègUm de VûrtUuUmon hruchiale de la plaque venimlaiérafe antérieure (AVI.) des Antiarcha. A, Chuchinoiepis dongmoensis
long Dzuy <& Janvier, Dévonien inférieur du Viêt-Nam, vue postérieure (d'après TONu DZLIY tSi JANVIER. 1990. modifié par
une préparation supplémentaire de UHDG-VND27d}. B, Vanchienolepis langsonensi.s Tong Üzity de Janvier. Dévonien inférieur
du Viêt-Nam. vue latérale (principalement d'aptvs le spécimen VIÏDG VND47 de la figure 5C). C. Grenfcllaspis. Dévonien
supérieur d'Australie (d'après VOUNC & /JtANG. 1992). D, Bothriolepis maephersoni Young. Dévonien de TAntarctique (d'après
Young. 19BB)- Échelle, l mm pour A. B, et 5 mm pour D.
— 145 —
piercing the AVL plate behind the brachial process. Thanks to Stensio’s (1948) thorough de¬
scription of the bothriolepid Bolhriolepis ccmaclensis /rom the Late Devonian of Miguasha, Qué¬
bec, the structure of the rather complex ball-and-socket brachial articulation of advanccd antiarchs
is now wel) kriown. It has been completed by delailed studies on the asterolepid Asterolepis
ornata from f.atvia (Gross, 1931; Lyarskaya, 1981) and bothriolepids from Australia (YOUNG
& Zhang, 1992). However, virtually nothing was known of the endoskelelon of antiarchs. until
the discovery of perichondrally ossified mandibular arch éléments in a Bothhnlepis spécimen
from the Laie Devonian of Australia (YouNG, 1984a).
As early as 1958, a peculiar antiarch, Sinulepis macrocephala, was de.scribed by Lui &
Pan (1958) front the Devonian of China, but. sincc it possessed typical jointed appendages,
similar to tho.se of the Bothriolepidoidei, the unusual structure of its skull-roof (in particular the
very elongated nuchal plate, and the preorbital dépréssion) did not raise rnuch attention. Neverthe-
less, it was placed in a family of its own, the Sinolepidae,
In the early I960's. some even more peculiar antiarchs were discovered in the Early
Devonian of Ytmnan, China (Liu, 1963). They differed from ail previousiy known antiarchs by
the lack of a complex brachial articulation, and by a number of features in their skull-roof that
could be regarded as primitive (long nuchal and short premedian plates). Dr. CliANG Mee mann
(Beijing) was studying Ihis remarkable material in Stockholm when the “Great Cultural Révo¬
lution" broke out. She had to retum to China with lier slill unpublished material, part of which
appeared in pnnt only in 1978 in two papers by Chang Kuo JUI (1978) and ZHANG GUORUi
(= Chang Küü-jui) (1978) respectively. A more detailed description of the saine specimens by
Chang Mee mann appeared two ycars later (M.M. Zhang. 1980). These papers revealed the
morphology of what is now regarded as ihc most primitive antiarchs, the Yunnanolepiformes
(Yunnanolepis, PhymoJepia). which are possibly a paraphyleiic groiip (Tong Dzuy & Janvier,
1990). The Yunnanolepiformes differed from ail previously known antiarchs by the lack of a
brachial process and axillary foramen, their area for the articulation of the pectoral fin, or pectoral
fenestra, being a mere recess in the AVL plate (Fig. 2A, B)
There was no known intermediate between the typical ball-and-socket brachial articulation
of the Euantiarchi (Boihriolepidoidca and Asierolepidoidca) and the very simple structure in the
Yunnanolepiformes until 1984, when Zhanc GuoruI described a new genus, Pracondylolepis,
found in association with the Yunnanolepiformes in lhe Early Devonian of Yunnan. Procondv-
lolepis and the clo.sely related genus Chuchinolepis, display a sort of process prolonging the
prepectoral corner (pbp. Fig. lA). yet not shaped like that of the Euantiarchi and lacking a large
axillary foramen for the passage of the brachial nerves and blood vc.ssels. These seemed to hâve
passed through minute foramina piercing the brachial articulation area (f, Figs. 4, S). By this
time, cladisiic analyses of a number of characters of the skull-roof and thoracic armour clearly
suggested that the Sinolepidae were the sister-group of either the Euantiarchi (Janvier & Pan,
1982) or the Boihriolcpidoidei (YoUNG, 1984b. 1988). It could thus be predicted that, when
discovered, the brachial process of the Sinolepidae might appear to be eitlier intcnnodiaio between
that of Procondylolepis and that of the Euantiarchi, or simply idenlical to that of either the
former or the latter.
The recent dicovery of a rich Early Devonian antiarch fauna in northern Vietnam (TONG
Dzuy & Janvier. 1990) has provided new data which do not really meet these expectations.
— 147 —
This fauna comprises typical yunnanolepiforms [Yumuinolepis, Fig. 2A, B), a procondylolepiform
{Chuchinolepis, Fig. 2C), and a small form referred to the Sinolepidae, Vanchienolepis (Figs. I B,
5B-D), in which the dermal brachial articulation area could be observed. The latter shows no
resemblance to either that of the Procondylolepiformcs or that of ihc Euantiarchi. apart from
the presence of an axillary foramen, which rather recalls the Euantiarchi (axf, Fig. IB), Al the
same time, the brachial articulation of a new sinolepid, Grenfellaspis, from the Late Devonian
of Australia has been described, showing another type of brachial process (Fig. IC; RlTCHlE, et
ai, 1992; YouNG & Zhang, 1992). Finally, yet another type of brachial articulation area is
described in a sinolepid-like anterior ventrolateral plate from Wuding, Yunnan, China (Fig. 7)
Four questions then arose:
1- Whal are the homologies between the varions structures observed in the brachial artic¬
ulation area of antiarchs?
2 - How did the fin plates articulate with the anterior ventrolateral plate in the various
antiarchan groups?
3 - Are the Sinolepidae monophyletic?
4 - At which level of the cladogram of the Antiarcha does the appendage-like pectoral fin
structure appear?
Young & Zhang (1992) recently published a paper which answers the first two questions,
and is largely convergent with the results 1 presented during the Miguasha symposium.
The data presented in this paper are taken from three sources of malerial: Early Devonian
(most probably Laie Lochkovian or Early Pragian) antiarchs from Vietnam and China, and an
Eifelian antiarch from Iran. The material from Vietnam (Yunnanolepis. Chuchinolepis,
Vanchienolepis) is from the localitie.s of Dong Mo and Trang Xa (Lang Son and Bac Thai districts
respectively) and has been coliccted in a collaboration between the University of Hanoi and the
Laboratoire de Paléontologie, MNHN, Paris. The material from China has been collected by H.
Lelièvre and D. Goujet (Paris) during the excursion of the meeting on “Early Vertebrates and
Related Problems of Evolutionary Biplogy” (Beijing, 1987). The material from Vietnam belongs
to the collection of the Department of Geology of Hanoi University, Vietnam (LTHDG). The
material from China is registered in the Collections of the Muséum National d'Histoire Naturelle,
Paris (MNHN). The material from Iran belongs to the Mu.seum of the Geological Survey of
Iran, Tehran (MGSI).
The material from Vietnam has been prepared with an air-abrasive as well as mechanically,
with a needle. The material from China has been prepared chemically, with 10% formic acid.
Fig. 2. — Dermal thoracic armour of two Yunnanolepiformes (A, B) and a Procondylolepiforme (C) from the Early Devonian
of Dong Mo, Lang Son. Vieuum. m Ulerai view, showing the bmchial articular area, A. Yutmanoltpis bachoetisis Tong Dzuy
& Janvier. B, deprati Tfing D)?uy Sl Janvier. C, Churhirudepi.s drmgmaensi^x Tong Dzuy & Janvier (skull-roof added),
(from Tong Dzi'V & J^NV^I:R, Scalc bar: 10 mni.
Cuirasse ihoracique de deux Yunnanolépi/artfies (A, Bl et d'un Brovnndylotêpifonne (C) du Dévonien inférieur de Dnng Mo,
Lang Son. Viêt-Nam. en vue htêrale pour montrer h région de rarticulation hrat hude. A. Yunnanolepis bachoensis Tong
Dzuy & Janvier. B. Y. deprati Tong Dzuy <!& Janvier C. Chuchinolepis dongmoen.sjs Tong Dzuy Janvier (toit crânien
ajouté) (d'oprés TONG DZl'Y jAPVikJt, t990). Échefie : fO mm
— 148 —
The material from Iran is preserved as impressions, and casts of the natural moulds hâve been
made with silicone rubber.
Abbreviations
adr
apr
axf
bra
brc
brp
Cd, Cv
cit
cr
cr
df
esl
f
fgr
fp
fpl
fsc
Ml, Mm
n
pbp
PDL
PL
PP
ppc
PVL
pvr
scap
anterodorsal ridge, ride aruérodorsaie \
ornamented “apron” on anterior surface of internai transverse crest
(postbranchial lamina), “apron” ornementé sur la surface antérieure
de la crête transverse (lame posthranchiale) ;
axillary foramen, /f;ra/nen axillaire ',
brachial articulation area, région de l'articulation brachiale',
brachial canal for blood vessels and nerves, canal brachial
pour vaisseaux sanguins et nerfs',
brachial process, processus brachial ;
proximal dorsal and ventral central plates of appendage,
plaques centrales proximale dorsale et proximale ventrale ;
transverse internai crest. crête transverse interne',
presumed pedal crest, crête ventrale présumée ',
ventral crest (or pedal crest). crête ventrale;
dorsal articular fossa, fosse articulaire dorsale ;
ear-shaped lamina, lame en forme d'oreille;
foramina for brachial nerves and blood vessels, foramina pour les nerfs
brachiaux et les vaisseaux sanguins;
groove on médial surface of the parabrachial process, possibly correspond-
ing to the latéral wall of the funnel pit, sillon sur la surface médiale
du processus parabrachial ;
funnel pit, ouverture en entonnoir;
tile-shaped fin plates, plaques des nageoires en forme de tuile ;
fin seules, écailles des nageoires;
latéral and médial marginal plates of appendage, plaques marginales
latérale et médiale de l'appendice ;
notch for a process of the posterior ventrolateral plate, encoche pour un
processus de la plaque ventrolatérale postérieure ;
parabrachial process, processus parabrachial ;
posterior dorsolateral plate, plaque posté rodorsale;
posterolatral plate, plaque postérolatérale;
pedal part of brachial process, partie pédieuse du processus brachial ;
prepectoral corner, angle prépecloral ;
posterior ventrolatral plate, plaque ventrolatérale postérieure ;
posteroventral ridge, ride ventrale postérieure ;
recess lying behind tlie transverse internai crest, recessus en arrière de la
crête transverse interne ;
funnel-shaped perichondral bone of the scapulocoracoid, os perichondral
du scapulocoracoïde ;
— 149 —
scap perichondral bone of scapulocoracoid, os périchondral en forme de trémis
du scapulocoracoïde ;
vf ventral articular fossa, fosse articulaire ventrale -,
vfe ventral fenestration in the thoracic amtout, fenestration ventrale
de la cuirasse thoracique.
THE BRACHIAL ARTICULATION AREA OF THE AVL PLATE
The area of the AVL plate on which the pectoral fin or appendagc articulâtes is now fairly
well known in a wide range of antiarchan taxa. Il comprises the pectoral fenestra proper (scap,
Figs. lA, 4), lined with the perichondral bone of the scapulocoracoid (this area being. however,
much reduced in most antiarchs), and the dermal articular area on which the fin plates articulale
with the AVL plate. It is briefly described here in order of what is generally belicved to be an
order of increasing complexity.
Yunnanolepifor.mes
The brachial articulation is known in varions species of Yunnanolepis (M.M. Zhang, 1980;
TONG DZUY & Janvier, 1990) and displays viriually the same structure. It is a small recess
corresponding esseniially to the pectoral fenestra in the AVL plaie (bra, Fig. 3.8), with no con-
spicuous crest or process, other than a pointed prolongation of the prepectoral corner of the
plate (Fig. 2A, B). The main question about this type of brachial articulation area is how nerves
and blood vessels passed from the brachial plexi toward the pectoral fin. Grinding serial sections
of the AVL plate of Yunnanolepis depruti from Vietnam show a minute canal which may hâve
played this rôle (brc, Fig. 3.3). This canal is issued from the internai recess (r, Fig. 3.1) which
is limited anteriorly by the postbranchial lamina (or anterior transverse crest, cil, Fig. 3.3) of
the AVL plate, then it bends posterolaterally toward the pectoral fenestra. One particular detail
is worth noticing; this canal is lined by a thickened sheath of bone. which looks like perichondral
bone. When reaching the brachial recess, thi.s canal widens and ils lining seems to continue for
a short distance beyond the wall of the recess (Fig. 3.6. 7) a condition which suggests thaï it
was still surrounded by cartilage. One may thus suggest that the brachial rccesS was, at least
in part, filled With a cartilaginous plug (possibly a remuant of the scapulocoracoid) on which
the endoskeleton of the pectoral fin could articulate. At this level, the proximal derrnal plates
of the fin may nol hâve played a noie in the brachial articulation (YoUNG & ZHANG, 1992). At
least, in Phymolepis (G.R. ZHANG, 1978; M.M. ZHANG, 1980), ihere seems to be no trace of a
dermal articulation between the fin plates and the AVL plate. Whether the pectoral fins of the
Yunnanolepiformes were already jointed appendages is not known. but a specimen from the
Lower Devonian of Vietnam (see below. Fig. 8) may suggest that its distal end was still scale-
covered and mobile.
The brachial recess in some Yunnanolepiformes (in particular Y. deprati, Fig. 2B) is so small
(its breadth is 2 mm for a 2 cm long AVL plate) that one may wonder if the fin was not on the
verge to disappearance in at least some members of the group (a parallel with tremataspids
among osteostracans).
— 150 —
Fig. 3. — Yunnanolepis deprali Tong Dzuy & Janvier. Early Devonian of Vielnam, iransverse serial grinding sections through
the anlerior ventrolateral plate (UHDG-VND27o). A, outline of the plate, .showing the levels of lhe respective .sections (1 to
9, front front lo rear). Scale bar; I mm.
Yunnanolepis dcprati Tong Dzuy <$ Janvier, Dévonien inférieur du Viêt-Nam, sections sériées transverses à travers la plaque
ventrolatéraie antérieure (UHDG-VND27o). A. contour de la plaque montrant les différents niveaux des sections (I à 9 de
l'arrière vers T avant). Échelle • I mm.
Procondylolepiformes
The brachial articulation of the Procondylolepiformes has been described first in Procon-
dylolepis (G. R. ZHANG, 1984; YOUNG & ZHANG, 1992) and later in Chuchinolepis (TONG DZUY
& Janvier, 1990, Figs. lA, 2C. 4). these two généra being closely related or even possibly
synonymous. There, the articulation area of the AVL plate is much larger, the prepectoral corner
being produced into a massive process, the parabrachial process (pbp, Figs. lA, 4), hollowed
distally by a piriform dépréssion (df, Figs. IA, 4.4). The wall of this area bears, in addition, a
— 151 —
number of ridges and grooves which Young & Zhang (1992) bave homologized with the struc¬
tures observed in the Euantiarchi. In this taxon, like in the Yunnanolepiformes, the pectoral
fenestra propcr is filled with the perichondral bone of the scapulocaracoid (scap, Figs. 1 A, 4.7)
and pierced by foramina for the vessels and nerves to Ihc pectoral fin (f, Fig. 4.8). Ail the details
recorded by Zh.ANG (1984) and YottNG & ZHANG (1992) in Procoitdylolepis could be confirmed
by the grinding sections ihrough the AVL plate of Chuchinolepis dnnf;i)ioensis front Vietnam
(Fig. 4).
G. R. Zhang ( 1984) has also described the proximal portion of the pectoral appendage-like
fin of Procondylolepis, though not ariiculated with the AVL plate and he proposed one possible
way in which this tin could articiilate to the brachial recess. In both the Chinese and the Viet-
namese procondylolepiform ntaterial. une of the proximal plates of the pectoral fin bears a spoon-
shaped knob which is likely to hâve been housed in the part of the articulation area that YouNG
and Zhang (1982) regard as homologous to the ventral urticular fossa of the Euantiarchi (vf,
Fig. 1 A, C). the dorsal one (Fig. ID) being the piriform dépression on the tip of the parabrachial
process (df, Figs. lA. 4.4)
Zhang (1984) suggested that the process in the Procondylolepi formes is homologous to
the brachial process of the Euantiarchi. In conirast, Tong Dzuy & Janvirr (1990), termed it
as the “parabrachial process” (pbp, Fig. LA), and regarded it as too dorsal in position to be the
brachial process proper. Young & Zrang (1992) now propose a hypolhesis of homology which
seems quile satisfactory, considering that the groove on the médial side of the parabrachial process
(fgr, Figs. lA. 4.7) corresponds to part of the wall of the “funnel pit" in the Euantiarchi (fp,
Fig. ID). In fact, in both case, the wall of the groove and the pit are marked by particular
growth Unes found nowhere else in this area. However. if one considers that Ihc parabrachial
process is the homologue of the brachial process of the Euantiarchi its distal dépréssion could
correspond to the area of insertion for the protractor muscle of Ihc pectoral appendages.
The Procondylolepiformes arc now known from almost complété specimens of Cliu-
chinolepis (ToNG Dzuy & Janvier, 1990; Fig. 2C), which suggest that they are more clo.sely
related to Euantiarchi than to Ihc Yunnanolepiformes. However. this group has many autapo-
morphies, such as the very short AVL plates, very long AMD plate, and very fine-grained or¬
namentation.
Sinolepidae
Sinolepis macrocephala (LlU & PAN, 1958), from the Late Devonian of China, has long
been the only known species of this group, which allies elongated nuchal plates and a large
prcorbital dépression in the skull-roof, with hothriolepidoid-like thoracic armour and paired ap¬
pendages. For this reason, it was regarded by JANVIER & PAN ( 1982) as the sister-group of the
Euantiarchi. Long (198.3) erecled the taxon Sinolepidoidei foi Sinolepis and possibly Xi-
chonolepis, defined by very narrow ventral lamina of Ihc AVL and PVL plates. Later, Young
(1984b) characierizcd the Sinolepidae by a large ventral fenestration in the thoracic armour, and
included in this farnily the généra Sinolepis. Xiciumolepis. Dayaoshania and Liujiangolepis from
the Late and Early Devonian of China, and GrenfeUaspis. from the Late Devonian of Australia
(Ritchie et al., 1992; see this article for details on the in-group phylogeny). TONG Dzi.iY &
Janvier (1990) added to this farnily VancUivnolepis. from the Early Devonian of Vietnam. Like
— 153 —
ail other sinolepids, Vanchienolepis has a large ventral fenestra in the thoracic armour and, thus,
no médian ventral plate. Thanks to the excellent préservation of the material from Dong Mo,
Vietnam, the brachial articulation area of this minute form could be observed (Figs. IB, 5B-D).
Il displays a relatively large axillary foramen (a.xf. Fig. IB), like in the Euaniiarchi, but the
articulation area proper is quile different from both the Procondylolepiformes and the Euaniiarchi.
There is neiiher a parabrachial nor a true brachial process and the prepcctoral corner lines a
deep, almo.sl conical dépression, possibly for the abducior muscles of the fin. In the ventral part
of the latler arises an ear-shaped dermal lamina (esl, Figs. IB, 5B), the ventral surface of which
is connected to the margin of the articulation area by a short ridge or crest which séparâtes two
shallow dépréssions (er, Figs. IB, 5B). The boiiom of the cone-shaped dépréssion in the centre
of the area seems to be pierced by a minute canal. In addition. D. Goujet (Paris) has kindly
permitted me to study a well preserved small antiarch from the Early DeVonian of Qujing, China,
which displays very much the same characters as Vanchienolepis and is preserved with the pro¬
ximal part of the right pectoral fin In iis natural position (Fig. 6, sec below).
A comparison between the brachial articulation area of Vanchienolepis and thaï of //vr-
canaspis, a supposedly primitive euantiarch from the Eifelian of Khush-Yeilagh, Iran, may suggest
that the ventrally placed pedal part of the brachial process in Hyrcanaspis (pp. Fig. 5A) corres¬
ponds to the small ridge which, in Vanchienolepis and the Chinese form just mentioned, eonneets
the ear-shaped lamina to ihc margin of the articulation area (cr. Figs. IB. 5B. 6A-B). This hy-
pothesis of homology implies that the ear-shaped lamina could be the brachial process in a
primitive State. But in this case, we mcct again with the problem of the comparison to the
Procondylolepiforme.s. Young & ZHANt; (1992) model of homology implies that a very large
ventral articular fossa is primitive for the Euaniiarchi. whereas the supposedly primitive Euan-
tiarchi, such as Hyrcanaspis hâve a ventrally placed pedal ridge, which séparâtes a small to
moderately large ventral fossa (vf. Fig. 5A), from a very large dorsal fossa (df, Fig. 5A). TONG
Dzuy & Janvier (1990) suggcsled that the ear-shaped lamina of Vanchienolepis could be rep-
resented in the Procondylolepiformes by the “ventral crcscenlifoim ridge” which lines dorsal ly
the ventral articular fossa (vf, Fig. lA) and occupics very much the same position. However,
nothing more than topological arguments supports this statement. Another possibility (G. YoUNG,
pers. comm.) could be that the large process which prolongs poslerodorsally the prepectoral
corner in Vanchienolepis is the homologue of the parabrachial process of the Procondy¬
lolepiforme.s and of the dorsal articulation of Grenfellaspis.
A further variation of the sinolepid brachial articulation is .shown by a peculiar AVL plate
of an undelcrmined sinolepid from Qujing, China (Fig. 7). It has a large médian ventral fenestra¬
tion (vfe, Fig. 7), the presumed sinolepid autapomorphy, but otherwise differs markedly from
the AVL in both Vanchienolepis (Figs. IB, 5C) and Grenfellaspis (Fig. IC). The latéral lamina
of the plate is embayed by a deep longitudinal notch, reaching as far anteriorly as the brachial
Fig. 4. — ChiH'hinohfm donamoensif: Tong D/uy & Janvier. Early Devonian of Vieinam, transverse serial grinding .sections
through the anlcrior venlroUileral plate (LIHDG-VND27m). A. oiitline of the plaie, showing the level of the respective sections
(1 to 9, from front lo rear). Scale bar: I nm*.
Chuchinolepiîs dongmoensis VonR Ozh\ d Jimvien Dévonien inférieur du Viêt-Nam. .sections sériée.^ transverses à travers la
plaque venïroUitértde antèrieurr \VHDG-VN[)27m). A, contour de la plaque montrant les différents niveaux des sections il
à 9 de l\mmt vers rarrUrel. Échelle : I mm.
— 154 —
Fig. 5. — A. Hxnimaspi.s hlierki .lanvicr & Pan. MiUtlIcr Dcvoniaii of Iran, right antcrior venirolateral plaie in ventral a.speci,
showiiig the brachial proce.ss (MGSI 151. l'roni Janvier & Pan 1982). B, Vanchietiolepis sp.. Oujing. Yunnan. China, righl
AVL plate in ventral aspect, showing tlie ■ear-shaped lamina” (hased on MNHN-CHDOl). C, D. Vemchieiiopleph langsonensis
Tong Dzuy & Janvier. Enrly Devoniaii of Dong Mo. Vietnam. S.E.M. photograph of ihe brachial articulation area of ihe
right AVL plate in latéral (C) and ventral (D) aspects; lhe spécimen has been prepared wilh the iransl'er method. and Ihc
axillary fenestra în fdled with silicone (UHDG-VND46a). Scalc bar I mm.
A. Hyrcanaspis bliecki Janvier A Pan. Dévonien moyen tltran, pUiffiie ventrnlniérale tiniérietire en vite venirale. montrant
le processus brachial (MGSJ 151, d’après Janvier & Pan I9S21 H. Vanchicnolcpis sp.. Qnjing, Ynnnan, Chine, plaque AVL
diviie en vue ventrale montrant ”la lame en forme d'oreille” (d'après MNHN-CHD Oh. C. D. Vanchienoplepis langsonensis
Tong Dzuy & Janxier. Dévonien inférieur de Dong Mo. Viêt-Nam. photographie de la région de rarticulation brachiale d'une
plaque AVL droite prise au en vue latérale. (O en vue ventrale (D! ; les spécimens ont été préparés par la méthode
de tninsfert. et la fenêtre axillaire est remplie de silicone (VHDG VND46al Échelle : I mm.
Fig. 6. — Vanchienolrpis .sp.. Early Devonian ot Qujing, Yunnan. China (MNHN'CHDOI ), unterior venirolateral plate and pectoral
appendage of the righl side of imperfecl dermal armour in lalcral (A), venira! (B) and dorsal (C) aspects. Areas filled with
matrix obliqucly hatched. other plates of the armour in white. Caméra lucida drawing. .Scale bar: 1 mm.
Vanchicnolcpis .sp.. Devonien inférieur de Qujing. Yunnan. Chine (MNHN CHD 01). plaque X'entrolatérale antérieure et ap¬
pendice pectoral dntits d’une cuira.ssc thoraciffuc mal conser\>ée. (A) en vue latérale, (B) en vue ventrale. (C) en vue dorsale.
Les légions non dégagées .sont hachurées. Dessin à la chambre claire. Échelle : / mm.
— 156 —
articulation area, and the margins of which indicate (by the presence of an overlap area) that
it was partly filled by a corresponding process of the PVL plate (n, Fig. 7). However, the foremost
part of this notch has smoolh margins, and corresponds in position to the axillary foramen. The
prepectoral corner is very much like in Vanchienolepis, that is, broadly rounded in shape (ppc,
Fig. 7A), and there is also a clear funnel-shaped dépréssion, lined with perichondral bone and
FlG. 7. - ?XUh(>fU’lepis sp-, Early Devonian of Qujing. Yunnan, China (MNHN CHD 02), righl anlcrior venlrolateral plate in
ventral (A), dorsal tB) ^nd media) (C) aspects, and detail of the brachial articulation area in posteroventral view (D). Caméra
lucida drawing- Scalc bar. 10 mm,
?Xichonelepi*: sp.. Dihonien inféneur Je Qujinfi. Yunnan, Chine (MNHN CHD 02), plaque venimlalérale antérieure en vue
ventrale (A), doraaïe tR) et médiale (C). et détail de l'articulation brachiale en vue postéroventnile (D). Dessin à la chambre
claire. Échelle: H) mm.
— 157 —
ending with a small canal (scap, Fig. 7D). Clearly, this conical sheath of perichondral bone, the
internai surface of which is smooth and the extemal surface rough, lined intemally a plug of
cartilage, in the same way as ascribed above to Yumumolepis. The surface of the brachial ar¬
ticulation area beats only two faint ridges. One is anterodorsal and extends frorn the perichondral
funnel to the prepcctoral corner (adr, Fig. 7D). and may correspond in part to the parabrachial
process of the Procondylolepiformes. The other one extends posteroventrally front the perichon¬
dral funnel to the ventral margin of the area (pvr, Fig. 7D), atid may possibly correspond to the
crescentiform ridge of the Procondylolepiformes or the ear-shaped process of Vmchienolepis.
We are thus in a situation where the Sinolepidae display ihrec very different types of struc¬
ture of the brachial articulation area. One (Fig. 7D) is very simple, almost comparable to that
in Yunnanalepis, another is more complex (Figs. IB, 5C, Vanchienolepis), with an incipient
brachial process, and a third one (Fig. IC, Grenfellaspix) is more like in the Euantiarchi. with
dorsal and ventral articulât fossae and a funnel pii surrounded with dermal bone. Moreover, the
Vanchienolepis-hke specimen from Qujing (Fig. 6) possesses a skull-roof which is remarkably
similar to that of the Yunnanolepiformes. and quire different from thaï of both Sinolepis and the
Euantiarchi. A small skull-roof from Dong Mo (TONG-DZUY & JA.VVIER, 1990. Fig. 14) referred
with doubt 10 Veine hienolepis is aiso almost indistingüishable from that of the Yunnanolepiformes.
This raiscs the question of the monophyly of the Sinolepidae, which. to date, are charac-
terised only by the presence of a large ventral fenestration in the ihoracic armour (vfe, Figs. 6,
7) and the reduced ventral laminae of the AVL and PVl. plates (LONG 1983; Ritciiie et ai
1992). This characteristic might be regardcd ple.siomorphous if the out-group for the antiarchs
is the Rhenanida (GOUET, 1984). In fact, ail known rhenanids are devoid of médian ventral
plate and possess a large ventral space limiled by the AVL plates. If the ventral fenestration is
plesiomorphous, then the Sinolepidae woiild be non-monophyletic, and possibly paraphylelic.
Conversely, the médian ventral plate would hâve deveioped independently several times. since
it is présent in the Yunnanolepiformes. Procondylolepiformes and Euantiarchi. This question can
be solved only in the framework of an extensive cladistic analysis of the Antiarcha, involving
many other characters, which is beyond the scopc of this paper.
Euantiarchi
The typical brachial articulation of the Euantiarchi comprises the helmet-shaped brachial
process (brp, Figs. ID, 5A), pierced by a médian “funnel pif’ (fp, Fig. ID), and attached to the
brachial recess by a pedicle, the pedal part of the process (pp, Figs. ID, 5 A). The latter séparâtes
two deep dépréssions or fossae, dorsal and ventral (vf, df, Figs. ID. 5A), which aecommodate
the dorsal and ventral proximal central plates of the appendage respeclively. In addition, there
is a relatively large axillary foramen (axf, Fig. ID). The pattern of the brachial articulation area
in the Euantiarchi is quite homogeneous, but .Ianvier & PAN (1982) hâve suggested that the
anteroventral position of the pedal part of the process (the fiat surface of the process facing
posterodorsally) is plesiomoiphous for the group, since it occurs in most of the earliest known
Euantiarchi (e.g. Hyrcanaspis and some Asterolepidoids; Fig. 5A). This would be consistent with
the hypothesis of homology in this area proposed here beiween Vanchienolepis and the Euantiarchi
in this paper, in particular the re.semblance between the pedal part of the brachial process in
— 158 —
Hyrcanaspis and the small ridge which arises ventrally to the ear-shaped process in
Vanchienolepis (Fig. 5A, B).
THE PECTORAL FIN
In the non-euantiarchan antiarchs the dermal covering of the pectoral fin is partly known
in Phymolepis (referred to the Yunnanolepiformes, K. J. Chang 1978, G. Zhang 1978, M.M.
Zhang 1980), Procondylolepis (G. ZHANG 1984), Chtichinolepis (TONG Dzuy & JANVIER, 1990),
Vanchienolepis (or a closely related form, Fig. 6), Sinulepis (LlU & P’ AN 1958) and Liujiangolepis
(Wang, 1987). Tliere is no clear evidence that the paired fins were jointed in Phymolepis, Pro-
condytolepis, Chuchinolepis and Vanchienolepis. However, the occurrence of a fragment of a
siender di.stal fin segment quite similar to that of Liujiangolepis (WANG, 1987. Fig. 1) in asso¬
ciation with remains of Chuchinolepis (TONG DzUY & JANVIER, 1987, l'ig 6F) may suggest that
the paired fins of the Procondylolepiformes were jointed. The pectoral fin plates of Vanchienolepis
sp. from Qujing (Fig. 6) are quite similar to those of Phymolepis (G. R. ZHANG, 1978, Fig. Il;
PI. 6.9; M.M. Zhang, 1980, PI. 5.1), that is, polygonal and not elongated in shape. In this spéci¬
men, the proximal end of the dermal fin seeras to hâve been made up of four plates,, two centrais
(Cd, Cv, Fig. 6A) and two marginals, but only three of them are actually preserved. The ventral
central plate (Cv, Fig. 6A, B) abuts against the small ventral ridge (cr, Fig. 6A, B), suggested
here as being homologous to the pedal ridge of euantiarchs. The other plates do not contact the
AVL plate in this specimen.
In a specimen of Yunnanolepis sp., quite clo.se to Y. chii Liu, from the Bac bun Formation
of Trang Xa. Vietnam (TONC DZIJY & JANVIER, 1994). an assemblage of tile-shaped plalelets
and minute seules are preserved against the latéral wall of the trunk armour, and may be inter-
preied as a pectoral fin (Fig. 8). The tile-shaped platelcls look exactly like appendage plates of
other antiarchs (fpl, Fig. 8A), and a transverse section of this assemblage shows that they are
arranged more or less in a tube-shaped pattern (Fig. 8B). The minute scales seem to fill the
gaps between the two major tile-shaped platelets, and become more and more abondant toward
the rear of the specimen (fsc, Fig. 8A). This may suggest that the distal end of the pectoral fin
in Yunnanolepis was still covered with small seules, and not with large dermal plates. It may
hâve formed a flatlened club, or a pad comparable to the paired fins of osteostracans, for example
(Janvier, 1978, Fig. 2). It cannot be ruled out. however. that this assemblage is part of the
body squamation, folded along the thoracic armour. yet the larger plates do not match any of
the body scales or scutes observed in these early Antiarcha.
Fig. 8. — Yunnanolepis sp., Eariy Devonian of Trang Xa, Thai Nguyên. Vietnam. Left postérolatéral part of a thoracic armour
a.ssociated with presumed dermal covering of the pector.'il fin. A. caméra lucida dr,iwing, areas siill covered with matrix
obliqiiely hutched. B, transversc t>eclion through the uppci edge of the specimen in A. matrix obliquely hatched, section of
dermal boucs in black (LIHDG-VND70). Scalc bar I mm.
Yunnanolepis sp.. Dévonien inférieur Je l'rann Xa. Thai Nguyên. Yiêi Nain. Région posté mhué raie gauche d'une ruimsse
ihnrariijue os.soi iée à la cauverluir Jermique probable de lu nageoire peelorale. A. des.\in à la chambre claire, les régions
non préparées sonl hachurées par des traits obliques. B. coupe transversale à travers le bord supérieur du spécimen figuré
en A. sédiment représenté par des hachures obliques, coupes de l'os indiquées en noir lUHDG-VNDTOl. Échelle : I mm.
— 160 —
DISCUSSIONS AND CONCLUSIONS
These new data on the structure of the brachial articulation in antiarchs confirm the presence
of a small, penchondrally lined canal piercing the brachial recess in Yunnanolepis. They also
confirm that the Procondylolepiformes posscssed a small pectoral fenestra. filled with perichon-
dral bone, and pierced by three minute forarnina. It is thiis clear that, beside the considérable
réduction of the endoskeleta! component of the pectoral fin articulation, there may also be a
thickening of the perichondral bone of the scapulocoracoid, which makes it hardly distinguishable
from the dermal bone of the AVL plate. A similar process can also be observed for example in
the ptyctodontid Chelyphorus (Mark-Kurik. e1 al. 1991), where, in addition, the brachial ar-
ticular surface is very small and almost funnel-shaped, like in early antiarchs. In contrast to the
Yunnanolepi formes and Procondylolepiformes, there are considérable différences in the organi-
zation of the brachial articulation area in three généra referred lo the Sinolepidae: Vanchienolepis.
Grenfelkispis and the unnamed specimen described here (Fig. 7). The brachial articulation area
of the AVL plate in Vanchienolepis displays an ear-shaped ventral lamina, or proce.ss, which is
tentatively compared here to the ventrolaterally placed brachial process of suppo.sedly primitive
euantiarchs, such as Hyrcunaspis. This .structural di.sparity of the Sinolepidae, as to the brachial
articulation may signify thaï this family is not monophyletic. In this case, the large ventral
fenestration of the Ihoracic armour, hitherto regarded as the synapomorphy of the group, would
be either a symplesiomorphy for antiarchs or for the group including sinolepids and euantiarchs
only, or a homoplasy in the three “sinolcpid" généra, It is thus clear that any transformational
approach to the structure of the brachial articular area of the Antiarcha rnusl be considered in
the framework of a phylogenetic analysis of the entire group, based also on other characteristics.
A specimen of Yunnanolepis sp. from the Lower Devonian of Vietnam displays whai may
be the distal portion of the pectoral fin, which looks as if covered with minute scales, and not
large dermal plates. Although admittedly a poor evidence, this may suggest thaï the appendage-
like structure of the antiarchan pectoral fin was not y'et achieved in Yunnanolepis.
Literature cited
Chang, K.J., 1978. — Early Devonian antiarchs from Shuifengshan, Yunnan. In: Symposium on the Devonian
System of South China. Geological press, Beijing: 292-293. [In Chinese],
GOL'IET, D., 1984. — Placoderm interrelationships; a new interprétation, with a short review of placoderm classi¬
fications. Proc. Linn. Soc. New South Wales, 107 (3): 211-243.
GrOSS, W., 1931. — Asierolepis ornata Eichw. und das Antiarchi-Problem. Palaeontographica A, 75: 1-62.
Janvier, Ph.. 1978. — Les nageoires paires des ostéostracés et la position systématique des céphalaspidomorphes.
Annls Patéont. (vert.), 64 (2) : 113-142.
JANVIER, Ph. & J. P' AN, 1982. — Hyrcunaspis hliecki n. g., n. sp., a new primitive euantiarch (Antiarcha,
Placodermil from the Eifelian of noriheasiem Iran, with a discussion on aniiarch phylogeny. N. Jb. geol.
Paldont. abh., 164; 364-392.
LIU, T, S. & K. P' an, 1958. — Devonian fishes from the Wutung sériés near Nanking. China. Paloeont. Sinica
141: 1-41. [In Chinese and Engli.sh].
LIU, Y.H., 1963. — On the antiarchi from Qujing. Vertebr. PalAsiat., 7; 39-45. [In Chinese and English summary].
Lyarskaya, L.A., 1981. — Baliic Devonian Placodermi. Asterolepidae, Zinatne, Riga.
— 161 —
Long, J. a., 1983. — New bothriolepid fishes from the Early Devonian of Victoria, Australia. Palaeontology,
26: 295-320.
Mark-Kurik, E., s. Ivanov & O. Obrucheva, 1991. — The endoskeleton of shoulder girdle in ptyctodonts
(Placodermi). Proc. Estonian Acad. Sci. Geol, 40 (4): 160-164.
Miller, h., 184I. — The Old Red Sandstone. I*' ed., Adam and Charles, Edinburgh.
RITCHIE, A,, S.T. Wang. G.C. YOUNG & G.R. Zhang, 1992. — The Sinolepidae, a family of Antiarchs (Pla-
coderni fishes) from the Devonian of South China and Eastern Australia. Rec.'i Austral. Mus., 44: 319-370.
STENSIO, E.A., 1948. — On the Placodermi of the Upper Devonian of East Greenland. 2. Antiarchi: subfamily
Bothriolepinae. With an attempt at a révision of the previousiy described species of that family. Meddram
Groenland, 139: 1-622.
TONG DZUY, T. & Ph. Janvier. 1987. — Les vertébrés dévoniens du Viêt-Nam. Annls paléont. (vert.). 73 (3) :
165-194,
— 1990. — Les vertébrés du Dévonien inférieur du Bac Bo oriental (provinces de Bac Thaï et Lang Son,
Viêt-Nam). Bull. Mus. natl. Hist. mit., Paris, 4° sén, (C) 12 (2) : 143-223.
— 1994. — New Early Devonian vertébrales from Trang Xa, Bac Thai, Vietnam, with remarks on the distribution
of the vertebrate remains in the Song Cau group. J. southea.st Asian Earth Sci. 10: 235-243.
Wang, S. T., 1987. — A new antiarchi from the Early Devonian of Guangxi. Vertebr PalAsiat., 25 (2): 81-90.
[In Chinese with English abstractj.
YoUNG, G.C., 1984a. — Reconstruction of the jaws and braincase in the Devonian placoderm fish Bothriolepis.
Palaeontology, 27 (3): 635-661.
— 1984b. — Comments on the Phylogeny and Biogeography of Antiarchs (Devonian placoderm fishes) and
the use of fossils in Biogeography. Proc. Linn. Soc. New South Wales, 107: 443-473.
— 1988. — Antiarchs (placoderm fishes) from the Devonian Aztec siltstone, Southern Victoria Land, Antarctica.
Palaeamographica A, 2: I-I25.
YOUNG. G.C. & G.R. Zhang, 1992. — Structure and function of the pectoral joint and operculum in Antiarchs,
Devonian placoderm fishes. Palaeontology, 35 (2): 443-464.
Zhang, g., 1978. — The Antiarchs from the Early Devonian of Yunnan. Vertebr. PalAsiat., 16 (3): 148-186.
[In Chinese with English abstract].
— 1980. — New malerial of Xichonolepis and discussion on some of its morphological characteristics. Vertebr.
PalAsiat., 18 (4): 272-280. |ln Chine.se with English abstract].
— 1984. — New form of the Antiarchi with primitive brachial process from Early Devonian of Yunnan. Vertebr.
PalAsiat., 22 (2): 82-91. [In Chine.se with English abstract].
Zhang, M.M., 1980. — Preliminary note on a Lower Devonian Antiarch from Yunnan, China. Vertebr. PalAsiat.,
28 (3): 179-190. [In Chinese with English abstract].
Bull. Mus. naîl. Hist. nat., Paris, 4^ sér., 17, 1995
Section C, n° 1-4 : 163-207.
Description of Maideria falipoui n. g., n. sp., a long snouted
brachythoracid (Vertebrata, Placodermi, Arthrodira)
from the Givetian of Maider (South Morocco),
with a phylogenetic analysis of primitive brachythoracids
by Hervé LELIÈVRE
Abstract. — Maideria falipoui n. .sp., n. g., a new primitive long snouted brachythoracid Irom the Lower
or Middle Givetian of South Morocco (Presaharian Anti-Atlas) rs described. The inonophyletic group Migmato-
cephala, a taxon erected by White. 1952. is redetined, together with the monophyly Eubrachythoraci. A phylo¬
genetic analysis has been performed using PAUP prograin bused on 53 characters coded for 12 taxa. Three
equally parsimonious topologies hâve heen found. in which Maideria is considered as the most primitive brachy¬
thoracid, and Holonema included in Eubrachythoraci.
Keywords. — Maideria falipoui, Givetian, Morocco, Migmalocephala, phylogenetic analysis.
Description de Maideria falipoui n. g., n. sp., un brachyhturaci à museau long
(Vertebrata, Placodermi, Arthrodira) du Givétien du Maider (sud marocain)
et analyse phylogénétique des brachythoraci primitifs
Résumé. — Maideria. un nouveau genre de brachythoraci dti Dévonien moyen (Givétien inférieur ou moyen)
du Maider. Aiiii-Ailas présaharien, est décrit. Une analyse phylogénétique informatisée des relations de parenté
entre les brachythoraci primitifs (Migmalocephala) et les Eubrachythoraci, conduite à Paidc du logiciel de par¬
cimonie PAUP, a permis d'isoler mois topologies également pamimonieuses. Dans l’arbre consensus trois groupes
monophylétiques sont définis. Le taxon supragénérique monophylétlque, Migmatocephala, créé par WittiE, 1952
est utilisé pour regrouper un ensemble de genres autrefois as.six:iés au sein des brachythoraci primitifs. Maideria
falipoui représente le taxon le plus primitif des brachythoraci, et le genre Holonema est placé au sein des Eu¬
brachythoraci.
Mots-clés. — Maideria falipoui, Givétien, Maroc, Migmatocephala, analyse phylogénétique.
H. Lelièvre, Laboratoire de Paléontologie, Muséum national d’Histoire naturelle et URA 12 du CNRS, S, rue Buffon, 75005
Paris, France.
Introduction
Devonian Moroccan fish faunas are best known from the Upper Devonian layers of Tafilalt
(Lehman, 1956. 1976, 1977. 1978; Lelièvre, 1991) where, mo.stly, giani placoderms hâve been
described, together with the remains of an eusthenopterid (LEHMAN, 1978; LELIÈVRE & JANVIER,
1986), and some isolated fragments of sarcopterygian.s of which some has been referred to
cœlacanthids (LELIÈVRE & JANVIER. 1988). The more westerly situated Devonian Maider Basin
has not been so exiensively investigated. Lehm.an (1976) mentioned the occurrence of isolated
— 164
placoderm remains in the Frasnian, Northwest of Fezzoïi. He figured two incomplète médian
dorsal plates of the poorly known genus Aspidichthys (Lehman, 1976; PI. 9, Figs. C, D), and
some thoracic dermal plates of Holonema (LEHMAN. 1977; PI. 3, Fig. F). Recently, I hâve col-
lected remains of selenosteids, and isolated Clenacanthus spines in the sarne area in the Frasnian
of the Jbel Issoumour.
The type specimen of Maideria described below has been generously given to the Muséum
national d'Histoire naturelle by M. Christian Falipou. who purchased it in one of the numerous
fossils shops of ihis area of South Morocco. The type material cornes from somewhere in the
Maider, although the précisé locality remains unknown. The other specimens MCD 186, 187,
191 corne from either the Jbel Issoumour or the Jbel Merakib, respectively in the North and in
the South of Maider. Ail the specimens were excellently preserved in a marine limestone which
contains conodonls, indicaiing a lowcr or middie givetian âge.
In the same sections of the Givetian of the Maider other fish remains hâve been found in
association wilh Maideria. They compose a new Middie Devonian fish fauna in which varions
taxa hâve been identified: an eastmanosteid represenled by a left dorsolateral plate, left and
right anterior ventrolateral plates belonging to a different eubrachythoracid genus new pctalichthy-
ids represented by incompletely preserved .skull-roofs, an inferognalhal plate of a ptyctodontid
referred to Paleomylus, and microvertebrates remains, mainly seules of acanlhodians and chon-
drichthyans. Finally, and for the first time in the Devonian of Africa, a dipnoan palate was
found. The description of the entire fauna will be given in a fortheoming paper.
Abbreviatiüns
ADL Cf.
AL
a.pr
ASG
a.tr
AVL
cf.PVL
C
cr.inf
cr.pb
cr.po.
cr.pr
CSC
d.end.e
d.end.i
dp.m eu
d.pro.pr
end. fi
f.pi
fo.hy
anterior dorsolateral contact surface, xurface de contact
pour la plaque ADL',
anterior latéral plate, plaque antérolatérale ',
antorbital dermal process, prace.'isus dermique antéorbitaire ;
anterior superognathal. superognathal antérieur',
anterior teeth row, rangée de dent.'i antérieure.s '.
anterior ventrolateral plate, plaque ventrolatérale antérieure ',
posterior ventrolateral conUict surface, xurface de contact pour la plaque PVL ',
central plate, plaque centrale ',
inframarginal crista, crête inframarginale ;
postbranchial crista, crête postbranchiale ',
postorbital crista. crête postorbitaire ',
carinal process, processu.s carinal',
central sensory line, sillon sensoriel central',
external endolymphatic duel, ouverture externe du ductus endolymphatique ',
internai endolymphatic duct, ouverture interne du ductus endolymphatique',
cuccularis dépréssion, dépression cucculaire',
dermal preorbital process, processus dermique préorbitaire',
endocranial rmsare, fissure endocrânienne ',
pineal fossa, /<7.ï.ve//e pinéale ',
hyoid muscle fossa, fosse pour le muscle hyo'ide ;
— 165 —
IL cf
IN
ioc.ot
ioc.pt
laf
le
l.iob
l.tr
M
MD
mp
n.cap
nn
Nu
?o.a. PN
occ
orb
P
PDL cf
PM
PN oa
PNu
PrO
PtO
pap
pbe
p.emb
pmc
pn.p
PP-
p.pr
p.pt
pr.apo
pr. ect
pr.in
pr. m
pr. ob
pr.ppo
pr.so
interolateral contact face, surface de contact pour la plaque IL ',
intemasal plate, plaque internasale ;
otic branch of infraorbital sensory line, branche otique
de la ligne sensorielle infraohiiaire ;
postorbilal branch of infraorbital sensory line, branche postorbitaire
de la ligne senst/rielle infraorbitaire ;
latéral articular fossa. yb.we articulaire latérale ',
main latéral sensory line, ligne sensorielle principale
infraobstantic lamina, lame infraobstantique
latéral teeth row, rangée de dents latérales'.
marginal plate, plaque marginale ',
médian dorsal plate, plaque médiane dorsale',
middle pit-line. pit-line moyenne ',
nasal capsule, capsule nasale ',
nasal notch, encoche nasale ',
nuchal plate, plaque nuchale ;
contact face for postnasal plates, contact pour les plaques postnasales',
occipital sensory line cross-commissure, commissure sensorielle occipitale ',
orbit, orbite ',
pineal plate, plaque pinéale',
posterior dorsolateral plate contact surface, surface de contact
pour la plaque PDL '.
postmarginal plate, plaque postmarginale ',
overiapped area for postnasal plate, aire de contact pour la plaque postnasale ',
paranuchal plate, plaque paranuchale ',
preorbital plate, plaque préorbi taire',
postorbital plate, plaque poslorbitaire ;
para-articular process. processus para-articulaire ',
postbranehial embayment, incision postbranchiale ',
pectoral embayment. incision pectorale',
postmarginal sensory line, ligne sensorielle postmarginale ',
postnuchal process. processus postnuchal ;
posterior pit-line, pit-line postérieure ',
posterior process of nuchal plate, processus postérieur de la plaque nuchale ;
pineal p\\, fossette pinéale',
anterior postorbital process, processus antérieur postorbitaire ',
ectethmoid process, processus ectethmoïde ',
internasal process. processus internasal ;
médial process of antérolatéral plate, processus médial de la plaque
antérolatérale ;
obstantic process, processus ohstantique ',
posterior postorbital process, processus postorbitaire postérieur ',
supraorbital process, processus supraorbitaire ;
— 166 —
pt.pr. posterior médian process of nuchal plate, processus postéromédian
de la plaque nuchale ;
R rostral plate, plaque rostrale\
SM submarginal plate, plaque submarginale ;
SO cf suborbital plate contact surface, surface de contact pour la plaque
suborhitaire ;
Sp m spinal margin, bord spinal’,
soa subobstantic area of skull-roof, aire subobstantique du toit crânien ;
soc supraorbital sensory line, ligne sensorielle supraorbitaire ;
suo.v supraorbital vault, voûte supraorbitaire ’,
svg.f supravagal fossa. fosse supravagale ;
th.pre pre-endolymphatic thickening, épaississement pré-endolymphatique ’,
vts transverse ventral sensory line, ligne sensorielle ventrale.
SYSTEMATIC PALAEONTOLOGY
Ordre ARTHRODIRA Woodward, 1891a
Family indet.
Genus MAIDERIA n. g.
Etymology. — from Maider, an Arabie name which means the place where the trees grow
without water.
Diagnosis. — A brachythoracid with a long closed and upturned snout composed of the
rostral and, ventrally, by a broad intemasal plate.
Remarks. — Potential autapomorphies might be included in the définition, as for instance
the posterior médian process of the anterior latéral plate (MCD 187), when similar material will
be found associated with characteristic plates of Maideria.
Type-locality. — Maider Basin, exact locality unknown.
Type-level. — Lower or Middle Givetian.
Maideria falipoui n. g., n. sp.
(Figs. 1-12)
Type-SPECIES. — Maideria falipoui n. sp.
Etymology. — After Christian Falipou who gave the specimen to the Muséum national
d’Histoire naturelle, Paris.
Diagnosis. — The same as for the genus, by monotypy.
Holotype. — Collection number: MCD 184, an almost complété skull-roof with the left
anterior superognathal in anatomical position.
Other material. — It includes an anterior and fragmentary part of a rostral plate, as¬
sociated with an almost complété right anterior ventrolateral plate (MCD 190).
Recently, new material of Maideria has been given by C. Falipou to the Muséum national
d’Histoire naturelle. It cornes from both the Northern (Jbel I.ssoumour) and Southern (Jbel Mer-
— 167 —
akib) parts of lhe Maider. This material is composed of an almost complété skull-roof (MCD
191), an isolated médian dorsal plate (MCD 186), and a right anterior latéral plate (MCD 187).
Although MCD 1 86, 1 87 were not associated with typical material belonging to Maideria, these
two plates are referred to this form according to their dcrmal ornamentation which consists of
tubercles, sometimes aligned in rows.
Ali this material lias been chemically prepared using a solution of formic acid diluted at
10%. Phosphatic microremains were collected and belong to vertebrates (see below) and cono-
donts which were ideniified by P. BULTYNCK (Brussels) as;
Polygnalhus linguiforniis Unguiformis Hinde. 1879
Polygnathus hciniansalus Bultynck, 1987.
The latter species is well known in different, but successive conodont zones; P. ensensis,
P. timorerisis and P. varcus, distributed from the Lower Givetian to the Middle Givetian respec-
tively. No other typical invertebrate was associated. therefore it is still impossible to know the
précisé straiigraphical level where Maideria cornes from. Isolated acanthodian scales of the
Clieiracaritfu>ides-lypc, acanthodids with an unornamented crown, Cladolepis type scales, and
isolated platelets of rhenanid type with pointed tubercles hâve been collected from the same
sample. Ail these microremains are badly prcserved, abraded and black-coloured, indicating that
they hâve been submitted to beat.
DESCRIPTION
The type-specimen is an almost complété skull-roof with most of the snout preserved, and
with only it.s right po.sterolatcral corner mis.sing. No cheek plate is known, but the left anterior
superognathal is complclely prcserved. The thoracic armour is represented by a right anterior
ventrolateral, a médian dorsal and a right anterior latéral plate which are lentatively referred to
Maideria on the ground of their ornamentation.
The overall shape of the type skull-roof is longer than broad, and strongly arched trans-
versely (Figs. 2, 7). TTie estimated breadth/length index is 86%. a ratio which makes it nearer
to the proportions in Eastmanosieus calliaspis (87.2%, in DENNIS-BRYAN, 1987) than to long-
snouted brachylhoracids from Gogo {Cumuropiscis concinnus, 48%; Rulfnsieus, 31,7%; Latn-
camurus, 65%>). Typical coccosteids such as Caccosteus cuspidalus (140-148%) hâve a broader
skull-roof. The orbits are relatively large, deep and face laterally. The snout is broad and strongly
upturned. The ornamentation is composed of tubercles with both stellate and non-stellate bases.
These are small and rounded. equal in size, except those from the tip to the ventral margin of
the rostrum, which are larger, closcly-scl and more or less regularly arranged in rows. The same
pattern is found on a narrow strip bordering the dorsal médial margin of the orbit, where the
tubercles are smaller and regularly spaced.
No suture is visible on the dorsal surface of the type-specimen (F'igs. 1,7), but some could
be located on radiographs (Fig. 2). This condition is not exclusive to Maideria, and it has been
aiso mentioned for Buchanosteus (Gardiner & MtLES, 1990; 190; White & TOOMBS, 1972,
PI. 2, Fig. 3). The second skull-roof (MCD 191) is of almost same size, but shows the sutures
— 168 —
FiG. 1. — Maideria falipoui n. g., n. sp. Holotype specimen MCD 184. Dorsal view of the skull-roof. Scale bar: 1 cm.
Maideria falipoui n. g., n. sp. Holotype MCD 184. Vue dorsale du toit crânien. Échelle : 1 cm.
(Fig. 3). The attempted reconstructions of the skull-roof in dorsal, ventral and latéral views (Figs.
9, 10) are combined from both specimens (MCD 184 and 191).
The ventral surface of the skull-roof does not exhibit any well-defined dermal structures,
and those which are usually dcscribed in eubrachythoracids are apparently absent in Maideria,
which thus retains a plesiomorphic condition.
— 170 —
Some measurements of the skull-roof are given, following the standard sériés of Miles &
Dennis (1979, Figs. I, 2, 3).
Nuchal plate (Nu)
This plate is almost entirely preserved, and its posterior mediai margin is shown in MCD
191. U is relatively short, and represents approximately 37% of the skull-roof length. Its shape
is almost trapezoid, and the anterior suture is straight in dorsal view, and convex in ventral
view (Figs. 8D, 5).
Its viscéral face is fiat, and a shallow mediai dépréssion extends anteriorly to the presumed
position of the poorly developed posterior process (pt.pr, Fig. 9). The posterior mediai région
is not preserved in the holotype, and badly preserved in MCD 191, and I cannot affirm that the
two small. medially placed, posteriorly openmg dépréssions correspond to the nuchal pits (Fig.
8DL Nevertheless. I assume that they did not open ventrally. the problem being to know whether
they opened dorsally or posteriorly. These last two possibilities are considered plesiomorphic,
and close to die dolichothoracid condition (e.g. Dicksoriosteus, GoUJET, 1984, Fig. 31). There
is no posterior nuchal thickening (Fig. 8B), as usually seen in primitive brachythoracids (see
Lelièvre et ai. 1990: 60-61). The latéral part of this thickening is only developed in connection
with the latéral position of the articular fossa (laf). In comparison with typical primitive brachy¬
thoracids, as defined by Lelièvre (1984a, b; 1988), the nuchal plate is short, and its general
shape and proportions suggest the condition met with in eubrachythoracid skull-roofs,
Paranuchal plaie (PNu)
The left plate is well preserved in both skull-roofs (MCD 184, 191). The almost straight
anterior margin is in contact with the postorbital plate, thereby separating the central from the
marginal plates, a condition which probably evolved several limes in placoderms. There is a
distinct posterior lobe, well defined in MCD 191 (Fig. 3), but not clearly distinguishable in the
radiograph (Fig. 2). The suture belween the paranuchal and the marginal plates runs parallel to
the postmarginal sensory line (pmc). a disposition shared with Autineosteux (LELIÈVRE. 1984b,
Fig. Il, Btichanosteus (YOUNG, 1979, Fig I) and Taemaxosieus novaustmcamhncus (White,
1978, Fig. 112). A postnuchal process (pn.p) is well defined in MCD 191 (Figs. 3, 9). The
subobstantic skull-roof area (soa) is very long (due to the strong posterior curvaturc of the skull-
— 171 —
Fig. 3. — Maideria falipoui n. g., n. sp. Skull-roof in dorsal view, MCD 191. Scale bar: 1 cm.
Maideria falipoui n. g., n. sp. spécimen MCD 191. Vue dorsale du toit crânien. Échelle : 1 cm.
roof), but the extension of the contact with the thoracic armour is small (Fig. 10). The dorsal
surface is grooved by three sensory lines: the main latéral sensory line (le), the posterior pit-line
(pp), which does not contact posteriorly the main latéral line in the holotype, and the occipital
commissure (occ). The external opening of the endolymphatic duct (d.end.e) is elongated, and
more anteriorly placed than is usual in brachythoracids.
— 172 —
Fig. 4. — Maideria falipoui n. g., n. sp. Partly preserved anterior
pari of a skull-roof MCD 197. Dorsal view. Scale bar: 1 cm.
Maideria falipoui n. g., tu sp. Vue dorsale de la région antérieure
du toit crânien MCD 197. Échelle : l cm.
The latéral articular fossa (laf) is well preserved, but is small in comparison with the typical
primitive brachythoracid condition where this fossa is enlarged and higher medially than laterally.
The pararticular process (pap. Figs. 5, 10) is reduced, and situated below the posterior skull-roof
margin. It is usually well developed in primitive brachythoracids and projects beyond the posterior
margin of the skull-roof. On the ventral surface, the cuccularis dépréssion (dp.m eu, Fig. 5) is
shallow, and its anterior limits are clearly delineated by a small ridge which represents a remnant
of the neurocranial walls in both MCD 184 and 191. The endolymphatic duct (d.end.i) is slightly
developed as a depressed tube. Us anterior position is the same as in Buchanosteus (YoUNG,
1979, Fig. 2), but there is no such a long perichondral tube as seen in Antineosteus (LELIÈVRE,
1984a, PI. 3c). The latter condition is considered as correlated with a long posterior part of the
skull-roof (Lelièvre, 1984b). Posteriorly, the supravagal fossa (svg.f) is preserved together with
a small part of the endocranium which bears the two posteriormost openings for the spino-occip-
ital nerves.
Postmarginal plate (PM)
The left plate is preserved in both skull-roofs and does not hâve the usual triangular shape.
Its anterior margin is sinuous, and its surface is grooved by the postmarginal sensory line (pmc,
Figs. 1, 9, 10).
The viscéral surface bears a low crest which is the distal part of the inframarginal crista
(cr.inf, Fig. 5).
Marginal plate (M)
The left plate is completely preserved in both specimens MCD 184, 191. It is in contact
with the postorbital, paranuchal, and postmarginal plates (Figs. 3, 9, 10). There is no contact
— 173 —
Fie. 5. — Maideria falipoui n. g., n. sp. Specimen MCD 191, ventral view of lhe lefi side. Scale bar: 1 cm.
Maideria falipoui n. g., n. sp. Spécimen MCD I9J, vue ventrale du côté gauche. Échelle : I cm.
with the central plate, a condition which occurs in different species of Holonema, but aiso in
some Eubrachythoraci. Contrary to the elongate marginal plate of typical primitive brachythor-
acids (e.g. Hornostius. Antineosteus, Arenipiscis, Buchanosteus) this bone is only slightly longer
than broad.
The viscéral surface shows a well preserved inframarginal crista (cr.inf), an extension of
the endocranial postorbital process (pr.ppo; Fig. 5). This crista is low and slightly sinuous, re-
— 174 —
calling that of Buchanosteus (YOUNG, 1979, Fig. 2). The margins of this crista run almost parallel,
and a small oval dépression is seen at the distal end of its groove in the holotype. The anterior
margin of the groove turns anteriorly to reach the latéral margin of the skull-roof, contrary to
what is seen in Buchanosteus. and isolâtes a small area which corresponds to the hyoid muscle
fossa of Buchanosteus (fo.hy; YOUNG, 1979, Fig. 2).
Three sensory lines occur on the marginal plate; ihc poslmarginal sensory line (pmc), a
short part of the main latéral line, and the otic branch of infraorbital sensory line (ioc.ot). The
course of the latter is parallel to the suture betwecn the marginal and paranuchal plates, and
situated medially, a disposition shared with primitive brachythoracids and regarded as a synapo-
morphy (character 2, in LELIÈVRE, 1988, Fig. 4), even if the marginal plate remains short.
Postorbital plate (PtO)
This plate is a relatively small component of the skull-roof and its latéral margin forms
the posterior part of the dorsal orbital margin (Figs. 3, 9). It is in contact with the preorbital,
central, paranuchal and marginal plates and lacks the latéral elongated process of Taemasosteus
(White, 1978, Fig. 82) ox Arenipiscis (YouNG, 1981. Fig. 9). The length of the latéral margin
represents less than half of ihe latéral skull-roof margin. A long and stender posterior process
séparâtes the anterior part of the marginal and paranuchal plates (Fig. 9).
The viscéral surface exhibits the rnost conspicuous structures of the skull-roof, Anteriorly
to the hyoid muscle fossa, a ridge of perichondral bonc. runs from the latéral margin of the
skull-roof and makes a shaip angle to join the posterior dermal supraorbital crista, or postorbiial
crista (cr.po; see ai.so C.ARR, 1991; 380). The area situated between the anterior part of the hyoid
muscle fossa and the posterior région of the postorbital crista corresponds to the anterior post¬
orbital process (pr.apo) of Buchanosteus. The shallow supraorbital vault (suo.v) is embayed for
the supraorbital proce.ss (pr.so; Figs. 5, 6). and is bounded off posteriorly by the postorbital
crista, which may be considered as the only developed portion of the latéral Consolidated part
(Fig. 5). There is no triangular dépréssion, as in camuropiscids (tri; Dennis & Miles, 1979b.
Fig. 16).
There is no distinct dorsal overlap area for the comaci with the suborbital plate. The dermal
postorbital process is wcll defined and probably had a posterior contact area with the suborbital
plate, which was loosely attached to the skull-roof, unlike the condition in the camuropiscids
(Dennis & MtLES, 1979b, Fig. 3).
Central plates (C)
Both plates are entirely preserved in the holotype and show an asymmetrical development,
the left one being broader than the right one (Fig. 2), a condition which occurs also in An-
tineosteus. MCD 191 (Fig, 3), shows the opposite asymmetry. Their médian suture is almost
straight in the holotype and sinuous in MCD 191. There is no contact with the pineal plate, as
in most primitive brachythoracids, except Homnstius (Heintz, 1934. Fig. 1 ). Usually, this contact
occurs in eubrachythoracids, where the pineal prolrudes bciwcen the anterior margin of the cen¬
trais The general shape of the central plate, without any anterior or latéral lobe, is typical for
primitive brachythoracids and is probably linked with the séparation from the pineal plate by
the preorbital plates. The viscéral surface is fiat, and the prc-endolymphatic Ihickening is lacking.
— 175 —
The sensory Unes are normally developed, with the supraorbital (soc), and the central sensory
Unes (esc), which are both separated. The middie (tnp) and posterior pit-lines (pp), are présent
and the latter shows a peculiar pattern on the right side of the holotype (Fig. 1).
Preorbital plate (PrO)
The preorbitals hâve a postpineal contact, and their médian suture is sinuous (Fig. 4). The
latéral margin forms more than half of the dorsal orbital margin, but the dermal anteorbital
process (a. pr). is apparently formed by the rostral plate, or an expansion of the postnasals, but
this cannoi be checked.
The viscéral surface shows no contact area for the attachment of the suborbital lamina of
the suborbital plate. Accordingly, its médial margin is grooved for a contact with the postnasal
plate (?oa. PN, Fig. 6B). Il is paobably this latter plate which cstablishes ventrally the contact
with the suborbital plate, as it may also be indicated by the ventrolateral position of the nostrils
(nn, Fig. 6A). This suggests thaï the poslnasal plates probably participated to the ventral anterior
margin of the orbit, in a pattern which is sirnilar to that in camuropiscids, but also to such
dolichothoracids as Dicksonosteus (GouJET, 1984, Figs. 3B. 50). Considering the définition of
the camuropi.scids given by LONG (1988: 235). “...the postnasal plates large, excluding contact
belween the suborbital and preorbital plates...” does not appear to be a synapomorphy of the
camuropiscids (sec also Long, 1990), since il is also met within dolichothoracid, which has
anteriorly placed orhits. and probably also within Maicleria.
The supraorbital vaull is almost fiat (suo.v). except in ils posterior part where it thickens
to form Ibc anlerior part of ihe poslorbital crista. Its médial margin is clearly limited by remuants
of perichondral bone of the endocranial wall. in the middie part of the dorsal orbital margin, a
projection of the perichondral bone indicates the position of tlie endocranial supraorbital process
(pr..sü), which lies more posteriorly than in Buchemosteus (YotJNG, 1979, Fig. 2). The perichondral
bone is preserved anteriorly on both sides, with lhe Icfl side bctier preserved in the holotype.
This région shows the latéral part of the rhino-eihmoidian fissure (end. 11; Fig. 10). which opened
between the rostral capsule and the anlerior part of lhe eiidocranium in the ectethmoid région.
The left anterior superognathal (ASG) is siill aliached to the ectethmoid endocranial process
(pr.ect; Figs. 6B, 10). Its occurrence is known in Biichanosieus and certains Spitsbergen doli¬
chothoracids such as Dicksonosteus (GOUJET, 1984, Fig. 8 A).
Remarks: Recently Mn.E.S & Gardiner (1990: 194) argued for lhe absence of the ethmoid
fissure, with a perichondral continuity belween lhe ethmoid part of the neurocranium and the
rostral capsule in placodemis. In this. they contradicted the observations of YoliNG ( 1979. 1986),
and overlooked the data published by GouJET (1984) on Spitsbergen dolichothoracids. In both
Buchanoiieus and some taxa from Spitsbergen. the presence of this fissure is clear. Goujet
(1984: 231-233; Fig. 8) defined three different conditions of this fi.ssure aniong arthrodires. Bu-
chanosteiis and sonie dolicholJioracids share the sanie disposition: an open fis.sure. with a rostral
capsule covered denrially by lhe rostral and the pineal plate.s, and somelimc.s by lhe poslnasal
plates. The pineal plate may be broad with its latéral margin reaching the dorsal orbital margin,
and its posterior margin coinciding with the ethmoid fi.ssure. This explains why the two parts
of the skull-roof are often found separated (YoUNO, 1979, PI. lA, B; Goujet, 1984: 232).
— 176 —
The cranial fissure of Maideria can be considered to belong to the second type defined by
Goujet (1984), where the ethmoid région is complété and forms anteriorly a transverse internai
septum (see Stensiô, 1963, Figs. 52A-D). The fusion between both endocranial structures is
reinforced dorsally by either a broader pineal plate, a proccss of the preorbital plate, or both.
This condition is found in certain arctolepids (Lehmanosreux, Dick.ionosTeus, Heintzosteus, see
Goujet, 1984).
The internai transverse septum between the two ossifications is only partly preserved in
Maideria, and so does not allow to conclude as to the condition of the structure in this taxon.
The pineal is relatively well developed and its latéral margins do not reach the orbit. It is large
and dermally reinforcing the rhino-elhmoidian fissure, as probably did the preorbital plates with
their developed médial suture, a condition which occurs in most of the primitive brachythoracids
{Aniineosteus, Buchanosteus, Arenipiscis, Envlasreus).
Other data on the endocranial ethmoid région of brachythoracids are provided by some
Gogo species: Rolfosieus (Dennis & Miles, 1979a), indsoscuium (Dennis & Miles, 1981),
Eastmanosteus calliaspis (Dennis-Bryan, 1987), and rccently Latocamiinis (Long, 1988). None
of these clearly shows an open rhino-ethmoidian fissure, but the well preserved ethmoidian région
of Latocanuirus (LONG. 1988, Figs. 10, 12) may well fit in the second of GouJET's types, where
both ossifications are tightly fused, and where the rostral capsule is reduced to the nasal capsules.
The remaining part of the rhino-elhrnoidian fissure rs represemed by perichondral trabecles en-
closing a blood vascular plexus. However, it seems that in eubrachythoracids the rostral région
is shortened, even in long-snouted Gogo généra, since the nasal capsules bear a more dorsal
position and are more closely sel. The structure of the etlimoidian part of the endocranium in
Latacamunis is reminiscent of what Stensiô (1963) dcscribed in Tapbiosieus (STENSIÔ, 1963,
Fig. 52A-B) or PhoUdosieus (Stf.nSIÔ, 1963, Figs. 5 IC, 75), except for the anteriormost part
of the endocranium, which is reconslrucied. I consider both Tupinosteiis and Pfiolidosteus, to-
gelher with Laiocamunis, as belonging to the same second type retained by GOUJET (1984).
Tremaiosteus J'ontanellux (STENSIÔ, 1963, Figs. 9 IB, C), which has been considered by Goujet
(1984: 233) as being a possible représentative of a third type, does not, in my opinion, show a
marked différence from the condition observed in Tapinosteus or PhoUdosieus. Even less is known
about the dorsal rostral ossification of Trematosteus.
Another brachythoracid ethmoidian structure is represented by both species of Torosteus
(GaRDINER & MILE.S, 1990. Figs. 14, 15, 29), Eastmanosteus calliaspis (DENNIS- Bryan, 1987,
Fig. 16A-C), or Dunkleosteus marsaisi (pers, obs. on Moroccan material), where the ethmoidian
ossification is probably cartilaginous, except for the well-defined ectethmoid process (Dennis-
Bryan, 1987, Figs. 15C, D). Nevertheless, a new structure occurs, where the nasal capsules are
strongly ossified and shaped into cupules pierced by numerous foramina for the fila olfactoria.
Po.steriorly. the cupules are opened by a short canal for the olfaciory tract (Gardiner & Miles,
1990, Fig. 29).
Finally, YouNG’s proposai (1986: 20), that the division between the rostral capsule and the
remaining part of the endocranium, and the séparation of the nasal capsules, are placoderm sym-
plesiomorphies sound likely. However. the condition of the nasal capsule in Petromyzon (‘where
the nasal capsules are attached to the braincase by connective tissue’). argued for by YOUNG in
his proposai, does not seem to orientate this character. Even if it seems obvions that the per-
— 177 —
Fig. 6. — Maideria falipnui n. g., n. sp. Holotype specimen MCD 184. A, anlerior view. B, ventral view of the anterior part of
the skull-roof. Scale bar: 1 cm.
Maideria falipoui n. g., n. sp., Holotype MCD 184. A. vue antérieure. B, vue ventrale de la région antérieure du toit crânien.
Échelle : l cm.
— 178
sislence of this fissure in placoderms can be interpreted as plesiomorphic, its closure or replace¬
ment by a blood vascular plexus is also a tendency reinforcing Young’s interprétation of this
fissure as a plesiomorphic condition.
Pineal plate (P)
This bone is longer than broad, with a relatively well developed dorsal surface. Its anterior
margin is placed anteriorly to the orbits. It is in contact with the preorbital and rostral plates
(Figs. 3, 4, 9).
Ventrally. the pineal fossa (f.pi; Fig. 6B) is deep, and broader than long, a small posteriorly
situated ridge thickens the surface and could be considered either as the probable position of
the cérébral vein, or also as the dorsal position of the rhino-ethmoidian fissure.
Rostral plate (R)
This plate is a wcll-developed bone, triangular in shape in dorsal view, with a large ventral
lamina which ends in a straight margin, giving Maideria an elongate, clo.sed snoul (Figs. 2, 6,
10). Laterally, the rostral plate is produced into the dermal antorbital process (a.pr), which forms
the anterior part of the dorsal margin of the orbit. Its anterior position gives the orbit an elongated
shape, with an inclined anterior descending margin (Figs. 6A, 10). The rostral plate is in contact
posteriorly with the pineal and preorbital plates. The supraorbital sensory line (soc) is pre.sent
on the latéral parts of the dorsal surfaee, a condition shared with Holonema westolli (MILES,
1971, Fig. 6A). The snout is fiat dorsally, but upturned, and its base is broad. The nostrils open
ventrolaterally, and their dermal margin makes an open ring, closed laterally by a perichondral
ossification (Fig. 6A).
On the ventral surface of the holotype. a dorsal, perichondral part of the right nasal capsule
is preserved (n.cap; Fig. 6B). There is a posterior constriction, followed by a cylindrical canal,
probably for the olfactory tract as in Eastmanosteus caUiaspis (Dennis-Bryan, 1987, Fig. 16B).
Internasal plate (IN)
The limits of this plate are very clear on the radiograph of the holotype (Fig. 2). It appears
as a broad, laterally extended plate. Ils latéral margin is embayed, along the mcdial border of
the incurrent nostril notch (nn), in a way which reminds of Goodradigbeenn (White, 1978, Fig.
26D). The outer surface, or anterior lamina, is omamented with large tubercles, which confirm
its dermal origin (Fig. 6B). The récurrent lamina shows two symmetrical, shallow dépréssions
which enclosed the ventral part of the nasal capsules, separated by a blunt, finely tuberculated,
and basally enlarged internasal process (pr.in). The excurrent nostrils were probaly lying laterally
to this process.
The internasal bone is known in Coccosteus cuspidatus (Miles & Westoll, 1968, Fig. 12
D-G), wherc il also contacts the rostral plate. Its dimensions are much smaller than in Maideria.
According to GOUJET (1984; 215-216), the occurrence of an internasal plate in Kujdanowiaspis
remains questionable.
Anterior superognathal (ASG)
This is the only known gnathal élément. It is preserved in the holotype, and is still attached
in its anatomical position to the endocranial ectethmoid process (Fig. 6B). It is a broad element.
— 179 —
Fig. 7. — Maideria falipoui n. g., n. sp. Holotype speciraen, MCD 184. A, dorsal view. B, lefl latéral view. C, ventral view.
Scale bar: 1 cm.
Maideria falipoui n. g., n. sp. Holotype MCD 184. A, vue dorsale. B, vue latérale gauche. C. vue ventrale. Échelle : I cm.
180 —
Fig. 8. — Maideria falipoui n, g„ n. sp. A-D, spécimen MCD 191. A. left latéral view. B, po.sterior view. C, dorsal view. D,
ventral view. E. specimen MCD 197, dorsal view. Scale bar: I cm.
Maideria falipoui n. g., n. sp. A-D, spécimen MCD 191. A, vue latérale gauche. B, vue postérieure. C, vue dorsale. D. vue
ventrale. E, spécimen MCD 197 en vue dorsale. Échelle : I cm.
— 182 —
the occlusal surface of which is depressed and covered with small pointed tubercles, which
decrease in size from the periphery to the centre of the plate. Its anterior latéral and latéral
margins bear a row of “teeth” (a.tr, l.tr; Fig. 6B). The plate projects medially as a narrowing
process. Dorsally, the surface is gently curved transversally, but there is no dorsal process. This
structure is considered to be one of the eubrachyihoracid synapornorphy. The anterior superog-
nalhal of Maideria is plesiomorphic in lacking a dorsal process, and also in having an omamented
occlusal surface.
The gnathal element of primitive brachythoracids are poorly known in most of them, with
only the poslerior superognathal and the inferognathal described in Goadradigbeeon (White,
1978, Figs. 24. 44-49), and the inferognathal known in Antineosieus and Homostiiis. Unfor-
tunately, none of the gnathal éléments is known in Buchannsieus . When compared with the doli-
chothoracid An tolepis (GoujET, 1984, Figs. 74, 82), the superognathal plate of Maideria shares
the presence of a tuberculation on the occlusal surface. But it differs by its overall shape, rec-
tangular, and lack of individualised teeth; no radial disposition of the “denticles” occurs.
Nu
Fig. 10. — Maideria falipoui n. g., n. sp. Reconstruction of the skull-roof in left latéral view, based on MCD 184, 191, 197.
Scale bar: I cm.
Maideria falipoui n. g., n. sp. Reconstitution en vue latérale gauche du toit crânien. D’après les spécimens MCD 184, 191,
197. Échelle : 1 cm.
Anterior ventrolateral plate (AVL)
The only specimen of this plate was associated with a portion of a typical rostral plate of
Maideria (Fig. IIE-F) and is therefore referred to this genus. The anterior part is missing but
— 183 —
the postérolatéral, posterior and médial margins are well preserved. The ornamentation eonsists
of relatively small and scattered tubercles, which are larger in a latéral zone, near the ventral
edge of the pectoral emargination (p. emb). The pectoral fenestra must hâve occupied a posterior
position, much as in Witliamsaspis hedfordi (White, 1952, Figs. 1, 2), with which it also shares
a long spinal margin. The surface of the bone at the level of the pectoral emargination is slightiy
bulging.
The posterior région of the viscéral surface shows a contact surface for the posterior ven-
trolateral plate, with a ridge running forward front the posterior latéral corner to the centre of
radiation of the plate.
The ventral thoracic shield of Maideria differs from that oï Antineosleus and Homosiiiis in
having a posterior ventrolateral plate. The organisation of the thoracic shield may be doser to
Buchanosieits, as figured by Long (1984, Fig. 16F), where the spinal plate is large (White &
Toombs, 1972, Fig. 23) and the pectoral fenestra posteriorly closed.
Médian dorsal plate (MD)
This plate (Fig. IIA-B) and a right anterior latéral plate are provisionally referred to
Maideria on the only basis of the ornamentation, which is, however, a weak argument.
The médian dorsal plate is longer than broad, with a straight anterior margin and a well-
developed posterior process (pt.pr), not .shown on figure IIA-B. The ornamentation is composed
of small tubercles near the centre of radiation. At tlte periphery lhey tend to be arranged in
lines, just as on the dorsal orbital margin and rostral plate of the skull-roof
The ventral surface is concave, with two pairs of overlapping areas. The smaller anterior
one is for the anterior dorsolateral plate (ADL cf.), and the posterior onc for the posterior dor-
solateral plate (PDL cf ). The ventral kecl is barely developed anteriorly, but higher posteriorly
and ends with a posteriorly excavated carinal process (cr.pr). These characters, and the general
outline of the plate, evoke the médian dorsal plate of Buchanosteiis (White. 1972, Fig. 17). An
excavated carinal process occurs in eubrachythoracids, but is absent in other primitive brachy-
thoracids when available.
Antérolatéral plate (AL)
Only one complète plate of the right .side is known (Figs. IIC-D, 12). It is broader than
high, and its posterior margin is produced into a médian process (pr.m). The postbranchial lamina
is short and covered with pointed tooth-like denticles. The obstantic process (pr.ob) is anteriorly
projected and hollowed by a small dépréssion which represents the dorsal limit of the infraobstan-
tic lamina (l.iob).
The inner surface shows a thin postbranchial crista (cr.pb.), the dorsal part of which bounds
off a short contact area for the anterior dorsolateral plate (ADL cf.).
The posterior médian process, the long ventral margin and the almost horizontal dorsal
margin seem to be characteristic of Maideria. but an elongated anterior latéral plate is also
found in camuropiscids (Dennis & Miles, 1979b, Figs. 2, 12; Long, 1988, Fig. 2; 1990,
Fig. 1).
— 184 —
FiG. Il - — Maideria falipnui n. g., n. sp. A-B, specimen MCD 186. médian dorsal plate. A. dorsal view. B, ventral view. C-D,
specimen MCD 187, antérolatéral plate. C. latéral view, D. mcdial view. E-F, specimen MCD 190, left anterior ventrolateral
plate. E, ventral (curer) view; F, internai view. Scale bar: I cm.
Maideria falipoui n. n. sp. A-B, plaque médiane dorsale. MCD JiH6. A, vue dorsale; B, vue ventrale. C-D, plaque latérale
antérieure. MCD 187. C, vue latérale. D. vue interne. E-F. plaque ventrolatérale antérieure, MCD 190. E, vue externe, F.
vue interne. Échelle : 1 cm.
185
FlO. 12. — Maideria falipoui n. g., n. sp. Specimen MCD 187, anterior latéral plate. A, latéral view. B, médial view. Scale bar:
I cm.
Maideria falipoui n. g., n. sp. Plaque latérale antérieure, MCD 187. A. vue externe: B. vue interne. Échelle : I cm.
— 186 —
PHYLOGENETIC ANALYSIS
Phylogenetic analyses of the “primitive brachythoracids” hâve been attempted by White
(1978). Young (1979. 1981), Lelièvre (1984a, b; 1988), whilst the attention of the other workers
has been drawn towards Ihc interrelalionships of eubrachythoracids (e.g. Long, 1988; Gardiner
& Mll-ES. 1990; Carr. 1991). Holonenui is always considered to be the most primitive brachy-
thoracid; Homasiius and Buchannsieus are good modcls for primitive brachythoracids. However
the interrelationships of the 'primitive' brachythoracids are still imclear, probably because of the
quite different patterns of the head and trunk shiclds. This situation is indirectly a conséquence
of the exceptional préservation and diversification of the Upper Devonian Gogo and Wildungen
eubrachythoracid material. which has no équivalent for primitive brachythoracids. But some of
the questions formulated by Young (1981: 269) still hâve no answer.
A matrix of charaeters has been established in order lo work out the interrelationships of
the primitive brachythoracids; 53 charaeters bave been defined from a matrix initially elaborated
for brachythoracid interrelationships. This matter has been debated recently by Carr (1991),
and will be discussed in connection with the description of Upper Devonian Moroccan brachy¬
thoracids.
CHARACTER.S DEFtNED ON THE .SKUI.I.-ROOF
1. Dermal plates of the skull-roof with overlapping surfaces: absent (0), présent (1).
2. Structure of endocranial posterior postorbital process: two branches (0), one branch (1).
3. Development of a rostrum: absent (0), présent and closed (1). présent and tubular (2).
The derived pachyosteomorph Oxyosteus is not considered in this définition, its elongated
rostrum is downturned and its anterior région remains unprepared on the original material.
4. Shapc of rosirai plate; broader than long (0). iriangular in dorsal view (I), with a posterior
process giving a ‘T shape' outline (2), see C.ARR (1991).
5. Position of the anterior edge of the pineal plate, compared with the anterior edge of the orbit:
posterior (0), anterior or on the same level (1).
6. Postnuchal process: ab.sent (0), présent (I).
7. Position of the levator muscle pits on the nuchal plate: posterodorsal (0), posteroventral (1),
ventral (2).
8. Shape of the anterior nuchal margin on the dorsal surface: convex (0), straight ( I ), concave (2).
The primitive condition is indicated by dolichothoracids. Carr (1991; 372, character 10)
retained a straight margin as the primitive State.
9. Shapc of the posterior nuchal margin: .straight (0), convex (1). concave (2).
10. Posterior nuchal thickening: présent only under the paranuchal viscéral surface (il corresponds
to the development of the dermal articulation) (0), developed under ail the occipital région of
the skull-roof (1) (see Lelièvre et al., 1990).
— 187 —
11. Length of nuchal and paranuchal plaies: short (0), long (1).
The élongation of the nuchal and paranuchal plates could be associated with the élongation
of the endolymphatic tube (see Anlineosteus, LELIÈVRE 1984b, Fig. 3, PI. 3C). Short paranuchal
and nuchal plates do not seem to bc correlated with a complété posterior Consolidated arch,
which is absent in Maideria. Jn the case of a complété development of this posterior arch, the
endolymphatic tube remains short, and is sometimes included in the latéral part of lhe posterior
thickening in certain Eubrachylhoraci (e.g. Dunkleoxteus). The position of the CVPNu/M or PlO
triple point, relatively to the PNu/C/Nu triple point: posterior (0) or anterior (1), defined by
Carr (1991, character 31) is probably correlated with this character and therefore is not used
here.
12. Paranuchal plate process onto the central plate determining a latéral lobe: absent (0), présent
(1).
This character could also be identified when the anterior margin of the paranuchal is straight;
this is the condition of Maideria. The position of the triple point PrO/PtO/C relative to the
posterior triple point PtO/M/C or to PtO/PNu/C: parallels the midline or with the anterior point
latéral (0). posterior point latéral to anterior point (1), as defined by CARR (1991, character 32),
is another way to define the development of the latéral lobe of the central plates. The définition
provided here is more simply expressed.
13. Shape of the condyle (or fossa) of the dermal articulation: ovoid (0), higher medially than
laterally (1).
14. Suborbital plate: not overlapping the postorbital plate (0), overlapping the postorbital plate
(I), (Gardiner & Miles, 1990, character 22.9; Carr, 1991, character 53).
15. Palatoquadrate as a single unit (0), separate quadrate and autopalatine ossifications (1), (Miles
& Dennis, 1979).
16. Preorbital plate embayment of the central plate: absent (0), présent (I).
17. Posterior lobe of the central plate protrudring between the nuchal and paranuchal plates:
absent (0), présent (1).
18. Contact between central and marginal plates: présent (0), absent (1).
The derived State occurred probably several times in placoderm history. VÉZINA (1990: 681)
retained this character in his diagnosis of lhe plourdosieids. Allhough il is présent in ail the
généra included in the Plourdosteidae (even Torosteus'. Gardiner & MILES, 1990), il also occurs
in other brachythoracids (e.g. Maideria, Holonenia, Pholidvsteus, Tapiuosleus, Enseosteus, Ta-
filalichthys), and most of the actinolepid généra, (t gives to this character a large distribution
which could be interpreted as homoplaslic. The long marginal plate of certain primitive brachy-
thoracids obviousiy leads to a contact between the two plates, and could also be correlated with
the development of the latéral lobe of the central plate.
19. Position of lhe contact between preorbital plates: posterior to the pineal plate (0), anterior
(1), absence of contact (2).
— 188 —
The occurrence of a rostro-pîneal plate does not influence the interprétation of this character,
but in some dolichothoracids the condition is different. There is no contact in Arctolepis, and
most actinolepids hâve a contact between the preorbital plates posterior to the pineal plate. Some
phlyctaeniids show both conditions (e.g. Heinlzosleus\ Goujet, 1984, Figs. 94, 97, 106). The
pineal-preorbital région is usually broad in dolichothoracids and primitive brachythoracids. The
relations and extent of these plates are probably determined by the presence of the rhino-eth-
moidian fissure.
20. Dermal proce.ss on the preorbital plate; absent (0), présent (1).
In eubrachythoracids the derived State may be correlated with the latéral position of the
orbits (character 24), The dermal preorbital process is defined as the most anterior part of the
dorsal orbital margin. The process could be developed front different plates in different groups:
front the postna.sal in Dlcksonostens and the camuropiscids but in a more ventral position, and
front the rostropincal plate in Buchamstem, in which the postnasal plate is still unknown, In
eubrachythoracid, ils occurrence implies a contact between the suborbital and preorbital plates,
as the postnasal plates arc more anteriorly placcd and in contact with the anterior margin of the
preorbital plate, the suborbital plate and the latéral margin of the rosirai plate (see C\RR, 1991:
characters 17. 54; Dennis & Miles, 1979b: 313, character 19). It is cicar that a dermal preorbital
process occurs wben there is a contact with the suborbital plate, with the exception of Homof:tius
and camuropiscids. In my opinion. Honwstius and camuropiscids lack a preorbital dermal process;
ihus character 54 of Carr (1991) is correlated with the presence of the postnasal plate forming
part of the orbit (Carr, 1991, character 26), or to the presence of a rostro-pineal plate, which
is considered to be plesiomorphic for arthrodires. Finally the problem of the homology of the
dermal preorbital process in these different groups will be resolved when more information will
be available on Buchanosieus. and when the question of a possible fusion of the postnasal plates
to the rostro-pineal plate will receive an answer. The plesiomorphic condition is a dermal pre¬
orbital process as part of the postnasal plate, a pattern shared by actinolepids (Mark-Kurik,
1973, Fig. lA) and phlycateniids.
21. Postérolatéral process of the postorbital plate: absent (0), présent (1).
22. Composition of the dorsal orbital margin; preorbital and postorbital plates plus postnasal or
rostral or rostropincal plates (0), preorbital and poslorbital plates only (1).
The primitive State as defined here includes different plate arrangements in the dorsal orbital
margin; the rostral plate in Hnlonema, the autapomorphic condition of Aniineus'ieus, in which
only the poslorbital plate constitulcs the dorsal orbital margin (coded as irrelevanl in the data
matrix); in Buclianoxteus, the rostro-pineal plate forming the anterior corner of ihc orbit; the
postnasal plate in Dicksoiiosietis and the camuropiscids; and finally the marginal plate in the
posterior part of the orbital margin, in Rhinosteus, Melanosteus and ollier selcnosieids.
23. Position and size of the orbits; small and anteriorly placed (0). small and laterally placed
(1), enlarged and latéral (2).
This character seems to be correlated with the length of the contact between the cheek
piales and the latéral margin of the skull-roof (CARR, 1991, character 61), and probably also to
— 189 —
the development of a suborbital lamina in eubrachythoracids (see Lelièvre, 1988, character 19).
Homostius cannot be scored owing to its autapomorphic orbital position.
24. Triangular depre.s.sion po.sterior to the supraorbital vault (Carr, 1991, character 3): absent
(0), présent (I).
In Maideria, the development of this dépréssion is related to the presence of a well-defined
dermal postorbilal proee.ss. Biichanosteus is considered to show the derived State although the
shape of the dépréssion is elongated.
25. Length of the contact betwecn cheek plates and the latéral margin of the skull-roof: long
(0), short (1).
It is diftlcull to be précisé as to the length of this contact. Here. the contact is rated on
the basis of the comparison between the length of the latéral margin of the skull-roof and the
width between the dermal articulations, which I considcr as a stable proportion in brachythoracids
(a short latéral skull-roof is less lhan twice this width).
26. Shape of submarginal plate: large (0), elongated (1), small and square (2).
The submarginal plate of primitive brachythoracids is known in Buclumosteus (YoUNG,
1979; Whtte & ToOMfiS. 1972. Hig. 16). Antineosteus (LELIÈVRE, 1984b). Homostius (Heintz,
1934), and partly in Goodracligheeon (White, 1978). However the .submarginal plate is identified
without doubi only in Antineosteus and Buclumosteus. The relations with adjacent plates and
the hyomandibular are difficult to déterminé for the other primitive brachythoracid généra. Two
derived States hâve been distinguished, in contrast to Carr (.1991, character 60) who coded only
for one. Two derived .States are necessary in order to take into account the condition m oiitgroup
taxa and camuropiscids, because the anatomical relationships between the marginal and suborbital
plates are imclear, and also whelher or not they are in contact (Carr, 1991, character 55) is
not an independent character. Those généra wilh a small, square-shaped and supposedly reduced
submarginal (camuropiscids and Rhinosteus) hâve a contact between the marginal and the sub¬
marginal plates. Other character States, not included in this analysis, could be distinguisJied for
advanced brachythoracids: submarginal plate elongated and vertical, or fused to the postmarginal
plate, but they are not taken into account here.
27. Development of a suborbital lamina of the suborbital plate (Lelièvre, 1988: 293): absent
(0), présent (1).
This character seems to be correlated with the position of the orbit, although the disposition
in Homostius is an exception. The derived State includes several bone patterns in different Late
Devonian généra such as Tafilalichthys (Lehman, 1956), Melanosteus (Lelièvre et al., 1987),
Gymnotrachelus, and Heintzichthys (Carr, 1991). This problem, briefly discussed by LELIÈVRE
et al. (1987), has been reviewed recently by Carr (1991).
CHARACTERS DEHNED on THE GNATHAL PLATES
28. Dorsal process of the anterior superognathal: absent (0), présent (1).
— 190 —
Miles (1971; 150, Fig. 59) described the anterior superognathal élément of Holonema west-
olli as a small, unpaired, symmetrical plate. 1 agréé with Miles’ interprétation, and consider
this gnathal élément to lack a dorsal process strictly homologous to that of other brachythoracids.
29. “Teeth” developed on the occlusal surface of the anterior superognathal: absent (0), présent
on the anterior margin (1), présent on anterior and latéral margins (2).
30. Occlusal surface of the anterior superognathal: denticulated (0), smooth (including crushing
surface) (1).
The anterior superognathal of Dicksonosteus is unknown, but it can be assumed to be similar
to the same denticulated élément in Arctolepis decipiens (GOUJET, 1984, Fig. 82). It should be
noted that the upper gnathal éléments of the juvénile individiials of Rolfosteus are denticulated
(Dennis & miles, I979b; 306), but they are of a crushing type in the adults. Some Early
Devonian actinolepids from North America have a denticulated infcrognathal associated to an
anterior crushing superognathal lacking denticles (D. GouJET pers. comm.). Because of this onto-
genetic and positional variation, the plesiomorphic State for arthrodires is questionable.
31. Infcrognathal plate with a posterior non-biting portion: absent (0). présent (1).
This character is used by Miles & Dennis (1979), and Carr (1991). The non-biting blade
portion of Dunkleosteus in Heintz’s de.scription (19.32), may be linked with the presence of a
single inferognatltal ossification centre. It is not clear whether the occurrence of a ventral groove
in the blade région is strictly homologous.
32. Occlusal surface of the infcrognathal plate: denticles présent (0), denticles absent (1).
The plesiomorphic State for this character is based on the morphology of this élément
observed in Dicksonoxteus (GOUJET. 1984. Fig. 40). and on isolated actinolepid inferognathals
(Denison. 1958) referred to Aerhaxpis (D. GouJET pers. comm ), Although the upper gnathal
éléments are broad and lack tubercles, the dorsal surface of the infcrognathal is narrow. den¬
ticulated posteriorly, with two well-developed anterior denticles. There is no symphysial tooth,
and the oblique anterior margin beats no denticle. The infcrognathal of juvénile individuals of
Incisoscuium exhibits the plesiomorphic character State (Dennis & Miles, 1981, Fig. 12B-D).
33. Ventral surface of the infcrognathal formed by a deep groove limited by two laminae, with
the labial one more developed: presence of a deep groove and two laminae (0), absence of a
groove (1).
In Aniineosteus (LELIÈVRE, 1984b, Fig. I4B) and Goodradigbeeun (WillTE, 1978, Figs. 47-
49), the ventral surface of the infcrognathal is occupied by a deep groove. An isolated inferog-
nathal from the Lower Devonian of Battery Point Formation (Québec), which probably belongs
to the primitive brachythoracid ForiUonaspis (PAGEAU, 1982), shows the same plesiomorphic
condition. Homostius is coded as plesiomorphic according to Mark-Kurik (1992, Fig. 2).
Remarks: The posterior superognathal élément of Goodradigheeon (White, 1978, Figs.
44-46), and Holonema westolli (MiLRS, 1971) has a denticulated occlu.sal surface and is almost
rectangular in shape, without a dorsal process. This suggests that in basal brachythoracids, in
which the condition is unknown, the élément should resemble dolichothoracids like Dicksonosteus
(GouJET, 1984, Fig. 82; PI. 18.1) and Aciinolepis spinosa (Mark-Kurik, 1985, Fig. 3).
— 191 —
Whitf. ( 1952, Figs. 31-35) figurecl isolated posterognathal éléments from the Early Devonian
of the Goodradigbee River, which hâve a dorsal process and lack denticulation. They show the
derived condition and belong to an eubrachythoracid.
Remarks on the parasphenoid
The parasphenoid is known in the following brachythoracid généra; Buchanosteus (White
& Toombs, 1972, Figs. 5-7; Yoüng, 1979, Fig. 17; only the ventral surface is figured), An-
lineosteus (Lelièvre. 1988. Figs. 2A-C; 3A-C). Coccosteus (Miles & Westoll. 1968, Fig. 18A-
B) , Panxiosteus (Wang, 1979, Fig. 2), liitaummasteus calliaspis (Dennis-Bry.an, 1987, Fig. 17A-
C) , Dunkleosteus (DüNKLE & Bungart, 1946), flanytoomhsia (Miles & Dennis. 1979, Fig.
I3A-D), Pholidosteiis (StrnsiÔ, 1963, Fig. 75), Tapirtasieus (STENSICf, 1963. Fig. 63A-B). Inci-
soscutum (De.NNIS & Miles. 1981, Figs. 13, 15), TaJUalichthys (LELIÈVRE, 1991, Fig. 4), Biiller-
ichthys, BnmiDnkhîhys (Dennis & MILES, 1980. Figs. 3C-D; 9A-C), Mekinasieus (I.JîLIÈVRE et
ai. 1987, PI. 2C-E), Treimtosteus (Stensiô, 1963, Figs. S7A, 92A), Brachyosteiis (STENSIO,
1963: 352, but still not figured), Errumenosteus (Stensiô, 1963. Fig. 115E-G). Pachyosteiis
(Stensiô, 1963, Fig. 115H-J), Torosleus (MILES & Gardiner, 1990, Figs. 9, 24). Laiocumiirus
(Long, 1988, Fig. 1 1 ), Heiutzichthys (Carr, 1991, Fig. SA-C) and Tilanichlhys sp. (pers. ob.serv.
in the Cleveland Muséum collections).
Buchanosteus and Anlineosleus are considered as primitive brachythoracid s and their par-
asphenoids share some charactcristics. In both généra, the parasphenoid is short and broad without
a developed prehypophysial région, the ventral surface is tuberculated. Because of the poor in¬
formation on the parasphenoid of other primitive brachythoracid généra, they hâve not been
used herein. Nevertheless, it seems that there is a tendency towards an élongation of the pre¬
hypophysial région, the disappearance of the palatine tuberculation, the development of a médian
crista on the ventral surface, and the disposition of the groove for the carotid artery (K. Den-
nis-Bryan, pers. comm.; Carr, 1991).
ChaRACTERS DEFINED on THE TtlORACIC ARMOUR
34. Posterior margin of the pectoral fenestra: closed (0), open (I),
Primitive brachythoracids display both closed and open pectoral fenestrae. The latter con¬
dition is seen in Antineosteus and Homostius which lack the posterior ventrolateral and posterior
médian ventral plates. Probably the posterior opening of the pectoral fenestra occurred at least
twice in brachythoracid évolution in different ways. The opening of the fenestra occurs either
by a loss of the posterior plates (see character 36), or by the loss of contact between the posterior
latéral and posterior ventrolateral plates (pachyosteomorph arlhrodires), or by a combination of
both. Some brachythoracids bave lost the posterior latéral plate (e.g. Holonema and Iiicisoscurum;
Gardiner & Mii.es. 1990: 198).
35. Length of the latéral pectoral process of the spinal plate: long (0), short (I).
Primitively the spinal plate was in contact with three plates: (e.g. Dicksonosteus and Arc-
tolepis), the anterior latéral plate dorsally, the interolateral plate anteriorly and the anterior ven¬
trolateral plate ventrally. Thus a .séparation between the anterior latéral and anterior ventrolateral
— 192 —
plates is considered to be the plesiomorphic condition. Homostius shows this condition because
of a short spinal plate (pseudospinal ot' Dennis & Miles, 1981) and a pectoral incision (Mark-
Kurik, 1963). Four généra analysed in this study lack information conceming the spinal pattern
with adjacent plates: Anlineosleus, Taemoxostcu.s, Arenipiscis, Moideria. With the exception of
camuropiscids, the remaining généra hâve a spinal contact with the three adjacent plates men-
tioned above. Camuropiscids lack a contact between the .spinal and the inlcrolaieral plates because
the spinal is limited to a posterior position giving an anterior contact between the anterior latéral
and ventrolateral plates. Thus two characters used by Carr (1991), |intcrolatcral-spinal contact
(his characier 38) and anterior laleral-anterior ventrolateral plates contact (his character 40)]
define the same anatomical dispo.siton. When there is a contact between the anterior latéral plate
and the anterior ventrolateral plate, then there is no contact between the interolateral plate and
the spinal plate, a pattern which is exclusive to camuropiscids.
Only the interolateral and spinal plates contact has been scored. The plesiomorphic State
[(0) = présent] is defined referring to the conditions of Dicksnnnsteus (GOUJET. 1984; 137, Fig.
72C) mû. Arctoîepis decipieiis (GOU.(ET, 1984, Figs. 86, 87). This character polarity differs from
that of Carr (1991), whose coding statement may be wrong. ba.scd on the Dicksonosieus pattern
(see Carr, 1991, characters 38-40). This contact is long in camuropiscids, because the spinal
plate has a posterior position j.see Dennis & Miles (i979b; 325), Carr (1991; 374, character
38)].
36. Posterior ventrolateral and posterior médian ventral plates; pre.sent (0), absent (1).
The absence of lhese plates could be concluded from the straight posterior margin of the
anterior ventrolateral plate and/or from the absence of a contact surface on its viscéral surface.
This character is correlated with an open pectoral fenestra (character 34). but is treated .separately
because we hâve no précisé idea of the process implied in the opening of the pectoral fenestra
in each genus. This character is not treated as two separate characters, because no taxon shows
the loss of one of the two plates.
37. Orientation of the posibranchial lamina of the interolateral plate and of the anterior border
of the anterior latéral plate. Straight, in dorsal view, with a latéral branchial space anteriorly
inclined (0), convex in dorsal view, with a latéral branchial space either slightly inclined anteriorly
or nearly vertical (I).
The anterior border of the anterior latéral plate defines the orientation of the branchial
space.
38. Shape of the médian dorsal plate: longer than broad (with or without a posterior spine) (0),
shorter than broad (1).
39. Médian dorsal plate with a posterior expansion or spine: présent (0), absent (I).
The plesiomoiphic character State is coded by Carr (1991) as a rounded posterior région
(no posterior expansion). I consider the condition in Dicksonosieus to be plesiomorphic, that is,
a posteriorly rounded posterior expansion. A similar condition is présent in others dolichothoracids
such as Heintzosteiîs (Goluet, 1984, Fig. 106 B), mû Arctolepis decipiens (GoUJET, 1984, Figs.
86, 87) which hâve a pointed posterior poinled.
— ]93 —
40. Ventral surface of médian dorsal plate: presence of a longitudinal groove (0), presence of a
keel and a carinal process (1), presence of a posteriorly excavated carinal process (2).
Gardiner & Miles (1990: 192) did not distinguish the second derived State of this character,
which is constant at the cubrachythoracid level. However a posteriorly excavated carinal process
is not always correlated with the occurrence of a posterior expansion, because Dunkleosteus has
a short médian dorsal plate with a posteriorly excavated carinal process.
41. Branchial lamina of the interolateral plate: unornamented with a .short ventral lamina (0),
omamented with a short ventral lamina (1), ornamented with a large ventral lamina (2).
The plesiomorphic State for this character is based on the interolateral plate oï Dicksonosteus
arcticus (GOUJET, 1984, Fig. 65). but the same character State is also found in some pachy-
osteomorph arthrodires [e.g. TafUalichthys lavocati and Heintzichthys gouldii (Carr, 1991, Fig.
9B, C)] in which it could be parallely derived.
42. Anterior latéral plate with a high dorsal lamina (YoUNü, 1981); absent (0), présent (1).
No characteristic can be defined on the scapulocoracoid as it is only known in Buchanosteus
(White & TOOMBS, 1972, Fig. 18; PI. 9, Fig. 4). In this genus, the scapulocoracoid is short
with a closed pectoral fenestra, but we ignore what is ils length in primitive brachythoracids
with an open pectoral fenestra (e.g. Antineosteus, HomosUus)^ although the development of the
spinal plate and its relationship with the scapulocoracoid may be involved. The scapulocoracoid
is known but incomplète in Holonema westolli (Miles, 1971, Fig. 91).
CHARACTERS USING SENSORY LINES
43. Supraorbital sensory line on the rostral plate; absent (0). présent (1).
44. Supraorbital sensory line on the central plate (YOUNG. 1981): absent (0), présent (1).
45. Position of the otic branch of the infraorbital sensory line on the marginal plate: near the
latéral margin of the plate (0), near the médial margin of the plate (1).
46. Postsuborbital sensory line on the suborbital plate; absent (0), présent (1) (primitive brachy-
thoracid synapomorphy in Lelièvre, 1988: 294).
47. Relation between the supraoral and infraorbital sensory lines on the suborbital plate: con-
nected (0), separate(l).
The supraoral sensory line may be absent on the suborbital of certain pachyosteomorphs
(e.g. Tafilalichthys) and certain généra from the Upper Devonian Cleveland Shales and is not
scored here.
48. Orientation of the occipital cross-commissure; directed towards or reaching the nuchal plate
(0), directed onto the nuchal gap, and extending on the extrascapular plates, if preserved (1),
absent (2).
The primitive State has been defined after the condition met within Arctolepis decipiens,
with an occipital commissure Crossing the nuchal plate (GouiET, 1984, Fig. 77, see also Bucha¬
nosteus, Young, 1979, Fig. 1).
— 194 —
49. Ventral sensory line on the anterior ventrolateral plate: absent (0), présent (1). See Carr
(1991, character 79) and Miles (1971, Fig. 108).
50. Main latéral sensory line on the posterior dorsolateral plate: absent (0), présent (1).
51. Main sensory line as a groove on the médian dorsal plate: absent (0), présent (1).
52. Suborbital sensory pits: absent (0), présent (1).
53. Angle between the suborbital and postorbital branches of the infraorbital sensory line: open
(more than 90“) (0), closed (less than 90°) (1).
PHYLOGENETIC PATTERNS
Only seven généra of “primitive brachythoracids” hâve been taken into account in this analy¬
sis. Others 17 primitive brachythoracids taxa hâve been described in the literature, but most of
them are too poorly known to be coded in the matrix. Those taxa are:
Jiushengshia longoccipita Wang & Wang. 1983
Euleptaspis depressa Gross. 1933 and the Euleptaspis species A and B mentioned by 0RVIG
(1969)
Errolosieus goodradigheensis Young, 1981
Goodradigheeon australimum White, 1978
Kueichowlepis sinensi P’an, Wang & Liu, 1975
Burnnjucoxteus asywmetricus White. 1978
WHliamsaspis hedjardi White. 1978
Gemuendenaspis angiista Miles, 1962
ForiUonaspis lehmuni Pageau, 1982.
These généra share some characters eilher with the Migmatocephala or with brachythoracids
as defined here (Migmatocephala plus Eubrachythoraci). The different .species of Homostius are
not discussed, and only Homostius sidcatus is scored in the matrix, based on Heintz’s description
(1934). completed by Mark-Kurik (1992: [11-\1%). Holouema has been coded by using the
complété description of Holouema westoHi by MILES (1971), from the Frasnian of Gogo, Tity-
osteus rieversi has been coded on the basis of Otto's de.scription (1992).
Two outgroups hâve been coded - Dicksonosteus and Arctolepis — they were chosen mainly
because of their completeness. Fifty three characters hâve been defined of which fourteen are
multistate characters, 51% of the characters are defined on the skull-roof. 11.3% on the gnathal
éléments. 17% on the thoracic armour and 20.7% on the sensory Unes pattern. An analysis of
the 53 unweighted and unordered characters (Deltran optimization) and Branch and Sound al-
gorithm with PAUP (SwofeORD, 1991) gave 17 equally parsimonious topologies (CI = 0.583,
HI = 0.443) with 1 15 evolutionary steps. In those topologies the position of Arenipiscis was the
most ambiguous.
Arenispiscis westolli (YouNG, 1981) is the most incomplète taxon included in this .set of
brachythoracids, 47.1% of its characters are coded. Its dclction is an important gain because
— 195 —
only 4 topologies at 110 evolutionary steps are found, with the following indices: Cl = 0.600,
HI = 0.427, RI = 0.654, and its délétion may be argued for only on the basis of the largest number
of missing data (see Cloutier, 1991: 410). Most of the other taxa were fairly complété with
regard to the characters suidied: Dicksonosleus (94.3% of ail characters), Aivtolepis (96%), An-
lineosieus (86.8%), Homosiius (86.8%), Buchanosieus (83%), Hohmema westolli (98.1%), Taema-
sosteus (60.3%), camuropiscids, Coccosteus cuspidcitus, Incisoscutum ritchei (100%), Maideria
(73.5%), Tityasleux (54.7%). Neverlheless, Arenipiscis shares with the Migmatocephala lheir iwo
synapomorphies II [1] and 38 [IJ.
In these four equally parsimonious topologies a reversai on character 26 [1-^0] for one
of the topologies at the node imiting Hohnema to the clade A and clade B is considered as
impossible. In fact this reversai implies the transformation of an elongated submarginal plate
- the condition met with in Ccccosteus cuspidatus - to the condition met in Hohnema, which
has a very large plate. The morphologicaJ structure retained in the définition of that character
concerns the overall shape of the subinarginal plate, but it appears to be unprecised, as il concems
only the shape of this plate and not, for example, the overlapping surfaces and the relalionships
of the submarginal plate with the adjacent plates, which could be potentially more informative.
But the submarginal is rarely preserved and the définition and the coding of the overlapping
surfaces is dilTicult to establish for each taxon considered here. So this character has been deleted.
The run of PAUP in this new condition gave three equally parsimonious topologies at 108 evo¬
lutionary .steps. with a CI = 0.602, HI = 0.426. RI = 0.656 (see Fig. 13 A-C).
A run of PAUP with character 26 ordered gives four equally parsimonious trees with 1 1 1
evolutionary steps. Three of the four topologies are the same as the one discussed (Fig. 13A-C).
In the fourth topology Hohnema is placed as the sister taxon of the Migmatocephala and Eu-
brachythoraci; in this case character 26 [1] is a uniquely shared derived character for the basal
brachythoracid clade, along with an inferognathal plate with a non-biling postcrior portion, that
is, character 31 LU- This topology expresses the current opinion of authors about the phylogenetic
position of Hohnema within the brachythoracids. This position of Hohnema resis on the con¬
gruence of both characters. as a run of PAUP with the délétion of character 31 gives three
equally parsimonious topologies in which Hohnema is placcd in the Eubrachyihoraci (as in Fig.
13A-C). In the analysis provided here I shall retain the run with ail characters unordered.
In the strict consensus tree (Fig. 14; Mikevitch CI = 0.520), three major monophyletic groups
are identified. The basal brachythoracid clade, and Iwo basal clades, the Migmatocephala, or
clade A, and the eubrachythoracid. or clade B, respectively.
For a long lirnc the monophyly of brachythoracids has been recognized and diagnosed by
different authors (YoUNC, 1979; GOUJET, 1984; Carr, 1991). At this node four synapomorphies
given by those authors. are retained of which three are unique shared dérivé features:
— dermal plates of the skull-roof developping overlapping surface 1 [1];
— one branch in the posterior endocranial postorbital process 2 [1];
— presence of a postnuchal proce.ss 6 [IJ.
Character 35 [Ij (short latéral pectoral process of the spinal plate) is retained as a synapo-
morphy for brachythoracids only when Buchanosieus and Maideria are respectively the sister
taxa of clade A and clade B (Fig. 13 B).
— 196 —
A
B
Dicksonosteus
Arctolepis decipiens
MakJeria
- Buchanosteus
Clade A
Clade B
Fig. 13. — A-C, three equally parsimonious topologies of the interrelationships among brachythoracids. From a matrice of 53
unordered characters. 107 steps, from with PAUP 3.0S. The statistics are: CI = 0.602. HI = 0.430, RI = 0.656. The synapo-
morphies occuring at each nodes arc placed in brackets. Clade A for ihe Migmatocephala. clade B for the Eubrachylhoraci.
A-C, trois topologies égofemeiU parcimonieuses des relations de parenté des Brachythoracii à partir d’une matrice de 53
caractères non ordonnés par PAUP id - 0,602: Hl = 0,430 ; RI = 0,656) (version 3.0s). Les synapomorphies retenues à
chaque nœud .\ont indiquées entre crochets. Les Migmatocephala correspondent au clade A et les fMhrachythoracH corres¬
pondent au clade B.
The basal brachythoracid clade is diagnosed also by six homoplastic characters of which
four are shared in each one of the three topologies (Fig. 13A-C):
— presence of a posterior lobe of the central plate which protrudes between the nuchal
and the paranuchal plates 17 [1 (CI = 0.500)];
— médian dorsal plate with a carinal process posteriorly excavated 40 [2] (CI = 0.667);
— presence of the supraorbital sensory line on the central plate 44 [1] (CI = 0.667);
— presence of the otic branch of the infraorbital sensory line near the médial margin of
the marginal plate 45 [1] (CI = 0.500).
— 197 —
Two homoplastic characters, 21 and 46, appear in the topologies 1, 2 and 3 respectively
(Fig. 13A-C). Character 21 [1] presence of a postérolatéral process of the postorbital plate. In
the topology 1 (Fig. 13A), this character has a low value CI = 0.333, and supports a reversai at
the basal cubrachythoracid cladc (clade B), because camuropiscids and Incisoscutiim share the
plesioitiorphic State of that character, and Coccostem cuspidatus sharcs the aponiorphic State
with both clade A, Bmhanosteus and Muideria. In the two other topologies, character 21 does
not support a reversai because of the respective position of Buchanosleus and Maidcria (Fig. I3B-
C). Character 46 [1] presence of a postsuborbital sensory line on the suborbital plate. This
character (Cl =0.500) .supports a reversai (1 — > 0) in the basal clade [Coccosteus cuspidatus +
Iiicisoscutum] as camuropiscids share the plesiomoiphic State with clade A (i.c. a postsuborbital
sensory line on the suborbital plate).
Two other basal clades are defmed in the strict consensus tree, the Migmatocephala (White,
1972) referred to as clade A, and the Eubrachythoraci, or clade B.
The basal clade migmatocephala
This clade is diagnosed by two uniquely shared derived character (CI = 1.000):
— long nuchal and paranuchal plates 11 [1] and;
— médian dorsal plate shorter than broad 38 [1].
Three homoplastic characters (39, 40 and 42) occur at this node of which only one is com-
mon lo ail topologies (Fig, 13A-C):
— the absence of a posteriorly excavated carinal process (see above for the homoplastic
characters of the basal brachythoracid clade) 40 [1] (CI = 0.667). The explanation for this trans¬
formation [2^1] is the occurrence of the apomorhic State in Maideria-, and the presence of the
plesiomorphic State in Htdoneina, which led to consider this genus as a “primitive” brachythoracid
(Young, 1981. Fig. 5).
The two other homoplastic characters are;
— absence of a posterior spine of the médian dorsal plate 39 [I] (CI = 0.333). This ho-
moplasy occurs in the topology 2 and 3. It supports a reversai in Coccosteus cuspidatus in the
three topologies (presence of the plesiomorphic State), and appears in parallel in the basal clade
B in the topologies 2 and 3 (Fig. 13B-C), its CI (Cl = 0.333) has a low value;
— presence of a high dorsal lamina of the anterior latéral plate 42 |l| (CI = 0.50')) in the
topology I when Buchanosteus is the sisler taxon of (clade A + clade B]. On the contrary this
character is interpretcd as a uniquely shared derived character in the topologies 2 and 3 (Fig. I4B-
C), when Buchanosleus is the sister taxon of clade A.
Two clades are diagnosed in clade A. The first one is the clade [Tityosteus + [Antineosteus
+ Homostius] ] and is supported by one synapomorphy;
— absence of the occipital cross-commissure 48 [2]. And two homoplastic characters;
— a médial ly higher articuiar condyle of the anterior dorsolateral plate 13(1] (Cl = 0.333),
a character which is parai lely derived in HoIonema\
— a pectoral fenestra open by absence of the posterior ventrolateral plate 34 [1]
(CI = 0.500).
— 198 —
Character 13 [I] is derived parallely in Holonema and Buchanosteus in the three topologies,
like character 34 [1] which appears in parallel in Incisoscutum, even though this genus still has
posteroventral and posleromedian ventral plates.
The other clade [Antineosteiis + Homostius] is supported by a single uniquely derived
character:
— absence of poslerior latéral and posterior ventrolaleral plates 36 [1].
Four homoplastic characters are common in the three topologies:
— posteroventral position of the levator muscles pits on the ventral surface of the nuchal
plate 7 [1] (0.667);
— no overlapping contact between the suborbital and postorbital plates 14 1 1 1 (CI = 0.333).
This character supports two reversais in the topology 1 , of which one occurs in Holonema, and
one reversai in the topologies 2 and 3. The latter reversai is common to ail topologies;
— inferognathal with a posterior non biting portion 31 [1] (Cl = 0.500). This character is
parallely derived in clades [Antineosieus + Homosüus] and [camuropiscids + [Coccosteus cuspi-
daius + Incisoscuium] ];
— no supraorbital sensory line on the centrai plate, 44 [I — >0] (CI = 0.667). This character,
coded as polymorphie in Arctolepis decipiens, supports a reversai at this node in each topology.
The basal clade eubrachythoracf
The basal Eubrachythoraci clade, or clade B, is supported by four uniquely shared derived
characters (CI = I.OOO):
— preorbital plate embayment of the central plate 16 [1];
— no denticulation on the occlusal surface of the anterior superognathal plate 30 [1];
— supraoral and infraorbital sensory Unes connected on the suborbital plate 47 [1] and;
— occipital cross-commissure directed toward the nuchal gap and/or présent on the extras-
capular plates 48 1 1].
Nine homoplastic characters support this clade. of which only three are common to the
three topologies (Fig. I3A-C), lhey are:
— a posterior position of the anterior edge of the pineal plate compared to the anterior
edge of orbit 5 [1 -9 0J (Cl = 0.500). This character supports the same reversai in Tityosteus:
— small and laterally placed orbits 23 |l] (Cl = 0.750);
— an omamented branchial lamina with a large ventral lamina of the interolateral plate
41 [2] (CI = 0.667). This character supports a reversai in Coccosteus ciispidatus as a terminal
taxon which has a short ventral lamina of interolateral plate (41 [l |).
The other six homoplastic characters supporting this clade B are:
— paranuchal plate process onto the central plate determining a latéral lobe 12 [1]
(CI = 0.500). This homoplasy is parallely derived for the clade A;
— no contact between central and marginal plates 18 [1] (CI = 0.333). This homoplasy is
common to the topologies 1 and 3 for the clade Eubrachythoraci;
— 199 —
— loss of contact between preorbital and pineal plates 19 [2] (CI = 0.400). This character
supports a reversai for camuropiscids (19 [1—^0]), and is parallely derived in Homostius and
Tityosteus in both topologies 2 and 3;
— ab.sence of postérolatéral process of the postorbital plate 21 [1 ->0] (CI = 0.333). This
character is a reversai in the topology I (see discussion on this character in the diagnosis of
basal cladc A);
— médian dorsal plate without a posterior spine 39 [I] (Cl = 0.333), This character is ho-
moplastic with respect to the cladc Migmatoccphala and supports a reversai [I — >0], in Coccosteus
cuspidatus as a terminal taxon in both topologies 2 and 3;
— presence of a ventral sensory line on the anterior ventrolateral plate 49 [1] (CI = 0.500).
This character is parallely derived in Maideria as a terminal taxon, in topologies 1 and 3. and
constitutes a uniquely shared dérivé character in topology 2, for the clade uniting Maideria and
clade B as sister taxa.
Within the basal clade Eubrachyihoraci a monophyletic group units [camuropiscids + \Coc-
costeus cuspidatus + Incisoscuium] ] and is diagnosed by six uniquely shared derived characters
in each one of the three topologies (Fig. 13A-C):
— a concave posterior margin of the nuchal plate, 9 [1];
— a continuons posterior nuchal thickening under the entire occipital région of the skull-
roof, 10 [1|.
— separatc quadrate and autopalatine ossifications, 15 [1];
— the presence of a dorsal process of the anterior superognathal, 28 [Ij;
— an occlusal surface of the inferognathal plate without denticle, 32 [l);
— the interolateral postbranchial lamina, and the anterior border of the antérolatéral plate
convex in dorsal view with a latéral branchial space anteriorly inclined, 37 [1].
Seven homoplastic characters are retained at this level, of which five are common to each
topology:
— triangular shape of the rostral plate in dorsal view, 4 [ 1 ] (CI = 0.500);
— a short contact between the cheek plate and the latéral margin of the skull-roof 25 [1]
(CI = 0.500). Character 25 is homoplastic (parallely derived) with respect to Maideria;
— development of '“teeth” on anterior and latéral margins of the occlusal surface of the
anterior superognathal plate, 29 [2] (CI = 0.667). This character supports the transformation (29
[2^1]) for camuropiscids in each topology;
— inferognathal plate with a posterior. non-biting portion 31 [I] (Cl = 0.500). Character
3 1 is also homoplastic (parallely derived) with the clade [Antineosteus + Homosiius] in the ihree
most parsimoniüus topologies (Fig. I3A-C);
— absence of a deep groove liniitcd by two lamina on the ventral face of the inferognathal,
33 [1] (Cl = 0.500). This character is parallely derived in Homostius.
Two more homoplastic characters appear independently in topology 2 and 3:
— the posteroventral position of the fossa for the levator muscles on the ventral face of
the nuchal plate, 7 [1 j. This multistate homoplastic character is retained also at the node uniting
the basal clade A and Buchanosteus in topology 2;
— 200 —
— suborbital plate overlapping postorbital plate, 14 [1] (CI = 0.333). This character supports
a reversai (14 [1 ^0]), at the basal node of the clade [Antineosteus + Homostius] in topologies
2 and 3.
The three most parsimonious topologies differ by the position of two taxa. Buchanosteus
and Maiderki. In topology ! (Fig. 13A), Buchanosteus is excluded from clade A bccause it does
not .share synapomorphies 11 fl] and 38 fl], and Maitleriu from clade B because it does not
share .synapomorphies 16 [1], 30 fl], 47 [1], 48 [1| which diagnose it. The characters 12 (I]
and 35 [l| arc synampomorphies supporting the clade [Buchanosteus + fclade A + clade B] ].
In topology 2 (Fig. 13B), the node uniting Buchanosteus and clade A is diagnosed by syn-
apomorphy 42 fl] fan anterior latéral plate with a high dorsal lamina), and by eight homoplastic
characters (7 fl], 8 f2], 12 fl], 14 fl], 21 fl]. 26 fl], 41 fl], 51 fl]). Maideria is united to
clade B by sharing synapomorphy 49 fl] (presence of a ventral sensory line on the anterior
ventrolateral plate), and one homoplasy (character 18 fl]).
In topology 3 (Fig. 13C), Buchanosteus is linked to clade B by the same synapomorphy
as in topology 2, and also by six homoplasies (8 f2], 14 fl], 21 fl], 26 fl], 41 fl], 52 fl]),
which are common to topology 2. In topology 3, the node uniting fclade B + [Buchanosteus +
clade A] ] is supported by two homoplastic characters (46 fl] and 7 fl]) and by two uniquely
shared dérivé characters: paranuchal piale process determining a latéral lobe of the central plate
(12 fl]), and by a short latéral pectoral process of the spinal plate (35 fl J).
lll|.2tl|.6[ll
48 121
36111
I6[ II,. 301 11.4711], 481 II
9121.10111,0111,
281 11, 321 U, .37111
- Dicksonosteus
• Arctolepis decipiens
- Maideria -
-Buchanosteus
- Tæmasosteus
- Tityosteus
-Antineosteus
-Homostius —
• Hotonema
Migmatocephala
• Camufopiscids
- Incisoscutum
- Coccosteus cuspidahjs — '
Eubrachythoraci
Brachythoraci
Fig. 14. — Slrici consensus ircc of the three topologies, with a classification of brachythoracids, from PAUP 3.0 s, at 107 steps
including 12 taxa and 53 unordered characters. The synapomorphies occuring at each nodes are placed in brackets.
Arhre consensus strict des trois topologies également parcimonieuses, avec une classification des brachythoracides obtenue
à partir de PAUP 3,0 s {}08 pas, 12 taxa, 53 caractères non ordonnés). Les synapomorphies défini.^isunt chaque nœud sont
placées entre crochets.
— 201 —
SYSTEMATIC REMARKS
Compared with the phylogenetic analysis of Carr (1991, Fig. 20) the phylogenetic scheme
presenied herein (Fig. 14) is more resolved wilh respecl to relationships of lhe whole brachy-
thoracids, e.Kcepl for pachyosteomorph relationships whicli are not the topic of this analysis. The
définition of the monophyly of lhe "primitive brachythoracids” given by Carr (1991) only for
Homostius and Buchantisteus agréés with the synapomorphies retaincd in lhe phylogeny (Fig. 14).
The monophyly of lhe Eubrachythoraci, supported by four synapomorphies, will probably be
mainlained when pachyosteomorph taxa will be added to Ihis analysis.
The taxon Migmatocephala, erected by WHlTli (1972), includes Antineosteus, Homostius,
Tœmasosteus, Tityosteus, and Arenipiscis (.sec conimenis abovc), but not Buchanosteus as en-
visaged by WHITE. because ils phylogenetic position is not fixed according to lhe discussed
phylogenetic analysis. Although Goodradigheeon, was not analy.scd here, il shares lhe same mor-
phological pattern of the inferognathal plate as Antineosteus and, consequenlly, could be included
in the Migmatocephala. The characters used by WittTE (1972: 381) to characlerize the Migma¬
tocephala (i.e. separate rostropineal plate, short preorbital plates wilh complété médial contact,
orbil large and directed obliquely forward), are not retained as synapomoiphies for this clade,
but rather interpreted as plesiotnorphic features or not coded in the matrix. CARR (1991) gave
a diagnosis of the 'primitive brachytlioracids’ in which one synaponioiphy is shared with the
présent analysis; the long paranuchal and nuchal plates. The character (53) does not support the
monophyly of Migmatocephala, while it appears in Carr’s analysis as a synapomorphy
(character 82). This discrepancy is explained by the facl that lhe taxa coded are not the same
and because of the different coding. 1 consider Buchanosteus as plesiomorphic for this character.
Carr’s character 31 is not coded in my analysis. In the présent analysis, lhe Eubrachythoraci
includes Holonerna (Fig. 14). This conclu.sion differs from Carr’s phylogeny (1991, see Fig. 2üB,
D), and this phylogenetic position of Holonerna explains the différences between the two diag¬
nosis for lhe Eubrachythoraci. The monophyly of the coccosleomorph arthrodires (Carr, 1991)
[camuropiscid-s + [Coccosteus cuspidulus A Incisosculum] ] (Fig. 14). is supported by six syn¬
apomorphies of which two are shared in both analysis, characters 10 [l] and 15 | l|.
The presence of Holonerna as the most primitive Eubrachythoraci is argued for by four
synapomorphies and implies the interprétation of some characters as homoplastic features while
they are commonly used lo argue for the phylogenetic position of Holonerna as a primitive
brachythoracid. These characters are: lhe absence of a cannai process on the médian dorsal plate
(character 40[0]), lhe occurrence of a large submarginal plate (character 26(01). lhe co-ossified
palatoquadrale (character 15[0]), and a long thoracic armour. One stress lhe facl thaï some of
this characters are functional. Maideria is the most primitive brachythoracid but il is incorapletcly
known. Some characters are interpreted as homoplastic such as the development of a long snout.
This feature was known until now in lhe Late Devonian Eubrachythoraci from Gogo (Australia)
and Wildungen (Germany ). The (Kcurrence of the ventral sensory line on the anterior venirolaleral
plate is retained as the only uniquely shared derived feature to place Maideria as the sister-
taxon of Eubrachythoraci, this phylogenetic position occurs in only one of the topologies
(Fig. 13B).
Coccosteomorph arthrodires including camuropiscids. Incisosvutum. and Coccosteus cuspi-
datus are monophyletic, but an analysis including Eastmanosteus calliaspis, plourdosteids or
torosteids, Moroccan dunkleosteids, Dunkleosteiis terelli and pachyosteomorphs (aspinothoracid
arthrodires) will be a test for some of the synapomorphies considered in this analysis (Fig. 14).
POSSIBLE EVOLUTIONARY TRENDS WITHIN BRACHYTHORACIDS
Placoderms are known from the Middle Silurian (GOUJET. pers. comm. on Chinese material).
Brachythoracids appeared as early as the Entsian in the Gundwana (Morocco. Iran and Australia)
whcrc they arc both dated by conodonts. Among placoderms. brachythoracids are considered as
the mosi derived and diversified group. They hâve their younge.sl représentatives in the Famen-
nian. For a very long time brachythoracids were considered to be homogenous, bul some authors
nevertheless recognised a mosaic évolution, in contrast Mil ES ( 1969) considered brachythoracids
as ‘a valid evolutionary group even though the différences between them in the development of
the trunk shield are not aiways clear-cut’. Evolutionary trends within brachythoracids are pro-
posed considering the most recent phylogenetic analyses (Young. 1981; Gardiner & Miles,
1990; Carr, 1991 ).
Evolutionary trends relative to the skull-roof are most difficult to trace by comparison to
the variable pattern of lhe Migmatocephala and the more stable one of tlie Eubrachythoraci. The
postenor part of the skull-roof is constrained to a greater stability when a posteriorly broad and
thick nuchal région has been developed in connection with the development of a dermal artic¬
ulation, and the long nuchal and paranuchal plates hâve been lost This région is strengthened
by a complété nuchal thickening within the Eubrachythoraci. bul a variation occiirs as to the
disposition of lhe nuchal pits on lhe ventral surface of the nuchal plate, and the development
of the concavity of the posterior margin of the skull-roof.
The prcntichal part of the skull-roof exhibits the most variable pattern, and several of them
may be dcscribed. The présence of a rostropincal plate occurs in buchanosteids (Biichanosteus
and Envl(is(Ciis) and in Arenipiscis^ according to (Young. 1981. Fig. .“i). The rostral plate is
primitively wide, as in Antiiwosit^us and then tends to become triangular shapc as in the Eu¬
brachythoraci. A rostropincal plate is known to date only in Australian or Gondwanan brachy-
thoracid taxa.
The orbits are primitively anteriorly placed in the Migmatocephala, whereas they face later-
ally in the Eubrachythoraci, lhe latéral position is not retained as a synapomorphy. contrary to
Lei.IF.VRE (1984a, 1988). The composition of lhe dorsal orbital margin changes as well. In the
outgroups and the Migmatocephala, the dorsal orbital margin is composed by threc or more
plates, including the posina.sal, preorbital and posloibital plates. In the Eubrachythoraci, only
the preorbital and lhe postorbilal plates coiistilute the dorsal margin of the orbit; the postnasal
piales are situated in a more anlerior position, together with the anterior nostrils. One can as-
sociate this pattern with the résorption of the elhmoidian fissure and ils replacement by a blood
vascular plexus, related to lhe pineal plate pattern, the course of the médial contact between the
preorbital plates, and the more anteriormedial position of the nasal capsules (see comments p. 175-
176). The development of the suborbilal lamina of the suborbilal plate is more pronounced in
— 203 —
the Eubrachythoraci because of the latéral position of the orbits, while it is short in the Mig-
matocephala because of the more anteriorly located orbits. The remodelling of this région and,
mainly, the displacement of the posinasal plates in a more anteromedial position implies a contact
between the suborbital and the preorbital plate. This contact was between the suborbital and
postnasal plates in the Migmatocephala and Buchanosteus. This latter disposition is retained in
camuropiscids. One exception lo this general scheme is given by the autapomorphic pattern of
Homostius.
A closed angle (less than 90”) between the two branches of the infraorbilal sensory line
on the suborbital plate, considercd as a .synapomorphy of the Migmatocephala (Lelièvre. 1984a.
1988), does nol support any monophyletic group A tendency lowards the disappearance of the
supraoral sensory line is observed in pachyosteomorph.
The development of the ventral structures of the skull-roof in Eubrachythoraci increases.
compared to their relative importance in Migmatocephala. Il is the case for the latéral Consolidated
région and the development of the supraorbital vault; these charactcrs were not coded here, but
by Carr (1991: 381).
For a long lime, the trilobate central plates hâve been considered as diagnostic of the ‘coc-
cosleids’. Carr (1991: 379) has shown the ambiguity of this lerm, and proposed to subdivide
this characier into three discrète characters, among which the presence of an embayment for the
preorbital plate in the central plate is a synapomorphy of the clade (camuropiscids + [Coccosteus
cuspidatus + lncisoscutum\ \ or of the clade ‘coccosleomorph arthrodires’ of Carr (1991).
Even though the gnalhal éléments of the Migmatocephala are imperfectiy known. their in-
ferognathal seem to exhibit such plesiomorphic features as the presence of many denticles and
a blade portion opened ventrally. It would be astonishing if new discoveries of gnathal éléments
of the Migmatocephala differ fundamentally from this plesiomorphic type, which consisis of
gnathal éléments with many denticles. as found in Goodradigbeeon and Anüneosteus. This irend
is supported by one of the four synapomorphies diagnosing the Eubrachythoraci: the absence of
denticles of the anterior superognathal plate, and aiso by the occurrence of a dorsal process on
the anterior superognathal plate, which supports the monophyly of the basal clade (camuropiscids
+ [Cocco.çft’M.r cuspidatus + Incisoscutuiii J J.
The thoracic armour of the Migmatocephala reveals different patterns. The pectoral fenestra
is either open (e.g. Antineosteus and Homostius) or closed in Buchanosteus. The former dispo¬
sition is linked lo a short thoractc armour, with a developed condyle on the anterior dorsolalcral
plate and a short médian dorsal plate bearing ventrally a keel and a pronounced unexcavated
carinal process. A posteriorly excavated process is constant in coccosteomorphs and pachyosteo-
morphs wether or not the médian dorsal plate is long; however it occurs ai.so in Buchanosteus
and Maideria. The position of Holonema shows lhat this functional character defined on the
médian dorsal plate could be absent of the diagnosis of the basal Eubrachythoraci clade.
The loss of the posierior médian ventral and poslerior ventral plates is a synapomorphy of
Antineosteus and Homostius (may be also Tityosteus). It is associated with both short médian
dorsal plate and latéral wall of the thoracic armour.
Two di.spositions occur for the spinal plate. A short spinal plate (the p.seudospinal plate of
Miles & Dennis, 1979; .see also Gardiner & Miles, 1990: 198) lacking a latéral process and
an internai spinal pit, is found in Homostius. Another disposition occurs in Buchanosteus, in
— 204 —
which the spinal plate is long and straight according lo White & Toombs (1972); however
nothing is known about the internai surface of this plate. This disposition is the spinal structure
retained as plesiomorphic by Gardiner & Miles (1990) for Coccosteus, Plourdosleus, Harry-
toomhsia and Torosteus for instance. Réduction and transformations of the spinal plate may well
hâve occurred several times; thus, phylogenetic irends are difficult to trace, e.xcepl for the absence
of the latéral pectoral proccss in brachylhoracids. Somc brachythoracid généra hâve an anterior
latéral plate with a high dorsal lamina, a synapomorphy uniling Btichaïuisieiis with the Migma-
tocephala. Other characters of the thoracic plates, such as the development of the apron, hâve
been discussed by White (1952). His conclusion does nol takc into account the anterior orien¬
tation of the ventral lamina of the interolateral plate and of the branchial space. Character 41
deals with the development of the ventral lamina of the interolateral plate, together with the
occuiTcncc of an ornamentation. The presence of the omamentation is derived for Eubrachythoraci
and Migmatocephala, but the development of the ventral lamina, which remains short in Coc-
cosieus cuspidcmis, as well as in the Migmatocephala, is parallely derived. While Hokmema,
camuropiscids and Incisoscutum share a large ventral lamina.
The Migmatocephala is a clade, charactcrized by a particular morphological design of the
skull-roof. The earliest record of this taxon is Emsian. while the youngest record is probably
from the Lower Givetian, with Homostius as the youngest known genus, and described only
from Laurasia (Scotland, Estonia and Canada). There is no représentative during the Middle
Devonian in the Gondwana, but the clade is the most diversified in Australia, where the oldest
record is found.
Acknowledgements
I want to expres.s my ihunks lo R. Cl.OlTiHR, D. F. GoL'Jl-T. Ph. Janvii-R and G, C. YOUNG, for
valuable commenis on the preliminary drafts of the manuscripl. Thanks to C. Fai.ipoo who gave generousiy
some of the specimens described in this paper. I thank Dr M. Bkn Said and Dr M. Dahma.ni of the
Ministère des Mines et de l'Énergie of Rabat, Maroc, for the facilities they provided me during .several
field Works on the Devonian of Tafilalt and Maider, K. Bryan-Dennis and R. Cakr for usefui discussions
and encouragements on placoderm évolution, and the anonymous reviewer(s| of the final paper. Thanks
to D. Serrette (URA 12 du CNRS) for the photographs.
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Table I. — Data malrix of 53 characters for 12 taxa. Arenipiscis, while nol laken into accouiit in ihe interrelationships of brachythoracids, is coded in the data
matrix. f0| = plcsiomorphic stalc, [!-2] = apomorphic States, f?| = character State missing. Synapomorphies (CI = l.ÜOO) are indicated in bold.
Matrice de données de 53 caraclères pour J 2 uaa. Le codage des caractères r/'Arenipiscis est donné bien que ce liixon n’ait pas été pris en compte dans
l'analyse des relations de parentés des BrochythoracU. lOf = état plésiomorphe. 11-2} - états dérivés, {?] = caractère non nhser\‘é. Les synapomorphies
dont le Cl = 1.000 sont indiquées en gras.
207
Bull. Mus. natl. Hist. nat.. Paris, 4® sér., 17, 1995
Section C, n" 1-4 : 209-226.
Plicatodus jordani n. g., n. sp., a new xenacanthid shark
from the Lower Permian of Europe
(Saar-Nahe Basin, Germany)
by Oliver HAMPE
(A contribution to IGCP 328-Palaeozoic Microvertebrates)
Abstract. — By means of a partial anterior skeleton within a nodule, a new xenacanthid shark, Plicatodus
jordani n. g., n .sp., is described front the Lower Permian of the SW-Germaii Saar-Nahe Basin. Its tricuspidate
teeth show wuvy cristae of hybodontoid pattern, and an extreraely lluttened base with a coronal button, histo-
logically made of orthodentine. These characterLstics are different from the currently known xenacanthid généra.
The Bohemian ‘'Orthacanihus" plicuius belongs to the sanie genus and is reviewed here. A cladogram of the
order Xenacanthida is given, ba.sed only on hard parts, using ctenacanthids for oulgroup comparisori.
Keywnrds. — Venehrata, Chondrichihyes, new taxon, Lower Permian. Germany, anatomy, phylogeny.
Plicalodus jordani n. g., n. sp., un nouveau xénacanthe
du Permien inférieur d’Europe (bassin de la Sarre, Allemagne)
Résumé. — Un nouveau requin Xénacanthide, Plicalodus jordani n. g., n. sp., du Permien inférieur du
bassin de la Sarre (sud-ouest de l'Allemagne) est décrit à partir de la partie antérieure fragmentaire d'un squelette
contenu dans un nodule. Ses dents tricuspides présentent des crêtes ondulées semblables à celles des Hybodon-
toïdes. et une base très aplatie portant un bouton coronal formé d 'orthodentine. Ces caractères diffèrent complè¬
tement de ceux que l'on connaît des autres genres de Xénacanthides. «Ortliacanthus» plicatus de Bohème est
révisé et attribué à ce nouveau genre. Enfin un cladogrammc de l’ordre des Xenacanthida est proposé; il est
construit sur les seuls caractères de.s dents et des épines, et utilise les Cténacanthides comme groupe extérieur
pour la comparaison.
MoLs-clés. — Vertebrata, Chondrichthyes, nouveau taxon. Permien inférieur. Allemagne, anatomie, phylo¬
génie.
O. Hampe, Institut fur Geowissenschaften, LE Palaontologie, Johannes Gutenberg-Universitat, D-55099 Mainz, Allemagne, Ger¬
many.
Introduction
The Xenacanthida are a fossil order of elasmobranchs of predominantly Paleozoic âge, which
very succe.ssfully adapted to freshwater. Their remains are known from many sites in the world.
They occur in North America (e.g. Hotton, 1952; Texas; LUND, 1975: Appalachians; Masson
& Rust, 1984; Canadian Atlantic Provinces). Europe (e.g. Hampe, 1989; Germany; Fritsch,
1889: Bohemia; Heyler & POPLIN, 1989: France; Agassiz, 1843; UK; Heintz, 1934: Norway;
SOLER, in Mit.: Spain; SCHNEIDER, pers. observ.; Ukraine), South America (Würdig-Maciel,
1975: Brazil); India (Jain, 1980) and Australia (TURNER, 1982).
— 210 —
The SW-German Saar-Nahe basin consists of Upper Carboniferous and Lower Permian flu-
vio-lacustrine deposits which are very rich in xenacanlhid material. It is thc larges! Permo-Car-
boniferous molasse basin within the Variscan orogenic chains (SCHÀFER, 1989) in Central Europe.
Surface access is possible within an area of 100 x40 km ju.st South of the Renish Schiefergebirgc.
Within the Saar-Nahe Basin isolated teeth and many articulated skeletons are distributed in over
one hundred localities of lacustrine and deltaic environments.
The main characteristics of xcnacanthid sharks arc: an elongated dorsal fin extending from
dircctiy bchind the shoulder girdle to thc level of lhe usually diphycercal caudal fin, from which
it is separated by a notch: lhe skeleton of the pectoral fins shows a long segmented central axis
with radiais diverging from both the pre- and postaxial borders r‘archiplerygium"-type); ail
xenacanthids possess a dorsal spine, which articulâtes with Lhe neurocranium or can be placed
in its back in the neighbourhood of thc shoulder girdle (Kner. 1867; Fritsch, 1889, 1895;
JAEKEI., 1906; ZangERL. 1981; Heidtke. 1982; KlaUSEWITZ. 1986, 1987; ZiDEK, 1988; PoPUN
& Heyler, 1989).
Xenacanthids are often recognized by their distinctive dentition. Their teeth hâve a tricuspid
Crown with two latéral main cusps and an often distinctiy .smallcr and more délicate médian
cuspule. The base is drawn out lingually and bears a coronal button on its top and a basal
tubercle on its bottom side. Compréhensive investigations of teeth of the généra Ort/iacanthus.
Xenacanthiis and Triodus are given by Hampe (1988a. b; 1989; 1991). The terminology used
in ihis article is based on these papers.
A recently discovered nodule from the “Lebacher Tonei.sensteinlager” (found at the Uni-
versity of Leipzig by SCHNEIDER) shows a partial craniai skeleton of a xcnacanthid (including
parts of the palatoquadrate, mandible, branchial skeleton. shoulder girdle, spine fragment) with
teeth having some features tolally different to the known généra.
Fritsch ( 1 889) described an isolated tooth from the Stephanian B from Bohemia under
the name Onhiicantlnts plicatiis. Only a few additional teeth of this kind were subsequently
collected from boreholes of approximately the same stratigraphie level (ZajIc, pers. comm.).
The Bohemian teeth and the SW-German nodule belong to a new genus called Plicatodus.
This paper deals with the présentation of the species P. jordani (n. sp.; Germany) and P. plicatus
(Fritsch; Bohemia).
Abbreviations
ang angle between crown and base in latéral view, angle entre la couronne
et la hase en vue latérale ;
bs base, base-,
bt basal tubercle, tubercule basal ;
cb coronal button, bouton coronal ;
ebr ceratobranchials, cératohranchiaux -,
chy ceratohyale, cératohyal ;
cr crown, couronne',
dep basal dépréssion of basal tubercle, dépression basale du tubercule basal ',
gd gill denticles, denticules branchiaux:
le latéral cusps, cuspides latérales'.
— 211 —
man mandible (Meckel’s cartilage), mandibule (cartilage de Meckel);
me médian cuspule, petite cuspide médiane ',
na neural arches, arcs neuraux ',
nf nutrient foraniina, nourriciers-,
pc pulp cavity of spine, cavité pulpaire de l’épine-,
pq palatoquadrate, palatocarré ;
SC scapulocoracoid, scapulacuracuïde ',
sh lingual shaft of coronal button, prolongement lingual du bouton coronal;
sp spine, épine',
tpr tongue-shaped process of the base, processus linguiforme de la base ;
va ventral arches, arcs ventraux',
vc vertical cristae, crêtes verticales.
BAF Bergakademie Freiberg, Germany;
GPL WB Geophysik, University of Leipzig, Germany;
NMVP Nârodni Muzeum of Prague, Czech Republic;
UUG Ustrednf ûstav geologicky, Prague (“Geological Survey”), CZ.
MATERIAL AND METHODS
The relatively poor material of the new taxon Plicatodus (low number of teeth) was inves-
tigated at the National Muséum in Prague and at the Bergakademie in Freiberg/Saxony. The
Lebach-nodule was lent from the University of Leipzig. Ail material was compared with the
diverse and rich xenacanthid fauiia from the Upper Carboniferous and Lower Permian deposits
of the Saar-Nahe and Bohemian basins,
The documentation of the anterior skeleton, which is the only persistent part within the
nodule, was supported by X-ray examination.
The histological .structure of the teeth of Plicatodus jordani is shown by application of
fluorescence microscopy. For this method no thin sections, but only cuts with a polished surface
of the objects are needed to analyze them under incident light.
Fluorescence microscopy uses transmitted light and, in particular, incident fight for the ex¬
citation of fluorescence radiation. If an object is irridiated by short-wave excitation light, fluoresc-
ing substances will omit light of spécifie colors, while the non-fluorescing background remains
dark. Suitable excitation filters are used to select those wavelengths which cause fluorescence
exacTly out of the light coming from the source. AU other wavelengths which do not contribute
to the fluorescence in question are eut off by barrier filters. For this investigation an excitation
with blue light (range 420-490 nm) was used.
Polished sections of teeth, prepared oui of the replacement battery of the nodule, were
made in the following way; single teeth were embedded in bio-resin; then the object was eut
and during repeated grinding-down a sériés of cuts after the principle of tomography had been
obtained (for detailed information to this procedure, see Hampe, 1991).
— 212 —
Ail investigations were carried ont using a research microscope with an incident light fluores¬
cence illuminator, equipped with filtercube de vices, halogen lamp and automatic caméra.
The vascularization System is documented by the existence of broken teeth or by mechani-
cally eut material.
SYSTEMATIC PALEONTOLOGY
Class CHONDRICHTHYES Huxley, 1880
Subclass ELASMOBRANCHll Bonaparte, 1838
Order XENACANTHIDA Ghkman, 1964
Family XenacanthIDAE Fritsch, 1889
Genus PLICATODHS n. g.
Type SPECIES. — PUcatodus jordani n. g., n. sp.
DIAGNOSIS. — Dorsal spine, laterally equiped with a single row of denticles, which articu¬
lâtes with the occipital région of the head; tricuspidate teeth; crown wearing curved or wavy,
sometimes splitted vertical cristae (hybodontoid pattern); often extremely flattened base; rounded
coronal button on the upperside of the base; rhomboid or rounded basal tubercle with depressed
Socket on the bottom side.
Etymology. — After the peculiar pattern of cristae on the teeth (lat.: plica = crease).
Remarks. — Several characteristics of Triodus and Xenacanthus are combined within the
genus PUcatodus.
PUcatodus shares wide lumina of the pulp cavities and vertical cristae bcaring cusps with
Triodus. However, the hybodont-like pattern of the cristae is different from that of Triodus. Gener-
ally common between Xenacanthus and PUcatodus are the llaltened base, the large number of
nutrient foramina and the often relatively .small and fiat coronal button. The cusps of most
Xenacanthus species hâve lanceolate cross-section, which are only slightly indicated in Plica-
todus.
Referred species. — PUcatodus pUcatus (Fritsch, 1889), Stephanian B of Bohemia/CZ;
PUcatodus jordani n. sp., Lower Rotliegend of the Saar-Nahe Basin/SW-Germany; (?) PUcatodus
santosi (Würdig-Maciel, 1975), Upper Permian of Porto Alegre/Brazil.
Plicatodus jordani n. sp.
(Figs. 1-5)
1988 Xenacanthus plicatus A. Schneider: 74, Figs. 3.7, 4; PI. I, Fig. 11.
Diagnosis. — A species of the genus Plicatodus with following characteristics: dorsal spine
which articulâtes with the neurocranium, having rows of denticles situated on its latéral faces.
Teeth with a height of 1-3.5 mm; cross-section of cusps near the base elliptical, doser to the
tip polygonal (cristae!); height of médian cusp reaching 1/2 to 1/3 that of latéral cusps; latéral
cusps having between 4 and 10 partly wavy or curved vertical cristae (hybodonl pattern); outline
of the base rounded with a mesio-distal extent; Hat and rounded. .sometimes rhomboid coronal
— 213 —
button with short suggested shaft; about 16 nutrient foramina on the upperside of the base;
bottom side showing a rhomboid-shaped or rounded basal tubercle with basal dépréssion and
7-15 nutrient foramina; angle between crown and base in latéral view about 100"; vascularization
System consists of a wide pulp cavity below the crown and lingually positioned anastomosing
nutrient canals; crown and base, including coronal button constructed of orthodentine; no
enameloid tissue developed.
Holotype. — GPL 3828a, b, nodule (original plus counterpart) including a partial anterior
skeleton.
Type LOCALITY. — “Lebach” (probably from Rümmelbach-Gresaubach area). Saar-Nahe basin.
Type HORIZUn. — "Lebaeher Toneiscn.siein-Lager” = Humberg-Bank, Uppermost Lauterecken
to Odemheim-Schichten (L-OIO. aftcr BOY & FiCHTER, 1982). Lower Permian.
Etymoeogy. — In honor of the famous H. JORDAN, who had collected and described many
fossils of the “Lebaeher Toneisenstein-Geoden” in the lasl centui7.
DESCRIPTION
The specimen is preserved within a nodule from the famous “Lebaeher Toneisenstein-
Lager”, where hundreds of that kind had been collected during last century. The diameter of
the geode is approximately 14x9 cm.
In GPL 3S28a are observed the left mandible, the surface of the right quadrate région and
mandible. the shoulder girdie, the spine which is partially covered with matrix, and some neural
and ventral arches (Fig. I). The replacement teelh of the right mandible can be seen in basal
view. Behind the jaws, there is also a small area with accumulaled gill dcnticle.s. Each has a
height of about 1-2 mm and mainly consists of two crescent-shaped curved cusps (Fig. 3b) and
a base with some large nutrient foramina and a peg-shaped exlremity.
The counterpart (GPL 3828b) shows the right upper and lower jaw, the impression of the
left mandible. a partial shoulder girdie. the distal portion of the spine, branchial arches, and
teeth of the right palatoquadrate in lingual view (Fig. 2). Some of the information was supported
by radiograph observation.
FIead
The neurocranium is siiuatcd deep in sédiment. .No exact outlines are visible. The cleaver-
shaped, slighlly damaged palatoquadrate has an anterior palatine région (pars palatina) and a
posterior quadrate région (pars quadrata) in which the fairly crushed palatine région seems to
be relatively thin. The quadrate is elevated behind the orbit at 1/3 of the height of palatine
portion. Us anterior border forms the hind margin of the orbit. The posterior margin is convex
and curves gently backwards and downwards. Generally the outlines are not very well docu-
mented. The knob-like articular process is partially covered and not clearly in view.
The much more massive mandible (McckeFs cartilage) becomes reduced in height in the
anterior part, ending like a stem. The posterior half is excavated ventrally on the internai side
to form a fossa; leaving the ventrolateral edge standing out at Ihc exlernal side as a ridge upon
— 214 —
GPL 3828 a
GPL 3828 b
Fig. I. — Pficatodiis jordani n. g., n. sp., GPL 3828a and b, hololype. Partial anterior skeleton from the nodule of the “Lebacher
Toncisenstein-Lager”, Lower Rotliegend (L-OlO), Saar-Nahe Basin. Abbreviations, see lexl. The length of the .spine, drawn
abovc. corresponds wilh 6 cm.
Plicalodus jordani n. g., n. sp., GPL S828a et b, holotype. Partie' antérieure du squelette pmvenant du nodule de la “Lebacher
Toneisenstein Lager'\ Rotliegend inférieur il.-OÎO). bassin de la Sarre. Abréviations, voir texte. La longueur de l'épine dessinée
au-dessus est de 6 cm.
— 215 —
Fig. 2. — Plk ütodus jordani n. g., n. sp., GPL 3828. B. hulolypc. Replacement teeth of the right palatoquadrate in lingual view.
Scale bar wiih intervals of 1 mm.
Plicatodus jordani n. g., n. sp.. GPL 3828. B. bolotype. Dents de remplacement du palatocarré droit en vue linguale. Gra¬
duations de l'échelle: I mm.
which the M. adductor mandibulae inserted during life. The very posterior part, including the
articular région of the mandible, is crushed.
Of the hyoid arch, only the left ceratohyale in GPL 3828b is preserved. It shows an outline
like that of the mandible.
The branchial skeleton consists of five arches, but there is no clear division or séparation
into the single éléments. Probably these are the ceratobranchials.
POSTCRANIAL SKELETON
The pectoral girdle is formed by a pair of large leaf-like scapulocoracoid cartilages which
can be observed qiiite well. They hâve a typical xcnacanthid morphology showing two flexures;
a lower one separated the coracoid part (in this level the posterior directed articular crest for
the pectoral fin can be found), and an upper one. In both halves of the nodule, a row of neural
arches is siluated dorsally between head and .scapulocoracoids and behind the shoulder girdle.
Ventral arches arc only behind shoulder girdle.
S FINE
The dorsal spine, a main characteristic of xcnacanthid sharks, resembles that of genus Tri-
odus which has a row of denticles on each latéral side. The large pulp cavity has normal pro-
— 216 —
portions; the diameter of the cavity in the niiddle and most proximal régions is about 1/2 and
4/7 as long as the average cross-section respectively. The overall length of the spine can be
estimated at greater than 8 cm.
Teeth
The teeth of this newly defined species hâve a height between 1 and 3.5 cm. Their médian
cusp reaches about 1/2 to 1/3 that of the latéral cusps. In cross-section the cusps are elliptical
near the base and become polygonal towards the apical direction. The upper part of the distal
cusp has a sigmoidal curvature, visible from the lingual and labial side. The sculpture of the
cusps consists of 4 to 10. sometimes splitted, cristae. In part, the vertical cristae hâve a wavy,
S-shaped fonn, very similar to that known In hybodont sharks; sometimes they run nearly straight.
The cristae oiiginate at the tip and occupy the upper 3/4 of the cusps.
The base shows a discus-like character: fairly Hat, connected with mesio-distal extension.
A tongue-shaped process is located at the distal pointed curvature of the base. It is separated
by a lingually positioned indentation (Fig. 3d).
On the upper side. a Hat, rounded, sometimes rhomboid coronal button is situated which
also can hâve an oviform outline in labio-lingual extension. A short shaft is indicated. About
16 foramina arc irregularly disiributed on the upperside of the base.
The bottom side has a rhombic to ovoid and considerably strong basal tubercle with a
concave dépréssion. The number of nutrient foramina amounts to about seven larger ones; alto-
gether about 10-15 are possible.
The angle between base and crown in latéral view cornes to approximately 100°.
The vascularization System consists of a wide pulp cavity (Fig. 4) below the cusps. From
this cavity a wide canal extends into each cusp. In this case, the hard tissues of the cu.sps
dcvcloped ralhcr thin. In the médian part of the base, the cavity is divided into a low number
of large canals Crossing through. Multiple nutrient canals with a small internai diameter pass
through the base only in the lingual part.
The dentition of Plicalodus jordani is distinctly heterodontous. The anterior and posterior
teeth are smaller, whereas lhe laterals hâve the largest size. The mesial cusp is vertically oriented.
often with sigmoidal curvature in its latéral view. The distal cusp is directed distally. One set
of teeth include approximately 20-22 tooth familles. Within the holotype, five rows of teeth can
be identified a.s being replacements,
Commissurals of different morphology are known (Fig. 3c). Their height extends to 1 mm.
The Crown bears only two cusps, each showing about 3-4 cristae. Only 2 nutrient foramina
are situated on the upperside of the base. The coronal button is very small and has a narrow,
lingual shaft. There is nothing yet known concerning the bottom side of the commissurals.
HtSTOLOGY
The teeth of Plicatodus jordani, crown as well as the base, consists almost entirely of or-
thodentine (Fig. 5a), like in Triodus (see Hampe, 1991), circumpulpously developed, fluorescing
in light yellow and brownish colors. The design of the dentinal tubules can be demonstrated
— 217 —
d e
FlG. 3. — Tecth of PUratodus joniani. A, GPL 3828b. lingual view. B, GPL 3828b. labial view. C. GPL 3828b. commissural
teeth in lingual view. D, E. GPL 3828a. both in basal view'. The figures show only fragmcniary leeih; they have been drawn
direclly from lhe leplacement of the holotype. The schemes in the upper right présent the general morphology; for abbreviations,
see text. Scalcs: 2 mm.
Dents de Plicatodus jordani. A. GPL 3828b. vue linguale. B. GPL 3828h. vue labiale. C. GPL 3828h. dent commissurale en
vue linguale. D. E. CPI. 3828a, toutes deu.x en vue ba.sale. Les figures montrent seulement des dents fragmentaires qui ont
été dessinées directement à partir du remplacement de l’holotype. Les schémas du haut à droite montrent la morphologie
générale : pour les abréviations, voir le texte. Échelles : 2 mm.
— 218 —
Fin. 4. — Vasculariz:ilion .System oP Plimlodus jordoni in lin¬
gual view. The widc pulp canals wifhin the cusps and a
large caviiy below the ciown arc characleristic loutline
^ brnken line; enional bulinn = dt»tled line).
Système de vasculansudon de Plicaiodus jordani en vue
linjiitale. Les larges t imnux fmlfHiires ù l'intèrvurdes cus-
pides et une vaste cavité putpaire sous la couronne sont
caractéristiques (contour extérieur = tireté : bouton co-
ronal = pointillé).
bcst in horizontal sections of the cusps (Fig. 5b). Near the pulp cavity they are usually arrangée!
in parallel, but show an arborescent embranchment in the outer zones.
In vertical section the material of the relatively fiat coronal button looks rather homogeneous.
It is suspected, that the button aiso contains orthodentine (Fig. 5c). An enameloid is absent.
Plicatodus plicatus Fritsch, 1889
(Fig. 6)
1889 Orthacanthus plicatus Fritsch: 112; PI. 88, Fig. 13.
1988 Xenacanthus plicatus A. Schneider: 74. Figs. 3, 6; PI. I, Fig. 10.
HOLOTYPE. — NMVP -M 305, one tooth.
Type loc.'VLITY. — Knezeves near Rakonitz, Bohemia/CZ.
Type horizon. — “Grauer Schieferton”, Kounov member, Upper Stephanian B.
Occurrence. — Stephanian B and C (?) of Rakonitz basin, Bohemia/CZ (see ZAJi'c &
Stamberg, 1985).
Description. — The five investigated teeth are housed in the Nârodni Muzeum in Prague
and in the collection of the Geological Survey of the Czech Republic.
Teeth
Their height is documented between 2.5 and 6 mm. The médian cusp reaches 1/4 to 1/3
that of the latéral cusps. Often accessory cuspules can be found beside the médian one. The
latéral cusps look comparatively massive. They hâve an elliplical (slightly lanceolate) cross-sec¬
tion. In labial-lingual view the latéral cusps are sigmoidally curved throughout their upper part.
— 219 —
Fig. 5. — Hi.slology of PUcatodits jordani. A, vertical section of an entire toolh: crown and base consisl of orlhodentine with
clearly dcTinablc growth tainellac (x^43). B. horizontal section of a latéral ciisp: in direction to the cenler (pulp border), the
dcniinal tuhiilcs arc arrunged ncarly in paruHcl; m ihc outer ^ones lhey show un arborescent cmhranchment txX7). C. vertical
section throngh Ihc médian part of a buse: circuinpulpously devcloped orÜKKJentinc wilh Ihrce large central pulp catials and
four small nutrtent canals helow the coronal button. Thcre is no différence asccrtainablc duc to the histological structure of
the coronal button (x70).
Histologie de Plicalutlus jordani. 4, scvtioti verticule d'utte dent entière : ta couronne et lu hase consistent eu de l't>rtht>dentine
avec des stries de croissance bien définies li. seexion hon:<mtale d'une cuspide huémle: en direction du centre
(marge pulpatrc). tes lubuUs de la dentim sont dispftsrs presque pontUèlenieul ; dans ta zone tLiierne. elles pré\euttnl des
ramifications (x 87). C, section verticale a travers la partie médiane de la base : orthodentine péripulpaire avec trois grands
canaux pulpaires centraux et quatre canaux nourriciers sous le bouton coronal. Il n'y a pas de différence notoire due à la
structure histologique du boulon coronal (x 70).
On the ciisps’ surface, between 10 and 14 strong and wavy vertical cristae are visible which
do not regularly originale at the tip. Generally the cristae cover the entire height of the cusps.
This kind of pattern can be noticed in hybodont sharks.
The base is very Hat (“pizza”) and mesio-distally elongated. The lobe-like shaped mesial
edge is often bent downwards (Fig. 6a. c).
The upper side of the base has a small rounded and fiat coronal button, sometimes with a
short and broad shaft. The number of nutrient foramina cannot be generalized due to the low
volume of malerial, but there could be approximately 10, including one central foramen in front
of the médian cuspule.
— 220 —
g h
Fig. 6. — Plicatodus plicaliis, Slephanian B and C (?), Rakonitz basin. A, NMVP-M 305. Knezeves. B, UUG-YA 1370, Nemys-
lovicc. C. UUG-YA 1371, Susno (ail in labial view). D. UUG-YA 1372, Meprobylice (separate latéral cusp). E, F, BAF
wiihtiut number, Kounovâ (basal and latéral aspects). G, H. BAF without iiumber. Kounovâ (labial and lingual aspects).
Scales: 2 mm.
Plicatodus plicatus, Slépkanien B et C {?), bassin de Rakonitz. ,3. NMVP-M 305, Knezeves. B. UUG-YA 1370, Nemyslovice,
C, UUG-YA 1371, Susno (routes en vue labiale), D, UUG-YA 1372, Meprobylice (cuspide latérale séparée). E, F, BAF .sans
numéro. Kounovâ (vues basale et latérale). G, H, BAF sans numéro. Kounovâ (vues labiale et linguale). Échelles : 2 mm.
— 221 —
On the bottom side, a basal tubercle with softly indicated dépréssion is fairly wide labially.
On the basal area, about 12 nutrient foramina can be counted, Sometimes these openings are
shaped like slots.
The angle between crown and base in latéral view can occasionally be relatively large;
regulary it is about 115°.
RESULTS
Generally, cartilage éléments of xenacanthids are not very suitable for spécifie and generic
détermination within the order (SCHWIND, peis. observ.). On one hand. their morphology is very
similar, on the other hand, their outlines dépend on the quality of préservation.
The oiilline of Plicalodus’ palatoquadrate does not differ from that of Kenacanthiis or Tri-
odus. The general morphology of the upper jaw is considerably similar in ail représentatives of
the family Xenacanthidae. In addition to that, the degree of intraspecific variation, especially of
the lower jaw and of the scapulocoracoid. is relatively high, so that these éléments should not
to be used for species détermination.
For comparison, detailed descriptions about the morphology of the cranium and the shoulder
girdle are given in the following literalure; for Xenacanthus and Triodus e.g. in Fritsch (1895),
Reis (1897), MoY-Tiiomas & Whitb (1939), ScHWiND (1991); for Orthacanthm in HOTTON
(1952), Hejdtke (1982), Heyler & POfUN (1989).
The proportions of the dorsal spine of Plicaiodus, which should hâve been articulated with
the occipital région of the braincase, closely resemble that of Triodus.
A first description of the teeth from the holotype of Plicaiodus jordani was briefly outlined
by Schneider (1988) under the name “Xenacanihus" plicatus A. P. jordani show.s strong af-
finities with the Upper Carboniferous, P. plicatus from Bohemia.
Both species are characterized by the following fealures: ihc Strong and hybodont-like pattern
of cristae; distal cusps with a sigmoidal curvaturc in their upper part; a fiat, di.scus-shaped base;
relatively small and plain coronal button.
Différences are: P. pHcauis shows short intégral or S-shapcd vertical cristae on the entire
surface of the cusps, whereas in P. jordani the cristae are situated only in the upper 3/4 of the
cusps. Fuithermore, the base of P. plicatus has a downward bent mesial lobe. In eonlrast to thaï,
P. jordani shows a lobe or longue posilioned distally which regularly doesn’t bend downwards.
P. plicatus often has accessory médian cuspules which lack in P. jordani. The concave
dépréssion of the basal tubercle is more évident in P. jordani.
With "Xenacanihus" santosi (WürdiCi-MaCiel, 1975. Pis 8-10; PI. 15, Figs. 1-4), from the
Upper Permian of Brazil, another species belonging to genus Plicaiodus possibly exists. The
cristae on the cusps of the Braz.ilian teeth are closely similar in number and structure to those
of other species of the genus. Their sculpture is only slighlly slronger lhan in P. jordani. AIso,
the cusps are more massive and less slcndcr than in the Bohemian and Ihc SW-German shark.
Différences exist mainly in the morphology of the base. In “Xenacanihus’' santosi, the base
is stronger and higher and beats a relatively large and strong coronal button on the upperside.
The large number of nutrient foramina corresponds to P. jordani and P. plicatus.
— 222 —
As opposée! to P. plicatus, the Brazilian species has a low number of cristae. In P. plicatus
the cristae are also more weakiy developed. A similarity with P. plicatus is indicated by the
partly slot-like appearence of the nutrient foramina. Moreover, "Xenacanthus" santosi and P.
plicatus show a less depressed basal lubercle on the botton side of the base than does P- jordani.
Like in ail other xenacanihids, PUcutodus also lacks an enameloid-like tissue covering the
teeth. This is a characteristic feature of this order (see Hampe, 1991).
Close similaritles concerning the hislological structure exist with the genus Triodus, in
having widely luminated vascularization systents within a tooth. entirely constructed of circum-
pulpously developed orthodentine. lu Plicaiadiis. the pulp cavity in the médian part of the base
is more divided than in Triodus, which mostly has only onc single cavity. Piicatadus shows
here a low number of canals. In contrast to this. Ortiiacanthus and Xenacanthus hâve a base
made of trabecular denline and a vascularization system with naiTow lumina.
An important characteristic of Plicatodus is that the Hat coronal button seems to consist
of orthodentine. too In ail other généra the coronal button is composed of trabecular dentine.
This can be valued as an autapomorphic feature for cladistic analysis (sec below).
The structure and distribution of the dentine tubules can be stated as quite individual.
Whereas in Orthacanthus the tubules are parallel and widely spaced. they arc closcly spaced in
parallel in Xenacanthus. Triodus has a ramified network. Plicatodus shows an arborescent em-
branchment near the tooth's surface, becoming single and parallel towards the pulp.
CONCLUSIONS
Commonly. the opinion of the vast majority has been that the Xenacanthida are a specialized
group of ctenacanthiform sharks. Whereas Schaeffer (1981) based his conclusions mainly on
neurocranial characteristics, MAISEY (1984) and PoPl.lN & Heyler (1989) added several other
features, such as spine and fin morphology. However. YOUNC (1982) Came to the rcsult that
ctenacanthids are more closely related to more derived elasmobranchs than they are to the
xenacanthids.
In this article a cladogram is constructed, using the ctenacanthids for outgroup comparison.
The scheme includes the généra Orthacanthus. Xenacanthus. Triodus and Plicatodus based only
on hard parts, bccause often remnants of calcilled and fossilized cartilages are damaged and not
easy to rcconstruct. In this case, I altach gréai importance to the suggested cladogram (Fig. 7).
The taxonomie position of Dick's Diplodoselache woodi, often placed into the .Xenacanthida
(e.g. ZangeRL, 1981; SCHNlilDER, 1988; PoPL.tN & Heyeer, 1989). still remains unclear. Its
paired and unpaired fins (pectoral fins with uniserial axial structure like in .symmoriids,, strongly
heterocercal caudal fin), the spinc morphology (no dcniicles visible), and the tooth histology
(trabecular dentine within the whole tooth, crown coated with an orthodentine and an enameloid
layer, see DlCK, 1981) show mainly ctenacanthoid characteristics.
Carroll (1988) mentioned that Diplodoselache is identifiable as a xenacanthid only by
its dentition (in this case restricted to the external morphology) and long dorsal fin. Recently
Gaudin (1991) placed Diplodoselache into a sister group relation.ship with xenacanthids.
— 223 —
Orthacanthus Xenacanthus
13
12
11
Triodus PUcatodus
FiG. 7. — Cladogram of the généra of the order Xenacanthida. For explanation. see text. Apomorphous State first, plesiomorphous
State second.
Clado^ramme des genres de l'ordre des Xenacanthida. Pour les explications, voir te texte. État dérive en premier, état plé-
siomorphe en second.
[1] Teelh üicuspidate wiili distinctly separaied cusps; plesiomorphous; teeih ofien multicuspidaie and proximally fused cusps,
e.g. in cienacanthoid sharks;
[2] lack of niilrient foraiiiina on the labial side of the base; plesiomorphous; several nutrienl foramina exist on the labial
side, e.g. in ctenacanthids;
[3] upperside of base wûls wcll defined, strong coronal buiion; plesiomorphous; lack of a wcll dcvelopcd coronal button in
ctenacanthids;
[41 bottoni side of base wilh prominent labial process. callcd basal tubercle; plesiomorphous; no basal tuberclc in ctenacanthids,
here sometimes unly a labial edge, half-moon shapeü;
[51 Crown connisU of orlhodenüne; plesiomr>iphou.s; crown consists of trabecular dentine. ail ctenacanthoids;
[6) absence of an enatneloid layer: plesiomorphous: crown wilh cnameloid. e.g, in ail ctenacanthids;
[71 surface of cusps without sculpture, reversai in [14] and [15|; plesiomorphous; cu.sps having crisiae. gencrally in ctena¬
canthids;
[8] dorsal spine wilh lalerally arranged denticles; plesiomorphous: two rows of denticles on the back side of the spine. e.g.
in ctenacanthids;
[91 basal tuberclc usually with concave dépréssion = apomorphy I for development of the basal tubercle; plesiomorphous:
no basal tubercle in ctenacanthids, only half-moon shaped labial edge;
[101 ba.se consists of orthodentine; plesiomorphous: ba.se consists of trabecular dentine, ail ctenacanthoids;
[11] number of nulrieni foramina regularly less than eight per side of base; plesiomorphous; nuinber of nutrient foramina
more than elghi. ctenacamhoid sharks;.
[12] ba.sal tubercle prommeni and ruundcd = apomorphy U for development of the basal tubercle; plesiomorphous: no ba.sal
tuberclc in ctenacanthids;
[13} crown with laterully serraied edges; plesiomorphous; no serraiion known in iceih of ctenacamhoid sharks;
[14] reversai; cusps hâve straight vertical cristac: parallclapomorphy wilh ctenacanthids;
[15] reversai: cusps hâve wavy crisiae (hybodont pattern); plesiomorphous: straight vertical cristae. e.g. in a large number
of ctenacanthids;
[16] coronal button consists of orthodentine; ple.siomofphous: knob-like cxiremily in ctenacanthids of trabecular dentine.
— 224 —
The Xenacanthida seem to be a monophyletic group, as shown in six synapomorphous
characteristics common to ail généra.
1. Tricuspidate leeth with distinctly separate cusps.
2. Loss of nutrienl foramina on the labial side of the base.
3. Well-defined coronal button.
4. Bottom side of base with clearly separated basal tubercle.
5. Crown made of orthodentine.
6. Absence of a covering enanieloid layer.
Generally, the teeth of xenacanthids hâve lost the sculpture on the cusps in comparison with
the ctenacanthids |7|. But some of the généra, as a reversai, redeveloped spécial types of sculpture
againi Triodus' cusps hâve straight vertical cristae [14J. And Plicatodus shows a hybodont pattern
of wavy cristae [15],
The family Xenacanthidae (including généra Xenacanthus, Triodus and newly described Pli¬
catodus) is distinguished by the following synapomorphies; dorsal spine with laterally arranged
denticles [8] and a basal tubercle on teeth, having a usually developed concave dépréssion [9 =
apomorphy 1 for development of the basal tubercle],
Triodus and Plicatodus are combined under the synapomorphous character of a base which
always con.si.sts histologically of orthodentine [10].
Furthermore, Plicatodus can be separated by a coronal button which consists of orthodentine,
too [16], assessed here as an autapomorphous feature. Other autapomorphous characteristics are
présent in Orlhacanthus (only genus within the family Orthacanthidae): distinct and rounded
basal tubercle [12 = apomorphy II for development of the basal tubercle] and cusps with laterally
placed serrated edges [13].
One homoplasy can be stated, in a number of nutrient foramina regulary less than 8 per
side of the base [11], between Orthacanthus and Triodus.
The geology of the horizon Plicatodus jordatd came from, the Humberg-Bank, indicates
that this xenacanthid probably lived in near-shore environment of large and relatively deep lakes.
Nothing is known about diet, but in analogy to Triodus and Xenacanthus with partially
similar habitats, P. jordani might hâve been able to devour paleoniscoids, acanthodians, and
possibly epibenthic organisms like small crustaceans.
Acknowledgements
I like to thank Dr L. Eibmann, Leipzig, for the loan of the “Lebach"-nodule. I wish to express my
cordial thanks to Dr M. Manourova and Dr J. ZajIc, Prague, for their coopération. They enabled the
Work on the Bohemian material of the Muséums’ and Surveys’ collections. I am very much indebted to
Dr W. Mr-RK, Bingen/Rhein for making some x-ray photographs of the nodule and to Mr K. Schuchmann
for the préparation of teeth for the histological investigations. 1 aiso would like to thank Pr-Dr J. A. Boy,
Main/, Pr-Dr J. Schneider, Freiberg/Saxony, and Dr C. Schwind. Phetchaburi/Thailand, for discussion
and valuable advice. The carefui review of Dr R. Lünd, New York, and Dr C. POPLIN, Paris, is gratefully
acknowledged.
— 225 —
Addendum
The new taxon Plicatodus jordani was prepublished by Schneider & Zaji'C (1994) attachée!
to Hampe (1994). The name was known by the authors from a manuscript of this article which
was submitted on June Ist 1992! However, the définition of the genus is lacking in Schneider
& Zaji'C (1994). That fails to conform ICZN Art. 13a (i). Therefore. the generic taxon Plicatodus
is not available after SCHNEIDER & Z.MfC (see also ICZN Art. llh (iii); 13c]. The species name
“jordani” appeared in SCHNEIDER & ZajIc only in a legend of a figure (Fig. 27) which shows
only the variation of the sculpture on different teeth. A siifficient description is missing. According
to this circumstance, the species must be considered as a nomen nudum. Moreover, due to the
now presented publication, the taxon is made available by a correct définition and it must take
the authorship and date of this publication [after ICZN Art. 50, 21; see also p. 260!].
International Trust for Zoological Nomenclature. 1985. — International Code of Zoological Nomenclature. 3rd.
ed., H. Charlesworth and Co. Ltd. Huddersfield.
Schneider, .1. W.. & J. ZajIc, 1994. — Xenacanthiden (Pi.sces, Chondrichthyes) des mitteleuropaischen Oberkar-
bon und Perm - Révision der Originale zu Goldfuss 1847, Beyrich 1848, Kner 1867 und Fritsch 1879-1890.
Freiherger Forsch.-fleft., C, 452: 101-151.
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— 226 —
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drichthyes) in the light of Carboniferous and Permian French material. Act. Mus. Reginae Hradecensis, ser.
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Bull. Mus. natl. Hisî. nat., Paris, 4® sér., 17, 1995
Section C, n" 1-4 : 227-234.
Ontogenetic development of the squamation
in some Palaeoniscoid fîshes
by Dmitry Es IN
(A contribution to IGCP 328-Palaeo7.oic Microvertebrates)
Abstract. — Analysis of the skeleton and nutnerous scales of Amhlypterina costata (Eichwald) and Acro-
pholis sp. (Actnoplerygii, Palaeoni.scodei) front the Upper Permian of the Ea.st-European Platform permits to
distinguish the stages of development of the squamation during gaiwth. There are three inaiu stages: juvénile,
subadult and adult, each being characterized by different degrees of expression of the morphological structures,
including the shape of the bony plate, the sculpture, the aniculation device and the shape of the tubercles on
the ganoin surface. The formation of the squamation in palaeoniscids differs from that in living teleo.sts by the
presence of two centres of the .squamation development, in the antenor part of the body and the caudal lobe,
and by the longer time of development. .‘Xpart from these différences, the ontogenetic development of the squama¬
tion in these two groups proceeds in the same way.
Keywords. — Actinopterygii, Palaeoniscoidei, Upper Permian, ontogeny, .squamation.
Développement ontogénétique de la squamation
chez quelques poissons paiéoniscides
Résumé. — L'analyse du squelette et de nombreuses écailles de Amhlypterina coxtata (Eichwald) et
d'Acropholis sp. (Actinopterygii, Palaeoniscoidei) du Permien supérieur de la plateforme est-européenne permet
de distinguer entre les différents états du développement de la squamation pendant la croissance. Trois états se
différencient : juvénile, subadulte et adulte, chacun étant caractérisé par des degrés différents de l'expression de
structures morphologiques, dont : la forme générale des plaques dermiques, l'ornementation et la forme des
tubercules à la surface de la ganoine. La formation de la squamation des paiéoniscides est différente de celle
des téléostéens actuels par la présence de deux centres à partir de.squels s’cbnuchcnt la squamation, dans la
région antérieure du corps et dans le lobe caudal, et par la durée du développement. Dans ces deux groupes,
excepté ces différences, le développement ontogénétique de la squamation .se déroule de la même façon.
Mots-clés. — Actinopterygii, Palaeoniscoidei, Permien supérieur, ontogénie, squamation.
D. E.SIN, Department of Paleonlology, Faculty of Geitlogy. Mosrow State t/niverisly, Mnxcow. II9S99, Riisxia.
Introduction
The ontogenesis of palaeoniscids has been very little studied. Only a few researchers (Blot,
1966; SCHULTZE & Bardack, 1987) hâve examined some aspects of this coniplicated problem.
The lack of works concerning this problem can be explained chiefly by the scarcity of the material
allowing such studies, the poor understanding of the taxonomy of the group, and perhaps some
other minor rea.sons.
— 228 —
The ontogenetic development of the scales and squamation has been studied until now,
although the works on this subject could hâve provided a number of interesting data as to the
position of the superorder Palaeonisci among actinopterygians.
The présent paper deals wilh the ontogenetic development of two palaeoniscid species Acro-
phulis sp. Elonichthyiformes and Amhlypierina cosraut (Eichwald) Palaeonisciformes. The scales
of these species are easily distinguished and show some morphological features which are easily
observable in their development from the earliest stages, and can be used as reliable taxonomie
characters for species and généra.
In addition to the ontogenetic development of the individual palaeoniscoid scales, that of
the enlire squamation is of considérable interest. Such studies were made by using the whole
bodies of the two species mentioned above.
However, the available material was poorly preserved and did noi allow adéquate compari-
sons. Therefore, we used the data from Schultze & Bardack (1987) on size changes in the
scales of Elnnichlhys hipsilepis and " peltigerus from the Mazon Creek Formation (Illinois,
USA).
The development of the palaeoniscid squamation during growth was compared with that of
the Recent Teleostei {Canissius auratiis), because the latter hâve the least number of common
features with palaeoniscids, but retain a close relationships with them. The common features of
the ontogenetic development of the palaeoniscid and teleost squamations seems thus to be general
for the ail actinopterygians (Cladistians, Chondrosteans, Holosleans).
MATERIAL AND METHODS
This Work on the author’s material, collected in the Tikhie Gory Site (Middie Prikamie)
and ichthyoliths from the Tongue-4 site (South Priouralie), provided by M. F. IVACItNENKO. The
entire bodies and isolated scales of Acropholis sp. and Amhlypterina cosiala (Eichwald) studied
here represent the different growth stages. These two species were selected because of their
numerous features which permit the distinction of their scales at ail stages in each ichthyolith
a.s.semblage from the respective sites. The study of each parlicular stage was ba.sed on the scales
from different parts of the body. The récognition of the stage of the scale development was
based on the comparison wilh the body scales in complété individuals of different groth stages.
This work incorporâtes information from the analysis of more than 500 isolated scales of each
species, seven skeletons and associated fragments of Acropholis sp., and five skeletons of A.
costata. Detail study was made with CamSean and Jeol scanning électron miscroscopes.
RESULTS
Palaoniscoid scale development during growth
The development of the palaeoniscoid scales proceeds gradually and it is rather difficult
to distinguish phases in this process. Nevertheless, we can already recognize three main stages
— 229 —
of the development and three corresponding types of scale structure; juvénile, subadult and adult.
There are also intermediate types between there three stages.
Juvénile type
The size of these scales ranges from 0.3 to 0.5 mm. They consist of a quadrangular or
rounded bony plate. The presence of the ganoin ridges and their size dépend on their position
on the body. There are more ganoid ridges on the scales in the centre of the developing squama-
tion than on the margins. In the eatly stages, palaeoniscoid scales are ail similar in structure
and can hardly be distinguished. However, the scales of A. cusiaia and AcmphaHs sp. in our
samples show certain différences. These généra are referred to different orders and their phyletic
lineages hâve diverged rather early. lherefore their respective characters occur already in the
early stages of their ontogeny.
The majority of the scales in the Palaeonisciformes is characterized by a weak development
of the external ornamentation al any stage of their oniogenesis. Even juvénile scales, usually
better ornamented than adult ones. possess (in ,4. costaUt) the flaltened ridges, widening at the
base. The Elonichthyi formes, and particularly the Acropholiidae, are ornamented with large
ridges. The juvénile scales of Acropholis sp. usually possess one or two thin ridges, strongly
raised above the bony plate. Juvénile scales lack the keel, peg and socket. The characteristic
structures of the adult Acropholis (e.g. the strongly developed anterodorsal angle of the scale)
is not pronounced- The ganoin surface shows a microsculpture which consisls of lubercles ranging
from 3 to 5 microns (Fig. IG, H). The tuberclcs are distributed regularly and cover ail the
externally expo.sed ganoin surface. The juvénile scales are characterized by the elongate shape
of the tubercles (Fig. IH). The long axis of the rubercles is directed anteroposteriorly and rellccts
the main direction of the scale growth.
Subadult type
When at the subadult stage of the development, the scales usually show the basic structure
of those of adult individuals (Fig. IC, D). However, some juvénile features are still présent
(weak development of the peg and socket articulation, elongate shape of the tuberclcs in some
parts of the squamatioii). On the external surface of many subadult scales, there are still boun-
daries between the juvénile ganoin ridges. although the latter tend to fuse and form a uniform
ganoin surface. This is best scen in A. cosîata (Fig. ID).
The tubercles on the ganoin surface arc rounded in shape, although they cannot be observed
on ail scales because the rate of scale growth varies in the different parts of the body. As a
resuit, the tubercles on the scales in the areas of more intensive growth relain an elongated
shape, The features which are lacking in juvénile scales (keel, peg and socket) appear al this
stage. Some unique characters (e.g. the development of the anterodorsal angle of the scales in
Acropholis sp.) also appear at this stage.
Adult type
Adult scales hâve the full set of features : the structure of ail scales at this stage are well
developed. The scale size in adult Acropholis sp. reaches 5-8 mm (Fig. lE), and 3-5 mm in
— 230 —
Fig. 1. — Palaeoniscid scales on different otages of (he onlogenelic devclopmenl. A, juvénile scalc of Acwpholis sp. B, juvénile
.scale of Amblypienna cosfata. C. subadull scale oi' AcrophoUs v/». D. Subadult scalc of 4. cosrata. E. aduli scale of Acropholis
sp. F, aduli scalc of 4. n/stuiu. G, ganoin surface (aduh scale). M. ganoiu .surface tjuvenile .scale). Scale bar: A*F. 10 ^m;
G-H, 100 Mm.
ÉcüilUw de paléofûsddvs ù differents âges de leur développenwm omogénérigue. A. écaille juvénile de Acropholis sp. B.
écaille juvénile de AmbJyplcrinu coslufa. C. écaille d‘un suhaduhe de Acropholis sp. D, èmille d'un suhadulle de A. costata.
fl, écaille adulte de Acropholis sp, F. écaille adulte de A. costata. G, surface de ganaine iécaille adultel H, surface de
giinoine {écuillt' juvénile). Echelles : A^F K) \im ; G-H, HHl fi/w.
— 231 —
Amblypterina. The scalc acquires laxonomically important features after the completion of the
full development of the major morphological éléments. Among these features in the Amblypterina
are the nearly smooth ganoin surface and the characteristic serration of its anterior margin
(Fig. IF). Représentatives of AcrophoUs sp. are distinguished by the shape and arrangement of
the ridges and the contour of their cross-section.
TRENDS AND TIMING IN SCALE GROWTH
The major changes in the palaeoniscoid scale growth relate to the complexity of the shape
and contour of the bony plate and external ornamentation.
The bony plate: in the juvénile stage,, the bony plate of the spccies studied here has a rather
simple, rounded or quadrangular outline.
The articular éléments are absent and appear only at the subadult stage.
The external ornamentation: the development of the ganoin is more complicated. In the
juvénile stage, the external ornamentation of the scales in all palaeoniscids shows one or three
ganoin ridges. The latter can be either separated (Avropholis sp.) or closely set anteriorly {A.
costata). The ridges are flattened and quadrangular in cross section. The microsculpture of the
ganoin surface consists of elongated tubercles. The subséquent development of the sculpture on
the external surface varies. In scales of AcrophoUs sp.,. the ridges grow faster in heighl than in
breadth. By contrast, in A. costata, the ganoin ridges grow laterally, but very little in height.
At the subadult stage, the shape of the tubercles on the ganoin surface changes from elongated
to rounded. In A. costata, the ganoin covers the enlire external surface of the scalc and the
limits between the juvénile ridges are well pronounced. At the same stage of the development,
AcrophoUs sp. distinctiy shows the bifurcation of the anterior ends of the ridges and the fusion
of their caudal ends. The adult stage is characterized by the sinoolhening of the sculpture. In
A. costata. the limits between the ridges disappear completely. In AcrophoUs .sp., at the same
stage, the increasing breadth of the ridges results in their fusion and the subséquent réduction
of the sculptured surface. The formation of dic anterior margin of the external .surface and the
sculpture characters are achieved.
SQUAMATION DEVELOPMENT IN THE RECENT TELEOSTEI
The ontogenetic development of the squamation of the living Teleostei is considered on
the basis of Carassiiis auratus (DlMlTRlEVA, 1957). The formation of the fir.st scale.s begins
when the body Icngth rcaches 12-16 mm. The first .scales appear on the areas A and B (Fig. 2)
and along the latéral line, up to the beginning of the caudal tin. The dorsal and ventral parts
remain naked. At the ncxt stage, when the body length reaches 16-19 mm. the scales cover the
entire body, cxcept the région between the operciilum and pectoral fins. The formation of the
squamation is completed when the body length reaches 23 mm. However, it must be noted that
this development does not proceed similarly in all Recent teleost. Rutilas rutilus caspiens, when
less than 18 mm in length, shows the part of the body below the latéral line covered with scales.
— 232 —
Fig. 2. — The different areas of lhe squamation in fishes.
Les différentes zones de la squamation chez les poissons.
Lucioperca luciuperca, at the lenglh of 33 mm, has the anterior dorsal and ventral parts free of
squamation.
The development of the palaeoniscoid squamation differ from that of the Recent teleosteans,
although bolh share .some common features. As ScHULTZIi & Bardack (1987) showed on the
basi.s of the development of the two palaeoniscoid species "Elauichthys" pelfygerus and "Elan-
ichthys" hypsilepis from the Mazon Creek fauna, and according to my own observations, the
formation of the squamation begins in 19-20 mm long individuals. The ridge seules appear first,
then the scales of the area (Fig. 2) (E.SIN, 1990) and the scales pierced hy the pores of the
latéral line canal. There are two areas of development of the squamation in the next stage
(25 mm). The first one concerns the areas "A”* “B”, and "C" (partiy). and the second one is
situated in the caudal lobe. Then, at the length of 34-37 mm, the .scales on the areas “C” and
“D” meet lo form a distinct limit belween the body and caudal fin, which show respectively
different scale arrangements. The areas around the dorsal, anal, pelvic and pectoral fins remain
naked. Later, in the majority of adult palaeoniscids, these régions become covered with small,
rounded or quadrangular scales, which hâve some spécifie structures.
The squamation samples of A. coslata and Acropholis sp. do not contradict the pattern of
squamation development considered above.
DISCUSSION
Taxonomic Features
Taxonomically important characters in palaeoniscid ontogeny appear successively. The
characters on higher taxonomic rank (order or family) appear by the end of the juvénile stage
and are completely formed at the subadult stage. The first of ail the.se features concern the shape
of the bony plate and the characteristics of the articulation éléments, i.e. the shape of the anterior.
— 233 —
upper and lower margins, the length/height ratio, the breadth of the dipping surface, and the
shape and size of the peg, socket and keel.
Species-Icvcl charactcrs are formcd during the transition to the subadult stage of scale
development. They usually are represented by ornamentation features of the cxternal surface,
i.e. the aspect of the anterior margin serration and the shape and arrangement of the ridges,
grooves and other structures of the external surface. In the latter phases of the subadult stage,
scales undergo some additional alterations but the taxonomically important features remain un-
changed.
Palaeoni.scoid scales which are in the earliest stage of the development resemble very much
those of the earliest actinopterygians (Andreolepis and Lophosteus) by the lack, or very weak
development of the keel, peg and socket, and the ornamentation of the ganoin, repre.sented by
elongate, separatc ridges.
The absence of the articulation device has at least two explanations. It may be due either
to the biogenetic law, or to the active mode of life and intensive body growth in the juvénile
stages.
RESEMBLANCES AND DIFFERENCES IN SQUAMATION DEVELOPMENT
Both similarities and différences in the squamation development can be observed between
palaeoniscids and teleosteans. Both groups are characlerized by the beginning of the squamation
development on the Banks of the anterior part of the body and along the latéral line. In both
cases, the late stages of the formation of the .squamation are marked by the appearance of the
scales on the ventral part and around lhe fins.
The most significant différence is the presence of two indépendant centres of scale formation
in palaeoniscids: on the body and on the caudal lobe. This is nol observed in teleosteans.
It is rather difficuU to explatn the presence of these two zones of squamation development
in palaeoniscids. It can be sugge.sted thaï the development of scales on the caudal lobe may be
related to the strong loading on this part ol the body when the fish moves. The absence of
ossified skelelon. in this case, was presumably compensated by lhe early appearance of the ex-
oskelelon. Teleosteans avoid such a problem becausc their endoskcleton is well ossified in the
early growth stages.
It is worthy noticing that the first scales to appear in both the palaeoniscids and teleosteans
occur at nearly lhe same stage of the development (viz. al the 14 to 30 mm body length stage),
but the squamation in teleosteans' forms is considerably fasler. The formation of the squamation
in Carassius auraius is achieved when the body length reaches 9 mm, whereas in palaeoniscids
the ontogeneiic changes of lhe squamation are nof achieved at the 60 mm stage, that is, this
process lakcs much more time.
The longer squamation development in palaeoniscids, unlike thaï of teleosteans, seems to
allow the formation of better developed and more complicated structures. The presence of a
considérable amount of features in the palaeoniscoid scales slrongly increases their taxonomie
importance.
— 234
Clearly, more knowledge regarding the ontogeny of these fishes is required to résolve this
problem.
The study of the development of the squamation and isolated scales may indicate whether
the specimen studied should be assigned to a new species or represents another stage of the
ontogenetic development of a previously known species.
The shape of the tubercles of ganoin is a useful feature for the detennination of the individual
stages of the development.
The élongation of the tubercles seems to be the resuit of the intensive scale growth in the
early stages of the development, wtth a more rapid growth in height than in breadth. In the
adult stages, the tubercles are rounded in shape.
The presence of elongated tubercles covering the entire external surface is an evidence for
a juvénile stage.
The absence of the squamation in some parts of the body may be évident for the uncompleted
individual development. In this case, it should be proved Üiat the specimen under considération
does not represent the juvénile stage of a previously described species. Perhaps, the illustration
of the généra Phanewsteon (Traquair, 1877-1914; FrjtscH, 1859), Kkhkassia, Lapkozubia
(Minich & Minich, 1990), and Carhoveles are based on such juvénile forms.
Acknowledgemcnts
I am indebted to M.F. Ivachnenko, Paleontological Institute, Russian Academy of Sciences, Moscow,
for the scale maierial contributed. Many thanks to S.V. Nikolaeva and O.V. Lebedev both from the
Paleontological Institute, Russian Academy of Sciences, Moscow, who assisted greatly in the préparation
of the présent manuscript.
Literature cited
Blot. J., 1966. — Étude des Palaéonisciformes du bassin houiller de Commentry (Allier, France). Cah. Paléont.,
éd. CNRS, Paris.
Dimitrieva, E.N.. 1957. Morpho-ecological analysis of the two species of Carassius. In: Raboty po aetapno.sti
razvitiu ko.stislykh ryb. î'rudy Inst. Morphol. Zhivotnykh.. 16: Isdatelstvo Akademii Nauk SSSR, Moscow:
102-170, (In Russian).
K.SIN, D., 1990. — Squamation of Amhlyplerina coslata (Eichwald) and Palaeoniscid taxonomy on the isolated
scales. Pahoni. Zhtirnal.^ 3: 89-96. [In Ru-ssian].
FRtTSCH, A.J., 1895. — Fauna der Gaskhole und der Kalksteine der Permoformation Bohenies. 3. Selbstverlag,
Praha.
MtNtCH. M.G. & A.V. .MtNtCH, 1990. — Révision of some Palaeonisci and new fi.shes from the Upper Pennian
of the East-European Plalform and opportunités for their utilization in siratigiaphy. In; Voprosy geologii
Yuzhnogo Urala tNizhnego Povolzhia: Izdatelstvo Saratovskogo Universiteia, Saratov: 84-104. |ln Russian).
SctIULTZE, H. -P, & D B.ARDACK, 1987. — Diversity and size changes in palaeoni.sciform fishes (Actinopterygii.
Pisces) from the Pennsylvanian Mazon Creek fauna. Illinois, USA. J. Vert. Paleont.. 7 ( I): 1-23.
TRaQUAIR, R. h., 1877-1914. — Ganoid fishes of the British Carboniferous formations. 1. Palaeoniscidae. Palae-
ontographical Society, London.
Write, E.I., 1927. — The fish-fauna of the Cementstones of Foulden, Berwickshire. Trans. R. Soc., Edinburgh.
55: 225-287.
Bull. Mus. natl. Hist. nat., Paris, 4® sér., 17, 1995
Section C, n“ 1-4 : 235-268.
Diabolepis and its bearing on the relationships
between porolepiforms and dipnoans
by CHANG Mee-Mann
Abstract. — This study reveals new morphological features of Diabolepis based on new specimens and
further préparation of previously available materials. Cranial characters are summarized and analyzed in order
to provide a basis for discussing the relationships of Diabolepis. The cranium of Diabolepis shows a number of
primitive sarcopterygian characters. Prcvioits hesitation in placing Diabolepis in the Dipnoi mainly aro.se from
these primitive sarcopterygian features. In Diabolepis, the plerygoid plate and lower jaw bear more dipnoan
characters thun the cranium. Although these features in the pterygoid plate and lower jaw arc typical of the
dipnoan condition, uncertainty as to whether the lower jaw. pterygoids and cranium belong to the same animal
was used as the main rcason for not accepting Diabolepis as a dipnoan. The présent study reveafs further évidence
that the lower jaw, pterygoids and the cranium belong to the same form. For example, the processes alung the
médian inargin of the dorsal surface of the palatoquadrate fit well into the corresponding fossae on lhe ventral
side of the neurocranium. This is corroborated by similar disposition of dermal bones, tooth morphology and
wear patterns shown on the palate and lingual face of the lower jaw. These and other uniquely shared features
lend further support to a close relationship between Diabolepis and dipnoans. The significance of the Diabolepis
and its bearing on the cluse relationship between dipnoans and porolepiforms (including Powichthys and Youn-
golepis) are further discussed.
Keywords. — Vcrtebiata. Sarcopterygii, Dipnoi. Devonian. China, anatomy, phylogeny.
Diabolepis et sa signiricalion quant aux relations de parenté
entre les Porolépiformes et les Dipneustes
Résumé. — Cette étude révèle de nouveaux caractères morphologiques de Diabolepis, sur la base de nou¬
veaux spécimens et la préparation d'ancien matériel. Les caractères crâniens sont énumérés et analysés de manière
à fournir une base â la discussion des relations de pimenté de Diabolepis. Le crâne de Diabolepis présente nombre
de caractères primitifs de Sarcoptérygiens, qui sont à l’origine de l'hésitation à placer Diabolepis parmi les
Dipneustes. Chez Diabolepis. les plaques ptérygoi'dicnnes et la mandibule présentent plus de caractères de Di-
pneusles que le cr.âne. Bien que ces caractères des plaques ptérygoïdiennes et de la mandibule soient typiques
des Dipneustes, l’incenitude sut leur appartenance au même animal était la principale raison pour ne pas re¬
connaître Diabolepis comme un Dipneuste. Cette étude confimie que le crâne, les mandibules et les ptérygoîdc.s
appartiennent à la même forme. Par exemple, les processus du bord mé.sial de la face dorsale du palatocarré
correspondent bien aux fosses de la face ventrale de l’endocrâne. Cela est corroboré par une disposition similaire
des os dermiques, la morphologie dentaire et les surfaces d’usure sur le palais et la face linguale de la mandibule.
Ces caractères, ainsi que d'autre, s. qui sont uniques aux Dipneustes renforcent l'hypothèse d’une relation étroite
entre Diabolepis et ce groupe. La signification de Diabolepis et sa portée quant à la relation entre les Dipneustes
et les Porolépiformes (incluant Powichthys et Youngolepis) sont discutées.
Mots-clés. — Vertebrata, Sarcopterygii, Dipnoi, Dévonien, Chine, anatomie, phylogénie.
M.-M. Chang, Institute of Vertébrale Paleontology and Paleoanthropology, Academia Sinica, PO. Box 643, Beijing 100044,
China.
— 236 —
Introduction
Diaholepis was suggested as the sister-group of ail previousiy known dipnoans when it vvas
described (CHANG & Yu,. 1984). Since lhen the problem of ils relationship has been disciissed
by a sériés of authors, of which soine agréé with CllANG & Yu (Maisf.y. 1986; .lANVIRR. 1986;
Forey, 1987; SMITH & Chang, 1990) whilc olhers variously disagree (SCHULTZE. 1987;
ScHULTZE & Campbell. 1987; Campbell & Barwick, 1987; P/\nchen & S.mithson, 1987).
When Diaholepis speraïus wm firsl described. the malerial referred lo the species. i.e. parts of
crania, plerygoids and lovver jaw rami, were not found articulated but detaehed. The cranium
shows quite a few primitive sarcopterygian characiers, whereas the pterygoid plates and lower
jaws look more dipnoan-likc. Il is precisely the primitive sarcopterygian eharacters of the cranium
that caused hésitation in placing Diaholepis among dipnoans (SCHULTZE, 1987: 40). There has
been little doubt in rclerring the ptcrygoid.s and lower jaws to dipnoans. The main reason for
the pterygoid piales and lower jaws lo be assigned to the same species as the crania was the
tooih morphology and wear patterns, which are similar to those of the premaxilla, vomer and
parasphenoid. In order to find more evidence for suggesting that the cranium, pterygoid plate
and lowet Jaw belong to the same form and to piovide the basis for further discussion of the
relationships of Diaholepis and the interrelationships of sarcopterygians, we présent here a survey
of the ncurocranium and palatoquadrate, together with a summary of the features of the parts
of the skull mentioned elsewhere.
ABBREV1AT10N.S
ano anterior nasal opening, narine antérieure \
asp ascending proeess of parasphenoid. processus ascendant du parasphénoïde
c. ju jugular canal, canal jugulaire ',
dbpt dermal basipierygoid proeess, processus du basiptérygoïde dermique'.
De denlary, dentaire;
Dmpt dermomctapierygoid, dermométaptérygoïde ',
dpd expanded distal portion of dentary, portion élargie du dentaire '.
Dpi dermopalatiiie, dennopalatin ;
dpp dorsal palatal proeess, processus palatin dorsal ;
d. Pq dépréssion on viscéral side of pterygoid plate occupied by palatoquadrate,
dépression sur lu face viscénde de la plaque ptérygoïdienne, occupée par
le palatocarré '.
dt dorsal ihikcning of pterygoid plate (area of pterygoid plate exposed latéral
to palatoquadrate), épaississement dorsal de Ut plaque ptérygoïdienne,
(région de la plaque ptérygoïdienne exposée latéralement au palatocarré) ',
Eept ectoptery'goid. ecloptérygoïde '.
Enpt entopterygoid, euioptérygoïde ;
f.lab fenestra in wall of otic ca.p'su\e, fenêtres dans la paroi de la capsule otique,.
gr.ju jugular groove, sillon jugulaire',
gr.v.subhy groove for subhyoidean vein, sillon pour la veine subhyoïdienne'.
— 237 —
hyd dorsal arlicular area for hyomandibular, surface articulaire dorsale
pour l’hyomandibulaire ;
Idl-4 infradentaries 1-4, infradentaires l-4\
la.com commi.ssural lamina, lame commissurale ;
le latéral commissure, commissure latérale \
Ip labial pit, dépression latérale;
n. pno notch for posterior nasal opening, échancrure pour la narine postérieure ;
om orbital margin, bord orbitaire;
pif prolingual ficid, champ prolingual ;
Pmx premaxilla, prewa.n7/«iVe ;
Pq palatoquadratc, palatocarré ;
Pq.aup pars autopalatina. partie autopalatine ;
Pq.pqu pars pterygoquadrata, partie ptérygoquadraticjue ;
Pq.qu pars quadrata, partie quadratique ;
ptp pterygoid tootli plate, plaque dentaire ptérygoïdienne ;
r. supj suprajugular ridge, crête stiprajugulaire ;
s. soc bone .sériés carrying supraorbital sensory canal (nasal sériés), série d’os
portant le canal de la ligne sensorielle supra-orbitaire (série nasale);
s.st supratemporal sériés, série supratemporale ;
W-1 Westoll-lines, lignes de Westoll.
DESCRIPTION
Skull roof and sensory line canals
The following account is largely based on specimens V7237 (Fig. 1 ) and V7238 where the
skull roof is complété. Référencé is made to V7241 (with only the snout preserved) where nec-
essary. The former two specimens differ in shape and proportion. In V7237 the skull roof is
broader and its maximum breadth (measured at the level of the posterior margin of the orbit)
is 83% of the total skull length, while in V7238 it is 67%. In V7238 the orbit is much larger
(its diameter is 25% of the skull length) Ihan in V7237 ( 15%). hence more posteriorly situated
posterior margin of the orbit (Fig. 2). This makes the portion of the skull roof anterinr to the
posterior margin of the orbit and the prepineal length in V7238 (45% and 39% of the skull
length) much longer than those of V7237 (37%> and 33% respeciively). As noted by Chang &
Yu (1984). the smailcr size of V7238 (only half the length of V7237) sugge.sts that it is most
probably a juvénile individual and this is consistent with the observation that the orbit is com-
paratively larger in juvénile fishes than in adults (cf. SCHULTZE. 1984: 5).
Despite of the différences in proportion and shape. the two specimens show a similar bone
pattern in the skull roof. The dorsal surface is on the whole plane. No pineal opening lias been
observed, though a distinct médian élévation at the level of the posterior part of the orbit marks
the position of the pineal body. In V7237, the skull roof is slightly domed anterior to the pinçai
élévation, between the supraorbital sensory canal loups, whereas in V7238 and V7239 a distinct
1. — Diabolepis speratus (CHANG & Yu), Lower Devonian, Yunnan, China. Skull roof in dorsal view, (from CHANG & Yu,
1984. Fig. IB).
Diabolepis speratus (CHANG & Yu), Dévonien inférieur, Yunnan, Chine. Toit crânien en vue dorsale, (d'après CHANG & Yu,
1984. fig. IB).
— 239 —
small dépréssion is présent behind the pineal élévation. No suture can be seen in the anterior
part of the skull roof, except for one that bounding the premaxilla.
The skull roof is not divided into anterior and posterior shields, as it is in non-dipnoan
sarcopterygians. Ch.\NG & Yu (1984) suggested that the pair of bones at the rear of the skull
roof, that bear the middle and posterior pit-lines can be compared with the 1-bones of dipnoans,
or postparietals (parietals of Chang & Yu) in other sarcopterygians, The pair of bones in front
of I-bones, bearing the anterior pit-lines, was in turn compared with the J-bones of dipnoans,
or parietals (frontals of ChaNG & Yu) of other sarcopterygians. If the posterior border of the
J-bone is taken as the boundary between the anterior and posterior portions of the skull roof,
comparable to the fronto-ethmoidal and pariétal shields (according to jARVlK's terminology) of
non-dipnoan sarcopterygians, then the anterior portion is rather long, representing 73% of the
skull length in V7237 and 80% in V7238. The J-bones and the anterior portions of the I-bones
are separated by a médian element, suggested to be the B-bone. Along the posterior margin of
the B-bone and the anteromedial and médial margins of the 1-bones, fine but distinct, concentric
, 2 mm, b
Fig. 2. — Diaholepis speratus (Chang & Yu), Lower Devonian, Yunnan, China. Skull roof in latéral view. A, specimen V7237;
B, specimen V7238.
Diaholepis speratus (CHANG & Yu), Dévonien inférieur, Yunnan, Chine. Toit crânien en vue latérale. A, spécimen V7237 ;
B, spécimen V723H.
— 240 —
Unes hâve been observed. No doubt they are Westoll-lines. In V7237 the B-bone is anteriorly
delimited by faint sutures. These, and other complété and incomplète sutures in front of them,
mark out a mosaic of small bones, which are variable in size and shape. In V7238 there are no
sutures to indicate the antcrior margin of the B-hone, which thus merges imperceptibly into the
anterior portion of the skull roof. The bone sériés cairying the supraorbital sensory canal and
sutures marking a fevv small bones médial to the posterior ones of this bone séries are seen in
both V7237 and V7238. The bone sériés traverscd by the supraorbital sensory canal, apparently
comparable to the nasal serie.s, or K, l,, etc. bone sériés as suggested by Chanci & Yu, extends
backwards well beyond the orbit. The posterior éléments of this séries, are delimited by distinct
sutures and are short and broad, Iransver.sely elongated, with parallel anterior and posterior
borders, and arc roughly hexagonal in shape. Latéral to this bone senes. behind the orbit. the
latéral margin of the skull roof is formed by another sériés of small bones, which are often
pentagonal in shape. We suggest that they correspond to the supratemporal sériés (X. Yl, Y2-
bonesl. The sériés is long in both specimens, approximately 60% of the total skull Icnglh in
WlTil and 45% in V7238. The pentagonal and hexagonal sériés of bones are tightiy interlocked.
In V7237, latéral to the marginal sériés, al the level of the J-bone. there are several bones of
still smaller size and irregular shape. The number of bones in ail these sériés varies from specimen
to specimen and from one side to the other in the same specimen.
The premaxilla is the only separate bone in the snoui. No sensory canal porc has been
observed to pierce the bone. It consists of a broad anteromedial and a narrow postérolatéral
divisions. Owing to the marked downward and inward bending of the mouth a considérable
portion of the anteromedial division and the entire postérolatéral division lie inside the mouth
cavity. The proportion of the premaxilla which remains outside the mouth cavity and is covered
with cosmine varies fnsm specimen to specimen. In V7239 and V7240 the portion remaining
outside is relatively large, with distinct sutures between it and the adjacent bones. whereas in
V7237 il is much smaller and scems to he squeezed between the adjacent bones with no smooth
sutures (Fig. 3). In V7238 the premaxilla is not preserved. The anterior external nasal opening
is situated ventrally, lying at the margin of the mouth. with the premaxilla as ils ventral (posterior)
border. Latéral to the anterior nasal opening, the antérolatéral margin of the skull roof shows a
long and narrow overlap area, apparently for the lacrymal. Médial to iliis overlap area, the margin
shows a rounded notch having a cosmine-covered border. The posterior nasal opening is most probably
located in this notch, dorsal (anterior) to tlie distal portion of the premaxilla. In any case, both
nostrils must thus be situated dorsal (anterior) to the premaxilla. Tlie expression “outside (or inside)
the mouth cavity" is not used here becau.se il is not topographically accurate. A nanow area of
bone, which merges poslcriorly with the skull roof, divides the two nasal openings. This area of
bone may correspond to the latéral rosirai of osteolepift)rms and porolepiforms.
The course of the supraorbital sensory canal is shown by single row of pores opening on
the skull roof. As mentioned above, the posterior portion of the canal is carried by a sériés of
clearly delineated small bones. As in V7238. the supraorbital sensory canal pores are often si¬
tuated in the sutures between these small bones. In the same specimen, the posteriormost pores
for this canal lie at the suture between the J-bone and the anteriorly adjoining élément of the
small bone sériés. This suggests thaï the posterior end of the supraorbital sensory canal extends
backwards into the .I-bone and ends antérolatéral to the anterior pit-line. There is no postorbital
— 241 —
Pmx
/
Fig. 3. — DUiholepis speralus (Chang & Yu), Lower Devonian, Yunnan, China. Snoul in anterovcntrai view, V7237.
Diabolepis speralus (Chang & Yu), Dévonien inférieur, Yunnan, Chine. Museau en vue aniéroventrale, V7237.
junction between the supraorbital and infraorbital sensory canals. In the snout, no pores of the
infraorbital sensory canal can be seen, but the suture between the premaxilla and the adjoining
part of the skull roof behind it exhibits a number of kinks in V7239, V7240 and V9527, it tums
upon itself more or less abmptly at several points, like the corresponding suture in Youngolepis.
In this last form the pores through which branching tubes from the infraorbital sensory canal
and the ethmoidal cominissural canal open to the surface are situated at the kinks in the suture
(Chang, 1982, Fig. 6C). Pores of this kind seem al.so to be présent at certain kinks in the suture
in V7239. The anterior portion of the infraorbital canal and the ethmoidal commissural canal
were discovered by serial grinding of Youngolepis (Chang, 1982, Fig. 4, secs. 19, 24), but there
is no direct observation so far to confirm the presence of these parts of the canals in Diabolepis.
In Youngolepis. posterior to the premaxilla, the bone probably corresponding lo the latéral rosirai
in Eusthenopleron (ClIANG, 1982, Figs. 5D, 6C). which foirns the ventromedial border of the
anterior external nasal opening and sutures with the premaxilla from behind, roofs the sections
of the sensory canals mentioned above (CHANG, 1982. Pis 8.5). In Diabolepis, where no similar
bony strip under the anterior nasal opening exists, these sections of the infraorbital and ethmoidal
sensory canals. if présent, could only lie in the skin above the lower border of the anterior nasal
opening, but not enclosed in bone. Moreover, as noted above, the suture bounding off the pre¬
maxilla in V7237 has an entirely different appearance than that in V7239 and V7240. Thus. it
is not unwise to assume that the anterior portions of the infraorbital and ethmoidal commissural
canals in Diabolepis are eilher absent or interrupted at the anterior nostril. No pore of the main
sensory canal can be iraced on the dorsal surface of the skull. The restoration of the course of
this canal by SCHUL.TZE & Campbell (1987, Fig. Id) is obviously made according to convention,
not from the specimens.
Under the latéral edge of the posterior éléments of the supralemporal sériés, a laterally
facing longitudinal groove, similar to that in Youngolepis (Chang, 1982, Fig. 4 secs. 392-444),
is seen in \1231 and V7238. It is conceivabic thaï the main canal, like that in Youngolepis, ran
along the edge of the supralemporal sériés.
The anterior pil-line is restricted to the J-bone in both V7237 and V7238. The middie and
posterior pit-lines are normal and symmetrical. The middie pit-line extends to Y2 in V7238,
— 242 —
while in V7237 the lines vary in course and extension (Fig. I). This kind of variation is commonly
met with in dipnoans (MILES, 1977).
The extrascapular sériés is not preserved.
Among ostcichthyans, the skull roof pattern of Diaholepis cornes closest to that of dipnoans
on the basis of the following shared characters:
1. there is a médian bone (B) in the posterior part of the skull roof;
2. the bones carrying the anterior and middle + posterior pit-lines are separated or partially
separated by this médian bone;
3. the supraorbital sensory canal extends back to the J-bone, but not to the supratemporal sériés,
and there is no postorbital junction between it and the infraorbital canal;
4. the infraorbital canal is probably interrupted at the anterior nostril;
5. the posterior éléments of the nasal sériés and the anterior éléments of the supratemporal sériés
lie side by side;
6. there are Wesloll-lines.
Diaholepis agréés with primitive dipnoans {i.e. Dipnarhynchus and Uranolophus) but differs
from later ones in:
1. 1-bones meeting behind the médian B-bone;
2. supraorbital sensory canal entering J-bone without joining the infraorbital canals posterior to
the orbit. in contrast with the supraorbital canal extending from the nasal to supratemporal sériés
and joining the infraorbital canal in X-bone in later dipnoans;
3. parts of the nasal sériés and supratemporal sériés lying in the same transverse plane rather
than one sériés lying in front of the other, as in later dipnoans.
In addition, the snout in Diaholepis is comparatively short, the orbit and the pineal élévation
are relatively anteriorly positioned, and the supratemporal sériés (X Yl, Y2) is, like in early
dipnoans, longer than in later ones. As mentioned above. the length in V72.37 and V7238 is
50% and 45% respectively of the skull length, while il is 50% for Uranolophus and 44% for
Dipnorhynchus. but in Chirodipterus australis it is between 39%: and 46%' (Mil. ES. 1977: 232).
Regarding other sarcopterygians, the skull roof of Diaholepis shows greater similarily to
Yoiingolepis than to other forms. In both généra the premaxilla is a separate bone and not traversed
by a sen.sory line (shared aiso with Powichthys and cuclacanth.N), and the main lateralline canal
runs alone the latéral edge of the skull roof. If the J-bone can be homologized with the pariétal,
so thaï ils posterior margin is the posterior margin of the anterior portion (frontal shield) of the
skull roof, then this portion in Diaholepis, Yoiingoiepis and Powichthys is rather long, at any
rate longer than thaï of ail other non-dipnoan sarcopterygians.
NEIIROCRANIUM and DERMAL bones COVERING IT.S ventral SURFACE
Ethrooidal région
This région is broad and short in Diaholepis. Its ventral face is, in large part, covered by
the premaxilla and vomer. In ail specimens where the premaxilla is preserved, as a resuit of the
— 243 —
strong downward bending of the snout, much of its anteromedial division and the entire post¬
érolatéral division lie inside the mouth cavity and are entirely covered with blunt teeth that
show traces of wear. In V7239, where a large portion of the premaxilla lies inside the mouth,
the teeth (or perhaps tubercles) are of rather irregular shape, especially those situated next to
the cosmine covering on the exposed portion of the premaxilla. The premaxilla is thin and narrow
at its posterior end and the length of this posterior division varies; in some specimens it does
not reach the level of the postnasal wall. Posterior to the premaxilla the ventral face of the
c.hyp
Fig. 4. — Diabolepis speratus (Chang & Yu), Lower Devonian, Yunnan, China. Anterior cranial division in ventral view, V9527.
Diabolepis speratus (CHANG & Yu), Dévonien inférieur, Yunnan, Chine. Division crânienne antérieure en vue ventrale, V9527.
— 244 —
ethmoidal région is covered by a paired vomer of rectangular shape, studded entirely with teeth
which merge with the tooth-bearing portion of the premaxilla to form a continuons tooth patch.
The bone area between the two nasal openings may afso bear teeth or tubercles, Thus on the
left side in the newly prepared specimen V9527 (Fig. 4), this area and the médial border of the
anterior nasal opening formed by the premaxilla are .studded with teeth or tubercles, while in
V7237 the médial half of the area is covered by cosmine and the left half with tubercles. In
V7240 the area is comparatively extensive and entirely covered with smooth cosmine. This var¬
iation in the tooth-bearing portion of the upper jaw indicates that the position of the outer border
of the portion of the upper jaw occluding w'ith the tooth-bearing portion of the lower jaw (see
below) varies in different specimens. And if we take the outer border of the tooth-bearing portion
as the mouth margin. then the position of this margin varies frora specimen to specimen.
In specimens where the vomer is not preserved, the vomerine area shows an uneven surface
divided by grooves into raised areas of irrcgular shape and size, and looks exactly like this area
in Youngolepis. Between the two vomers is the only exposed area of the ventral face of the
ethmoidal région. When the vomers are in position, a deep dépréssion is formed in the midiine
between them and the premaxillae.
The ventral portion of the postnasal wall is rather thick, especially laterally. This wall,
uniike the roughiy transverse postnasal wall of that of the non-dipnoan sarcopterygians. stretches
obliquely posteromedially, and passes gradually into the latéral wall of the orbitotemporal région.
The surface of the ventral margin of the postnasal wall is smooth and bears no sign of a latéral
.on
Fig. 5. — Diabolepis spemtus (Chang & Yu), Lower Devonian, Yunnan. China. Anterior cranial division in postero-ventrolateral
view showing the openings in ihc postnasal and latéral walls of the neurocranium, V72.‘Î9.
Diabolepis speratus (Chang & Yu), Dévonien inférieur. Yunnan, Chine. Division crânienne antérieure en vue posîéro-
ventrolatérale. montrant le.s ouvertures dans les cloisons postnasale et latérale du neurocrâne, V7239.
— 245 —
articular area for lhe palatoquadraie comparable to thaï in Eiisthenopternn (JarvIk, 1942, Fig. 48)
and porolepiforms (JARvIk, 1972, PI. 9.2; BJERRING, 1989, Fig. 2A). The same smooth ventral
surface of lhe postnasal wall is also seen in Voungolepis, Powichthys and dipnoans. Three open-
ings are visible on the posterior face of the postnasal wall (Fig. 5). The largest, situated in the
ventromedial pan; of lhe wall, can easüy bc compared wiih the orbitonasal canal in Yoitngolepis
and other sarcopterygians. A small opening situated in the dorsomedial part of the wall, just
under the skull roof. wa.s niost probably Iraver.sed by lhe ramus ophthalmicus lateralis. The Ihird
opening lies belween these two, in lhe médial portion of lhe postnasal wall, and is comparable
wilh profundus canal in other sarcopterygians.
A network of fine, reticulating canals uncovered through a break in the dorsal wall of the
right nasal cavity of V724I recalls the rostral tubuli in Youngolepis, Powichthys and dipnoans.
Orbitotemporal région
In this région lhe braincasc is narrow and deep. Extending dorsolaterally, just behind lhe
ethmoidal région and tightiy applied to lhe lower face of the .skull roof, is the extensive tectum
orbitale (CltANC & Smith. 1992, Fig. 10). Ftow far it extends backwards can nol be made out.
The médian portion of the ventral face of this région is occupied by the long, narrow parasphenoid
which bears a promineiit dentition and extends anteriorly to the ethmoidal région where it meets
the vomer. The parasphenoid dius prevents the pierygoids front meeting ai the midiine. The
anterior portion of lhe parasphenoid shows some variation in toolh arrangement. In V7239. lhere
are three longitudinal rows fornied by raihcr large tcelh (Chang Sl Yu, 1984, Fig. 2 A, B). In
V7240, the médian row is formed by three large teeth and the second of them is clearly folded
at the base, while the two latéral rows of smaller teeth are not regularly arranged (CtlANC &
Yu. 1984. Fig. 2C, D). Ail large teeth are worn. In V9527 (Fig. 4), the anterior portion of the
parasphenoid is covered with randomly scattered teeth of different sizes and a few new, unworn
teeth can be observed in places where old teeth are worn or partially resorbed. The niiddle
portion of the parasphenoid, which is usually the deepest portion of the bone and bence most
subject to wear, is. in large paît, covered with extensive patches uf worn dentine rather than by
discrète teeth. Posterior to (his part the teeth become smaller and irregular in shape. V7240 and
V9527 show the bucco-hypophy.sial opening in a dépréssion in the posterior part of the para¬
sphenoid. Around the Opening are small denticles. The parasphenoid is flanked along its entire
length by deep. dorsomedially extending wings, which give it a troughiike dorsal surface. This
Irough accommodâtes the high and narrow ventral part (including the suborbital ledge) of the
inlerorbital portion of the braincasc. The latéral surface of the parasphenoid wing bears long,
irregular grooves and ridges running obliquely anterodorsally. The parasphenoid in V9527 ends
abruptly behind the bucco-hypophysial opening and has a tiny medial process along the posterior
margin. Immcdiatcly posterior to lhe opening, the postérolatéral corners of the parasphenoid
protrude to form a pair of pronouneed processes. In V7240 the parasphenoid shows a pair of
short latéral proccsscs al approximaiely the same level as in V9257, The parasphenoid in this
specimen extends furlher backwards than in V9527, and posterior to the short process just men-
tioned there is another pair of fairly high ascending processes, which exiend dorsolaterally to
abut against the latéral wall of lhe neurocraniurn posterior to the basiplerygoid process (Chang
& Yu, 1984). This posterior pair of processes in V724() can be compared with the ascending
— 246 —
processes of the parasphenoid in other osteichthyans, though it is absent in coelacanths and
dipnoans. If this interprétation is correct, the anterior pair of processes seen in both V7240 and
V9527 must be homologous with the dermal basipterygoid process, otherwise présent only in
advanced actinopierygians (Gardiner, 1984; 276). The parasphenoid is restricted to the anterior
cranial division and does not cover the ventral surface of the otoccipital region.
The large optic nerve foramen opens anteriorly in the latéral w'all of the braincase where
it is surrounded on its upper, posterior and lower margins by a thick ridge (Fig. 5). The
ventral wall of the neurocranium is wide anteriorly to the optic foramen, and beats a pair
of broad fossae delimited by the vomer anteriorly and the parasphenoid medially, Each of
these fossae extend medially between the suborbital ledge (or subocular shelf), which is
enclosed in the latéral wtngs of the parasphenoid and the ventrolateral face of the braincase,
dorsolaterally lo the parasphenoid (Fig. 11). They correspond topographically to the fossa
autopalatina in Porulepis (JarvIk, 1972, Figs. 9A, 16A-C, 20A. B; BjERRtNG, 1989, Fig. 2A)
Powîchthys (JesseN,, 1980, Fig. 5) and Youngolepis (Chang. 1982, Figs. 7A, 15A), but
extend much further medially. The dorsolateral margin of each fossa is thickened into a
ridge which probably corresponds to the “olfactory ridge” (or crista suspcndens) in Porolepis
(J.ARViK. 1942, Fig. .17) and Powichthys (JESSEN, 1980. Fig. 5) and the similar structure in Youn¬
golepis (Chang, 1982. Fig. I5A). As a matter of fact, the term “olfactory ridge” was originally
proposed by JARVtK (1937: 9.5; Figs. 10-16) for Eusrhenoptemn wenjukowi to designate a longi¬
tudinal, rounded ridge on the latéral face of the anterior portion of the orbitntemporal region.
This ridge, which embraces the olfactory canal, extends from the médial part of the postnasal
wall backwards almost to the optic foramen. Ventral to the olfactory ridge in Eusthenopteron
wenjukowi, the latéral face of the orbitotemporal region is provided with a strongly developed,
downwardly directed crest, the crista suspendens (JarvIK, 1937, Figs. 10-16), In
Eusthenopteron foordi the crista is not .situated immediately below the olfactory ridge, but
is in the form of a few protubérances on the thin, ventral part of the intcrorbital wall (JarvIk,
1937: 101; 1942: 439; Figs. 47B, 48-50). In Porolepis the term “olfactory ridge” was applied
to a ridge on the ventrolateral border of the orbitotemporal region, extending from the ven-
tromedial part of the postnasal wall backwards, ventrally to the optic foramen Al the tran¬
sition between the ethnioidal and orbitotemporal régions in Porolepis, the ridge is rather
Sharp and directed slightiy downwards and to this sharp part of the ridge the term “crista
suspendens” was applied (JarvIk, 1942: 361; Fig. 37; PI. 3.1, 2, PI. 4). In fact, the “olfactory
ridge” in Porolepis .seems to hâve little to do with the olfactory canal, and the crista sus¬
pendens is just a more pronounced part of the ridge. The ridge, together with the crista,
forms the upper border of the fossa autopalatina which is unique to porolepiforms, Powichthys,
Youngolepis and Diaholepis. In Powichthys and Youngolepis, the term “olfactory ridge” was bor-
rowed from porolepiforms for the ridge bordering the fossa autopalatina from above. In both
forms, the ridge usually extends postcroventrally from the posterior margin of the articular area
for the ethmoidal process of the palaloquadrate, and runs ventral to the optic foramen to merge
posteriorly with the horizontal portion of the basipterygoid process (JESSEN, 1980, Fig. 5; Chang,
1982, Fig. 15), and as in Porolepis it has nothing to do with the olfactory canal. It is approxi-
mately in tlie position of the “olfactory ridge” (and crista suspendens) in Porolepis and the crista
— 247 —
suspendens in Eusthenopteron wenjukowi. Therefore, the term crisla suspendens is used here
instead of olfactory ridge in Powichihys, Youngolepis, Diabolepis and porolepiforms.
In different specimens of Youngolepis the size and the extent of the fossa autopalatina varies
considerably. In most specimens, behind lhe articular area for the ethmoidal process of the pa-
latoquadrale the ventral Wall of the braincase cxtends laterally well beyond the latéral margin
of the parasphenoid (Chang. 1982. Figs. 4 sec. 130, 7 A, 10; Pis 8.1, 3-5, 10, ll.l). In .soine specimens,
e.g. V6179, the sharp crista suspendens (“olfactory ridge” in Cha.NO, 1982, Fig 15) is well-
developed, and mcrges posteriorly with the horizontal portion of lhe basiptcrygoid process. In
such specimens a rather deep fossa autopalatina is formed between the ventral wall of the brain¬
case and the usually well-developed suborbital ledge. In other specimens where the crista sus¬
pendens is less developed and rounded or even hardly noticeable, and not continuons posteriorly
with the horizontal portion of lhe basiplerygoid process, the fossa autopalatina is shallow and
lhe suborbital ledge ts narrow (e.g. V6227: ClIANO. 1982. PI. 11. 2). In different généra and
species of porolepiforms the situation also varies, lu Glypfolepis groenhmdicu both the ventral
wall of the braincase and the suborbital ledge with lhe parasphenoid are very broad, the an-
teromedial articular lamina of lhe palatoquadrate is deeply inserted in the fossa autopalatina and
even fused in one or two areas with the suborhital ledge (JARVlK, 1972: 71; Bjbrring, 1989,
Fig. 2A), while in a specimen of Glyptolepis (BMNH, P. 47838) from the Middie Old Red
Sandstone ncar Pennyland the suborhital ledge is narrow, the crista suspendens is hardly dis-
cernible, and the fossa autopalatina is shallow. In Porotepis and Youngolepis. the ventral wall
of the braincase extends laterally beyond lhe latéral margin of the parasphenoid (JARVlK. 1972,
Fig. 9A) and the crista suspendens extends posteriorly dorsal to the horizontal portion of the
basipterygoid process (JARVlK, 1972, Fig. 20A). In some specimens of Porolepis the fossa au¬
topalatina is deep but in others it is shallow and no articular areas devoid of periosteal lining
has been found (jARVtK, 1972: 5455). In Holtipiychius the fossa autopalatina is deep and the
crista suspendens extends backwards to join the horizontal portion of the basipterygoid process
(jARViK, 1972, Fig. 20B). Powichihys does not show a well-developed fossa autopalatina (Jessen,
1980: 199).
In Diabolepis, there is an elongated dépréssion on the underside of the anterior part of the
crista suspendens (Fig. 1 1 ), possibly receiving a similarly shaped process from lhe palatoquadrate
(see below). Further backwards, posterior to the fossa autopalatina and ventrally to the optic
foramen, the ventrolateral wall of the neurocranium bears a rather deep and wéll-delineated de^
pression on either side of the parasphenoid. There is no periosteal lining in the boltom of lhe
dépréssion, and it is probable thaf it is one of lhe areas where the palatoquadrate articulâtes
(see below). In as much as no comparable structure has yet been found in closely relaled fomi.
the dépréssion is named from its topographical position as the suborbital fossa. Behind Ihis de-
pression. posterovenlral to the optic foramen, lhe latéral wall of the orbitotemporal région exhibils
a small opening which, in V7239, is surrounded by pronounced ridges and a stout, rounded
process on its ventral side. In V7240, however, it is followed by a groove on the ventrolateral
surface of the braincase (CHANG & Yu, 1984, Fig. 2D). Tins opening cannot be inierpretcd at
présent, but judging from ils position and by comparison with primitive dipnoans, il seerns proba¬
ble that it was traversed by the ophthalmic artery. In V7240. there is a well-developed basipte¬
rygoid process similar to that of porolepiforms and Youngolepis, with laterally expanded
— 248 —
horizontal and dorsal portions, but situatcd higher on the latéral wall of the braincase. In
porolepiforms, Powichthys and Youngolepis the basiptcrygoid process is situated low down, and
its anterior horizontal portion is either continuons with the crista suspendens (Glyptolepis,
Holoptychius, Powichthys and most specimens of Youngolepis) or at the same level as the sub¬
orbital ledge [Pütvlcpis and some Youngolepis). In osteolepiforms the position of the basipter-
ygoid proccss is rather high and the suborbital ledge tums up steepiy tu merge inlo the
basiptcrygoid process (jARViK, 1980. Fig. 86A). No descending proccss of the sphenoid (Jessen,
1980) has been found in DiaboLepis.
Otic région
V7237 is the only specimen with a prepared posterior part of the neurocranium. In this
specimen the occipital portion, together with the cranial portion of the notochordal canal, is
missing. Similar examples are often seen in Youngolepis where the occipital région of the neu-
rocraniuni is separated from the otic région by a latéral occipital fissure which runs downwards
from the posterodorsal part of the neurocranium and bcnds forwards ventrally to reach the post-
eromedial corner of the vestibular fontanelle. Allhough the ventral surface of the otic région is
badly damaged, the remaining part (Fig. 6A) slill show slriking similaritics to Youngolepis. The
dorsal surface of this région is tighily applied against the dermai boues of the skull, leaving no
space for ridges or muscle insertions. The latéral commissure, as in Youngolepis, stretches post-
erodorsally and forms the latéral wall of lhe wide jugular canal. Though its posteroventral surface
is damaged. one can infer from its similar extension to that of Youngolepis lhat the articulation
of the hyomandibula was rather extensive and most probably consisted of two areas. Posteriorly,
the jugular canal is followed by the wide jugular groove on the ventrolateral face of lhe otic
région. The dorsolateral margin of rhe groove is bounded off by a ridge similar to lhe suprajugular
ridge in Youngolepis (ChanO, 1982: 52; Fig. 12; = Jugular ridge in Eusthennpiemn. JarvIk,
1980, Fig. 86). This ridge follows the curve of lhe jugular groove and is interrupted anteriorly
by another groove running laterally probably for the subhyoidean vein, as was suggcslcd for
Youngolepis. The ridge is rather weak and bcars no obvions process at its posterior end com¬
parable to lhe parampullar process in Youngolepis. The ventral margin of lhe vcniromedial wall
of the jugular groove is broken. On the posterior portion of the preserved part of the wall there
is a large notch with periosteal lining. This mtist represent the upper margin of the large foramen
in the latéral Wall of the otic capsule which otherwise is présent only in Youngolepis (Chang,
1982: 53) and Nesides (JARVlK. 1954, Fig. 4A). So far as it has been possible to préparé it. the
cranial cavity in the otoccipilal région is almost identical with that of Youngolepis. Since no
wall are preserved belween the otic capsules and the cranial cavity, the cranium in this région
displays a large cavity. A Youngolepis specimen (V6557) in the same State of préservation as
to the otoccipilal région shows exactiy the same structure (Fig. 6b).
Palate
Dermai palate
The dermai palate in Diabolepis is represented by a single pair of tooth plates, the pterygoid
plates. The plates hâve already been described in detail by Chang & Yu (1984) and Smith &
— 249
Fig. 6. — Incomplète crania in ventral view showing dorsolateral part of otic région. A. D'tabolepis, V7237. B. Youngoiepis,
V6557.
Crânes incomplets, en vue ventrale, montrant la partie dorso-latérale de la région otique. A, Diabolepis. V7237. B, Youn¬
goiepis, V6557.
Chang (1990). Only a summary is presented here for further di.scussion. The pterygoid plate
has a fairly broad horizontal portion and a comparatively small postero-ventrolaterally curved
quadrate ramus. The buccal surface of the horizontal portion is slightly concave and bcars regular
rows of teeth while the médial, posteromedial, and latéral margins of lhe horizontal portion, and
the buccal surface of the quadrate ramus are covered with irregularsized, randomly scattered
denticles. In many specimens. the posterior région of the horizontal part shows extensive, irmgular
patches of worn dentine that are apparently deposiled on top of worn teeth. These were interpreted
by Smith & Chang (1990) as reparative tissue. and as a tissue unique to dipnoans (syndentine).
Ail worn dentine surfaces in Diabolepis show a punctate pattern of rings of cîrcumpulpal dentine
(Smith & Chang, 1990. Fig. 4E). The circumpulpal dentine and associated interstitial dentine
are aiso considered lo bc restrieted lu dipnoans (Smith el ai, 1984). A left pterygoid (V953Ü)
and a left lower jaw looth plate (V953r) of very small size werc found by WANG Nienzhong
while sorting acidprepared microvertebrates from the Diaholepis-bcânng locality. The pterygoid
plate (Fig. 7A, B) is similar in shape and proportion to the larger (adult) plate.s. Its length from
the anteromedial angle to the distal end of the quadrate ramus is approximately 2.7 mm. and its
width from the antérolatéral corner lo the médial margin is 1.2 mm. This size falls near to the
lower jaw tooth plate of a juvénile Neoceratodus forsteri described by Kemp (1979, Fig. I4C)
— 250 —
a I 0.5 m m, b ,0.2 iti m ,
FiG- 7. — Diaboiepis speratus (Chang & YUJ, Lower ücvonian, Yunnan, China. Pierygoid looih plate in ventral view (A) and
enlargcd portion showing traces of wear (A), V9530.
Diaboiepis speratus {ChanG Yu), Devunien inférieur, Ytmnan, Chine. Plaqt4e dentaire ptérygoïdienne en iMé* ventrale (A)
et portion agrandie montrant des traces d'usure (B). V95S0.
with a body length of 8,7 cm and thi.s pterygoid might belong to a juvénile individual of com¬
parable size, The plate is slightiy concave in ils middle part and covered by regularly arranged
rows of teeth. and is thus similar to the larger pterygoid plates. As in Ihcse plates Ihc teeth are
arranged in radial rows with the center of radiation approximately in the middle of the post-
cromcdial margin. However, rows of teetli parallel to the antérolatéral (labial) margin can also
be dislinguished in the anterior part of the plate. Tins might impiy thaï the teeth in each row
wcrc formed wilhin the same period, i.e. they are of the same génération. The largest teeth are
situated along the labial margin which indicates that new teeth were added from this margin
(Smith & Chang, 1990). Ou the postérolatéral part of the horizontal portion and the quadrate
ramus the teeth become much smaller and lose their regular arrangement. The teeth are pointed
espccially in the anterior part of the plate. No small denticle are observed on this plate, between
the regular rows of teeth or the extensive patches of wom dentine covering the tooth rows. Ail
this shows that this small plate must be from a juvénile, although traces of wear are already
shown on the teeth in the middle part of the plate. Wear of the occlusal surface of the tooth
plates was also mentioned by Kemp (1979: 255, table 1) in juvénile (stage viii) Neocemtodus
forsteri.
Palatoquadrate
The palatoquadrate of Diaboiepis was not co-ossified with the neurocranium. It is firmly
attached to the viscéral side of the pterygoid plate, the latter forming its latéral, médial and
— 251 —
posteromedial margins, and therefore it is usually preserved wilh detached pterygoid plates. The
intimate contact between the palatoquadrate and lhe pterygoid plate often makes it difficult to
trace the boundary between them. This is why, in the preliminary description of Diabolepis
(Chang & Yu. 1984), the palatoquadrate was not recognized, and its dorsal surface was laken
as the viscéral surface of the pterygoid plate. A rcccntly eolicctcd pterygoid plate (V9055),
without attached palatoquadrate (Fig. SA), makes it possible lo unravel the outline of the latter.
The palatoquadrate consists of a hroad anterior. horizontal portion overlying the horizontal part
of the pterygoid plate, and a postero-ventrolaterally extending quadrate portion that overlies the
quadrate ramus of the pterygoid plate. The orientation of the quadrate is difficult to judge, since
its distal end is not preserved. But as l^r as we can .sec front the extent of the quadrate ramus
it inust hâve been roughly vertical. A small postérolatéral, .semicircular, thickened area of lhe
pterygoid plate, just in front of the quadrate, is exposed latéral to the palatoquadrate in exactiy
the same way as the dorsal thickening on the viscéral surface of the pterygoid plate in fossil
dipnoans (Fig, SB; Milës, 1977, Figs. 76, 77 etc.). It differs only in its smaller size and more
posterior position. In Dipnorhychiis sussmilchi it was reported that the palatoquadrate and pte¬
rygoid are tightiy fused, so that it is difficult to separate the Iwo bones (THOMSON & CAMPBELL,
1971: 66). However, a figure in Campbell & Barwick (1982, Fig. 15a) and a specimen (BMNH,
Fig. 8. — A, Diabolepis speratu^ (Chang & Yu). Lower Devonian, Yunnan. China; incomplète pterygoid tooth plate in viscéral
view. V9055. B. Chiwdipmus, Upper Devonian of Australiu, pterygoid looih plaie in vlsceriü view (modified from Miles,
1977, Fig. 76a). C, Clxpioirpis, Middle Devonian of Greenland, palatoquadrate wilh assocîatcd domial boncs in viscéral view
(from JamvIK. 1972. Fig. 25A).
A. Diabolepis spcralus fCfrAA'G de Yu), Dévonien infétieun )'iouiait, Chine, fl, Chinxliplcrus. Dévonien supérieur d'Austridie ;
plaque dentaire ptées fityidicnnt ou'omplète en vwf visvérnU' (d'après MfLES, 1977, Jif*. 76it. modi/té}. C, Clyplolepjs, Dévonien
moyen du GOfentand, palatoiarré et os dermiques associés en vue viscérale (d'après J\RViK. 1972, fig. 2SA}.
— 252 —
P. 33699) clearly show a suture between the exposed area of the pterygoid and the palatoquadrate
in Ihis species. Judging from the smooth and concave posterior paît of the latéral margin of the
pterygoid in Uranolophus (Denison, 1968, Figs. 8, 9), a small exposed area of the pterygoid
might also exist in this région. The condition in Diabolepis also rccalls that in porolepiforms,
e.g. Glvpiolepts groenlandicu (Fig. 8C, .lARVlK 1972, Fig. 25 A), where the exposed area of the
entopierygoid plate is small and posterioriy posiiioncd. The entopterygoid bordering the post¬
érolatéral margin of the palatoquadrate lias been described in almosl ail sarcopterygians, e.g.
Eusthenoptenm (for osteolepiforms; Fig. 9 A; JARVIK. 1980, Fig. 107A), Glyptolepis, Hulaptychiiis
(fur porolepiforms; JarvIk, 1972. Fig. 33B, E). In lhese two groups this exposed area is very
smooth, probably to allow contraction of the adductor muscles passing from the palatoquadrate
lu the lower jaw (JarvIK, 1980: 174). In coelacanlhs, due to the lack of the comtnissural lamina
of the palatoquadrate, almosr the entire dorsal surface of the entopterygoid is exposed in latéral
view (Fig. 9B; J.ARVlK. 1980, Figs. 218, 219). In early tetrapods, such as fchihyostega. the dorsal
surface of the palaie has never been ohserved As far as we can judge from its ventral surface
(JarvIk, 1980, Fig. 171B), its postérolatéral margin would also be bordered by the entopterygoid.
Pl<j. 9. — Palaloqu^ilralc wilh associaied dermal bones in latéral view. A. Eusthetwpreron, Laie Devonian of Canada {from J.^RV^K.
1980. Fig. I07A): B. huimeria. Recent (faim JARVIK. 1980, Fig. 219); C. Amia, Recent (from Jarvîk, 19X0. Fig. 40A); D,
PitiyiJivru.s, Recent (Imm JakVIK. 1980. Fig. 2340.
PaloffK'drré os dermiques ussneiês eu vue latérale. A. Eusihenopteron, Dévonien .supérieur du Canada id’aprè.'i JakvIk.
/9(W, yïg. t07Al: B. Lalimeria, artuel id'après JahvIk. 19S0, fig. 219); C, Amia. actuel (d'après Jarvîk, 1980, fig. 40A) :
D. Polypîcruî», actuel (d'après Jar\']k, /9H0. fig. 234C).
In actinopterygians (Fig. 9C) and Polypterus (Fig. 9D), on the contrary, it is not the entopterygoid
but the ectopterygoid which borders the postérolatéral margin of the palatoquadrate. The en-
lopterygoid and dermometapterygoid in these fonns cover only the médial portion of the ventral
surface of the palatoquadrate (JarvIk, 1980, Figs. 40A, 234C, 236, 245B). In sarcopterygians
the ectopterygoid and dcrmopalatine covers the antérolatéral, but never the postérolatéral margin
of the palatoquadrate. An area of the entopterygoid cxposed latéral to the postérolatéral margin
of the palatoquadrate seem.s thus to be a sarcopterygian character.
The anterior. horizontal portion of the palatoquadrate in Diabolepis is tlat and broad and,
on the whole, follows the outiine of the pterygoid plate, although it is much narrower than the
pterygoid, owing to the thick médial and posteromedial rims formed by the lattcr. A striking,
unique feature is the sharp, transverse ridge on the middie part of the dorsal .surface of the
horizontal portion of the palatoquadrate. This ridge arises near the antérolatéral corner of the
palatoquadrate, extends medially, and then bends slightiy posteromedial ly to mergc with a strong
process at the médial margin of the palatoquadrate. The only structure which is at ail similar
is the dorsal palatal process in Urannlaphus (Denison, 1968, Fig. 4), Dipni/rhynchiis (White,
1965; BMNH P. 33699; THOMSON & CAMPBELL, 1971. “latéral palatal process", Fig. 26;
Campbell & Barwick, 1982, “dorsal palatal process”, Fig. 14) and Sirmtiahykus (Bernacsek,
1977: 194, Figs. 8, 9) (Fig. 10). This proce.ss was regardcd as endoskeletal by Denison (1968:
374) and Thomson & Campbei.l (1971: 68). Miles, on the contrary, seemed to consider the
process as exoskeletal. He named it the dorsal process of the entopterygoid and described it as
arising from the top of a dorsal thickening comparable with the dorsal thickening on the pterygoid
plate of Chirodipterus and other advanced dipnoans (Miles. 1977: 174; Figs. 76, 77). Miles
dpp
■ 4 mm.
Fig. 10. — Stomiahykus thiaodus Bcrnacsck, Middie Dcvonian of Canada. Palale in righl ventrolaterai view showing ihe pterygoid
tooth plates and palatoquadrate with broken righl margin. NMC 22600.
Stomiahykus thiaodus Bernacsek, Dévonien moyen du Canada. Palais en vue ventrolatérale droite, montrant les plaques
dentaires ptéryffoïdiennes et le palatocarré. dont le hord droit est brisé. NMC 22600.
— 254 —
further compared this process with the short ascending process of the pterygoid plate in
Gnathorhiza which, according to Berman (1976: 1026), articulated with the latéral surface of
the broad, flange-like descending process of the skull roof, i.e. bone K-M, and tended to regard
the dorsal and ascending processes throughoul fossil and recent dipnoans as homologoiis. The
descending process from the skull roof and the ascending process from the pterygoid plate in
Recent dipnoans are undoubtedly cxoskeletal. So are the processes of the same name in
Gnathorhiza, as far as it can be understood from BERMAN (1976). In the preliminary description
of Diabolepis (CtLANG & Yl), 1984), since the palaloquadrale was not recognized, the dorsal
transverse ridge of the palatoquadrate was interpreted as comparable to the dorsal thickening
(= the e.Kposed area of the entopterygoid) on the viscéral surface of the entopterygoid plate.
Until the pterygoid plate without the palatoquadrate attached (V9055) was found, it was not
realized that the dorsal thickening of the entopterygoid in Diabolepis (arid probably also in Dip-
norhynchiis and Urunolophus) is very .small and situated posteriorly. Consequently, the dorsal
process (or ridge» of the palatoquadrate and the dorsal thickening of the entopterygoid are iwo
different Ihings. The former is an endoskeletal process on the latéral part of the palatoquadrate,
whereas the latter is a ihickcned area of the entopterygoid exposed laterally to the postérolatéral
margin of the palatoquadrate and situated behind the former. A dorsal process (or ridge) of the
palatoquadrate lias been found in Dipnnrhynrhus. Uranolophus, Slomiahykus and Diabolepis. As
to its function, nothing new can be added.
Anterior to the transverse dorsal ridge and antérolatéral to the strong process at the médial
margin of the palatoquadrate mentioned above is an elongated ridgelike process which has an
anterolateral-posteiontedial orientation, reaching the antérolatéral margin of the palatoquadrate.
On the anteromcdial side of the ridge. overlying the anteromedial part of the pterygoid plate,
is a thin lamina of thé palatoquadrate which may lie comparable with the anteromedial articular
lamina of the palatoquadrate in porolcpiforms, e.g. in Glyptolepis (lARViK, 1972, Fig. 25). If we
assume that the pterygoid plate with the palatoquadrate is situated on the side of the parasphenoid,
so that the slightiy convex médial margin of the pterygoid plate matches the slightly concave
latéral margin of the parasphenoid, and that the protruded anteromedial corner of the pterygoid
plate fits into the space lined medially and anteriorly by the parasphenoid and the vomer. then
the strong process and the ridge mentioned above on the palatoquadrate arc received by the
suborbital fos.sa under the latéral border of the ventral surface of the neurocranium and the
elongated fossa on the crista suspendens respeciivcly. The thin, anteromedial lamina of the pa¬
latoquadrate fits in the fossa palatina (Fig. 1 1 ). Since the bottom of the suborbital fossa is not
periosteally lined there is still the possibility of fusion or synchondrosis between the palato¬
quadrate and the neurocranium in this région. An articulation between the palatoquadrate and
the latéral portion of the postnasal wall, like that in porolcpiforms and probably Euslhenopteron,
cannot exist. since the ventral .surface of the postnasal wall is smooth and the anterior margin
of the palatoquadrate, in this position, is situated some distance behind the postnasal wall. The
two articulations described herc in Diabolepis resemble the two spécial buttressing régions in
the palatebraincase contact described by Thomson & Campbell (1971: 66) in Dipnorhynchus.
One of those is a buttress of the palate under the root of the postnasal wall. and the other is a
thickening of the viscéral palate immediately anterior to the oplic nerve foramen. As in Dip-
narhyncluis, the dorsal surface of the palate in Uranolophus is also thickened to buttress the
— 255 —
anteromedial articular
Fig. 11. — Diabolepis speratus (Chang & Yu), Lower Devonian, Yunnan, China. A, partial reconstruction of ventral side of the
anterior portion of the cranium with the left pterygoid tooth plate in situ, based on specimens V7237, 7239, 7240 and 9054.
B, pterygoid tooth plate with palatoquadrate in viscéral view, V9054.
Diabolepis speratus (CHANG & Yu), Dévonien inférieur, Yunnan. Chine. A. reconstitution partielle de la portion antérieure
du crâne, avec la plaque dentaire ptérygoXdienne gauche en position anatomique, d’après les spécimens V7237, 7239, 7240
et 9054. B, plaque dentaire ptérygoïdienne avec palatocarré en vue viscérale, V9054.
braincase underneath the postnasal wall and just in front of the optic foramen (THOMSON &
Campbell, 1971: 81). With the pterygoid plate and the palatoquadrate thus applied against the
neurocranium, the groove following the opening on the latéral wall of the neurocranium, behind
the suborbital fossa (in V7240) is, situated between the ventral wall of the braincase and the
palatoquadrate, and if the two were to fuse, a canal would be formed which opens at the bottom
of the orbit. This is the condition in Dipnorhynchiis sussmilchi, where a distinct ridge on the
dorsal surface of the palate can be seen before the canal for the ophthalmic artery opens an-
teromedially to the dorsal process of the palatoquadrate (Thomson & Campbell, 1971: 68;
Campbell & Barwick, 1982, Fig. 16).
— 256 —
It is generally accepted that in Recent and fossil adult dipnoans, the palatoquadrate is fused
with the neurocraniuni through three processes, the otic process lo the otic région; and the basal
and ascendjng processes to the postcrior part of the orbitotcniporal région. It is aiso accepted
that there is a strong pars ptcrygoquadruia but no pars autopalalina in dipnoans. According to
Bertmar's study of the embryology of Neaceratodus (1965). a processus pterygoideus of the
palatoquadrate is developed in the 11.5 mm and 14.5 mm stages. However, it never chondrifies
but forms a ligament at the 16 mm stage (p. 89). MlUE.S (1971: 103) could not trace anything
comparable to the pterygoid process in fossil dipnoans. Jarvik (1980: 4U0-402V. however. sug-
gested that the pars autopalatina in dipnoans was incorporaled in the neurocranium, based on
an assumed relation, ship of dipnoans with sharks.
A comparison of the palatoquadrate of Diaholepis with those of eaiiy fossil dipnoans. i.e.
Dipnorhynchu.s & Uranolnphus, supports jARVtK's suggestion that the pars autopalatina is still
présent in primitive fossil dipnoans. In spccimens of Diaholepis the palatoquadrate is never co-
ossified wilh the neurocranium but is attached to the viscéral surface of the pterygoid plate. It
is well-developed in having a pars autopalatina and a pars quadrata with a commissural lamina
between thern The dorsal palatal lidgc seems lo be conncclcd with the commissural lamina.
There is no latéral ethmoidal articular process on the palatoquadrate. but the médial one is présent
in the form the oblique ridge and the anteromediul articular lamina. There is a .strong suborbital
articulation. The équivalent articulation in other fishes cannot be decided al the moment, though
Maisey (1986) suggested it is no more variable than the orbital articulation among recent squal-
omorphs. Judging from the normally developed basipterygoid process, a basal process must be
présent on the palatoquadrate. In early fo.ssil dipnoans such as Dipnurhynchus and Uranolophus
the pars autopalatina and the commissural lamina must also be présent. Le. the part situated at.
and latéral to. the buttress under the root of the postnasal wall, the pari with the thickening
under the optic foramen, and the part bearing the dorsal palatal process. Thçse parts fuse with
the ventral wall of the neurocraniuni, adding to lhe .suborbital ledge and makiiig it much broader
than in other osteichthyans. In later dipnoans, though there is no direct evidence for Ihis, the
broad latéral extension of the suborbital ledge and the shape of the impression lefi by the ventral
face of the neurocranium on the viscéral surface of the pterygoid plates suggest that the pars
autopalatina, and probably the commissural lamina, mighl be présent and ineoiporatcd in the
neurocranium. The différence between early and later dipnoans is that the dorsal palatal process
is absent in the later, as is possibly the adjacent pari of lhe palatoquadrate. This is probably the
reason why the exposed area of the entopterygoid in later forms is more extensive and situated
more anteriorly.
It is of interest to compare the palatoquadrate of Diaholepis wilh that of Powichthys, Glyp-
tolepis (porolepiforins) and Eusihenopteron (osteolepifonns). In Powichthys, as in Diaholepis,
the ventral surface of the postnasal wall is .smooth and there can be no latéral ethmoidal artic¬
ulation. However, lhe médial ethmoidal articulation is rather strong, wilh a well-defined bean-
shaped area devoid of periosteal lining on the neurocranium and an ethmoidal process on the
palatoquadrate (JHSSEN, 1989, Figs. 4, 5; Pis 1.1. 2). According lo JESSEN (1980; 199), the fossa
autopalatina in Powichthys is not as well-developed as in Porolepis, Holoptychius and Glyp-
tolepis,. but a sufficienily well-developed anlcromedial articular lamina is présent in the detached
palatoquadralea associated with Powichihv.s, that Jessen (1980: 182) referred to porolepiforms.
— 257 —
The otic shelf in Powichthys (p. 205) decreases in breadth anteriorly and there is no possibility
for such a paratemporal articulation as in Eusthenopteron. Judging from the well-developed
basipterygoid process, a basal process must be présent in Powichthys.
No palatoquadrate lias been found in Yuuiigolepis. On the evidence of the neufocranium,
however. a palatoquadrate sirnilar to that of Powichthys can be suggested- That is, there must
be a palatoquadrate vvilh the etlimoidal articulation concentrated in the médial side of the post¬
nasal Wall, and formed by articulations between the well-defined articulai' area and the fossa
autopalatina of the neurocranium on the one hand, and the ethmoidal process and the anteromedial
articular lamina of the palatoquadrate on the other. A basal process must also be présent in
Youngolepis, judging from the structure of the basipterygoid process. For the same reason as in
Powichthys, there can be no paratemporal articulation. Since there is no suprapterygoid process
in Youngolepis or Powichthys. it is difficult to infer whether an ascending process was connected
to the palatoquadrate or not. In the detached palatoquadrate associated with Powichthys, however,
a rather extensive processus ascendens with ridges for attachment of muscles was indicated by
Jessen (1980. Figs. 1. 2; PI. I).
The palatoquadrate in porolepiforms shows an ethmoidal articulation with the postnasal wall
on its latéral side, unhke that in Diabolepis, Powichthys and Youngolepis. Although there is no
well-defined area comparable to that in Youngolepis and Powichthys for the médial articulation,
there is aiways a fnssa autopalatina in varions degree of development received the rather extensive
anteromedial articular lamina of the palatoquadrate. A basal articulation must also be présent.
The grinding sériés of Glyptolepis groenlandica shows a fusion in ail these areas (JarvIk, 1972:
57; Bjerrinü, 1989. Figs. 2 A, 3B). Since there is no articular area without periosteal lining on
the ascending process, it is suggested hy JarvIk (1972: 71) that there was only a ligamentous
connection between the ascending process and the suprapterygoid process. As in Youngolepis
and Powichthys. the otic shelf Is concave ventrally and decreases in breadth anteriorly, and the
paratemporal articulation is absent.
In Eusthenopteron the palatoquadrate is, on the w'hole, sirnilar to that of porolepiforms.
However. it has a strong apical process which fits inlo the well-defined articular area in the
médial side of the postnasal wall, lacks the anteromedial articular lamina and the related fossa
autopalatina on the neurocranium, has a better formed articulation between the ascending process
and the suprapterygoid process. and has a paratemporal process for articulation with the thick
anterior end of the otic shelf. The latter seems to be an autapomorphy of Eusthenopteron (or
osteolepiforms).
Lower jaw
The lower Jaw of Diabolepis is the part of its skull that is most suggestive of dipnoans.
The main reason why Campbell & Barwick (1987: 36) doubted that Diabolepis was a dipnoan
was the uncertainty as to whether the lower jaw, pterygoids and cranium belonged to the same
animal. The structure of the lower jaw of Diabolepis is. in general, very sirnilar to thaï of tooth
platebearing dipnoans. Il shows, on its cxternal face, a comparatively short dentary and four
infradentaries lying in a row (as in early dipnoans). It is almosl impossible to trace the sutures
between these bones because of the cosmine covenng. In only one specimen, V7248, where the
superficial bone layer is worn away, can the houndaries between the four infradentaries be made
— 258 —
out by following the sutures and the lines radiating from the centres of the bones (Fig. 12). A
short, posterior division of the suture between the dentary and infradentary 4 can be .seen on
V7248, whereas the rest of the suture can only be estimated according to the dorsal extent of
ihe sutures between the infradentaries and the radiation of their bone structures. The inllected
dorsal portion of the dentary is covered with small teeth which are not arranged in one row
along the margin. but scattered lo form a toolh patch, prohably occluding with the tooth band
on the anterior portion of the upper jaw formed by the prcmaxillary and vomerine teeth. In
other dipnoans the dentary is usually not a toothbearing honc, excepl in a few forms where
tubercles or rows of tubercles are observed on its latéral margin (e.g. Griphognathus', Miles,
1977, Fig. 98; Uranolophus. Denison, 1968, Fig. 14A). The labial tooth plates (Semon, 1899)
which appear in early embryonic stages of Neoceratodus dcgenerate at a later stage and finally
disappear, and may indicale the presence of a toothbearing dentary in the early phylogeny of
dipnoans. Behind the inflected toothbearing portion, the dentary of Diabolepis extends further
backwards along the lower border of the labial pit and the lower jaw margin in the form of a
long, narrow strip. It ends at a point dorsal to the anterior part of infradentary 4, latéral to the
De
1
I
4 mm
t «
Fig. 12. — Diabolepis speratus (Chang & Yu), Lower Devonian, Yunnan, China. Right lower jaw rami in external view, V7248.
Diabolepis speratus (Chang & Yu), Dévonien inférieur. Yunnan, Chine. Branche droite de la mandibule en vue externe,
V7248.
— 259
Fig. 13. — Diabolepis speratus (Chang & Yu),
Lower Devonian, Yunnan, China. Right
lower jaw rami in buccal view, V9527.
Diabolepis speratus (Chang & YV), Dévonien
inférieur. Yunnan. Chine. Branche droite de
la mandibule en vue buccale. V9527.
posterior part of the lower tooth plate and the adductor fossa. This narrow, posterior extension
of the dentary is divided into two longitudinal portions, a latéral one covered with cosmine and
a médial one devoid of cosmine. In a specimen (V9529, Fig. 13) newly collected by Fan Junhang,
the upper (inner) border of the cosmine-covered portion bears numerous denticles with shiny
surfaces. In V7248, no signs of denticles or teeth are seen along the corresponding border, but
broken, irregular tooth-like structures can be seen along the inner margin of the portion devoid
of cosmine. In V7249, as in most other dipnoans, the lower jaw margin behind the inflected
part of the dentary, either the cosmine-covered part or the part devoid of cosmine, lacks any
kind of teeth or denticles. In V7248 the distal portion of the cosmine-covered part of the dentary
is slightly expanded. This small, oval portion resembles the small rounded piece of cosmine-
covered boue occupyiiig a similar position in V7249 (CHANG & Yu, 1984, Fig. 5B; Smith &
Chang, 1990, Fig. IB). It seems thaï this small piece of bone in V7249 is the broken, distal,
expanded end of the cosmine-covered part of dentary (Fig. 14). On the internai (buccal) side of
the lower jaw there is only one extensive dermal bone, the prearticular (but see Smith & CHANG,
1990), that is entirely covered with teeth or denticles, as is the case with ils opposing bone in
the upper jaw, the pterygoid plate. The dorsal surface of the prearticular is rhombic in shape
and differentiated from the rest of the plate. It is on the whole convex (e.g. in V7247 and
V7249), so as to match the reciprocally concave ventral surface of the pterygoid plate, although
the convexity is much less conspicuous in some specimens (e.g. V7248 and V9529) where the
— 260 —
teeth are worn. The dorsal surface of the prearticular is characterized by a regular arrangement
of teeth in radiating rows. The tooth rows converge in a posteromedial direction and the worn
teeth fuse at the posteromedial corner of the dorsal face to from a patch of continuons, worn
dentine resembling the heel of the tooth plate in later dipnoans such as Speanesydrion.
Hohidipterus and Dipterus. AH this makes the prearticular closely resemble the tooth plate of
later dipnoans with only two différences,
I - Not only the dorsal surface but aiso the remaining part of the bone, from the symphyseal
portion along the entire lingual side to the area around the glenoid fossa, is covered with small,
randomly scattered denticles. In most dipnoans with tooth plates, the parts of the pterygoid that
are not covered by the tooth plates are usually smooth, although denticles in the lingual groove
(prolingual field) and around the inner and posterior margin of the tooth plates are seen in
Speoneaydrkm (CAMPBELL & Barwick, 1984. Fig, 30). A prearticular extensively covered with
denticles is also found in Uranolophus (Df.NISON, 1968, Fig. 14) and Criphognathus (Miles,
1977, Figs. 98, 100b), although the area of bone latéral to the tooth ridge in the former and
below the denticulated area in the latter is still smooth. In Glyptolepis the prolingual field, an
Fig. 14. — Diabotepis speratus (Chang & Yu), Lower Devonian, Yunnan, China. Tentative reconstruction of lowcr jaw in dorsal
view, mainly bascd on V7248 and V7249.
Diubolepis speraïus {ÇUANG & Yü). Dévonien inférieur, Yunnan, Chine. Essai de rec onstitution de ta mandibule en vue dorsale,
d'après principalement les spécimens V724S et V7249.
— 261 —
area approximately corresponding to the lingual groove in dipnoans, is covered with numerous
sniall dental plates (jARViK, 1963, Figs. 14A-B, I5A-B), but no dental plates below the den-
ticulated area of the prearticular were shown by the grinding sériés.
2 - No adsymphysial plate like that présent in inany other dipnoans. e.g. Griphoguathiis,
Chirodipterus, Htilodiplerus. Rliynclwdipterus, Diptenis, lias been observed in Diaholepis.
The posterior portion of the lower jaw ramus is much more slender than its anterior portion
or the corresponding portion in other dipnoans. The adductor fossa is of the usual dipitoan type.
It is small and narrow, somewhat slit-like and flaiiked by the prearticular medially, and the
dentary and infradentary 4 latéral ly. Behind the fossa, in V7249, the dermal bones of both extemal
and internai sides extend up and then towards each other to form the postérolatéral border of
the adductor fossa. The glenoid fossa is not preserved. Since the posterior portion of the lower
jaw is thin, the articulation for the quadrate cannot be very strong. This seeins to accord with
the slender quadrate. On the latéral side of the lower Jaw, behind the tooth-bearing portion of
the dentary, is the labial pii, which i.s characieristic for dipnoans.
The small preailicular tooth plate (Fig. 15), found by Wang .Nienzhong (V953I), falls in
the same size range as the Juvénile lower Jaw tooth plate mentioned above (Kemp, 1979, Fig.
I4C), with a length of 2.9 mm and a width of 1.1 mm. The plate shows slight différences in
shape, proportions and arrangement of teeth frorn those of the larger (adult) plates. The occlusal
surface of the entire plate is notably convex. However. unlike the adult plates, there is no wcll-
defined, rhombic, dorsal portion differentiated from the rest of the plate. No particularly regular
Fig. 15. — Diaholepis speralus (Cmang & Yu), Lower Devonian, Yuiinan, China. Prearticular tooth plate in buccal view (A)
and enlarged portion showing traces of wear (B). V9531.
Diaholepis speralus {ChaN(J & Yv). Dévonien inférieur, Yiinnan, Chine. Plaque dentaire préarticulaire en vue buccale (A) et
portion agrandie nwnlranl des traces d'usure (B). V953I.
— 262 —
pattern of tooth arrangement could be made out. Three conspicuous, pointed teeth are situated
at the antérolatéral (labial) margin, which might give some hint of the growth pattern of the
plate, i.e. new teeth added from the labial margin, as mentioned by SMITH & Chang (1990).
The teeth in the middle part of the plate bear faint traces of wear.
DISCUSSION AND CONCLUSIONS
The characters of DiaboLepis described above and their distribution in other sarcopterygians
are summarized in the following table (table 1).
The characters used in table 1 are:
1. Appearance of médian bone in skull roof.
2. Numerous bones carrying the supraorbital sensory canal.
3. Anterior mosaic in skull roof.
4. Premaxilla independent.
5. Westoll-lines.
6. Interruption of the infraorbital sensory canal at anterior nostril.
7. Cosmine présent.
8. Main lateral-line canal running along edge of supratemporal sériés.
9. Posterior éléments of the nasal sériés and anterior éléments of the supratemporal sériés lying
side by side.
10. Fenestra ventrolateralis présent.
11. Vomerine area with uneven surface divided by grooves into raised areas of irregular shape
and size.
12. “Rostral tubuli”.
13. Tectum orbitale extensive.
14. Suborbital articulation between palatoquadrate and neurocranium.
15. Basipterygoid process laterally expanded.
16. Part of ophthalmic artery canal between ventral wall of braincase and palatoquadrate.
17. Médial ethmoidal articulation between the anteromedial articular lamina of the palatoquadrate
and the fossa autopalatina of the neurocranium.
18. Vomers separated from each other.
19. Dorsal palatal process (ridge) présent.
— 263 —
20. Marginal teeth reduced, teeth on premaxilla and dentary, if présent, never consisting of a
single row of conical teeth.
21. Labial pit.
22. Small number of dernial bones covering the palate and the lingual side of the lower jaw.
23. Regular arrangement of the teeth (radial rows) on the dorsal surface of the prearticular and
the ventral suface of the pterygoid.
24. Prolingual field covered with denticles.
25. Syndentine, circumpulpal dentine, and associated interstitial dentine.
The characters chosen here are ail présent in Diabolepis and restricted to the head région,
many characters occurring in other sarcopterygian groups, but not présent in Diabolepis, are not
included. It is obvious from lhe table that Diabolepis and dipnoans share most characters (1-25).
Among them ten (1, 5, 14, 16, 19-23, 25) are uniquely shared. Alhough characters 14, 15. 17
are used with the assumplion that lhe articulations w'ere fused in dipnoans and character 17
deserves observation on more spécimens to be confirmed. the re-st are w'ell understood through
extensive comparison. The ten characters mentioned above are mainly related to the palatoqua-
drate, jaw and bite, while the cranium of Diabolepis 'ihows quite a few primitive sarcopterygian
or osteichthyan characters, e.g. lhe présence of a premaxilla; the excurrent nostril occupying a
position latéral to the premaxilla; the long parasphenoid extending anteriorly to the ventral side
of the ethmoidal région, separating the pterygoids in the midline and restricted only to the anterior
cranial portion; the folded teeth; the otic région of lhe neurocranium entirely lined by the skull
roof, leaving no space for any ridges or muscle insertion; the palatoquadrate not fused with the
neurocranium; etc. It is precisely thc.se primitive sarcopterygian characters which caused he.si-
tation in placing Diabolepis among dipnoans. In spite of the few primitive characters seen on
the pterygoid plate and the lowcr jaw' (boih pterygoid and prearticular extensively covered with
teeth and denticles. dentary with teeth, and four infradentaries), they bear more dipnoan characters
than the cranium and, on the whole, look more dipnoan-like. There has been little doubl in
referring them to dipnoans. Now that the palatoquadrate and related parts of the neurocranium
are better known, it is more certain that the parts mentioned above belong to the samc animal.
First, the ridge-like process and the stout process on the médian margin of the dorsal surface
of the palatoquadrate fit well into the elotigated fossa on the ventral side of the crista suspendens
and the suborbital fossa on the ventral wall ot the braincasc below the optic foramen. This
relates the palatoquadrate and pterygoid plate to the cranium with certainty. Then, lhe palate
and lingual surface of the lower jaw show a similar disposition of dermal bones, i.e. the toothed
patch on the inwardiy bending portion of the dentary corresponds to the toothed band on lhe
anterior end of the upper jaw forined jointly by the premaxilla and vomer, and the dorsal surface
of the preanicular corresponds to the ventral surface of the pterygoid. The surfaces of the last
two bones are reciprocally curved to fit each other and are covered with similarly arranged,
radiate rows of teeth. The wear pattern is also very similar. The wom tooth bases are coated
with enamel, and the wom dentine shows the punciatc pattern of rings of circumpulpal dentine
seen in the lip tissue of Griphognathus (Smith & Chang, 1990). Thus, increased evidence suggest
Table 1. — Distribution of characters of Diabolepis in sarcopterygians. +, yes; -, no; F, suggested fusion between neurocranium and palatoquatrate; ?, data not
available; N, not applicable.
Distribution des caractères de Diabolepis chez les Sarcoptérygiens. +, présent ; -, absent; F, fusion possible entre le neurocrâne et le palatocarré ; ?, donnée
inconnue ; N. non appliquable.
264
— 265 —
that the cranium, plerygoid plate and lower jaw belong to the saine form and the close relationship
between Diabolepis and dipnoans suggested by uniquely shared derived characters is further
strengthened.
The rest of characters shared by Diabolepis and dipnoans falls into two sets, one is shared
by them and porolepiforms, Powiclitbys, and Yonngolepis-, the other is shared by ihem,
Powichihys, and Youngulepis, or shared by Diabolepis and Yonngolepis alone. The first set of
characters includes 2, 3, 13. 15. 17, 18, and 24. In characters 15 and 17 the relatcd parts of
the palatoquadiate in dipnoans are assunied to be fused wilh ihe neuroeraniuni, in characters 2
and 3 the bones carrying the supraorbital sensory canal and those of the anterior mosaic of the
skull roof are suggested to be fused with each other in Yonngolepis, and in 24 the stalc of (he
denticle covering in the prolingual field in Yonngolepis and Powichthys is not y et known. How-
ever, these characters show a possible close relationship between porolepiforms. including
Powichthys and Yonngolepis, and dipnoans. including Diabolepis. The second set of characters
includes 4, 6, 8, 9 and 1 1 . Thcy seem to group Powichihys and Yonngolepis with Diabolepis
and dipnoans or Yonngolepis with Diabolepis.
If Diabolepis is to be included in the group Dipnoi, the définition of the group would
certainly be changed and, conseqtienily, a few characters supposed to be shared by dipnoans
and tetrapods are to be deleted. As Forey (1987: 84) pointed out, sonie fossils provide evidence
that question .some of the characters u»ed to support the lheory of lungfish / letrapod sistergroup
relationship. In the case of Diabolepis, the pterygoids meeting at the midiine and the short pa-
rasphenoid would be taken away from the lisl of characters uniquely shared by dipnoans and
tetrapods proposed by Rosen el al. (1981). This often happens when a new la\on is discovered
and its relation to known taxa is restored. To delcte a few characters from, or to add a few to
the définition of certain groups is not the only rcfincmeiit that Diabolepis can offer. The most
interesting change broughi about by Diabolepis, considered together with Yonngolepis. is to pro¬
vide an alternative hypothesis for ihe inlerrelationships of sarcopterygians supported by evidence
others than whal we knew before. That is. the close relationship between dipnoans and
porolepiforms. in contrast to the close relationship between dipnoans and tetrapods. When
Powichthys, a much purolepiform-like “rhipidistian” was discovered from the Lower Devonian
of the Arctic Canada (JESSEN. 1975). the siniilarities between it and dipnoans vt'ere alrcady iioticcd
by Rosen et al. (1981: 165). The characters shared by Powichthys. Yonngolepis and
porolepifomis, i.e. a fossa autopalatina, foramen for the pituitary vein anterodorsal to the basipte-
rygoid process, vomers widely separated by the internasal pils and parasphenoid, intcrnasal ridge
and much eiilarged, downwardiy pointing basipterygoid process, werc indicated by GARDINER
(1984: 404) (o group them together. He further suggested a sister-group relationship between
porolepiforms + Yonngolepis and dipnoans + tetrapods (Gardiner, 1984, Fig. 147) on (lie basis
of two characters, namely. the immobilization of the intracranial joint and the cosmine porecaiial
System in which the niesh canals are without a horizontal partition and the porecanals are enamel-
lined. However, from the two characters the .second one Is shared only by porolepifomis and
dipnoans (see also RosEN et al., 1981: 257). Maisey (1986: 232-240; Fig. 14; see also JANVIER,
1986) was the first to note the porolepiform / dipnoan sister-group relationship. He started from
the two characters mentioned by Gardiner and added the rostral tubuli and the dipnoan-like
pectoral endoskelcton with a single sériés of “mesomeres” of Glyptolepis to show that
— 266 —
porolepiforms are a paraphyletic group of “stem dipnoans”. The number of characters shared by
porolepiforms and dipnoans has been increasing with further work on the newiy discovered
Powichthys, Yoimgolepis and Diabolepis as well as previonsly known sarcopterygians. From the
four characters suggesled for Youngolepis, Powichthys and porolepiforms by Gardinfr. three
(fossa autopalalina, vomers separated by intemasal pit, and enlargcd, downwardly pointing
basipterygoid procoss) vvcrc observed in Diabolepis. The fourth, the position of the pituilary
vein has yei lo be found out in Diabolepis. A beitcr uoderstanding of known characters hâve
been reached through examination of new spécimens. The fossa autopalalina. as we now under-
stand it, i.s the space for the anteromedial lamina of the palaioquadrate to inserl or to ailiculate.
New shared characters. such as the prolingual ficld covered with dcnticlcs, numerous bones car-
rying the supraorbiial .sensory canal, the anterior mosaic of the skull roof. etc. bave been added.
Close relalionship between Diabolepis and dipnoans and the grouping of porolepiforms with
dipnoans were shown in cladograms of sarcopteiygians appeared in quite a few newiy published
papers (YU. 1990; CHANO. I99|; FOREY et al., 1991; AHLDERG. 1991; ClouTIER. 1992).
SCHULTZE (1991. 1992) aiso accepts the sister-group relalionship between Diabolepi.s and dip-
noans, though not yet thaï between porolepiforms and dipnoans. With shared characters in régions
others ihan the skull added. and analysis of character distribution in sarcopterygians as a whole,
a clearer picture of the inleirelationships of sarcopterygians can probably bc obiained,
Acknowledgements
The main part of this paper was donc al the Natural History Muséum, London, supported by a Ouest
Research Fellowship from the Royal Society. I would like to extend my most sincere gratitude to Dr Moya
Smith. Division of .\natomy and Cell Biology. United Medical and Dental Schools of Guy’s and St.
Thomas's Hospitals, London, for applying the grant and for lier continuous help during my work in London.
I am particulafiy obliged lo Dr Roger Mii.F.s for reading lhe manuscript and encouragement. I am indebted
to Dr Peter FoRtv. Department of Palacomology. NHM, London, for .supplying specimens for comparison
and working facililies and lo liitn and Dr Colin PattKRSOK for reading and commcnliiig the manuscript.
1 am graieful to Dr Stephen Cui .vihaa, Canadian Muséum of Nature, futawa for loan of .'immiahvkus
specimens. My ihanks go to WANG Nien/hong for providing the small tooth plates (V9530 and V9531)
from his microverlebraie material and lo Fan Junhang for lhe lower jaw rami V9529. I would also like
to extend my gratitude to Marius ARSENAULT for providing funds for attending and presenting this paper
at the Symposium hcid in Miguasha. My thanks are also extended to Mrs Hii Huiqing for making the
figures and OUYANO Lîan for her help in préparation of the photos..
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Section C, n° 1-4 : 269-285 .
A functional interprétation of the anteriormost vertebrae
and skull of Eusthenopteron
by Edward C. HITCHCOCK
Abstract. — Mechanical préparation of a specimen of Eusthenopteron foordi bas revealed the articulated
anterior portion of the vertébral column, allowing for a comprehensive redescription and analysis of this région.
Neural arches are smaller than more posterior trunk segments, and do not fu.se dorsally as neural spines. Incipient
zygapophyses occur latéral or ventrolateral to the nerve cord. întercentra are paired, but do fuse in some specimens.
Large blade-like supraneural spines are présent above neural arches I, 3, and 5, but not 2 or 4. The supraneural
spines supported a nmscular coinpiex involved in feediiig not only through raising the snout, but aiso by dépréssion
of the lower jaws induced by the forward swing of the quadrate. Flexion of the intracranial joint is likely res-
ponsible for the initiation of Jaw closure during feeding
Keywords. — Vertebrata, Sarcopteiy'gii. Osteolepiformes, Devonian, Canada, functional anatomy.
Interprétation fonctionnelle
des vertèbres les plus antérieures et du crâne d’ Eusthenopteron
Résumé. — La préparation mécanique d’un spécimen é’ Eusthenopteron foordi a révélé la partie antérieure
articulée de la colonne vertébrale, permettant ainsi une redescription et une analyse détaillées de cette région.
Les arcs neuraux sont plus petits que dans les segments plus postérieurs du tronc et ne sont pas fusionnés
dorsalement en épines neurales. Des ébauches de zygapophyses apparaissent latéralement ou ventro-latéralement
à la moelle épinière. Le.s intercentres sont pairs, mais ne sont pas fusionnés sur certains spécimens. De grandes
épines supraneurale.s en forme de lames sont présentes au-dessus des arcs neuraux 1,. 3, et 5. mais absentes des
arcs neuraux 2 et 4. Les épines supraneurales soutenaient un complexe musculaire mis en jeu dans la manducation,
non seulement en relevant le museau, mais aussi en favorisant l’abaissement de la mandibule, induit par le
basculement antérieur du carré. La flexion de l’articulation intracrânienne est vraisemblablement responsable du
déclenchement de la fermeture de la bouche lors de la manducation.
Mots-clés. — Vertebrata, Sarcopterygii, Ostéolépiformes, Dévonien, Canada, anatomie fonctionnelle.
E. C. Hitchcock, Redpath Muséum, McGill University, 859 Sherbrooke St. West, Montreal. Canada, HSA 2K6. Présent address:
Department of Anatomy and Neurobiology, Dalhousie University, Halifax. Nova Scotia, Canada, B3H 4H7.
Introduction
The o.steolepiform rhipidistians are considered by most paleontologists to be the si.ster-group
of tetrapods, or the group from which the tetrapods arose (Wat.SON, 1926; Jarvîk, 1942; THOM¬
SON, 1962; Panchen & Smithson, 1987; but for an alternate view see Patterson, 1980; Rosen
et ai, 1981). Any study of the origin of tetrapods must therefore rely heavily on knowledge of
the osteolepiform rhipidistians. One character of tetrapods not présent in fish is an atlas-axis
— 270 —
complex. In order to shed some light on the history of this structure the anteriormost vertebrae
are examined in Eusthenopieron, which is one of the best known rhipidistians, thanks to the life
Work of Professor Erik JARVlK.
Previous descriptions of the anteriormost région of the vertébral column of Eusthenopieron
foordi based on grinding sériés (JARVtK, 1975, 1980), and disarticulated remains (Andrews &
Westoll, 1970), conflict with one another. My intent in this paper is to clarify this discrepancy
by préparation and direct observation of a three dimensional skull of Eusthenopieron in which
the anterior part of the vertébral column is intact, and détermine the functional significance of
these éléments in conjunction with structures of the cranium. As this région is associated with
the epaxial muscles involved in skull movement, this problem also involves the functional mor-
phology of feeding mechanics in this fish.
Skull mobilily and feeding mechanics hâve been studied previously in coelacanths (Lauder,
1980; Lund et al., 1985) and rhipidistians (THOMSON, 1967) in an effort to understand the rôle,
if any, of a bipartite braincase in these groups. A different model is discussed in this paper,
wherein the snout région is flexed at the initiation rather than at the end of jaw closure.
— 271 —
MATERIALS AND METHODS
Ail the specimens of Eusthenoptewn examined were collected from the Escuminac Forma¬
tion on the Rcstigoiiche River, on the south coast of the Gaspé Peninsula, Quebec, Canada. This
site is now a provincial park. Parc de Miguasha. and is the location of the Musée d’Histoire
naturelle de Miguasha (MHNM).
The specimens used in this study are as follows:
— GN 79Ü (Cambridge University, Muséum of Zoology). A short sériés of vertebrae.
— MHNM 06-216. An articulated sériés of trunk vertebrae.
— MHNM 06-12-196. The ventral half of the otoccipital portion of the endocranium.
— ROM 1234 (Royal Ontario Muséum, Toronto. Canada). An endocranium, first described
by SteR-NBERG (19411.
— ROM 1245. .'kn almost complété vertébral column in ventral aspect with some skull
bones.
— BMNH P. 6796a (The NaUiral History Muséum. London, United Kingdom). A large
three dimensional skull, behind which lies much postcranial material, mostly disarticulated.
— RM 14234 (Redpath Muséum, McGill University, Montreal. Canada). A complété three
dimensional skull. Mechanical préparation exposed the anterior portion of the vertébral column
and the occiput. This specimen forms the basis of this research.
Mechanical préparation of RM 14234 and MHNM 06-12-196 was done using a Chicago
Pneumatic CP-9361-1 Air Scribe. Délicate préparation was performed using a mounted needle.
Some Chemical préparation was done using 10?c acetic acid. VINAC B- 15 polyvinyl acetate
was used as a consolidant.
RESULTS
Observations of the brainca.se of Eusthenopteron
The anatomy of the braincase of Eusthenopteron has been previously described in great
detail (JarvIk, 1954, 1980; Bjerring, 1971. 1978). During the course of this study some ad-
ditional features were revealed.
Posterior and ventral to the jugular canal on the posterior face of the latéral commissure
lies a process. presumably for the origin of the adductor hyomandibularis (Bjerring. 1971;
JarvIk, 1980) which has not previously been described in detail. The latéral face of this process
(Fig. 1) bcars a groove continuons with the jugular canal. The dorsal margin of the process
forms a slight ridge which extends anteriorly into the Jugular canal, indicating that the vessels
that passed through the jugular canal diverged, The course of one vessel passes médial to the
process and follows the contour of the braincase, while the other passes between this process
and the hyomandibular, A groove on the médial face of the proximal end of the hyomandibular,
possibly for a large vessel. substantiates this. The jugular groove along the side of the braincase,
which has been well documented (JarvIk. 1954; 1980), ends posteriorly at the latéral occipital
fissure below the postotical process.
— 272 —
FîG. I. — Tlie left jugular canal ot' specinien MHNM 06-12-196 in dorsolateral view. Hatching inclicates sectioned bone, and
arrows indicate ihe direction of vcssels Icaving the canal posteriorly. (From HITCHCOCK, 1992. Fig. 4).
Canal jugulaire gauche du spécimen MHNM 06-J2-J96 en vue dorso-latérale. Les hachures indiquent l'os sectionné et les
flèches indiquent la direction des vaisseaux quittant le canal postérieurement. (D’après HITCHCOCK. 1992, fig. 4).
Médial to the process for the origin of the adductor hyomandibularis, and extending ante-
riorly from the postotical process on the ventral surface of the parotic crest, is a conspicuous
crescentic ridge (see the reconstruction in Fig. 7A). The ventral portion of this structure forms
the dorsal margin of the jugular groove, and has been termed the jugular ridge (JarvIk, 1980).
This was first documented in Ectmieorhachis (described as Megalichthys) (Romer. 1937), and
was interpreted as the origin for the adductor opercularis. This is corroborated by the position
of origin of this muscle in Latimeria (MllXOT & ANTHONY, 1958). It lies dorsal to the origin
of the adductor hyomandibularis and posterior to the dorsal articulation of the hyomandibular.
Ventral to the jugular groove and posterior to the ventral head of the hyomandibular is a
région withoui ossification. JarvIk ( 1980) suggests that the cavity in this area probably contained
the saccule. and also suggests that the surface was pierced by a fenestra ovalis. The surface of
this région is ossified in Eclosteorhachis (Romer, 1937), but shows no evidence of a fenestra
ovalis. Without direct evidence of an opening comparable to the fenestra ovalis of tetrapods, a
elaim that a fenestra ovalis is présent in Eusthenuptewn is prématuré.
The ANTERIOR VERTEBRAE OF Eusthenopteron
The anterior portion of the vertébral column of Eusthenopteron has been described pre-
viously by JarvIk (1975, 1980) based on serially ground sections, and by Andrews & Westoll
(1970) based on disarticulated material. JarvIk's (1975) reconstruction shows a large supraneural
blade over the first two neural arches, which he interpreted as the fused supraneurals of these
two segments, and small supraneurals above each succeeding segment up to about segment 10
(Fig. 2A). He also reconstructs the “interdorsals" with small tlanges extending up to cup the
ventral surface of the neural canal, and with foramina for the dorsal and ventral roots of the
— 273 —
spinal nerves. In this reconstruction, ribs are présent from the fifth or sixth segment back. The
reconstruction by ANDREWS & Westoll (1970) includes no supraneurals, and the segments are
spaced farther apart (Fig. 2B). There is little if any différence between the anterior and trunk
vertebrae in their reconstruction. The reconstruction was made from disarticulated material (spéci¬
men BMNH P. 6796a), and the élément shown as the neural arch of segment 3 (Andrews &
Westoll, 1970, Fig. 20a) is likely a supraneural (pers. observ.). By préparation and direct ob¬
servation of articulated material, the discrepancies between these two previous reconstructions
can be resolved.
In RM 14234, vertebrae 2 through 5 are articulated and not greatly disturbed from the
position they would hâve held in life (Fig. 3). The first neural arch is rotated horizontally so
Occ
Fig. 2. — Previous reconstruclions of ihe cranio-vertebraJ joint in Eusthenopteron. A. based on JARViK (1975); B, based on
Andrews & Westoll (1970, text and figures).
Précédentes reconstitutions de l'articulation cranio-vertébrale chez Eusthenopteron. A, selon JarvIk (1975) : B, selon ANDREWS
& Westoll (1970, texte et figures).
— 274 —
that the nature of its articulation with the occiput cannot be seen. The first intercentrum is also
disarticulaled, lying ventrolateral to intercentrum 2. There is a gap between neural arches 5 and
6, owing to arch 5 having been pushed anteriorly and arch 6 pushed posteroventrally. Intercentrum
7 is articulated with intercentrum 6; however its arch is obscured by two or three disarticulated
arches that lie at the posterior margin of the block. Supraneural spines are présent above the
neural arches of segments 1, 3, and 5, while there are no ossified spines above arches 2 and 4,
and there is no indication of a neural or supraneural ossification above arch 6.
Ail the intercentra appear to be paired crescents in ROM 1245. In BMNH P. 6796a and
GN 790, some of the intercentra are fused, producing horseshoe-shaped unitary intercentra. This
does not seem to be size related. GN 790 has intercentra 9 mm in diameter and BMNH P. 6796a
has intercentra 18 mm in diameter, while ROM 1245 has intercentra roughiy 20 mm or more
in diameter but shows no fusion (these centra are splayed, so that the diameter is estimated).
Ail the intercentra visible in ROM 1245 and RM 14234 hâve a vertical ridge of unfinished bone
on the latéral face, and immediately posterior to this a vertical groove for the intersegmental
artery (Fig. 4). The whole extemal surface of the posterior half of the centmm is of periosteal
bone, except for the ridge which was probably continuons with the myoseptum. Anterior to the
ridge there is some perio.steal bone missing, particularly in the dorsal half. This differs from the
description by Andrews & Westoll (1970) in which the dorsal half of the entire centrum was
described as being devoid of periosteal cover. The ventral surface of the intercentrum is flattened
and smooth, with neither the ridge nor groove extending to this région. In life the two halves
of the intercentrum would hâve abutted ventrally such that the flattened ventral régions would
Fig. 3. — The articulated anterior portion of the vertébral column of Eusthetioptenm exposed by préparation of specimen RM
14234. Note that the exposed surface is not fiai, .so that some of the éléments appear distorted. For details of individual
éléments, see figures 4 to 6.
Portion articulée de la colonne vertébrale r/'Eusihenopteron révélée par la préparation du spécimen RM 14234. Noter que
la surface exposée n 'est pas plate, de sorte que quelques‘Uns des éléments apparaissent comme déformés. Pour te détail de
chaque élément, voir les figures 4 à 6.
— 275 —
Fig. 4. — The intercentra of specimen RM 14234.
Intercentres du spécimen RM 14234.
form a channel, concave ventrally. for the dorsal aorta (ANDREWS & Westoll, 1970; JARVlK,
1980). The dorsal end of the latéral face, which underlies the neural arch, bears a slight depre.s-
sion. Neilher the ridge nor groove exlend to this région. Therc is no evidence of suturai contact
between intercentrum and arch. None of the first seven intercenira show evidence of parapophyses
or ribs. The firsl and second intercentra in RM 14234 appear to be narrower and less robust
than in succeeding segments, This may be due to préservation, since in ROM 1245 ail exposed
intercentra appear to be equally robust.
The neural arches are small and closely spaced. Arches 2 through 6 are similar in shape
(Fig. 5), while arch I is rotated 90 degrees so that its posterior margin is obscured by arch 2,
and its complété outline cannot be seen. The ventral portion of each arch that overlaps the
intercentrum is more vertical when viewed laterally, and more oblique when viewed anteriorly
or posteriori y. The dorsal portion, which covers the .spinal cord. is angled posterodorsally when
viewed laterally, but appears more vertical than the ventral half when viewed in anterior or
posterior aspect. The latéral surface is smooth as is .seen in more posterior arches and spines,
with no striations or muscle .scars, except for a longitudinal boss on the ventrolateral margin of
arch 1, Because of the orientation of the dorsal portion of the arches, they lie close to one
another, with tire dorsal half of one arch extending over the ventral half of the following arch,
although there are no articulating facets. These incipient zygapophy-ses occur latéral or ven¬
trolateral to the spinal cord and are pairc4, whcreas in most trunk and caudal segments incipient
zygapophyse.s occur dorsal to the nerve cord on the neural spines, and are médian.
In RM 14234, the pleurocentra (interdorsals of JarvIk) présent between the ventral halves
of successive neural arches are small and poorly preserved, and as such it is difficult to ascertain
their exact shape (Fig. 5). They are higher than wide, with a convex latéral surface of fragile
periosteal bone. There is no evidence of nerve canals, and their position between the ventral
halves of successive arches below the incipient zygapophyses and adjacent to the dorsal extremity
— 276 —
Na1
Fig. 5. — The pleurocentra and neural arches of RM 14234.
Pleurocentres et arcs neuraux de RM 14234.
SN1
SN3
Fig. 6. — The supraneurals of RM 14234.
Supraneuraux de RM 14234.
SN 5
of the intercentrum implies a position on the dorsolateral surface of the notochord, rather than
latéral to the spinal cord.
The supraneural spines in RM 14234 are larger than any previously described for
Eusthenopteron foordi (Figs. 3, 6, 7). Supraneurals are présent above arches 1, 3 and 5. There
is insufficienl space between successive supraneurals to accommodate supraneurals above arch
2 or 4. Each is broad and lies in line with the dorsal portion of the arch with which it is
a.ssociated. The latéral surface of each is marked with distinct longitudinal striations, and the
anterior and posterior margins bear thin flanges and grooves. The ventral margins are rounded,
showing no evidence of articulation with the arches. They are at least as thick as the neural
spines of the trunk segments, and are probably of cancellons bone, as indicated by the fact that
supraneural 5 has been crushed in the middle, but suffered little deformation around the periphery.
The spines are unpaired médian éléments.
— 277 —
Supraneural 1 has been deformed anterodorsally, but is roughly ogival in outline with a
flattened ventral margin (Fig. 6) and is the broadest of the supraneurals. The anterior margin is
rough and uneven, with a thin médian flange which was presumably continuous with the dorsal
médian septum. Three deep grooves run to the anterior margin, one ventrally and two dorsally.
The dorsal grooves are separated by a ridge, and extend for almost one third of the width of
SN1 SN3 SN5
Occ
A
B C
Fig. 7. — A reconstruction of the anteriormost vertebrae and occiput of specimen RM 14234. A, left latéral view; B, anterior
view; C, posterior view. (From HITCHCOCK, 1992, Fig. 13).
Reconstitution des vertèbres les plus antérieures et de l'occiput du spécimen RM 14234. A, vue latérale gauche ; B. vue
antérieure: C. vue postérieure. (D'après HITCHCOCK, 1992, ftg. 13).
— 278 —
the bone. The latéral surface is covered by tiny striations, niostly longitudinally, but some slightly
oblique.
Supraneural 3 is also oval, but narrower than SN I (Fig. 6). It bears longitudinal striations
and one deep groove across the dorsal tip. The anlerior face bears a groove along its middie
third. bordered top and bottom by raised processes, which are extensions of latéral ridges. The
posterior margin of this élément is not marked by a médian Hange. Supraneural 5 is narrower
than botb SN 1 and 3, being almost rectangular in shape with the dorsal end slightly wider than
the ventral end, The striations are less distinct, and this élément is more crushed than the others.
A distinct médian flange lies along the posterior margin. while a short groove is visible in the
upper part of the lower half of the anterior margin.
A portion of a spine, broken transversely, lies dorsal to the column at the posterior margin
of the specimen. Uniike the first three stipraneurals it is not crushed, and its surface is smoother,
although it still bears striations and a small process. Uniike a neural arch, it bears a periosteal
covering and is convex on both sides. It is uncertain whether it is a supraneural for segment 6
or 7, or if it is the dorsal half of a more posterior neural spine. The latter seems more likely,
owing to the texture of the bone and its resemblance to more posterior spines of other specimens.
DISCUSSION
Develop.ment of supraneurals
Ossified éléments dorsal to the neural arches are common in fishes. Embryologically these
éléments may either grow upward from the neural arches as neural spines. or down towards the
neural arches as dérivatives of fin radiais (Goodrich. 1930). In fossil fishes these éléments may
be fully formed in cartilage before becoming ossified. obscuring the direction of growth and
confounding their developmental origins.
Euathenopternu has long bladedike neural spines on trunk and tail segments. Rod-like dorsal
fin radiais are found only in association with the fins: one proximal radial with the first dorsal
fin, two with the second dorsal fin (one of which is fused with the middie radiais), and fused
to the neural spines in the caudal fin. This suggests that the supraneurals were derived most
probably from the neural spines.
Elsewhere in the vertébral column of Eusthenopteron lhere is ossification at the junction
of the myoseptum and dorsal médian septum immediately dorsal to the neural arches. No such
ossification is présent dorsal to neural arches 2, 4 and 6, which indicates that the myotomes
may hâve been fused, at least medially, and that the myoseptum did not intersect the médian
septum in these places, but this cannot be proven.
Variation within the vertébral column of Eusthenopteron
The anteriormost segments of the vertébral column differ from the more posterior trunk
and tail régions in Eusthenopteron. The trunk and tail segments hâve long neural and haemal
spines projecting posterodorsally and posteroventrally. respectively, spanning several succeeding
segments (Fig. 8B, C). In the trunk and tail of fishes, the myotomes of the right and left sides
— 279 —
Fig. 8- — Régional variation in Ihc vertébral eolumn of Eusihenopieron. A. anierior. segments 3 to 6; B, mid trunk, approximaicly
segments 20 to 23; C, posterior trunk, approximatcly segments 40 lu 42. B and C based parlly on Andrews & Westoll
(1970).
Varialiom de Ici morphologie de la coUnow vertébrale selon les régions du corps chez Euslhenopleron. .4. partie antérieure,
segments 3 ù 6 ; B, partie moyenne du tronc, approximativement segments 211 à 23 ; C, partie postérieure du tronc, approxi¬
mativement segments 40 à 42. B et C fondées en partie sur ,\,'tDKEWS dt WtSTUu. (1970).
contract altemately to produce a strong oscillation at the tail for locomotion. The neural and
haemal spines act to limit the latéral tlexibility of the trunk during locomotion so that the force
can be maximized at the tail (HiLDEBRAND. 1988). This pattern doe.s not absolutely restrict latéral
flexion but allows for latéral flexibility of thebody if the muscles of only one side arc contracted.
The myotomes in the région between the skull and the pectoral girdle are not used primarily
for locomotion (JarvIk. 1980) but for respiration and feeding. The epaxial musculature has a
large area of insertion on the posterior and latéral faces of the braincase in Ainia (JarvIk. 1980)
and Laiimerici (MiLLOT & ANTHONY, 1958) and probably in Eusihenopteron as well judging by
the deep fossa bridgei. For raising the skull or for ventilation of the gills, the muscles in this
région act bilaterally, rather than altemately, .so that both opercula are opened simultaneously,
or in raising the head both .sides of the back t)f the skull are pulled back simultaneously.
This explains why the morphology of the anteriormost vertébral éléments differs from that
of more posterior segments. Inslcad of acting to rcsist latéral flexion of the vertébral eolumn,
the spines in this région act to bridge the myotomes of the two sides with a solid connection.
Bilateral contraction of ihc epaxial musculature would act to pull back the top of the skull, and
raise the snout. The close proximily of the neural spines in more posterior segments severely
restricts vertical flexion of the vertébral eolumn. In ihe anterior région of the vertébral eolumn,
the lack of ossified éléments above arches 2 and 4 allows the suprancurals of segments 1, 3
and 5 to be pulled doser together to allow dorsal flexion. The decoupling of neural arches and
supraneurals allows the supraneurals to move independently of the arches. Thus the rapid move-
ment of the supraneurals during a powerfiil contraction of the epaxial muscles would not place
great stress on the spinal cord.
Skui.i. kinf.tics and feeding mecranics
The function and degree of kinetism of the skull in Eusthenopteron and other osteolepiforms
remains a controversial issue. It is believed by many paleontologists (Watson, 1926; Romer,
1937; Thom.son, 1967; 1969) that significant movement was possible between ethmosphenoid
— 280 —
Fig. 9. — The separate skeletal units that comprise the head of Eusthenopteron. The hatched areas on the snout and .skull roof
indicate the région of overlap by the cheek plate. (From Hitchcock, 1992, Fig. 1; based in part on jARVlK, 1980, Figs.
107. 110, 112).
Les différentes unités squelettiques comprises dans la tête d' Eusthenopteron. Les zones hachurées sur le museau et le toit
crânien indiquent la zone de recouvrement par la plaque de la joue. (D'après HITCHCOCK. 1992, fig. 1. (en partie d’après
Jarvik. 1980, figs 107, 110. 112).
and otoccipital portions of the braincase, while others (JarvIk, 1954; 1980; Bjerring, 1971;
1978) believe that kinetism is impossible if the interconnections between ail the components are
consi dered.
The following examination of the components of the head (Fig. 9), starting from the hy-
pobranchial apparatus and working up, describes the mobility of which the skull was likely
capable. The ceratohyals of the hypobranchial apparatus are braced against the inner surface of
— 281 —
the lower jaw. The principal function of Ihis apparatus is the ventral expansion of the oralo-
branchial cavity. Such an expansion is produced by contraction of the stemohyoideus muscle
pulling the basket posteriorly. This also generates a strong latéral force on the posterior extremity
of the jaws, as in modem bony fish (Ai.f.xANDER. 1970). The loose symphysial connection of
the lower jaws implies that ihe angle, between them was not tïxed. If the posterior end of the
lower jaws moved lalerally, the quadrate must follow or the jaws would disarticulate. There
must thcrcfore be somc degrce of latéral movement of the palatoqiiadrate wjth respect to the
endocranium. The articulation of the palatoquadrate to the otical shelf lies in line with the ar¬
ticulation of the processus connectcns and would not prcvent movement of the intracranial joint.
Thomson (.1967) .States that the palatoquadrate was not connected to the otical shelf, but whether
this connection of the palatoquadrate exists or not is of little importance to its mobility. Also
contrary to ThoMvSON (1967) and Smithson & Thomson (1982) there appears to be no finn
connection between the hyomandibular and the palatoquadrate.
If the palatoquadrate hinges laterally then there must also be .some flexibility of the cheek,
because ihc cctopterygoid abuts the médial surface of the maxilla, The small areas where the
cheek overlaps the skull roof and snout likely allowed some sliding and would not preveni the
cheek from moving laterally. The sliding nature of the overlap of the postorbital bone of the
cheek plate across the hinge line would also not prevent mobility of the intracranial joint. The
processes of the supmtemporal (intertemporal of JaKVIK) extending below the hinge line would
limit, but not prevent skull kincsis. Muscle scars on the ventral surface of the braincase indicate
the presence of a large subcephalic (or basicranial) muscle mass, which in the iiving Latimena
is responsible for flexion of the intracranial joint (MlI.LOT & ANTHONY. 1958).
The feeding mechanism in Eusthenapteron (Fig. 10) was probably much like thaï proposed
for Latimeria by L.AUDER (1980), which differs from the interprétation by Thomson (1967).
The initial action in the feeding mechanism of Eunlhenn/Heron was the contraction of the anterior
epaxial muscles to raise the skull. The result of this was not only to raise the upper jaws, but
also to depress the lower jaws. Contraction of the strong anterior epaxial muscles resulted in
the posterodorsal rotation of the endocranium, which pivoted around a point posterior to the
occiput, at the dorsal margin of the notochord. The palatoquadrate. which is aiiached to the
endocranium at .scvcral points, rotated with it, thrusting the quadrate joint forward. In this initial
phase of jaw opcning, as the endocranium is swung upward, the quadrate joint is swung likc a
pendulum through an arc from a point below and behind the occiput to a point below and in
front. The effective lever has the dorsal part of the occiput as the short arm. the occipital-vertebral
joint as the fulcrum, and the quadrate articulation as the distal point of the long arm. The motion
of the sort arm (dorsal part of occiput) is magnified in the long arm (quadrate) by a factor of
about twelve to one.
The lower jaw is a lever with the short arm between the quadrate articulation and the
latéral process of the ceratohyal. The long arm is from this articulation to the symphysis, and
is about five times as long as the short arm. The fulcrum is below and in front of the articular
so that the rotation of the tnandible is in the opposite direction to that of the palatoquadrate.
The motion of the skull is magnified in the motion of the quadrate and is magnified again in
the swing of the symphysis. Thus the short powerful contraction of the epaxial muscles not only
raises the skull and upper jaws, but is also responsible for the rapid lowering of the mandibles.
— 282 —
Fig. 10. — The feeding meclianisni of Eusthenopteron. A. from the re.sling position, the epaxial musculature inserling in Ihe
fossa bridgei contracts, pulling the skull up and back (B): C. the notochord compresses slightiy. then releases the stored
energy, hyperextending the ethmosphenoid. This snaps the quadralc forward, rotating the lower Jaw around the articulation
with ceratohyal 1; D, initiation of jaw closurc is through contraction of the subcephalic muscle.s. w^hich swings the quadrate
posteriorly, rotating the lower Jaw inlo position for final Jaw closure through contraction of the adductor muscles (El.
Mécanisme de la manducation chez Eusthenopteron. A, à partir de la position de repos, la muscu/ofure épaxiole qui s'insère
dans la fosse de Bridge se contracte, tirant le crâne vers le haut et vers rarrièfe iB) : C. la notochorde se comprime
légèrement, puis relâche l'énergie emmagasinée en mettant rethmosphénoïde en forte extension. Cela a pour effet de propulser
le carré vers l’avunt. faisant pivoter la mandibule autour de rarticulation avec le ceratohyal / ,• D, le déclenchement de la
fermeture de la houche se fait par contraction des muscles suhcépiudiques. qui projelient le carré vers Varrière. faisant
ainsi pivoter la niandihule dans sa position finale de fenneiure des mâchoires par contraction des muscles adducteurs (E).
— 283 —
Since the skull is raised as a unit, there is no need for a large muscle mass to raise the
ethmosphenoid with respect to the otoccipital, and indeed none has been found (Millot &
Anthony, 1958; Thomson, 1967; JarvIk, 1980). The ethmosphenoid may be slow in raising,
because of some compressibility of the notochord. but this compressibility may hâve played a
part in jaw opcning and closing. The notochord may hâve actcd as an elastic elemeni iti the
intracranial joint, so that as the otoccipital is pulled back and up, rotation of the ethmosphenoid
is delayed by its inerlia and the energy is stored in the notochord like a compressed spring.
When the otoccipital is exlended maximally, the notochord spring releases its energy and the
ethmosphenoid snaps up and bccomes hyperextended, further increasing the swing of the quadrate.
The stretched notochord would then help in the downward accélération of the ethmosphenoid
during the initial phase of jaw closure.
If the tower jaw is depresscd by a forward swing of the quadrate, then initiation of jaw
closure may bc by way of a rearward sw'ing of the quadrate. Such a swing may be induced by
means of the subcephalic (or basicranial) muscles. Contraction of thcse muscles produces a ro¬
tation of the ethmosphenoid and palaioquadrate around the processus connectens, and the quadrate
is thrust posteriorly. swinging the lower jaw in the reverse of the manner of opening, without
having to overcome the inertia of the entire skull. The fulcrum this time is the intracranial joint.
The long lever arm is longer than in the opening sequence, and the short lever arm is the effective
position of the subcephalic muscles. The fulcrum of the mandible initially is the area of insertion
of the anteriormost (deep) portion of the adductor mandibulae. which has the mosl posteriorly
directed fibres (Thomson, 1967; J.^RV1K., 1980). Because the intracranial joint is located more
anterior than the occiput, the swing of the quadrate has a greaicr vertical component than in
initial phase of the opening sequence. so that tn the later stage of its swing both the quadrate
and the adductors act to lift the mandible. In this way a slight flexure of the intracranial joint
has a large effect on the gape Final jaw closure is by contraction of the posterior (latéral)
portions of the adductor mandibulae, which pull the jaw up against the skull.
This model is aiso in agreement with LUND et al. (1985), who daim that the crushing
aspect of etltmospheiioid flexion, i.e, Thomson’s (1967) model of rhipidistians and Lauder’s
(1980) model of Latimeria, in which ethmosphenoid contraction is the lasl phase of jaw closure
and is used to puncture prey, has been exaggerated, parlicularly when it concerns coelacanths
with feeble dentition.
Simultaneous ventral and latéral expansions of the hypobranchial apparatus and cheeks
increase the volume of the oralobranchial cavity. This aIso forces the stylohyal laterally, and
in conjonction with the protraction of the hyomandibular the operctilars are forced open. Ail
of these actions help to produce suction to aid prey capture. This may well continue late in
the cycle tn conipensate for the volume réduction caused by closing the jaws, as in Anna
(Lauder, 1979). Use of the subcephalic muscles to initiale jaw closure does not draw the
palatoquadrate complex medially, while muscular action direcily on the palatoquadrate would.
This would help prevent the oralobranchial cavity front becoming prematurely redueed in
volume during jaw closure.
— 284 —
CONCLUSION
The anterior portion of the vertébral column in Eiisthenopternn possesses large blade-like
supraneural spincs separate from the neural arches, above arches l. 3, and 5. The supraneurals
act to bridge the epaxial myotomes of the right and left sides, and are positioned to allow rapid
and powerful contraction of these muscles. The contraction of these muscles pulls the skull
back, raising the snoul and .swinging the quadrate forward. This forward .swing of the quadiate
combined with the posterovcntral motion of the hypobranchial apparatus acts to rotale the lower
jaws downward. The final stage of jaw opening involves the hyperextension of the ethmosphe-
noid, furlher increasing the gape. Initiation of jaw closure may be through contraction of the
subcephalic muscles, in the reverse of the final stage of jaw opening. Jaw closure is completed
by contraction of the adductor muscles, pulling the lower jaws up against the skull. In this
model there is a greater swing of the quadrate lhan m previous models. due to a greater par¬
ticipation of the otoccipital, and the fact that the hyomandibular is not firmly connected to the
palatoquadrate. This model also places a greater emphasis on the suction aspect of the feeding
mechanism of Eusthenopleron, and less on the biting aspect of previous models.
Acknowledgements
I would like lo thank R. L. Carroll for sponsoring this proJect, J. A. Clack, P. Forey, and
M. Arsenault for allowing me to examine material in their collections, and P.-Y. Gagnier, P. Ahlberg,
M.I. COATES and S. M. Andrews for helpful discussions on this and other topics.
LtlERATURE CITED
Alexander, R. M., 1970. — Functional Design in Fishes. Hutchison, London.
Andrews, S. M. & T. S. Westoll, 1970. — The postcranial skeleton of Eusthenopteron foordi Whiteaves.
Trans. R. Soc. Edinburgh. 68: 207-329.
Bjerring, H- C. 1971. — The nerve .supply lo the second metamere basicruniul muscle in osleolepiform verte-
brates, with some lemarks on the basic composition of the endocranium. Acia. Zool. ISlockholm), 52: 189-
225.
— 1978. — The “intracranial joint” versus the “ventral otic fissure" Acta. Zool, (Stockholm). 59: 203-214.
Carroll, R. L., 1987. — Vertebrale Paleontology and Evolution. Freeman, New York.
Goodrich, E- S., 1930. — Studies on the Structure and Development of Venebrates. Macmillan, London.
Hildebrand, m., 1988. — Analysis of Vertebrate .Structure. 3rd ed., John Wiley & Sons, New-York.
Hitchcock. E. C., 1992. — The Anierior-most Vertebrae and Occiput of Eusthenopteron: Implications in the
Origin of the Tetrapod Alla.s-Axis Complex. Master's Dissertation. McGill Universily, Montreal.
JarvIk, e., 1942. — On the structure of the snout of Cro.ssopteiygians and lower gnathostomes in general. Zool
Bidr. Uppsala, 21: 235-675.
— 1954. — On the vi.sceral skeleton in Eusthenopteron with a discussion of the parasphenoid and palatoquadrate
in fishes. K. s\‘enska Vetensk. Akad. Handl, 4 (5): 1-104.
— 1975. — On the saccus endolymphaticus and adjascent structures in osteolepiforms, anurans, and urodeles.
Coll. im. CNRS. 218; 191-21 1
— 1980. — Basic Structure and Evolution of Verlebrates. Vol. I. Academie Press. London.
Lauder. g. V., 1979. — Feeding mechanics in primitive teleosLs and in the halecomorph fish Amia calva. J.
Zool. 187: 543-578.
— 285
— 1980. — The rôle of the hyoid apparatus in the feeding mechanism of the coelacanth Latimeria chalumnae.
Copeia, 1980 (1): 1-9.
LUND, W. L., R. LUND & G. A. Klein, 1985. — Coelacanth feeding mechanisms and ecology of the Bear Gulch
coelacanths. In: Compte rendu du ix® Congrès International de Stratigraphie et de Géologie du Carbonifère :
492-500.
MILLOT, J. & J. Anthony, 1958. — Anatomie de Latimeria chalumnae. 1. Squelette, muscles et formations de
soutien. Éd. CNRS, Paris.
Panchen, a. L. & T. R. SMITHSON, 1987. — Character diagnosis, fossils and the origin of tetrapods. Biol. Rev.,
62: 341-438.
Patterson, C., 1980. — The origin of tetrapods, historical introduction to the problem. In: The Terrestrial
Environment and the Origin of Land Vertebrates, A. L. Panchen, ed. Syst. Assoc. Spec. Vol. 15. Academie
Press, London: 159-175.
Romer, a. s., 1937. — The braincase of the Carboniferous crossopterygian Megalichthys nitidus. Bull. Mus.
Comp. Zool. Harv. Univ., 82 (I): 1-73.
ROSEN, D. E., P. L. FOREY, b. g. Gardiner & C. Patterson, 1981. — Lungfishes, tetrapods, paleontology,
and plesiomorphy. Bull. Am. Mus. Nat. Hist., 167 (4): 159-276.
Smithson, T. R. & K. S. Thomson, 1982. — The hyomandibular of Eusthenopteron foordi Whiteaves (Pisces,
Crossopterygii) and the early évolution of the tetrapod stapes. Zool. J. Linn. Soc. London, 74: 93-103.
Sternberg, R. M., 1941. — Cranial morphology of the Devonian crossopterygian Eusthenopteron. Univ. Toronto
Stud, Geol. Ser., 45: 1-48.
Thomson, K. S., 1962. — Rhipidistian classification in relation to the origin of the tetrapods. Breviora, 166:
1-12.
— 1967. — Mechanisms of intracranial kinetics in fossil rhipidistian fishes (Crossopterygii) and their relatives.
J. Linn. Soc. (Zool.), 46: 223-253.
— 1969. — The biology of the lobe finned fishes. Biol. Rev., 44: 91-154.
Watson D. M. s., 1926. — The évolution and origin of the Amphibia. Phil. Trans. R. Soc., London B, 214:
169-257.
Bull. Mus. narl. Hist. nat.. Paris. 4' sér., 17, 1995
Section C, n“ 1-4 : 287-341,
Morphology of a new osteolepidid fish from Russia
by Oleg A. LEBEDEV
AbstracC. — The morphology ot a new Devonian osleolepiiliU Itsh, Medoeviu kila n. g., n. .sp. is described.
The specimen originales IVom an unknown locality. and dariiig wa.s madc oa ihe busis ol' a cooth of Phoehutlus
australiensis Long, morphotype I (GivTtR. 1990), found during ihe chemital préparation. This .siiggesis an âge
ranging from thc lowcr P. irachytera to lhe SiphonoiMlu pnw.sitlcaui tonodoni rones (Upper Eamennian). .A
slighily younger âge is suggested by lhe diseovcry of seale.s ideniieal to tfiose of Medoeviii in lhe Late Toiirnaisiun
of Bélarus. The perfect ihree-dlmerisioiuil State of préservation allow.s ilie .snidy of ihe derniul .skelelon of lhe
skull, the iieurofranium, viscéral arches and lhe posicranial skeleton of lhe anicrior part of the irunk. Tire new
form is charuclerized by lhe connection of hypobranchial 4 to hypobranchial 3, a condition known ciscwhere in
the porolepifonn Ciypiolepis givenUiiuliiv Jarvik. and by geiicrally cycloid seales with a médian hoss on the
inner surface, combined with a cosininc-covered external surface. The crista parotica is directed buckwards and
supports both the labnlai' and the cxtraiemporal along thc siiiurc between ihem. No apomorphic featiire is found
at présent for the Osteolepididae and the group niay be considered to be paraphyletie with respect to lhe Kusthenop-
teridae, Rhi/odopsidae, Ctmowindridae, Megalichihytdae and Lamprololepididue.
Keywords. — Vertebrata, Osleolcpiformcs, Late Devonian, Russia, anatoniy, phylogeny.
Morphologie d'un nouvel Osteolepididae de Russie
Résumé. — La morphologie d'un nouveau poisson Ostéolépididé, Mednevia lata n. g., n. sp. est décrite.
Le spécimen provient d’une localité inconnue, et .sa datation a été effectuée sur la base d’une dent de Phoebodus
australiensis Long, morpholype 1 (Gi.NrrrR, 1990), trouvée lors de la préparation chimique du spécimen. Cela
suggère un âge allant de la zone de Coriodontes il Pulmattdepis traehytera inférieure <i la zone à Siplunuidella
praesiilcata (Famennien supérieur). Un âge légèrement plus récent peut aussi être avancé sur la base de la dé¬
couverte d’écailles identiques â celles de Medne\ ui dans le Tournaisien supérieur de Bélarus, L'élal de conservalion
parfait et tridimeniioniicl du .spécimen a permi.s l'étude du .squelette dennique du crâne, du iietirocrâne. des arcs
viscérau.v et du squelette posicrânien de la partie antérieure du tronc. Cette nouvelle forme diffère des autres
Osiéolépididés par le conract entre les hypobranchiaux 4 et 3. caractère connu ailleui-s chez le Porolépiforme
Glyptolepi.s .^roenlaiidica .fatvik, ainsi que par des écailles cycloïdes pourvues d’une bosse médiane sur leur face
interne. La crista parotica est dirigée posterieurement et soutient à la fois le tabulaire et re.stratemporal, le long
de leur .suture cuiniTiune. Aucun caractère apomorphe ne peut être défini pour les üstéolépididés. qui peuvent
donc être considérés comme paruphylétiques par rapport aux Eusthenopiéridés, Rhizodontidés, Canowindridés,
Mégalichthyidés et Lamproiolépididés.
Mots-clé.s. — Vertebrata. Ostéolépiformes, Dévonien supérieur. Russie, anatomie, phylogénie,
O. A. Lebedev, Palaeontological Institute of the Russian Academy of Sciences, 123. Profsoyuznaya St., Moscow, 1 17647, Russia.
Introduction
The study of the moiphology of the osteolepiform fishes i.s perhaps one of the most
thoroughiy explored fields in vertebrate palaeontology but, in contrast to Eusthenopteridae, bril-
liantly investigated by E, .IarvIk in a sériés of works on Eustlienopteron foordi, the study of
the osteolepidids is much more modest. due to their usually poorer State of préservation.
— 288 —
The study of the endocranial structures is restricted to a few papers by Fischer (1852),
Watson (1925, 1926, 1954), JarvIk (1942, 1966, 1980), Romer (1937, 1941), Thomson (1964a,
b, 1965, 1966, 1967), Janvier (1978, 1980), Janvier & Marcoux (1976), Janvier et al. (1979),
VOROBYEVA (1975, 1977a.. b. 1981). VOROBYEVA & Lebedev (1986a). Lebedev (1983), Long
(1985b. 1987) and such structures as the viscéral arches were previously entirely unknown.
A new three-dimensionally preserved specimen, unlortunately derived from an unknown
locality, provides a possibility to answer some questions on the morphology and relationships
of the osteolepidid fishes. It is noted that no unique apomorphic features are known for the
moment for the Osteolepididae and the group may be regarded as paraphyletic with respect to
other osteolepiform familles.
The new form possesses several features which demonstrate the close relationship of the
Osteolepididae with the Eusthenopteridae,
Abbreviations
aal gr
ab
abc ar
acf
aci fo
ad fo
ad s
ahy ri
an O
ano pr
ano pr gr
aom fo
aor fo
ap pt
ar fo
ar ri + kn
asc pr
au P
av gr
bbl
bb2
groove for the afferent artery of the first branchial unit, sillon pour l’artère
afférente de la première unité branchiale
anterior buttress of the endoskeletal shoulder girdle, arc-boutant antérieur
de la ceinture scapulaire endosquelettique:
anterior area of the attachment surface of the basis cranii muscle on the
otico-occipital block, zone antérieure de l’aire d’insertion du muscle
basicrânien sur le bloc oiico-occipitul ;
auxillary connecting facet of the autopalatine, facette de contact
auxilliaire pour l’autopalatiiT,
foramen for the a. carotis interna, yivrawen pour l’artère carotide interne ',
adductor fossa, fos.w pour les muscles adducteurs',
adsymphyseal plate, plaque adsymphysaire ',
ridge for the insertion of m. hyomandibularis, crête pour l’insertion
du muscle hyomandibulaire ',
anocleithrum. anocleithrum ;
anocleithral process, processus anacleithral ;
groove of the cleiihrum housing the anocleithral process, sillon du
cleithrum logeant le processus anocleithral ;
foramen for the a. ophthalmica mzgna, foramen pour l’artère
ophthalmique principale ;
foramen for the orbital -inety, foramen pour l’artère orbitaire:
apical process of the autopalatine, processus apical de l’autopalatin',
foramen for the articular canal, /ir/nmen pour le canal articulaire:
articulation ridge and knob of scale. ctète articulaire et processus des écailles :
ascending process of the palatoquadrate, processus ascendant du palatocarré ;
autopalatine, autopalatin:
groove for the vertébral artery, sillon pour l’artère vertébrale:
anterior basibranchial élément, élément basibranchial antérieur :
posterior basibranchial élément, élément basibranchial postérieur :
— 289 —
bc fen
bh fo
bp pr
b pr
ca hu
ch2
clav
clav ar
clei
CO pi
ers
da gr
db
dl ri
dmax pr
dm pr
dmp pi
dm pr
eal gr
ect ri
ent fo
epa tu
esl
esm
et
exl ar
ex no
fra fo
ghy tu
gl
gla
gl fo
basicranial fenestra, fenêtre basicrânienne ;
buccohypophyseal foramen, foramen bucco-hypophysaire ;
basipterygoid process, processus basiptérygoïde \
basal process of the palatoquadrate, processus basal du palatocarré ;
humerai head, tête humérale ;
cératohyal 2. cératohyal 2;
clavicula, clavicule ;
articulation area of the cleithrum for the clavicle, surface d’articulation
pour la clavicule sur le cleithrum ;
cleithrum, cleithrum;
coronoid fang pit in autopalatine, dépression pour le croc coronoïdien
dans l'autopalatin;
crista suspendens, crista suspendens ;
groove for the dorsal aorta, sillon pour l’aorte dorsale ;
dorsal bultress of the endoskeletal shoulder girdle, arc-boutant dorsal
de la ceinture scapulaire endosquelettique;
dorsolateral ridge, crête dorsolutérale ;
dorsal maxillary process. processus maxillaire dorsal;
dorsomedial process of autopalatine, processus dorsomédial de l’ autopalatin ;
pit for the articulation with the dorsomedial process of the palatoquadrate,
dépression pour l’articulation avec le processus dorsomédial du palatocarré;
dorsomedial process of the autopalatine, processus dorsomédial
de l ’uiitopalatin :
groove for the efferent artery of the first branchial unit, sillon pour l’artère
efférente de la première unité branchiale ;
ectepicondylar ridge, crête ectépicondylaire ;
entepicondylar foramen, foramen entépicondylaire ;
tubercle on the ventral side of the ethmoid, between the anterior processes
of the parasphenoid. tubercule sur la face ventrale de l’ethmoïde, entre le
processus antérieur et le parasphénoïde ;
latéral exlrascapular, extrascapulaire latéral;
médian extrascapular, extrascapulaire médian ;
extratemporal, extratemporal;
operculura area overlapped by the latéral extrascapular, zone de l’operculaire
recouverte par V extrascapulaire latéral;
external nostrils, narines externes;
foramen for the r. frontalis anterior of the n. profundus, foramen
pour le rameau frontal antérieur du nerf profond ;
tubercle on the urohyal for the origin of m. geniohyoideus, tubercule
sur l’ urohyal pour l'insertion du muscle géniohyoïdien;
glenoid fossa, fosse glénoïde ;
latéral gular, gulaire latéral;
glenoid foramen, foramen glénoïdien ;
— 290 —
gme
har d
har V
hb4 ar
hu ri
hy ar
hyc
ial tu
ici
ici ar
iosc fo
ipbl ar
ipb2 ar
it
it ar
ivc
ju
ju gr
ju ri
juv
le
Ij no
Im oar
lpch2 ar
Is pr
ma fa
médian gular, gulaire médian ;
dorsal articulation area for the hyomandibula, articulation dorsale
pour l’hyomandibulaire ;
ventral articulation area for the hyomandibula, articulation ventrale
pour rityotnandibulaire ;
articulation area for hypobranchial 4 on the hypobranchial 3, surface
d'articulation pour V hypobranchial 4 sur l' hypobranchial 3;
humerai ridge, crête humérale',
articulation facet on the opercular for the opercular process of hyomandibula,
surface articulaire sur l'operculaire pour le processus operculaire
de l’hyomandibutaire ;
orifice of the hyomandibular canal, orifice du canal hyomandibulaire
lubercles for lhe attachment of the interarcual ligament, tubercules
pour l'attache du ligament interarcual ;
interclavicle. interclavicule :
overlap area for lhe interclavicle. sutface de recouvrement pour i interclavicule',
foramen of lhe infraorbilal sensory canal in the postorbital, foramen
du canal sensoriel infraorhitaire dans le postorbitaire ;
articular area for lhe infrapharyngobranchial I, surface d'articulation
pour l’ infrapharyngobranchial 1 :
articular area for the infrapharyngobranchial 2, surface d'articulation
pour r infrapharyngobranchial 2;
intertemporal, intertemporal ;
intertemporal contact area on the postorbital, surface de contact pour
i intertemporal sur le postorbitaire
intervomerine canal, canal intervomérin-,
jugal. jugal ;
jugular groove, sillon jugulaire',
jugular ridge. crête Jugulaire ',
jugular vein groove on hyomandibular, sillon pour la veine jugulaire
sur r hyomandibulaire ;
latéral commissure, commissure latérale ;
notch in the anlerior edge of lhe submandibulo-branchiostegal
for the lower jaw contact, encoche dans le bord antérieur du
submandibulo-branchiostège. pour te contact avec la mandibule',
lacrymo-maxillary overlapping area, surface de recouvrement lacrymo-maxillaire ',
subopercular area contacting lhe latéral process of lhe ceratohyal 2,
zone du sous-opeivulaire en contact avec le processus latéral du cératohyal 2 ;
latéral supraorbilal process of the ethmoid, processus supraorbitaire
latéral de l 'ethmoïde ;
anteromedial articulation facet of the palatoquadrate, surface
d’articulation antéromédiale du palatocarré -,
— 291 —
mamp
mbpr fac gr
mem ar
me ri
mgh pi
mlb tu
mm
moi pi
mov2-3 ri
mp
mrb ar
msc ar
mshy
mtv2 ri
my ri
mx
na ar
nbcv
nsp
oa gr
oem no
ol fo
ol ri
onc n
op
op ar
op pr
area of attachment for the posterior portion of m. adductor mandibulae,
surface d'insertion pour la portion postérieure du muscle adducteur
de la mandibule ;
groove for the médial branch of the palatal ramus of the n. facialis,
sillon pour la branche médiale du rameau palatin du nerj' facial;
médial lamina of the cleitlvrum overlapped by the operculum and suboperculum,
lame médiale du cleithrum recouverte par l'apercule et le sous-opercule;
médian ridge of the interclaviclc. crête médiane de l’interclavicule ;
insertion pit of the m. geniohyoideus, dépression pour l'insertion
du muscle géniohyoïdien;
tubercles for the attachment of the principal portion of m, levator bulbi,
tubercules pour l ‘insertion de la portion principale du muscle levator bulbi ;
mentomandibular, mentomandibulaire ;
pit for the attachment of the m. obliquas inferior of the eyeball,
dépression pour l’insertion du muscle oblique inférieur de l’œil;
ridge for the attachment of the m. obliquus ventralis, crête pour
l’insertion du muscle oblique ventral;
metapterygoid, métaptérygnide ;
attachment area for the m. retractor bulbi, aire d’insertion du muscle
rétracta r bulbi ;
attachment area for the m. subcephalicus, aire d’insertion du muscle
subcéplial ique ;
pocket in the basibranchial 1 for the insertion of m. stemohyoideus,
poche dans le basibranchial / pour l’insertion du muscle sternohyo'idien ;
ridge for the m. transversalis ventralis. crête pour le muscle transversal ventral;
myoseptal ridge on the intercentrum, crête myoseptale sur l ’ intercentre ;
maxilla, maxillaire;
articulation lacets for the neural 'dich, facettes d'articulation pour l’arc neural;
orifice for the ventral branch of the nasobasal canal, orifice de la branche
ventrale du canal nasobasal;
neural spine, épine neurale;
groove for the occipital artery, sillon pour l’artère occipitale;
notch for the oblique eye muscles, encoche pour le muscle oblique de l’œil;
orifice for the r, ophtalmicus lateralis, orifice pour le rameau ophthalmique
du nerf latéral ;
olfactory ridge. crête olfactive ;
notch for the passage of the orbitonasal canal, échancrure pour le passage
du canal orbitonasal ;
opère ul 11 m . operculaire ;
opercular articulation area of the hyomandibula, articulation operculaire
de l’hyomandibulaire;
opercular processes of the post-temporal and supracleithrum,
processus operculaires du post-temporal et supracleithrum;
292
pa
pano pr ar
Pa O
pa pi
pb
pbc ar
pca gr
pe ri
pi
pnc
pn pi
pnw
po
po ar
pot pr
ppal fo
pra pr
pr con
pr fo
pr hy
Pt
ptf
pt pr
qu
qj
rece
rhy gr
roi fo
rotl fo
roVII fo
rpa fo
sa fo
parasphenoid, parasphénoïde ;
area on the cleithrum for the overlap with the posterior process
of the anocleithrum. surface du cleithrum pour le recouvrement par le
processus postérieur de l 'anocleithrum ;
pores of the Paul’s organ, pores de l'organe de Paul;
anterior parasphenoid pit, dépression antérieure du parasphénoïde ;
posterior bultress of the endoskeletal shoulder girdle, arc-boutant
postérieur de la ceinture scapulaire endosquelettique;
posterior area of the attachment surface for the m. basis cranii
on the otico-occipital block, région postérieure de la surface d’insertion
du muscle hasicrânien sur le bloc otico-occipital;
postchoanal anastomosis, anastomose postchoanale ;
pectoral ridge, crête pectorale;
pineal foramen, foramen pinéal ;
palato-nasal canal, canal palato-nasal ;
prenasal pit. dépression prénasale ;
postnasal wall, cloison postnasale ;
postorbital, postorbitaire;
intertemporal process for the postorbital overlap, processus de
l'intertemporal pour le recouvrement postorbitaire ;
postotic process, processus postotique ;
foramen for the posterior palato-nasal canal, foramen du canal palato-nasal
postérieur;
anterior process of the prearticular, processus antérieur du préarticulaire ;
processus connectens, processus conncctens;
foramen for the n. profundus, /orome/i pour le nerf profond ;
pocket for the insertion of the m. protractor hyomandibularis, recessus
pour l’insertion du muscle protracteur de l’hyomandibulaire ;
post-temporal, post-temporal ;
post-temporal fossa, fosse post-temporale ;
paratemporal process, processus paratemporal ;
quadratum, carré;
quadratojugal, quadrato jugal ;
attachment area of the m. rectus cervicis on the urohyal, surface d’insertion
du muscle rectus cervicis sur l' urohyal;
groove for the r. hyoideus, sillon pour le rameau hyoïdien ;
foramen for the r. ophtalmicus lateralis, foramen pour le rameau
ophthalmique du nerf latéral ;
foramen for the r. oticus lateralis, foramen pour le rameau otique du nerf latéral ;
foramen for the r. opercularis VII, foramen pour le rameau operculaire
du nerf VII;
foramen for the r. palatinus, foramen pour le rameau palatin ;
foramen of the suprangular canal, /oramen du canal surpra-angulaire ;
— 293 —
sel
SCO fo
SC pro
sgi fo
sh re
smb
smb f
so 1
sol
so2
so2 ar
sop
sop f
spbl ar
spepo fo
spepod + ro fo
sq
sr
ssc fo
stl fo
stl gr
sty ar
su + de ri
sup tu
tp rb tu
tri no
uh ar
val pr
supracleithrum, sup racle ithrum ;
supracoracoid foramen, foramen supracoracoïdien ;
anocleithrum process for the supracleithrum overlap, processus de
l’anocleithrum pour te recouvrement du supracleithrum-,
supraglenoid foramen, /bramen supraglénofdien :
spiraculo-hyomandibular recess, récessas spiraculo-hyomandibulaire-,
submandibulo-branchiostegal, submandibulo-branchiostège ;
ventral facet of the ceratohyal 1 contacting the submandibulo-branchiostegal,
facette ventrale du ceratohyal 1 en contact avec le submandibulo-
branchiostège ;
suborbital ledge, rebord sous-orbitaire-,
anterior supraorbital, supraorbitaire antérieur-,
posterior supraorbital, supraorbitaire postérieur -,
intertemporal process for the supraorbital 2 overlap, processus de
r intertemporal pour le recouvrement du supraorbitaire 2;
suboperculum, sous-ope tvulaire ;
latéral facet of the ceratohyal 1 contacting the suboperculum,
facette latérale du ceratohyal t en contact avec le sous-operculaire -,
articulation knob for the suprapharyngobranchial 1, tubercule
d’articulation pour le suprapharyngobranchial 1 ;
posterior foramen of the spiracular cam\, foramen postérieur du canal
spiraculaire ;
foramen for the posterior diverticle of the spiracular canal and the r. oticus,
foramen pour le diverticule postérieur du canal spiraculaire et le rameau
otiepte du nerf latéral;
squamosal, squamosal ;
sublingual rod, tige sublinguale -,
subscapular fossa, fosse subscapulaire ;
foramen for the r. supratemporalis lateralis, foramen pour le rameau
supratemporal du nerf latéral ;
groove for the r. supratemporalis lateralis, sillon pour le rameau
supratemporal du nerf latéral ;
articulation facet for the stylohyal on the hyomandibula, facette
d’articulation pour le stylohyal sur l’hyomandibulaire -,
supinator and deltoid ridges, crêtes supinatrice et deltoïde;
suprapterygoid articulation tubercle, tubercule pour l’articulation
supraptérygoide ;
tubercle for the attachment of the transverse portion of m. retractor bulbi,
tubercule pour l'insertion de la portion transversale du muscle retractor bulbi;
trigeminal notch, encoche trigêminale -,
area on the basibranchial 1 for the attachment of the urohyal,
surface de contact entre le basibranchial I et F urohyal-,
antérolatéral process of the vomer, processus antérolatéral du vomer-.
— 294 —
vam pr anteromedial process of the vomer, processus antéromédial du vomer;
vca fo foramen for the v. cerebralis anterior, foramen pour la veine cérébrale
antérieure ;
V font vestibular fontanelle, fontanelle veslibulaire ;
vo vomer, vomer ',
vo de dépréssion for the vomer in the ventral side of the ethmoid,
dépression pour le vomer dans la paroi ventrale de l’ethmoïde
vpit fo foramen for the pituitary v^m, foramen pour la veine pituitaire ',
vvl vertical lamina of the vomer, lame verticale du vomer -,
3-7 submandibular plates, plaques submandibulaires',
II-XII cranial nerve foramina, foramens pour les nerfs crâniens II-XII.
MATERIALS AND METHODS
The specimen described here was kindly donated to the author by Pr Georgy Ts. Medoyev,
Polytechnical Institute, Alma-Ata, Kazakhstan. It cornes from an unknown locality and no in¬
formation on its âge and place of origin is available. The préparation of the specimen has yielded
a tooth of Phoebodus australiensis Long (morphotype 1, GiNTER, 1990), which suggests an âge
interval ranging from the lower Palmaiolepis trachyiera to the Siphonodella praesulcata (Upper
Devonian, Upper Famennian) conodont zones.
Alternatiag dating information originales from subsurface deposits of Belrus (borehole 326,
depth 322.0, specimen 14b) that yielded fragmented scales of the same peculiar appearance as
in Medoevia (see description of scale below). The deposits were dated as Lower Tournaisian
(Upinian) by ostracods (V. 1. Akhimovich. V. K. Golubtsov, pers. commun. 1994). The speci¬
men of Medoevia described here may thus aiso be Lower Tournaisian in âge.
The specimen was a yellowish-grey mari nodule, which contained a three-dimensionally
preserved skull, but slightiy compressed from the side.s. The posterior part of the skull was
damaged by transverse cracks filled with calcite cementation, that resulted in the disintegration
of .some bones in this région; most of the branchial arches were damaged.
Préparation was carried out by 10% solution of acetic acid, the remaining clay being removed
with a mounted needle. The material is represented by an almost complété skull, shoulder girdle,
humérus, vertebrae and anterior squamation. After préparation the specimen was separated into
individual bones.
The material is kept in the Paleontological Institute, Academy of Sciences of Russia, Mos-
cow, specimen number PIN 4482/1.
SYSTEMATIC PALEONTOLOGY
Order OSTEOLEPIFORMES Berg, 1937
Family OSTEOLEPIDIDAE Cope, 1889
Genus MEDOEVIA n. g.
Type species. — Medoevia lata n. sp.
— 295 —
Etymology. — Named after Pr George Ts. Medoyev, who kindly donated the specimen
to the author.
Diagnosis. — An osteolepidid fish with a skull length of about 90 mm and estimated body
length of about 45-50 cm. The anterior and latéral surfaces of the snout are almo.st vertical,
with externat narial openings visible from above. The ethmo.sphenoid-otico-occipital length ratio
(b/a) is 1.22. The ethtnoid-ethmosphenoid length ratio (r/b) is 0.44. The preorbital length is to
the orbital + postorbital divisions together as 0.56. The pineal foramen is situalcd in the middle
of the orbital région and opposite the anterior ends of the pariétal pit-lines. The poslpinealeth-
mosphenoid shield length ratio is 0.28. The panetal pit-iines are widely displaced from ihc médian
suture, laterally. The anterior end of the parasphenoid is bifid.. The otic capsules are shifted
postérolatéral ly, heiicc the trapézoïdal shape of the otico-occipital shield. The trigeminal nolch
is situated at the level of the intracranial gap. The cheek plate is 1.5 times longer than the
otico-occipilal shield. The maximum depth of the maxdla is 0.20 of its length. The length of
the latéral gular is 2.5 times more than its width, the pit-line being situated in the anterior third
of the boue. Hypobranchial 4 articulâtes with hypobranchial 3. The scales are predominantly
cycloid, with a médian internai boss and a cosmine-covered external surface.
Medoevia lata n. .sp.
Diagnosis. — As for the genus.
Holotype. — PIN 2879/5. The anterior part of an individual, including the skull, shoulder
girdie, humérus, veilebrae and scattered scales.
Type horizon and LOCALITY, — Unknown, probably Upper Devonian.
Etymology. — From latus (Latin): broad.
DESCRIPTION
The head is rather flattened and broad. The length of the skull is about 1 .5 times its maximum
width. The cosmine covers ail the dermal bones of the skull and shoulder girdie, except the
interclavicle. clavicles and part of the cleithra (Fig. lA-D).
Dermal bones of the f.thmosphenoid (fronto-ethmoidal) block
The ethmosphenoid shield is the widest at the level of the preorbital corners (Fig. 2A. B).
The anterior surface of the snout is almost vertical. The external nostrils (exno) are elliptical
in shape and their long axis is horizontal, they are situated slighlly anleriorly and dorsally to
the apex of the subnasal corner and are visible from above. The premaxillary margin is slightly
sinusoïdal in outline, its médial part being projected ventrally. The lacrimo-maxillary overlap
area (Im oar) is almost twice higher than long. The dermal bones of the ethmosphenoid shield
are fused, without any trace of suture, with the exception of the médian suture between the
parietals. caudally to the pineal foramen (pi), supraorbitals I. 2 (sol, 2) and intertemporal (it).
The pineal foramen is situated in ihe middle of the orbital division opposite the anterior ends
— 296 —
Fig. 1A. — Medoevia lata n. g., n. sp., reconstruction of the skull and shoulder girdle in dorsal view. Scale bar: 10 mm.
Medoevia lata n. g., n. sp., reconstitution du crâne et de la ceinture pectorale en vue dorsale. Échelle: 10 mm.
of the pariétal pit-lines. The pores of the seismo-sensory canal are small, numerous and are
distinguishable only in the anterior part of the ethmosphenoid shield.
The toothed part of the naso-rostropremaxilla bears a row of about 15 small teeth (Fig.
2B). The médial tooth pair is slightly bigger than the others, as in Megistolepis (Vorobyeva,
1977a), Gogonasus (LONG, 1985b, 1987) and Chrysolepis (LEBEDEV, 1983). The palatal lamina
— 297
sel
Fig. 1B. — Medoevia lata n. g., n. sp., reconstruction of the skull and shoulder girdie in latéral view. Scale bar: 10 mm.
Medoevia lata n. g., n. sp,, reconstitution du crâne et de la ceinture pectorale en vue latérale. Échelle : 10 mm.
of the naso-rostropremaxilla forms medially two symmetrical, short tongue-like processes, which
support a prominent ridge separating the prenasal pits of the ethmoid. Laterally to these processes
the palatal lamina is insignificanlly developed, except for the médial processes for the suturai
contact with the vomers.
The latéral edges of lhe ethmosphenoid shield are much abraded and no overlapping surfaces
with the supraorbiials 1 and 2 can be observed. The posterior tectal is fu.sed to the shield without
any trace of a suture. The supraorbital 1 (Fig. 3A. B) is a short rectangular plate bearing a
rugosity in the anterior half of its médial surface. A group of small pores of Paul’s organ (Pao)
|This terni, introduced by VorOBYEVA & Lebedev (1986) in honour of Estonian paleontologist
V. Paul, who first described the groups of .small sensory pores in Osieolepis sp. {Gyroptychius
paiili Vorobyeva, 1977) (Paul, 1940)| is situated in the middle of its latéral surface. The .supraor¬
bital 2 (Fig. 3C, D) is generally arch-shaped, with a process that wedges between the anterior
margin of the intertemporal and the pariétal. The supraorbital sensory line canal enters tins bone
from the pariétal at the anterior margin and curves, passing to lhe intertemporal from the médial
side of the dorsal process of supraorbital 2.
The intertemporal is irrcgularly trapézoïdal in shape (Fig. 3E, F). It possesses two pointed
processes for overlapping; an anterior one for the supraorbital 2 (so2 ar) and a posterior one
for the postorbital (po ar).
The vomer (Figs. ID, 4A-D; vo) is a rectangular plate with a high, curved tooth-bearing
lamina on its ventral side. The anterior border of the vertical lamina (vvl) is situated below the
anterior border of the parasphenoid (pa) and the dorsal, fiat tongue-like anteromedial processes
— 298 —
Fig. IC. — Medoevia lata n. g., n. sp., reconstruction of the skull and shoulder girdle in ventral view. Scale bar: 10 mm.
Medoevia lata n. g., n. sp., reconstitution du crâne et de la ceinture pectorale en vue ventrale. Echelle : 10 mm.
(vam pr) almost corne in contact in the midline and cover the area between it and the posterior
edge of the prenasal pits (pn pi), thus forming the posterior margin of the anterior palatal fossa
(Fig. 2B). The antérolatéral process (val pr) forms a short and massive suturai contact with the
latéral process of the palatal lamina of the naso-rostropremaxilla, and thus the anterior margin
of the exochoanal passage. The latéral side of the vertical lamina is a continuation of the dorso-
medial articulation facet of the ethmoid and its latéral surface is rugose (Fig. 2E, F). The latéral
surface of the posterior portion of the vertical lamina forms the médial wall of a conspicuous
— 299 —
Fig. 1D. — Medoevia lata n. g. n. sp., mounted braincase and left upper jaw in ventral view. Scale bar: 10 mm.
Medoevia lata n. g., n. sp., neurocrâne et mâchoire supérieure gauche montés, en vue ventrale. Échelle: 10 mm.
— 300 —
Fig. 2A-D. — Medoevia lara n. g., n. sp. Ethmosphenoid block. A. dorsal view: B. ventral view: C. latéral view; D, poslerior
view. Scale bar: U) mm.
Medoevia lata n. n. sp.. hloc ethmosphénoïdien. A. vue dorsale: B. vue ventrale: C. vue latérale: D. vue postérieure,
flchelle : 10 mm.
— 301 —
fra fo
Fig. 2E, F. — Medoevia lata n. g., n. sp. Ethmosphenuid block, posterior ventrolaleral view. Scale bar: 10 mm.
Medoevia lata n. g., n. sp., bloc ethmosphénoïdien en vue ventrolatérale postérieure. Échelle : W mm.
fenestra exochoanalis, together with the anterior process of the dermopaiatine, with which it
forms a vertical suturai junction. The ventral edge of the vertical lamina bears a posterior row
of the comparatively large teeth and 2-3 anterior rovvs of small ones. The ventral portions of
the anterior part of the vertical lamina meet together medially. Forming a large intervomerine
canal (ivc). Its dorsal wall is mainly formed by the ventral surface of the ethmoid.
The exochoanal passage (Fig. ID) is difficult to see on the photograph because of the dis-
placemenl of the éléments during fossilization. The maxilla and adjoining dermopaiatine are
shifted to the righi side. so that there is no clear contact between their anterior ends and the
naso-rosiropremaxillary and vomer respectively. Nevertheless, the loose bones on the right side
of the head show contact areas and. when put together, cleaiiy shows a large, elongated, and
functional exochoanal opening. This contradicts the widespread opinion about the absence a
choana in osteolcpiforms (for example, ROSEN et al., 1981).
The anterior part of the parasphenoid is bifide divided by a narrow slit until the level of
the posterior margin of the vomers. A sharp ciest supports the denticulated plate of the para¬
sphenoid rostrally and the anterior corner of the plate bears a small pit; the bottom of which is
rugose. The function of this pit is uncertain (pa pi). The denticulated plate itself is rather short
and wide, its length being about 2.5 times more than its maximum width. The small orifice of
the bucco-hypophyseal foramen (bh fo) is situated close to the posterior margin of the denticulated
plate.
SCLEROTIC RING ELEMENTS
Nineteen loose sclerotic ring éléments hâve been found. Their breadth is so variable that
it is possible that the left ring comprised a different number of éléments than the right one, as
suggested by some plates showing incomplète fusion (Fig. 3G, H). The éléments are rectangular
— 302 —
FlO. 3. — Medoevio lata n. g., n. sp. Dermal bones of lhe ethmosphenoid shield and the sclerolic ring éléments. A, B, supraorbital
1; C, D. supraorbital 2; E. F. inicrtcmporal; G. H. sclerotic éléments. A, C, E. G, latéral views; B. D. F. H. médial views.
Scale bar: 10 mm, except for G and H: 1.5 mm.
Medoevia lata n. g., n. sp. Os dermiques du bouclier ethmosphénoïdien et éléments de l'anneau sclérotique. A, B. supraorbitaire
1 ; C. D, supraorbitaire 2; E, F, intertemporal : G, H, éléments de t 'anneau sclérotique. A, C, E, G, vues latérales : B, D,
F. H, vues médiales. Échelles: 10 mm, sauf pour G et H : 1,5 mm.
in shape, curved and almost smooth on both surfaces, except for poorly marked grooves parallel
to the margins. Their inner and the outer edges are slightly rounded.
NEUROCRANIAL COMPONENT OF THE ETHMOSPHENOID DIVISION
The neurocranium is well ossified. The length of the ethmoid represents about 1/3 of the
total length of the ethmosphenoid. The interorbital wall is deepest above the parasphenoid
(Figs. 2C, 5).
— 303 —
Fig. 4. — Medoevia lata n. g., n. sp. Right vomer. A, ventral view; B, dorsal view; C, anterior view; D, posterior view. Scale
bar: 10 mm.
Medoevia lata n. g., n. sp. Vomer droit. A, vue ventrale; B, vue dorsale; C, vue antérieure; D, vue postérieure. Échelle:
10 mm.
The prenasal pits (Fig. 2C) are much deeper than in Eusthenopteron (JARVIk, 1942, 1980).
The latéral wall of lhe pit is occupied by lhe orifice of the ventral branch of the nasobasal canal
(nbcv), which also shows the more anterior course of its latéral (?) branch. The anterior orifice
of the palato-nasal canal (pnc) is situated slightly behind the foramen of lhe ventral branch of
the nasobasal canal and may be traced between the ventral surface of the ethmoid and lhe dorsal
surface of the vomerine process of the palatal lamina of the naso-rostropremaxillary.
The ventral surface of the ethmoid région in Medoevia is much shorter and broader than
in Eusthenopteron (JarvIk, 1942), so that the pits for the dorsal, thickened part of the vomers
(vo de) are not situated anteriorly to the anteromedial articulation surface for the palatoquadrate,
but opposite to it. The anterior process of lhe parasphenoid becomes very closely fused to the
ventral surface of the ethmoid, and lhere is a small, well marked médian lubercle between its
two branches. This boss (epa tu) is situated dorsally to lhe junclion of the médial parts of the
vertical laminae of the vomers, and its fonction is unclear. The dépréssion for the vomers bears
a groove (mbpr fac gr), running rostro-caudally along the latéral margin of the anterior processes
of the parasphenoid. This groove may represent the canal for the médial branch of the palatal
ramus of the n. facial is.
The posterior surface of the ethmoid is subdivided into the dorsolateral and medioventral
parts by the massive olfactory ridge (ol ri; Fig. 2E, F). It continues backwards up to lhe foramen
for the n. opticus (II), and lies ventrally to it; anteriorly it bears the médial articular facet (ma
fa) for the process of the palatoquadrate, and immediately laterally to it, at the ventral edge of
— 304 —
the postnasal wall (pnw), there is a small rugose tubercle, thaï mighl hâve served for the at-
tachment of the transverse portion of the m. retractor hulhi (tp rh tu).
The dorsoiateral part is, in its turn, subdivided into dorsomedial and dorsolateral areas by
the buitrcss of the latéral supraorhital lamina, or the dorsolateral ridge (dl ri). The dorsolateral
ridge passe.s baekwardiy lo the latéral surface of the interorbital wall and joins the olfactory
ridge in front of the foramen for the oplic ncrve. The latéral supraorhital process (Is pr) is
llaltened and only slighlly convex, in conlrast to Eusthenopternn, where it is almost rounded in
transverse section ( JarvIk, 1942). Il runs postero-laterally along the ventral surface of the dermal
rootlng hones, but the continuation of this process is destroyed. The dorsomedial area is a deep,
anteriorly directed dépréssion. Its anterior wall is pierced by several foramina, the most con-
spiciious of which is situated al the dorsolateral corner, or just ventrally to the dorsolateral ridge,
depending from the side of the specimen, and may represent the posterior orifice of the canal
for the r. ophialmicus lateralis (ol fo).
The dorsolateral area is a large, anteriorly directed pit, which contains another smaller el-
liptical pit in the dorsomedial part of its anterior wall: the latter is pierced by Iwo large and
3-4 smaller foramina. The veniralmost large foramen is the back of the funnel-shaped canal for
the main branch of the n. profundus (pr fo), that opens in the nasal cavity donsolaterally to the
foramen for the olfactory canal. There are two foramina on the right-hand side, which might be
interpreled as the openings of the canal for the r. Ifontalis anterior of the n. profundus: the first
One is situated dorsolateral ly to the main foramen and ihc second one slightiy ventrolaterally.
The lefl-hand side shows only one dorsolateral foramen, which is more probably for the nerve
mentioned above (fra fo), The other foramina situated in the elliptical pit, may be for the other
(possibly dorsal) branches of the profundus nerve, as in Thursius estonicus (VOROBYEVA, 1977a).
A small foramen, dorsolaterally to this group, may represent the passage for the v. cerebralis
anterior (vca fo), as in Thursius estonicus (VOROBYEVA, 1977a).
ol fo
dl ri
sup tu
mlb tu
Im oar
vpit fo
ipb.| ar
da gr
Fig. 5. — Medoevia lata n. g., n. sp. Drawing of the ethmosphenoid and otico-occipital blocks in laiera) view. Scale bar: 10
mm.
Medoevia lata n. g., n. sp. Dessin des blocs ethmosphénoidien et otico-occipital en vue latérale. Échelle: 10 mm.
— 305 —
The postnasal wall is short and the orbitonasal canal passed by the shallow notch (onc n)
of its médial part; the latéral edge of the passage is lined by the shallow notch at the tip of the
medio-dorsal process of the maxilla, its médial edge by the dorsal side of the anterior end of
the dermopalaline and the latéral side of the anteromedial articulation buttress of the autopalatine.
The ventral edge of Üie postnasal wall is silualed at the level of the midpart of the facet for
the médial ethmoid articulation of the palatoquadrate.
The position of the orbitonasal canal varies among osteolepiforms. It may be a large opening,
where the postnasal wall is deep, as in Euxihenopieron foordi (JarvIk, 1937, 1942, 1966, 1980),
Thursius estoniens (VOROUYEVA, I977aj, or. if il is short, as a notch in the rnedial part of the
postnasal wall, as in Jarvikina wenjiikowi (PIN 54/121. PIN 2986/2), Eusthennpteron obruchevi
(PIN 1737/42). Shirolepis ananjevi (PIN 782/1) (pers. obs.) and probably Gogonasus (LONG,
1985b). Accepting ihe interprétation of this structure as transmitting the orbitonasal vein (Millot
& Anthony. 1958), it may bc concluded thaï ils position was variable and has no spécial phy-
logenetic meaning.
The médial ethmoidal articulation facet for the palatoquadrate (ma fa) is oval, elongated,
with an oblique main axis direcied rostro-caudally and dorsoventrally, forming an angle of about
45“ to the vertical plane.
In the area bordered by the parasphenoid ventrally, the olfactory ridge dorsally and the
basipterygoid process posteriorly, there is a large, shallow. dépréssion, which is subdivided into
several pits and beats ridges and tubercles (Figs. 2C, 5). Ils anlcriormost part is a deep, rounded
pit, situated po.sleromedially to the médial ethmoidal articulation facet.
When the palatoquadrate complex is connected, it is situated above its dorsal surface and
might serve the attachmeni of the m. obliquus inferior of the eyeball (moi pi). There are small
tubercles on the antenot edge of the pit on the left-hand side- and on its posterior edge on the
right-hand side. They may indicate the position of the attachmeni for aponeuroses. The pit re-
ceiving the dorsomedial process of lhe palatoquadrate (dmp pi) is a rather shallow, elongated
structure, which is situated posterovenlrally to the pit described above. Its dorsal wall has an
area of finely perforated bone and the shallow ridge above il bears 2-4 massive rugose tubercles,
lhat probably housed lhe attachmeni of lhe principal portion of the m. levator bulbi (mlb lu).
In contrast to Eusthenoptemn, the crista suspendens (ers) begins posteriorly to these tubercles
and is rather poorly developed. Its posterior end is situated above the basisphenoid articulation.
The interorbital région of the elhmosphenoid is a rather high and thin structure, but thickens
posteriorly; its maximum thickness is reached between lhe basipterygoid and lhe suprapterygoid
processes. This area is half as long as the breadth of the elhmosphenoid shield; that is. approxi-
mately the saine index as in Gogonasus (Long, 1985bi. The suborbital ledge (so I), uriginaling
from the junction of lhe interorbiial wall with the parasphenoid, is a sharp-edged ridge, which
begins anteriorly to the foramen for the n. opticus and extends backwardly, gradually lurning
into the basipterygoid process (tap pr). There are two symmetrical projections at the beginning
of the ledge. one of which is hook-shaped, and the olher is a kiiob. The foramen for the a.
carotis interna (aci fo) lies ventral to the most projecting part of this edge; the latter forms a
sharp-edged crest, supporting the basipterygoid process anteriorly. There is a notch between the
crest and the processes mentioned above.
— 306 —
The basipterygoid process displays two major facets for the basal process of the palato-
quadrate; the dorsal one faces anterolaterally and the ventral one antero-dorsolaterally. The dorsal
facet is concave and the ventral one is mostly convex. The latéral surface of the basipterygoid
process bears a rugose area for the muscle attachment tm. subcephalicus, msc ar). The most
proximal part of ihis area bears either a small pocket on one side. or a ridge on the other, for
the aponeurosis of the superficial ligament of the muscle. The muscle seems to havc been paired,
as the ventral surface shows no traces of its attachment.
The foramen for the n. opticus (11) is large, situated opposite the dorsalmost end of the
basipterygoid process, and sfightly in front of its anterior end. The posterior part of the olfactory
ridge is occupied by the area of attachment for the m. retractor buibi (mrb ar). and the foramen
for the n. opticus is situated in the middle of its posterior part. The margins of the area are
marked by a gentle ridge anterodorsally and a row of tubercles of varions sizes posterioriy and
ventrally. The midpoint of the anterior portion of the area is occupied by a small patch of bone
devoid of the periosteal ossification. Its function is unclear.
The n. oculomotoriiis (IH) mighl hâve lel't the brain cavity through the same foramen as
the n. opticus. as in O^teolepis ( WatSON, 1954), Gymprycitius puuli, and Megistolepis klementzi
(VOROBYEVA, 1977a), The foramen for the n. trochlearis (IV) may be one of the small l'oramina
situated below tire exoskeletal roof and above the boss of the suprapterygoid aiticulation (sup tu).
The foramen for the a. ophtalmica magna is situated in a groove, ventrally to the cdsta
suspendons and in front of the basipterygoid process on the right-hand side. This unusual position,
below the dorsal margin of the palatoquadrate is compensated by the subséquent course of the
vessel, which passes dorsally via a small groove, crosses the crisla suspendons and reaches the
margin of the area for the attachment of the m. retractor buibi; on the left'hand side the corres-
ponding canal is enclosed in a vertical ridge, and opens by a large orifice ventrally to the foramen
for the n. opticus (aom fo). The pituitary vein leaves the braincase through a large pituitary
foramen situated at the base of the basipterygoid process, anterioiiy to it and in a deep pit lying
at the level of ils midheight (vpit fo).
The processus connectens (pr con; Fig. 2D) is situated rather far caudally front the dorsal
part of the basipterygoid process, making the posterior surface of the ethmosphenoid anteriorly
inclined at an angle of about 70'’ to the horizontal plane. Its posterior and latéral surfaces are
devoid of periosteal Iming, except on a patch in the middle of its latéral surface at the left-hand
side, The unossified surface is continued tu the bottom of the cranial cavity. The suprapterygoid
process (sup tu) is a massive boss, supporting the postérolatéral corner of the ethmosphenoid
shield. There is a massive, rugose vertical ridge in front of it, which could serve the attachment
of the m. levator arci palatini, lining the ascending process of the palatoquadrate anteriorly.
Otico-occipital division
The otico-occipital block differs in general shape and proportions from that of
Eusthenoptenm. Megalichthys, Ecto.il eorhaebis, Osteolepis and Megaponni.i (JARVtK, 1954, 1972,
1975; Romer. 1937, 1941, Thomson, 1965, 1966, 1967; Vorobyeva. 1977a) (Fig. 6A, B) and
is similar in outline to that of Sipbonadu.i (Fischer, 1852). The anterior part of this portion is
low, the deepest part being at the level of the posterior edge of the skull roof. The major différence
with other taxa resta on its outline in ventral view; its maximum widih is shortiy before the
— 307 —
anterior limit of the occipital région, which, in contrast to the otico-occipital of the five first
généra mentioned above, is not diamond-shaped, but trapeze-shaped, with a very broad base,
The dermal bones of the otico-occipital (“pariétal”) shield are fused, with the exception of
the médian suture between the two postparietals anteriorly. A short segment of this suture is
seen close lo the posterior margin of thcse bones and the well-marked suture between the tabular
and extratemporal (et). This suture is supported by the crista parotica, which is broad, so that
a large part of the extratemporal is connected with this endocranial structure.
The anterior margin of the shield is almost straight, with only a shallow embayment for
the jonction with the po.steiior margin of the parietals; the openings of the infraorbitai canals
open at this level. Thcre is no overlapped .surface for the postorbital, which suggests, that the
Joint between the posiparietal and parietals was kinetic. The spiracular notch looks rathcr deep,
due to the latéral extension of the posterior corners of the shield. The posterior margin ol the
shield is arched, its médial part being the most convex; it beats a sériés of shallow pockcl-like
notches for the contact with the extrascapulars.
The médian extrascapular (esm) is much smaller than the latéral ones (esl) (Fig. 6C-F).
The latéral extrascapular-otico-occipital length ratio is 0.70, that is, the highest among oste-
olepiforms. except Marsdenichthys, in which this index is 0.8.
NEUROCRANIAL COMPONENT of THE OTICO-OCCIPITAL DIVISION
Neither the latéral occipital, nor the ventral otic fissures are preserved in the adult stage
in Medoevia (the gaps on both sides of the specimen (Figs. ID, 6B) are cracks, with some bone
missing on the right-hand side and being out of contact on the left side), although the vestibular
fontanelle (v font) is rather large. Its shape and extension is similar to that observed in Mega-
pomus heckeri Vorobyeva, 1977a, and contrasts to that in Megalichthys Romcr, 1937, where it
is completely ossified. The length of the basicranial fenestra (bc fen) is about onc half of the
total length of the otico-occipital division. The temporal région is rather long and narrow and
the otic capsules are shifted backwards and laterally in comparison to those in Eiisthenopteron.
The post-temporal fossae (ptf) are comparatively short due to the shift of the otic région
backwards. The endochondral roofing of the fossae is almost complété, with the exception of a
narrow strip of the free exoskeleton of the ventral side of the skull roof. The walls of the post¬
temporal fossae are rather rugose. suggesting that it served the insertion of the epaxial trunk
muscles (Fig. 6G. H). The curved groove in the floor of the fossae may be interpreted as the
passage for the r. supratemporalis latéral is (stl gr), which pierces the floor of the post-temporal
fossa in Amici (JARVIK, 1980). In Medoevia, this groove passes from the posterior edge of the
fossa forwards along its médial side. crosses it suddenly in its middle and then runs in the
laterally towards a large posterior foramen of the spiracular canal (spepo fo). There is a smaller
orifice postero-laterally to it, which is connected with the former by a short groove or a canal,
overlain by a short bar, There are two large forainina in the anterior wall of the post-temporal
fossa in Megapoinus, described by VOROBYEVA (1977a). and interpreted as a paired canal for
the r. oticus VII and a posterior diverticle of the spiracular organ; in Medoevia, it is propo.sed
that the large canal housed the posterior diverticle of the spiracular canal and the r. oticus VII
(spepod + ro fo), and the smaller foramen transmitted the r. supratemporalis lateralis, which passes
to the crista parotica in Eusthenopteron (jARViK, 1980).
— 308 —
Fig. 6A*F. — Medoevia lara n. g., n. sp., otico-occipilal division. A. B. G, H. otico-occipital hlock: C. D. médian exirascapular;
E. F. latéral extrascapular. A, C, E. dorsal view: B, D, F, ventral vie\s. Seule bar: 10 mm.
.Medoevia lata n. .t,'-. //■ V’ - divisiftn olico-ortipilalt', A. R. G. H. hlac (ftico-oi i ipaa! : (' /), cMrtiM jpultiiri iindinn f f
extrasmpuhihi' lah‘nil. vut’ d<ft‘Mile : B, L). F, vue ventrale. Echelle: H) nnti.
— 309 —
Fig. 6G. H. — Medoevia lata n. g., n. sp., oblique cross-section through the subtemporal fossae of lhe otico-occipital block in
posterior view. Scale bar: 10 mm.
Medoevia laia n. g., n. sp., section transversale oblique à travers les fosses subtemponiles du bloc otico-occipital en vue
postérieure. Échelle: 10 tnm.
The médian paratemporal articular area, i.e. the anteroventral corner of lhe otico-occipiial
block is, as in Eusthenopternn. devoid of pcriosteal lining. and accommodaled lhe processus
connectens of the cthmosphenoid. The contact of the posterior tips between the connecting
processes wilh lhe lemporal walls is marked by lhe verlical extension of the spoiigy articulation
area and by the cotTesponding ventral protrusion of the antero-niedial corner of the ventral sur¬
face. The aiticulalion area is continued backwards by lhe ventral edge of the inedial walls of
the basicranial fenestra and no doubt served the cartilaginous junction wilh the arcuals. The
latéral surface of lhe ntic shelf (Fig. 5), which is equally deep along ils entire length and .slraight,
in contrast to that of Eustlienopieron and Megulkhlhys. where it curves venlrally, and bears a
group of sevcral small and one large foramina. Venlrally to this area, on the ventral surface,
liais Is une iiiorc large stponing. Thèse inay be inlerpreiesl as ihe foramina for the r. palatinus
'v II II pu fo) and the orbital artery taor fop
The lacialis canal runs postero-venirolaterally, gives off the canal for lhe r. palatinus, and
ihcn opens in the floor of the jiigular canal medially to the latéral commissure. The otic shelf
is most prominent anteriorly; therc, the bottom of lhe jugular groove is pierced by the large
orifice for the v. cerebralis media. The largest orifice in the latéral wall of the cranial cavity is
the trigeminus (V) foramen, which is separated from the inlraeranial slit by a ihick bar forming
the anterior edge of the wall. Close to it, and posteriorly, there is a smailcr orifice, which is
single on lhe right-hand side and double (8-shaped) on lhe lefl-hand one, and could transmit
the r. ophtalmicus lateralis (roi fo). The.se two foramina are siluated in a shallow dépression
between the deep. postero-medially directed pocket for the m. levator arci palalini and the jugular
groove (,ju gr). The ventral and latéral walls of the pocket are strongly rugose and ils posterodorsal
corner is pierced by a small foramen, probably for the orbital artery, which descended from lhe
groove for the occipital artery. The posterior wall of the pocket for the m. levator arci palatini
is pierced dorsally, right at the limit between the ventral surface of the dennal shield and the
dorsal surface of the endocranium, by a small foramen. Tliis foramen is probably for a branch
— 310 —
of the r. oticus lateralis, which lies close to the pit for the spiracular sense organ. This pit is
situated dorsomedially in the anterior wall of the otic capsule. The orifice of the anterior canal
of the r. oticus lateralis (rotl fo) is situated above the jugular groove and anteriorly to the ventral
orifice for the spiracular canal. It is connected with the latter by a distinct, backwardiy running
groove.
The jugular canal is continued backwards, and limited dorsally by a sharp-edged jugular
ridge (Ju ri) which continues backwards almost to the articulation knob for the suprapharyngo-
branchial I (spbl ar). They are separated by a vertical groove for the r. supratemporalis lateralis
(sti gr), aiTsing dorsally fmm the glossopharyngeus (IX) foramen. The articulation facet just
mentioned occupies the postero-ventrolateral surface of the poslotic (pot pr) proçess. In contrast,
the articulai' areas for the infrapharyngobranchials 1 (ipbl ar) and 2 (ipb2 ar) are covered with
penchondral bone and are represented by small tubercles situated as in Eusthenopleron. behind
the vestibular fontanelle and at the level of the ventrolaterally directed process lying ventrally
to the edge of the basicranial fontanelle.
The groove for the dorsal aorta (da gr) passes anteriorly to the latéral surface of the otic
capsule and obviously ran against the surface of the cartilage of the otic capsule. The dorsal
and ventral articular areas for the hyomandibula arc .situated as in other osteolepiforms, that is,
ventrally and donsally to the jugular canal, on the poslcrior surface of the latéral commissure
(le). A tubercle with a roügh surface, probably for the m. adductor hyômandibulae, is situated
anteriorly to the ventral articular area (BJERlîlNG. 1971).
In contrast to the condition in Megapoma. the groove for the dorsal aorta does not give
off an enclosed canal for the occipiîo-veriebral artery, but a vertical groove ninning dorsally
along the latéral surface of the occipital. This groove gives off anteriorly and posteriorly branches
which enter a small foramen dorsolaterally. A short canal for the occipital artety (oa gr) runs
anterodorsally from this point to meet a small pit between the latéral occipital surface and the
foramen for the n. vagus (X), which opens on the posterior surface médial to the postotic process.
Dorsally, the groove for the occipital artery runs along the latéral surface and Icads to a small
foramen situated ventrolaterally to the occipital plug. Two smaller foramina lie in front of the
origin of the groove for the occipital artery, the posterior one being joined by a groove of the
same system of branching grooves for blood vessels. J.\RViK ( 1980) describes in the sarne position
two small foramina in Eusthenopteroiu and calls them the eanals for the '‘spino-occipital nerves”.
The rearmost of these two foramina is found in a similar position in Megalichthys (Romer,
1937) and is suggested to transmit the n. hypoglossus (XII). The groove for the vertébral artery
(av gr) is seen only on the right side; it Icavcs the occipilo-vertebral groove and passes post-
erodorsally to the edge of the braincase.
Approximately at the midiength of the basicranial fenestra. The canal for this nerve origi-
nates in the antero-ventromedial part of the floor of the otic capsule and passed through it.
There are two surfaces for the altachinent of the basis cranii muscles (Fig. 6B). The anterior
one (abc ar) has the shape of a triangle whose angles are situated respectively at the anterior
tip of the basal plate of the otoccipital anteriorly, the abducens nerve foramen laterally, and the
edge of the ventral hyomandibular facet mcdially. Its latéral side is represented by the edge of
the otic shelf. The second muscle attachment area (pbc ar) is situated posteromedially to the
first one and occupies the space limited by the vestibular fontanelle laterally, the basicranial
— 311
fontanelle antérolatéral ly, and a well-marked ridge, which continues the latéral edge of the lutter
posteriorly up to the level of the tubercle for the attachment of the infrapharyngobranchial 2,
and then runs laterally towards the groove for the dorsal aorta. The anterior dépréssion probably
housed the insertion of the subcephalic muscle and the posterior one. as pointed out by VOROBY-
EVA (1977a), coiild acconimodatc the insertion of its antagonisl. JarvIk (1980) suggested the
presence of a sériés of basicranial muscles, front 1 to 6, and noied thaï corresponding muscles
(basicranial 4 and 5) are found in the embryonic stages of modem amphihians and, probably,
in the adults of some cxlînct fishes (JARViK. 1972). Anotber possible interprétation is that it
housed the insertion of the palatoquadratc dcprc.s.sor or levator of the branehial arches.
The ventral wall of the brain cavity, which is ossified in the posterior half of the otico-
occipital bloek beats anteriorly a narrow strip devoid of periostcal lining dorsally and bordered
by its Sharp rising edges laterally. Caudally. this ridge becomes wider and the periosteal layer
turns into a funnel which leads to paired çanals, running posteroventrally (rom the brain cavity.
The posterior surface of the ventral wall of the brain cavity is totally devoid of periosteal lining.
JarvIk (1980) reconstructs a médian basilar artery. but it is possible, that this artery was paired
and occupied a groove laterally. The canal runs toward a foramen in the latéral surface of the
occipital division, which is situated before the emergence of the occipital artery frnm the oc-
cipito- vertébral artery, and tliis canal may thus hâve housed the commissure between the oc-
cipito-vertebral and basilar arteries, The médian structure might serve for the attachment of the
brain membranes.
In contrast to Euslhennpieron, only one (suprachordal) arcual plate was ossified in Medoevia.
It is a wide and short, rectangular ossification (Fig. 7A-C) who.se dorsal surface is smoolh,
except in a médial,, unossified area similar to that of the lloor in the posterior part of the brain
cavity, yet a little broader. The latéral surfaces are almost rectangular and blunt, and contacted
with the spongy surfaces on the médial sides of the ventral part of the temporal wall. The ventral
surface of the arcual plate is concave to cover the notochord.
The dorsal wall of the braincase in Medoevia is uneven, possibly due to the attachment
for the brain membranes. Therc is a pair of small pits in its antero-laleral corners, which give
rise to the shallow grooves running posteriorly up to the point .situated slightly behind the foramen
for the r ophtalmicus lateralis. This area corresponds to the mesencephalon and the paired im¬
pressions might be due to the lobi optici. Starling front this point the rugosity of the surface
increases and, behind the sinus supenor, the widlh of ihc dorsal surface dccrcases twice. Thcre
appears a double groove. both branches of which unité to pass caudally, This groove reaches a
large funnel-shaped foramen of a vertical, unpaired canal which is displaced to the right and
extends to the supraotic cavity. Behind it, the dorsal wall of the cavity slopes down, as its latéral
Fig. 7. — Medoevia lara n. g., n. sp., arcual plaie. A, dorsal
view; B. ventral view; C, anterior view. Scaie bar: 10 mm.
Medoevia lata n. g., n. sp.. plaque atvuale. A. vue dorsale ;
B. vue ventrale: C, vue anlérieure. Échelle: W mm.
— 312 —
walls corne doser to each other, thereby marking the posterior surface of the cerebellum. Ventrally
to it the latéral wall is pierced by the foramen for the n. vagus (X) and the n. liniae lateralis,
which pass through a common canal. Ventrally, a smaller foramen pénétrâtes the ventrolateral
wall of the brain cavity and may be for the hypoglossus canal. The short and thin glossopharyn-
geus canal pénétrâtes the postérolatéral part of the wall of the otic cavity.
The médial wall of the otic cavity is, as in Eusthenaptercm, unossified. The general pattern
of the seniicircular canals, ampullae, utricuUis diverticle and sacculus is the same as in the latter,
except for its position in relation to the .supraolic canals. The sinus superior is situated opposite
the ventral orifice of the anterior dorsal canal issued trom the supraotic cavity, while in
Eiisthenopteron it is situated behind the sinus. The anterior canals of the supraolic cavity are
narrower than in Eusthenopteron and the médian wall between them disappears only at a short
distance after the anterior extremity of the posterior vertical semicircular canal.
DERMAI BONES of THE CHEEK PLATE
The anterior edge of the médial surface of the postorbital (Figs. lA, B, 8A, B; po) shows
a large opening for the sensory line canal (iosc fo), which is bordered posteriorly by a sharp-edged
crest runing ventrally towards the overlappitig surface for the supraorbital 2. Dorsally. this crest
forms a small platform, which serves for the contact with the posterior process of the intertem¬
poral (it ar). The anteroventral corner bears short crests which are parallel to the orbital margin.
Thèse crcsls arc prolongcd onlo the orbital margin and poslerovenirally onto the jugal (ju). This
bone (Figs. lA. B, 8C, D) is rather long and participâtes to the orbital margin. Sensory canals
enclosed within the bone are marked by ndges on its médial surface. The ossification center
bears several large and numerous small nutrient porcs. The squamosal (Figs. IA. B. 8E. F: sq)
is diamond-shaped. and displays the general osteolepid condition, Its pit line is situated rather
far dorsally from the ventral margin. bifurcates dorsally on the right-hand side. The quadratojugal
pit-line (Figs. IA, B, 8G. H; qj) is arch-shaped, .starting anteroventrally and ihen extends post-
erodorsally. In its middle part, it gives off a ventral branch which almost reaches the bone margin.
The dorsal iiiaxillary process (Fig. 81, J; dmax pr) is directed anterodorsally. The notch between
the latter and the anterior process of the maxilla forms the posterior wall of the exochoana. The
médial surface of the dorsal maxillary process and the maxilla itself bear a junction surface for
the latéral side of the dermopalatine. The alar process is rather well developed and extends
backwardly up to level of the deepest portion of the bone.
PaLATOQUADRATE and A.SSOCIATED PLATES
The palatoquadrate in Medoevia agréés in many respects with that of Osteolepis macw-
lepidoius (Watson, 1954), the general configuration and major articulation areas being very similar
(Fig. 9A-E), and, conversely, they differ from tho.se in the Middle Devonian Thursius estonicus
and Gyroptychius pauh, described by VOROBYEVA (1977a). The palatoquadrate complex of
(IIOLMGREN & StenSIO, l936;JARViK, 1942, 1944a. 1954, 1980) is some-
what longer, the ascending process being displaced far backwards.
The vertical dermopalatine plate is almost twice as long as its horizontal plate (Fig. lOA-D).
The anterior process of ils vertical lamina is jointed to the posterior edge of the vertical plate
— 313 —
Fig. 8. — Medoevia lata n. g., n. sp., dermal boncs of lhe cheek plate. A, B, postorbital; C. D, jugal, E, F, squamosal; G, H,
quadraiojugal; I, J, nia.xilla. A, C, E, G, i, latéral view; B, D, F, H. J, médial view. Scale bar: 10 mm.
Medoevia lata n. g., n. sp., os dermiques de la joue. A, B. postorhitaire ; C. D. jugal. E, F. squamosal: G, H. quadratojugal ;
/, J. maxillaire. A. C. E. G. I. vue latérale: B. D. F. H. J. vue médiate. Échelle: W mm.
of the vomer by a suture. The vertical lamina is deepest opposite the fang pair, where its ventral
edge bears a row of rather large denticles. The dentition of ils other parts consists of the 2-3
rows of smaller teeth. The anterior process lines dorsally a large pit in the endoskeletal bone,
which houses the tip of the coronoid fang, and makes a nolch in the anterior margin of the
horizontal plate. The similar, yel shallower, pit for another coronoid fang is lined by the posterior
— 314 —
Fig. 9A, B. — Medoevia lata n. g., n. sp., palatoquadraie complex. A. B, médial view. Scale bar: 10 mm.
Medoevia lata tu g., ru sp., complexe pakitocarré. A, B, vue médiale. Échelle: 10 mm.
margin of the dermopalatine and the anterior margin of lhe ectopterygoid. There is only one
pair of fangs on the ectopterygoid, and the posterior portion of the ventral surface of the horizontal
lamina is fiat. The dermal lining of the pit for the third pair of coronoid fangs is pierced by a
rounded orifice in the middle of the horizontal lamina of the ectopterygoid.
The posterior palatonasal canal (ppal fo) pierces the dorso-lateral ridge of the dermopalatine
and cornes oui to its dorsal surface to be continued forwards by the anterior palatonasal canal.
The groove for the postchoanal anastomosis (pca gr) follows the dorsal part of the anterior process
of the dermopalatine towards the small notch on its médial margin, then it tums backwards.
— 315 —
Fig. 9C-E. — Medoevia lata n. g., n. sp., palatoquadrate complex. C, ventral view; D, E, latéral view. Scale bar: 10 mm.
Medoevia lata n. g., n, sp., complexe palatocarré. C, vue ventrale; D, E, vue latérale. Échelle: 10 mm.
— 316 —
The sutures of the pars autopalatinum (aup) with lhe entopterygoid can easily be traced in
the area posterior to the apical (ap pr) and dorsomedial (dm pr) processes (Fig. 9B, E). Laterally
(Fig. 9C), on the horizontal plate, the suture passes near the edge of the coronoid fang pit (co
pi) of the autopalatinc. then lovvards the posteroniedial edge of the overlying dermopalatine,
where it becomes hidden by the overlying ventrolateral margin of the entopterygoid. Dorsally,
the suture lines the basal process of the palatoquadrate (bpr) posteriorly. The suture bctwcen
the autopalatine and the metaplcrygoid (nip) is riot clearly visible. The suture bctween the
metapterygoid and entopterygoid appears above the basal process. strongly bends anteriorly and
then backwards along the dorsal margin of the palatoquadrate complex. gradually becoming in-
distinguishable posteriorly. The suture between the quadratc (qu) and the entopterygoid follows
the posterior margin of the latter. but becomes indistinguishable dorsally. and its relationshtp
with the posterior end of the metapterygoid is not cleur. The latéral side of the palatoquadrate
complex (Fig. 9D, E) clearly shows the suture between the entopterygoid, metapterygoid and
autopalatine; lhe dermal componenl clearly overlies the endochondral ones, sincc the sutures on
the surface are strongly displaced towards the centre of the complex, relatively to their position
on the médial surface.
The apical process of the autopalatine part (Fig. 9C, E) is only slightly separaled from the
dorsomedial one by a small, yet distinct, groove probably for lhe passage of a branch of lhe
palatine artei^. The notch for tlie oblique eye muscles (oem no) in Medaevia is, in contrast to
Eustheiiopteron, very shallow, although it participâtes in the formation of the foramen, together
with the ethmoid. A shallow notch limits the anteromedial ethmoidal articulation facet laterally,
forming lhe wall of ils buttress. Tliis notch formels the médial wall of lhe orbilonasal canal. The
horizontal plate of the autopalatine, on which rest the palatine and eciopterygoid, consisis of
two areas; lhe mcdial one faces venirally and bears two pits açcommodating lhe coronoid fangs
of lhe lower jaw and forms two pockels under lhe entopterygoid for lhe médial processes of
the palatine and the eciopterygoid. The main pan of this surface is uneven and rugose, .Anolher
area is much narrower and shorter, and extends between the anterior pit for lhe coronoid fang
to the posterior pit (Fig. 9C-E). The surface of this area is densely ornamented with a network
of the vascular grooves, probably for banches of the r. maxillaris. The posterior part of this
edge is sharpened and bears a patch of unfinishcd bone. facing ilie maxilla. This area probably
served as an auxiliary connecting point (aef) with the maxilla beyond ils contact with lhe palatine
and eciopterygoid.
The anteromedial ethmoidal articulation area of the palatoquadrate is situated at the antér¬
olatéral corner of its autopalatine part, and on the posteromedial margin of the choana.
The dorsomedial process (dm pr) is a hemisphaerical plate of the autopalaiine (Fig. lüC).
Its surface is smooth and bears tiny pores. The dorsal edge of the médial margin of the horizontal
plate of the palatoquadrate shows a Sharp crcsi which reaches the basal process and served for
the attachmeiit to the suspending crest of the ethmosphenoid, by lhe means of a ligament. The
basal process (b pr) consists of the two adjacent faccis. partly separated by a pit situated just
ahead of the anterior margin of the dentigerous plate of the entopterygoid.
This pit faces lhe crest in front of the muscle scar for the attachment of the subcephalic
muscle on the basisphenoid. A similar pit is situated immediately above the dorsal facet of the
— 317 —
FlG. 10. — Medoevia lata n. g., n. sp., dermopalatine and ectopterygoid. A, ventral view; B, dorsal view; C, latéral view; D,
médial view. Scale bar; 10 mm.
Medoevia lata n. g., n. sp., dermopalutin et ectoptérygoïde. A, vue ventrale ; B. vue dorsale; C. vue latérale; D, vue médiale
view. Échelle : 10 mm.
basal articulation and faces the edge of the dorsal slope of the basipterygoid buttress on the
basisphenoid.
The ascending proces.s of the palatoquadrate complex (asc pr) overhangs the facet of the
basal articulation and is much produccd forwardly; its dorsal margin is a facet for the suprapte-
rygoid articulation, which is devoid of periosteal layer and was probably connected to the su-
prapterygoid process by means of a ligament. The anteriormost part of the ascending process is
beak-shapcd. Its surface is smooth and abuts against the slight oblique crest on the surface of
the lalerosphenoid, above lhe foramen for lhe optic nerve.
The dorsal margin of the ascending process is slightiy swollen, and bounds off the anterior
part of the Irigeminal notch (tri no), which is rather small In Eusfhenvpteron the posterior part
of this process rcaches the otico-occipital block of the endocranium. In Medoevia, on the contrary,
the trigeminal notch is situated as in Ostenlepis. opposite the intracranial gap, so that the anterior
otic connection is fomned by the paratemporal process (pt pr). The latéral surface of the para-
temporal process i.s riigose, and, although it does not clearly reach the dermal skull roof, there
could exist a ligament connection with a knob on the anterior margin of the ventral surface of
the supraiemporal.
The dorsomedial margin of the palatoquadrate is thickened and strongly bent medially, the
quadrate articulation being fmally inclined by 45“ relatively to the long axis of the skull, The
posterodorsal surface of the palatoquadrate bears a long, deep furrow along its contact with the
entoplerygoid. The bottom of this structure referred to by JARVtK (1954) as the spiraculo-
hyomandibular rece.ss (sh re) is folded posteriorly; this portion housed the ventral edge of the
hyomandibular.
— 318 —
There is a prominent oblique ridge beginning close to the posterior end of the ectopterygoid
and extending postero-dorsally. Ventrally to the spiracular slil, it reaches the dorsal margin of
the entopterygoid, and then forms posteriorly a recess between it and the main part of the pa-
latoquadrate plate. This shelf is least pronounced opposite the beginning of the folding of the
spiraculo-hyomaridibular groove. A this level, the shagreen field of the entoptery^goid forms a
posteriorly directed longue. Ventrally to this longue, there is an articulation facet with an un-
finished periosteal surface. The rôle of this facet is unknown.
The latéral surface of the palatoquadrate complex bears numerous muscle scars (Fig. 9D,
E). The most conspicuous of lhem is a rugose field in the postcrodorsal part, which could re-
present the insertion area for the posterior portion of the m. adductor mandibulae (mamp). This
area begins opposite the latéral commissure and occupies a deep dépréssion, formed by the en¬
topterygoid and the laterally tumed quadrate part. The dorsal surface of the auiopalatine part
bears a rough superficial ornamentation suggestive of a muscle insertion: a strong ridge. running
along the edge of the embayment below the ascending process, may also correspond to a muscle
insertion. The latéral surface of the ascending process also bears ridges and uneven tubercles,
characteristic for areas of muscle atlachment. The lutter may hâve housed the insertion of the
anterior portion of the m. adductor mandibulae. Altcrnatively, il may hâve been for the médial
portion of this muscle, while the ridge just mentioned .served as the attachment of its anterior
portion. The rugose area on the dorsal surface of the autopalatine part more probably served
the insertion of the principal portion of the m. levator bulbi.
Lower JAW
No suture between the extemal dermal bones of the lower jaw is visible in Medoevia, apart
from a short trace posteriorly, between the denlary and the suprangular (Fig. 11 A). The pores
of the sensory canal are numerous and scattered over the ventral half of its latéral surface. The
only visible pit-line is lhat situated on the suprangular. The length of the adductor fossa (ad fo)
represents one third of the total length of the jaw.
A pair of the anterior teeth in the dentary tooth row is about (wice as large a.s the others
(Fig. 11 B, C). Posteriorly, the tooth row ends in the anterior third of the adductor fossa. Post-
eromedially to the dentary part of the symphysis anses a butlress which is formed by the Meck-
elian bone (mentomandibular, mm). Its médial part is not fully ossified and a perichondral surface
faces a similar one in the opposite lower Jaw ramus. The perichondral surface is prolonged
posteroventrally to form a small patch at the base of the buttress, immediately above the anterior
opening for the mandibular sensory line canal, but its function is unknown. A deep pit is situated
dorsolaterally to it and is interpreled by JESSEN (1966) as the area for the insertion of the m.
geniohyoideus (mgh pi). The buttress is capped with a rectangular, shagreen-covered adsymphy-
sial plate (ads), which meets posteriorly the vertical lamina of the anterior coronoid, The teeth
on the top of the vertical laminae of ail the three coronoids are disposed in several rows, the
larges! being situated close to the fangs, and those parts of the laminae which support the fangs
laterally are prominently raised above the leve-l of the dentigerous edge of the dentary. The
anterior coronoid is the largest, and the posterior one is the smallest of ail three. its fang being
half the size of that on the precoronoid. The floor of the coronoid fossae is made up by a thin
lamina formed by the Meckelian bone.
— 319 —
The praearticular anterior process (pra pr) contacts the posterior médial process of the
splenial opposite the anterior fang of the first coronoid. The suture here is much obliterated but
still visible. Its latéral margin, where it is fused with the coronoids, is sinusoidal. The médial
margin is straight, and one can cleariy see the contact with the Meckelian bone, which connects
the praearticular with the lower margin of the jaw, composed by the infradentaries.
Posteriorly the praearticular extends a.s far as the middle of the lower jaw articulation, the
shagreen of minute teeth being gradually replacedby small pits and a neiwork of shallow crests.
A well pronounced ridge runs along the posterior end of the bone. parallel to the edge of the
adductor fossa. A strip of its ventral surface is devoid of ornamentation.
The praearticular canal for the chorda tympani starts with a large foramen (pra fo) in the
posteroventral edge of the bone and runs forward, piercing the médial wall of the adductor
Fig. 11. — Medoevia lata n. g., n. sp., lower jaw. A, latéral view; B, médial view; C, dorsal view. Scale bar: 10 mm.
Medoevia lata n. g., n. sp., mâchoire inférieure. A, vue latérale; B, vue médiale: C, vue dorsale. Échelle: JO mm.
fossa. Further anteriorly, it is represented by a groove. The largest Meckelian fenestra is situated
opposite the first coronoid fossa, and the next two much smaller fenestrae are opposite the second
coronoid pit and the front of the adductor fossa.
A foramen situated ventrally to the posterior opening of the prearticular canal inay represent
the opening of the arlicular canal (ar fo), Patches of incompletely ossificd bone with a peri-
chondral lining are situated anteriorly and posteriorly to it, and connected with the posterior
surface of the articular. These structures may serve the connection with the ‘tongue-like’ process
of ceratohyal 2 (.lARVlK, 1980). The dorsal opening of the supra-angular canal (sa fo) enters the
jaw righi above the mandibular joint. There arc two openings in the adductor fossa on the an¬
térolatéral edge of the articular: a larger one ventrally and a smaller one dorsally, both probably
serving as outlets of the supra-angular canal.
The püsterodorsal edge of the dentary and the supra-angular are devoid of cosmine coveriiig,
since thi.s area was covered by the ventral lamina of the quadratojugal. This area extends as far
back as the posterior end of the mandibular articulation. Ventrally, the supra-angular shows a
short, but deep notch latéral ly to the articulation surface for the ceratohyal 2.
OPERCULO-SUBMANDIBULAR SERIES AND GULAR
The opercular in Medoevia is almost twice as large as the subopercular (Fig. 12A-D). It is
about 1.3 times longer than deep. Ils anterodorsal margin forms a depres.sed contact area, dévoid
of cosmine, for the latéral extra.scapular (exi ar ). The anterior margin exhibits a narrow, slightly
curved overlap surface for the preopercular. The rugose articulation facei for the contact with
the opercular process of the hyomandibula (hy ar) is situated at the anterodorsal corner, close
to the anterior margin of the bone, The subopercular is much lowcr than in eusihenopterids
(J.ARVlK, 1944a, 1952; Vorobyeva, 1977a). Its overlap surface with the opercular is only slightly
curved. The anterior margin projects medially and its ventral part is slightly embayed for the
contact with the posterior end of the lower jaw. The pit for the contact with the latéral process
of ceratohyal 2 is accompanied by a rugose area anteriorly (epchZ ar)i which is situated within
the dorsal half of the bone, close to its anterior margin.
The médian gular in Medoevia (Fig. 13 A. B) is rounded in shape. Its latéral parts contacted
the anterior infradental Hanges of the lower jaw, There is a well-marked, curved pit-linc on the
ventral surface of this bone. The latéral gulars (Fig. 13 C, D) are rather broad and short, their
length being only about 2.5 times more than their maximum width. The pit-line is situated in
the anterior third of the bone. The médian gular overlaps the corresponding surfaces which are
devoid of cosmine on the anteromedial margins of the latéral ones. The left latéral gular slightly
overlaps the right one to close the slit between them; there is a corresponding cosmine-covered
depressed area along the médial margin of the right latéral gular. The posterior edge of the bone
is rounded and almost transversal in position. Its dorsal surface is covered by a network of
va.scular grooves.
The .submandibulo-branchiostegal (Fig. 14A, B) is roughly oval in shape and shows two
surfaces separated by a sharp ridge anteriorly. Its latéral lamina is only partiy cosmine-covered.
The anterior edge of the overlapped surface shows a small notch for the contact with the posterior
end of the lower jaw (Ij no).
— 321 —
FlG. 12. — Medoevîa lata n. g., n. sp. A, B, opercular; C, D, subopercular; A, C, latéral view; B, D, médial view. Scale bar:
10 mm.
Medoevia lata n. g., n. sp. A, B, operculaire ; C. D. sous-operculaire. A, C, vue latérale; B, D, vue médiale. Echelle : 10 mm.
There are five submandibulars (Fig. 14C-J), the anterior one extending slightly in front of
the level of the posterior end of the médian gular. The size of the plates is not equal on either
sides. For example, the left submandibular 5 is almost 1.5 times longer than the corresponding
élément on the right side. The pit-line of the submandibular 7 almost crosses the bone trans-
versally.
— 322 —
Fig. 13. — Medoevia lata n. g., n. sp. A, B, médian gular; C, D, latéral gular. A, C, ventral view; B. D, dorsal view. Scale bar:
10 mm.
Medoevia lata n. g., n. sp. A, B, gulaire médiane: C. D. gulaire latérale; A. C, vue ventrale; B, D. vue dorsale. Echelle;
iO mm.
Dental plates of the mouth cavity and pharynx
About five hundred dental plates of varions size and shape are présent in the material (Fig.
I5A-G). Due to the compression of the head during fos.silization, and to the Chemical préparation
of the specimen, almost ail of them became detached, so that only the paraotical plates (Fig.
15 A, B) can be identified readily, since they are the largest ones. These are almost fiat and
pentagonal in shape. Their ventral surface bears simple, short and blunt denticles, the dorsal
surface being uneven and covered by numerous, small nutrient foramina. The size of the others
varies from 0.8 mm to several millimeters in diameter. Their outlines differ from rounded or
oval to polygonal or irregular, a diamond-shaped type with a thick base being common. There
are four major types of denticulation:
1 - short and blunt denticles, either with a single apex or multicuspid (Fig. 15F);
2 - conical ones of varions length, inclined in one direction relatively to the basal plate;
— 323 —
Fig. 14. — Medoevia laîa n g., n. sp., bones of the submandibular sériés. A, B, submandibulo-branchiosiegcil plate; C, D, sub-
mandibular 7; E, F. submandibular 6; G, H, left submandibular 5; I. J, submandibular 4; A, C, E, G, I, ventral view; B, D,
F, H, J, dorsal view. Scale bar: 10 mm.
Medoevia lata n. g., n. sp.^ os de la série suhmandihutaire. A, B, plaque submandîbuh-bmnchiostégale : C, D, submandibulaire
7 ; E, F submandibulaire 6 : G. H. st4btTuindibulaire 5 gauche : I. J. submandibulaire 4. A, C, E, G, /, vue ventrale ; B, D,
F, H, J, vue dorsale. Échelle : 10 mm.
3 - transitional types between the first two (Fig. 15C-E);
4 - tiny cônes forming a row along the edge of a pit in the middle of an otherwise smooth
plate; which resemble in position the denticles described below on the anocleithrum, cleithrum
and clavicle (Fig. 15G).
Hyoid arch
The hyomandibula of osteolepiforms is known in Eusthenopteron foordi (Westoll, 1943;
JARViK, 1954. 1980; Smithson & THOMSON, 1982), Megalichlhys (WaTSON. 1926; Romer,
1941), Osteolepis (THOMSON, 1965), Jarvikina wenjukowi and Thursius estoniens (VOROBYEVA,
1977a).
The general shape of the hyomandibula in Medoevia (Fig. 16A, B) does not differ signif-
icantly from that in Eusthenopteron, being slightiy deeper, the distal end being broader and
shorter and the angle of tlie postero-dorsal edge being more acute than in the latter. The opercular
articulation area (op ar) is a triangular dépréssion devoid of periostal cover and situated on the
latéral surface of the bone. This corresponds to the opercular process, but it is évident that the
process itself was composed of cartilage. The laterally directed ridge, which forms a pocket for
— 324 —
Fig. 15. — Medoevia lata n. g., n. sp., dental plates uf the moiilh cavity and pharynx. A, B, paraotical plate. A, ventral view;
B, dorsal view. C, D, scale bar: 2.2 mm; E, G, scale bar; 3 mm; F, scale bar; 3.2 mm.
Medoevia lata n. g., n. sp., plaques dentées de la bouche et du pharynx. A. B, plaque paraotique ; A, vue ventrale : B, vue
dorsale; C, D, échelle: 2.2 mm; E, G, échelle: 3 mm : E. échelle: 3,2 mm.
the insertion of the m. protractor hyomandibularis (prhy) is distal to the opercular process, thus
the position of the insertion of this muscle is displaced distally in comparison to its position in
Eusihenopteran. Distally, and very close ventrally to it. there is another rounded muscle scar of
unknown nature. The ridge for the insertion of the m. adductor hyomandibularis (ahy ri) is situated
exactiy in the same position us in Eusthenopieron. The proximal surface of the médial side bears
a groove with rugose walls nearly to the middle of the bone. A wide groove with a similar
ornamentation is found on the médial side of the bone, dorsally to the ridge for the attachment
of the m, adductor hyomandibularis and obviously represents an impression of the jugular vein
(juv). The mosl proximal evidence for the r, hyomandibularis is the orifice of the hyomandibular
canal (hyc) which pierces the bone and appears on the latéral side shortiy before the level of
the anterior margin of the notch for the opercular process, then passing distally. The wall of the
canal is pierced medially by a small foramen for the r. opercularis VII (ro VII fo).
The groove for the r. hyoïdeus (rhy gr) is observed proximally al the dorsal edge of the
bone; thus, the branching of the truncus hyomandibularis occurred more proximally and left no
traces on its surface. The groove for the r. hyoideus extends to the base of the opercular process
and it is impossible ta trace it more distally. The articulation facet for the stylohyal (sly ar) is
small and situated at the very tip of the distal process, heing displaced medially.
— 325 —
Fig. 16. — Medoevia lata n. g., n. sp., hyomandibula. A, latéral
view; B, médial view. Scale bar: 10 mm.
Medoevia lata n. g., n. sp.. hyomandibulaire. A, vue laté¬
rale: B. vue médiale. Échelle: ÎO mm.
The stylohyal was probably not ossified. As in Eusthenopteron, the ceratohyal consists of
two éléments: the ceratohyal 1 (chl) and ceratohyal 2 (ch2). The posterior élément, or ceratohyal
1 (Fig. I7C-F), is a rather .short rod of complicated construction. A widc and deep oblique groove
crosses its dorsolateral surface, and it bears four articulation facets: distal, proximal, ventral and
latéral. The latéral and ventral facets are accompanied by pits, which lie proximally to them in
both cases. The latéral facet (sop f) mighl serve the articulation with the suboperculum and the
ventral one (smb f) connects the bone with the submandibulo-branchio.stegal plate. The ceratohyal
2 (Fig. I7A. B) is a large plate-like bone. characlerized by an almost straight anterior margin
and a crescent-shaped posterior onc. Ils anterior edge bears a pronounced groove for the anterior
continuation of the effereni arlery of the first branchial unit (eal gr). The dorsal surface bears
a network of vascular grooves, which branch off from a notch in the proximoventral corner.
The hypohyal (Fig. 17G, H) is a massive iriangular bone, with a curved groove for the anterior
portion of the efferent artery (eal gr). Its latéral surface is rugose and served the attachment of
the anterior end of the interarcual ligament.
The basibranchial sériés and branchial arches
The éléments of the basibranchial sériés and the branchial arches are described in
Eusthenopteron foordi and Glyptolepis graenlandica (JarvIk, 1954, 1962, 1963, 1972, 1980). It
is described here for the first tîme in an osteolepidid.
The basibranchial sériés consists of the two éléments (Fig. 18A, B; bbl, 2), basibranchial
1 and basibranchial 2. The foremost element, or basibranchial 1 is a mas.sive heptagonal bone
with two articulation facets on each side, for the hypobranchials 1 and 2, a pair of facets on
the anterior margin for the hypohyals, a médian facet posteriorly for the basibranchial 2, and a
paired area devoid of the periosteal lining, close to the anterior margin of the ventral side, for
the ligamentous or carülaginous attachment of the urohyal (uh ar). The posterior part of its
— 326 —
FiG. 17. — Mecioevia lata n. g., n. sp., éléments of the hyoid arch. A, B, ceratohyal 2; C-F, ceralohyal 1; G, H, hypohyal. A,
G, posterior view; B, H, anterior view; C, médial view; D, latéral view; E, ventral view; F, dorsal view. Scale bar: 10 mm
Medoevia lata «. g., n. sp., éléments de l'arc hyoïdien. A, B. céraiohyal 2: C-F, cératohyal l ; G. H. hypohyal. A, G. vue
postérieure : B, H, vue antérieure ; C, vue médiale ; D. vue latérale ; E. vue ventrale : F. vue dorsale. Échelle : 10 mm.
ventral surface bears a deep, anterodorsally directed pocket; its bottom is rugose and bears several
vascular, possibly nutrient foramina; this pocket may bave served for the insertion of the paired
aponeiiroses of m. stemohyoideus (tnshy). The transverse crest, which bounds off the pocket
anleroventrally, extends between the articulation surfaces of the first pair of hypobranchials; its
edge is devoid of periosteal lining, thereby sugge.siing that it is a trace of the limit between the
anterior and the posterior component.s (basihyal + basibranchial proper) of the bone. Its dorsal
surface is rugose and obviously supported the denticulated plates of the mouth cavity. The second
basibranchial element is a short, horseshoe-shaped element, that was connected to the posterior
articulation surface of basibranchial 1. Its ventral notch accommodated the ascending plate of
the urohyal. The posterior surface shows a pair of articulation facels for the hypobranchials of
the third branchial arch.
A very poorly preserved sublingual rod (Fig. 18A; sr) is présent. It is triangular in cross-
section and very lightly ossified, possessing no periosteal lining over its dorsal ridge. Anteriorly,
its dorsal ridge bccomes higher and its basal part narrower.
The general shape of the urohyal (Fig. I9A, B) is similar to that in Eusthenopteran (JARVÎK,
1954, 1980), though more elongated in shape. The anterior part of its dorsal edge is a sharp
— 327 —
Fig. 18. — Medoevia lata n. g., n. sp., mounled eleraenis of
lhe hyoid and branchial arches. A, dorsal view; B, ventral
view. Scale bar: 10 mm.
Medoevia lata «. g., n. sp., arcs hyoïdiens et branchiaux
montés. A. vue dorsale: B. vue ventrale. Échelle: JO mm.
crest, interrupted by two poorly ossified areas, where it touched the transversal ridges of the
ventral side of the basibranchial 1. Posteriorly, the edge becomes blunt until the posterior end
of the bone. The posteroventral corner of the bone bears a small notch. Its ventral surface is
fiat and striated, probably due to the attachment of a ligament. The characteristic feature of its
latéral surfaces is an oblique, anteroventrally directed ridge, ventrally to which the surface of
the bone is rugose. This rugose surface may hâve served the attachment of m. rectus cervicis
(rece). The tubercle in the middie of the ventral edge could hâve been the attachment of m.
geniohyoideus (ghy tu).
The hypobranchials 1-3 are rather uniformly built and differ by the arrangement of the
grooves, tubercles and ridges (Figs. 18A, B, 19C-F). The most conspicuous feature of the ventral
surface of hypobranchial 1 is a longitudinal groove, which probably housed the afferent artery
— 328 —
of the first branchial unit (aal gr). Proximally, there are iwo tubercles on either sides of this
groove. The proximal part of the dorsal surface of this bone shows a slight rugosity and two
patches devoid or periosteal lining, which might represent the attachment area for the interarcual
ligament (ial tu). The dorsal surface of hypobranchiul 2 bears only a massive, oblique rostro-
caudal ridge. followed by a smaller ridge and a pii in front of ils posterior portion for the mm.
transversalis venlralis 2 (mlv2 ri) and obliquus vcnlralis 2 (mov2 ri ). A small tubercle lacking
periosteal lining îs situated in the middle of the anterior edge of the bone, opposite a similar
structure in the poslerodorsal area of ihc hypohial I. The dorsal surface of the hypobranchial 3
(Fig. I9E, F) is smoolh, but the ventral one présents three tubercles in the middle of the bone,
connected to cach other by a distinct ridge. The anterior tubercle is lhe largest, and the smallest
one is located posteriorly to it; this pair constilutes the anterior margin of a deep pit. The third
tubercle is more like a short process; it is ubutted by a short ridge anteriorly and limils another
pit on the posterior side of the bone. It is likely thaï the largest tubercle served. as in Glyptolepis
groenlandica (JARVIK, 1962, 1963, 1972, 1980), lhe articulation of hypobranchial 4 (hby ar).
The smaller tubercles seem to hâve served the attachment of the m. obliquus ventralis 3 (mov3
tu).
POSTCRANIAL SKELETON
The dorsal boncs of the shouldcr girdic (po.st-temporal, supracleithrum and anocleithrum)
arc described only in a few osleolepiform llshes, such as Euslhenapteimi (JarvIk, 1944b, 1980),
Osleolepis (JARViK, 1948) and Canon indnt (l.ONO. 1985c).
The post-temporal in Medoevia (Fig. 20A,. B) is a convex, rectangular bone. Its anterior
overlapped surface is not preserved on either sides. so thaï the mode of articulation with the
extrascapulars is not clear. The latéral (operculari process (op pr) is much larger lhan in
Eusthenopteron. The supracleithrum (Fig. 20C, D) is aboul half the size of the post-temporal.
Anteriorly it bears a long triangular process. medially to the anterior opemng of the main latéral
line sensory canal, for the contact with ihc post-temporal. Its latéral portion overlapped by the
opercular (op pr) is also broad. A short, oblique pit-line is situated close to the anterior edge
of the non-overlapped surface.
Fin. 19. — Medoevia lata n. g., n. sp. A. B. urohyal; C, D. hypobranchial 1; F, F, hypobranchial 3. A, latéral view; B, E, dorsal
view; C, ventral view; E, ventromeUial view; F, dorsolaieral view. Scale bar: 10 min.
Medoevia lata «. g., n. sp. A. H, urohyal : C. D, hypahmnehiat /; E, /% hypobranchial J. A, vue latérale: B. E, vue dorso-
latérale ; C. vue ventrale: E, vue médioventrale : E. vue dorsolatérale. Échelle: ÎO mm.
— 329 —
The anocleithrum in Medoevia (Fig. 20E, F) differs significantly in shape from that of
Eusthenopteron and is doser to that of Canowindra (LONG, 1985c). The anocleithral process
(ano pr) is very well developed, its length being half of the total bone length, and the angle it
forms with the main plate is about 90*’. Its inedial side bears a long, massive ridge, which runs
towards the apex of the process. The process for the articulation with the supracleithrum (sc pr)
is large and ralher elongated in shape. Laterally, the cosmine iayer is resorbed and replaced by
scarce, bi- or tricuspidate denticles on bony tubercles. The cleithiuin in Medoevia (Fig. 21A-C)
has the typical overall shape for osteolepiforms, but soine of its features are peculiar. The ventral
and dorsal laniinae are approximately equal in length. forming between them an angle of about
140". The cosmine cover is practically absent, except on a patch posleriorly in the central part
of the bone (Fig. 21A). The rest of the extemal dermal omament is a neiwork of high ridges
bounding off deep pils. The tops of the ridges bear one row of bi- or tricuspidate. caudally
directed denticles. like those on the anocleithrum, A deep and narrow area, between the main
ornamented surface and the overlap area for the opercular and subopercular bears minute pits
and tubercles, the latter being capped with the same type of denticles, with 5-7 cusps, like on
the posterior surface of the bone.
The process of the cleithrum is only insignificantly developed because the extemal area
overlapped by the clavicle (clav ar) is extremely small. as in MegalUhrhys hibberti (ANDREWS
& Westoll, I97()b) and the “osteolepid B” from the Upper Devoman of Armutgd^lek Tepe,
Turkey (JANVIER & Marcoux. 1976; JANVIER. 1980). The breadth of the inwardly bent area
overlapped by the operculum and suboperculum (mem ar) is similar to that in Osteolcpis nutc-
rolepidonis (JARVÎK, 1948). Judging from the structure of the antero-medial margin of the
cleithrum, this bone never reached the interclavicle. The médial surface of the dorsal part of
the cleithmm (Fig. 2 IB) show's a prominent ridge on its anierior edge. formed by the anierior
lamina. It is bordered posteriori}' by a groove receiving the anocleithral process (ano pr gr). A
shallow, depre.ssed area situated posleriorly (pano pr ar) receives Üie large posterior process of
the anocleithrum, There is a well-marked groove for the overlap of the vertical process of the
clavicle vcntrally. It begins on the latéral surface, then extends along the anterior edge of the
cleithrum. and passes to the medial surface up to the ventral buttress of the .scapulocoracoid.
The clavicle is completely devoid of cosmine (Fig. 22D, E). The two clavicles are oniy
partly preserved but allow a recontruction of the bone. The ornamentation of ihcir ventral surface
consists of pits. the largesi of them being situated proximally. Smaller pits are disiributed along
the margins of the ventral lamina, its centre being smooth with the exception of small nutrient
foramina. The edges of the large pits are provided with medially directed dentine denticles. the
dorsolateral lamina bears the same type separale miilticuspidate denticles as the cleithrum. The
medial edge of the dorsal side of the ventral lamina bears a clearly defincd overlap surface for
the interclavicle (ici ar), which is devoid of the slight radial ridges, that are seen over the rest
of the surface. The posteromedial edge of the ventral lamina is depressed. It runs posleriorly to
form a groove. bordered by a mas.sive crest laterally. This groove housed the anteroventral process
of the cleithrum. The crest runs posterodorsally on its latéral surface up to the midheight of the
ascending process. The latéral surface of the ascending process bears an overlap surface, which
fits the antérolatéral edge of the medially reflected lamina of tlie cleithmm, forming the post¬
érolatéral w'all of the branchial chamber. The rest of the latéral surface serves as its prolongation.
— 330 —
Fig. 20. — Medoevia lata n. g., n. sp., dnrsal éléments
of the pectoral girdle. A. B. post-lemporal: C, D,
supracleitlirum; E. F. ant)cleifhnjm. A. C. E, dorsal
view; B, D, F. ventral view. Seule bar: 10 mm.
Medoevia lata n. g., n. sp.. éléments dorsaux de la
ceinture pectorale. A. B. post-teinporal : C\ D. su-
pracleithrum : E. F. anocleirhrum. A. C. E. vue dor¬
sale : B. D. F, vue ventrale. Échelle : 10 mm.
The overlapped surface bears vertical crests for the attachment ligaments, the free surface being
smooth.
The interclavicle is a thin, oval symmetrical plate, which is slightly shorter than that in
Eusthenoptewn (JarvIk, 1944b). Its dorsal surface is smooth. There is a very slight and shallow
dépréssion close to its anterior margin. The ventral surface is subdivided inlo two symmetrical
halves by a médian ridge (Fig. 22C; me ri) and, contrary to Eusthenopteron, the ornamentation
is lacking.
Endoskeletal shoulder girdle and pectoral fin
The endoskeletal shoulder girdle in Medoevia agréés in general with that in Eusthenopteron
(Andrews & Westoll, 1970a; JarvIk, 1980), Megalichthys (Andrews & Westoll, 1970b),
— 331 —
Fig. 21. — Medoevia lata n. g., n. sp,, cleithrum and endoskeletal pectoral girdle. A, latéral view; B, médial view; C, posterior
view. Scale bar: 10 mm.
Medocvia lala n. g., n. sp., cleithrum et ceinture pectorale endosqueletticjue. A. vue latérale: B. vue médiale: C, vue pos¬
térieure. échelle: 10 mm.
Ectosteorhachis (THOMSON & Rackoff, 1974) and the “osteolepids A and B” (Janvier & Mar-
coux, 1976; Janvier, 1978, 1980). The foot of the dorsal butiress (db) is the largest, and has
a significant dorsal extent (Fig. 21 B, C). Anteriorly, it almost contacts the margin of the cleithrum.
The glenoid fossa (gl) faces posteriorly. It is roughly reclangular to oval in shape. rather lhan
pear-shaped, and its surface is screw-shaped. It is bordered by a sharp ridge of periosteal bone,
probably for the connective tis.sues of the joint. The ventral and dorsal surfaces are separaled
from the médial one by sharp ridges. The glenoid foramen (gl fo) is situated in the posteroventral
corner of its médial surface; it is continued internally by a short canal leading into the bone
mass, and then branching and opening posteriorly on the ventral surface by two small foramina
divided by a short ridge. Another longitudinal ridge divides the ventral surface into two areas
and ends by a rugose area, anteriorly to the latéral foramen. A distinct muscle attachment area
is situated between the dorsal edge of the glenoid fossa and the supraglenoid canal. The supra-
— 332 —
Fig. 22. — Medoevia lata n. g., n. sp. A, B, ventral lamina of the clavicle; C, interclavicle. A, C, ventral view; B, dorsal view.
Scale bar: 10 mm.
Medoevia lata n. g., n. sp. A, B, lame ventrale de la clavicule ; C, interclavicule. A, C, vue ventrale : B, vue dorsale. Echelle:
10 mm.
coracoid foramen (sco fo) is the largest. the opening of the subscapular fossa (ssc fo) is somewhat
smaller and the supraglenoid foramen (sgi fo) is the smallest of ail three.
The humérus (Fig. 23A-F) is incompletely preserved. its distal end. including the radial
and the preaxial side of the ulnar condyle being eroded away. The humerai head (ca hu) fits
well the glenoid fossa of the scapulocoracoid, being somewhat rectangular to oval and screw-
shaped. The ectepicondylar ridge (ect ri) is a short cresi on the distal part of the bone, and is
interrupted by an eroded surface. There are two prominent ridges on the dorsal surface of the
bone (Fig. 23A, D), .separated by a smooth, deep. broad and regular groove. The longer ridge
starts from the very edge of the humerai head in its dorsal part and runs toward the distal end
of the bone. Another one runs parallel to the distal part of the posterior edge of the ectepicondylar
process, then turns proximally to border the entepicondylar foramen (Fig. 23C, F).
The supinator process joins the deltoid process distally forming together a massive, rugose
ridge (su + de ri). It is connected distally, as in Eusthenopteron, with the entepicondylar ridge
by a bony bridge over the entepicondylar foramen (ent fo).
— 333 —
Fig. 23. — Medoevia laia n. g., n. sp., humérus. A, D, dorsal view; B, E, ventral view; C, F, proximo-postaxial view. Scale bar;
10 mm.
Medoevia lata n. g., n. sp., humérus. A, D. rue dorsale: B. E, vue ventrale : C. E, vue prosimo-pustaxude. Échelle: 10 mm.
The humerai ridge (hu ri) is even more fluted than in Eiisthenoptenm. It is perforated by
a row of five foramina of different size (Fig. 23B, E), iwo of them being lhe largest. The most
postaxial one is lhe entepicondylar foramen, which is. unlike in Eu.ithenoptenm, situated within
the general row. and not separated from lhe others by a ridge. Proximally, the humerai ridge
meets the pectoral one (pl ri), which is represented by a massive, rugose knob situated close to
the antenor edge of the humerai head, Anolher rugose surface borders the edge belween the
pectoral and the dcltoid ridges.
Vertebrae
Several éléments of lhe anterior vertebrae are preserved in Medoevia, including three
complété and several broken intercentra, two pleurocentra and six separate halves of lhe neural
arches. The composition of the vertebra is as in Osteolepis panderi (ANDREWS & Westoi.l,
1970b) (Fig. 24A, B) The intercentra arc represented by unpaired, cre.scenl-shapcd éléments,
similar to those of Udistinia (THOMSON & VAUGHN. 19fi8) and Etixthenopleron (ANDREWS &
Westole, 1970a). The notochordal canal is rather wide, and the centra are correspondingly thin-
walled (Fig. 24C). Their ventral side is slightiy rugose and featureless. The latéral side bears a
well-marked ridge in lhe middie. which mighi rcprcsenl the line of allachmeni for the myoseptum
(my ri), separated from the anterior and posterior edges by slighl grooves sometimes pierced by
nutrient foramina (Fig. 24D).
The pleurocentrum is a paired, small, deep triangle-shaped élément (Fig. 24E). Its dorsome-
dial edge is composed of an unfinished bone margin, that might reflecl the cartilaginous nature
of the bridge which connccls lhe two halves and séparâtes the notochord from the neural canal.
Two articulation facets for the neural arch (na ar) are présent: a larger. anterior one and a smaller
posterior one, the former being slightiy displaced ventrally. The anterior facet might represent
the place for the atiachment of the neural arch of the same segment, while lhe posterior one
might serve for the atiachment with the anterior end of the next neural arch posteriorly. The
— 334 —
Fig. 24. — Medoevia Iota n. g., n. sp., elemenis of ihe vertébral
column. A, B, reconstruction of the vertebrae; C, D, in-
tercentrum; E. pleurocentrum: F, G, neural arch element.
A, D, E. F. latéral view: B, C, anterior view; G, médial
view. Scale bar: 10 mm.
Medoevia lata n. g., n. sp., éléments de la colonne verté¬
brale. A. B. reconstitution des vertèbres: C. D, intercen¬
tre ; E. pleurocentre. F. G. éléments de l’arc neural. A.
D, E, F, vue latérale: B, C. vue antérieure: G. vue mé¬
diale. Échelle : W mm.
intersegmenlal arlery or the ventral spinal nerve could pass through a well-marked groove be-
tween these two facets.
The neural arches differ from each other by the length and breadth of the neural spines
(Fig. 24F). These éléments are composed of two separate halves, as in Osteolepis (Andrews
& Westoll. 1970b). These were probably connected by means of cartilage, since there is a
strip of the bone surface devoid of periosteal lining above the neural canal (Fig. 24G). The
médian surface of the neural spines is smooth, implying that they were free. The neural arches
were probably connected to each other as small, incompletely ossified zygapophysis tubercles
are présent at the back of the arch, above the neural canal.
— 335 —
SCALES
The scales in Medoevia differ significantly from the standard osleolepid pattern (Fig. 25A-
H). Their external surface bears a distinct groove separating the overlapped part from the free
part. The latter is covered wilh cosmine, as in typical osteolepids, but the overlapped portion
is ornamented with fine ridges, forming an iiTCgular network (Fig. 25 A), whereas it is smooth
or slightly rugose in the othcr known osteolepids (e.g. Jarvik, 1948). The internai surface is
quite typical for the eiisthcnopterids and rhizodontids, being ornamented with concentric growth
rings, w'hich are best sçen in ihc anterior part of the scale (Fig. 25B). The posterior part of the
central area is covered by nurnerotis vascular foramina. and its centre is occupied by a distinct
knob. It is often accompanied by a vestige of the weakly developed osteolepid-like articulation
ridge which tapers gradually (ar ri + kn), so that there is no articulation process to contact its
dorsal neighbour. The posterior margin of the inner surface is smooth. The scales are thin, rela-
tively to their size.
The .scales of the anterior dorsal row' are rounded or slightly shorter than wide. The over¬
lapped surface may represent up to a half of the total scale leiigth. The tlank seules are roughly
rhomboid in shape. their corners being rounded (Fig. 25C-F). Some of them are very elongated.
The scales which cover the base of the pectoral fin are built in a gcnerally the same manner,
but not well enough preserved to add more details. A single small, thick and wedge-shaped scale
with a very narrow overlapped portion might represent a basal scute (Fig. 25G- H).
Fig. 25. — Medoevia laia n. g., n. sp., scales. A. B. dorsal row scale; C-F. Bank scales; G. H. basal scute (?). A, C, E, G, outer
surface; B. D. F, H, internai surface. Scale bar: 10 mm.
Medoevia lata n. g., n. sp., écailles. A, B, écailles de la rangée dorsale: C F. écailles des flancs; G, H, écusson basal {?).
A, C, E, Cl, surface externe; B, D, F. H. surface interne. Échelle ; 10 mm.
— 336 —
DISCUSSION
The reserach on osteolepiform is historically based on the extremely well studied material
on Eustliennpteron jonrdi. For decades the characiers of this spccics wcrc adopted as defining
the entirc order Osleolepiformes, whilc the large number of species referred lo as the Osteo-
lepididae were practically overlooked bccause of the poor information of lheir internai mor-
phology. This rcsulted in the question whether the Osteolepiformes are paraphyletic or a clade,
which was raised several times by various aulhors, for cxarnple Janvier (1980) and ROSEN ei
al. (1981). The views in the latter paper were opposed by PANCHEN & SMlTHSON (1987), who
also critictsed most of the characters used by Andrews (1973) to define the Osteolepiformes,
although they accepted two of them (enlarged seules at the base of the fin lobes and unjointed
radiais of the médian fins) and added a new character: the unique type of cheek plate, composed
of seven bones of approximately equal ,size. Nevertheless, the same condition is obsen'ed in the
Panderichthyida (Vorobyeva, 1989; Vorobyhva & SCHULTZE, 1991) and Rhizodontida
(Andrews, 1985). Long (1985a) suggested several characters which he regarded as autapomor-
phic for the Osteolepiformes, such as a cheek complex including an enlarged lachrymah the
subverlical preopercular, the partially exposed anocleithrum, and the same basal seules as pro-
posed by ANDREWS (1973). The basal seules are afso know'n in the Canowindridac (YoUNG et
al., 1992), but this group possess more than seven bones in the cheek plate; morcover, the latter
character is apparently also présent in tetrapods. In lchthyo.nega (JarvIk, 1952, 1980), Acan-
thoste^u (ClaCK & COATLS, 1993) and Crassi^yrinus (PANCHEN, 1985; PANCHEN & SMlTHSON,
1987) there exists a bar-like, subvertical preopercular as well. Younq et al. (1992) accept the
basal sentes and the omamented dermal anocleithrum of the previous authors and add the presence
of a single pair of external nares. The last feature might be used as synapomorphy for oste-
olepiforms, panderichthyds and tetrapods, but the first two are indeed apomorphic for oste-
olepiforms. This taxon is thus defmed by at least three characters.
1. The presence of the basal seules at the base of ail fins except the caudal one.
2. Unjointed radiais of médian fins.
3. Large, omamented anocleithmm.
On the basis of these characters five families are included in the order: Osteolepididae,
Eusthenopteridae, Rhizodopsidac, Megalichthyidae and Canowindridac. The Lamprotolepididae
may be tentatively assigned here to the Osteolepiformes, yet they are incompletely known.
In order to analyse the osteolepidid-eusthenopterid inicrrelaiionships, one has to define which
unique features might be used to define the Osteolepididae and in what respect they differ from
eusthenopterids (rhizodontids venju JarvIk).
Marsilenichthys langiocdpitus Long and Medoevia lata n. g., n. sp.. display several features
which suggest their somewhat intermediate position between these twogroups, thereby generating
a fairly confusing situation where things seemed lo be clear before.
JarvIk (1980) lists several characters. which serve to separate the Osteolepididae from the
“Rhizodontidac” (Eusthenopteridae). These include the presence of the extratemporal, the oblique
— 337 —
position of the crista parotica, the connection of the parasymphysial (adsymphysial) dental plate
to the vertical lamina of the anterior coronoid, and the presence of rhomboid scales, which ail
characterize the Osteolepididae. The postspiracular plate, the rostro-caudal direction of the crista
parotica. the gap between the adsymphysial plate and the vertical lamina of the anterior coronoid
and the cycloid scales characterize the “Rhizodontidae”. The similarities between the two groiips
are numerous and might be recognized either as synapomorphic or symplesiomoiphic, depending
on the fcature tmder considération. Long (1985a) disctissed the problem of the relalionships
between the osteolepidids and eusthenopterids. He stated that one character, the ihin cycloid
scales devoid of cosmine layer, clearly séparâtes Marsclenichthys from ail other osteolepidids.
Unfortunately, the other characters listed above are not observed in Marsdenichthys, because of
its incompleteness.
The postspiracular plate is, according to JarvIk (1980). borne by the anterodorsal part of
the hyomandihula and belongs to the operctilogular sériés. In Medoevia the tabular-extratemporal
suture ovcrlays ihe crista parotica. the latter supporiing a large portion of the extralemporal.
This leeds us to suggcst that this bonc either became fused with the tabulai- in eusthenopterids
or disappCarcd, while the postspiracular is originally independent from it. The direction of the
crista parotica is well known oniy in some ostcolepiforms. such as Osteolepii (Wat,SON. 1954),
Megalichthys (Romer, 1937; BlERRiNG, 1972), Euxthenoptemn (.fARVlK, 1954, and later works)
Megapamus (VOROBYHVA. 1977a). Jannkina (VOROBVF.VA, I960. 1962, 1977a; VOROBYEVA &
Obruchev. 1964), Rhizodopsis (SÀVE-SÔDERBERGH, 1936). and Medoevia. The picture of the
Ostealepis braincase in WATSON's paper is rather poor and the figured neurocranium gives the
impression of being incompletely ossified, so the précisé position of this structure is difficult
to establish.
Megalichthys and Rhizodopsis (although these two généra belong to separate families not
reviewed here) show the oblique course of the crista parotica. but in Eusthenopteron. Jan ikina,
Megapomits and Medoevia the structure under con.sideration is directed posteriorly. This character
is thus variable.
Such fealures as the contact of the adsymphysial plate with the anterior end of the pre-
coronoid vertical plate seem to be unconvincing, as ihey var> even intra.spccifically, for example
in Chrysolepis oiiensis (Lebedev, 1983) and Chry.solepis sp. (collection 2921 of the Palaeonto-
logical Inslitute, Moscow; Lebedev, pers. obs.). in which both types and the intermediate con¬
dition are tound. In Medoevia this contact is realized.
The complété absence of cosmine over the bonc and scalc surface is charactcristic for the
genus Glyptopomus (.IarvIk, 1950). the .same is described by Jessbn (1966) in Latvius sp. A.
The absence of cosmine cover over the outer surface of the scales is mentioned by JarvIk
(1948) in several species of Scottish osteolepidids. such as Thursius niacrolepidotus, Osteolepis
macrolepidoias and G'yropiycbiiis sp. iiidet. 2, as a variation, Some of the spécimens described,
for example Osteolepis macivlepidotus (JarvIk, 1948. Fig. 6B, D) display a déviation from the
typical osteolepidid scale pattern, being omamented on the overlapped surfaces and showing no
groove that usually séparâtes il from the free surface. The scales of Gyroptychius .sp. inc. 2
(JarvIk, 1948, Fig. 6C; PI. 37, Figs. 9. 12) seem to vary from a rhomboid to a cycloid shape,
their viscéral surfaces being omamented with the concentric growth ornamentation and a short
wedge-shaped boss, which is characteristic for eusthenopterids.
— 338 —
In Marsdenichthys (LONG, 1985a, Figs. 2a, b, 6a) the posterior edge of the scales is pointed,
a.s is well seen on the photographs and drawings. The boss on the internai surface is supported
by a short ridge (Long, 1985a, Fig. 6b), as in Medoevia (Fig. 25B).
The scales in Medoevia apparently display another version of the same evolutionary event.
as they retain the primitive continuous cosmine cover, although their general shape is close to
that vvhich is regarded typical for eusthenopterids,
The complété loss of cosmine cover in Glyptopomus, Latvius sp. A and Marsdenichthys, its
partial résorption in almosi ail known “standard” osicolepidids, or its reorganization in Lamprotolepis
and Vilitichihys (VOROBYEVA, 1977a) show that this process occurred several times in osteolepiform
évolution, and that the “cycloidization” and “decosminisation” took place in parallel.
Of the character list proposed by JarVIk (1980) to distinguish between the osteolepidids
and eusthenopterids, only the rétention of the separate exiratemporal seems to be a stable one.
Thi.s character is, however, observed in the Canowindridac (LONG, 1987; YoUNG et al., 1992).
A character that inequivocally séparâtes eusthenopterids from the osteolepidids, as far as
it is known at présent, is the mode of junction between the vomers and the anterior part of the
parasphenoid. The posterior processes of the vomers are absent, or developcd only slightly (for
example, in Gyropiychius pauli) in osteolepidids, while in ail known eusthenopterids these
processes extend backwards on either sides of the parasphenoid. The major différence here is
in the overlapping pattern. In osteolepidids the anterior part of the parasphenoid is underlain by
the posteromedial parts of the vomers. In contrast, in eusthenopterids, the posterior processes
of the vomers form the dorsal and ventral shelves, which incorporate the latéral edges of the
parasphenoid on both sides, or simply fuse to it by means of a complicated suture (JARViK,
1937, 1942. 1980; VüRUBYEVA, 1977a).
In Panderichthys rhomlwlepis the vomers aiso possess relatively long posterior processes,
but they overlap the parasphenoid dorsally (pers. obs. PIN 2846/2). It may be suggested that
this advanced construction evolved to enforce the biting fonction of the anterior part of the
upper jaws in large and active predators.
No apomorphy is thus known to date for the Osteolepididae and the group may be considered
paraphylctic with respect to Eusthenopteridae, Rhiz.odopsidae. Canowindridae, Megalichlhyidae
and Lamprotolepididae.
In Medoevia the hypobranchial 4 articulâtes with the hypobranchial 3, the posterior face
of the basibranchial 2 being entirely occupied by the attachment for hypobranchials 3. This
condition is observed in Glyptolepis groenlandica (JarvIk, 1963, 1980) and the basibranchial-
hypobranchial construction in Medoevia displays an intermediate pattern between the latter and
that in Eusthenopteron, where there are two basibranchials (JarvIk, 1954, 1980). However, this
feature is regarded here as either the rétention of the condition in the common ancestor to oste-
olepiforms and porolepiforms, or a parallelism.
Acknowledgements
The author is gratefui to Pr Marius Arsi-nault. who made possible the original présentation of this
material at the International Symposium on the Study of Lower Vertebrates, Park of Miguasha, Quebec.
The most useful critical remarks were made by Pr H. Bjerring during the session and discussions. Drawings
were performed by Mr V. D. Kolgan'OV, and photographs by Mr A. O. KuzMiN.
— 339 —
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Bull. Mus. naîl. Hist. nat.. Paris. 4^ sér., 17, 1995
Section C, n" 1-4 ; 343-357.
On the neural crest cells of the Australian lungfîsh
by Anne KeMP
Abstract. — Recent publications referring to the possible importance of the neural crest In the development
of dental and skeletal structures in lower vertebrates bave plaeed considérable emphasis on this embryonic tissue.
However, a doser examination of the evidence for neural crest involvemcnt in lower vertebrate development
suggests tbat too mucb empbasis on the part played by the neural crest may bc unwarranted. In embryos of at
least one of these groups. the dipnoi. the cells of the neural crest may noi form a part of the mesenchyme from
which the dental and skeletal structures develop.
Keywords. — Neural crest, embryology, dental structures, skeletal structures, dipnoi.
À propos des cellules de la crête neurale chez le dipneuste d’Australie
Résumé. — Les publications récentes qui traitent de l'importance possible de la crête neurale dans le
développement de la dentition et du squelette des Vertébrés primitifs ont donné à ce tissu embryonnaire un intérêt
considérable. Cependant, un examen plus précis de rmiplication de la crête neurale dans le développement des
Vertébrés primitifs suggère que trop d'importance est donnée au rôle joué par la crête neurale. Chez les embryons
d'un de ces groupes, les dipneustes. les cellules de la crête neurale ne font peut-être pas partie du mésenchyme
à partir duquel se développent les structures dentaires ou squelettiques.
Mots-clé.s. — Crête neurale, embryologie, dentition, .squelette, dipneustes.
A. Kemp, Department of Anatomical Sciences, Vniversity of Queensland, Brishane, Queensland 4072, Australia.
Introduction
In the lasi few ycars, there has been increasing interest in an embryonic structure known
as the neural crest. This consists of cells which migrate within early embryos from their initial
position between cells of the neural plate, that are destined to form the nervous System, and the
presumptive epithelium. Evidence foi the importance of these cells in development cornes mainly
from tetrapod embryos. and has indicated a central rôle for neural crest cells in the formation
of organs as diverse as glandular structures, pigment cells, skeletal éléments and teeth (Le
Douarin, 1982). Recent publications on fos.sil lower vertebrate hard tissue histology hâve laid
considérable emphasis on the importance of the neural crest in forming bone and dental tissue
(Halstead, 1987, Smith, 1991, Smith & Hall, 1990). However, an examination of the pub-
lished experimental evidence for neural crest involvement in development of recent vertebrates
below the tetrapod level of organisation, and an experimental study of the neural crest in dipnoans,
suggest that in fish embryos. the neural crest may not play an important rôle in the embryological
development of organs other than the nervous System (Conel. I9-'H. 1942; LamERS ei al., 1981;
— 344 —
Sadaghiani & VIELKIND, 1990, 1991) or parts of the chondrocranium (Langille & Hall,
1988a, 1988b; Newth, 1951, 1956).
Techniques of extiipation of presumptive neural crest cells, cell marking experiments and
immunofluore.sence microscopy with a mouse monoclonal head neural crest antibody (HNK-I )
bave been applied to embryos of the receni Australian lungfish, Neoceratodits forsteri. This con¬
tribution reports preliminary results of these experiments. and indicales the direction of future
research. it is also suggested that caution in the use of neural crest theory is advisable when
discussing developmental processes and phylogenetic relationships in fossil lower vertebrates.
Abbreviations
a archenteron, archeutéroir,
b blastema of tooth and bone, blastème dentaire et osseux ',
b blood cell showing autofluorescence, cellule sanguine autofluorecente
bl bone blastema, blastème osseux',
d dermal papilla (tooth primordium), papille dermique (primordium dentaire);
e ectoderm. ectoderme ;
en endoderm, endoderme :
f forebrain région, région cérébrale antérieure ;
h hindbrain région, région cérébrale postérieure ;
m midbrain région, région cérébrale moyenne ;
me mesoderm, mésoderme',
ms mesenchyme. mésenchyme;
n notochord. notochorde;
ne neural crest, crête neurale;
np neural plate, plaque neurale;
np, nt nerve tissue. tissu nerveux;
nt nervous tissue, tissu nerveux;
O oral endothélium, endothélium oral;
P periphcral nerve fibre in section, //ère nerveuse périphérique en section;
Np pigment, pigment;
t transverse crest, crête transverse.
MATERIALS AND METHODS
Embryos of N. forsteri were collected from Enoggera Réservoir, South-East Queensland,
(1972-73) and the Brisbane River near Fernvale, also in South-East Queensland, and reared in
the laboratory according to the methods described in KF.MH (1981). Stages of development follow
those described by Kemp (1982). Extirpations and marking experiments were carried out on
embryos of stages 17-25, and these were reared subséquent to the operation until stage 48. Stages
17-25 cover development from the earUest appearance of the neural plate, through formation of
the neural folds and neural tube and early development of head structures. Stage 48 is a hatchling
— 345 —
with Sharp conical teeth and voracious feeding habits, usually feeding on small soft bodied in-
vertebrates. Descriptions of the morphological aspects of neural crest development and immuno¬
fluorescence experiments are based on two additional sériés of fixed embryos from stages 17-46.
At the latter stage, tooth development is established, although the hatchling has not yet begun
to feed.
Because development of N. forsteri is superficially more similar to development of urodele
amphibia than to development of other fish embryos, techniques of extirpation and cell marking
worked out for urodeles (de BEER, 1946; HoRSTADius & Sellman, 1942; RuGH. 1963; Sellman,
1955) were adapted for the présent sériés of experiments on lungfish embryos. Embryos w'ere
decapsulated mechanically in stérile Holtfreter's solution and transfered to operating dishes con-
taining a layer of 2% agar covercd in stérile Holtfreter’s .solution. Portions of the presumptive
neural crest were removed from the edge of the neural plate or neural folds according to the
diagrams in figure 1. At stages 17 and 18 cells were removed from presumptive fore, mid or
Fig. l. — OutUne drawings oi Neoceratodus forsteri neurulae showing the areas of neural crest cells extirpated or stained in the
experiments. A, stage 17. B, stage 19. C, stage 22. D, stage 25. Seule = 1 mm.
Dessin de la neurula de Neoceratodus forsteri montrant les aires des crêtes neurales expérimentées A, stade 17: B, stade
19: C. stade 22: D, stade 25. Échelle = 1 mm.
— 346 —
hind brain régions at the edge of the neural plate (Fig. lA). From stages 19-23, cells were
removed from the crest of the neural folds in presumptive fore, mid and hind brain régions, and
from the tranverse crest that lies in the anterior midline of the developing nervous system (Fig.
IB. C). At stage 24 and later, epithelium and underlying tissue above the fore, mid and hind
brain régions were extirpatcd (Fig, ID). Two serie.s of operations were performed, one invol ving
unilatéral removal of cells and the other bilateral. The control sériés was decapsulated and treated
subsequently in the same way. but the embryos were not subjected to extirpation. After the
operations, embryos were left in the operating dishes for two hours to permit the edges of the
cctodcrm and neural folds to scal. They were then transferred to individual crystallising dishes
with an agar base and containing stérile Holtfreter’s solution, and kept in the.se dishes until they
reached stage 48. Fenicillin and streptomycin were added to operating and rearing media at a
final concentration of 0.001% of each antibiotic.
For vital staining experiments, dyes were applied to areas at the edge of the neural région
of decapsulated embryos (Fig. lA-C), using methods outlined in RUGH (1963). Thèse experiments
were only donc on embryos before the neural folds had closed and become covered by epithelium.
They were performed in operating dishes and the embryos transferred later to crystallising dishes.
Dyes used w'ere Bismarck brown, neutral red, methylene blue and ni le blue sulphate.
Kmbryos used for the descriptive sériés were fixed in Karnovsky’s fixative, washed in buffer,
dchydrated in alcohol and embedded in méthacrylate re.sin Sections were eut at 3 or 4 mm and
stained with toluidine blue in phoshate buffered saline at pH 7.4. Embryos used for immuno-
fluore.scence experiments were fixed in chilled fixative containing 0.5% glutaraldehyde and 2.5%
paraformaldéhyde in phosphate buffer (pH 7.4), washed and dehydrated in the cold. embedded
in paraffin wax (mciting point 56 c) and sectioned at 10 mm. Températures were not allowed
to fisc above 60'’C during processing, and specimens were stored at 4‘’C to maximise protection
of the antigens. Immunofluorc.scence tests with HNK-I mouse monoclonal egg followed the
methods of SADIGHIANI & VlELKlND (1989). Assays were carried out at 4‘^'C to minimise non-
specific bonding with antibody. Controls consisted of sections that were treated with non-specific
mouse egg instead of HNK-1 mouse egg. A second sériés of Controls using buffer instead of
non-specific egg was also used.
RESULTS
Neural cre.st cells in the normai. lungfish embryo
Uncleaved eggs of N. forsteri contain granules of melanin pigment laid down in the develop¬
ing oocyst and found in the outermost layer of cytoplasm in the fertilised egg. It is most dense
in the animal pôle of the egg which lies uppermost in the egg membranes. During cleavage it
remains mostly in cells of the animal pôle (Fig. 2A) and during blastula formation it remains
mostly in ectodermal cells. Significant quantities of egg pigment are subsequently found in cells
of the presumptive nervous System (Fig. 2B).
The neural plate in N. forsteri is first visible in embryos of stage 17 as a flattened area
extending forwards from the slit shaped blastopore, and is quickly delineated by concentration
of egg pigment granules lying within the presumptive neural folds (Fig. 2B). As the edges of
347 —
the plate begin to form folds the concentration of the pigment granules becomes more obvious.
Development of the brain in N. forsteri is precocious, and by stage 20 fore, mid and hind brain
régions are discernible, although the neural folds are still in an early stage of development (Fig.
2C). As in amphibian embryos (Horstadius & SEl.L.MAN, 1942), a distinct transverse crest
develops (Fig. 2D). Closure of the neural folds progresses through stages 21-23 (Fig. 2D) and
a neural tube is complété anteriorly by stage 24. Posterior closure follows. Al stage 25. the
neural tube is covered by epithelium and development of the brain and associated structures is
continuing (Fig. 2E, F), by stage 35 (Fig. 2G), the nervous System is already funciional at a
rudimentary level.
Despite the precocity of brain development, the best that can be said of the neural crest
of N. forsteri is thaï there is little of it and that il enlers the embryo late. Up to stage 20, there
are no migrating neural crest cells (ectomesenchymc cells), nor are there cells of en-
domesenchymc origin (derived front the endoderm) within the embryo (Fig. 3A, B). Only the
primary gemt layers of ecloderm, mesoderm and endoderm are présent. A section of the pré¬
somptive nervous System and associated tissues at .stage 17 reveals no neural crest cells (Fig.
3 A). A section through the Hank of an embryo of stage 20 bas only cells of ecloderm, mesoderm
and endoderm. and no mesenchyme cells of any type (Fig. 3B).
Neural crest cells begin to move inwards at stage 20, front the forebrain région, but not
from the transversc crest. mid or hind brain ve.sicle.s or from the presumptive spinal cord. In
subséquent stages, the process of invagination of neural crest cells continues, involving the nerve
cord of progressively more posterior régions. These cells are clearly eetodermal in origin, with
small yolk globules and some pigment granules. They remain close to the neural folds, and are
soon organi.sed into cranial and spinal ganglia. At stage 20. and later, additional free cells are
présent within the embryo, belween the ecloderm and the mesoderm of the head région, but
these are associated with developing foregut or mesoderm. and contain large quantities of sizeable
yolk globule.s, too large and too many for the cells to hâve been derived from ecloderm. Furiher
research on this subject is continuing, but it could be that ihe bulk of the mesenchyme is derived
from mesoderm or endoderm in this lungfish.
Ectomesenchyme and endomesenchyme cells can be distinguished at early stages of develop¬
ment by the differing number of granules of egg pigment and the different sizes and numbers
of yolk globules that they contain. Ectomesenchyme cells hâve larger numbers of pigment
granules, and endomesenchyme cells hâve larger and more yolk globules. Each mesenchyme
resemblcs the cells from which il originales, Ectomesenchyme and endome.senchyme start to
appear within the embryo al stage 23. when the neural folds begin to close, as a few scattered
cells in the spaccs beiween the ecloderm and the developing internai tissues. Ectomesenchyme
cells are not numerous. and resemble the cells of the neural tissue, from which they apparenlly
originale (Fig. 3C), in numbers of granules of egg pigment and in the sizes and numbers of
yolk globules. By stage 36. cells with relatively numerous and large yolk globules are common
within the embryo, and il is difficult to dislinguish any with the characteri.slics expected of
ectomesenchyme cells (Fig. 3D). Following the faie of mesenchyme cells by methods of light
microscopy aione in dipnoan embryos is unfortunately no longer possible afier the neural folds
hâve closed and tissues and organs hâve begun to differentiate within the embryo. As development
continues, the yolk and egg pigment profiles so characteristic of early development become less
— 349 —
reliable as indicators of tissue of origin (ectomesenchyme or endomesenchyme). Yolk globules
are quickly used up, particiilarly in the most actively developing cells, as a source of nutrients
for growth and différentiation. Granules of egg pigment are passed from cell to cell and are
eventually voided by epithélial cells or into the gut lumen. Endomesenchyme and ec¬
tomesenchyme cells soon look alike. and are lightly yolked willi a scattering of cgg pigment
granules wiihin the cytoplasm. By stage 40 (Fig. 3E), before organogenesis lias produced rcc-
ognisable dental and skeletal tissues in N. forsieri. the origin of the mesenchyme cells that will
play a part in the development of those tissues cannot be determined on characteristics visible
in the light microscope. Few of the mesenchyme cells hâve any yolk left. though most of the
cells of the oral endothélium are still heavily yolked (Fig. 3E). By the time tooth and jaw primor-
dia can be distinguished, at stage 44, the oral endoderm has almost losi its distinctive features
as well (Fig. 3F).
Extirpation experiments
Extirpations of presumptive neural crest were performed in embryos of stages 17-25, ranging
from embryos in which the neural folds were barely discernible, to stages in which migration
of crest cells and development of brain and associated structures is advanced. Since development
of the primary brain vesicles in N. forsreri is so precocious, division of the presumtive brain
région into fore, mid and hind brain areas is possible well before the neural crest cells star! to
migrate. Early experiments involving the removal of large amounts of tissue rcsulted in the
death of the operated embryos wiihin a few days, and extensive extirpation of material was
discontinued. Laicr experiments invol ved the removal of only small amounts, and ablations were
restricted to the removal of groups of cells at the edge of the plate or folds. or at the crest of
the neural tube. Damage to presumptive neural tissue wiihin the folds was avoided, as early
experiments showed that N. forsieri embryos are imable to tolerate such injury.
Experiments w'cre carried out as cggs became available, beginning in 1972 and 1973, and
continuing in 1978 and in subséquent years. .Season by season, the results were the same. Ablation
of presumptive neural crest tissue. performed at any stage between 17 and 25. had the same
effect. The experiments were ail négative. Operated fish (Fig. 4A) grew and dcveloped as well
as Controls (Fig. 4B). They had normal pigment patterns, normal sense organs, and normal head
morphology. The chondrocrania of hatchlings thaï develop from operated embryos hâve the same
structure as those that develop in control embryos The extirpations performed on lungfish
embryos in these experiments had no meusurable effects on subséquent development.
Fig. 2. — Photographs of normal embryos of N. forsteri. A, siage 2-3. showing egg pigment at the surface of the anima] pôle
région wherc cleavage furrows arc forming. B, stage 18 showing egg pigment concenirated within the developing neural
plate. C, stage 20 showing fore, raid and hind brain régions of the developing neural folds. D. stage 23 showing iransverse
crest, fore, mid and hind brain vesicles of the closing neural folds. E. stage 25 in latéral view showing prominent hind brain
région. F, stage 25 iii ventral view showing fore, inicl and hind brain. ü. stage in dv^r.sal vtew. Scalc = 1 mm.
Photographies d'un etnhr\'nu normal de N. l'orstcri A, .stade 2-J montrant le piftmeni Je l'æuj en surface ci la région du
pôle animal ot) s'amotx’c la segnwnfafion. d. mtJe montranr la concentration du pigment Je l'tvu/ et le développement
de la plaque neiiralf. C stade 20 montrant les régions antrrieurt moyenne et postérieure du reneau et le développement
des replis neuraux- stade 23 montrani In crête ttYtnsverse. les vêsk ule.s cérehrale-s antérieure, moyenne et postérieure du
tube netreux se refermanr. h, stade 25 en vue tiuéra/c montrant la région po.ste'neitrc du cetyeau. F, stade 25 en vue \ entrale
montrant tes régions antèricurv. moyenne ef poMcrivure du cen'fau. G. .\ludr J5 en vue dorsale, kchelle - I mm.
— 350 —
— 351 —
Cells marking experiments
Vital dyes used traditionally lo stain living cells of amphibian embryos did not work with
embryonnic cells of N. forsteri. Bismarck brown was too close to the natural background colour
of the embryo lo bc usefui as a cell marker. Neulral red did noi stain the cells. Methylene blue
and nile blue sulphate had the effect of a refined extirpation, because the stained cells died and
were sloughed off by the embryo. Attempts to mark neural cresi cells in lungfish embryos with
these dyes were abandoned early in the prqject, as suiiable egg.s were scarce.
IMMUNOHISTOCHEMI.STRY
Immunofluorescence studies of fixed, normal lungfish embryos gave a partial answer to the
question of neural cresi involvement in development of these fish, HNK-1 antibody produces a
positive response in certain cells and tissues of N. forsteri embryos. In early stages, while the
neural tube is closing and the brain is differentiating. cells thaï are destined to form parts of
the nervous System and some of the mesenchyme cells react positively to HNK-l, although the
reaction is weak. The quantiiy ol yolk globules and the small ainounts of cytoplastn présent in
ail of the cells in early stages of development makc détection of a positive rcsult diffieult, and
neural cresi cells are not présent in large numbers. Even at this early stage, mosl of the
mesenchyme cells are négative. In later stages, when organogenesis is beginning, the re.sponse
to HNK-l antibody is more localised. Al stage 44. when the skeletal tissues are beginning to
form, and derrnal papillae are présent under the oral endothélium, only those structures lhat are
part of the nervous system, the brain. spinal cord. cranial ganglia or peripheral nerves. as well
as sense organs like the eye. fluoresce when tested with this antibody (Fig. 4C). Other tissues
of the head, with the exception of red blood cells within blood vessels, do not show fluorescence.
Derrnal papillae. mesenchyme cells below the papillae, and oral endothélium is uniformiy néga¬
tive. The same resull is obtained at stage 46, when extracellular matrix of tooth, bone and cartilage
has begun to appear (Fig. 4D) Cells associated with the nervous system are positive, and cells
associated with the devcloping skeletal structures arc négative. Branches of the peripheral nervous
Fig. 3. — Photnniicrographs of sections of normal N. forsteri embryos showing distribution of eciornescnchyme and en-
domesenchyme. A. detail from the head neural plate région in an embryo of stage 17; no neural crest cells are présent. B,
detail of section ihrough the flank of an embryo of stage 20 showing ecioderm, inesoderm and endoderm cells. C, detail of
the closing neural folds in the head région nf an embryo of stage 23 showing neural crest cells migrating from the developing
nervous syslcm. D. çeciion through the devcloping hind brain of an embryo of stage ^6 sht'wing inca*ase in amount of
mesenchyme and loss of disiincttve characiers of ihe cells. t, bloitema below the foregui endoderm of an embryo of stage
40, in the région of the developing looih primordia, mesenchyme celK bave no yolk letl. but ihe oral endothélium i.s heavily
yolked, F. looth and jaw blastcmn at stage 44. show’ing a single derrnal papillct (toolh primordium). oral cndoihclial cells
still contiun yolk. Seules • 0.1 mm.
Photo}(rapHirs an microsrope optique de coupes d'embryon norniot de N. fursten mnnlrant la ripartilion de rectomésenvhyme
et de remiom^senchyme. A, dcruil de Ut réfiton anténettre de Ui plaque neurale d un embtyon au uade 17: absence- de
cellule de la t ivte neutede. B, détail d'unt coupe au traders du Jluni d'un embryon au stade 20 mouinint les cellules de
Vectoüerme, du mèsodenne et de l 'endoderme. C. detail de lo fermeture des feuillets neurtna de la rryjun de lu tête d’un
embryon au suide 23 montrant la miyraiion des cellules de lu d'été neurale à partir du système nerveux ernhryonnatre. D.
coupe d travers lu reyion postérieure du cerxrau d'au emltrynri au stude 36 ruonlnait une coru enirntion de tnésetu hyme et
une perte de l 'individuuUsalion des t elluU.s. E, blastème situe venlrolement ou tubr diyestif anterieur endodermique d'un
embryon au stade 40. dans Ut tègton du iléy'elopfreoicnt du printordlutn dentaire, les cellules rncsenchyntateuses ne présentent
aucun reste de cifellus rnai.s l'rudothèllurn de ta rtxian r/rale w.hi <:hiir}ié de viiellus. F, hin.sfrme de/ttairr vt de lu mâchoire
au stade 44 montrvrtf une papille dermique isolée tprirnnrdium dentaire} ; tes cellules endothéliales orales cniitienneril encore
du vitcllus. Échelle = O.î mm.
— 352 —
Fig. 4, — Experimental and control hatchlings of N. forsreri. A, an apparently normal hatchling developing from an embryo in
which lhe midbrain crest was removed at stage 19. B. a normal hatchling of stage 48 developing from a control embryo
decapsulaled at stage 19. C. a section through the moiilh région of a hatchling of .stage 44, reacted with HNK-1; neural tissue
shows fluorescence, and mcsenchyme cells of tooth and bone blastema do not. Circular spots on the photograph are con¬
taminants D. section through the head région of a hatchling of stage 46, rcacled with llNK-1 ; neural tissue shows fluorescence,
and developing tooth cusps. bone blastema and cartilage cells are négative Circular spots are contaminanl.s, Svales = (I l mm.
Ctmtrdle et e^pêrimention de mtiiveaU'itèi de N. forsicri. 4, noiivcun-ttc apparettitneftl riPrnmt pppvenppi d’un emhn'un put
U subi l'cibkilipn de ht ttrèle du ren'euu moyen au stpde 19. H, un iiouveou-né mirmid île stiuie UH développé à partir d'un
embryon dèenpsulé au stade 19. C. euupe à tntveu la région de la bouche d'un nouveau-né au stade 44, téartivée avec
HNK-I : le tissu neural présente une fluptvscence il l'inverse de.s cellule.s mésentbymaieuscs des blastèmes dentaires et osseii.K,
Us lâches circulaires sont des canlanimalions- li. enupe de h tête d'un nouveau-né de stade 46. réatiivée avir HNK I .■ le
ti.s.\u neural inuiitre une fluarnsrciirr et le développement des dents, les blastèmes osseiis et les cellules cartilagineuses sont
en relief. Les tâches circulaires sont des contaminations. Échelle = 0,1 mm.
— 353 —
sytem within a blastema are positive, but the blastema cells themselves are not (Fig. 4C, D).
Melanin cells below the skin and mesenchyme cells in other parts of the body are also négative.
With the exception of red blood eells, which exhibit autofluorescence in control and experimental
sections, cells and tissues in control sections are uniformly négative.
DISCUSSION
Evidence for the existence of neural crcst cells in fish embryos is based historically on
light microscopy, and there is little doubl that neural crest cells migrate in embryos of lower
vertebratcs as they do in higher vertebrates (Ka.stCHENKO, 1888; LOPASHOV, 1944). Considered
opinion on the early studies of the neural cre.st supported a limited rôle in development for the
neural crest in lower vertebratcs. and Goodrich (1930) recommendcd caution in ihc interprétation
of the results of studies into the neural crest. Additional évidence of the importance of the neural
crest in development of fish and agnathans is based largely on extirpation experiments (Newth,
1951, 1956; LanciLLE & HALL, 1988a. b). However, an apparenlly positive rcsult in such ex¬
periments is no more reliable than an apparently négative one. If the part extirpated is small,
régulation may occur. Other cells are able to take the place of the ablated material, and the
embryo may develop normally despite lhe deficiency. If the pail extirpated is large, the operation
may interféré witit the normal development of the animal, and give incorrect results because
the embryo bas developed pathologically. Since the presumptive neural crest is so close to the
neural plate, removal al the sanie time of significant amounts of tissue destined to form parts
of the brain is hard to avoid. and tliis increases lhe possibility of abnormal development.
Removal of tissue presumed to be responsible for the development of certain structures in
an embryo has always been the classical method of determining the origin of a tissue. It is
concluded that the extirpated material vvas responsible for the structure if this structure is missing
after the operated embryo has been allowed to develop for a reasonable length of time. This
method is, in practice, as crude as it sounds, because of the possibility that the embryo is unable
to continue normal development for reasons that hâve nothing to do with lhe missing cells. As
a resuit, extirpation of presumptive cells has fallen out of faveur with experimental embryologists,
especially now thaï more sophi.slicaied methods of analysis of dcvelopmenlal proce.sses are avail-
able (Ei<ICK.SON, 1986).
The négative results obtained in the extirpation experiments with N. forsteri embryos hâve
several possible explanations. It is possible that the quantily of presumptive neural crest cells
removed was so small thaï lhe cells left behmd were able to take over the function and fate of
the missing cells. In other words. dipnoan embryos are capable of régulation. A second possibility
is that the neural crest is not particularly important in lungfish for the development of tissues
and organs outside the nervous System. The extirpation experiments do not answer the fundamen-
lal question of which organs in dipnoan embryos receive a contribution of neural crest cells in
the normal course of events. Nor can this be determined by observation of cell characterislics,
because lhe.se change as development proceeds. The question of the origin of head structures
like the cranial ganglia, peripheral nerves and the mesenchymal blastema of skeletal and dental
tissues has to be taekied indirecily.
Marking of presumptive neural cresl cells in some way prior to migration and following
ihe marked cells in the developing embryo bas been used frequently in embryos of higher verte-
brates. However, this technique is open to serions error, not the least being the transfer of marker
from one cell to anolher during development (Wf.ston, 1967). Other constraints include the use
of markers that do not harm the cells or alter normal behaviour of the marked cells during
morphogenesis. The agent used should be easily visualised in whole or dissected embryos, and
should be preserved in situ for histological examination (Weston, 1967). Most fish embryos
are notoriousiy difficult to manipulate in this way. and lungfish embryos are no exception. How¬
ever, sophisticated marking techniques using new stains are now available. Minute amounts of
these stains are injected into the cells of living embryos, and the.se are then allowed to continue
normal development. The stain can later be visualised after the cells hâve moved around in the
embryo. This technique involves minimal interférence with embryological processes, and is cur-
rently being tested on lungfish embryos.
New advances in immunofluorescence microscopy hâve allowed the use of an élégant and
simple technique to follow movement.s of the neural crest cells in developing fish embryos without
interfering with the normal course of development. HNK-1. a rnouse monoclonal antibody. binds
with receptors on and within cells of fish and arnphibian embryos and can be visualised by
attaching a fluorescein labelled antibody to the primary antigen-antibody complex. After the
reaction, cells that carry the relèvent antigen show fluorescence in ultraviolet light, and cells
that hâve no antigen do not. This technique, applied to cells of Xiphuphoms embryos by
Sadaghiani & VlBLKJND (1989), relies on the presence of an antigen in the neural crest cells
of fish embryos that will react with an antibody, HNK-I, developed against the neural crest
cells of higher vertebrates, These authors used the antibody successfully to trace the initial mi¬
gration of neural cre.st cells in teleost embryos. They did not follow the cells to the target organs.
In a later paper, Üiese authors used immunofluoresence labelling in whole mounts of three species
of teleost fish, Xiphophorus maculatiis, Xiphophorus helleri and Cry-ias latipex, to follow streams
of neural crest cells in developing embryos (Sadaghianj & Vielkind, 1990a), Cells following
a lalerovenlral pathway entered the pharyngeal gills and the intestinal wall. Neural crest cells
in the trunk accumulate around somiles and then migrate ventrally. and some of lhese cells may
be pre-melanocytcs and precursors of the latéral line. Most neural crest cells were traced to
lissues a.ssociated with the nervous System. They also State thaï a small number of cells from
the rostral streams may represent cells that participate in the formation of the cephalic skeleton.
Growth of explanted neural crest cells in vitro (SADAGttiA-Ni & Vielkind, 199()b) provides no
additional information on the fate of teleost neural crest cells. A study of another teleost, the
cyprinid Barbus cbonchonius, using cell marking and transplantation techniques (LAMERS et al.,
1981), indicates that neural crest cells in this species are involved in the formation of a number
of lissues, mosily associated with the nervous System and the adrenal gland, but not bone, teeth
or cartilage.
The présent prcliminary resuit using immunofluorescence techniques in N. forsteri suggests
that neural crest cells of this species are not responsible for the formation of dental and skeletal
tissues. Their rôle in N. forsteri seems to be confmed to the formation of cranial ganglia and
peripheral nerves. This resuit is not particularly surprising in view of the evidence from a .study
of sections of developing embryos, and of the négative results of extirpation experiments. The
— 355 —
normality of the operated embryos shows incidentally that lungfish are capable of régulation.
Further experiments on N. forsteri embryos, using more spécifie antibodies to cell adhesion
molécules are currently underway.
It is possible thaï me.senchyme cclls in N, forsteri, desiincd to form dental and skeletal
structures, do actually originale from the neural crest. and reacl positivcly to HNK-1 anlibody
in an early stage of development, during the migration phase when they cannot be recognised
as presumptive dental and skeletal structures, and later lo.se their reactivity. However. cells that
form the cranial ganglia and peripheral nerves retain the ability to reacl positively even after
the ganglia and nerves hâve begun to differentiate. SadaghIANI & Vielkind (lOWa) note that
the neural crest epilope can be lost from non-neural dérivatives of the neural crest as migration
proceeds, and that HNK-I antibody can ai.so rccognise cclls that are not of neural crest origin.
Clearly more extensive and précisé studies arc nccessary.
It may be that lungfish are so unchanged in an evolutionary sense, and so far from the
main stream of vertebrate évolution that their neural crest cells are atypical. However, if lungfish
are not phylogenetically abenant. these results could hâve significant implications for embryo-
logical theory in that they suggest that there may be an evolutionary progression in the importance
of the neural crest in vertebrate development. Il may be thaï, in lower vertébrales the function
of the neural crest is limiled to the formation of the cranial ganglia and peripheral nerves. as
Goodrich ( 1930) recognised. Alternatively, neural crest cells may play a rôle only in the in¬
duction of tissue in the lower vertebrate embryo. However, the actual involvement of neural
crest cells in the genesis of diverse organs in primitive fishes has yel to be proved beyond
doubt, and elaborate hypothèses based on the importance of the neural crest in formation of the
complex dental and skeletal structures of fishes may wcll be prématuré.
New studies on the hard tissue microstructure of fossilised lower vertebrates (Smith, 1991)
and of conodonis (Sansüm, 1991; Sansom et al., 1991) hâve assigned a central rôle to the
function of cells derived from the neural crest in the formation of dental and skeletal structures
in these species. Thèse researchers no longer refer to the rôle of the neural crest in the formation
of the skeletal éléments of conodonts in their most recent contribution, (Sansom et al., 1992),
but the earlier statements are made despiic the dearth of closely rclated living relativcjs of these
fossils in which the assertions could be tested experimentally. Even in living species of lower
vertebrates. the evidence for the involvement of neural crest cells in bone and in dental structures
is not particularly conclusive. Newth (1951, 1956), working with lampreys that hâve no bone
and no teeth, and Langh.i.f. & Hau. (1988) working with a teleost. Cryzias latipes. thaï has
both bone and teeth, desenbe the contribution of neural crest to the chondrocranium only, and
their work is based on extirpation experiments. The latest reviews on this subject do not provide
additional evidence on the contribution of neural crest cells to bones and teeth of fish (Erickson,
1986; Halstead, 1987; Smith & Hall, 1990). The first paper is a general review that does
not emphasise lower vertebrates, and the last two simpiy reiterate the statement that dental and
skeletal structures in fishes are derived from cells of the neural crest. There is now some evidence
to suggest that neural crest cells may not be important for the formation of dental and skeletal
structures of at least one species of primitive vertebrate, the Australian lungfish, N. forsteri. It
may be that, in primitive vertebrates, the neural crest theory has as little relevance as the now
outdated germ layer theory. Fortunately, analysis of cell interactions and the controlling mech-
— 356 —
anisms operating during différentiation and morphogenesis provide more stimulating and impor¬
tant questions for future research (Bard, 1990).
Acknowledgements
I am deeply grateful to the late Dr M. C. Bleakly, formerly of the Zoology Department, University
of Queensland, for suggesting this prpject while 1 was one ot his postgraduate students in 1970, and for
his advice and support early in the work. The assistance, later in the project, of Dr Q. Bone, FRS, of the
Plymouth Marine Laboratory, who sent me the HNK-1 antibody, and of Pr Stern who provided il, is aiso
gratelully acknowledged. Without the advice of Dr BONt. and the advice and cquipment madc available
to me by Dr D. Kkmp of CSIRÜ longpocket laboratories, Brisbane. this work would not hâve been possible.
Thanks are aIso due to Dr R. Li'NO of .Adelphi University. New York, who dciivered this paper at the VII
International Symposium on studies of Early Vcrtcbratcs at Miguasha. Quebec, in June. 1991. 1 am aiso
grateful to Mrs P. Wüudgate of the Queensland Muséum. Brisbane. who lyped early drafts of the man-
uscript, and to the lan Potter Foundation of Melbourne for the provision of grants for travel and equipment.
This work was carried out while the author was a postgraduate student in the Department of Zoology
at the University of Queensland, and later during the tenure of an honorary research fellowship at the
Queensland Muséum.
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embryos. Development. 110: 197-209.
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Dijfer., 32: 513-520.
Sansom, I. J., 1991. — The earliest neural crest-derived tissues and their pre.sence in conodonts. abstract. Palae-
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Sansom. I. J.. .M. P. Smith & H. A. Armstrong, 1991. — The Earliest occurrence of neural crest-derived
tissue and the presence of cellular bone in conodonts. Canadian Palaeontology Conférence, I, Vancouver,
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Sansom, I. J., M. P. Smith, h. a. Armstrong & M. M. Smith. 1992. — Presence of the Earliest Vertebrate
hard tissues in conodonts. Science. 256: 1308-1311.
Sellman, s., 1955. — Some experiments on the détermination of larval teeth in Ambvstoma mexicanum. Odont.
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Smith, M. M., 1991. — Putative skeletal neural crest cells in early Late Ordovician Vertebrates front Colorado.
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Bull. Mus. natl. Hist. nat.. Paris, 4*^ sér.. 17. 1995
Section C. n" 1-4 : 359-372.
Acanthostega gunnari, a primitive, aquatic tetrapod?
by Jennifer A. CLACK and Michael 1. COATES
Abstract. — The slalus of the Upper Devonian Acanthostega gunnari as a tetrapod is considered in the
light of the apomorphic characlers whioh it shares with other tetrapods. and of the plesiomorphic characlers
which it retain.s in common with osteolepiform fishes. It shares about two-thirds of lhe characlers recently listed
as tetrapod autapomorphies. Of the plesiomorphic features which it retains, somc may be truly primitive, whereas
olhers may be associaied with secondary modification for an aquatic habitus, After considération of ihese
eharacters. we conclude that parsimony demands lhat they be interpreted as primitive. We then address the question
of how tetrapods may be defined, given the likely discovery of more iransitional forms in the future. Possession
of digits remains the most compelling character in practice at the présent, but we point out its potential inade-
quacies for the future.
Keywords. — Greenland, Upper Devonian, tetrapod, systematics. parsimony, aquatic habitus.
Acanthostega gunnari est-il un tétrapode aquatique primitif?
Résumé. — Le statut de tétrapode d'Acanihastega gunnari du Dévonien supérieur est analysé à la lumière
des caractères apomorphes qu’il partage avec les autres tétrapodes, et des caractères plésiomorphes qu’il partage
avec les ostéolépiformes. Il possède environ les deux tiers des caractères dérivés définis chez les tétrapodes.
Parmi les caractères primitifs qu'il présente, certains le soin réellement, mais d'autres pourraient être interprétés
comme des adaptations à la vie aquatique. Une analyse parcimonieuse de ces car.actère.s impose de les considérer
comme des caractères primitifs. Nous po.sons alors la question de la définition des tétrapodes, si l’on considère
comme probable la découverte d’autres formes intermédiaires dans le futur. La présence de doigts reste le caractère
le plus contraignant, tout en soulignant son insuffisance pour le futur.
Mots-clés. — Groenland, Dévonien supérieur, tétrapode, systématique, parcimonie, vie aquatique.
J. A. Clsck. Universiiy Muséum of /jology Oowning Street, Cambridge CB2 3EJ. UK.
M. I. CoATES, Medawar Building, Department of Biology, Vniversity College London, Gower St., London WCIE 6BT.
Introduction
The origin of tetrapods is one of the perennial problems of vertebrate palaeontology and
it has been addressed from many points of view. When did tetrapods arise’? How did their niany
apparently unique features evolve front those of a fish ancestor? Why did tetrapods invade the
land? (For a review of some of these, see COATES & Clack this volume.) From w'hich group
of fishes did they evolve, and who are their closest living relatives? (For example. WatSün,
1926; Westoll, 1943: Rosen et al.. 1981; SchulTZE, 1987; Panchen & SMITItSON. 1987;
Forey et al., 1991 and référencés therein). Many of the,se problems hâve been plagued by a
dearth of data until very recently. khthyostega from the Upper Devonian of East Greenland,
described first by SÀVE-SODKRBERGH (1932) and subsequently by JARViK (1952, 19.55. 1980),
— 360 —
has provided most information, with lantalising scraps front other parts of the world (Campbell
& Bell, 1977; Lebedev, 1984. 1985; Ahlberg, 1991; Ahlberg et al. 1994). This was ail that
represenied this most crucial event of vertebrate évolution.
One problem which had not been considered, parlly as a rcsull of this lack of data, was
precisely how tetrapods are defined. Tetrapods, considered monophyletic by the majorily of work-
ers (e.g. WESTOIL. 1943; THOMSON. 1968; GaFFNBY, 1979. ROSF.N et al., 1981; Panchen &
Smithson, 1987; SCHULTZE. 1991, but see JaRVIK, 1980 For a contrary opinion), hâve been
characteiized by a large number of unique characlers which distinguish ihcm from their nearest
fish relatives (whichever group that is considered to be). The question of how onc might cate-
gorize an animal which possessed only some of these characters had not been addressed. To put
it another way, at what point during tbe évolution of the group can an animal sirictiy be called
a tetrapod? Is there a single character which constitutes the sine qua non for tetrapods. and how
should it be recognisedV With the lack of data on early tenapods. this had ne ver ari sen as a
potential problem among fossll animais. A further related question, likewise hampered by the
paucity of the fossil record, involves the sequence in which the unique characters of tetrapods
arose, how characlers might be intcrdependent, which were acquired in relation to terrestrialisa-
tion and which preceded it.
Acanilinstega gnnnari is a second genus from the Upper Devonian of East Greenland
(JarvIk, 1952). Remurkablc materiul has been recovcred from the Britta Dal formation, Gauss
Halv0 (Bendix-AlmgREEN et al., 1990), and includes information on most of the skeletal anat-
omy of this form. .\('anthostega has proved to be salisfyingly primitive (Cl.ACK, 1989), illumi-
natingly unconventional (Coates & Clack, 1990) and unprecedentedly fish-like (COATES &
Clack, 1991) for a tetrapod. (t provides a new perspective on the acquisition of tetrapod
characters. both in teints of the sequence and the circumstances in which they arose and rcquires
us to look again at the définition of the group. since in many respects it appears to be a iransiiional
form. Below we consider first, how Acanthostega measures up to previous diagnoses of tetrapods,
then we consider whether it is primitively or secondarily aqualic in those features in which it
is fish-like, and thirdly we givc some tliought to which. if any, single character could be con¬
sidered to define tetrapods as a group.
Acanthostega AND THE APOMORPHIES OF TETRAPODS
Three papers, published over the last several years hâve given analyses of the apomorphies
of tetrapods. AH of them accept the monophyly of tetrapods. as it is acceptcd here. The first of
them was by Gaffney (1979), who attempted to test the monophyly first of tetrapods as a
whole, then a subgrotip within this which he called Neotetrapoda. He gave a list of 11 characters
for the first set and fivc for the second. The second paper was thaï of Panchen & Smithson
(1987) whose analysis formed part of a wider assessinent of the relationships of tetrapods to
fish groups. They acceptcd many (though not ail) of Gaffney’s characters and added three others.
Godfrey’.s account ( 1989) of the postcratiial skeleton of Greererpetan listed a total of 41. which
included most of those ciied by Gaffney and Panchen & Smithson, along with a substantial
— 361 —
number of new ones. His character iisl was included in an appendix withoul discussion or réf¬
érencés, though many of the postcranial chai'acters were inentioned in the text. SCHULTZE (1987,
1991) commenled further on Gaffney's and Panchen & Smithson’s papers in an aitempt to
characterize a plesioinorphic tetrapod.
In addition to the apomorphies listed by lhe above authors, Clack (1988) suggested two
other characters of lhe lower jaw which appeared to be unique to tetrapods. These characters
are listed wilh référencés in table 1. One point to note is thaï a single character of one author
might be split into several by another, making straightforward counting of characters impossible.
This, of course, has implications for any parsimony analysis, and emphasises how difficult it is
to choose the most parsimonious cladogram from among a number of competing attempls.
Much of lhe skeleton of Acanthostega is now understood. and can be compared directly
wilh these lists For breviiy, Godfrey's list is used as the basis of comparison; individual
characters are discussed as necessary. in the order and with the numbers in which Godfrey
listed them.
It can be seen that Acanthostega possesses the majority of the apomorphies listed by GOD-
FREY, but lacks a significant number of others. Those which Acanthostega shares unequivocally
with other tetrapods will not be discussed further.
7. “No operculum”,
It is not clear exactiy what Godfrey meant by this character, but we take it to refer to
the loss of the operculogular sériés which covers the gill chamber in fishes, rather than the
small bone which articulâtes with the fenestra ovalis and stapes in Lissamphibia. As the former,
it requires some discussion in the light of discoveries about the branchial sériés ot Acanthostega.
COATES & Cl.'\CK (1991) suggested the possibiiily that Acanthostega relained a functional gill-
apparatus and an open opercular chamber. bascd on evidence from the branchial skeleton and
shoulder girdie. This implies rétention of an opercular flap, though of soft tissue as in larval or
paedomorphic urodeles and the more derived modem lungfishes. This cannol be fully tested by
fossil malerial, however. .IarvIk (1980) described a subopercular in Ichthyostega so thaï complété
loss of lhe bony opercular sériés cannot be an apumorphy of tetrapods. but only of a subgroup
as Gaffney (1979) suggested.
JarvIk (1952) described Acanthostega as retaining a preopercular bone in the suspensorium.
We assume lhe homology of this bone to the fish preopercular to be correct, and can confirm
its presence in our material. It is aiso pre.sent in the holotype of Crassigyrinus (Panchen, 1973,
1985) and in Ichthyostega (JarvIk, 1980). Though lhe bone is not pari of lhe opercular sériés,
rétention is a primitive character and il is lost in other tetrapods.
11. “A fenestra ovalis in the otic capsule (?). not yet known in Ichthyostega or Crassigyrinus” .
Despite relalively well-preserved material. the relevant région in Acanthostega is also poorly
known (Clack, 1992), but as Lombard & Bolt (1992) point out, it is poorly preserved in
most early fossil tetrapods, and its presence has been reconsiructed in most of those in which
it has been described. One exception to this is Greererpeton burkemorani (Smithson, 1982).
The origins. homologies and history of lhe fenestra ovalis de.serve further study, but until then
should not be taken unquestioningly as a tetrapod apomorphy.
13. “Unossifted lalerosphenoid région of the braincase".
— 362 —
Godfrey cites Clack & Holmes (1988) for an alternative view. They suggested that the
degree of ossification of the braincase was not very reliable as a taxonomie character among
different groups of tetrapods. Acanihosiega appears to possess an ossified laterosphenoid région,
but the significance of this is uncertain. This character is unreliable as a tetrapod apomorphy.
16. “Some latéral line organs (neuromast System) held in canals, no longer covered by bone
(lower mandible)”.
In Acanthostega, ail the latéral Unes on the skull and lower jaw, with the exception of a
short section on the jugal/postorbital, were held in tubes running through the bone, as they were
in Ichthyustega. These two earliest tetrapods therefore retain what is usually regarded as the
fish-like condition. In Greererpeion, some of the canals were still held in tubes, though most
were exposed in grooves, This character-state seems to be variable among early tetrapods. Neu-
romasts lying in open grooves are known among modem fishes, and although their distribution
i,s not cntirely consistent, the character appears to be found more often among animais living
in still waters, or it may represent a paedomorphic State (CooMBS et al., 1988). It may not be
a Sound character to use as an apomorphy of tetrapods, though further study may shed more
light on it as an ecological indicator.
19. “Well-ossified pre- and postzygapophyses”.
Ichthyosiega possesses appréciable zygapophyscs. whilc by contrast Acanihosiega is now
known to lack them almost entirely. Il resembles Crussigyrinus more closely in this. Crassigyrinus
is usually regarded as being secondarily aquatic (Panchen, 1985), the zygapophyscs reduced
as a resuit, so the question arises of whether Acanihosiega has likewise lost them secondarily
or whether it primitively lacked this character found in most other tetrapods.
20. "Ribs that are well dcveloped and tumed ventrally".
Uniike Ichthyo.stega which has massive overlupping ribs, Acanihosiega has short ribs with
poorly developed hcads. They do not lum ventrally to any significant degree. In this they resemble
the ribs of Greererpeion, though they are shorter. as far as can be judged, Greererpeion, like
Crassigyrinus, is generally regarded as secondarily aquatic, and as with the zygapophyscs, the
question is whether Acanihosiega is primitive in lacking well-developed ribs or secondarily
aquatic. Crassigyrinus has massive ribs, so small ribs and aquatic habits may not be correlated.
21. “Ribs that extend from the atlas neural arch to caudal 5 or 6”.
The distribution of ribs along the axis in Acanihosiega is incompletely known, though it
appears to hâve atlantal ribs, and immediately post-sacral ones. Cervical and some thoracic ribs
are aiso known.
22. “The loss of ail bones above the cleithra”.
The anocleithra is now known from Devonian and post-Devonian tetrapods. The first was
described from Tulerpeion (Lebedev, 1984), and Panchen & Smithson recognised this in their
assessment of the character. They cited “dermal pectoral girdic consisting at most of paired
supracleithra \ i.e. anocleithra], cleithra and clavicles". Acanihosiega is known to possess an ano-
cleithrum (COATES & Clack, 1991). and an unidcntified bone associated with the holotype of
Pholiderpeton scutigerum, a Coal Measures embolomere (Clack, 1987), can now be interpreted
as an anocleilhrum. Figure 2a of GoDi'REY (1989) shows what appears to be a very similar bone
— 363 —
on a specimen (CMNH 10931) of Greererpeton but it needs to be re-examined with this in
mind. Presence of the anocleithrum may be more comnion among lhe earliest tetrapods than bas
been previously recognised, but it is certainly a primitive, fish-like character retained by Acan-
thostegu. Loss cannot be an apomorphy of tetrapods. However, loss of the remaining supra-
cleithral sériés and loss of contact between head and dermal pectoral girdle do seem to be a
tetrapod apomorphy, which Acanthostega shares.
23. “A large, dorsally expanded scapular blade”.
This was included with a query by Panchbn & Smithson., while Gaffnfy defined it as
“scapulocoracoid relatively larger than dermal shoulder gLrdle” and included the condition of
the endoskcletal girdle as a complcx charactcr with the dermal girdle. Ichthyostega is described
by JarvIk (1980) as lacking a dorsally expanded scapular blade, and we can confirm this de¬
scription. Acunihostega shows a very similat condition, in which the dermal cleithrum is co-
ossified with the scapular région of the endoskcletal girdle, and while the junction cannot be
certainly identified, it is obvions that the endochondral component was restricted to the more
ventral parts of the girdle. The lutter bears some similarities to that of Panderichthys (VOROBYEVA
& SCHULTZE, 1991). This is another character in which Acanthostega appears to be primitive,
and réfutés another postulated tetrapod apomorphy.
24. “A shaft-like cleithrum".
Many of the same comments appiy to this character. The cleithra of both Acanthostega and
Ichthyostega are substantial. and both are intimately connected to the endoskeletal girdle, which
is relatively smaller than in most other tetrapods.
Nexi follows a séries of characters of the limbs and digits. In Gaffney’s original list, a
single character. "carjtus, tarsus and dactyly" was cited, presumably in the belief that these fea-
tures were co-equal, interdependenl, and evolved contemporaneousiy. PancHEN <üc Smithson
split this complex into six scparate characters. while GODFTtEY used ten differently constituted
ones. U is now évident from Acanthostega that “carpus. tarsus and dactyly’ is a complex of
separate innovations which may be independent. may not hâve evolved together, and may not
ail characterize tetrapods.
28. “An olccranon on the uina”.
Acanthostega lacks an olecranon on the ulna. This character may be interpreted as either
primitive or a secondary réduction resulting from aquatic adaptation. It will be assessed further
below.
Panchen & Smhuson (their character d) cite the following: “radius and ulna (and tibia
and fibula) parallel (and primitively independent) ossifications both bearing articular surfaces
for the carpus (tarsus) distally". Acanthostega lacks obvious articulating surfaces on the ulna
distally (COATES & ClacK, 1990).
30. “Distinct digits (dactyly)”.
Panchen & Smithson give a more detailed définition; “manus and pes lerminating in a
sériés of separate load-bearing digits, each with a skeleton of articulated phalanges joined pro-
ximally to a metacarpal or metatarsal”, This définition rides oui the digits of Acanthostega, which
appear not ta be load-bearing (COATES & Clack, 1990). Though both Acunihostega and Ichthy-
— 364 —
ostega possess distinct digits, they are unconventional tetrapods in the number found on each
limb. It was generally assumed that five is the fundamental tetrapod formula, and neither GOD-
FREY nor Panchen & Smithson specified the number of digits which might be apomorphic for
tetrapods. This is fortunate, since it is now known that each of the three described Devonian
tetrapod limbs sported more than five (COATES & Clack, 1990), eight in the case of Acan-
thostega.
31. “At least one pair of sacral ribs”.
The sacral ribs and centra of Acanthostega and Ichlhyostega remain unknown.
32. “Long, posterior directed sacral nb, lying against mesial face of ilium”.
The sacral ribs of Acanthostega and Ichlhyostega remain unknown. PANCHEN & SMITHSON
combine these two characters (31, 32) as their character 1 and extend it to “ilium of pelvic
girdle on each side directly connected to one or more sacral vertebrae by specialised sacral
ribs". It should be noted that in many early tetrapods, the exact nature of the connection between
the sacral rib and the ilium is poorly understood, and in many cases seems to hâve been formed
only by soft tissue rather than by bony articulations.
33. “Pubis, ischium and ilium in pelvis".
Allhough Acanthostega shows no sutures in the pelvic plate, these three régions are assumed
to be represented, as they are in Ichthyostega.
34. “An anterior and posterior tongue-like projection on either side of the supra-acetabular
buttress”.
Acanthostega has no anterior tongue-like projection (COATES, in prep.).
39. “Wrist and knee joints hinge-like, elbow and ankle rotatory”.
Panchen <&, Smithson separate this into two characters; g) “wri.st joint incorporating the
radius and forming a hinge” and i) “rotatory ankle joint incorporating the tibia”. The wrist joint
of Acanthostega is uniike that of any other known tetrapod, and ils range of movement was
probably very limited. The ankle-joints of both Acanthostega and Ichthyostega are very similar
to each other, and as with the wrist-joint, were very limited in movement. It is highly improbable
that they were rotatory (Coates & Clack, this volume).
Panchen & Smithson aiso give an additional tetrapod apomorphy, concerning the pattern
of the dermal çheek bones. Acanthostega displays this pattern, with a jugal - quadratojugal
suture separating squamosal and maxilla, but is has now also been reported in on one side of
one specimen of Panderichthys (VOROBYEVA & SCHüLTZE, 1991). Acanthostega also shares
several characters of the lower jaw with most other tetrapods. including an anterior coronoid -
pre-splenial suture, and a surangular contribution to the adductor fossa (Clack, 1988). In both
of these characters, Ichthyostega shows the non-tetrapod condition (JarvIk, 1980). These
characters will be described and further tetrapod apomorphies of the lower jaw will be discussed
in a forthcoming paper by one of the current authors (J. A. C.) and P. E. Ahlberg. Early tetrapods
also share characters of the dermal armour, in tenus of the form and distribution of scutes,
which appear to be apomorphic, but which hâve yet to be formally defined. Acanthostega and
Ichlhyostega (pers. obs.) share these characters.
— 365 —
Of the 41 characters listed by GODHREY (1989) as tetrapod apomorphies, Acanthostega ex-
hibits 26 unequivocally. It also shares at least four additional characters not listed by GODFREY,
making a total of 30 out of 45. Counted thus, informally speaking and noting the caveat above,
this makes it just two-thirds a tetrapod. Of the remaining characters, four are unknown or un-
certain not only in Acunthosiega but in many other early tetrapods, and one may be a poor
taxonomie character. In the remaining eight characters. Acanthostega shows the non-tetrapod,
presumed plesiornorphic condition. Some of these are also found in Ichthyostega. Considération
of these characters will follow.
PLESIOMORPHIC CHARACTERS OF Acanthostega
Acanthostega shows a suite of characters in which it is plesiornorphic for tetrapods, some
of which it shares with Ichthyostega and others in which it is unique among tetrapods. Other
apparently plesiornorphic characters could be secondarily acquired as a resuit of aquatic habits,
rather than retentions from a primitively aquatic State. Examinaiion of these characters may help
to polarise them, .so that they can be u.sed in subséquent analyses of the relationships of tetrapods,
the sequence of acquisition of tetrapod characters and the évolution of terrestriality,
Acanthostega shares several apparently plesiornorphic characters with Ichthyostega in ad¬
dition to those mentioned above. One character complex concems the braincase, and ha.s no
obvions bearing on whether the animais were aquatic or not. Though the prc.served braincases
of the two généra are very different in most respects, they both share the plesiornorphic condition
of a notochordal basi-occipital, and the ventral cranial fissure, though sutured, remains exposed
in the adult by rétention of a short parasphenoid (Clack, 1994). This character has featured in
analyses of the relationships of tetrapods to fishes (RoSEN et al., 1981; PanchEN, 1985) in
which it has been argued that tetrapods and lungfishes were similar in having a long parasphenoid
which sealed the ventral cranial fi.ssure. It i,s now clear that in the earliest tetrapods parasphenoid
and basi-occipital were not tirrnly uniled. even in Carboniferous and Permian généra (CLack
& Holmes, 1988; Clack, 1994). It is important to characterize the plesiornorphic condition of
any group in un analysis of its relationships (ScHULTZE, 1987).
The second character complex concems the tail, and suggests that the animais were pre-
dominantly aquatic. Both retain lepidotrichia in the tail-fin, supported by a sériés of radiais,
though in Acanthostega the lepidotrichia were relatively much longer than in Ichthyostega. As
described above. both also share characters of the pectoral girdie including the proportions of
the endoskeleial girdie (which is probably plesiornorphic) and the co-ossification of that with
the cleithrum (whose polarity is diffrcult to evaluate). Neither of these is obviously an adaptation
for aquatic or tcrrc.strial living.
Another suite of characters in which Acanthostega appears to be uniquely primitive concern
the rétention of a well-ossified, grooved hyobranchial skeleton and a post-branchial lamina of
the cleithrum. In both these, Acanthostega is remarkably fish-like (Coates & Clack, 1991).
We hâve interpreted them as indicating that the animal was primarily and primitively aquatic,
but altematively, they could be non-functional plesiomorphies.
— 366 —
Characters in which Acanthostega is fish-like, but which hâve no obvious connection with
habit include: rétention of the anocleithrum; remarkably fish-like vomers and palatal dentition
(Clack, 1994); lack of suture between the prearticular and any but the most anlerior splenial
(Ahlbf.RG & Clack, in prep.); and the proportions of the radius and ulna (Coatrs & Clack,
1990). In the latter, it most closely re.sembles the osleolepiform Eusihenopienm, and is uniike
ail other known tetrapods including Ichlhyostega.
The remaining characters from the list in which Acanthostega does not show the apomorphic
tetrapod condition could ail be interpreted as aquatic adaptations. These include: the latéral line
canals catried in tubes in the boue; lack of zygapophyses; short, straight ribs; no olecranon on
the ulna; and paddie-like limbs with non-rotatory ankie joint. Acanthostega. though possessing
indisputable digits. is unusual in having eight per limb which appcar to fomi an effective paddie
rather than a load bearing appendage. In addition. Acanthostega possesses a plate-like, relatively
heavy stapes (Clack, 1989) which has been intetpeted as the basic condition for tetrapods. but
which inay be an aquatic adaptation.
Acanthostega. PRIMITIVELY OR SECONDARILY AQUATIC?
There can be little doubt that Acanthostega was an aquatic animal. Taking into account ail
its fish-like features, we get a consistent picture of a swamp-dwelling air-gtilper, living and
feeding in water. The question is. was it a transitional form retaining many characters of its
fish-like ancestor but not yet having evolved the full complément of tetrapod characters, or a
specialized form derived from a more terrestrial ancestor which nevertheless retains many plesio-
morphic features? It could also be thaï at this early stage of tetrapod history, these two possibilities
are not .so far removed from one another.
We hâve argued eisewhere (COATBS & Clack, 1990, 1991) that the fonn of the limbs and
rétention of the fish-like gill skeleton indicate an animal which was primitively aquatic. Our
study of the limbs suggested that they were more likely to hâve evolved for use in water rather
than on land. They seem plausible as paddles but not as load-bearing legs, and evidence from
developmental biology (ShUBIN & ALBLRCH, 1986) suggests that more than five digits, as found
in Acanthostega. Ichthyostega and Tulerpeton. more likely represent a primitive condition, with
the pentadactyl limb derived by réduction.
We followed this by discovery of the gill skeleton. which atigmented the picture of an
aquatic gill-breather. Many of the fish-like features of Acanthostega accord with this idea. How-
ever, we can be accused of somc circularity of reasoning. Acanthostega manifestly exhibits many
characters of tetrapods some of which are usually taken to be associated with évolution of ter-
restriality and loss of gill-breathing. It has lost the operculogular sériés from the skull, bones
which are associated with use of gills in fishes. More compelling still is the presence of a large
pelvic plate, which is usually taken to be coitelated with support of the hind-limbs in the charac-
teristic rear-limb propulsion of tetrapods. It seems hard for some to accept the évolution of the
pelvis separate from the évolution of walking.
We counter these arguments thus. The two more derived généra of modem lungfishes,
swamp-dwelling air-gulpers, hâve lost those bones of the skull associated with gill-breathing.
— 367
and hâve a soft opercular wall. Although Acanthostega has a pelvis, we cannot yet be sure that
it was attached to the vertébral column; certainly there is no evidence of a bony connection.
We can put forward some scénarios (untestable) for why a pelvis might bave evolved. (Risking
levity, we suggesi: to provide support for hindlimbs during undcrwater propulsion and rapid
changes of direction; during digging of nests or burrows; for use in amplexus.) What we find
difficult to accept are, on the one hand. rétention of lhe tail-fin wilh lepidotrichia more extensive
than those of Ichihyostega if the animal had a more terrestrial ancesior, and on the other hand,
the idea that the primitive, fish-like proportions of the radius and uina should hâve been re-
evolved in Acaiiiluixtega when ail oihcr secondarily aquatic tetrapods retain normal tetrapod
proportions there.
These arguments are admittedly subjective, both sides based on préjudices and preferences.
Are there more objective means for judging the issue? For rcasons outlined above, simply count-
ing characters is unsatisfactory. Perhaps ihc problem should be approached from a different point
of view. Assuming tetrapods evolved from fish or fish-like anccstors, their origins would be
from aquatic animafs. The plesiomorphic condition would be for the carliest tetrapods to be
aquatic, in other words the null hypothesis should be that the earliest ictapods were aquatic,
uniess this can be refuted by good evidence. To argue that Acanthostega was secondarily aquatic
and that the gill-skeleton and post-branchial lamina were non-funclional retentions .seems less
than parsimoniou.s. Given its complément of primitive and fish-like characters, it is simplest to
argue that it was exactiy that.
This begs the question of what would constitute good evidence of terrestriality. Load-bearing
wrists and ankles and their associated movements, with perhaps réduction in the number of digits
to five or fewer may be the best, though this would be difficult to establish in many fossil
tetrapods.
This problem is exacerbated by the transitional nature of the environments in which these
early tetrapods presumably lived, neither fully aquatic, nor fully terrestrial, but vegetation-choked
swampy marginal habitats. It is not surprising therefore that we find difficulty in distinguishing
aquatic from terrestrial organisms.
THE ACQUISITION OF TETRAPOD CHARACTERS
Acanthostega and Ichthyostega tell us a number of things about the sequence of acquisition
of tetrapod characters. For example, we can infer that loss of most of the supracleithral sériés
occurred before consolidation of the braincase and development of a true occiput. Development
of the humérus into the form characteristic of tetrapods occurred before the development of the
typical tetrapod scapulocoracoid.
If wc are right in our assessment of Acanthostega as a primitively aquatic tetrapod, we can
make other inferences. Eoss of the gulars, subinandibulars and separate bony operculars occurred
before loss of gill-breathing; digits evolved before the more typical tetrapod joints of wrists and
ankles; legs and pelvis arose before walking on land.
On the other hand we may find that further discoveries may complicate tlie issue. We already
know that Ichthyostega is more primitive than Acanthostega in some respects such as the form
— 368 —
of the lower jaw, while Acanthostega is more primitive than Ichlfiyostega in others such as the
form of the radius and ulna and the post-branchial lamina of the shoulder girdle. Fragmentary
remains of tetrapods front the Devonian of Scotland (Ahlberg, 1991) possibly indicate animais
that had tetrapod-like hind limbs and girdles, but fish-like humeri, while some from Latvia hâve
more fish-like lower jaws with tetrapod-like dermal pectoral girdles (Ahlberg et ul., 1994).
Acquisition of tetrapod-like characters may exhibit musaic évolution comparable to that
évident during the transition from mammal-like reptiles to mammals (Kemp, 1982). As with
mammals, we may hâve to define tetrapods on possession of a single, more or less arbitrarily
chosen character as the transition becomes better documented. It will hâve to be a skeletal
character. Functional assumptions such as ‘breathing through nasal openings and walking on
feet’ (Schultze, 1991; 30) will not be appropriatc and may well not hâve been true of the
earliest tetrapods.
Panchen & Smithson (1987) express a commonly accepted view when they State (p. 366) :
“It is agreed by Gaffney. Rüsen et al. and ourselves, together with numerous previous workers,
thaï the carpus. tarsus and dactyly of tetrapods is iheir most important autapomorphy”. As we
hâve seen, this is not a single apomorphy. Dactyly may hâve ariscn before a truc carpus or
tarsus. Dactyly appears to be produced as a resuit of developmental processes common to ail
sarcopterygians (SHttBIN & Albrrch, 1986) and may prove difficult to define as more iransitional
form.s art distovered. A sarcopterygian with segmented post-axial radiais could be said to exhibit
dactyly. Transitional forms can be envisaged with digits on one pair of limbs (likely the hind)
but not on the other or in which the limbs bore digits but in which the supracleithral sériés was
still présent.
At the présent time, the présence of digits is, in practice, the single character which we
use to define tetrapods. Had Acanthostega possessed un.segmented post-axial radiais with or
without lepidotrichia (and given the proportions of radius and ulna we were almost expecting
this). we should hâve hesitated to call it a tetrapod. Nevertheless, we should like to point ont
the potential inadequacies of this character for the future. Choice of anoihcr will dépend upon
what is shown among further fossil forms about the sequence of acquisition of characters. For
example, if the supracleithral sériés were lost only aftei development of digits, loss of this sériés
might be seen as more significani. On the other hand we may view what appears to be a ‘neutral’
or not obviousiy adaptive character, like consolidation of the snout bones, as a more useful
choice. Then again. it may become clear that the enlarged pelvic plate is corrclatcd with develop¬
ment of hind-limbs with ankles and digits before the forc-limb becamc recognisably tetrapod,
in which case the pelvic plate may be the most significant tetrapod character. It seems that the
contrast in the structure of the pelvis of fishes and tetrapods is one of the greatest between
them, and even the homologies of the éléments are disputed (PANCHEN & .Smith,son. 1990).
The advantages of an alternative and completely contrasting melhod were recently aruged
for by Gauthier et ul. (1988). This method éliminâtes the difficulties of a définition based on
key characters, utilising instead a phylogenetic or node-based définition. Thus according to this
définition, the term “Tetrapoda” is defined as that clade above the node represented by the com¬
mon ancestor of modem amniotes and anamniotes. This définition lias subsequently generated
much discussion (e.g. Lucas, 1992; Rowe & Gauthier. 1992; de Queiroz & Gauthier, 1992;
Patterson, 1993) but the current paper is not the place to consider its relative merits. Work
— 369 —
in progress bas considered the position of Acanthostega and other early tetrapods under this
régime, and will be published with a description of the postcranial anatomy of Tulerpeton by
LEBEDEV & COATES.
The origin of tetrapods has long been a source of spéculation and debate, not less so now,
but as we discover new fossils our spéculations and hypothèses hâve a sounder base, they can
take off in new directions and we can perhaps ask more readily answerable questions. We hope
that discovery and description of Acanthostega is just the beginning.
Table 1. — Tetrapod apomorphies and Acanthostega. Numbers from GODFREY, 1989. G-number
given in GaefnEY, 1979 (including Neotetrapod apomorphies). PS-, letters given in
Panchen & SMITHSON, 1987: 369 ??, condition unknown or uncertain in Acanthostega.
Italics, character absent in Acanthostega.
Liste des apomorphies des tétrapodes ef J 'Acanthostega. Les nombres sont tirés de GoDFREY,
1989. G- nombre donné dans Gaffney, 1979 (incluant les apomorphies des néotétrapodes).
PS-, lettres données dans Panchen & Smithson, 1987 : 369 ??, Condition inconnue ou in¬
certaine chez Acanthostega.
G4 PSa
G13
G6 PSe
G5 PSb
G15
Gll
G8 PSj
PSk
1. Single pair of nasal bones;
2. Parietals wider than frontals;
3. Postparietals shorter than parietals;
4. Tabular tubercle on occipital surface;
5. Jugal forms at least half of lower orbit margin;
6. Médial abutment of pterygoids below cultriform process;
7. No operculum\
8. No médian gular;
9. No submandibulars;
10. ‘Peg and socket’ basal articulation;
11. Fenestra ovalis??;
12. Stapes?;
13. Unossified laterosphenoid?',
14. Sphenethmoid Y-shaped anteriorly, V-shaped posteriorly;
15. Loss of tusk and replacement pair on at lea.st one coronoid;
16. Sonie latéral Unes in canals, not tubes in the bone lower mandible;
17. Dermal sculpturing characteristic pits and ridges;
18. Differentiated atlas and axis, with atlas arch halves,
and relalivety massive axis arch;
19. Well-ossified zygapophyses;
20. Ribs well-developed and turned ventrally;
21. Ribs extend from atlas to caudal 5 or 6;
22. Loss of ait bones above the cleithrum;
23. Large dor.sally expanded scapular blade;
24. Shaft-like cleithrum;
25. Large interclavicle;
— 370 —
Preaxial keel on humérus;
Rectangular entepicondyle;
Olecranon on ulna:
Carpal and tarsal éléments;
Digits;
At least one pair of sacral libs ??;
Long posteriorly directed sacral rib, lying against mesial face of ilium ??;
Pubis, ischium and ilium in pelvis;
Anterior and posterior projection on either side of supra acetabular buttress;
Laterally directed acetabulum;
Puboischiadic plate pierced by foramina;
Well-developed adductor crest on fémur;
Two canals pierce distal end of fémur;
Wrist and knee Joints hinge-like, elhow and ankle rotatory;
Articulât condyle on distal end of tibia;
Intermedium articulating directly with tibia and fibula;
Other tetrapod apomoiphies présent in Acanihosiega.
Autres apomorphies de tétrapodes présentes chez Acanthostega.
PSn Dermal cheek pattern (Panchen & Smithson, 1987);
Anterior coronoid / presplenial suture (Clack, 1988);
Surangular contribution to adductor fossa (Clack, 1988);
Fomi and distribution of dermal sentes.
Other tetrapod apomorphies absent in Acanthostega.
Autres apomorphies de tétrapodes absentes chez Acanthostega.
PSd
G12
G14
G16
Radius and ulna both bearing articulât surfaces for the carpus distally;
Persistent notochord excluded from braincase;
Médian bony fin supports with lepidotrichia absent;
Ethmosphenoid and parachordal (otico-occipital) portions
of braincase solidiy fused in adult, not separated by a suture.
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Section C. n° 1-4 ; 373-388.
Romer’s gap: tetrapod origins and terrestriality
by Michael I. COATES and Jennifer A. CLACK
Abstract. — New data derived l'rom recent discoveries of Devonian tetrapods necessitate a révision of
frequently expres.sed palaeoecological and morphogenetic scénarios conceming the fish-letrapod transition. Many
current hypothèses link tetrapod origin closely to lerrestriahMiion in a theleological explanalion of tetrapod évo¬
lution. In contra.st, RoMhR cinphasised thc séparation of these two events. Ro.vikR’.s view is corrtthorated by new
data that indicates that tetrapods- were originally aquaiic and preceded the e-arlicst known terrestrial fauna by
- 25 mya. Three varjed Upper Devonian tetrapods aie no« known m detail," Aciinthosteym, hhthywtesu, and
Tulerpeton. New reconstructions of Acanthoitcga and leluhyosti’ga are presented, including prelittiinary details
of the acanthostegid vertébral column, pelvic girdie, and hind linjb. Aainrhoircga, anaiornically closest lo oste-
olepiform fish. is prcserved in active fluvial channels. Ichlhyoitega is re-inierpreted -as having a seal-liKe post-
cranial skelelon; Tulerpeton. rcseinbling more recenl Carboniferous tetrapods, is found in shallow marine
sédiments. Tliere is litile support for an exclusively freshwater tetrapod ongin. Comparison of acanthostegid
anatomy wilh Panderichthya. and quantified changes between small and large spécimens of Eusthenopteron, sug-
gest dissociated heterochronic changes in early tetrapod évolution. Early tetrapod remains coïncide wiih the
Frasnian-Famennian extinction, which includcd massive déplétion of the oxygcn-contcni of marine surface-waters.
High faunal turnover, the adaptive advantage conferred upon air-breathers. and the possibility that early tetrapods
occupied marine environments, suggest that this extinction event facilitated the evolutionary radiation of early
or near-teirapods.
Keyword.s. — Devonian tetrapods. aquatic origin, heterochrony, Frasnian-Famennian extinction, marine en¬
vironment.
La lacune de Ro.mi'.k : le.s origines des tétrapodes
et l'adaptation à la vie terrestre
Ré-sumé, — De nouvelles données tirées des decouvertes récente.s sur les tétrapodes dévoniens nécessitent
une révision des scénarios les plus couramment établis sur la paléo-écologie et la morphogenèse de la transition
entre les poissons el les tétrapodes. Les hypothèses courantes raltachenl rprigine des tétrapodes à une terrestra-
lisation selon une explication théologique de l'évolution des tétrapodes. À l’inverse le point de vue de Romkr
est corroboré par une nouvelle donnée qui indique que les télrapodes éiaienl à l’origine aquatiques et précédèrent
le.s premières faunes terrestres de 25 millions d’années. Trois tétrapodes du Dévonien supérieur sont connus en
détail : Acantho.'itega, Ichihyoslega et Tulerpeton. De nouvelles reconstitutions d’Acantho.\lega et tl' Ichthyo.ilega
sont présentées, dont des détails préliminaires de la colonne vertébrale, de la ceinture pelvienne et du membre
po.stérieur d' Acanthn.nega. Ce dernier est anatomiquement proche des ostéolépiformes. il est conservé dans des
sédiments de chenaux fluviaux, le squelette postcrânien ù' lehlhyo.ttega est réinlerprété à la lumière de celui des
phoques ; Tulerpeton. trouvé dans des sédiments marins de faible profondeur, ressemble plus aux tétrapodes car-
bonitères, plu.s técents. Une origine duli;aquicole des létrapodes est peu étayée. La comparaison de l'anatomie
à'Acanthü.uega avec celle de Panderichthys ainsi que les changements quantifiés entre des spécimens petits et
grands à' Euatlirnopteron suggèrent une hétérochronie dissociée dans l’évolution des ptemiers. tétrapodes. L’ex¬
tinction du Frasnicn-Famennien coïncide avec la découverte de restes des premiers létrapodes. laquelle est ac¬
compagnée d'une baisse importante de la concentration en oxygène de la tranche d'eau supérieure des mers. La
conjugaison d'un renouvellement de faune, de l’avantage adaptatif que constitue la respiration .lérienne et de la
possibilité que le.s premiers létrapodes aient occupé un environnement marin suggèrent que cette exunciion a pu
faciliter la radiation évolutive des premiers tétrapodes.
Mots-clés, — Télrapodes dévoniens, origine aquatique, hétérochronie, extinction du Frasnien-Famennien,
environnement marin.
M. I. CoATB-s, Medawar Building. Department of Biotogy. Univerxit}' College London. Ciower St.. London WCIE 6BT
J. A. Clack, Vniyersity Muséum of Zoology, Downing Street. Cambridge CB2 3EJ. UK.
Introduction
A wealth of new data on early tetrapod fossils from the Upper Devonian of Groenland,
Russia. and Scoiland. allow us to rea.s.sess frequently expressed théories of tetrapod origin and
terreslriality. The phylogcnctic implications of these data are discussed elsewhere in this volume
(Clack & COATES). Phylogcnctic analysis has to précédé discus.sion of palaeobiological
scénarios, althoiigh thc latler may subsequently help to résolve systematic problems (e.g. Camp-
BETi. & Barwick, 1988). Many hypothèses of the fish-tetrapod transition can be classified as
either palaeoecologica! or morphological transformation scénarios. In this paper these not entirely
distinct aspects of tetrapod évolution will be reviewed briefly and separately. Biogeographical
theones of the location of the fish-tetrapod transition are not discussed in detail, although recent
finds from Seotland ( Aulberg, 1991a) and Latvia (Gee. 1991 ). suggest that early or near-tetrapod
distribution may be broader than has boen proposed rccently (e.g. LONG, 199()a).
PALAEOECOLOGICAL SCENARIOS, PAST THEORIES
Most palaeoecological models of early tetrapod life hâve been influenced by the works of
Barrell (1916) and Watson (1926). Barreee proposed that tetrapods arose in fresh waters,
from Ouviaiile l’ishcs during the Lower Devonian The environment consisted of a warm climate
and seasonally drying river plains remote from continental margins. where terrestrial locomotion
and air breaihing conferred considérable advantages upon the proto-tetrapods. Watson’s con-
trasting scénario consisted of swarapy pools enclosed by endless (Carboniferous) coal forests
within which large embolomerous anthracosaurs such as “Eogyrinus” {Pholiderpemn, Clack,
1987), swam iising their long, deep tails, and whose small limbs were regarded as entirely un-
suited for terrestrial use. Scasonal drought prompted terrestrial forays in search of new habitats,
which Watson compared to the passage of estant eels from one ditch to another; a significant
limblcss feat.
Romer cffectively combined both hypothèses in what has corne to be thc prevailing te-
trapod-origin .scénario (summarised in 1958, and référencés therein) set in BarRREL’s Devonian
red-beds rather than Wat.son’s Carboniferous coal-measures. Save-Soderbergh's (1932) dis-
covery of Upper Devonian (Famennian) tetrapods (Ichihyostega, Ichlhyostegopsis^ and Acan-
thostegu, JARVtK. 1952) enabled ROMER to couple these to Watson’s “raison d'être" (Romer,
1958; 365) for pool to pool tran.smigration. However, limbs were argued to hâve evolved specifi-
cally as an adaptation enabling aquatic animais to migrate from drying pools to those of a less
ephemeral nature. Romer’.s was, therefore. a paradoxical scénario, in which limbs evolved for
terrestrial use, in order to facilitate an extended aquatic lifestyle. The first fully terrestrial verté¬
brale faunas were envisaged to occur much later. at the Permo-Carboniferous boundary, con¬
comitant with the origin of amniotes and abundant terrestrial food resources.
Many of the coniemporary criticisms of Romer’s scénario were based, in part, upon a mis-
reading which ignored his emphasis upon the huge temporal gap (65 mya) between the earliest
tetrapod skeletal remains, and the earliest terrestrial vertebrate faunas. For example. Gunter
(1956) and INGER (1957) accused Romer of arguing for a saltatory tetrapod origin, within the
— 375 —
instant of a catastrophic drought. They and others, including Orton (1954) and GofN and Gunter
(1956), aiso argued that the vertebrate inhabitants of drying pools today huddle in the remaining
moisture, and disperse only if the surrounding environment is sufficienily wet. Inger demanded
continuousiy humid conditions for the évolution of tetrapods and terrestrialily, whereas Orton
argued for the origin of the leirapod limb as a fossorial device, to as.sist aeslivation rather than
as an aid for dispersai, GUNTER provided the broadest of functional scénarios; it is probably the
earliest argument for a fully aquatic origin for the tetrapod limb. In support of this, Gunter
listed numerous examples of aclitiopterygians which walk under the water, a lheme relumed to
by Edwards (1989). This pi'ovided an incipicnt stage bctwcen fins consisting mostly of dcrmal
bone, and endoskeletally supporlcd, highiy muscular tetrapod limbs. Gunter envisaged aquatic
ance.stral tetrapods bcing marginalized by larger predators (Berry’s. 1918, in Gunter, 1956)
("swarming hordes of ganoid pirates"), and only after refuge was found in shallows were limbs
and girdies evolved to cope with terrestrial loads. This model circumvented the progressionist
trap in which phrases siich as the '‘invasion" or "colonization of diy land" implied orthogenetic
evolutionary processes. Gunter cannily differentiated limbs from fins by the absence of lepidotri-
chia, but hi.s support for Eaton’s (1951) hypothesis that fin-ray loss provided an adaptive premium
during time spent out of water, returned to the oithodox view of limb origination as inextricably
linked to tciTCstrialisation. Romer’s scénario was never considered to be mutually exclusive of
Gunter's, but related more closely to the .subséquent fine-luning of limb development.
Romer's 1958 summary provided an effective reply to many of these criticisms (but ne-
glected Gunter's views on the aquatic origin of limbs. and inarginalization). Romer's scénario
was based iipon a sériés of important assumptions; that the Devonian red-beds were deposited
under semi-arid conditions; that although forcsis had devclopcd by the late Devonian, they did
not constitute evidence of a conlinuously moist cHmale. If any repre.sentative Mid- to Upper
Devonian fish fauna was examined, and Romer used the Escuminac assemblage as lus prefened
example. 95% of any "catch" consisted of fish with lungs (lungs having a major adaptive value
during conditions of .seasonal dnnight); the potential food suppiy on land was meagre, and this
delayed the development of the first terrestrial vertebrate faunas. The first true land dwcllers
were concluded to bc Zirvo/i.s-like, living at the Carboniferous-Permian boundary, after the origin
of insects, which provided necessary terrestrial food.
Ecophysiological arguments were aIso applied to the water-land transition, with especial
référencé to osmorégulation (summarized in LlTTUE. 1990). Physiological constraints may hâve
determined whelher the earliest terrestrial vertebrates emerged from the fresh waters of Barrel’s
continental flood plains, or from the sait waters of continental margins, estuaries and lagoons.
The ecophysiological case dérivés from the evidence of blood composition and osmotic pressure:
most amphibians are hypo-osmotic, and unable to toierate rising osmotic pressure from dessication
or rising salinity in the external medium. They are considered to be osmotic “regulators" rather
than "toléra tors", and only the development of a less permeable skin and larger size enabled
the colonization of a dessicating environment. Amphibian.s, and therefore the earliest tetrapods,
were concluded to hâve evolved in fresh waters. Furthermore, inhabitants of oxygen depleted,
warm ephemeral or swampy freshwater habitats would aiready bave been subjected to intense
sélective pre.ssure to evolve aerial breathing, a key physiological prerequisite for the évolution
of terrestriality. ThomSON’s (1980) palaeoecological review of Devonian sarcopterygians, which
— 376 —
included the closest known relatives of early tetrapods, disagreed. Only very few, mostly Late
Devonian taxa, were restricted to freshwater deposits, and early tetrapods were associated with
fishes also known to occur in marine sédiments. Thomson concluded that most sarcopterygians
were anadromous, living in the .sea but entering fresh waters to brced and fced in the brackish
shallows of estuaries and Coastal lagoons. These migrations may hâve been seasonal. and tied
closely to the development of the first continental ecosystems. With these data, THOMSON asked
if the first tetrapods could, unquestionably, be assumed to be fully freshwater animais. Support
for this hypothesis has been supplemented by Bray’s (1985) suggestion that the ionic composi¬
tions of Devonian marine and fresh waters were far less distinct than today’s équivalents. LlTrLE
(1990: 181). however, concluded that in contrast to the freshwater habitat, there was difficulty
in idcntifying the sélection pressures for airbrealhing in a marine environment.
Until 1986, the earliest availahle glimpse of telrapod évolution remaincd that of khthyostega
with its fish-like tail trailing symbolically in the water (Milncr et al., 1986). Almost ail water-
land, fish-ietrapod hypothèses centred upon khthyostega, despite this being a generic name ap-
plied to a composite reconstruction (JakvIk, 1952; 1980; Bjorring 1988, 1989), derived from
the llve species erected by Save-Südurberüh (1932). The validiiy of Save-Soderbergh’s
spécifie diagnoses, based upon variations in dermal skull proportions and composition, has never
been reviewed. JARViK's statemcnl that "khthyostega in many regards is more spccialized than
latcr appeaiing tetrapods and is far from being sorne kind of prototetrapod” (1980: 222) has
been mostly ignored. However, the sum of the data available in 1986, and discoveries reported
since then, amount to a considérable improvement upon the évidence available to Romer, pre-
1960.
Many of these discoveries are included in MtLNER et u/.’s (1986) review, including a sum-
mary of the earliest known terrestrial vertehrate fauna: East Kirkton, Scotland (WoOD et al,
1985; Rolfe et ai, 1993), with an estimated âge of 338 mya (Scottish Upper Visean). Knowledge
of Devonian tetrapods has improved similarly. Tetrapod trackways hâve been described from the
Upper Devonian (probably Frasnian) (Wakren & Wakefield. 1972) and much less certainly,
the Lower Devonian (WARREN et ai. 1986) of Australia, and the Middlc Devonian (Givetian)
of Scotland (Rogers, 1990). Campbell & Bell (1977.) described a pos.sible tetrapod jaw from
the Upper Devonian of Australia (Meta.x}'gnathus). and LEBEDEV (1984, 1985. 199()a) partially
described the articulated appcndicular and incomplète axial skeleton of a new tetrapod Tiilerpeton,
from the Upper Devonian Andreyevka-2 locality of the Tula Région. Russia (see Lebedev, 1990b,
for a detailed faunal review). Lebedev & ClaCK (1993) hâve now recognised the presence of
at least two tetrapods among the cranial fragments ascribed to this material, but the articulated
postcranial type-material (currently being redescribed by LEBEttEV & COATES) remains suffi-
ciently well preserved to be diagnostic, and displays significant affinities with Panchen Sl Smith-
son's (1988) reptiliomorph ramus. In 1987, an Anglo-Danish expédition to East Groenland
collected new specimens of khthyostega. and Acanthostega (PANCHEN. 1988), and the sedimento-
logical contexl of Devonian tetrapod material was recorded ni situ (BENDl.x-ALMCiREEN et ai,
1990). The acanthostegid material has already yielded important information about the évolution
of the tetrapod middie-ear (CLACK, 1989), the structure of the earliest known limbs (COATES &
Cl.ACK, 1990; COATES, 1991), and the presence of internai gills (COATES & CLACK, 1991). Much
of this information has been obtained from what is probably the most complété known specimen
— 377 —
of a Devonian tetrapod. Most recently, Ahlberg (1991a) has described tetrapod or near-tetrapod
fragmentary fossils from the Upper Devonian (Frasnian) of Scotland, and, wilh Lebedev & LUK-
SEVICS, found similarly aged tetrapod-like specimens in Latvia (Gee, 1991).
Studies of tctrapod-likc fish hâve parallelcd advances in our knowledge of fish-like tctrapods.
CriticismN of Rosen et al. ‘s (1981) proposai of dipnoan.s a.s ihc tetrapod sister-group hâve been
elaborated elscwhere (e.g. PaNCHEN & Smithson. 1987; CAMPBELL & BARW'ICK. 1984. 1988).
In ihis article a sister-group relationship bciween o.sleolepiforms and teirapods is accepted (e.g.
Schultze, 1987 fincluding rhizodonts and pandcrichthyids plus tetrapods in a trichotomy with
osteolepiformsl; Ahlberg, 1991b), whcrein nictnber.s of the family Panderichthyidae (Voroby-
EVA, 1968) are considered to be the closest relatives of tetrapods. Recent descriptions of pander-
ichthyids include Elpistostege watsoni, from the Upper Devonian (Frasnian). Escuminac
Formation, of Canada (SCHULTZE & Arsenault, 1985) and Panderichthys rhambolepis. from
the Upper Devonian (Frasnian) of Latvia (VOROBYEVA & SCHLXTZE, 1991).
We now know that by the end of the Devonian many more organisms had made the transition
to the terrcstrial environment than Romer perceived. Shear (1991) summarises current rcsearch
into the earliest terreslrial ecosystems. By the end of the Devonian, architeclurally modem forests
and other plant communities had bccome established; nearly ail lhe main clades and adaptations
(excluding flowers and fruit) had emerged. Well devcloped Huer faunas had evoivcd, consisting
of small detrilivorous and predatory arthropods, and insects had emerged from lhe myriapod-
hexapod lineage. One responsc to the foregoing review mighl be simply to shunt Romer’s
scénario a few tens of millions of years furlher into the past. but this fails to disenlangle the
tetrapod and lerrestriality problem any furlher. and accepts Shear's curious statemeni that lhe
skeletons of the earliest tetrapods (meaning Ichihyosiega and Acantho.^tega] are “already quite
modem".
NEW DATA
Even if ail specimens that contributed to the reconstruction of Ichthyostega dérivé from a
single species, several important régions of the skelelon remain unknown. These include lhe
présence or absence of an atlas-axis complex, the structure of the manus, the form of the sacral
région and the post-sacral insertion of the lail. The hind limb is now known to be paddle-like
rather then leg-like, and septa- rather than pentadactylous (COATES & Clack, 1990). As in most
fishes, the humérus is significanily larger than lhe fémur (ai.so noted in SCHMAI.HALtSEN, 1968,
and BjerriNC, 1988), and in contrast to the paddle-like hind limb, the massive forelimbs are
permanently flexed al lhe elbow, with short radii ariiculating entirely beneath the anterior humerai
flanges. Although the tail retains fish-like lepidotrichia. it appears to be hypocercal, and shorter
than those of other tetrapods. The broad, overlapping ribs were interpreled by JarvIk (1980) as
conferring stiffness to an otherwise fish-like trunk. Corroborative evidence for this interprétation
is provided by an analysis of the structure and fonction of the remarkably similar ribeage of
the arboreal, two-toed anteater, Cyclopes didactylus, (Fig. IB). Jenkins (1970) describes how,
with relalively little enhancement of the musculature, intercostal contraction effectively locks
the overlapping. expanded ribs logethcr into a .stiff, barrel-like form. This trick is utilised by C.
— 378 —
FIG. 1. — Skeletal rcconslructioiis of Devonian tetrapods from Eaal Greenland.
A. Acanthosiega gunnart: provisional re,storation omiuing ribs and gastralia. Slipplcd région of tail adapled from jARViK's
(1980, Fig. 156) rcstoralion of rail of Ichlhyoslega, allhough lepidoirichia are lengthened [o eontdrm with relative proportions
of incompletely prepared acanthostegid tail specimens, B. Expanded Ihoracolumbar ribs of Cyclopes didactylus (sternum
omitted) (from Jenki.ns. 1970. Fig. IA). C. New restoralion of Ichrhyoslega sp.. adapled principally from JarvIk (1980,
Fig. 170). Unknown régions of posicranial anatomy omitted. Upper jaw dentition adapled from Ichthyostega eigili (Save-
SüDERBERüH, 1972, Fig. 7); hindlimb from Co.ATES & CUACK 11990; Fig. Id-f) Seule bars = 10 cm
Ketonslitulimis du squelelle des leiriipodes dêioniens de l'est du Crveiilund.
A. Acanthosiega gimnari. reconslilulion partielle les côtes et les giisimlia manquent. Lu région caudale e.tl adaptée de celle
d' Ichlhyoslega Id'iiprés jAPViK. /b.RO, pig. /56) bien que les Icpidniriches aient été allonges en raison de leurs proportions
lelatives sur la région caudale de spécimens liicoinplêienieni préparés d 'Acanthosiega gunnart. B. côtes thoracolombaires
de Clyclopes didactylus (sans le sternum} d'après .IPStKtNS (IP70, Fig. IA), C, nouvelle reconstttution d 'Ichthyostega eigili
(SAVf-'iODERBFgOtl. 19.^2, Fig. 7). membre po.sléricur d'après COATES & ClACK (1990, Figs.. Id-f). Échelle = 10 cm.
didactylus to suspend itself horizontally from a branch, obtaining purchase with only its hind
limbs and prehensile tail, while extending its forelimbs laterally in a défensive posture, or grasp-
ing for a nearby twig. This demonstrates the extraordinary axial ridgidity which may be obtained
with a set of overlapping ribs, and challenges SCHMALHAüSEN’s (1968) inference from vertébral
morphology that the spinal musculature was differentiated sufficiently to resist terrestrial loads
unaided, with expanded ribs functioning principally as an insertion for strongly developed serrate
muscles, anchoring the pectoral girdle.
The conventional restoralion of Ichthyasiega as a vaguely urodele-like quadruped fails to
explain the presence of these unusual anatomical features. However, a group of extant aquatic
telrapods exhibits a number of unexpected similarities: the Pinnipedia (seals, sea lions and wal-
ruses). In these the pectoral limbs function as an anterior prop, while the pelvic limbs -serve as
propulsive paddies and rudders. The humerai and fémoral proportions are extremely similar to
— 379 —
those of Ichihyostega. In Mirounga leonina, the éléphant seal, the fémoral length is less than
two thirds of the humerai length. The hind limbs hâve the shortest toes within the middie of
the digital arch. paralelling the tiny digit within the digital arch of the ichthyostegid hind limb.
The pelvie girdies of pinnipeds and Iclithynsiega are both relatively narrow and skid-like. The
sacrum consists of a single, short stout rib abutting a posteriorly reinforced. anteriorly directed
facet on the inner face of the ilium. Although the .sacral rib of Ichthyoslega is unknown. the
large sacral facet is similarly directed and reinforced, unlike oiher earlv tctrapods in which the sacral
facet is barely identifiable (e.g. Arclieria'. Romer. 1957; Eoherpetotv, Smituson, 1985). Finally, pin-
niped ribs also hâve elongate. prominent uncinate flange.s, which are largest nearest to the dorsal
blade of the pectoral girdle. Figure IC shows a revised reconstruction of fchthyostega, in which the
posture has been alteied lo rellcct the seal-likc fealurcs of the postcranial skeleton.
Although we can only présent a provisional skeletal reconstruction ol Acanthostega, (Fig.
lA) it seems Hkely that it will eventually be known In considerably greater detail than our
curreni knowledge of Ichihyustega. The linear dimensions of the majority of Acanthostega spéci¬
mens are only two thirds those of rnost Ichthyoslega specimens. As Clack & COATES (this vol.)
hâve staled, Acanthostega has an apparently functional gill skeleton, and a more fish-like pectoral
girdle. The pelvie girdle is now known to hâve distinct antenor and posterior iliac processes
(contra Clack, 1988). Although the pelvie plate is relatively large, no clear sacral facet is présent,
and no sacral rib has bcen identified. Thus. although the nature of the sacrum remains obscure,
it is clcarly very different from lhat oI Ichthyoslega. The hind limb is already known in sufficient
detail (COATES, 1991) lo compare it with the hind paddie of Ichthyoslega. The fémur is more
slender and elongate, but the tibia and fibula are flatlened and broad, like those of Ichthyoslega.
The hind limb of Acanthostega is certainly longer than the fore limb, and more oar- than paddle-
like. The pes is restored provisionally to hâve eight digits, and an ankle consisting of relatively
few large components. The unusual fore limb morphology of Acanthostega has been discussed
elsewhere (COATES & Clack, 1990; COATES, 1991). It is remarkably fish-like, and appears to
be unsuited for terrestrial use. Fore limb movement may hâve been restricted to a moderate
degree of anlerodorsal extension, and posteroventral Hexion. The strap-shaped caput humeri pro¬
vides a hinge-like rather than rotary joint, but this is common among early letrapods. and ap¬
parently similar To that of Panderichthys (VOROBYEVA & SCHULTZE, 1991), The axial skeleton
of Acanthostega appears to be less suited for teiTestrial conditions than that of Ichthyoslega.
Each of the strongly rhachitomous vertebrae bears minimal zygapophyses and weakly ossified
neural arches. The notochordal canal is unconstricted. and together with the presence of short,
straight ribs (the post-pectoral distribution of which is uncertain), lhese features support an aquatic
functional interprétation. Only the apparently xenarthrous interarliculation of mid-trunk neural
arches suggests a degree of reinforcement, w'hich may be associated with increased axial loading.
The tail is already known to hâve longer lepidotrichia than Ichthyoslega. Finally, the skull appears
to hâve been more firmly bound ro the pectoral girdle, via the anocleithra and tabular homs.
Although uninformative about the degree of terrestrialisaiion, the presence of numerous, small
conical leeth in both jaw'S provides a further. prominent contrasl with Ichthyoslega, which has
an upper marginal dental arcade of more substanlial and well differenliated reeth.
Our knowledge of Tulerpeton is frustratingly incomplète. Lebedev's (1984; 1985; 1990a)
descriptions of the material show it to contain at least one form of early letrapod that resembles
— 380 —
Carboniferous tetrapods more than either Ichthyostega or Acanthostega. Currently, Lebedev &
COATES are redescribing the well articulaled postcranial remains (which constitute the type mate-
rial of Tulerpeton), and initial comparisons support this interprétation. The hexadactyl fore and
hind limbs appear to be more terrestrially adapied, and although the pectoral girdle retains an
anocleithrum, it lacks a post branchial lamina and no hyobranchial apparatus has been identified.
The axial skeleton i.s known from partially preserxed intercentra, but the arches, ribs, and entire
tail région are missing.
The diverse morphologies of these three Late Devonian tetrapods imply an earlier evo-
liitionary radiation, as yet only hinted at by the fragmentary remains from Australia, Scotland,
and Lalvia. Although Shear's (1991) review oullines the structure and composition of well
established terrestrial ccosystems by the end of the Devonian, none of the known tetrapods
appears to he terrestrial. Details of the palaeoenvironmental coniexts of each of the three
gênera are patchy, despite the Anglo-Danish expédition of 1987 collecting valuable sedi-
mentological data in situ (Bbndix-ALMGREEN et al., 1991.)) and LEBEDEv’s (I99üb) review
of the faunal contexl of Tulerpeton. Although a few acantho.stegid specimens h-ave been found
wiihin the Ichthyostega bearing sédiments, the reciprocal arrangement is not known to occur.
Frirnd et ul.'s ( 1983) comprehensive analysis of the Devonian formations of East Greenland
suggests that the fine red sandstone matrix of the Ichthyostega specimens corresponds to the
classic palaeoenvironmental settings proposed by B.\rrel and ROMER. However. it has now
been suggested that rather than being the produci of shallow ephemeral river Systems draining
into a flash-flooded continental, intramontane basin (consistent with the ‘'sea.sonally arid"
hypothesis), the sédiments may dérivé from tidal flats (13RAY, 1985) Réconciliation of this
interprétation with the more usual placing of the East Greenland Basin within the interior
of the Üld Red Sandstone continent (Laurentia) (e.g. Dineley. 1979), is achieved by the
presence of a major wrench faulting System, argued to hâve introduced marine conditions
into the Laurentian continental interior.
Most specimens of Acamhostega occur in contemporaneous sédiments consisting of silty
sandsiones, fluvial channel sandstones, and overbank siltstones (Bendix-Almgree.m et al.. 1990).
Sedimentological analysis indicates that Acanthostega was preserved in the active régions of a
mcandering fluvial channel System. Poorly preserved, large (50 mm diameterl lycopod branches
indicate the existence of abondant végétation within the vicinity of the channels. Invertebrate
fossils are almost entirely absent from the East Greenland Devonian tetrapod deposits, represented
only by burrows and arthropod trackways, The palaeoclimate is thought to hâve been monsoonal.
The high quality of the acanthostegid fossils suggests that they were not Lransported far, post-
morteni. Therefore the exclusive occurrence of Acanthostega within active channel deposits, and
known details of the .skeletal anatomy, suggesl very .strongly that this animal was principally
aquatic; .seemingly less terrestrial and more fish-like than khihyo.stega.
Tulerpeton, despite ils doser resemblance to ntore recein tetrapods (and tliereby assumed
grcater terrestriality). is found in a large, shallow marine basin, some considérable distance
from the nearest known land mass. The fauna and flora are known in greater detail than either
of the East Greenland deposits. Lebedev (1984. 1985, 1990a, b), reports the discovery of large
osteolepids. dipnoans. onychodonts, holocephalans, placoderms. numerous inveriebrate.s, charophytic
algae. and stromatolites.
— 381 —
None of these early tetrapod environments corresponds to the seasonally arid model proposed
by Romer. Furthermore, if Aciinthostega, Ichthynstega, and Tulerpeton are ranked according to
their apparent degree of terrestriality, the resuit is related inversely to the supposed proximity
of their remains to dry land. The thesis thaï ecophysiological constraints demand a freshwater
tetrapod origin and emergence onto land (LllTLE. I99U), although unrefuted. is inconsistent with
the most reeent palaeontological data, which appears to support ThomsON's (1980) suspicion
that early tetrapods lurked in bracklsh or saline iagoons. Icluhyaslega's burden as the tetrapod
ancestor (as noted by MllNER et ai, 1986) bas now been removed from ils siibstantial shoulders.
We hâve the prospect of at least three habitats in which to speculate about early tetrapod évo¬
lution, each of which is principally aquatic. These corroborate the proposais of Gcnter, Ed¬
wards. and ourselves, that limbs originated for use in water. And if the tetrapods originated
and diversified in aquatic habitats, then it may be naive to prolong the debate over which par-
ticular intennediate environment provided the unique transitional route to terrestriality. Factors
intluencing the emersion of e.xtant ainphibious fish are now known to be extremely varied. Sayer
& Davenport ( 1991 ( list the following categories: environmental dégradation (including oxygen
concentrations, température, waterborne pollutants, salinity, and pH or pCOj). biotic (including
compétition, prédation, terrestrial feeding, and reproduction), habitat drying (apparently never
investigated seriously), and voluntary emersion. We believe that it is significant thaï none of
the 59 amphibious actinoplerygian species. representing 16 marine and freshwater families, in-
cluded in SAYER & Davenport's review hâve evolved analogues of the tetrapod limb. Only in
the callichthyid amioured caifishes (nol even considered in Sayer & Davenport’s review) are
stilt-like spines developcd from the pectoral fins. Therc is clearly a need for a new, and more
comprehensive exaniinalion of ihc terrestrialisaiion of tetrapods than the confines of the current
manuscripl will allow.
MORPHOLOGICAL TRANSFORMATION SCENARIOS
Most early attempts to formulate morphological transformation scénarios concentrated upon
the change from paired fins to limbs. Key contributions to thi.s research are summarised in .Shi:bin
& Alberch (1986). In many respects morphological scénarios require an understanding of
developmental processes and patterning mechanisms, which are most effectively investigated in
the domain of developmental biology. However, the description of actual rather than hypoihelical
transitional morphologies may provide a test of certain developmental scénarios (e.g. COATES
& Clack, 1990). And a more general, comparative method utilising the terminology of heter-
ochrony is enabling more précisé descriptions to be made of the phenotypic changes throughout
phylogeny, which must resuit, in part, from changes in the régulation of these developmental
processes.
Long (1990a, b) has produced the most recent morphological transformation scénario to
bridge the flsh-tetrapod transition. The transformation passes from osteolepids, as exemplified
by Eusthenopteron fuordi, to early tetrapods, as exemplified by Crassigyrinus scoiivus. Acan-
thostegu and Ichthyostegu are considered to be more derived than Crassigyrinus (because of
absence of the intertemporal), and panderichthyids are referred to only sparingly. Once again.
— 382 —
recently published data concerning the East Greenland tetrapods and panderichthyids can provide
some intriguing new perspectives on this key event in tetrapod évolution. Long considered the
rôle of heterochronic changes between fish and tetrapod morphologies. Paedomorphosis was sug-
gested to hâve had a significant effect on the tran.sition, wiih early tetrapod and small (juvénile)
eusthenopterid skulls sharing many features. whereas peramorphic processes werc inferred to
hâve contributed to the transition from fin to limb. In ihis respect Long’s brief reviews suggested
that the origin of tetrapods incorporâtes “dissociated heterochrony” (McKiNNEY & McNamara,
1991).
Long's assumptions concerning the condition of the skull in juvénile specimens of
Euathenopleran are derived from SCHULTZE’s (1984) analysis of the différences between small
and large individuals from the Escuminac Formation, Canada. However. SCHUET7.E is carefui to
describe his material as a staiic sequence of small to large specimens, rather than as a dynamic
growth séries. The morphological changes, from the small (juvénile) morph in figure 2A to the
large (adult) morph in figure 2B. are characterized by performing a Cartesian transformation
(Thompson, 1942). Because of the conjecture that early tetrapod skulls are paedomorphic relative
to osteolepid skulls, the skull of Acatithosiega was subjected to the sanie Cartesian transformation:
undistoned in figure 2D, and transformed in figure 2E, into a hypothetical adult osteolepid-like
morphology. The résultant image is very similar to the latéral view of a panderichthyid skull
(Fig. 2F, aller Vorobyeva & SCHCLI’ZE, 1991). There are sevcral ways in which this resuit can
be mterpreted. If it is assumed that (i) panderichthyids are the clo.sest known sister-group of
tetrapods, (ii) that Acanihostegu represenis the plesioniorphic tetrapod condition, and (iii) that
allometric changes in eusthenopterid skull-onlogeny are conserved in early tetrapods (even if
unexpressed), then the hypoihesis (iv) thaï early tetrapod skulls are paedomotphic with respect
to osteolepiforms is corroborated. The stacked assumptions underlying this conclusion indicate
its extremely tenuous nature. The biological meaning of the structural transformation depicted
in figure 2 is unclear. No well corroborated phylogenetic hypothesis placing panderichthyids as
the sister-group of Acanihustega has yet been published. And if the subject of figure 2D is
moved anteriorly by only 10% of the orbital width, then the resiilt in ligure 2E resembles the
skull of a shüvel-nosed sturgeon. Nevcrtheless, we regard the resuit of the exercise as intriguing.
Long lisled a sériés of characters in which “juvénile” (i.e. small) skulls of Eusthenopteron
resemble early tetrapods (i.e. Cra.K.’iigyrinu.s). The first describes the leirapod-likc deep postorbital
contribution to the orbital rim. The same pattern is exhibited in Aiunthostega-, the Cartesian
transformation reslricls this région similarly in ihc hypothetical peramorphic l'orm, with attendant
posterior expansion of the postfrontal. The second describe.s a notched insertion in the squamosal
for the anierodorsal corner of the preopercular. This featurc is absent from the pandcrichlhyid-
acanihostegid transformation. The ihird describes a posteriorly direcled margin of the squamosal,
which contributes to the opercular hinge in small cuslhcnopicrids. This is similarly présent in
Acanthustega, where, on the basis of our description of a fish-like internai gill skeleton (COATES
& Clack, 1991), we would expect it to conirihuic to the support of a soft operculum. The
fourth describes the extensive contribution of the jugal to the orbital rim. This is also found in
Acanthostega. The fifth compares the presence of apparently fewer ossifications in the snout of
small eu.sthenopterid skulls with the limited number of bones in the snout of Crasxigyritnis\
again, this character is shared with ail early tetrapods. The sixth describes the shorter contact
— 383 —
FIG. 2. — Small. large, and transformed skulls of Eusthenopreron, Acanthostega and Panderichthys.
A-B, Cartesian transformation of lhe faterai side of ilie skull of a small Eusthenopteron foordi (A), demonstrating changes
towards an adult condition (B), adapted frora Schultze (1984. Fig. 5; mandibular, e.xtrascapular, and operculogular bones
omitted). C, skull roof of a small Eusthenopteron foordi in dorsal view (from SCHüLTZE. 1984, Fig. 6A).
D-E, Cartesian transformation from figures A-B applied to lhe latéral side of the skull of Acanthosiega gnnnari. D. resulting
in hypoiheiicûl pcramofpbic condition in figures E and F F, side view of flie skull of Panderichthys rhombolepis (adapted
from VOROBYfv^ & .Sri)i»i;r7E, 1991, Fig. 37; mandibular, cxlrascapular, and operculogular bone.s omitted).
Abbr-\ par, parielal; il, Intertcmporal.
Petits et grtmds crânes transformés c/ ‘Eusthenopteron. Acantliosiega et Panderichthys.
A-B, fr{4nsfotmaiinri conésienne d'un câté droit du crâne d'un jeune Eusthenopteron foordi en A. montrant les changements
vers la condition d'adulte en B,, (es plaques mandibiduires, estruscapulctires et apertulogulaires ne sont pas représentées
d’après ScHtlijy.r ( I^S4 Fig. 3). C, tffil crânien d'un Jeune Eusthenopteron foordi en vue dorsale, d'après SCHULTZE (1984,
Fig. 6A}.
D-E, iransfotVHition cartésienne des figures A et B appliquées au côté droit du crâne r/'Acanthostega gunnari. D. résultant
de la condition péramorphique hypothétique des figures E et F. F, vue latérale du crâne de Panderichthys rhombolepis
d'apres Vorobylva & SCHULTZE (1991, Fig. 37). les plaques mandibulaires, e.xtrascapulaires et operculogulaires ne sont
pas représentées.
Abrév. : par, pariétal ; il, intertcmporal.
— 384 —
between the cheek unil and lhe skull table. Again, this change is exhibiled by the acanthostegid
Cartesian transformation. The convex posterior edge of the grid indicates that this is a positive
allometric change; not an illusion created by the negatively allometric size of the orbit. The
seventh shared feature, intricate sutures, is, as LONG notes shared by ail taxa within the présent
discu.ssion, excliiding adult eusthenopterids.
From the list above, only the presence of a notched squamosal supports the contention that
Crassif^yrinits represents the most primitive known tetrapod skull. Other factors used to support
the peculiarly primitive interprétation of C rassi f;yri nus include the presence of an intertemporal,
and SCHULTZE &. ARSENAULT's (19851 observation thaï the dorsal position of the naris reseinbles
the non-panderichthyid osteolepiform condition. However, the notched squamosal is regarded as
convergent in the iight of panderichthyid morphology. The dorsal position of the naris in Cras-
sigyrinus may, aliematively, be inierpreicd as derived for carly tetrapods, in contrast to the ventral,
jaw-margin position of the naris in small eusthenopterids, panderichthyids, Acaïuhoslega, Ichthy-
ostega, and Prnierogyrimis (HOLMES, 1984). Intriguingly, a primitively low position for the te¬
trapod naris would support WESTOi.l.’s (1943) supposition thaï lhe dorsal migration of lhe naris
from the jaw margin during tetrapod on togen y (illustrated by 8-, 10-, and 1.5-mm himian embryos)
récapitulâtes phylogeny. The absence of an intertemporal may also dérivé from a paedomorphic
event in near-tetrapod phylogeny. SrHUi.fZE’s figure of a small eusthenopterid skull table (Fig.
2C) suggesls that it may lack a clearly differentialed intertemporal, wiih the résultant pariétal
resembling thaï of lilpistosl/^ge, in which a latéral proce.ss occupics lhe interiemporal région.
Godfrev' (1989) describes small skulls of the colosteid Greererpeton which also lack inlertem-
porals, although they are présent in larger specimens. As illustrated in CarROLL's (1990) dis¬
cussion of the remarkably small microsaur Quasicaecilia, small size appears to exert significanl
constrainis on lhe osteological complexiiy of ihc tetrapod skull, and may rcsult in total loss of
the temporal sériés. Milner (1988) argues that progenesis (sensu Gould, 1977) has had a pro-
found influence upon lhe évolution of living amphibians. We siiggest that the absence of an
interiemporal in Acanthostega, Ichthyostega and Elpistostege. may bc picsiomorphic with respect
to tetrapods. This may dérivé from a (progenetic) condition like thaï of lhe small eusthenopterid
skull table, but it should be emphasised thaï we hâve no knowledge of panderichthyid ontogeny.
The subséquent appearence of a tetrapod intertemporal-like bone, containing none of the sensory
canals found in osteolepid intertemporals, may therefore be derived independently.
CONCLUSION
Romer’s gap between the origin and terrestrialisation of tetrapods still represents a signif-
icant void in our understanding of tetrapod évolution (at the time of writing, this gap encompasses
the entire span of the Tournasian). The earlicsl terrestrial tetrapods are now known from lhe
Viscan, whereas lhe Laie Devonian Easl Greenland and Rus.sian .specimens. predated by an as-
sortmenl of trackways and skeletal fragments, repre.sent a stage by which tetrapods were already
morphologically diverse and occupied a range of different, but apparently aqualic, habitats. Of
the three known in anatomical detail, one, Acanilioslega, cannot be described as “already quite
modem’" (Shear, 1991), a .second, Ichthyostega^ is being revealcd as increasingly unusual and
— 385 —
specialized in its own righl, and the sedimentary and faunal context of the third, Tulerpeton,
provides support for Thomson’s doubts about the accepted freshwater origin of tetrapods. The
“Frasnian-Famennian” extinction (McGhee, 1989) may be a key-event in the évolution of te¬
trapods, which has, so far, remained uninlegrated with any of lhe letrapod-origin scénarios. A
devastating décliné in marine biodiversity appear.s lo hâve been caused by a Icthal température
drop, which, in tum, triggcred widespread anoxia in marine surface waters. Ail known early
tetrapod skeictal remains coincide with, or occur after the Late Devonian mass extinction event.
Evidence of widespread marine anoxia answers the principal ecophysiological objection to a
non-freshwater tetrapod origin. that it is difficult to see what the sélection pressures for air
breathing might hâve been in marine conditions. Mojphological data supports the hypothesis
that several aspects of early tetrapod anatomy were more fish-like than had been previously
supposed. As the anatomical gap between fish and tetrapod becomcs narrower, the gap hclween
origin and terrestriality become.s more clearly defined and much wider. Wc can begin to quantify
the nature and sequence of anatomical changes more precisely. Evidence frorn the earliesi known
limb skeletons aiready suggests a morphologically less restrictively defined period in tetrapod
évolution. Preliminary investigations into the rôle of heterochrony in the transition sugge.st a
paedomorphic origin for the tetrapod dermal skutl, dissociated from peramorphic évolution of
the appendicular and axial endoskelclon. Howevcr, dcspiie increased knowledge of ever doser
osteolepiform relatives (the panderichthyids), we cannol yet identify the nodal location of these
metamorphic events with any précision in tetrapod phylogenetic history.
Acknowledgments
We thank Oleg Lebedev for allowing us to examine specimens of Tulerpetoni Marius Arsenault
and the staff of the Parc de Miguasha for organising the symposium and pennis.sioti to study Elpistoste gc,
Frances WKl for photographing the text figures. The Royal Society of London provided funds enabling
M.I. CoATES to attend the Vlith International Syraopsium on lhe Sludies of Early Vertebrates. The Geo-
logical Survey of Greenland, Deiimark: the Carlsberg Foundation (Copenhagen); the Naiural Environment
Research Council: and the University Mu.seum of Zoology, Cambridge, .supported the 1987 Greenland ex¬
pédition, led by Dr S. E. Bendix-Almgreen, during which the new acanthostegid and ichthyostegid speci¬
mens were collected. This re.search was funded by the Natural Environment Research Council. We thank
Pr R. L. Carroll and Dr J. R. BOLT for reviewing the manuscript and suggesting numerous iraprovements.
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Section C, n" 1-4 : 389-445.
Problems of the phylogenetic analysis of paleozoic choanates
by Robert L. CARROLL
Abstract. — Phylogenetic analysis of Paleozoic tetrapods, using PanJurichthvs and Eusihenopleron as suc¬
cessive outgroups. shows Ichiliyo.swÿa, Acunihosii’na, Cransigyniuis. and loxommaiids as a sériés of outgroups
of the reniaining choanates. Temno.spondyl.s plus cniosteid.s are the sisler-group of anthracosaur.s and ail subséquent
tetrapod ga'up.s. Seytnourianioi'phs are the sisler-group ol an assemblage includjng two clades; one consisting
of Wesüothiana, diadectomorphs and amniotes, and the other consisting of the lepospondyl orders. Four equally
parsimonious cladograms werc found, two in which loxommatids were the sisler-group of colosicids and tcm-
nospondyls. and two in which the position of nectrideans and microsaurs were reversed. Majority tule consensus
trees up to 5 sleps beyond lhe most parsimonious iree retained this general pattern. Because of the great amount
of rnissing data, the aeiual relaiionships of Paleozoic tetrapods may be very different ihan the pattern suggested
by this phylogenetic analysis. The most scrious gap in our knowledge is caused by the absence of any fossil
evidence of the plcsiomorpliic sister-groups of the major tetrapod lineages during approximately 30 million years
of the Upper Dcvoniaii and Lower Carboniferoiis.
Keywords. — Paleo/oic tetrapods.. temnospondyls. colosteids, anibracosaurs. seymounamorphs, diadecio-
morphs, ammoies, microsaurs. parsimony analysis, Upper Devonian, Low'er Carboniferous.
Les problèmes de l'analyse phylogénétique des choanates du Paléo/.oïqne
Résumé. — Une analyse phylogénétique des tétrapodes paléozoïques, utilisant Panderichthys et Eusiheno-
pteron comme extragroupes successifs, montre c[u' Ichihyoxtega, Acunihostega. Crassigyrinun cl les loxommatides
sont une série de groupes- frères pour le restant des choanates. Les temnospondyles et les colostéides regroupés
en un seul ensemble constituent le groupe-frère des anthraco.saures et de tous les autres tétrapodes. Les seymou-
riamorphes sont le groupe-frère d'un ensemble réunissant çl incluanl deux clades . l'un regroupe Wesllnlhiana,
les diadectomorphes et les amniotes ; l'autre les lépospondylcs. Quatre cladogrammcs également parcimonieux
ont été irouvé.s. deux dans lesquels les loxommaude.s sont le groupe-frère des colostéides et des temnospondyles,
et deux autres où la position des neciridiens et des imcrosaures s'imerebange. Une analyse consensuelle fondée
sur la règle de la majoriu: maintient ce schéma général même en considérant jusqu'à cinq pas évolutifs au-delà
de la topologie la plus parcimonieuse. En raison du nombre important de données manquantes, les relations entre
les tétrapodes paléozoïques pourraient bien différer du schéma suggéré par celle analyse de caractères. La lacune
la plus sérieuse dans nos connaissances est due à l'absence de toute donnée fossile sur les groupes- frères plé-
siomorphes des principales lignées de tétrapodes durant une période d'environ 30 millions d'années se situant
du Dévonien supérieur au Carbonifère inférieur.
Mots-clés. — Tétrapodes paléozoïques, temnospondyles, colostéides. anthraeosaures, seymouriamorphes,
diadectomorphes. amniotes. microsaure.s, analyse de parcimonie. Dévonien supérieur. Carbonifère inférieur.
R. L. Carroll, Redpath Muséum and Department of Biology, McGill University, 1205 Dr Penfteld Avenue, Montreal, Canada,
HSA IBI.
Introduction
The fauna at Miguasha is rich and varied, with taxa representing much of the range of
vertebrate diversily in the Upper Devonian. Yet, 1 think of this locality almost entirely in ternis
of the genus Eiisthenopieron which, in many minds, epitomizes the concept of the ancestry of
land vertébrales. This genus was firsl recognized in lhe I9th ceniury, but knowledge of its anat-
— 390 —
omy continues to be exlended (JARViK, 1980; Hitchcock, 1995). Eusthenopteron remains the
single mosl important genus for establishing the polarity of skeletal trait transformations
throughout Paleozoic telrapods.
Ail living terrestrial vertebrates can be grouped in two major assemblages - the amniotes,
including reptiles, birds, and mammals, and the amphibians, including frogs, salamandcrs, and
caecilians. Amniotes are clearly a monophyletic group. characterized by unique shared dcrived
characters of their reproductive pattern. Unlike any other vertebrates, they possess extra-embry-
onic membranes - the amnion, chorion and allantois - that provide support, protection, and water
rétention so that the egg can be laid on land or retained in the body of the mother. Development
is direct, without an aquatic larval stage. In contrast, amphibians are primitive in the absence
of extra-embryonic membranes, and most généra lay their eggs in the water, as do fish, and
many havc an aquatic larval stage.
The ancestry of the modem amniote groups can be traced to the Upper Carboniferous where
they are represented by primitive members of the mammalian clade (the Synapsida; Rkisz, 1972),
early diapsids (RtîlSZ, 1981) (whose descendants include lepidosaurs. archosaurs, and birds). and
the more primitive anapsids, which presumably included the ancestors of turties (REtsz & Laurin,
1991). These early amniotes can be recogmzed by a number of skeletal synapomorphies
(Carroll, 1991; Smithson ei ul.. 1993) that clearly differentiate them from other Paleozoic
tetrapods.
In contrast. the modem amphibian orders can be traced no earlier than the Jurassic. Frogs
(Estes &. Reig. 1973) and caecilians (Jknkins & Walsh, 1993) are known from the Lower
Jurassic and salamandcrs appear in the Middle Jurassic (IVachnenko. 1978; Estes, 1981).
Although it is frequently assumed that the thrce modem amphibian groups share a unique common
ancestry (Mlt.NER, 1988; BOLT, 1991), no fossils arc known that illuslraie a morphology that
would be expected in an immédiate common ancestor, and only the frogs are generally recognized
as being linked with a particular group of Paleozoic tetrapods via intermediate forms (RaGE &
Rocek, 1989).
The recent description of a Lower Jurassic caecilian by JENKINS & WaI.SH (1993) demon-
strates the highly distinctive nature of this group early in hs liistory. The rétention of a primitively
closed skull roof .sttongly suggests an origin from Paleozoic amphibians distinct from that of
the open-roofed .salamandcrs and frogs. The ongin and spécifie relationships among the three
living amphibian groups remain one of the largest scale problems in vertebrate phylogeny.
Although the three major amniote groups can be traced back to the Upper Carboniferous, the
affinities of ancestral amniotes with other Paleozoic tetrapods are still subject to controversy.
This problem was recently exemplifîed in a paper by PancHRN & SNTTTHSON (1988) in which
alternative sister-group relationships with either anthracosaurs or microsaurs were debated.
The problems of the origin and interrclationships of the modem amphibian Imeages and
the spécifie affinities of early amniotes can only be solved by a thorough understanding of the
anatomy and relationships of ail groups of Paleozoic tetrapods. At présent, there is no generally
agreed upon phylogeny of this assemblage. MoSt of the groups that dominaled the Upper Car¬
boniferous and Permian are very clearly distinguished from one another when they first appear
in the fossil record in the late Lower Carboniferous (Carroll, 1992). No intermediate.s or
plausible common ancestors are recognized. Extremely imporant studies of Devonian amphibians
— 391 —
by Clack (1988, 1989, 1991, 1992), COATES & Clack (1990, 1991, 1995), Clack & COATES
(1995), and Lebedev & Coates (1993) show that these généra are both much more primitive
than the Carboniferous forms, and in many ways divergent. As yet, they provide little evidence
as to the probable interrelationships of any later tetrapods. Skeletal remains of Upper Devonian
tetrapods, and even older foot peints (THOMSON, 1993) point to the great antiquity of the group,
and the extremely long gap in tinte between the origin of land vertebrates and the appearance
of the divergent lineages in the mid-Carboniferous.
Donoghue ei al, (1989) and HUELSENBECK (1991) hâve emphasized difficulties that may
occur in establishing reliable phylogénies if the data is limited to modem taxa, without evidence
of more plesiotnorphic fossil relatives. In the case of Carboniferous tetrapods. ail evidence cornes
from fossils, but the gap between the first appearance of the advanced groups in the Visean and
later and the probably time of their initial divergence in the Frasnian or Famennian results in
a comparable problem. sincc we are ignorant of the plesiomorphic sister-groups of ail the derived
lineages under considération. A period of up to 50 million years may hâve elapsed between the
time that these lineages began to differentiate in the Late Devonian, and their first appearance
in the fossil record.
Fossil hâve been reported. but not yet described from the base of the Toumaisian (Carroll
et al., 1972), but the remains are limited to a few limb bones and a neural arch. They demonstrate
the présence of large labyrinthodonts, but provide little evidence of spécifie affinities with later
groups. The oldest described Carboniferous amphibian is the limbless aïstopod Letliiscus from
the Holkerian. New localities hâve been reported from the Asbian (SCHULTZE & BOLT, 1994;
Bolt, 1990). The first diverse fauna is from the Brigantian of Scotland (Rolee. 1993). The last
major groups to appear are the nectrideans and lysorophids, both in the Melekessklian. Their
ancestors may hâve diverged from other groups of tetrapods as much as 55 million years earlier.
Despite the long gap at the base of ail major tetrapod lineages, establishing their probable
interrelationships is greatly facilitated by knowledge of Devonian sarcopterygians such as
Eusthenopterpn which enable us to establish the polarity of character change throughout the
later Paleozoic.
Abbreviations
A, B, C, D, G, I, J, K, L. X, Y,
Z, 1-10 dermal plates in lungfish, mostly without obviously homology to bones
in choanates. plaques denniques des dipneustes sans homologies évidentes
avec tes os des choanates ;
a angular, angulaire;
anocl anocleithrum, anocleithrum;
apr anterior palatal recess, recessus palatin antérieur;
at anterior tecta!, tectal antérieur;
bb basibranchial. basihranchial ;
bo basioccipital, hasioccipital ;
bhf foramen for buccohypophysial duct, foramen pour le ductus buccohypohysaire ;
c centrale, centrale;
cb certobranchial, certobranchial ;
— 392 —
ch
chy
d
dr
dt
ect
en
enf
eo
epb
ept
f
fb
fe
fi b
fiba
fm
fp
gP
h
hh
hy
hyf
i
in
infb
it
j
juv
1
les
Iptr
Ir
m
mes
mr
n
na
ne
nscav
orbart
00
op
choana, choanes;
ceratohyal, cératohyal;
dentary, dentaire;
dorsal ridge, ride dorsale;
distal tarsal. tarsien distal;
ectopterygoid, ectoptérygoïde ;
entopterygoid, entoptéry’goïde ;
entepicondylar foramen, /oramen entépicondylaire ;
exoccipital, exoccipital ;
epibranchial, épibranchial ;
epipterygoid, épiptérygoïde ;
frontal, frontal;
fossa Bridgei, /o.WÉ’ de Bridge;
fémur, fémur;
fibula, péronné ;
fibulare, fihulaire;
foramen magnum, /oramen magnum;
footplate of stapes, base du stapes;
gular plate, plaque gulaire;
humérus, humérus;
hy pohy al , hypohyal ;
hyomandibular, hyomandibulaire ;
facet for hyomandibular, /acette pour l’ hyomandibulaire ;
intermedium, intermédiaire ;
intemasal, internasal ;
infrapharyngobranchial, infrapharyngobranchial ;
intertemporal, intertemporal ;
jugular, jugulaire ;
jugular vein, veine jugulaire;
lacrimal, lacrymal;
latéral extrascapular, extrascapulaire latéral;
latéral palatal tooth row, rangée dentaire palatale latérale;
latéral rostral, rostral latéral;
maxilla, maxillaire ;
médial extrascapula, extrascapulaire médial;
médial rostral, rostral médial;
nasal, nasal;
external naris, narine externe;
notochordal canal, canal notochordal ;
nasal cavity, cavité nasale;
orbital artery, artère orbitaire;
otic-occipital portion of braincase, partie otico-occipitale du neurocrâne
operculum, opercule:
— 393 —
opis
P
pal
palf
pdp
Pf
pm
po
pop
PP
prf
ps
psp
Pt
ptf
ptt
q
qj
r
ra
re
rmi
sa
sbm
sbr
sc-co
sel
smbp
sop
sp
spb
spel
sph
spr
sq
St
start
stb
stf
sty
t
thy-m
ti
opisthotic, opistliotique ;
pariétal, pariétal ;
palatine, palatin;
palatal fang, croc palatin;
palatal dental plates, plaque dentaire palatine;
postfrontal, postfrontal ;
premaxilla, prémaxillaire ;
postorbital, postorbitaire ;
preopercular, préoperculaire ;
postparietal, postpariétal ;
pre frontal, préfrontal;
parasphenoid, parasphénoïde ;
presplenial, présplénial ;
pterygoid, ptérygoïde;
post-temporal ïossa, fosse post-temporale;
post-temporal, post-temporal ;
quadrate, carré;
quadratojugal, quadratojugal ;
rostral, rostral ;
radius, radius;
radiale, radial;
ramus mandibularis intemus, rameau nerveux mandibulaire interne;
surangular, surangulaire ;
submandibulo-branchiostegal plate, plaque submandibulaire branchiostégale ;
sublingual rod, tige sublinguale ;
scapulocoracoid, scapulocoracoïde ;
supracleithrum, supracleithrum ;
submandibulo-branchiostegal plate, plaque submandibulaire branchiostégale ;
subopercular, sous-operculaire ;
splenial, splénial;
suprapharyngobranchial, banchial suprapharyngien ;
spiracular cleft, fente spiraculaire ;
sphenethmoid portion of braincase, région sphénetlimoïde du neurocrâne ;
spiracle, spiracle;
squamosal, squamosal;
supratemporal , supratemporal ;
stapedial artery, artère stapédiale;
distal blade of stapes, lame distale du stapes;
foramen for stapedial artety, foramen pour l’artère stapédiale;
stylohyal, stylohyal;
tabular, tabulaire;
truncus hyoideo-mandibularis, tronc hyoïdo-mandibulaire ;
tibia, tibia;
— 394 —
U ulna, ulna;
ul ulnare, ulnaire;
urh hurohyal, hurohyal;
V vomer, vomer;
vf vomerine fang, croc vomérien.
METHODOLOGY
Several factors must be established before we can détermine the interrelationships among
Paleozoic tetrapods.
A - Détermine that they are a monophyletic assemblage.
B - Establish the polarities of ail characters that vary within the group.
C - Establish that the subgroups (the orders of Paleozoic tetrapods) are each monophyletic
on the basis of unique apomorphies.
D - Détermine the derived character-states présent in the most primitive members of each
monophyletic subgroup.
E - Déterminé the homology of these derived characters from group to group.
1) The first of these requirements has been met through the work of Gafhney (1979),
Panchen & SMITHSON (1987), Godfrey (1989), VOROBYEVA & SCHULTZE (1991). and Clack
& COATES (1995) who hâve recognized many features that demonstrate the monophyly of tet¬
rapods. More than 50 derived characters are recognized in this study, uniring tetrapods and difl'er-
entiating them from choanate sarcopterygians. If. as argued by these authors, tetrapods are
monophyletic, their origin from osteolepiform sarcopterygians (including panderichthyids) is a
singular event that is the logical point from which to iniliate phylogcnetic analysis of ail tetrapods.
2) The next task is to establish the most appropriale outgroup for determining the polarity
of character State transformation among early tetrapods. This outgroup should be the most closely
related sister-group within the larger monophyletic assemblage including the group in question.
Rosen el al. (1981) may be correct in claiming that lungfish are the closest living sister-
group of tetrapods, but extensive evidence has accumulated to support much doser common
ancestry between Paleozoic tetrapods and Devonian osteolepiforms (including panderichthyids)
Albero (1991), Long (1990), Panchen & Smithson (1987), Thomson (1993), Schultze
(1986). Yu (1990).
VOROBYEVA & Schultze (1991) listed the folowing synapomorphies as uniting oste¬
olepiforms and tetrapods.
1. One extemal nasal opening.
2. Choana between premaxilla, maxilla, vomer, and dermopalatine.
3. Médian rostral fused with premaxilla.
4. Few unpaired or paired postrostrals.
5. Latéral rosirai ventral to external naris.
6. Large lacrimal.
7. Narrow preopercular bone at posterior margin of cheek.
8. Palatal recess unpaired and without bone cover.
— 395 —
9. Two-headed articulation of ribs.
10. Tetrapod articulation between humérus and scapulocoracoid.
11. Tetrapod pattern of proximal limb éléments.
Much more detailed comparison can be made belween Devonian osteolepiforms and let-
rapods than between either of these groups and the Dipnoi. Illustrations of a représentative
Devonian lungfish Chirodipterus are included in figures 1-3 to emphasize this fact. Every major
bone in the skull, vertébral column and appendicular skeleton of osteolepifonnes can be directly
compared wilh bones in the same relative position in early tetrapods. In conlrast, very few skull
bones in Dipnoi can be homologized with counterparts in either osteolepiforms or tetrapods.
The vertebrae and limbs are aiso clearly distinct. It would be impossible to establish the polarity
of the majority of character transformations in early tetrapods on the basis of the characlers in
any lungfish.
We are extremelv foriunaie in our work on early tetrapods (o hâve knowledge of the oste¬
olepiforms Eusthenopteron and Panderichthys to establish the primitive character State of most
of the skeleial characters thaï change within the choanates. Starting with the character States
that are présent in these généra, we can recognize the polarity of transformations in nearly even
bone in the body of early land vertébrales.
3) The monophyletic origin of most of the previously recognized groups of Paleozoic tet¬
rapods can be demonstrated on the basis of readily recognized apomorphies.
Acanthostena . unique configuration of tabular, acce.ssory articulation of neural arches without well-formed
zygopophyses.
Ichthyiisiega: médian postparieliil, unique pattern of attachment of braincase to back of skull table.
Crasxiüvrinus: unique size disparity of fore and hind limb, extremely deep cheek.
Loxcimmatid.s; keytiole shaped orbits.
Anthracosaurs: loitg labtilar horn. 5ih digii ofpes wilh lïve phalanges, functionally embulomerous vertebrae.
Seymouriainorphs: stapes articulaling wilh tabular. unique p.attern of swollen neural arches.
Wesrlftluarur- aniniote pattern of skull table, but 36 presacral vertebrae. forelimb much smaller than rear,
but not of pattern in Cnnsigyrtnus.
Diadectomorphs; .snlid attachment of supraoccipital vt ith dcrmal bones of occiput.
Amniotes. supra-occipital a broad plate of hune, loosely attached to postparietal and tabular dorsally, small
supraieinporal, tabular ami paired postparietal. canine teeth.
Nectridean.s; haemal urche.s fused to middie of centrtim, symmetrical to neural arches.
Aïstopods: extremely elongate body. réduction or absence of girdies, absence of limbs, first cervical centrum
articulâtes with circular dépréssion in occiput
Microsaurs; skull table lacking supratcmporal. tabular reaching postoibital and in some familles the post-
frontal.
Adelogyrinids: a single hone, hearing a posterior prcicess, occupies the position of the tabular. supratemporal
and sqtiamosal of other early tetrapods. postorbital reduced and does not enter margin of orbit, limbs
and etidochondral girdies lost bul dermal shoiilder girdle well-developed.
Lysorophids: open cheek, jaw suspension angled forward, limbs greally reduced.
Teranospundyls; impédance matching middie car.
Colosteids: "canine" teeth in premaxillae, closure of squamosal embayment.
Thi.s lisi is .shori, bul nol conlradicted by other characters.
Some of these groups may be paraphyletic. Theie is considérable évidence that temno-
spondyls are ihe sister-group of modem anurans, and possibly of other modem amphibians
(Milner, 1988). Microsaurs bave been suggesied as including the sister-taxa of caecilians (Car-
ROLL & CtiRRrE. 1975; Walsh, 1987) and possibly urodeles (Carrüll & Holmes, 1980). Di¬
adectomorphs probably include the sister-group of amniotes (Smitiison et al., 1993).
1a + 1b
\ St P
at ^ \ pr
na
2. — Latéral views of skull of s3rcoptcryg:iuns untl Acanthostega. A. the lunglish Chirodipterus (modified from MILES,
1977). B-C. lhe osieolcpiform rhipidistians Eustherwptefvn (modified from JarvIic 1980) and Panderichthys (modified from
VOROBYEVA & SCHLLTZE, 1991). D. Acanthosrega (drawing supplied by Dr Clack).
Crânes de san optérygiens et «/’Acanlho&tega en vues latérales. A, Chirodipterus, un dipneuste (modifié d'après Miles, 1977).
B-C, cnfssoptéiygiens rhipidistiens. Eusthenopteron (modifié d'après JaRVîk, 1980) et Panderichthys (modifié d’après
VOROBYCVA de SCHUtrzE, 1991). D. Acanthostcga (dessin Dr Clack).
1. — Skull roof of sarcopterygians and Acanthosîega. A, the lungfish Chirodipterus (modified from MILES, 1977). B-C, the
osteolcpiform rhipidistians Eusthenopteron (nnnlified from Jarvik, 1980) and Panderichthy.s (modified from Vorob^'EVa &
SCHUI.TZF.. 1991). D. Avunlhostcga (drawing suppJicd by Dr CLACK). Heavy lines un the skulJ of Eusihenoptetvn indicate
the line.*^ of inohility between ihc éléments of the dcrmal skull.
Toits iraniens de sarcoptêrygiens et d’Acanthosiegû. A, Chirodipterus. un dipneuste (modifié d'après Miles, 1977). B-C,
crossoplérygiens rhipidistiens, Eusthenopteron (modifié d'après JAHVtK, 1980) et Panderichthys (modifié d’après VorOBYEVA
<& ScHiU.TZE. 1991). D. Acanthosîega (dessin Dr ClACK). Les traits gras sur le toit crânien ‘Eusthenopteron indiquent les
zones de mohilité entre tes éléments du toit crânien dermique.
— 399 —
4) It is a great deal more difficult to establish what derived characters were présent in the
earliest members of the varions lineages. The well known fossils of ail orders are characterized
by many derived characters (appendix 1 and III), but any or ail may hâve evolved during the
25 million years or more between the initial radiation of tetrapods, sometime in the Middle to
Upper Devonian, and the appearance of more derived groups in the late Lower Carboniferous.
Obviousiy, only ihose characters that were présent in the earliest members of these groups can
demonstrate sister-groiip relationships with other groups of Paleozoic tetrapods (Donoghue,
1989).
5) The absence of knowledge of any tetrapods during the first 23 million years of the
Carboniferou.s aiso makcs it extremely difficult to establish the spécifie homology of derived
characters that are présent in different lineages in the later Carboniferous. Only those characters
that had evolved in the common ancestors of two or more lineages can be accepted as slrictly
homologous. In the absence of any immédiate ancestors, it is impossible to establish directly
whether or not characters in divergent lineages are homologous. On the other hand, it rnay be
possible to establish the probability of similar derived characters being homologous on the basis
of character changes within monophyletic groups. The absence of the character State in question
in some members of one (or both) of the groups suggests that ils presence in other members is
the resuit of convergence.
There are certainly many examples of similar derived conditions having evolved conver-
gently among different groups of Paleozoic tetrapods, each of which are differentiated by au-
tapontorphies élaboration of large inteipterygoid vacuities in advanced (but not primitive)
nectrideans as well as in ancestral lemnospondyls; suturai attachment of the basicranial articu¬
lation in advanced. but not primitive, members of both groups; closure of the squamosal em-
bayment in limnoscelid diadectomorphs, colosteids, some temnospondyls, and in the lepospondyl
groups; fusion of the proximal larsals into an asiragalus in the ancestors of amniotes, among
gephyrostegid anthracosaurs and among micros-aurs; suturai attachment of cheek and skull table
among advanced nectrideans, anthracosauroids (Anthracosaurus and seymouriamorphs). reptiles,
and micTosaurs; loss of the interlemporal in advanced but not primitive temnospondyls, and ad¬
vanced but not primitive loxommatoids.
Convergence, or homoplasy is certainly a commun featurc of these groups. but even more
common are characters for which there is no obvions evidence as to whether they are homologous
or convergent. Spool-shaped centra occur in amniotes, lepospondyls, and lissamphibians, but we
hâve no idea of the degree of homology of these structures (Carrou & Chorn, 1994). Loss
characters are common examples. Many groups lack the intertemporal bone (reptiles, Ichthy-
ostega, Acanthostega, microsaurs, nectrideans) but is this absence homologous? Other examples
Fig. 3. — Palatal views of the skulla of sarcoplerygians and Atunlhoslega. A, lhe Umgfish Chirodipterus (iiiodified froni Miles,
1977 t. B-C. ihc osleolepiform rhipidistmns Susthenopteron (modified trom JakvIk, 1980) and Panderichthys (modified front
VoROBvnvA & ScmiLTZi;. 1991). D, Ainnihostega (drawing supplied by Dr Clack).
Toits n'ônUns en vue palutaie de surropléry^ien.x et r/'Acanlho.'îtega. A. Chirodipterus, un dipneuste imodifté d'upeès Miles,
1977). B-C, crosmpie'ryt;icns rhipidistiens, Euslhcnoplcron (modifié d'après MkvIk, 1980) et Panderichthys (modifié d'après
VoEOimM di SniUirZE, 1991). D. Acatithobieg.i (dessin Dr CtACE).
— 400 —
include réduction of toes in the manus in temnospondyls, microsaurs, and lysorophids, loss of
palatal fangs in limnoscelids, araniotes, and ail lepospondyl groups, and loss of limbs in adelogy-
rinids and aïstopods. The common practice in forming data matrices for phylogenetic analysis
is to code these derived characters as if they were homologous, but this practice is not justified
if there is no way of determining whether they represenl one character (if they are homologous)
or two or more different characters (if they are nof). ünfortunately. there is no procedure in the
currently availablc phylogenetic packages for handling this type of uncertainty. It is commonly
argued that convergence is rare and that homoplasy can be established by incongruence with
other character transformations once the data is analyzed, but if the number of homoplastic
characters approach 50% of those being analyzed, it becomes impossible to identify them (Car-
ROLL & CURRIE, 1991; SCOTT & Janis, 1993).
Fig. 4. — Comparison of the hyomandibular in a rhipidistian and the stapes of letrapods. A, composite drawings of the occiputs
of Eusrhenopteron (on the left) and Greererpeton (on the right) showing the change in the pattern of blood vessels and
nerves related to the configuration of the hyomandibular and stapes (modified from Smithson, i982). B. stapes of Acanîhostega
(modiRed from ClaCK, 1992). C. stapes of the embotrunere Plioliderpetnn (modified from ClaCK. 1992). D. stapes of the
temnospondy! Creen'rpeton (modified from SMITHSON. 1982).
Comparaison vnfrt rhvomandibuhirr d'un rhipidislien et le stapes des tétrapodes. A, de.\.sins composites des régions occi¬
pitales i/'Euslhenopteron (à gauche) et de Greererpeton {à drtnteï montrant le changement dans la disposition des vaisseaux
sanguins et des nerfs en rapport avec lu pusiiion de l’hyonumdihuiaire et du stapes (modifié d'après SstnHSOiW, 1982). B,
stapes f/’Acanthostega (modijïé d’après Cl^CK. 19921 C, stapes de l'ernholomère Pholiilcrpclon (modifié d'après ClacK^
1992). D. idaper du temnospondyie Greererpeton (modifié d'après SMtTHSON, 19H2).
— 401 —
Fig. 5. — Hyoid apparatus of choanates. A, Eusthenopteron (madified from JaRVîk, 1980). B, Acanthostega (modified from
COATES & Clack. 1991). C, hyoid of Pann^lus (modified from Romer, 1969).
Appareil hyoïdien de choanates. A, Eusthenopteron ^modifié d’après JarvIk, J9S(}). B, Acanthostega {modifié d’après COATES
& Clack. 1991). C. os hyoïde de Pantylus (modifié d’après Romer, 1969).
Unfortunately, there are no immédiate ways around the problems of identifying which
derived characters were présent in the earliest members of the monophyletic subgroups, or de-
termining the homology of the characters that are présent when the groups do appear in the
fossil record. One may only hope that the derived characters of the earliest known members of
— 402 —
the individual groups reflect the condition in earlier members, and that mosL similar derived
characters are homologous. These problems must be borne in mind in considering the data pre-
sented here.
Taxa and characters
Thanks to the exhaustive descriptive work of JARVtK (1980, and works cited therein), AN¬
DREWS & Westoll (1970), and others, nearly every aspect of the skeletal anatomy of
Eusthenopternn is known in great detail. Panderichthys i.s less completely known. but shows
numerous derived characters in common with carly lelrapods that indicate thaï il is the closest
sisler-taxon of any currenlly known genus (Vororyeva & ScHi.’LTZE, 1991).
Ail of the major groups of Paleozoic tetrapods hâve been considcred, along with several
individual gênera of particular anatomical or phylogenetic significance. One i.solated genus that
represents a distinct anatomical pattern, Acheronliscux (Carroll, 1969b), was not included here
bccause the cranial anatomy is very incompletely known and the large number of gaps in the
data set would reduce the value of known character States in other taxa.
Data of tetrapod luxa were taken from the following sources.
ACtinihoiiegu: Clack (iyS8, 1989, 1991, 1993. and in press), COATES & ClaCK (1990, 1991), Clack & Coates
(1995) and per.s. eoniin.
Ichihyostega: Jarvik (1980. and references cited iherein), Cl.ack (1988, 1989. 1993, 1995), COATES & Clack
(1990, 1991) and pers. comm.
Cranstfiyrinuy. PaNCHEN (1985), PANCHEN & SmithsoN (1990), CL.ACK (1994).
Loxoninialids: BEAUMONT (1977); pending rede.scription, Spathicephalus i.s as.sumed to be a member of this
a.s.semblage.
Anthraco.salir.s; including Prolenigyrimn and other embolomeres HOLMES (1980, 1984), Panchen (1970, 1980),
Eoherpewn Smithson (19S5), and gephyrustegids C.arroll (1970), BOY & Bandel (1973).
Seymouriamorphs: including Seymouriidae WRITE (1939), BERMaN et uL (1987), Michael L.aURIN (pers. comm.)
and Discosaüriscidae Spinar (1952).
WestloihUma: SMITHSON (1989), SMITHSON & ROLFE (1990), SMITHSON et al. (1993).
Diadectomorphs; Llmnoscelidae Romer (1946). FraCas.SO (1987), Tseajaiidae Moss (1972). Diadectidae Sumida
& LOMB.ARLI (1991). Limnoscelis was used cxclusively as a basis of c.stablishing the primitive character
.States of this group.
Amnimes: Pelvcosaurs. pmtorothyrids, Carboniferous diapsids Carroll (1964, 1969a, 1982, 1986b, 1991), Reisz
(1972, 1981).
Nectrideans: Bossy (1976), A. C. Milner (1977), A. C. MiLNER (1980),
Aïstopods: Bairu (1964). McGinnis (1967), Wellstead (1982), and Carroll (work in progress).
Microsaurs: CARROLL & Gaskill (1978). Carroll (1992), Carroll et al. (1991).
.Adelogyrinids; ANORLW.s & Carroll (1991),
Lysorophids; WhLLSTHAD (1991).
Temnospondyls: A. R. MiLNER (1990, 1993).
Colosteidae: S.MITILSON (1982), GODEREY (1989), and HOOK (1983).
The most primitive character States recognized within each group were established (appen¬
dices I & II). In drawing up the character list. ail aspects of the skelelon were evaluated. Begin-
ning with Eusrlwnoptemn, ail characters were considered that differed significantly among these
taxa. Some were nol considered further because their State was not known in many taxa. Others
were omitled because lhey showed very great variability within one or more groups and so it
was difficult to establish the primitive State for each. For example the pattern of dermal sculp-
turing, and the spécifie number of marginal teeth.
— 403 —
Although not an exhaustive list, the characters are représentative of ail aspects of the skeletal
System. If ail these characters were known in the earliest members of ail these groups, they
would almost certainly be sufficient to establish their branching sequence.
COMMENTS ON SELECTED CHARACTERS
4. The general course of the latéral line canals on the skull of osteolepifonns exhibits a consistent
pattern which is variously altered in different groups of tetrapods. Unfortunately this is a very
difficult character to use in phylogenetic analysis. The osteolepiform pattern may be présent
during early development in ail Paleozoic amphibians that retain a distinct aquatic larval stages.
The conspicuous expression of the canals in permanently aquatic Triassic amphibians illustrâtes
the ease with which this System can revert to a primitive pattern.
6. This is one of the few characters for which the State in the immédiate tetrapod ancesTor is
contentious. Apparently the ventral orientation is derived among the most primitive tetrapods,
and then reverses in the ancestor(s) of the advanced lineages.
17-18. There is question regarding the homology of the tetrapod septomaxilla. Panchen (1967)
made a sirnng case for homology with the latéral rostral, but Ci.aCK (1993) pointed out positional
similarity between the bone identified as the septomaxilla in loxommatids and the anterior tectal.
24. BOLT ( 1990) has reported the discovery of a Mississippian tetrapod exhibiting many features
of later anthracosaurs but possessmg the more primitive pattern of the skull roof in which the
tabular is separated from the pariétal by the supratemporal. Unfortunately, it is awkward to include
the few character States of this animal that hâve so far been mentioned in the literature without
being able to make comparison with the scores of other characters that can be cited for other
taxa.
31. In ail temnospondyls and colosteids there is an extensive open space between the palatal
ramus of the pierygoid and a narrow cultrifonn process of tlie pterygoid. In other taxa, including
some microsaurs and lysorophids represented only by généra with much smaller skulls, there is
a large space between the palatal rami of the pierygoids, occupied by the relativcly wider base
of the braincase. but the remainder of the skulls are so different that there is very little likelihood
that the character is homologous.
70. The médial surface of the lower jaw varies considerably in the presence or absence of large
openings and the spécifie distribution of smaller fenestra. These différences hâve no obvions
relationship to major phylogenetic divisions, but are included in the data set since they may
eventually prove useful in characterizing taxa at some hierarchical level.
83. As in the case of the latéral line canals, the hyoid apparatus may hâve been highly elaborated
and relatively similar in the early larval stages of most Paleozoic tetrapods.. The configuration
in the few adulls in which it is known differ widely (Fig. 6, see also ANDREWS & CARROLL,
1991), but there is little evidence that the différences can be associated with particular taxonomie
groups.
— 405 —
92, 102. The most striking feature by which Panderichthys differs from most early tetrapods
and other osteolepiforms is in the absence of pleurocentra. Since this condition also exists in
two groups of early tetrapods it may be an important due to their affinities. Unfortunately there
is no way to be certain of the polarity of the character change or the homology of the character
States.
104. The area of the sacrum is not exposed in any of the known specimens oi Acanthostega or
Ichthyostega. For that reason, this character is scored as ? The presence of a well-defined iliac
blade, however, strongly indicates that at least one vertebra must hâve served the rôle of a
sacral.
150, 151, 152, 153, 154, 172-177. Carpals and tarsals are frequently poorly ossified and are
only rarely well-articiilated. Their number and pattern has the potential to be useful in phylo-
genetic studies. but the rarity of adequately preserved material means that the.se data cannot be
relied on at présent.
No characters hâve been weighted or constrained from reversai. Some characters such as
the degree of torsion of the humérus and posterior extent of the purasphenoid presumably evolved
progressively within particular lineages, but since comparison is being made between lineages
as well, Iherç is no évidence that change was progressive between the particular taxa in which
these characters are known. Hence, no characters hâve been ordered.
PHYLOGENETIC ANALYSIS
The character list and data matrix are shown in appendices I and II. Illustrations of sar-
copterygians and early tetrapods are shown in Figures 1-6. Other illustrations of more derived
Paleozoic tetrapods appear in Carroll (1992). The data matrix was processed by the phylo-
genetic package PAftP. 3.1 (Swofford, 1993), run on a Macintosh LC III, using the Deltran
option. The four shortest trees hâve 454 .steps. Tree 2 appcars as figure 7. Panderichthys and
Eusthenoptemn appear as successive outgroups of tetrapods. Acanihnstega, Ichthyostega, Cras-
sigyrinns, and loxommatids succeed one another as progressively more derived tetrapods. They
are followed by a group consisting of colosteids and tcmnospondyls which appears as the sister-
group of ail more derived tetrapods, The next more derived group is the anthracosaurs, followed
by the seymouriamorphs. The seymouriamorphs are the sister- group of ail other early tetrapods,
which are represented on one hand by Westlothiana. diadectomorphs and amniotes, and on the
Fig. 6. — Fore and hind limh.s of riiipldi.stian and tetrapods. A-B, fore and hind linibs of Euathcnoplenm (inudificd from Andrews
& Wo^TOLL, 1^70). C, forclimb of AcamhoMega. Position and identification of carpaJs very spéculative. D, hindlimb of
/chrhyosiegü. (C-D, counc&y of Dr COATES).
Membres anièneurs et postérieurs de rliipidistiens et de tétrapodes. A-R. membres antérieurs et postérieurs r/'Euslhenopieron
(modifié ddprès ANDftPWS & Wfstou., I97Ü). C. membre antérieur d'Acii\Ü'\oslcg,z. La position et l’identification des carpiens
sont très hyputhetuptes. [), membre rf’IchlhyUiiUîga. (C-D, a\€c l'aimable autorisation du Dr CoATES).
— 406 —
2
Eusîhenopteron
Panderichthys
Acanthostega
Ichthyosiega
Crassigyrinus
L
L
29
26
l_
r
!5
L
20
22
Loxommatids
Anthracosaurs
Seymouriamofphs
■ ■— Westlothiana
Diadectomorphs
19
«— Amniotes
Nectrideans
Microsaurs
Adelogyrinids
» Aistopods
Lysorophids
1 Colosteids
28
* Temnospondyls
Fig. 7. — Cladogram of Paleozoic choanates. One of four most parsimonious irees generated by PAUP 3.1 using the Deltran
option, based on data matrix in Appendix II. Apomorphy iist reproduced as Appendix III.
Ocidogramme des choanates paléozoïques. L’un des quatre arbres le plus parcimonieux généré par PAUP 3.1 en utilisant l'option
Deltran. d'après la matrice de données de l’appendice fl. La liste des apomorphies est donnée dans l'appendice fil.
other hand by the lepospondyl assemblage. The other three most parsimonious trees (Fig. 8)
differ in having loxommatids as the sister-group of colosteids and temnospondyls. or in the rela¬
tive position of the microsaurs and nectrideans among the lepospondyls. These trees fit the general
impression of the affinities of the "labyrinthodonls” as a sequence of progressively more derived
groups, the lepospondyls as a natural group. and ihc amniotes allied with diadectomorphs. It is
somewhat unexpected to find the seymouriamorphs as the sister-group of lepospondyls as vvell
as amniotes.
If the number of steps is increased by one, the number of trees increases by three. In two,
Westlothiana is the sister-group of amniotes, rather than of diadectomorphs and amniotes, and
in one temnospondyls and colosteids are together more derived than the anthracosaurs.
Among the 24 trees with 456 steps, the following novelties appear ; amniotes as the plesio-
morphic sister-group of diadectomorphs and Westlothiana, loxommatids and loxommatids plus
temnospondyls, and colosteids as the sister-group of seymouriamorphs and ail more advanced
tetrapods, neclideans rather than lysorophids as the sister-group of adelogyrinids and aistopods,
nectrideans and lysorophids as sister-taxa. Westlothiana as the sister-group of the lepospondyls
and this assemblage as the sister-group of tlie diadectomorphs and amniotes, and Westlothiana
as the sister-group of the assemblage including diadectomorphs, amniotes and lepospondyls.
Fifty-three trees were generated at 457 steps, just thiee more than the most parsimonious.
A strict con.sensus of these trees resiilted in a polytomy involving the common ancestors of
colosteids and temnospondyls with Crassigyrinus, loxommatids, anthracosaurs, and the common
ancestors of ail more derived tetrapods. A second polytomy involves Westlothiana, diadecto-
— 407 —
Eusthenopteron
Panderichthys
Acanthostega
Ichthyostega
Crassigyrinus
Loxommatids
Colosteids
Temnospondyls
Anthracosaurs
Seymouriamorphs
Westlothiana
Diadectomorphs
Amniotes
Nectrideans
Microsaurs
Adelogyrinids
Aistopods
Lysorophids
Eusthenopteron
Panderichthys
Acanthostega
Ichthyostega
Crassigyrinus
Loxommatids
Anthracosaurs
Seymouriamorphs
Westlothiana
Diadectomorphs
Amniotes
Nectrideans
Microsaurs
Adelogyrinids
Aistopods
Lysorophids
Colosteids
Temnospondyls
14
El
13
hd
a
Eusthenopteron
Panderichthys
Acanthostega
Ichthyostega
Crassigyrinus
Loxommatids
Colosteids
Temnospondyls
Anthracosaurs
Seymouriamorphs
Westlothiana
Diadectomorphs
Amniotes
Nectrideans
14
13— Adelogyrinids
Aistopods
29
Lysorophids
Microsaurs
14
Eusthenopteron
Panderichthys
Acanthostega
Ichthyostega
Crassigyrinus
Loxommatids
Anthracosaurs
Seymouriamorphs
Westlothiana
Diadectomorphs
Amniotes
Nectrideans
Adelogyrinids
Aistopods
Lysorophids
Microsaurs
Colosteids
Temnospondyls
PiG g. — The four most parsimonious cladograms generated using the Deltran option, showing braneh length.
Les quatre arbres les plus parcimonieux, obtenus avec l’option Deltran, avec la longueur des branches
— 408 —
morphs, amniotes, and the common ancestry of the lepospondyls. The final polytomy involves
the common anceslry of adelogyrinids and aïstopods and the remaining lepospondyl groups.
At 458 steps, 1 16 trees were generated. The resolution between the lepospondyl and amniotes
and their immédiate sister-groups is lost in the strict concensus, but is still supported in the
majority ruie (50%) concensus tree. A similar pattern persists at 459 steps (Fig. 9).
Given the latitude (or constraint) of only five steps beyond the most parsimonous tree (less
than 1% of the total numbcr of steps), the. resolution of post-Devonian tetrapods is greatly re-
duced, but maintains many informative features. How significant is this 1% increase in the number
of steps?
Most systematists are satisfied with achieving full resolution of ail taxa (without polytomies)
in the most parsimonious cladograms. This assumes that the data set available is représentative
of the total variability of character States among the taxa involved. In the case of Paleozoic
tetrapods, there is considérable cvidence that the available information is very incomplète in
relationship to the total skelelal variability and the taxonomie diversity of the Paleozoic. The
cladograms alone demonstrate the great gap in information of early Carboniferous lineages. If
lepospondyls are a natural group (as indicated by nearly every tree generated) the lineages leading
to adelogyrinids, microsaurs, nectrideans, and lysorophids must hâve existed since at least the
time of occurrence of the first known lepospondyl, the aïstopod Lerhiscus, in the mid-Visean.
Yet lysorophids, microsaurs, and nectrideans are only known with assurance in the Upper Car¬
boniferous. If seymouriamorphs are the sister-group of both lepospondyls and the amniote as¬
semblage, their immédiate ancestors should also be présent in the Lower Carboniferous, but are
not known with assurance until the Upper Carboniferous. and for the seymouriamorphs, the Lower
Permian. There is no direct way to judge the estent of these gaps in ternis of missing data, but
it is almost certain that the early members of ail the lineages were more primitive than their
late Carboniferous dérivatives that contribute to the known data set.
A more spécifie measure of the absence of information is provided by the number of question
marks in the data set, which amount to approximately 15% of the total data. The number of
character States that are unknown is far greater than the number of steps involved in the trees
generated.
Systematic génération and analysis of trees beyond 459 steps become time con.suming. On
the other hand, one can design particular trees to establish how many steps are nccessary to
achieve spécifie relationships. For example, the number of additional steps necessary to produce
sister-group relationships between particular lepospondyls and particular labyrinthodonts, or be¬
tween amniotes and varions other groups. At six steps beyond the most parsimonious cladogram,
seymouriamorphs appear as the sister-group of Westlothiana, diadectomorphs, and amniotes to
the exclusion of lepospondyls, or Westlothiana becomes the si.ster-group of nectrideans. At ten
extra-steps, Westlothiana appears as the sister-group of lysorophids. At thirteen extra-steps:
Fig. 9. — A, strict consensus tree generated via Deliran, at Five steps mure than most parsimonious. B. majority rule (50%)
consensus tree generated via Dcllran, at five steps more than most parsimonious.
A, arbre consensus strict obtenu avec l'option Deltran, cet arbre a cinq pas de plus que l’arbre le plus parcimonieux. B,
arbre consensus, règle de majorité (50%) option Deltran. Ce! arbre a cinq pas de plus que l'arbre le plus parcimonieux.
— 409 —
Strict
Eusthenopteron
Panderichthys
Acanthostega
Ichthyostega
Crassigyrinus
Loxommatids
Anthracosaurs
Seymouriamorphs
Westlothiana
Diadectomorphs
Amniotes
Nectrideans
Microsaurs
Adelogyrinids
Aistopods
Lysorophids
Colosteids
Temnospondyls
Majority ruie
Eusthenopteron
Panderichthys
Acanthostega
Ichthyostega
Crassigyrinus
Loxommatids
Anthracosaurs
Seymouriamorphs
Westlothiana
Diadectomorphs
Amniotes
Nectrideans
Microsaurs
Adelogyrinids
Aistopods
Lysorophids
Colosteids
Temnospondyls
— 410 —
lysorophids are the sister-group of amniotes, diadectomorphs and West lot hiana. At 16 - sey-
mouriamorphs and temnospondyls are sister-groups; at 21 - seymouriamorphs and lysorophids;
at 28 - anthracosaurs and lysorophids; and at 32 - lysorophids and colosteids. The latter still
represents only a 7% increase in the total number of steps.
DELTRAN AND ACCTRAN
Another way to judge the relative adequacy of this data to détermine spécifie relationships
can be gained by comparison of the number and identity of the characters assigned by the al¬
ternative options Deltran and Acctran (Fig. 10).
The procedure followed by these options either accelerates or delays the lime at which a
particular character change is indicated, within the standard parsimony constraints (Swofford,
1993: 20). If two patterns of character distribution are equally parsimonious, but one involves
an earlier change in character State than the other, it will be selected by Acctran. Conversely,
Deltran delays the time at which the change is expressed in the cladogram. The amount of
flexibility in these cladograms is greatly increased by the absence of data, which precludes iden¬
tification of the spécifie point in the cladogram where a change must be recognized. Poorly
known forms such as loxommatids may occupy a considérable range of positions. There is no
différence in the pattern of branching that results from chosing the Deltran or Acctran option,
nor the total number of steps in the mosl parsimonious tree. On the other hand, the number of
characters that support each node are very clearly different (table 1 ). The number of character
changes between fish and tetrapods (in tree 2 of the most parsimonious trees) differs from 61
to 88, nearly a 50% increase. This gives a very different impre.ssion of the number and nature
of character changes that are involved in the origin of tetrapods. At the other end of the scale,
some terminal taxa were distinguished by many more steps under Deltran than wilh Acctran.
For example, Acanthostega shows 18 apomorphies with Deltran, and 9 with Acctran. Lysorophids
show 28 wilh Deltran and 17 with Acctran. These différences, between trees with globally equal
parsimony, is siarlling. Examinalion of the apomorphy list showed that nol only Ihc number,
but the spécifie characters involved differed signiFicantly depending on the option used.
Omilling the nodes leading to Eusihenopteron and Panderichtliys (which do not differ), the
number of character transformations in tree # 2 of the four most parsimonious trees recognized
by both Deltran and Acctran totals 292, compared with an addilional 270 .steps recognized by
one or the other option, but not both. This portion of the most parsimonious tree has 429 steps,
but only 292 of these transformations are spécifie to particular nodes. Two hundred and seventy
Fig. 10. — Comparison of branch lengihs in the most parsimonious trees generateti by A. Deltran, and B. Acctran. Both trees
total 454 steps.
Comparaison des longueurs de branches des arbres les plus parcimonieux obtenus par A. option Deltran et B, option Actran.
La longueur des arbres est de 454 pas évolutifs.
— 411 —
Eusthenopteron
Panderichthys
Acanthostega
Ichthyostega
Crassigyrinus
Loxommatids
Anthracosaurs
Seymouriamorphs
Westlothiana
Diadectomorphs
Amniotes
Nectrideans
Microsaurs
Adelogyrinids
Aistopods
Lysorophids
Colosteids
Temnospondyls
Eusthenopteron
Panderichthys
Acanthostega
Ichthyostega
Crassigyrinus
Loxommatids
Anthracosaurs
Seymouriamorphs
Westlothiana
Diadectomorphs
Amniotes
Nectrideans
Microsaurs
Adelogyrinids
Aistopods
Lysorophids
Colosteids
Temnospondyls
— 412 —
transformations may hâve occurred one or more nodes above or below. That is, 62.9% of the
assignments of character State changes are equi vocal as to node. Thèse character changes are
useful in establishing the geometry of the tree, since it does not differ from Deltan to Acctran,
but they can give a very misleading view of what spécifie changes characterize particular nodes
and taxa.
CONSIDERATION OF PARTICULAR NODES
Tins analysis shows a great many character States changes between known osteolepiform
fish and the carliest known tetrapods, Sixty or 61 are tabulated in the four most parsimonious
cladogram run under Deltran. and 88 in Acctran. These numbers are far in excess of those that
occur elsewhcre in thèse cladograms. This certainly rcllects a major change in structures
throughout the skeleton. and implies major différences in their way of life. Cl.ACK & COATES
(1995) emphasis that incrcasing knowledge of Acanthosiega and Icitfhyostcga arc bluring the
apparent distinction between fish and tetrapods and that subséquent discoveries are likely to
reduce this number until récognition of teirapod .status will dépend on formai définitions based
on the achievement of particular attributes. However. even discounting ail of the possible reversais
and homoplastic origin of advanced characters that may occur in early tetrapods, the currently
available evidence points to a major reorganization between osteolepiforms and early amphibians.
The taxa Acanthosiega, Ichihyoslega. Crassigyrinus. and loxommatids appear as progressive
steps in a scalu naiurae based on the progressive accumulation of derived characters with little
real resolution of interrelationships (see discussion of this problem in Panchen, 1991). The
characters cited by Panchen & SMITHSON (1988) to support spécifie inteiTelationships among
this assemblage may hâve greater significance than appears in these trees, but they are swamped
by other data.
Too liltle is yet known of loxommatids for their spécifie affinities to be established. In the
most parsimonious trees, three characters support a node uniting loxommatids with colosteids
and temnospondyls, compared with 10 uniting colosteids and temnospondyls to the exclusion of
loxommatids; the latter pattern is considered more probable. AH other Paleozoic tetrapods appear
to belong to two divergent groups, the colosteids and temnospondyls on one hand, and ail the
rest on the other.
Several papers hâve proposed a sister-group relationship between temnospondyls and mi¬
crosaurs (e.g. Smithson, 1985; MiLNER, 1994). For that reason a search was made to locate
trees constrained to show relationships between these groups. Four trees were found with a length
no less than 479 steps; 25 steps more than the most parsimonious trees. Four to Hve characters,
showing a great deal of homoplasy elsewhere in the tree, supported their sister-group status. On
the basis of the data presented here, the similar derived characters cited by Smithson & Milner
must be assumed to be homoplastic (e.g. the shape of the humérus) or primitive (e.g. support
of the braincase by contact between the exoccipitals and postparietals) (CaRROU. & ChorN,
1994). On the other hand, ail the cladograms generated strongly support a sister-group relationship
between colosteids and temnospondyls.
— 413 —
Seymouriamorphs occupy a crucial position in nearly every cladogram, at the base of a
radiation including diadectomorphs and amniotes on one hand and lepospondyls on the other.
This phylogenetic hypothesis raises several crucial and interrelated questions.
1 - Are seymouriamorphs a plausable sister-group of amniotes and lepospondyls?
2 - Are lepospondyls a plausable sister-group of amniotes?
3 - Are lepospondyls a natural group?
Critical to this problem is the putative monophyly of lepospondyls. Their unity is recognized
up to 4 steps bcyond the most par.simonious cladogram. Beyond this leveU one or other of the
orders may appear as the sister-group of other taxa in some trees, but even in cladograms
generated al 23 steps beyond the most parsimonious, the general cohésion of the group is reiained.
Despite the consistant unity of lepospondyls reflecled in these cladograms. analysis of the
supporting characiers does not give strong credence to this phylogenetic hypothesis.
The apomorphies of the lepospondyls differ in each cladogram, but in tree 2 of the most
parsimonious cladograms, their monophyly is supported by the following synapomorphies ac-
cording to the Deltran option (node 24).
7. Prefrontal enters narial opening.
12. Loss of squamosal embayment.
57. Loss of relractor pit.
85. Loss of proatlas.
86. Loss of atlas intercentrum.
87. Latéral expansion of atlas centrum.
101. Trunk intercentra lost.
162. Non-bifurcate iliac blade. Only 162 is not also recognized by Acctran.
In Acctran only;
59. Braincase supported by contact of opisthotic and skull roof.
71. Appearance of a short retroarticular process.
84. Broad articulating surface of occiput.
91. Axis intercentrum lost.
100. Capitulum of rib articulâtes with margin of more anterior centrum.
If lepospondyls are a monophyletic group, it would be expected that the most primitive
character States observed in any one subgroup would be plesiomorphic for lepospondyls as a
whole, unless there was strong cvidence for reversai. For that reason, the presence of a narrow
occipital articulation seen in adelogyrinids and aïstopods is presumably primitive for lepo¬
spondyls. The presence of a proatlas in aïstopods and lysorophids is much more likely to be a
primitive feature of lepospondyls than the resuit of re-elaboration of this élément in Iwo lineages.
Adelogyrinids appear to relain a squamosal embayment, but the fusion of the squamosal and
the tabular make the homology of this area difficull to evaluate. The bifurcale iliac blade pre.sent
in microsaurs is almost certainly a primitive feature for that order (since it is lo.st in Permian
généra), and is probably primitive for tetrapods and lost among lepospondyls. The présence of
intercentra in some part of the column in microsaurs may be primitive for lepospondyls. In most
— 414 —
lepospondyl groups the braincase is supported by contact between the postparietals and the ex-
occipitals, a condition that is probably primitive for tetrapods (CarroLL & Chorn, 1994). The
condition in some nectrideans of contact between the opisthotic and the skull roof is very unlikely
as a synapomorphy of lepospondyls. It is more likely that a retroarticular process evolved within
the lepospondyls, rather than being primitive for the group and then being lost. The loss of the
retractor pit for the rectus eye muscles seems a very unlikely reversai.
The current study reveals no certain cranial synapomorphies. The entrance of the prefrontal
into the narial opening might be primitive for the group. but aiso occurs in early colosteids. In
a recent évaluation of lepospondyl relationships (Carrolt & CHORN, 1994), three vertébral fea-
tures were recognized as apparent synapomorphies: atlas pleurocentrum formed as a single center
of ossification without a distinct alla.s intercenirum, proatlas lacking spécifie articulating surfaces
for the extcmal surface of the occiput, single cylindrical trunk centra occupying entire length
of segment. If study is concentrated on the lepospondyls, without atiempting to integrate the
character distribution within this group with that of ail other Paleozoic tetrapods to achieve a
single most parsimonious pattern, the number of unique derived characters that they ail share
is very limited, but may indicate a common origin, distinct front that of any other groups of
Paleozoic tetrapods.
Within the lepospondyls, the most constant feature of the cladograms is the sister-group
position of adelogyrinids and aïstopods. This can certainly be attributed to the common derived
condition of limb loss. When the data pertaining to limbs is omitted, adelogryinids and aïstopods
assume a variety of positions among the lepospondyls, but this does not alter the unity of the
group as a whole. Unfortunately, there is no direct way to judge whether limb loss is homologous
in the two groups. The very different pattern of the skulls. and the rétention of a primitive
pattern of the dermal shoulder girdie in adelogyrinids suggest that limb loss is not homologous
but occurred by homoplasy, as in the case a many lineages of limbless lizards (CREER, 1991).
Among the four most parsimonious trecs. the geometry of the lepospondyls differs in having
either the nectrideans (trees I and 3) or the microsaurs (trees 2 and 4) as the sister-group of
ail other lepospondyls. These différences are based on the timing of the loss of intercentra and
supratemporal, the gain and/or loss of a retroarticular process, and changes in the humerai shaft.
Either way, a number of reversais must be assumed.
The proposed sister-group relationship between amniotes, Westlothiana, and diadectomorphs
on one hand and lepospondyls on the other is even more difficult to assess. Node 25 shows the
following derived characters as uniting these groups.
4. Latéral line canals not expressed in adults.
23. Loss of intertemporal.
34. Absence of fangs on vomers.
35. Loss of palatal fangs.
38. Loss of labyrinthine infolding.
70. Large, elongaie foramina between prearticular, angular, and splenial.
77. Stapes inclined to margin of jaw.
99. Reduced length of transverse processes.
139. Réduction in length of entepicondyle.
— 415 —
Ail but 34, 70 and 77 are recognized by both Deltran and Acctran.
Acctran also recognizes:
12. Réduction of squamosal embayment.
15. Pre.sence of post-temporal fossa.
44. Cheek vertical.
63. One splenial.
84. Hcmispherical occipital condyle.
93. Arch and pleurocentrum of axis fused.
131. Distinct shaft of humérus.
132. Increased torsion of humérus.
150. Présence of pisiform.
Most characters that support these affiliations are subject to a number of reversais, and/or
are of uncertain homology. Characters 4, 12, 44, 63, 93, 99, 131, and 150 are probably not
présent in the most primitive lepospondyls, although they do occur in one or more généra within
this group. Character 15 is probably primitive for tetrapods, but changes in Seymouria and so
must reverse in a transition toward either amniotes or lepospondyls. It is not an appropriate
synapomorphy of lepospondyls and the amniote assemblage. The character State change indicated
by 84 is subsequently modified among lepospondyls, which hâve evolved very different patterns
of articulation between the occiput and the first cervical. It is not a synapomorphy of the two
groups. Labyrinthme infolding (38) is présent in the most primitive diadectomorphs. A large
opening on the médial surface of the lower jaw (70) is présent only sporadically in each group
and is an unreliable character for establishing relationships. It appears at this position in a clado-
gram in which nectrideans are the sister-group of other lepospondyls, but not if this position is
assumed by microsaurs.
It has been suggested (Carroll, 1986a, 1989) that several of the derived features shared
by lepospondyls and amniotes may be the resuit of small size, rather than common ancestry.
This applies particularly to the loss of palatal fangs, infolding of the enamel, and lo.ss of some
skull bones. The closure of the squamosal notch may hâve a similar explanation. To test this
hypothesis, characters 12, 23, 34, 35. 36, and 38 were removed from the data matrix. However,
this did not alter the basic pattern of the four most parsimonious trees, nor the seven generated
with one additional step. Among the 28 trees generated at two steps more than the most parsi¬
monious, one showed seymouriamorphs as the sister-group of lepospondyls, and the.se two as
the sister-group of amniotes, diadectomorphs, and Westlothiam. Seventy-one trees were generated
at three steps beyond most parsimonious. The strict consensus tree showed a polytomy of sey¬
mouriamorphs, Wesllothiana, diadectomorphs, amniotes, and the common ancestor of ail the lepo-
spondyl groups. Individual cladograms showed Westlothiana as the sister-group of lepospondyls,
and as the sister-group of lepo.spondyls plus diadectomorphs and amniotes, and seymouriamorphs
as the sistcr group of Westloihiaua, diadectomorphs and amniotes, and these logether as the
sister-group of lepo.spondyls, and seymouriamorphs as the sister-group of lepospondyls and these
together as the sister-group of diadectomorphs and amniotes. Nevertheless, the basic integrity
of the lepospondyls and the unity of Westlothiana, diadectomorphs, and amniotes remained despite
the removal of these characters.
— 416 —
Carroll (1989) has also argued that lhe cylindrical shape of the vertebrae may be con-
vergently achieved atnong early tetrapods, as it has been in teleosts and lissamphibians. Removal
of vertrebral characteristics from the data matrix leaves it so reduced (especially aniong limbless
lepospondyls) as to question the validity of any resulting trees. Resolution of this problem requires
discovery of the plesiomorphic sister-groups of both lepospondyls and the amniote assemblage
from the earliest Carboniferous to résolve lhe early stages in the évolution of iheir vertébral
patterns.
This leave only two characters, 77 and 139, that are not either subject to extensive reversais
or of dubious homology, to support the sister-group relationship of lepospondyls and the amniote
assemblage.
Whelher or not lepospondyls and amniotes are sister-groups, there remains the problem of
their affinity with seymourimorphs. According to the character change list generated via Deltran,
the following synapomorphies identify seymouriamorphs as lhe sister-group of higher tetrapods.
36. Loss of fangs on ectopterygoid.
43. Distinct epipterygoid.
59. Brainca.se supported by double articulation between tabular and opisthotic without con¬
tribution of stapes.
61. Reduced size of occipital articulation relative to size of foramen magnum.
68. Loss of parasymphysial fangs.
82. Stapes looses contact with palatoquadrate, but impédance matching middle ear not
developed.
88. Atlas pleurocentrum cylindrical.
92. Axis pleurocentrum cylindrical.
96. Supraneural canal does not penetrate arch.
102. Trunk pleurocentra cylindrical.
103. Reduced number of presacral vertebrae.
136. Loss of keel of humérus.
137. Separate supinator process.
180. Phalangeal count of pes 2, 3, 4, 5, 4.
Ail but 103 vvere also identified by Acctran, which also recognized:
77. Stapes extends toward jaw articulation modified in Seymouria.
132. Increased torsion of humérus.
176. Tibiale and intermedium distal to tibia.
Together, this appears as a very convincing list of synapomoiphies. The question then arises
as to the reliability of character States exhibited by known seymourimorphs to establish rela-
tionships with lepospondyls. If seymouriamorphs are the sister-group of lepospondyls (and lepo¬
spondyls are a natnral group), they must share an immédiate common ancestry no laler than the
mid-Visean, at which time the oldest lepospondyl Lethiscus is known. Had lhe character States
that are shared by known seymouriamorphs evolved by that time? In fact, seymouriamorphs are
known no earlier than the early Permian, some 60 million years laicr. Seymouriamorphs are the
only major group of tetrapods known in the Lower Permian that hâve no known représentatives
— 417 —
in the Carboniferous. Many character State changes occurred between the Lower Carboniferous
and the Lower Permian within other lineages, showing that character States in derived taxa do
not necessarily reflect their affinities vvith other groups that diverged in the Devonian or Lower
Carboniferous. For example, the following characters that seyinouriamorphs share with amniotes
and lepospondyls are also présent in advanced, but not primitive anthracosaurs: axis pleurocen-
trum cylindrical. supraneural canal does not penetrate arch, irunk pleurocentra cyliiidrical. reduced
number of presacral vertebrae. The character States exhibited by Permian seymourimorphs were
probably also derived relative to those of their plesiomorphic sister-group, but there is cunently
no way to know what character States their unktiown Carboniferous ancestors may hâve had.
This, however, is simpiy a matter of uncertainty, and does not provide any evidence contrary
to a sister-group relalionship with either lepospondyls or amniotes.
A sister-group relalionship between amniotes and diadectomorphs is now generally accepted
(SuMiDA & Lombard, 1991), and is well suppoiled by these cladograms. The most interesting
recent discovery that may be associated with the ancestry of amniotes is thaï of Wesüothiana
from the Brigantian of Scotland (SMITHSON et ai. 1993). The most parsimonious cladograms
indicate the same phylogentic position as hypothesi/ed by SMITHSON et al., as the sister-group
of diadectomorphs and amniotes. This is supported by the following synapomorphies, according
to Deltran.
3. Suturai attachment of postfrontal and pariétal to postorbital.
12. Loss of squamosal notch.
44. More vertical cheek.
63. One splenial.
95. Arches fused to centrum during development.
104. Two sacral vertebrae.
132. Increased torsion of humérus.
162. Reduced dorsal process of ilium.
Only 3, 95, 104 and 162 are also recognized by Acctran.
Acctran also recognizes;
15. Posttemporal opening between otic capsule, supraoccipital and cheek.
51. Supraoccipital a broad plate of bone closely attached to tabulars and otic capsule loose
attachment in amniotes.
60. Hemispherical occipital condyle a critical character, but not actually observed in Wesüothiana.
64. Two coronoids.
151. Pisiform also not observed in Wesüothiana.
176. Tibiale, intermedium and centrale distal to tibia.
In the next most parsimonious trees, Wesüothiana appears also as the sister-group of amni¬
otes. with diadectomorphs as the out-group. At two steps beyond the most parsimonious clado¬
grams, Wesüothiana is represented as either the sister-group of lepospondyls, or as the sister-group
of diadectomorphs to the exclusion of amniotes, or as the sister-group of an assemblage including
lepospondyls, diadectomorphs, and amniotes. As eisewhere in the cladogram, it is dilïicult to
— 418 —
argue for a spécifie phylogenetic position for this taxon. This may be attributed partially to the
fact that 20% of its anatomy remains unknown.
The uncertainties raised by this phylogenetic analysis indicate that we are still very far
from establishing a dependable phylogeny of Paleozoic choanates. As argued by Donaghue et
al. (1989), this can only be accomplished by a better knowledge of the more plesiomorphic
sister-groups of ail the taxa in question.
SUMMARY AND CONCLUSIONS
Phylogenetic analysis has been performed on a large data set représentative of the entire
skeleton of ail major groups of Paleozoic tetrapods. Fully resolved cladograms resuit in a
sequence of labyrinthodont groups that are successive sister-groups of an assemblage including
seymouriamorphs as the sister-group of two clades, the lepospondyls on one hand and Westlothi-
ana. diadeciomorphs and amniotes on the other. Up to five steps beyond the most parsimonious
cladogram, lhere is strong .support for a sequence of progressively more derivcd labyrinthodonts
groups in the order Acunthostega. Ichihyostega, Cnt.'t.iigyrinus, loxommatids, anthracosaurs and
seymouriamorphs. The affinities of colosteids and temnospondyls is strongly supporled but this
clade may appear either beknv or (riirely) ahove the position of the anthracosaurs. The lepo¬
spondyls and the clade including Wesllothiana, diadectomorph.s, and amniotes maintain their in-
tegrity at a level five steps beyond the most parsimonious trees.
Running the data alternatively with the Deltran and Acctran options shows that more than
60% of the character siale changes cannot be specified as occuring at parlicular nodes. This
ambiguity results from missing data, This can be attributed to two major factors; (1) lack of at
leasi some data from ail known taxa; (2) lack of any information of more plesiomorphic members
of recognized clades that must hâve been présent during the 30 million years of the Lower
Devonian and Early Carboniferous. but are nol known from the fossil record.
In the absence of data from more plesiomorphic members of the major groups. it is not
possible to détermine what derived charaeters were présent in the earliesl members of these
clades, or whether or notsimilar charaeters in different clades arc homologous. This is particularly
crucial in the case of seymouriamorphs which lack any Carboniferous représentative, but appear
as the sister-group of bolh lepospondyls and the clade including amniotes, both of which must
hâve diverged early in the Lower Carboniferous.
The pre.sence of numerous reversais, questionable homologies, and the scarciiy of well es-
tablishcd synapomoiphics cast doubts on the acceptance of the lepospondyls as a monophyletic
clade and on the sister-group status of lepospondyls and the assemblage including Westlothiana,
diadeciomorphs and amniotes.
No matter how cogcnl the underlying théories of phylogenetic sysiematics, or how effective
the computer software, there is no way to produce a reliable phylogeny in the absence of de-
pendable data. In the case of the radiation of early tetrapods, the almost complété absence of
data from the first 25 million years of the Carboniferous makes it extremely difficult to détermine
character States in the most plesiomorphic members of these clades that can be used to establish
— 419 —
sister-group relationships. The only solution to this problem is to discover and describe fossils
from this crucial stage in the évolution of vertebrates.
The data matrix presented here, should, nevertheless, provide a useful framework for sub¬
séquent Work on the phylogeny of early tetrapods. It provides a means of charactetizing each
particular clade. and for demonstrating what changes hâve occurred from one group to another.
The cladograms presented here should be recognized as a représentation of the most par-
simonioüs distribution of known character States, rather than of the biological relationship of
the taxa. PAUP and other computer packages are a conveiiienl way to manipulate data, but there
is no way in which they can déterminé wheiher or not characters are homologous, or whether
particular transformations are biologically probable. SCOTT & Janis (1993; 300) hâve discussed
this and related problems in a forceful, but humorous style, concluding, "... computer programs, ...
like the White Queen, can believe six impossible things before breakfast".
Acknüwledgements
I particularly wish to thank Drs Jermifer Clack and Michael Coates for providing unpublished draw-
ings and manu.script.s based on lheir current siudy of Aaiiilliostegn and Euxthenopteron. Ail illustrations
hâve been redrafted for this paper by Pamela Gaskill. Heinrich KAISER and Michael Lacrin assisted with
the cladistic analysis. This work was support by grants from the Natural Sciences and Engineering Research
Council of Canada.
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Table 1. — Comparison of number of character State changes recognized by Acctran and Deltran.
Tableau comparatif du nombre de changements d'états de caractères reconnus par les options Acctran et Deltran.
— 424 —
APPENDIX I
Distribution of character States in Paleozoic choanate vertebrates.
Data marked with * (pers. comm., Drs Clack and COATES).
Primitive choanate condition Derived condition
SKULL KINESIS
1- 0. Mobility between anterior and
posterior éléments of skull table
2- 0. Mobility between lacrimal and
prefrontal
3- 0. Mobility between skull table and
cheek latéral to postfrontal, intertem¬
poral, supratemporal, and tabular
1- 1. Interdigitating sutures connect; pariétal and in¬
tertemporal with postparietal and supratemporal;
(Panderichthys and ail tetrapods);
2- 1. Mobility lost {Panderichthys, ail tetrapods ex-
cept early ncctridcans);
3- 1. Suturai attachment of postfrontal and intertem¬
poral with postorbital {Panderichthys},,
3-2. Suturai attachment of pariétal and supratemporal
to postorbital and squamosal {Acanthostega);
3-3. Suturai attachment of postfrontal, pariétal, su¬
pratemporal, and tabular to postorbital and squamosal
{Ichthyostega}-,
3-4. Suturai attachment of postfrontal, intertemporal,
and supratemporal to postorbital squamosal (loxom-
matids, seymouriamorphs, temnospondyls);
3-5. Suturai attachment of postfrontal and pariétal to
postorbital (Westlothiana, diadectomorphs and amni-
otes);
3-6. Suturai attachment of pariétal to postorbital, mo¬
bility between postorbital and jugal (nectrideans);
3-7. Suturai attachment of postfrontal, (pariétal) and
tabular to postorbital and squamosal (microsaurs);
3-8. Suturai attachment of postfrontal and tabular-
squamosal to jugal and quadratojugal (adelogyrinids);
3-9. Suturai attachment of pariétal and tabular to
squamosal (lysorophids);
3-a. Suturai attachment of postfrontal, pariétal, (in¬
tertemporal), supratemporal, and tabular to postorbi¬
tal and squamosal (colosteids);
LATERAL LINE CANALS
4-0. Primitive configuration shown in 4-1. Latéral line canals not expressed in adults (West-
figure IB lothiana, ? diadectomorphs, amniotes, microsaurs, ly¬
sorophids, nectrideans, aïstopods);
— 425 —
5-0. Canals surrounded by bone 5-1. If présent, canals exposed superficially (ail te-
trapods except Devonian généra)'.
SKULL OPENINGS
6-0. Single narial opening on latéral
surface of snout
7-0. Nasal openings bordered by ante-
rior rostral and latéral tectal
8- 0. Pineal opening surrounded by
several small pineal plates
9- 0. Orbits facing laterally
10- 0. Bones surrounding orbit:
pre- and postfrontal, postorbital,
jugal, and lacrimal
11- 0. Orbit, round, oval, or rhomboidal
12- 0. Narrow slit for spiracle between
squamosal, tabular and supratemporal
6-1. Narial opening facing ventrally (Panderichthys,
Acanthostega, Ichthyostega, primitive anthracosaurs);
6- 2. Secondarily latéral position (ail tetrapods except
6-1);
7- 1. Opening bordered by anterior tectal, premaxilla,
and maxilla {Acanthostega)'.
7-2. Opening bordered by anterior tectal, latéral ros¬
tral, premaxilla and maxilla {Ichthyostega)',
7-3. Opening bordered by premaxilla, maxilla and
lacrimal (anthracosaurs);
7-4. Opening bordered by premaxilla, maxilla, lacri¬
mal, nasal, and scptomaxilla (loxommatids, seymouria-
morphs, Westlolhiana, diadeclomorphs; amniotes,
temnospondyls, and ? adelogyrinids);
7- 5. Opening bordered by premaxilla, maxilla, lacri¬
mal, nasal, prefrontal (? microsaurs, nectrideans, ly-
sorophids, aïstopods, colosteids);
8- 1 . Loss of pineal plates {Panderichthys and ail te¬
trapods);
8- 2. Loss of pineal opening (lysorophids);
9- 1. Orbits close to midiine and facing dorsally
{Panderichthys. Crassigyrinus),
10- 1. Pre-and postfrontal, postorbital, and jugal
{Ichthyostega, Acanthostega, Crassigyrinus)',
10-2. Frontal, pre- and postfrontal, postorbital, jugal,
lacrimal (amniotes);
10-3. Prefrontal. lacrimal, maxilla, palatine,
squamosal, pariétal (lysorophids);
10-4. Pre- and postfrontal, jugal, lacrimal
(adelogyrinids);
10- 5. Pre- and postfrontal, jugal. maxilla,
lacrimal (aïstopods);
11- 1. Keyhole shaped (loxommatids);
11- 2. Open posteriorly (lysorophids);
12- 1. Squamosal embayment bordered by tabular
and squamosal {Ichthyostega, Acanthostega)',
12-2. Squamosal embayment bordered by tabular,
supratemporal, and squamosal {Crassigyrinus. loxom¬
matids. anthracosaurs. seymouriamorphs);
— 426 —
12-3. Squamosal and supratemporal modified to sup¬
port tympanum (temnospondyls);
12-4. Notch reduced to slit between supratemporal
and squamosal {Westlothiana, diadectomorphs, amni-
otes);
12-5. Embayment in tabular squamosal (adelogy-
rinids);
12- 6. Loss of embayment (microsaurs, nectrideans,
lysorophids, aïstopods, colosteids);
13- 0. Cheek fully ossified 13-1. Postfrontal, postorbital, and jugal lost to form
large opening confluent with orbit (ly.sorophids);
13- 2. Large open space between squamosal and post¬
orbital and jugal covered with osteoderms (aïs¬
topods);
14- 0. Mouth terminal 14-1. Mouth subterminal (Panderichthys)\
15- 0. Large openings in occiput for 15-1. Fenestrae for fossa bridgei reduced to small
fossa bridgei post-temporal fossae, passing between; otic capsule
and tabular and postparietal (loxommatids, temno¬
spondyls, colosteids, microsaurs, ? aïstopods);
15-2. No openings (anthracosaurs, Crassigyrinus,
seymouriamorphs);
15-3. Post-temporal fossae between otic capsule, su-
praoccipital and cheek (diadectomorphs, amniotes);
15-4. Post-temporal fossae between otic capsule, ex¬
occipital, and postparietal (the nectridean Diplocer-
aspis);
15-5. Opening between otic capsule and tabular squa¬
mosal (adelogyrinids);
15- 6. Opening between exoccipital, postparietal and
supraoccipital (lysorophids);
INDIVIDUAL BONES OF SKULL ROOF
16- 0. Mosiac of numerous rostrals 16-1. Single pair of rostrals (internasals) (Acan-
thostega and loxommatids);
16- 2. Médian rostral (Ichthyostega)\
16-3. Opening in skull between premaxillae and
nasals (Crassigyrinus);
16-4. Elimination of rostrals (ail other tetrapods);
17- 0. Presence of latéral rostral 17-1. Loss of latéral rostral, or modification of this
bone to septomaxilla (ail tetrapods except Ichthy-
ostega and Crassigyrinus);
— Ml —
18- 0. Presence of anterior tectal
19- 0. Presence of preopercular
20- 0. Squainosal reaches maxilla, sepa-
rating jugal from quadratojugal
21- 0. Maxilla reaches quadratojugal
22- 0. Quadratojugal présent
23- 0. Presence of intertemporal
24-0. Tabular separated from pariétal
by supratemporal
25-0. Posterior margin of tabular
forms straight line or gently curved
surface with postparietal
26- 0. Supratemporal présent
27- 0. Postparietal paired
28- 0. Three extrascapular bones
29- 0. Operculum, consisting of opercu-
lar, subopercular, and submandibular
plates
18- 1. Loss of anterior tectal (ail tetrapods except
Ichthyostega, Acaniliostega, and Crassigyrinus. ? lo-
xommatids):
19- 1. Absence of preopercular (ail tetrapods except
Ichthyostega, Acanthostega, and Crassigyrinus)',
20- 1. Jugal and quadratojugal in contract separating
squamosal and maxilla (some .specimens of Pander-
ichthys and ail tetrapods);
21- 1. Jugal reaches jaw margin, separating excluding
jugal from skull marginquadratojugal and maxilla
(early amhracosaurs, seymouriamoiphs, Westlothiana,
diadectomorphs, amniotcs. ? ncctridcans, microsaurs);
22- 1. Loss of quadratojugal (lysorophids);
23- 1. Loss of intertemporal (the panderichthyid FJpis-
tostege, Devonian tetrapods, most loxommatids, most
temnospondyls, ail microsaurs, aïstopods, nec-
trideans, adelogyrinids, Acherontiscus, Westlothiana,
diadectomorphs, amniotes);
24- 1. Tabular in contact with pariétal in presence of
distinct supratemporal; (most anthracosaurs, sey-
mouriamorphs, Westlothiana, diadectomorphs. amni¬
otes, nectrideans);
24- 2. Tabular in contact with pariétal in absence of
separate supratemporal (microsaurs, lysorophids,
adelogyrinids);
25- 1. Posterior extension of tabular latéral to an em-
bayment (Acanthostega)',
25-2. Conspicuous tabular horn (anthracosaurs, ?
Crassigyrinu.s)',
25- 3. Posterior extension in conjonction with fused
squamosal (adelogyrinids);
26- 1. Supratemporal absent (microsaurs, lysorophids,
adelogyrinids);
27- 1. Posiparietals fused at midline (Ichthyostega, di¬
adectomorphs);
28- 1. Loss of extrascapulars (ail tetrapods);
29- 1. AU bones lo.st in tetrapods except for sub¬
opercular in Ichthyostega',
PALATE
30-0. Unpaired anterior palatal recess 30-1. Paired recesses (Acanthostega-, the colosteid
between premaxillae and vomers Greererpeton)-,
428 —
31- 0. No interpterygoid vacuity
32- 0. Premaxilla and maxilla form a
straight line latéral to the choana
33- 0. Premaxilla foiTns border of
choana
34- 0. Large fang and pit pairs on
vomers
35- 0. Large fang and pit pairs on
palatine
36- 0. Large fang and pit pairs on ec-
topterygoid
37- 0. Row of denticles latéral to
palatal fangs, bordering the choana
and meeting at the midiine of the
vomers;
38- 0. Labyrinthine infolding of dentine
39-0. Parasphenoid not covering ven¬
tral cranial fissure
40- 0. Teeth of upper and lowr jaw of
approximately the same size
41- 0. Base of otic-occipital covered
by parotic plates
42- 0. Endochondral palatoquadrate ar-
ticulating anteriorly with olfactory cap¬
sule
43- 0. Palatoquadrate incorporating
epipterygoid
30.2. Loss of recess (ail tetrapods except; Ichthy-
ostega, C rassi gyrinus, and loxommalids);
31- 1. Large interpterygoid vacuities (temnospondyls,
colosteids);
32- 1. Maxilla curves medially and is loosely, if at
ail,, attached lo premaxilla (Panderichthys, Ichthy-
ostegci. Acanthostega, early anthracosaurs);
33- 1. Premaxilla attached to vomer, excluded from
niargin of choana {Ichthyostega, C rassi gyrimts*)\
34- 1. Absence of fangs on vomers (anthracosaurs,
Wesihithiana, diadectomorphs. amniotes,, microsaurs,
nectrideans, adelogyrinids. lysorophids, aïstopods);
35- 1. Absence of fangs on palatine (Westlothiana, di¬
adectomorphs, amniotes, nectrideans, microsaurs,
adelogyrinids, lysorophids, aïstopods);
36- 1. Absence of fangs on ectopterygoid (Acan-
thostega, seymouriamorphs. Westlothiana, diadecto¬
morphs, amniotes, nectrideans. microsaurs,
adelogyrinids, lysorophids, aïstopods);
37- 1. Absence of denticle row (ail tetrapods except
Acanthostega, Crassigyrinus*)',
38- 1. Absence of infolding {Westlothiana, amniotes.
nectrideans, microsaurs, lysorophids, adelogyrinids.
aïstopods);
39- 1. Para.sphenoid extending only a short distance
across fissure {Acanthostega and C rassi gyrinus)',
39- 2. Parasphenoid covering much of basioccipital
(ail olher tetrapods);
40- 1. Conspicuously larger teeth in dentary than ma¬
xilla (colosteids, temnospondyls);
40- 2. Canine teeth in maxilla (amniotes);
41- 1. Loss of parotic plates (ail tetrapods);
42- 1. Loss of articulation between palatoquadrate and
olfactory capsule (ail tetrapods);
43- 1. Distinct epipteryoid (ail tetrapods except
Devonian généra, Crassigyrinus, loxommatids, primi¬
tive anthracosaurs and colosteids);
43-2. Loss of epipterygoid (lysorophids, ? aïstopods);
— 429 —
44-0. Cheek slopes posteriorly, jaw ar¬
ticulation behind occipital condyle
45-0. Jaw suspensorium continuons
with cheek
46- 0. Presence of ectopterygoid
47- 0. Pterygoid extends in a continu¬
ons
48-0. Palatoquadrate articulâtes freely
with base of braincase via basicranial
articulation
44-1. Cheek more vertical, jaw articulation approxi-
mately at level of occipital condyle (Wesllolhiana, di-
adectomorphs, amniotes, microsaurs, adelogyrinids);
44- 2. Jaw articulation significantly anterior to occi¬
pital condyle (lysorophids);
45- 1. Jaw suspensorium consisting of tabular and
squamosal angling forward front skull table (ly¬
sorophids):
45- 2. Suspensorium consisting of squamosal and
quadratojugal, angling posteriorly from .skull table
(aïstopods);
46- 1. Absence of ectopterygoid (lysorophids);
47- 1. Quadrale ramus of pterygoid deepiy curve
around adductor fossa embayed; to form transverse
flange without teeth (seymouriamorphs);
47- 2. Transverse tlange bears a row of denticles (di-
adectomorphs and amniotes);
48- 1. Restriction of mobility of palate and base of
braincase (colosteids, temnospondyls, microsaurs);
48-2. Loss of articulating surface on pterygoid
(adelogyrinids, lysorophids);
BRAINCASE
49- 0. Anterior ethmoid and posterior
50- 0. Both portions of braincase
ossified as single éléments
51-0. No separate supraoccipital
52-0. Nasal capsule fully ossified
49- 1. Loss of articulation (ail tetrapods); otic-occl-
pital appears capable of; articulation;
50- 1. Exoccipital, basioccipital, opisthotic. and pro-
otic separaiely ossified (ail tetrapods cxcept aïs¬
topods, condition in Ichthyoslega, Acanthostega not
descri bed);
51- 1. Supraoccipital a broad plate of bone closely at-
tached to tabulars and otic capsule (diadectomorphs);
51-2. Supraoccipital a broad plate of bone loosely at-
tached to the postparietals and separating them from
the exoocipitals (amniotes);
51-3. Supraoccipital a narrow ossification beneath
skull roof, not separating postparietals from exocci-
pitals (microsaurs);
51- 4. Supraoccipital reaching parietals between post¬
parietals, not separating postparietals from exoccipi-
tals (lysorophids);
52- 1. Posterior and latéral wall not ossified {Pander-
ichthys'y,
52-2. No ossification of nasal capsule (ail tetrapods);
— 430 —
53- 0. Basicranial process for articula¬
tion with palate on ethmoid élément
54- 0. Latéral commissure forms stout
ridge latéral to otic capsule and sur¬
rounds jugular canal
55- 0. Two surfaces for articulation hy-
omandibular on latéral commissure
56- 0. Large unossified area on ven-
trolateral wall of otic capsule
57- 0. Eye muscles not originating
from a retractor pit
58- 0. Absence of pleurosphenoid
59- 0. Braincase attached to back of
skull via grooves for otic capsule in
tabular
53- 1. Basicranial processes on basisphenoid (ail tet-
rapods);
54- 1. Loss of latéral commissure (ail tetrapods in
which braincase is known);
55- 1. Oval head of stapes articulâtes with margins
of fenestra ovalis of otic capsule (ail known tetrapods);
56- 1. Ossification of latéral wall except for area of
fenestra ovalis (ail tetrapods in which otic capsule is
known);
57- 1. Retractor pit in basisphenoid (anthracosaurs,
seymouriamorphs, diadectomorphs, and amniotes);
58- 1. Pleurosphenoid extending from basisphenoid
(lysorophids, some microsaurs);
59- 1. Back of braincase attached to skull roof by
processes from postparietal, not comparable to later
tetrapods (Ichthyostega);
59-2. Braincase support via double articulation be-
tween tabular and opisthotic plus stapes (early an¬
thracosaurs);
59-3. Braincase supported via double articulation be-
tween tabular and opisthotic (seymouriamorphs,
Westlothiana)',
59-4. Braincase supported by double articulation be-
tween tabular and opisthotic plus supraoccipital (di¬
adectomorphs);
59-5. Braincase supported by loose connection be-
tween supraoccipital and postparietal (amniotes);
59-6. Braincase supported by contact of opisthotic
with both tabular and postparietal (loxommatids);
59-7. Braincase supported by contact between ex-
occipitals and postparietals, as well as stapes
(colosteids);
59-8. Braincase supported by contact of opisthotics
and skull roof (nectrideans);
59-9. Otic capsule attached via exoccipital, su¬
praoccipital. and tabular (microsaurs);
59-a. Braincase supported by exoccipital and squa-
mosal tabular (adelogyrinids);
59-b. Braincase supported by otic capsule to su¬
praoccipital, postparietal and cheek (lysorophids);
59-c. Braincase supported by contact of postparietals
and exoccipitals (temnospondyls);
— 431 —
60-0. Otic-occi pilai élément of brain-
case penetrated by notochord, which
extends to ethmoid
61-0. Surface of occiput for articula¬
tion with anterior cervicals much
larger in vertical extent than foramen
magnum
60-1. Notochord does not extent to ethmoid (ail te-
trapod.s except Ichthyostega);
60-2. Occiput penetrated by circulât pit for notochord
(aïstopods);
60-3. Basioccipital deepiy penetrated by notochord
(Acanthûstega, Crassigyrinusy,
60-4. Basioccipital recessed for first cervical (loxom-
matids. anthracosaurs, colosteids seymouriamorphs,
temnospondyls, microsaurs, lysorophids, adelogy-
rinids);
60-5. Basioccipital does not contribute to articulation
with first cervical (nectrideans);
60- 6. Hemispherical occipital condyle (diadecto-
morphs, amniotes);
61- 1. Surface of occiput for articulation with first cer¬
vical significantly .smaller; in vertical extent than
foramen magnum (seymouriamorphs, diadecto-
morphs, amniotes, nectrideans, microsaurs, ly¬
sorophids, adelogyrinids, aïstopods);
LOWER JAW
62- 0. Dentary extends to articular,
surangular not reaching margin of jaw
63- 0. Two splenials
64-0. Three coronoids
65- 0. Large coronoid fangs
66- 0. Pits in coronoids to accommo-
date palatal fangs
67- 0. Parasymphysial (adsymphysial)
plate
68- 0. Parasymphysial fangs
Panderichthys
62- 1. Long exposure of surangular between dentary
and articular (ail tetrapods except Ichthyostega);
63- 1. One splenial (Westloihiana, diadectomorphs,
amniotes, nectrideans, aïstopods);
63- 2. No splenial (lysorophids);
64- 1. Two coronoids (diadectomorphs, amniotes);
64-2. One coronoid (nectrideans);
64- 3. No coronoids (lysorophids);
65- 1. Absence of coronoid fangs (ail tetrapods except
Crassigyrinids);
66- 1. Pits between coronoids (Panderichthys);
66-2. Pits in dentary above coronoids (Crassigy-
rinus);
66- 3. Pits in coronoids lost (ail other tetrapods);
67- 1. Loss of parasymphysial tooth plate (ail tetra¬
pods except Ichthyostega and primitive anthra¬
cosaurs);
68- 1. Absence of parasymphysial fangs, (Eusthenop-
teron, most anthracosaurs. seymouriamorphs, West-
lothiana, diadectomorphs, amniotes, nectrideans,
microsaurs, adelogyrinids, lysorophids. aïstopods);
— 432 —
69- 0. Meckelian bone
70- 0. Several small openings below
margin of prearticular
71- 0. Absence of retroarticular process
72- 0. Conspicuous open latéral line
canal between dentary and infraden-
tary bones
73- 0. Médian and principal gular
plates
69- 1. Loss of meckelian bone (ail tetrapods except
lchthyostega)\
70- 1. Serie.s of small openings in splenials and/or
angular (loxommatids. temnospondyls);
70-2. Small openings along suture between preartic¬
ular and angular and splenial and post.splenial (sey-
mouriamorphs);
70-3. Large elongate fenestra between prearticular,
angular, and splenial (Limnoscelis, nectrideans, aïs-
topods, colosteids);
70-4. Single small opening between splenial and
angular (amniotes);
70-5. Small foramen between prearticular and angular
(microsaurs);
70- 6. No foramina (lysorophids);
71- 1. Short retroarticular process (nectrideans,
adelogyrinids, lysorophids);
72- 1. Absence of this canal (ail tetrapods except
Acanthostega);
73- 1. Loss of gular plates (ail tetrapods);
VISCERAL ARCHES
74- 0. Hyomandibular large relative to
major cranial structures
75- 0. Narrow and elongate
76- 0. No separate dorsal process
77- 0. Extends posterolatero-ventrally
toward jaw articulation
78- 0. Contacts operculum via opercu-
lar facet. to inside of cheek via pre-
opercular facet, to stylohyal
79- 0. Proximal groove for truncus hy-
oideo-mandibularis of VII nerve
80- 0. No canal for stapedial branch of
orbital artery
74- 1. Stapes greatly reduced in relative size (ail tet¬
rapods);
75- 1. Shortened (ail tetrapods);
76- 1. Separate dorsal process (amniotes and some mi¬
crosaurs);
77- 1. Toward top of quadrate ramus of pterygoid
{Acanthostega. colosteids, early anthracosaurs);
77- 2, To notch in tabular {Seymouria)',
78- 1. These contacts lost (ail tetrapods);
79- 1. Loss of this canal {Panderichthys, ail te¬
trapods);
80- 1. Stapes penetrated by stapedial artery (ail te¬
trapods);
80-2. Secondai^ loss of stapedial foramen (seymouri-
amorphs. some microsaurs, lysorophids, aïstopods);
— 433 —
81- 0. Complex link between brain-
case, cheek, and operculum, a.s-
sociated with respiration and feeding
82- 0. Elongate hyomandibular links pa-
latoquadrate and otic capsule
83-0. Fully ossified complex of five
branchial arches, including médial
basibranchial(s). paired hypohylals,
ceratohyals, hypobranchials, and cera-
tobranchials ventrally. and epibran-
chials, infrapharyngobranchials, and
suprapharyngobrancliials dorsally. In
Eusthenopteron ail covered by dermal
dental plates
81- 1. Rôle of hyomandibular associated with feeding
much reduced or lost (ail tetrapods);
82- 1. Stapes reduced in size, but links otic capsule
with palatoquadrate {Acanthostega, primitive anthra-
cosaurs, colosicid.s);
82-2. Stapes loses broad contact with palatoquadrate
but not incorporated in an impédance matching Sys¬
tem (all other early tetrapods except temnospondyls);
82- 3. Incorporation of the stapes in an impédance
matching middle ear (temnospondyls);
83- 1. Dental plates and infrapharyngobranchials lost
variable réduction in other éléments (see figure 6)
(all tetrapods);
AXIAL SKELETON
VERTEBRAE
Three paired éléments per segment:
neural arches, dorsal posterior
pleurocentra. and ventral anterior
intercentra
84-0. No specialized articulation abut
between occiput and cervical vertebra
84-1. Margins of amphicoelous first centrum against
conical recess in occiput (aïstopods);
84-2. Central éléments of first cervical fit into circu-
lar dépréssion formed by exoccipilals and basioccip-
ital (Crasxigyrinus, anthracosaurs, seymouriamorphs,
colosteids, temnospondyls);
84-3. Eléments of atlas surround hemispherical occip¬
ital condyle (diadectomorphs, amniotes);
84-4. Narrow condyle of first cervical fits into a
recess in basioccipital (adelogyrinids);
84-5. Broadened anterior articulating surface of first
cervical articulâtes with strap-shaped surface of
basioccipital and exoccipitals (microsaurs and ly-
sorophids);
— 434 —
85-0. No separate element between
first cervical vertebra and occiput
86- 0. First cervical vertebra bas sepa¬
rate crescentic or paired intercentum
87- 0. First centrum no wider anteri-
orly than more posterior cervicals
88- 0. Pleurocentrum of First cervical
paired
89-0. First cervical arch not specia-
lized
90- 0. First cervical arch loosely at-
tached to centrum
91- 0. Intercentrum of second cervical
not fused to centrum of first cervical
92-0. Pleurocentrum of second cervi¬
cal paired
93- 0. Second cervical arch loosely at-
tached to centrum
94- 0. Neural arches of trunk paired
84- 6. Broadened anterior articulating surface of first
cervical articulâtes with exoccipitals, but not
basioccipital (nectrideans);
85- 1. Paired proatlantal éléments articulate with oc¬
ciput and/or atlas arch {Crnssi^yrinus, anlhracosaurs,
seymouriamorphs. diadectomorphs. amniotes. colosteids,
temnospondyls, lysorophid.s);
85-2. Médian “proatlas" linking occiput and first cer¬
vical (aïstopods);
85- 3. Secondary loss of proatlas (adelogyrinids, mi¬
crosaurs. nectrideans);
86- 1. Intercentrum of first cervical lost or incor-
porated into pleurocentrum (nectrideans, microsaurs,
adelogyrinids, lysorophids, aïstopods);
87- 1. Articulating surface of First centrum expanded
laterally (nectrideans. microsaurs, lysorophids);
88- 1. Atlas pleurocentrum cylindrical vertebra (.sey¬
mouriamorphs, diadeclomoiphs, amniotes, nec¬
trideans. microsaurs, adelogyrinids, lysorophids,
aïstopods);
89- 1. Atlas arch paired, smaller than axis arch (Acan-
thostega, Cra.ssigyrinus, anthracosaurs, seymouri¬
amorphs, diadectomorphs, amniotes, colosteids,
temnospondyls, adelogyrinids, microsaurs, ly¬
sorophids);
89- 2. Atlas arch fused dorsally (nectrideans, aïs¬
topods);
90- 1. Arch and pleurocentrum of first cervical verte¬
bra fu.sed (nectrideans, aïstopods);
91- 1. Intercentrum of axis fused to atlas centrum (di¬
adectomorphs):
91- 2. Axis intercentrum apparently lost (adelogy¬
rinids, lysorophids, nectrideans, aïstopods);
92- 1. Pleurocentrum of first cervical lost {Pander-
ichthys);
92- 2. Pleurocentrum of axis cylindridal (seymouri-
amoiphs, diadectomorphs, amniotes, microsaurs,
adelogyrinids, lysorophids, nectrideans, aïstopods);
93- 0. Arch and pleurocentrum of second cervical
vertebrae fused (diadectomorphs, amniotes, nec¬
trideans, aïstopods);
94- 1. Neural arches of trunk fused at midline (ail tet-
rapods except Crasxigyriniis, lysorophids);
— 435 —
95-0. Neural arches not firmly at¬
tachée! centra
96-0. Canal for supraneural ligament
pénétrâtes neural arch
97-0. Neural arches lack zygapophyses
98-0. Neural arches lack accessory
99-0. Long transverse process extend-
ing from arch
100-0. Intercentrum serves for articula¬
tion with capitulum of rib
101-0. Intercentra paired at least in
some régions of column
95-1. Paired neural arches suturally attached to
crescentic intercentra {Panderichthys)',
95-2. Neural arches articulate with crescentic inter¬
centra {Acanthostega*, Ichthyosiega)',
95-3. Arches closely articulating with pleurocentra
(anthracosaurs, seyinouriamorphs, colosteids, temno-
spondyls, adelogyrinids, lysorophids, some micro¬
saurs);
95-4. Arches become fused to centra during develop¬
ment (Westlothiana, ? diadectomorphs. amniotes);
95- 5. Arches indistinguishably fused to cylindrical
centra even in early stages of development (nec-
trideans, aïstopods);
96- 1. Supraneural canal does not penetrate arch (tem-
nospondyls, advanced anthracosaurs, seymouri-
amorphs, Westlothiana, diadectomorphs, amniotes,
nectrideans, microsaurs, adelogyrinids, ? lysorophids,
aïstopods);
97- 1. Prezygapophyses, but not postzygapophyses
{Crassigyrinus)-,
97- 2. Pre-and postzygapophyses (ail early tetrapods
except Acanthostega*, Crassigyrinus);
98- 1. Accessory articulating surfaces articulating sur¬
faces (Acanthostega, nectrideans, advanced aïsto¬
pods);
99- 1. Transverse process short (microsaurs, ly¬
sorophids, nectrideans, aïstopods, Westlothiana, di¬
adectomorphs, amniotes);
99- 2. Transverse process extending from centrum
(nectrideans);
100- 1. Capitulum of rib articulâtes with margin of
more anterior centrum (adelogyrinids, microsaurs, ly¬
sorophids);
100- 2. Capitulum articulation near anterior margin of
same centrum (aïstopods, nectrideans);
101- 1. Intercentra fused ventrally in posterior but not
anterior trunk région (Acanthostega*);
101-2. Intercentra, if présent, fused ventrally in ail
trunk régions (Panderichthys, and ail tetrapods except
Acanthostega);
101-3. Trunk intercentra absent (nectrideans, most
microsaurs, adelogyrinids, lysorophids, aïstopods);
— 436 —
102-0. Pleurocentra paired
103-0. Between 30 and 42 presacral
vertebrae
104-0. No sacral vertebrae
105-0. Haemal arches présent, not
fused to centra
102-1. Pleurocentra crescentic to horseshoe shaped
(primitive anthracosaurs);
102-2. Pleurocentra cylindrical (advanced anthra¬
cosaurs, seymouriamorphs, Westlothiana, diadecto-
morphs, amniotes, necirideans, microsaurs,
adclogyrinids. lysorophids, aïstopods, Acherontiscus);
102- 3. Pleurocentra absent {Pauderichthys. Crassigy-
rinits, loxommatids);
103- 1. 20-29 presacrals {Ichthyostega. seymouri¬
amorphs, nectrideans, microsaurs, diadectomorphs,
temnospondyls);
103- 2. 70 or more (adelogyrinids, lysorophids, aïs¬
topods);
104- 1. 1 sacral (anthracosaurs, seymouriamorphs,
colostcids. temnospondyls, nectrideans, microsaurs,
lysorophids);
104-2. 2 sacrais (Westlothiana, diadectomorphs,
amniotes);
104- 3. Sacrais secondarily lost (adelogyrinids, aïs¬
topods);
105- 1. Haemal arches lost (aïstopods);
105-2. Haemeal arches fused to centra (nectrideans);
RIBS
106-0. Ribs very short, linking neural
arch and intercentrum
107-0. Ribs loosely articulated to arch
and intercentrum
108-0. Ribs with cylindrical shafts
106-1. Ribs much more elongate (ail tetrapods except
Acanthosiega, uniess secondarily shorter);
106- 2. Ribs ?secondarily shortened in association
wilh large palatal vacuities (colosteids and temno¬
spondyls)'.
107- 1. Ribs suturally attached to intercentra and arch
(Panderiihtbys)',
107- 2. Capituluni articulating with posterior margin
of centrum (microsaurs, adelogyrinids);
108- 1. Ribs much widened so as to overlap one
another (Ichthyostega)-,
MEDIAN FINS
109- 0. Two distinct dorsal fins
110- 0. Diphycercal caudal fin with
Pariderichthys, modest aspect ratio
111-0. Distinct anal fin
109- 1. Dorsal fins lost (Panderichthys and ail tetra¬
pods);
110- 1. Narrow. pointed caudal fin (Acanthostega, and
Ichthyostega)-,
1 10-2. Tail lacks fin and lepidotrichia (ail other tetra¬
pods);
1 1 i-l. Anal fin lost (Panderichthys and ail tetrapods);
— 437 —
APPENDICULAR SKELETON
PECTORAL GIRDLE AND LIMH
112- 0. Dermal shoulder girdle con-
nected to operculum and skull roof
via po.st-temporal, supracleithrum and
anocleilhrum
113- 0. Interclavicle small
114- 0. Interclavicle oval
115- 0. Cleithrum extends ventrally to
midiine
116- 0. Cleithrum attached to three
processes of scapulocorocoid
1 1 7- 0. Postbranchial lamina of
cleithrum forming posterior border of
opercular chamber
118- 0. Distinct anleroventral process
of cleithrum that clasps dorsal
process of clavicle
119- 0. Claviclar .stem short and not ex-
posed latcrally
120- 0. Scapulocoracoid restricted to
glenoid région
121- 0. Scapulocoracoid a single
center of ossification
122- 0. Scapulocoracoid attached to
cleithrum by supraglenoid, infra-gle-
noid, and glenoid buttresses
112-1. Post-temporal and supracleithrum lost, but
anocleithrum retained (Acanthostega)-,
112- 2. Ail three bones lost (ail tetrapods except Acan-
thostega)',
113- 1. Interclavicle much enlarged (ail early tetra-
pods);
114- 1. Interclavicle with long posterior stem {Ichthy-
ostega, Acanthostega, anthracosaurs, seymouri-
amorphs, diadectomorphs. amniotes, lysorophids);
114-2. Among tetrapods. absence of distinct .stem
(Crassigyrimis, colosleids. temnospondyls. nec-
trideans, ? microsaurs, adelogyrinids);
114- 3. Interclavical lost (aïstopods);
115- 1. Cleithrum reduced ventrally to expose latéral
surface of scapulocoracoid (ail tetrapods);
116- 1. Cleithrum co-ossil’ied with latéral surface of
scapular blade (Devonian tetrapods);
116- 2. Cleithrum not co-ossilîed with latéral surface
of scapular blade (ail post-Devonian tetrapods);
117- 1. Loss of postbranchial lamina (ail tetrapods ex¬
cept Acanthostega);
118- 1. Loss of anteroventral process of cleithrum (ail
tetrapods except Acanthostega);
119- 1. Progressive élongation of stem (ail tetrapods);
119- 2. Loss of clavicle (aïstopods);
120- 1. Elaboration of coracoid région but not scapu¬
lar blade (Acanthostega and fchthyostega);
120-2. Elaboration of scapular blade as well as cora-
coid région (ail tetrapods except Acanthostega and
Ichthyostega);
120- 3. Loss of scapulocoracoid (adelogyrinids and
aïstopods);
121- 1. Two centers of ossification (seymouri-
amorphs);
121- 2. Three centers of ossification (amniotes);
122- 1. Three buttresses converge to form a single sur¬
face of attachment, separating foramina (123-125)
from cleithrum (Panderichthys);
— 438 —
123- 0. Supraglenoid foramen between
supraglenoid and glenoid buttresses
124- 0. Subscapular fossa between
supra- and infraglenoid buttresses
125- 0. Supracoracoid foramen be¬
tween infraglenoid and glenoid but¬
tresses
126- 0. Glenoid canal on médial sur¬
face of scapulocoracoid
127- 0. Glenoid pear-shaped faces pri-
marily posteriorly
128- 0. Pectoral fin small relative to
body
129- 0. Pectoral fin consisting more
half of fin web
130- 0. Limb bones fully ossified in
adult individuals with articulating sur¬
faces well-defined
131- 0. Humérus an essentially colum-
nar bone, with slightly expanded ex-
tremities
132-0. Proximal and distal areas of ex¬
pansion twisted at 20°
133-0. Proximal articulating surface
pear-shaped, no longer than glenoid
122- 2. Latéral surface of scapulocoracoid expands
below cleithrum (ail tetrapods);
123- 1. Supraglenoid foramen absent (Acanthostega,
colosteids, lysorophids);
124- 1 . A conspicuous dépréssion on the inner surface
of scapulocoracoid (ail early tetrapods);
124- 2. Lost of subscapular fossa (lysorophids);
1 25- 1 . One foramen exils through coracoid (most tet¬
rapods j;
125- 2. Two foramina (anthracosaurs, seymouri-
amorphs, amniotes, microsaurs);
126- 1. Canal absent (anthracosaurs, lysorophids);
127- 1. Glenoid extends onto coracoid, forming late-
rally facing articulating surface (ail tetrapods);
128- 1. Forelimb large relative to body (primitive te¬
trapods);
128- 2. Secondary réduction or limb loss {Crassigyri-
nux, Wexflotlmma, ? neclrideans, lysorophids, adelogy-
rinids. aïstopods);
129- 1. Fin web and lepidotrichia lost (ail than tetra-
pod.s);
130- 1. Reduced ossification resulting in ill-defined
articulating surfaces, even in mature individuals
( C rassigyrinus. ly sorophi ds ) ;
131- 1. Proximal and distal extremities expanded, but
shaft little developed (Devonian généra, Crassigy-
rinus. anthracosaurs, seymouriamorphs, diadecto-
morphs, colosteids, primitive temnospondyls,
neclrideans);
131-2. Distinct, narrow shaft (Wesilothiana, amniotes,
microsaurs, lysorophids);
131- 3. Humérus lost (adelogyrinids, aïstopods);
132- 1. Torsion 40° (Crassigyrinus, Ichthyostega)',
132-2. Torsion 25" to 39" (primitive anthracosaurs,
colosteids. ? neclrideans, lysorophids);
132-3. Torsion 45" (seymouriamorphs, primitive tem¬
nospondyls);
132- 4. Torsion 80" to 90" (Wesüothianu, diadecto-
moiphs, amniotes, advanced temnospondyls, micro¬
saurs);
133- 1. Articulating surface of greater length than gle¬
noid (ail tetrapods except Devonian généra);
— 439
134- 0. Oblique dorsal ridge extending
from mid-widlh of proximal dorsal
end of humérus to entepicondylar
ridge, enclosing one or more foramina
for radial nerves and blood ve.ssels
135- 0. No dcllopectora! cresl
136- 0. Anterior (preaxial) surface of
shaft rounded (without anterior keel)
137-0. No supinator process
138-0. Ectepicondylar ridge extends
distally to overlie area of ulnar articu¬
lation
139-0. Postaxial process of humérus
extends, as a narrow blade, postero-
distally from the posterordistal extrem-
ity of the shaft
140- 0. Entepicondylar foramen pierces
shaft along posterior surface and exits
at the distal base of the posiaxial
process
141- 0. Distal surface of humérus
grooved dorsally, as is the fémur, be-
tween the distal condyles
142- 0. Présence of a distal process be-
tween the postaxial process and the ar-
ticulating surface for the ulna
143- 0. Articulaling .surfaces for ulna
and radius terminal
134-1. Loss of foramina, but rétention of ridge (an-
thracosaurs);
134- 2. Loss of ridge and foramina (ail tetrapods ex-
cept Devonian gênera, Crassigyrinus, and anthra-
cosaurs);
135- 1. Dcllopectoral crest (ail tetrapods except
Devonian généra);
136- 1. Anterior keel (Devonian généra, Crassigy¬
rinus, anthracosaurs,. colosteids, nectrideans);
136- 2. Sccondary loss of keel (seymouriamorphs,
Westlothiana, diadectomorphs, amniotes, temno-
spondyls, microsaurs, lysorophids);
137- 1. Supinator process a part of anterior keel
(Devonian généra, anthracosaurs. colosteids);
137- 2. Separate supinator process extending from dis¬
tal end of shaft (seymouriamorphs. Westlothiana, di¬
adectomorphs, amniotes, advanced temnospondys,
? nectrideans);
138- 1. Ectepicondylar ridge extends obliquely ante-
riorly to overlie area of radial articulation (ail tet¬
rapods except Devonian généra, unless secondarily
lost);
138- 2. Ectepicondylar ridge lost (lysorophids):
139- 1. Entepicondyle (the tetrapod homologue of the
postaxial process) greatly enlarged proximally (ail
primitive tetrapods);
139- 2. As in 139-1, but distal extremity of entepi¬
condyle reduced to parallel entepicondyle (ail tet¬
rapods e.xcept Devonian généra, anthracosaurs, and
sey mou ri amorphs ) ;
140- 1. Entepicondylar foramen pénétrâtes entepicon¬
dyle close to its proximal margin (ail tetrapods, un¬
less lost);
140- 2. Entepicondylar foramen lost (most temno-
spondyls, lysorophids);
141- 1. Loss of groove (ail tetrapods except Acan-
thostega);
142- 1. Process greatly reduced (Ichthyostega)-,
142- 2. Process lost (ail other tetrapods);
143- 1. Articulating surfaces more ventral than distal
(ail tetrapods except Acanthostega);
— 440 —
144- 0. Articulating suri'ace for ulna
larger than for radius
145- 0. Conspicuous ventral diagonal
extends from anteroproximal to post-
erodistal surface of humérus ending at
base of postaxial process pierced by
numerous foramina
146- 0. Radius, a slender bone signifi-
cantly longer than humérus or ulna
147- 0. Radius does not articulate with
endochondral bone distally
148- 0. Ulna, a columnar bone
widened distally
149- 0. Ulna lacks olecranon
150-0. Ulna with massive distal articu¬
lation with ulnare and intermedium
151-0. 4 to 6 éléments recognized as
homologous with tetrapod carpals
152-0. Ulnare with large flattened
postaxial process
144- 1. Articulating surface for radius as large or
larger than for ulna (ail tetrapods);
145- 1. Ridge absent (ail tetrapods except ridge
Devonian généra and Crassigyrinus);
146-1. Radius shorter than humérus but extending
well beyond end of ulna {Pancierichthys, Acanthos-
tega):
146-2. Radius shorter than ulna in which olecranon
is ossified (ail other early tetrapods);
146- 3. Radius lost (adelogyrinids, aïstopods);
147- 1. Radius articulâtes with radiale and interme¬
dium (? anthracosaurs. seymouriamorphs. diadecto-
morphs, amniotes, temnospondyls);
148- 1. Ulna widest proximally (ail tetrapods);
148- 2. Ulna lost (adelogyrinids, aïstopods);
149- 1. Little development of olecranon (Acan-
thostega)',
149- 2. Substantial olecranon, unless secondarily re-
duced (ail other tetrapods);
150- 1. Broad articulation with ulnare (seymouria¬
morphs);
150- 2. Articulation with intermedium, ulnare, and
pisiform (diadectomorphs, amniotes, the microsaur
Pantylus):
151- 1. Carpus largely uno.ssified {Acanthostega.
primitive anthracosaurs, nectrideans, lysorophids);
151-2. 4 ossified carpals, not including pisiform or
distal carpals (seymouriamorphs);
151-3.7 ossified carpals including pisiform, and three
distal carpals. but not ccntralia (diadectomorphs);
151-4. Il carpafs, including pisiform and two cen-
tralia (amniotes);
151-5. Il carpals, including 4 ccntralia, but no
pisiform (temnospondyls);
151- 6. Carpals lost (adelogyrinids, aïstopods);
152- 1. Small rectangular ulnare. without postaxial
process (ail tetrapods);
152-2. Huge plate-like ulnare {PanderichthysY,
— 441 —
153- 0. Ulnare articulating with two
large carpal éléments distally, the
more latéral of which articulâtes with
two much smaller éléments
154- 0. Iniermedium long and flattened
distally between lepidotrichia
155- 0. No éléments recognized as dis¬
tal carpals, metacarpals, or digits
156- 0. Among tetrapods, more than 5
digits in manus (Devonian généra)
157-0. Among tetrapods, phalangeal
count of 3, 3, 3, 3, 4, 4, 4, 3
153-1. Ulnare articulâtes with centrale and 4th distal
carpal (diadectomorphs);
153- 2. Ulnare articulâtes with centrale and distal car-
pals 4 and 5 (amniotes);
154- 1. Small rectangular intermedium (ail tetrapods);
155- 1. Metacarpals and digits uniess secondarily lost
(ail tetrapods);
156- 1. 5 digits in rnanus (anthracosaurs, seymouri-
amorphs, diadectomorphs. amniotes, nectrideans);
156-2. 4 digits in manus (colosteids, temnospondyls,
microsaurs, lysorophids);
156- 3. Loss of digits (adelogyrinids, aïstopods);
157- 1. Phalangeal count of 2, 3, 4, 5, 3 (anthra¬
cosaurs. seymouriamorphs, diadectomorphs. Acan-
thostega, amniotes);
157-2. Phalangeal count of 2, 2, 3, 3 (colosteids, tem¬
nospondyls);
157-3. Phalangeal count of 2, 3 ?, 4, 3, 2 (nectrideans);
157-4. Phalangeal count of 2, 3, 3, 2-i- (microsaurs);
157-5. Phalangeal count of 3, 3 ?, 3, 2 (lysorophids);
PELVIC GIRDLE AND LtMB
158-0. Pelvic girdle a single paired
élément
159- 0. Pelvic girdle not attached to
vertébral column
160- 0. Pelvic girdle not attached at
the ventral midline
161- 0. Acetabulum facing posteriorly
162- 0. Iliac ramus of pelvis short
without blade attached to sacral ribs
158-1. Pelvic girdle consisiing of three areas of ossi¬
fications. pubis, ischium, and ilium (ail tetrapods un¬
iess secondarily redueed);
158- 2. Pelvic girdle lost (adelogyrinids, aïstopods);
159- 1. Pelvic girdle attached to the vertébral column
via one or more pairs of sacral ribs (ail tetrapods with
limbs);
160- 1. Halves of girdle joined ventrally via the pubo-
ischiadic symphysis (ail tetrapods);
161- I. Acetabulum facing laterally (ail tetrapods with
limbs);
162- 1. Iliac blade with short dorsal and longer poste-
rior process (Acanthoslega, Ichlhyostega, anthra¬
cosaurs);
162-2. Bifurcate iliac blade with larger dorsal but
shorter posterior process {C rassi gyrinus, seymouri¬
amorphs, microsaurs);
162-3. Redueed dorsal process extending from the
margin of posteriorly directed blade {Westlothiana,
diadectomorphs, amniotes);
— 442 —
163- 0. No openings in area of pubis
164- 0. No ossification in area of
ischium
165- 0. Fémur, a short columnar bone
with little development of ventral
ridge System
166- 0. Distal articulating surfaces nar-
row and terminal
167- 0. Tibia much longer than fémur
168- 0. Tibia flattened distally between
lepidotrichia
169- 0. Fibula with large, flattened
postaxial process
170- 0. Shaft of fibula stout and much
shorter than tibia
171- 0. Proximal articulating surface
with fémur larger than that of tibia
172- 0. Fibula articulating distally with
elongate, flattened fibulare and inter¬
medium
173- 0. Intermedium does not articu-
late distally with endochondral élé¬
ments
174- 0. Fibulare elongate, with postax¬
ial process
175- 0. Fibulare articulâtes with three
elongate éléments
162- 4. Non-bifurcate iliac blade, extending dorsally
and somewhat posteriorly (colosteids, temno-
spondyls, nectrideans, lysorophids);
163- 1. Two obturator foramina {Ichthyostega, anthra-
cosaurs);
163- 2. One obturator foramen (ail other tetrapods);
164- 1. Ischium a neomorph (ail tetrapods);
164- 2. Ischium not ossified (adelogyrinids, aïs-
topods);
165- 1. Fémur more elongate, with well-developed
ventral ridge System, including internai trochanter
and adductor crest (ail tetrapods unless secondarily
lost);
165-2. Adductor crest absent, intertrochanteric fossa
ill-defined {Crassigyrinus).,
165- 3. Fémur lost (adelogyrinids, aïstopods);
166- 1. Distal articulating surfaces broader and facing
ventrally as well as distally (ail tetrapods);
167- 1. Tibia shorter than fémur (ail early tetrapods);
167- 2. Tibia lost (adelogyrinids, aïstopods);
168- 1. Articulating facets for tarsals (ail tetrapods);
169- 1. Loss of postaxial process (ail tetrapods);
169- 2. Fibula lost (adelogyrinids, aïstopods);
170- 1. Shaft slightly shorter than tibia (Devonian te¬
trapods, nectrideans);
170- 2. Fibula longer than tibia (ail other early te¬
trapods);
171- 1. Area of proximal articulation with fémur small
than that of tibia (ail tetrapods);
172- 0. Fibulare and intermedium shorter, polygonal
éléments (ail tetrapods unless lost);
172- 1. Tarsals unossified (adelogyirnids, aïstopods);
173- 1. Inlermedium articulâtes with two more distal
tarsals (ail known primitive tetrapods except where
limbs are reduced);
173- 2. Intermedium integrated into astragalus (amni-
otes, some microsaurs);
174- 1. Short, without postaxial process (primitive te¬
trapods);
175- 1. Fibulare articulâtes with three distal tarsals
(Ichthyostega)',
— 443 —
176-0. No tarsal recognized distal to
tibia
177-0. No éléments recognized as cen-
tralia
178- 0. No éléments recognizable as
distal tarsals, metatarsals, or digits
179- 0. Among tetrapods, more than 5
digits in pes (Ichthyostega)
180- 0. Among tetrapods, phalangeal
count of 3, 4, 2, 3, 4, 4, 3 {Ichthy¬
ostega)
181- 0. Large, uniform cycloid scales
covering ail of trunk
182- 0 Dorsal scales présent
183- 0. Enlarged scales (basal sentes)
on each side of the bases of ail mé¬
dian and paired fins (except caudal)
184- 0. Lepidotrichia cover distal ends
of fins
175- 2. Fibulare articulâtes with distal tarsals 4 and
5 (other early tetrapods);
176- 1. Tibiale and intermedium distal to tibiato (sey-
mouriamorphs. microsaurs, lysorophids);
176-2. Tibiale, intermedium, and centrale distal to
tibia (anthracosaurs, ? Westlothiana, diadectomorphs,
colosteids. temnospondyls);
176- 3. Area of tibiale incorporated with intermedium
and proximal centrale, to form astragalus (amniotes,
some microsaurs);
177- 1. One centrale {Ichthyostega)',
177-2. Two centralia (amniotes);
177-3. Three centralia (microsaurs);
177- 4. Four centralia (anthracosaurs, ? Westlothiana,
colosteids, temnospondyls);
178- 1. Metatarsals and digits unless secondarily lost
(ail tetrapods);
179- 1. 5 digits (ail other early tetrapods unless lost);
179- 2. Digits of pes lost (adelogyrinids, aïstopods);
180- 1. 2. 3, 4. 5, 5 (anthracosaurs);
180-2. 2, 3, 4, 5, 4 (seymouriamorphs, Westlothiana,
diadectomorphs, amniotes);
180-3. 2, 2, 3, 4, 3 (colosteids, temnospondyls);
180-4. 2, 3, 4, 4, 2? (nectrideans);
180-5. 2, 3, 4, 5, 3 (microsaurs);
180- 6. 2, 3, 3, 3, 2 (lysorophids);
SCALES
181- 1. Clear distinction between dorsal and ventral
scales (ail early tetrapods);
182- 1. Dorsal scales absent {Crassigyrinus, anthra¬
cosaurs, diadectomorphs, amniotes, nectrideans, ly¬
sorophids);
182- 2. Pebbly dorsal ossicles (aïstopods);
183- 0. Loss of basal scutes {Panderichthys, ail tetra¬
pods);
184- 0. Lepidotrichia lost (ail tetrapods except caudal
région of Acanthostega, Ichthyostega).
— 444 —
APPENDIX II
Mode
Susthenoptejrcn
Panderichthys
Acanthostega
Ichthyostega
CrassigyrinuB
Loxommatids
Anthracosaurs
Seymour iamorphs
Wss tlcthiana
DiadectoBiorphs
Amniotes
Colosteids
Terono s pondy 1 s
Nectrideans
Microsaurs
Adelogyrinids
Lysorophids
Alstopods
Kode
Eusthenoptercn
Panderichthys
Acanthostega
Ich thyostega
Crassigyrinus
Loxocnmatids
Anthracosaui s
Seymour iamorphs
Westlothiana
Di adectomorphs
Amniotes
Colosteids
Temnospondyls
Nectrideans
Microsaurs
Adelogyrinids
Lysorophids
Alstopods
DATA MATRIX
0000000001111111111 2222222P.22333333333344444444445555555555
12345678901234567890123456789012345679901234567890123456789
ooooooooooooooooooooooüooooooooooonoooooooooooooooooooooooo
11 100101100001 ?ooooûûOooûooooûoioooooo?oôoûûQôoo???i ???????
11200111010100?liü0100101001il0100ai0010110000001?V21?l?0?0
11300121010100?2000100100011000110001000110000001?021???0?1
110012011 102002300Û10000?OÛ11000100000101:OOOD00110211?100?
114 0124 100] 2001 1 1?1 100000001100000001 02011Û000001 102 111 1006
11001131000200241111100120011201010010201100000011021111102
1140124100020024 1111100100011200000 110201 110001011021111103
1151?2410Q0400?411111011000112000?1111201 17100001 1 ?21111?03
11 5??24i000400.341111101 100111200011 11020111 100201 1121 111104
1151724 102040034111110110001 120001111 1221 11100201 1221 111105
Ila0l26100ù6û0l4111i0ûû000ûll] 1000000021 IlOOOÛOll 1021111007
114 0124 100030C114 111100000001 121 000001 02 1111000011 1021 11100c
10611251000600441111701100011200011111201110000011021111008
11717251000600141111101201011200011111201111000111321111009
1180124104050054111100123101120001111120117100021 L02lU100a
1191?25203261064111??11201011200011111201122U021142111101b
1101725105062074111170100001120001111120117020071002111100?
OOOOOOOOOOOOOOOOOÛOOOOOOOOOOOOOOOOOOOOOOl 111 mil 111 111 1111
66666666667777777777888888888899999999990000000000111111111
01234567890123456789012345678901234567890123456789012345678
00000000100000000000000000000007000000070000000000000000000
??00001000?0000000010000??0????71??1?007023000010 U 10000000
3010û?7??7?001il01111111?????l????i2?01??10??0100iumil00
00000 130000011 ?????7???107?7?????7 1272070201 7010111 12 11 1111
301 0002 1010ûil?????7?7?1210û?l?710000100023 770100 121 2 121211
40100131011011 ?????????l?10?????l????20??23??010012i??????l
40 100 13001001 U 1011 11 11 12 1000 100001 3020002 lOlûl 001212 11 12 11
41100131112011110211712121001100201312000221101001212111211
??ll?13?ll?OmiO??????l????77??7?14120lÛ22Û2ÛlÛ0l2 L2171211
61 111 13 111301111771111 713100110121141201022 12010012 12 111211
611111311140111110111121310011002114120102212010012 12111211
401001310130111101111 11121000100001302000200102001212121211
401Û013 1011011110111111121000100001302000201102001212121211
51 11213 11131117????????163i 1121221] 5] 2122321121001212121211
411001311150111170111121531111002013120117211010012 12171211
41 10713 111 7111 7714 3 10 110220131 200 1322301 0012 12 12 12 11
41 12313 11 161111100112 12 1531 1110230037201 1322101001212 111211
21117131113011110011212112101212211512012322311001212131211
Node
Eusthenopteron
Panderi chthys
Acanthostega
Ichthyostega
Crassigyrinus
Loxomrnat ids
Anthraco saur s
S eymour i amorphs
Westlothiana
Diadectomorphs
Amniotes
Colosteids
Temnospondyls
Nectrideans
Microsaurs
Adelogyrinids
Lysorophids
Alstopods
Node
Eusthenopteron
Panderlch thys
Acanthostega
Ichthyostega
Crassigyrinus
Loxommatids
Anthracosaurs
S eymou r i amorphs
Westlothiana
Diadectomorphs
Amniotes
Colosteids
Temnospondyls
Nectrideans
Microsaurs
Adelogyrinids
Lysorophids
Alstopods
— 445 —
11111111111111111111111111111111111111111111111111111111111
12222222222333333333344444444445555555555666666666677777777
90123456789012345678901234567890123456789012345678901234567
OOOOOOOOOOOOOOOÛOOOOOOOOOQOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO
1001000000000?0???0?0???0??10û00?2?00??000000??????????????
11021 ???11101000?11 01102010 111111 ??110011111?111111111?1???
1102011011101100Û11011111102?12????????11111111111111111111
12???????211111011?1?112?10??1?????????11112?121111211?????
12????????10?? ????????????????????????????????? ????????????
120201211 1101211111111121112112 ?11?111111111111111 121111224
121201201 1101312 122111121112112 121? 1111 111122 11 111121111?!?
1202 ?1??12 1024 12 12212 1121112?12??1??1??11113211111121 111224
120201101110141212212112111211223111111111132111111211?1?2?
12220120111024121221211211121122412111111113211111121121232
12021110111012 12 11112 1121 112 ?12?11??122 1111421 1111121111224
1202011011101212120121121112112051?112211114211111121111224
1202 ????11101?1211??211211 12 ?12?11??1131 1114711111 1111?!???
1202012 7111024 1212012112111 2?12??1?112411112211111121111213
13?2?????21?3??????????????3?2??6???13?2?????23?2?2??2?????
1202 12 ?1121122?2 12022212?? 12? 12 ?1???1251 1114 ?111111211?1?1?
23?2?????21?3??????????????3?2??6???13?2?????23?2?2??2?????
1111111
7788888
8901234
0?00000
0700010
1001710
1071710
7771111
???????
1111111
1121011
1121011
1121111
1121111
1131011
1131011
1141111
1151011
1271011
1161111
1271211
Bull. Mus. natl. Hist. nat, Paris, 4® sér., 17, 1995
Section C, n° 1-4 ; 447-459.
Revised Upper Silurian-Lower Devonian ichthyostratigraphy
of northern France and Southern Belgium (Artois-Ardenne)
by Alain BLIECK, Daniel GOUJET, Philippe JANVIER, and Francis MEILLIEZ
(Contribution to IGCP Project 328 “Palaeozoic Microvertebrates")
Abstract. — 39 localities within the Upper Silurian-Lower Devonian sequence of the Ardenne-Artois area
yield vertebrate species which allow corrélation with at least the vertebrate succession of the Welsh Borderland,
England, and uf Spitsbergen. Invertebrate fossils and palynomorphs suggest a corrélation with the marine faciès
elsewhere in Europe. Relatiug the vertebrate biostratigraphy to that of conodont-graptolite-dacryoconarids is pro-
blematic but the postulated acme of the local vertebrate faunas in the lower crouchi zone of Artois may be
related to the high sea level of the eurekaenxis zone, and the impoverishment of the upper leachi and lower
dunensis zones to the low sea level of the upper Lochkovian-Pragian.
Keywords. — Upper Silurian, Lower Devonian, vertebrates, northern France (Artois), Southern Belgium
(Ardenne), biostratigraphy, corrélation.
Révision de l’ichthyostratigraphie du Silurien supérieur-Dévonien inférieur du nord de la France
et du sud de la Belgique (Artois-Ardenne)
Résumé. — Le Silurien supérieur-Dévonien inférieur de la région Ardenne-Artois a livré 39 localités fos¬
silifères à Vertébrés que l’on peut corréler au moins aux séquences à Vertébrés de la Bordure Galloise (Angleterre)
et du Spiisberg. Les invèrtébrés et palynomorphes présents autorisent des corrélations avec les faciès marins,
ailleurs en Europe. La mise en relation de l’échelle biostratigraphique fondée sur les Vertébrés avec celle qui
e.st fondée .sur les Conodonie.s-Graptoliies-Dacryoconarides n’est pas résolue. Cependant l'acmé des faunes de
Vertébrés dans la partie inférieure de la zone à crouchi en Artois pounait être liée au haut niveau marin de la
zone à eurekaansis. A l'inverse, l'appauvrissement des faunes des zones à leachi supérieure et il dunensis inférieure
serait lié au bas niveau marin du Lochkovicn supérieur- Praguien.
Mots-clés. — Silurien supérieur, Dévonien inférieur. Vertébrés, nord de la France (Artois), sud de la Bel¬
gique (Ardenne), biostratigraphie, corrélation.
A. Blieck, K Meilliez, Univershé des Sciences et Technologies de Lille, Sciences de la Terre. URA 1365 et 719 du CNRS, 59655
Villeneuve d'Ascq Cedex. France.
D. Gouiet, Ph. Janvier. Muséum national d'histoire naturelle. Laboratoire de Paléontologie et URA 12 du CNRS. 75005 Paris,
France.
Introduction
This paper purposes to make available the résulta previously published in French on the
Upper Silurian-Lower Devonian ichthyofaunas of northern France and southem Belgium. The
most recent results hâve been presented in two papers by Blieck & Janvier (1989) and Blieck
& Goujet (1991), wherein older works are referred to and listed. We aiso deal with a biostrati-
— 448 —
graphical synlhesis on the iipper Pridoli to Emsian ichthyofaunas of lhe région, following the
tentative synthesis published thirteen years ago by one of us (Blieck, 1982a). This ichthyos-
tratigraphical scale is correlated with the spore-zonations of the Lower Old Red Sandstone (ORS)
faciès from Britain and Germany. which hâve been thcmselves correlated with the standard
Lochkovian-Pragian sequence of Bohemia (Streel et al., 1987). At the end of the paper, a
discussion is aiso initiated about corrélations with event-stratigraphy and eustatic curves for
Lower Devonian times.
GEOLOGICAL SETTING
Between the Channel and the Rhine river most Palaeozoic rocks crop out within the Ardenne
area, southeast of the Sambre and Meuse rivers (Fig. I ). North of them, within the Brabant area,
isolated small outcrops occur along valleys, below an unconformable Upper Cretaceous to Eocene
cover. West of lhe Ardenne. below the Upper Cretaceous cover, tiny outcrops are aligned along
the Artois hilly ridge as far as lhe Boulonnais, Examinaiion of ail thèse outcrops rcveals inter¬
mittent and differenliated lectonic acliviiy since the end of Cretaceous time.
AU these Palaeozoic rocks includc Devonian sédiments that were deposiied along the south-
em margin of the Old Red Sandstone Continent as a Variscan cover that rests unconformably
above a strongly folded Caledoman substratum. Lower Palaeozoic in âge Later on. the Car-
boniferous Variscan shortening has differentiated two major structural domains, the northern
Brabant Paraiitochlhon and the Southern Ardenne Allochthon. The.se domains are separated by
a complex faulied zone which is not the only one within the Allochthon. Thus the Ardenne
Allochthon appeans as a stack of large tectonic sheets dipping gently to the SSE rather lhan a
single huge nappe, lhe so-called Dinant Nappe (see discussion in MeILLIEZ & M.^NSY. 1990).
The bulk Variscan shortening is estimated at but ihis is not uniformly distributed; it is
higher acro.ss each ihrust zone and roughiy incrcases by adding effects southwards.
Between lhe Rhine river and the Liévin area (Fig. I and locality 4, Fig. 2), the frontal
faulted zone is made of anastomosing (lat-lying thrusts, together with the overlying Ardenne
Allochthon and the underlying Brabant Parautochthon. The well-known Midi Overthrust is one
of these faults. Such a structure is documented from deep seismic data and boreholes (see review
in Raoult, 1988). Between the Liévin area and the Channel. the frontal faulted zone is made
of sieepiy dipping faults that arc difficuli to discriminate from ihose the Cenozoic tectonics has
reactivated. Only some of these faults were mappcd during coal mining (which stopped in Decem-
ber 1990). The aclual link with the Boulonnais inlicr i.s still debated (B1 on Fig. I ).
The Ardenne Allochthon and the Brabant Parautochthon both encompass a Devono-Car-
boniferous Variscan cover unconformably overlying a Lower Palaeozoic substratum. Within the
Brabant Massif, the Variscan cover is unfolded and forms adjacent monoclines. Within the former,
the cover wraps around antiformal stacks with substratum inliers as a core. Similar arc the Rocroi,
Serpont and Stavelot massifs that déterminé a saddie separaling the Southern Neufehâteau syn-
clinorium from the northern Dinant synclinorium. Linear inliers lie along the frontal thrust zone
between Charicroi and Liège on the easl (Condroz antiformal stack BC on Fig. 1) and in the
Liévin area on lhe west (Lv).
— 449 —
FIG. I — Simplil'ied geolügicjl iiiap beiwcen ihc Chiinni:! anil the Rliine nvur. The Variscati shuriening has dîfFercniiated two
major slriiclural dojuaiii.'i rhat are '«parated by a complex gently soulh dipping Ihrust zone lA.O.F.: Ardcnnc Overthrust Front).
The Midi Overthrii.'ci is une of ihese thrusn. Eaeh of ihe ivvcj major domain* encompasses a Lower Paiaeoroic sedimentary
basemeni and a Ücvono-Dinanlian scdimcnlury eover. The biuemenl avas deFormetl and .subsequently eroded, giving ri*e to
the Calcdonian unctrnformity. Basemeni caii hc observed (hrotigh lhe BrabanI and Flandre-.sud (PS) horsl-lifce relieis within
the VarLsean Parauloehlhon, and ihixiugh the Rocroi, Siavelol, Senwni, Givonne. Condioz Sirip tBCi. Artois and Boulonnais
(Bl) inliers wiihin lhe Variscan Alluchihon. The name ■'synclinorium de Namui" has tn hc discatded as il braeVets various
.structura) domatils be|ow lhe Cnql Baüjp.
Boreholes; Bl- Boischool, Bd- BollanU. hp- Epinoy, Fo Focant. GIF Grand Hallcux, Gz- Gouzeaucoun, Ha- Huvchuige,
Jt- Jeumonl. Kr- Konzen. To- Tournai, VS- Vermandovilliers, Wc- Wépion.
Localilies; Aa- Aachen. Ar- Airas, .Av- Avesnes-v/Helpe. fla- Bastogne, Bh- Boham. Bo- Boulogne-.s/Mer, B.x- Bruxelles,
Ca- Cambrai. CM- Charleville-Mézières. Di- Dinani, Do- Douai, Du- Dunkerque, Cn- Gcnl, Gi- Givei, Lg- Liège. Li- Lille,
Lv- Liésin. Ma- Maubetige. Mh- Mnn.schau. Mo- Mons. Ms- Maasiriehl, Ml- Montreuil. My- Malmcdy. Na- Namur. Ro-
Rocroi. .SH- Saint Huhcti. SO Sainl Onis't. Tx- Theux. Va- Valencienne-.,
Carte gêc//(.tgii/iie .iimplifire entre lu Mtiiu hi- et te Rhin Le raiToun issement varisi/ue a différencié deux dntnaines xlrucliiraux
majeurs séparés pat une zone complexe de chevauchements- h pendage sud fothie iA.O.F. : rhevauchement jraatal urdennais).
La Faille du Midi esi l'un Je res rhevoueheivents. Chacun de ces Jeux domaines majeurs comparu’ un socle sédimvniaire
du Patéazoïi/ue inférieur el une touveriurr sédimcnitiirr dévono-dintmiienne. Le socle a éie déformé puis émdé dnunani
naissance à la discordance catedanienne. Ce socle peiii être observe' à lu faveur de relit/ties en horsi sur le Brabant et la
Flandre méridionale (f.Si dans le Paeauioclmnc Varisque. ainsi qu'à la faveur des- massifs de Rorrui. Staveloi, Serpont,
Givonne. de Jo Bonde du Condroz (BCl. des petits affleurements d'Artois et du mtissif de Fetyues dans te BaulnnnuiS (Bl)
dans lAllorhImte Vorisaue. ijt terme de - synclinorium de Namur e doit être aUiindonné puisqu'il ivcouvn’ des domaines
stniclnraux variés sous !e Bn.ssm Hoviller.
Forages: Bl- Boischoai, Bd- Bollund, Bp- Epinny, Fo- Fncani. OH- Grand Halleux, Gz- Gouzeaucourl. Ha- Haveiange. Jt-
Jeitmoni. A’.:- Kotizen. Th- Tournai. t^.V- Vermondoviltiers. Wc- Wépion
Localilés: Aa- .Aachen. Ar- Arras, .di - Ave.ine.s-s/Helpe. Ba- Ba.stogne, Bh- Bohain, Bo- Boulogne-.s/Mer, Bx- Bruxelles. Ca-
Cambrui, CM- Charles illr-Mêzières, Di- Dinani, Do- Douai, Du- Dunkenpie, Cn- Gent, Gi- Givel, l.g- IJége, Li- Lille, Lv-
Liévin. Ma- Mauheuge, Mil- Mnnsrhau, Mo- Mons, Ms- Maasiriehl. Ml- Montreuil, My- Malmédy, Na- Namur. Ro- Rocroi,
SH- Saini-Huberi, SO- Saini-Omer. 7a- Theux, Va- Valenciennes.
Il ha.s been .suggested (Meilliez et al., 1992) that within lhe BrabanI Parautochlhon, the
main WNW-ESE trend and its subsidiary SW-NE trend retlect the Upper Silurian (?) to Devonian
structural frame of the southem margin of the Old Red Sandstone Continent. Thts margin ac-
comodated a synsedimentary extension. The bulk southward thickening of the carly deposit.s and
— 450 —
the bulk norihward migration of lhe transgressive frontal line are in agreement with the image
of a tilted-blocks puzzle. The earliest and strongest induced subsidence occurs south of most of
the substratum inliers. Thus the Upper Silurian to Lower Devonian transition is likely to occur
under marine conditions SE of the Rocroi massif, in Liévin area, and probably SE of the Stavelot
massif (.see review in Meilliez et ai, 1992). Due to the same effect is the presence of Lower
Devonian with acritarchs at the bottom of an early graben in the Brabant Parautochthon ( VanGUE-
STAINE et al., 1989).
Ail the fossiliferous localities studied here belong to lhe Ardenne Allochthon, on either side
of the Dinant synclinorium (Fig. 2): 1-17 along the northern fringe and 24-25, 36, 37? along
the Southern fringe; 26-33, 35 in the Neufehâteau synclinorium; 18-23, 34 north of the Stavelot
massif.
THE SEQUENCE OF ARTOIS
Figure 3 is a summary of ail vertebrate taxa collected front shafts, boreholes and outerops
on the northern edge of the Dinant western concealed synclinorium. It is a synthesis of the
whole fauna, including the correcied data of Blieck & Janvier (1989, Figs. 3 and i 1 in which
printing mistakes occurred, particularly conceming the location of the Pteraspi.'i mstraia biozone).
We fmd in .Artois lhe biozones defined by E. 1. Write in the Lower ORS of the Weish Borderland;
this zonation was the first siich based on fishes, and the first biozonation in the Lower ORS
(référencés in Stubblefield, 1985). The Pmtnptemspis and Rhinopteraspù cmiichi zones were
foiind in Liévin shaft No 6 (Goi)JET & BLIECK, 1979). and the Pteraspi.’i rostrata zone in between
ai shaft Vimy Ibi.s (Blieck & Janvier. 1989), the Althaspis zone having been defined above
the R. crouchi zone (see WHITE, 1956). The Silurian/Devonian boundary bas been precisely iden-
tified al Vimy Ibis upon the appearancc of the chilinozoan Eisenuckirina bohemicu (at about
- 752 m; Racheboeue ed.. 1986. Figs. 12-13); and at Noulette upon the appearance of lhe bra-
chiopod Mesodouvillina (M.) iriciilta (at about -850m, ihid., in cenozone 111).
Above this subsurface sequence, the outeropping Matringhem Sandstones correspond to the
AB und/or Su spore-zones .lensu Steemans (1989. Femelle .section and Jaeger quarry, Fig. 84
and 107), based on the occurrence of Apiculiretusispura plicata, Dictyotrilete.s suhgranifer and
Emphanisporites rotatus as determined by Streel {in LECLERCQ, 1975, localities No 24 and 37;
loc. 24 being very near lhe Rhinapteraspis dunensis locality of Vincly; Bl.lECK & JANVIER, 1989).
The Matringhem Sandstones are thus dated as upper Pragian-lower Emsian.
Il musl be mentioned here that. at the base of the sequence, the Traquairaspi.s zone should
be renamed, following the advice of Hedberc (1979, p. 88). This zone is indeed defined after
two species of heterostracans collected first in the Weish Borderland. These specics hâve been
recently revi.sed by TarraNT (1991) under Phialaspis syniand.ii and Tonmhsaspis pacocki; so
TARRANT renames the Traquairaspis zone, the PhiaJaspis .symondsi-Toombsaspis pacocki zone
(ibid., p. 402). However it seems to one of us (A. B.) that both species hâve to be kept in a
single genus, Phialaspis. as originally made by Write (1946). So the Traquairaspis zone has
to be simply renamed Phialaspis zone (Figs. 3 and 5). Neveriheless none of the Phialaspis
species has been found in Artois where the Phialaspis zone is identified on other taxa (the
— 451 —
FIG. 2. — Lower Devonian localities of northern France and Southern Belgium, with heterostracans and other lower veriebrates,
after Bueck (1982a, Fig 1 coniplefed), Blieck & J-vnvirr Blieck & Goujet (1991).
a- Posr-palaco?oic, b- Uppcr Palaco/oic (Dcvonian-Carbonifcrousl, c- lx»wcr Palacozoic (Cambrian-Silurian), d- faults, e-
Midi ()venhru.si. f fuS-silUerous loualities.
I- Samcr. 2- Dcnnebreucq. !'• Vincly, 3* Pernei-cn-Arlois, 4- Licvin, 5* Vimy. 6- Beaumoni-en-Artois, 7- Qiiiévrechain, 8-
Wihérics, 9- Bois Uc Colfoninine. 10- Btnchc. M- Thuin, 12- l.andcÜcs. 13- Acoz. 14- Vitrivnl. 15- Ben Ahin. I6- Huy. 17-
Ombrei, 18* Fraiponl. !9- Nonceveux 20- Pepinsicr. 21- Fay.s, 22- Étang de la fiileppe, 23- Êiang d'Eupen. 24- Mondrepuis,
25- Moulin de Fetrogne, 26- Cadsbonrg, 27* Paliscul, 28- Glaireuse (» Villance), 29- Bois d'Aulrougc Rossart), 30- La
Mouline. 31- Bistogne, 32- Mandé Saini-nilenne, 33- Saini-Vith, 34- Hanics Fugnes (Hohes Yenn, Solchbuch, etc.),
35- Arville. 36- Vireux, 37- Coulonvillers. 38- Bolland.
Localités d'à^e üé\'onicn injérieut' thi nord de la Frafu e et du sud de la Belgique, ayant livré des Héiérostrarés et d'autres
Vertébrés, d'ftprês BUECK l/y82a, fig. /. complétéef. BUCCK à JANVIER (1989), BUECK <fi GOVJET ( t99t ).
a- posl-Patéoznïqtie, Paléoznique supérieur ( Dévonten-Carhonifêre), t - PQléoz.oïque inférieur (Cambrien'Silurien), d- failles,
e- Faille du Midi, /• localnés fds.slhtéivs.
/- Samer, 2- Dennebreucq, 2*- Vincly, J- Pemes-en-Anots, 4- Lié\-in, 5- Vimy, 6- Beaumoni-en-Artois, 7- Quiévrtchain, 8-
Wihéries. 9- de Colfontaine. 10’ Biitche, II- Thuin. 12- Landelies, 13- Àeoz. 14 Viirival. 15- Ben Ahin. 16- Huy. 17-
Ombrei, IS- Fraiponi, 19- Noncevetix, 2ü- Pepinster, 21- Pays, 22- Étang de la Gileppe. 23- Étang d'Eupen, 24- Mondrepuis,
25- Moulin de Fétrogne. 26- Carisbourg. 27- Palisetil, 28- Glaireuse (= ViUance), 29- Bois d'Aulrouge (= Rossart), 30- La
Mouline, 31- Bastogne, 32- Mandé Saint-Étienne. 33- Saint-Vith, 34- Hautes Fagnes (Hohes Venu: Zweifall, Solchbach, etc.),
35- ArvÜle, 36- Vireux. 37- Coulonvillers, 38- Bolland.
thelodonts Turinia pagei and Tu. sp. A which. in the Weish Borderland. are known in the ‘Tra-
quairaspis zone": Bmeck & GoijJET, 1986).
A main différence appears when compared to the Weish Borderland .sequence: the Liévin
Group of Artois has been fully cored and we know exactly the respective stratigraphical location
of all the fossiliferou.s horizons. No overlap of the different vertebrate index-species is indicated,
contrary to what is assumed in the Ardenne massif from the spore analysis (Steemans, 1989;
Streel ei al., 1987). This is one of the reasons why we could define a Pteraspis rosirata zone
in Vimy shafi No I bis (Blieck & Janvier, 1989).
When counting all the vertebrate species through the stratigraphical log (Fig. 3), the richest
horizon is found at Liévin shaft No 6, within the lower Pemes Formation (the so-called Pemes
— 452 —
FIG. 3. — Synthetic straligraphy of the uppermosl Silurian-Lower Devonian séquence of Artois (Pas-de-Calai.s. France); chrono-
and lithostratigraphy after RaCHEBŒUF ed. (I98fi), Leclercq (1975). a, invertebrate-ba.sed assemblage biozones (cenozones)
1-VI of RachEBŒL'V ed. (1986), wilh B. the bryozoan-bearing beds. b, vertebrale-ba.sed interval biozoncs (ichthyozones) of
Blieck & Janvier (1989). c. spore zones afier Steeman-S (1989; modified aecording lo Blieck & Goiuet. 1991) and
Streel m Leclercq (1975). d. vencbraie species aller Gouet & Blieck (1979), Blieck & Goiuet (1986), Blieck &
Janvier (1989). Tbe right column gives Ihc number nf species of each assemblage.
Abbr.: P. rosr. - Pternsph ruximla zone.
* Tmquttiraspia zone: Ibis biozonc should be renamed Phiultispi.s zone (= Phitilaspis s\montisi-Ttionihsa.spis pococki zone of
TaRRANI, 1991; Tuumhxiixph being considercd here a synonym nf Phiataspis).
Svnihèse xtroiit^raphiifue Jii Silurien lenninaPOrvunlvii Itijêneur li'Artois IPas-de-Lalais, h rance! ; chronu' et liilwstraiigra-
phle d’apris RAClltHaï f dd. ll9Sf>\. l.krLEXCtj 11975). n. biii.-iniex d'assemblai'es d'invenébrés (cénozones) ! à VI de R.x-
CIIPIKEUP éd. (/W6) nwe lex biiilcs à Bryozxxain's (R), h. binzintex d'inlenalle de Venébréx (ichthyozones) de Bueck &
Janvier Il9ft9l^ e. hiozpnes de xpuie.s d 'après STEEMA.ys ( Ivft9 ; modifié selon BuECK & GouJET ( 1991 ) et STRf.kL in LECLERCQ
(1975). d. espèces de Veriébrés d'après Gdujli à Bur.CK 11979). Blieck & Goujf.t ( I9H6), Bueck & Janvier (1989). La
colonne de droite donne le nonibi'e d'espèces pour choiftie assemblage.
Ahrév. : P. rosi. = zone d Pleraspis roslrala.
s 7.one à Traquairaspis : cette btozone devrait êlir rebaptixre zone à Phialaspis ( = zone à Phialaspis symondsi-Totimbsaspis
pococki de TarranI, 1991 ; Toombsaspis éiant considéré ici comme .synonyme de Phialaspis).
— 453 —
Sandstones, also known in outcrops at the Pernes quarries), at the base of the R. crouchi zone.
Nine taxa bave been collected here but we can add a tenth one, viz., Pteraspididae gen. et sp.
indet. GOUJF.T & BLIECK (1979, Fig. 3 D-F and PI. XXIII: 8), paitly based on fragmentary
cornual plates [ihid., Fig. 3 D-E) which kiok like those of bolh ParaiHeraspis juckuna and Imt-
novaspis siensioei (sensu ÜI.IECK. 1984). Above and below this horizon, the ichthyofauna is
much poorer, probably bccause of hoth scarce ouicrop.s and taphonomical conditions. Il can how-
ever be noted that this R. crouchi a.s.semblage (reconstructed by BUiCK & Janvier. 1989. Fig.
12) is correlated to the part of the Ben Nevis Formation of Spitsbergen where we find the
Protopteraspis vogti horizon (Goujet & BLIECK, 1977), which is also the richest horizon of the
Lochkovian sequence of Spitsbergen (Blieck et al., 1987, Fig. 2; 30 different généra). This
time span thus seems to correspond to an acme of the ichthyofaunas on both sides of Laureuropa.
THE SEQUENCE OF ARDENNE
In contrast to the Artois sequence, the Ardenne one is not continuons. It is compiled from
isolated, oulcropping fossil localities, which hâve bcen correlated to bolh the British and the
Artois séquences. Some arc linked to the spore zones of Stremans (1989), some are not (Fig. 4).
Generally speaking. there is a rather good agreenienl between the different seules, and we find
in Ardenne the crouclü-leachi-dunensis succession already defined in the Welsh Borderland.
However a problem arises:
a) Arville (lac. 35, Fig. 2). which bears an AItluispis leachi assemblage and is thus considered
stratigraphically younger than Nonceveux with its R. crouchi? specimens (Blieck & Güu.iet,
1991), has been correlated by Steemans ( 1989; in Streel et al.. 1987) to an aider spore zone
than Nonceveux (Fig. 4);
b) Belzdorf in the Siegen area of western Germany (= Betzdorf-Kirchen in Blieck &
Jahnke. 1980), yielded Rliinopieraspis dunensis and should be considered younger than Wihéries
or Fraipont (loc. 8. 18, Fig. 2) which yielded A. leachi; but Belzdorf is correlated by Steemans
(1989) to an older spore zone (Fig. 4).
These results led SlEFMANS to propose stratigraphical overlaps between the different pte-
raspid index-species crouchi-leachi-ditnensis (Fig. 4). The main contradiction to this scheme is
that no locality wilh crouchi + leachi or leachi + dunensis has ever been found. We thus hy-
pothesized reworked lhanalocenoses in the Ardenne spore a.ssemblages. which was denied by
Steemans (in Blieck & Goujet, 1991). The problem remains thus unresolvcd.
By means of corrélation with the chilinozoan succession of Brittany (France) and Bohemia
(Czech Republie), the spore zonation is linked to the Lochkovian-Pragian type sériés (Streel
et al., 1987). The Lochkovian/Pragian boundary falls within the leachi distribution inierval.
Futhermorc there is no définition of the “Gedinnian/Siegenian" boundary. neither in the type
Gedinne area of Belgium, nor in the type Siegen area of Germany.
A probable Pteraspis rostrata zone also occurs in the Ardenne massif at Ombret (loc. 17,
Fig. 2) but is not correlated to any part of the spore scale.
— 454 —
vy
to
C M
LOCHKOVIAN PRAGIAN EM5IAN
— 455 —
The richest assemblage was collecied in Arville and correlated to part of the succession of
northern Spain (Blieck & Goujet, 1991) because of the occurrence of the chondrichthyan
Leonodus Mader (1986; see aiso Wang, 1993),
INTERREGIONAL CORRELATION AND CONCLUSION
Six ichthyozones hâve been defined from the base of the Devonian up to the lower Emsian;
they hâve been originally documented in the Welsh Borderland of England, and then comple-
mented in Artois. Ardenne and part of the Rhenish Slate Massif (Fig. 5). Ail the ichthyozones
are intersal biozones, defined at their base on the first occurrence of their index-species. Due
to the scarcity of outcrops in these green. wet Atlantic provinces of western Europe, and to the
taphonomic conditions in several kilometers thick, detrital sériés (the Lower Old Red Sandstone),
the fossilifcrous record is not good and the précision of the ichthyozones is not veiy high.
We hâve indeed six ichthyozones for a time interval of about 18.5 million years (2U Ma
after CowiE & Bassett, 1989, and OUIN & Odin, 1990; re-evaluated by Fokdham, 1992:
- 408.5 Ma at base Lochkovian, - 390 Ma at base- Emsian), so an average duration of ca. 3 Ma
per ichthyozone (3.08 “exactly"). This is much less précisé than the spore zonation (Fig. 5), but
as précisé as the conodont succession of the Lower Devonian carbonate sequences which yield
seven conodont zones in the Lochkovian-Pragian time interval (HouSE. 1988; Oliver &
CHLUPAC, 1991; FORDHAM. 1992),
A major problem romains to be .solved, viz., to correlate the vertebrate and spore-based
succession to the conodont-graptolitc-dacryoconarid-based succession. The latter was uscd to ca-
librate the sca-level curvcs of varions continental platforms of Euramcrica (Dennison, 1985),
Australia and SW Siberia (Talent & Yolkin. 1987), and the Canadian Cordillera (MORROW
& Geldsetzer, 1988). A high .sea-lcvcl is in evidence in the mid-Lochkovian uppermost
eurekaenais conodont zone (Fig. 6). It might be that the acme of the vertebrate fauna at the
lower crouchi zone of Artois (Fig 3) is related to that high stand, but it lias to be demonstrated.
On another hand the impoverishment of the vertebrate fauna of the upper leachi and lower dunen-
sis zones (Figs. 3, 4) might be related to the low sea-level in the upper Lochkovian-Pragian
(Fig. 6) [However this review is mainly based upon agnathan taxic data and should be extended
to gnathostomes as well].
FIG. 4 — Synihetic stratigniphy ol ihe Lower Devonian sequence of Aidenne (Belgium) and pari of Ihc Rhenish Slate Massif
(Germany). a, clironosiraiigraphy and spore zonation of Stfemans (.1989, and in Streel er oi. J 987). b. distribution of the
spore-dated vertebrate localilics (ïaunal liais after BlIECK. & Jahnke, 1980; Blieck, 19823. b: Bl.lHCk & GtH'JF.T, 1991). c,
iilhostratigraphy of StreEL et al. (1987). d, lenlalive dintribulian of other vcrlehrale localiüe.s which aie not daled by spores.
Note thaï the Lower Devonian séries may be more than 3,500 m Ihick, particularly in the Arville région.
Synthèse strotigruphique tiu Dtvonien inférieur J'Arfirnne {Belgit^ue) et tJ'une partie du massif srhisteiLX rhénan {AUemagne).
a, chrofimiratigraphie et zones de spores de Stekmans (7989. et in STREEL el al,. I9H7). b. répartition des localités à Vertébrés
datées pur spores (tisfr.s fauniques d'après BlîECK âi jAfWKE. I9S0 : BtAECK. îyH2a. b : BUECK tfe GoUJHÏ. /99/). c. litho-
stratigraphie de Streel ci al. il9fi7). d, essai de répartitUm des autres localités à Vertchrés qui ne sont pas datées par
spores.
Notez que la série d'âge Dévonien inférieur peut dépasser les SSBBnt en épaisseur, en porfiruher dons la région d' Arville.
— 456 —
O C H K O V
.PRAGIAN
polynozone o ^ p a I y no z o n e MN •>) polynozone BZ o
' ’ tripapiidtuS'SDicula o micro rna t us ^newoortens is breconensis-zaya/lâtus
DOWNTON (>R0UP
(Up Lfdbury F«n.)
TTON GROUP
^1 '.“î i
o^lo ï
3 S I 3 § ■* 3 ^
i I 1 I I )
crouchf zone
I r I I I I
32
I eachi zone
’o
‘n ‘,c
\û P
V-r "3-
.û •
LOCH KOV I A N
5? _ LIÉVIN GROUP ( thictness^Sîl m ) _ I
ï< NOULETTE PERNE5 FORMATION |
x( 2 < - 1 - ■ " i
= / FORMATION • - 'pgRNES SANOSTONES'- ' V I M Y SAN DSTO NESi
-brar' - 1
NOULETTE
cnnLi A T m Al ^ <
. 'S '•1^1 fihinopt erç spi s
1^3 £ „3 c.ouca,
Alfhaspis leaehi
zone
■PRAGIAN-EMSIAN
I - \
I ï ~ ^ s I _
' - • ^ _ t* ^
|f R. dunen sis
I Z o n e ^
o?/
'GEDINNIAN'
(Gedinne région)
SIEGE-!
N lAN' I
EM5IAN
— 457 —
FIG. 6. — Qualitative eu.'ttatic curve.v for (A) Euramerica, (B) Australia, (C) SW Siberia. after Dennison (1985) and Talent &
Yolkin (1987, Fig. 5. madiFied according tii Oliver & Chlupac, 1991. fur the conodont biozone.s).
Abbr.: E. = lower Emvian Radinchrnnoiiietric data after Fordh.am (1992).
Courbes eustaîiijue,s qualitatives pour IA) V F.uramcrique. (B) l’Australie, (Cl la Sibérie du 51V( d’après Phnnison 11985) et
Talent <ê Yolkin (1987, Fig. 5. modifiée selon OuvEtt & Chlupac, 1991, pour les biozones de Conodontes).
Abrév. : E. = Etnsien inférieur. Données radiochronologiques d'après FoRDHAM (1992).
Acknowledgments
Pr D. L. Dineley is sincerely thanked for his suggestions and corrections on the manuscript.
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Tarrant, P. R., 1991. — The ostracoderm Phiala.^pi.^ front the Lower Devonian of the Welsh Borderland and
South Wales. Palaeontology, 34 (2): 399-438.
Vanguestaine, M., T. Servais & P. Steemans, 1989. — Biostratigraphy of 28 boreholes in the Brabant Massif.
In: Caledonides Brabant Midlands (Intern. Meet. Caled. Midlands Brabant Massif, Brussels, 1989): 46 (Ab¬
stract.)
Wang, Ronghu, 1993. — Taxonomie, Palôkologie und Biostratigraphie der Mikroichthyolithen aus dem Unter-
devon Keltiberiens, Spanien. Cour. Forsch.-Inst. Senckenberg, 161: 205 pp., 22 Figs.., 18 Pis.
White, E. I., 1946. — The genus Phialaspis and the “Psammosteus Limestones”. Quart. J. Geol. Soc., London,
101 (1945): 207-242.
— 1956. — Preliminary note on the range of Pteraspids in Western Europe. Bull. Inst. Roy. Sel. Nat. Belg.,
32 (10): 1-10.
Bull. Mus. natl. Hist. nat., Paris, 4^ sér., 17, 1995
Section C, n” 1-4 : 461-485.
Vertebrate microfauna from the Devonian/Carboniferous boundary
stratotype at La Serre, Montagne Noire (Hérault, France)
by Claire DERYCKE, Alain BLIECK and Susan TURNER
(Contribution to IGCP 328 “Palaeozoic Microvertebrates”)
Abstract. — Vertebrate microremains hâve been prepared by acid leaching from oolitic limestone beds at
the Devonian/Carboniferous boundary stratotype of La Serre, southea.stern Montagne Noire, Southern France.
They ail corne from the lowermost Carboniferou.s beds 89 lo 99, i.e. the sukara and kockeli deiiiilineutiis conodont
zones. Most remains are of elasmobranchs; Symmonuin sp., Siethacamlui.t? sp., Ctenacanthidae gen. et sp. indet.,
Phoehodus cf, P. iHisiralifiisis, Thrimuodus ftros, Prohwrodus ci, P. velusitis, P. sp., Elasmobranchil gen. et sp.
indet.. types A-C; with a few actinoplerygian teeth. The assemblage correlates well with other Upper Devonian-
Lower Carboniferou.s localities from the USA, western and eastern Etirope, southeast Asia, China, Moroccn and
Australia.
Keywords. — lehthyoliths, Devonian/Carboniferous boundary. auaioiype, Montagne Notre (France), bios-
tratigraphical corrélation, .systcmatics. elasmobranchs, actinopterygians.
La microfaune de Vertébrés du stratutype de la limite Dévonien/Carbonifère
à La Serre, Alontagne Noire (Hérault, France)
Résumé. — Plusieurs niveaux de calcaire oolhique du stratoiype de la limite Dévonien/Carbonifère, à La
Serre (Montagne Noire SE, France méridionale i, ont livré par attaque acide des microrestes de Vertébrés. Ils
proviennent des bancs 89 à 99, datés de la base du Carbonifère, c'est-à-dire des biozones de Conodontes à
sulcata et à kockeli-deninitteiinis. La plupart des microrestes sont ceux d'Élasmobranches : Symmorium sp.. Ste-
thacanthus? ,sp., Ctenacanthidae gen. et sp. indet., Phoehodus cf P. austrahemis, Thrimicudus lerox\ Prouicrodus
cf P. velustHS, P. sp-, Eissrnohranchii gen. et sp. indet., types A-C ; mai.S quelques dents d’ Açiinoptérygiens ont
aussi été extraites. L’assemblage est très proche de ceux qui ont été récoltés dans des localités du Dévonien
Supérieur-Carbonifère inferieur des Élat.s-L'nis, d'Europe occidentale et orientale. d’A.sie du sud-est. de Chine,
du Maroc et d'Australie.
Mots-clés. — Ichthyolithes, limite Dévonien/Carbonifère, stratotype. Montagne Noire (France), corrélation
biostratigraphique. systématique. Élasmobranches, Actinoptérygiens.
A. Bcieck Ai C. Dericke, Oniversilé tle.i .memes el technologies de Lille, Sciences de la terre, LIRA 1365 du CNRS, 59655
Villeneuve d'Ascq Cedex. France.
S. Turner, Queensland Muséum, PU Box 3300, South Brisbane, Qld. 4101, Australia.
Introduction
Late Palaeozoic vertebrate.s are rare in the Montagne Noire where three sections in the
Mont Peyroux-Pic-de-Bissüus and Cabrières areas hâve yielded few Devonian acanthodians,
cochliodonts, and placoderms. Among the latter, Metunosteus occitanus LELIÈVRE & GOUJET {in
Lelièvre et al., 1987) from the upper Frasnian Keliwasserkalk faciès of La Serre Formation,
— 462 —
at La Serre trench C, is the best preserved species and contributes interesling features to the
debate on phylogenetic relationships of selenosteid pachyosteomorph placoderms.
Acid leaching of diverse conodont-bearing carbonate rocks of the Devonian sequence of
this région was unsuccessfully carried oui by one of us (A. B.) in the search of vcrtebrate mi¬
croremains. However. during Dr R. Feist's (ÜSTL. Montpellier, France) work on the Devonian-
Carboniferous (D/C) sequence of Montagne Noire, which bcars on defining the D/C boundary
stratotype by the Subcommissions on Devonian and Carboniferous Stratigraphy of ICS (lUGS-
UNESCO), vertebrate microremains were found with conodonts by Dr G. Flajs (RWTH, Aachen,
Germany) in the basal Carboniferous beds (Flajs et al., 1988; Paproth et al, 1991). At the
same time, efforts of one of us (S.T.) lo organise Palaeozoic microvertebrate experts’ activities
led to the iGCP Project 328 (TURNER, 1991-92). One of the topics of this proJect is the D/C
boundary vertebrate stratigraphy, and thus the présent study.
GEOLOGICAL SETTING
The Montagne Noire is located in southem France, at the Southern edge of the Central
Massif West of the Alps. It is part of the southem Hercynian fold belt of Western Europe (Fig.
lA). There is a very complicated tectonic structure with nappes and klippen on the southeastern
flank. La Serre is located within the klippen area (“Écailles de Cabrières”; Fig. IB). These klippen
correspond to olistoliles in the syn- and post-iectonic Hercynian (Visean lo Namuriani wildflysch
of the Mont Pcyroux — Pic-de-Bissous nappe area (Engel et al, 1978, 1979, 1982). The recons-
tructed sedimentary sequence of the klippen shows a thick sériés of Lower Ordovician to Lower
Carboniferous rocks more than 1000 m thick and without significanl gaps. The Middle to Upper
Devonian and Lower Carboniferous beds of this sequence are chiefly limestones, with a dominant
uppermost Devonian to lowermost Carboniferous nodular-limestone faciès (“Griottes”).
In general, the upper Famennian-lower Tournaisian beds are not présent in the klippen (e.g.
at Tourière, Fig. IB) where the succession is inlerrupted by a few decimeters of argillites re-
FlO. I. — Location of the Revonian/Carboniferou.s boundary stratotype at t-a Serre, .southea-stem Montagne Noire, France. A,
location of Montagne Notre among üie Hercynian mas'ifs ol’ France (batched); B. location of La Serre in the klippen area
("Écailles de Cabrièrc.s") of southeastern Montagne Noire; C. the reference section La Serre trench E' with distribution of
index conodonts and Irilohitcs Ispeçics A. (PhilHhi’Iel rriipus) and Cnrhimocorsphe {Wmteiherifi<i?l funirepa corne frora the
neighbouriiig sections La Serre trench C and Col-de-l’Orte. respeciively], and environmcntal mlcrpretation of some dcpositional
and faunal cléments lafier FLAJ.S & Feist. I9!i8, Figs. I. 5. 6). Whiie: ooiitic iintcslones: datk grcy: various other limestones;
lighl grey: siliciclaslics. Vcrtehraïc microreniains hâve bcen prepured froni beds 89 lo 99.
Localisation tin stratotvpc de la limite Üct onien/Carbonifin à La Serre, au sud-e.st de la Montagne Noire, France. A, place
de la Montagne Notre parmt les massifs heiryntens de France {hachurés) ; B. place de tut Serre dans la région des klippes
C'ÉcatlIes de Cabrières") du sud-est de la Montagne Noire: C. coupe de référence de la tranchée E de la Serre, arec
disiribiiiion des ct/nodimies manfueurs et des Trilobiies //e.i espèces A. (Phillibole) crispus et Carbonocoryphe (Winterbergia?)
funirepa proviennent des coupes voisines de la Serre, tranchée G. et du Col de l’Orle respectivementl, avec interprétation
environnetneniale de quelques éléments sédiineniatres et .fauniques (d 'après Fuji & FblST. I9SS, figs I. 5. 6). En blanc :
calcaires ooliihiques : en gris fonce: autres calcaires: en gris clair: siliciclastiies. Les microrestes de Vertébrés ont été
estraits des niveaux S9 à 99.
— 464 —
presenting, at leas>t in part, the équivalent of the Hangenberg Shale of the Rhenish Slate Massif
(Germany). This shale constilutes a widespread faciès type at the D/C boundary and may corres¬
pond to a worldwide régressive eustatic event (référencés in Feist, 1983, 1990; FEIST & Flajs,
1987; Flajs & Feist, 1988). The only exception to this gap in the klippen area of Cabrières is
at La Serre Hül where uppermost Devonian clymenüd-bearing rocks are overlain by D/C tran-
silional biodetrital calcoolites yielding protognalhodid conodonts and trilobites, followed by lower
Tournaisian marly nodular liniestones. The La Serre trench E' (dug on the soulhem slope of the
hill) shows an uninterrupted carbonate sequence across the D/C boundary in the upper part of
the middic rnember of the Griottes Limeslonc; the section is not ovciuirncd here, and schistosity
and tccionic complications are absent. It has yiclded a faunaof conodonLs and trilobites (Fig. IC;
Flajs & Felst. 1988). but also cephalopods, brachiopods. coraLs. foraminifers, algae, conchos-
tracans, bryozoans, gasiropods, bivalves, ostracodes. and microproblematica (Legfland-Blain &
Martinez-Chacon. 1988; Semenoff-Tian-Chansky. 1988; Vachard, 1988; see a complété
faunal lisi in Feist, 1990, Fig. 35; Paproth et al, 1991. Fig. 6).
The D/C boundarj' transitional beds correspond to "a typical near-shore environment under
normal marine conditions” as indicated by the “abundant ooids, cortoids and benthic organisms
occurring throughout the section" (FI.AJ.S & FEIST, 1988: 65). They correspond to an oolitic
limcstone interval wilhin the “basinal”, pclagic limestone faciès of the sequence. This oolitic
interval contains “very rich. reworked conodont associations which are représentative of the entire
Upper Devonian” {ihid., p. 54-.55), but the authors concluded ihat the youngest éléments in the
associations allow “unequivocal stratigraphical dating". In contrasl, “macrofossils, such as trilo-
bites or brachiopods, hâve not been reworked” (ihid; see also LEGRAND-Bt.AiN & Martinez-
CllACON, 1988; 119-120). However, many of the calcareous microfossils are indicative of the
upper Famennian (".Striinian” of authors; Vachahij, 1988; 140-141), so the possihility of their
transportation cannol be excluded; however, “as they occur, at La Serre, within the sulcata Zone,
they extend into the lowermost Carboniferous” (ihid., p. 141).
Verlebrate microremains hâve been extracted from beds 89 to 99. le. front the lowermost
Carboniferous sukata (beds 89 to 98) and kockeli-deniilinealus (bed 99) conodont zones (Fig.
IC), No vertebrate has been pbtained from below the D/C boundary. It should be noted that at
La Serre the vertebrates seem to be restricted to the oolitic faciès. As part of the fauna is re¬
worked. it may be that the vertebrates are reworked as well. This could explain their restricted
stratigraphical range and it would be in accord with their poor préservation.
SYSTEMATICS
Only a few scales and teeth of gnathostome fishes hâve been obtained. They are not well
preserved. However, they extend to Southern France and its D/C boundary stratotype a vertebrate
assemblage already known worldwide. As these remains are scarce, no thin section has been
made; ail déterminations are based on external morphology. The scanning électron micrographs
were made on a Cambridge Stereoscan 240. The specimens are deposited in the vertebrate col¬
lection of the University of Lille, Villeneuve d’Ascq, France (CVUL).
— 465 —
Class CHONDRICHTHYES Huxley, 1880
Subclass ELASMOBRANCHII Bonaparte, 1838
Prfximinary Systematic remarks
In most recent papers on isolated Palaeozoic elasmobranch microreniains authors use
Zangerl’s (1981) classification (see also Carroll, 1988). However, instances of non-compli¬
ance with the rules of the International Code of Zoological Nomenclature (ICZN: Ride et al.,
1985) arc présent in thaï clas.sification.
The superfamilies Ctenacanthoidea, Hybodontoidea and Edestoidea are incorrectly attributed.
Becausc of ihc coordinaie status of family-group namcs (ICZN art. 36), the following corrections
hâve to he made: Ctenacanthoidea Zangerl, 1981, should be Ctcnacanthoidea Dean, 1909, based
on the fainily Cienacanihidae Dean, 1909; Hybodontoidea Zangerl, 1981, should be Hybodon¬
toidea Owen. 1846, based on the family Hybodoniidae Owen. 1846 (in Cappetta, 1987); and
Edestoidea Hay, 1930 (in ZANGERL, 1981) should be Edestoidea Jaekel, 1899, based on the
family Edestidae Jaekel, 1899.
The family name Phoebodontidae is attributed to WiLLIA.vis (1979) by ZANGERL (1981:
54). However, “WILLIAMS, 1979" is a Ph. D. dissertation (ref. in ZANGERL, 1981: 109) which
does not constitute a publication [ICZN art. 9 (II)]. The auihorship of tins family thus should
be given as Phoebodontidae Williams in ZAN'GERL, 1981. or strictly as Phoebodontidae Zangerl,
1981, although il was formally established by Williams (1985: 124).
The family name Diplodoselachidae is attributed to Dick (MS) by Zangerl (1981: 64),
but Dick’s paper was published the same year (DlCK. 1981); the correct authorship citation thus
is Diplodoselachidae Dick, 1981.
What also seems strange when looking at the proposed phylogenetic relationships of the
Eugeneodonlida ZANGERL (1981. Fig. 102; Eugeneodonliformes Zangerl. 1981. in CAPPETTA,
1987), is to hâve lhe ordinal name Eugeneodonlida creaied afier the family Eugeneodonlidae
which is included in lhe superfamily Caseodontoidea. It would hâve been préférable to name
the order after one of its constituent superfamilies, the Caseodontoidea or Edestoidea. Or why
not Edc.slida. which existed prior to ZanGERI.'s work (1981: 74)?
Another point to be made is that some of Zangf.rL's superfamilies or orders are not based
on familles; e.g. Hybodontoidea (ZANGERL, 1981: 56: but family Hybodontidae Owen, 1846
exists: CAPPETTA. 1987), Protacrodontoidea (regarded by Zangf.RL, 1981: 61, as équivalent to
family Tamiobatidae [Tamiobaiidae Hay, 1902 after Glikman in Obruchev, 1964; but not famio-
balidae Glikman, 1964 after ZANGERL]; but Tamiohatis is considered “not prcsently identifiable
as to order" by Zangerl, 1981: 102), Desmiodontida (ibid., p. 62), Coronodoniida (ihid., p. 68;
but family Coronodonlidae Harris, 1950 exists: Wit,Li.\MS, 1985: 132), Petalodonlida (Zangerl,
1981: 94, without family name for the non-prisiodontid petalodonts, although family Petalodon-
tidae Newben-y & Worthen, 1866 does exist), Squatinactida (ihid., p. 101; but family Squati-
nactidae is used by LliND, 1990: 4). It is, of course, always easier to criiicize than to create a
cohérent systcmatics (mainly when isolated, fragmentary microremains are concerned), but users
of Zangerl’s .system should be aware of lhe.se discrepancics. However. lhe lack of familles in
Zangerl's .systcmatics is not simply a matter of omissions. The discrepancics are due to legi-
— 466 —
timate différences of opinion vvhich stem primarily from the inadéquate record of the groups
concerned. The Petalodontidae is a good example, the name indeed exists but nobody knows
which généra it should include (J. ZiDEK, written comm., 1992). We follow Zangerl’s classi¬
fication, slightly modified.
Order SYMMORIIDA Zangerl, 1981
Family Symmoriidae Dean, 1909
Genus’sYMMORIUM Cope, 1893
Symmorium sp.
(Fig. 2; Pis 111, D; IV, B-C)
Referred material. — Three isolated teeth from beds 95 (CVUL 13) and 99 (CVUL 15-16).
Description and discussion
These three teeth are typically cladodont, i.e. multicuspidate with a tall central and shorter
latéral cusps. The kidney-shaped base with ihe labial side strongly concave Just below' the main
cusp (labial sinus) is the main character of Sywmonum fsee the amendcd generic diagnosis of
Wli.l.iAMS, 1985: 103). The central cusp is tall. lingually curved, and labially bears sharp and
narrow- longitudinal cristae w'hich converge in CVUL 16 (PI. IV, C). A cutting edge (carina) is
noticeable on the main cusp which is labially flattened and lingually strongly convex. Shorter
latéral cusps number one to three pairs, the second one being slightly taller. Their cross sections
are circular.
AH cusps are arranged along the labial margin of the base. The characters noted above are
those of S. reniforme (see Williams, 1985). However, as we hâve not seen the original material
of S. reniforme, and because our specimens are microscopie (max. 1.5mm long) and poorly
pre.served, we prêter staying in open nomenclature. According to Wili.iams (1985: 107), Sym¬
morium teeth possess an additional feature. "The inner of the latéral pairs (of denticles of the
Crown]... is produced outward so that a line drawn connecting the centers of the cusps would
describe a broad, low, “W” (PI. 7. Fig. 2)” as one of our specimens (PI. HI, D). One tooth (Fig.
2a) shows Iwo noticeable basolabial facels undemcalh the two latéral cusps, which is charac-
teristic of the genus Symmorium (ZiDEK, 1992: 152). On the two other teeth, it is not so évident
because one (Fig. 2b) is worn and the other (Fig. 2c) is recovered by recrystallisations.
Two teeth (PI. IV, B-C) possess an inclined main cusp; this asymmetry should be an in¬
dication of the position in the mouth. The base of CVUL 15 (PI. IV, B) is pierced by two large
foraminae on the lingual and aboral faces, connected by a canal which is exposed due to wear.
It looks like an hemiaulacorhize base sensu CASIER (1947). Symmorium sp. described by Long
(1990) from the late Famennian of northern Thailand differs from our sample mainly by the
shape of the base, which in the Thailand form is dumbbell-shaped. The specimens illustrated
by Wang (1989, PI. 28, 3; PI. 30, 5) from the Dapoushang section of south China aiso belong
to Symmorium.
— 467 —
b
C 0.5 mm
' CS.
FlG. 2. — Symmorium sp., isolated teeth, aboral views. a, CVUL 13 from bed 95, same as P). III, D, labial margin faces up. b,
CVUL 15 from bed 99, same as PI. IV, B, labial margin faces down. c, CVUL 16 from bed 99, same as PI. IV, C. labial
margin faces down.
Symmorium sp.. dents isolées, vîtes ahorales ou basales, a. CVUL 13 du banc 95. même spécimen que pl. ///. D, te bord
labial est tourné vers le haut. b. CVUL 15 du banc 99. même spécimen que pl. IV, B, le bord labial est orienté vers le bas.
c. CVUL 16 du banc 99, même spécimen que pi IV. C, le bord labial est tourné vers le bas.
Family Stethacanthidae Lund, 1974
Genus STETHACANTHUS Newberry, 1889
Stethacanthus? sp.
(Fig. 3; Pis 1, C; II, A-B; IV, D-F)
Referred material. — Isolated teeth from beds 89 (CVUL 3), 92-93 (CVUL 6-7), 99 (CVUL 17-19).
Description and discussion
CVUL 3 (Pl. I, C) is a cladodont tooth with a main central cusp and three pairs of latéral
cusps, ail arched lingually. The first and the third pairs of latéral cusps are shorter than the
second pair. The vertical cristae do not bifurcate near the base and are not accompanied by
intercalated cristae as is often the case in Symmorium. The two surfaces are separated by a
cutting edge (carina). The base is well drawn, triangular and punctuated by some foramina. On
the labial margin, it is produced into a rectangular basolabial articulating boss below the main
— 468 —
FlG. 3. — Stethacanthus? sp., isolated teeth, aboral views, labial margins face up. a, CVUL 3 from bed 89, same as PI. I, C. b,
CVUL 7 from bed 92-93. .same as PI. lî, B. c, CVUL 6 from bed 92-93. .sarae as PI. II. A. d. CVUL 17 from bed 99, same
as PI. IV. D. e, CVlfL 18 from bed 99, same as PI. IV. E. f. CVUL 19 from bed 99. same as PL IV. F.
Stethacanthus? sp., dents isolées, aborales ou basales, les bords labiaux sont tous orientés vers le haut, a, CVUL 3 du
banc 89. même .spécimen que pi. f. C. h. CVUL 7 du banc 92-93, même spécimen que pl. II. B. c, CVUL 6 du banc 92-93,
même spécimen que pl. IL A. d. CVUL 17 du banc 99. même spécimen que pl. IV. D. e. CVUL J 8 du banc 99. même
spécimen que pi IV. E. f, CVUL 19 du banc 99, même spécimen que pi IV L\
— 469 —
cusp and towards the inner margins of the first latéral cusps (Fig. 3). This is a distinctive character
of Stethacanthus according to WILLIAMS (1985). Abovc the latéral cusps is a distinct crest. How-
ever, a coronal view shows lingually on the base a button (lingual articulating boss) and a bound-
ary delineating the crown.
As is often the case in Ste/hacanlhiis, the two teeth from bed 92-93 (PI. 11, A-B) hâve five
cusps, ail of them broken. The central cusp is the tallest, and the latéral pair is taller than the
intermediate pair, as is apparent from the diameters of the cross .sections. The cristae are the
most évident on the lingual surface. The carina is not well defined, especially in CVUL 7 (PI.
11, B). The rectangular basolabial boss is visible just below the central cusp of CVUL 7 (PI. 11,
B). This tooth has a strongly concave aboral surface, which bears a central big foramen. Another
foramen is located just below the central cusp, and a third one is in the middie of the lingual
face of the base, in effect dividing the lingual articulating boss (Fig. 3b). The base appears to
be hemiaulacorhize sensu CASIER (1947).
Three other teeth, from bed 99 (PI. IV, D-F), hâve less broken but more worn cusps, The
longitudinal cristae are still visible on the central cusp of CVUL 17 (PI. IV. D). but nol on the
others. The bases are subtriangular or five-sided, with a prominent lingual boss and numerous
small foramina (Fig. 3d-f). A similar tooth with a sharpiy triangular base was illustrated by
Wang (1989, PI. 30, 5-6, ‘‘'Cladodus" sp.) and thought to be a new genus by Turner & Wang
(1992).
Superorder EUSELACHll Hay, 1902
Order CTENACANTHIFORMES Nelson, 1976
Superfamily CTENACANTHOIDEA Dean, 1909
Family CTENACANTHIDAE Dean, 1909
CTENACANTHIDAE gen. et sp. indet,
(Fig. 4b-c; Pis 11, C; 111, A)
Referred materi.vl. — Two isolated scales from beds 92-9.S (CVUL 8), 95 (CVUL 10).
Description and discussion
These are scarce, isolated, partially broken ctenacanthid scales {sensu Reif, 1978). The first
one, from bed 92-93 (PI. IL C). bears longitudinal ridges thaï anteriorly split into two or three
branches. The posterior concave surface which forms the neck is punctuated by a line of well
developed foramina (Fig. 4b). The scale is wider than high and the base is concave.
The second .scale. from bed 95 (PI. 111, A), is attributed to Ctenacanthidae with some doubt
because it has a vcry convex bony base (Fig. 4c). Its crown bears bifurcating ridges and its
anterior edge is locatcd on the diagonal axis of the square base. The ridges radiale from the
anterior edge to the postérolatéral corners of the crown.
We compare our scales wilh the ctenacanthid scale type of Reif (1978) which occurs in
Ctenacanthus castellalus and Goodrichthys eskdalensis. As very few publications deal with iso¬
lated scales, our taxonomie assignment must be considered tentative.
470 —
e
0.5 mm
■ ‘
C p.
Fig, 4. — a, Pmtacrodus sp., loolh CVUL 12 from bcd 95, sûmc as PI. III, C, basolabial view. b-c. Ctenacanthidae gen. et sp.
indet.. scales (bi CVUL 8 from bcd 92-93. .same as PI II, C. linauobasal view, and (c) CVUL 10 from bed 95, same as
PI. HL A, aboral view. d-e. Prtmcmdus cL R vctustus, associated ^celh CVUL 22 from bed 99, same as PI, IV, 1. labial or
lingual (d) and aboral (e) views,
a, Protacrodus Sf\, dent CVUL 12 du hanc 95. même spécimen que pi ///. C ^'ue hasolabiale. h-c, Ctenacanthidae gen. et
sp. indet., écailles ib) CVUL b du banc 92-93, même .spécimen que pi //. C. v«e Unguobasale, et (cl CVUL 10 du banc
95. même spécimen que pl- Ul. A. wif abarate ou basale, d-e, Protacrodus cf. P. veiusius, dents imbriquées CVUL 22 du
banc 99, même spécimen que pl. IV, I, Vues labiale ou linguale fd) et aborale ou basale (e).
Family PHOEBODONTIDAE Williams in Zangerl, 1981
Genus PHOEBODUS St. John & Worthen, 1875
Phoebodus cf. P. australiensis Long, 1990
(Fig. 5; Pl. IV, G-H)
Referred material. — Two fragmentary teeth from bed 99 (CVUL 20-21).
— 471 —
Description and discussion
These teeth lack small intermediate cusps. The lingual surfaces of the three cusps are or-
namented by five coarse cristae. The central cusp leans slightly towards one of the latéral cusps.
The base resembles a half-ellipse (Fig. 5b). Under lhe main cusp is a prominent basolabial boss.
A longitudinal groove (Fig. 5b) with some foramina is also apparent. These teeth are very similar
to P. aiisiraliensis Long (1990. Figs. 2-4; see also GiNTER, 1990, PI. £, 3-11) but the cusps are
more densely cristated on the tooth sides and their tips are not as pointed. On our maierial the
lingual torus shows more foramina (Fig. 5a) than on P. australienxis Long (1990). P. australiensis
is based on material froni Thailand. Long (1990) named this species australiensis because of
its resemhlance to other teeth from Australia (Phuebodus cf. F. pulitus in TURNER, 1982. Fig.
6 A-B; but also from China: Phoehodus politus in WANG & TURNER, 1985, Pis II, 1; III, 2).
However. it appears that the teeth from Australia and some from China differ from P. australiensis
in having more massive and erect cusps (see comments by Gl.NTER, 1990; 73-74; GiNTER &
IVANOV. 1992; Tlirner & Wang, 1992). So P. australiensis is known from Thailand, China,
Poland, France, and probably also Germany (after Ginter, 1990: 73; see Gross, 1973. PI. 34,
3) , whereas tJie Australian and some of the Chinese Phoebodus are not australiensis ! Neverthe-
less, few teeth from Guizhou, China, which WANG (1989. Pis 28, 2, 5; 29, 3-4; 30, I; PI. 31,
4) called "’Cladodus spp.", correspond to P. australiensis teeth (sec also Turner & Wang. 1992),
and are most like those from La Serre. This species appears to be typical of the latest Famennian
to early Tournaisian interval.
b
a
0.5 mm
C^.
Fig. 5. — Phoebodus cf. P. australiensis, isolated tooth CVUL 20 from bed 99, same as PI. IV, G. a, lingual view. b. aboral
view, labial margin faces up.
Phoebodus cf. P. australiensis, dent isolée CVUL 20 du banc 99, même spécimen que pi IV. G. a. vue linguale, b, vue ahorale
ou basale, le côté labial est orienté vers le haut.
— 472 —
Genus THRINACODUS St. John & Worthen, 1875
Thrinacodus ferox (Tumer, 1982)
(Pis III, B; IV, A)
1982 Harpago ferox Turner, p. 118-123, Figs. 2-5.
1983 Harpagodens Turner, p. 38.
1990 Thrinacodus (Harpagodens} ferox Tumer, 1982 [sic]; Lgng. 1990: 61-62, Fig. 5 H, J-M.
Referred material. — Two isolated leeth from beds 95 (CVUL 11) and 99 (CVUL 14).
Description and discussion
These microscopie grappling-hook-like teeth hâve three fang-shaped cusps whose lingual
surface is gently cristated. The base is elongate, twice as long as wide, It is punctuated by a
single foramen at the tip. This species appears to be ubiquitous from mid-Famennian to late
Toumaisian.
Superfamily Protacrodontoidea Zangerl, 1981
Family Protacrodontidae Zangerl, 1981
Genus PROTACRODUS Jaekel, 1921
Protacrodus cf. P. vetustus Jaekel, 1921
(Fig. 4d-e; PI. IV, I)
Preli-VINary remarks. — The name Protacrodontoidea was created by Za.ncerl (1981; 61). According to
ICZN article .J6a (Ride et al., 76). this naine is also estahlished with the sanie author and date for any
other ta.xon based upon the name-bearing type al other ranks in the family group with appropriate change of
suffis. So Protacrodontidae Wa.n'g & Ti rn'er, 1985 is a junior synonym of Protacrodontidae Zangerl. 1981.
Referred material. — Two assoeiated teeth from bed 99 (CVUL 22).
Description and discussion
These united teeth, as P. vetustus. hâve labio-lingually compressed crowns and a crest joining
ail the cusps (see, e.g. in Zangerl, 1981). The main, more-or-less central, conical cusp is flanked
by two or three smaller cusps on both sides. Ail cusps are strongly ridged. The tooth base bears
numerous large foramina essentially on its latéral faces (Fig. 4d).
Protacrodus sp.
(Fig. 4a; PI. 111, C)
Referred material. — One isolated tooth from bed 95 (CVUL 12).
Description and discussion
The Crown shows wide cusps slightiy cristated and linked by a sharp crest. It is rather high
and labio-lingually compressed. The labial side of the base is not offset against the crown.
— 473 —
whereas lingually lhe base is extended. A broken boss is présent underneath the central cusp
around which large foramina are organised in a dépréssion. The labial and lingual sides of the
base show small foramina (Fig. 4a).
ELASMOBRANCHII gen. et sp. indet.
Type A
(Fig. 6c; Pis I, D; IV, J)
Referred material. — Two isolated denticles from beds 89 (CVUL 4) and 99 (CVUL 23).
Description
These composite denticles are ovoid in coronal view and bear five or six cusps, arranged
in two rows, with the smallest cusp at the end of each row. Each cusp is triangular, smooth,
with a rounded tip, but the cusps of CVUL 23 (PI. IV, J) are more compressed. Both denticles
hâve a concave ba.se. These denticles are probably branchial or pharyngeal.
Type B
(PI. IV, K)
Referred material. — One isolated scale from bed 99 (destroyed during préparation).
Description
This scale bears three pointed cusps. Each cusp has a central, triangular portion which may
be either convex or concave, and thin latéral extensions.
Type C
(Fig. 6a-b; PI. I, A-B)
Referred material. — Two broken teeth from bed 89 (CVUL 1 and 2).
Description .and discussion
The base is approximately kidney-shaped, with a concave labial side and a convex lingual
side. Some foramina are visible on the aboral surface. The lingual surface of the cusps bears
widely spaced. converging cristae of varying length, whereas the labial face is nearly smooth.
The two faces are separated by a cutting edge (carina). The base bears three massive cusps. At
first glance, they appear to be asymmetrical with a latéral, pathological projection. However,
the projection seems to correspond to a broken cusp. Even though these teeth are reminiscent
of Symmorium (e.g. WILLIAMS, 1985), the more widely spaced longitudinal cristae on the cusps
and their asymmetry differ from lhat genus. The bases are subtriangular and one shows some
foramina at its lingual margin (Fig. 6a).
— 474 —
0.5 mm
t - J
Cï).
Fiü. 6. — Elasmobranchii gcn. el sp. indct. i'rom bed 89. a. Type C, tooth CVUL l. same as PI. I, A. ba.soIabial view, b, Type
C. tooth CVUL 2, .same as PI. I, B. basolabial view, c, Type A, branchial deniicle CVUL 4, same as PI. I, D, latéral view.
EUistnohrattcfiii geu. ei sp. indel. du banc 89. a, Type C, dent CVUL /. meme spécimen que pi /. A. vue hasolahiale. h, Type
C. dent CVUL 2. même spécimen que pi /, B, vue hasolahiale. c\ Type A, denricule branchial CVUL 4. même spécimen que
pi i O. vue latérale.
Class OSTEICHTHYES Huxley, 1880
Subclass ACTINOPTERYGII Klein, 1885
ACTINOPTERYGII gen. et sp. indet.
Type A
(PI. I, E)
Referred material. — A fragmentary tooth front bed 89 (CVUL 5).
Description
This fragment of curved, conical tooth is densely covered by thin, dashed lines of cristae
converging toward the tip. These lines obliquely approach the convex side which is broken but
clearly curved.
Type B
(PI. II, D)
Referred material. — A fragment of tooth front bed 92-93 (CVUL 9).
Description
This tooth is, as the latter, densely covered by dashed alignments of small cristae. It still
has its smooth cap of acrodin (PI. II, DI). An SEM enlargement shows the short, fusiform longi-
— 475 —
tudinal cristae of each line to altemate with those of the adjacent lines (PI. II, D2). This is
characteristic of the texture of ganoin (Schultze, 1977).
BIOSTRATIGRAPHY AND CORRELATION
Despite the paucity and restricted range of microvertebrates at the La Serre D/C section,
some biostratigraphical value can be discemed. The assemblage consists almost entirely of chon-
drichthyans, which is typical of Late Devonian and Early Carboniferous microvertebrate assem¬
blages. Equivalent macrofaunas are generally poor in shark remains. The La Serre assemblage
comprises leelh of phoebodonl, symmoriid, stethacanthid and protacrodoniid sharks, and scales
of probable ctenacanthid sharks. Associated are a few unusual actinopterygian teeth, which might
represent a new palaeoniscoid genus. This assemblage compares well with Late Devonian and
Early Carboniferous assemblages known from Europe Inorthem France and Southern Bcigium
(Crasquin, 1984). Germany (Gross. 1973; Mader & Schultze, 1987), Ru.ssia and Poland
(Ginter, 1990; Ginter & Ivanov, I992)|, and has éléments in common with roughly contem-
poraneous sites in .Morocco (DERYCKE. 1992), southeast Asia (Long, 1990; Wang & Turner,
1985), and the USA (KrElYRE & LUCA.S, 1992).
Symmoriutn reniforme Cope has long been known from the Lower to Upper Carboniferous
of the USA (Williams, 1985; Zanoerl, 1981). More recently, the genus has been recorded
from the Late Devonian to Early Carboniferous of Thailand and south China, the Lower Car¬
boniferous of Germany, the Late Devonian of Poland and Ru.ssia (refs. above) and ihe late Penn-
sylvanian of New Mexico (ZiDEK, 1992). Stcthacanthids appear by the mid-Famennian in Poland,
and are found in the Carboniferous of the USA, Europe, Thailand, China and Australia (Willi¬
ams, 1985). Phoebodont teeth are proving to be a usefui biostratigraphical tool for this time
interval (Ginter, 1992; GiNTER <!t rv.\NOV. 1992). They first appear in the Givetian of the USA
and possibly of Australia, and continue across the D/C houndary. Phaehodus austnilicrisis, P.
limpidus and P. sp. cf. P. australiensis seem to be typical of the laiesi Famennian to Early
Carboniferous in Thailand. south China, Poland and the Lirais (op. cil.) as wcll as at La Serre.
Thrinacodus feivx. probably a close relative of the phoebodonts. is often found in a.ssociation
with the above species in the Late Devonian (appearing with the marginifera conod<jnt 7one)
to late Tournaisian deposits. It has been reported from the latest Devonian of the USA (Kietzke
& Luc.kS, 1992) and the Lower Carboniferous of Australia, China. Turkey, parts of western
Europe, Poland and Russia, and is an easily recognizable fossil for this interval . Protacrodont
teeth occur frequently with phoebodont teeth and Thrinacodus ferox and generally hâve the same
Famennian to Early Carboniferous range, although in Australia they hâve only been found in
Devonian rocks. The assemblage described by Kietzke & Lucas (1992) from the D/C houndary
in the Sacramento Mounlains, New Mexico, also contain Phoehodus (“P. pnlitu.'i"). Proiacrodus
sp. cf. P. vetustus, protacrodonts similar to the ones from Australia and China, and Thrinacodus.
The authors assigned a Laie Devonian age to ihc fauna, although the presence of orodonts and
Helodus may indicate a younger age. Possibly this is another case of an assemblage righi on
the houndary, with incoming Carboniferous forms.
The La Serre assemblage lacks acanihodian scales of the Acanthodes type commonly found
at most other sites of this time interval, and bony-fish remains are cxceedingly sparse. This may
— 476 —
of course be due lo the small amount of material avai labié for study.
Of interest is the possible faciès corrélation which this assemblage suggests with a platformal
oolitic ümestone containing Siphonodella conodonts, trilobites, ammonoids, numerous brachiopods,
corals. foraminifers. algac and so on (Paproth et ai. 1991). A microassemblage of the same âge
from the Nanbiancun D/C boundary section conlained a very different fauna (Wang Cheng-yuan
in Yu. 1988. PI. 87). Al La Serre, the palaeoccological-geochemical analysis ol brachiopods suggests
“slightly dysacrobic conditions eoupled with slightiy lower salinities than during déposition of the
prcceding [latest Devonian] units. [Productivity increased dramatically to new levels accompanied
by warmer températures and shallowing of the sea”] (BRAND & LEGRAND-BlaiN, 1993)
Overall, the La Serre fauna correlates well with other latest Devonian or earliest Carbonife-
rotis faunas, with a slight tip in favour of the Lower Carboniferous sites in Europe and the USA
which include forms such as Symmurium Sp. cf. S. renifvrme, Protacrodus sp. cf. P. vetustus
and orodontids. This is not surprising as the La Serre ichlhyoliths corne from the lowermost
Carboniferous beds only. Phoebodiis australiensis is typical of the latest Devonian to earliest
Carboniferous interval in Thailand. south China and the Russian platform, and this is the first
western European locality for this species.
CONCLUSION
The assemblage from the La Serre D/C boundary section provides a supplementary record
of several important sharks which dominated the Late Devonian to Early Carboniferous margi¬
nal-marine platforms and pelagic environments of the world. Thrinacodus is not known for certain
from the Devonian of Europe but in France it is présent in the earliest Carboniferous. It is
known from the Late Devonian in Morncco, the marginal seas of the presumed north Gondwana
shoreline. Phoebodiis australiensis appears in the mid-Famennian trachytera zone and extends
into the e.xpansa- siilcata zones in soulheast Asia and the East European Russian platform fin-
cluding the Holy Cross Mountains (Poland). Moravia (Czech Republic). Timan. south Urals and
Kuznetsk (Russia); Hl.ADlt. et al.. I99h GiNTER & IVANOV, 1992], Similarly, the protacrodonts.
phoebodonts and stethacanthids. and pos.sibly the other shark groups as well seem to appear
during the latest Devonian in the eastem or north Gondwana région, before appearing in Europe
and the USA in earliest Carboniferous times. Of course, more re.search into the Late Devonian
microvertebrate faunas of the USA might clarify or nullify this hypothesis.
The éléments of the new assemblage constitute a group of rapidly di.spersing species. Closer
study of their taxonomy and occurrences now being carried out by participants in IGCP 328 is
refining their géographie and stratigraphical ranges.
Acknowledgments
We are graieful to R. Feist (Montpellier. France) who provided the samples for study. We had useful
discussions with A. Ivanov (St. Peter.sburg, Russia), O LEHEtiEv (Moscow, Russia), R. Lund (Adetphi
Univ.. NY. USA) and M. Gintcr (Warsaw. Poland). D. Vachard (Villeneuve d'Ascq) supplied data on
the slraligruphy of lhe La Serre section. H. -P. .ScilULTZE (Lawrence. KS, USA) helped wilh .several taxo¬
nomie assignments. M. CakidrOIT and J. CARftNTiHR (Villeneuve d’Ascq) secured the use of SEM and
the puper processing of SEM micrographs. S, TüRNER acknowledges grani.s from the Canadian and
— Ail —
Australian IGCP committees which enabled her to work in Canada and attend the Miguasha symposium,
and grant A 39132723 from the Australian Research Council for work on IGCP 328 and D/C matters. J.
ZiDEK (Socorro, NM, USA) and R. LUND helped a lot improving the manuscript.
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Plate I. — Venebralc microremains from bed 89 al La Serre, trench E’ (Montagne Noire. Hérault, France), basal Carboniferous
bed, Siphonodella sulcala conoilonl zone, upper part of middic member of Griottes Formation. A-B. Elasmobranchii gen. et
sp. indet. Type C. broken teelh CVUL I and 2. lingual views. C. Sleihacanthu.':? sp.. isolafed tooth CVUL 3, coronal view.
Labial margin faces down. D, Elasmobranchii gen. et .sp. indet. Type A. branchial denticle CVUL 4. coronal view. E. Acti¬
nopterygii gen ei sp. indet. Type A, broken toolti CVUL 5 in latéral view. Ail seule bars etpiul 11)0 ))m ("UM").
Micmn'stes de Vertébrés du banc SV de La Serre, tranchée E' (Montagne Noire. Bémult. France/, niveau basal du Carbonifère,
zone de vonodonles ù Siphonotlella sulcat.i, partit: snpérietin’ du membre tnoven de lu Formation des Griottes. .A-B. Ulûsmo-
branchii gen. et .\p. indet. Type C. dent.s ea.ssée.s CVUL I et 2. vues linguales. C. Slelhacanlhus 7 .rp.. dent isolée CVUL 3,
vue eoronalé. Le bord labial est orienté vers le bas. fi. Elasmobranchii gen. et sp. indet. Type .4. deniieule branchial CVUL
4. vue conmale E, Arlinoplriygü gen. et sp. indet. Type A, dent rossée CVUL ?. vue îutérule. Toutes tes échelles métriques
correspondent à tOfI pni C‘UM"i.
— 479 —
— 480 —
Plate II. — Vertebrate microremains from bed 92-93 at La Serre, trench E’ (Montagne Noire, Hérault, France), lowermost Car-
boniferous. Siphonodella sulcata conodont zone, upper part of middle member of Griottes Formation. A-B, Stethacanthus?
sp., broken teeth CVUL 6 and 7, coronal views. Labial margins face up. C, Ctenacanthidae gen. et sp. indet., scale CVUL
8, coronal view. Anterior margin faces up. D, Actinopterygii gen. et sp. indet. Type B, isolaled tooth CVUL 9, coronal view
with the acrodin tip (Dl) and detail of the ganoin surface (D2). AU scale bars are in |xm (“UM”).
Microrestes de Vertébrés du banc 92-93 de La Serre, tranchée E' (Montagne Noire, Hérault, France), niveau le plus bas du
Carbonifère, zone de conodontes à Siphonodella sulcata, partie supérieure du membre moyen de la Formation des Griottes.
A-B, Stethacanthus? sp., dents cassées CVUL 6 and 7, vues coronales. Les bords labiaux sont tournés vers le haut. C,
Ctenacanthidae gen. et sp. indet., écaille CVUL 8, vue coronale. Le bord antérieur est tourné vers le haut. D, Actinopterygii
gen. et sp. indet. Type B, dent isolée CVUL 9, vue coronale avec le capuchon d’acrodine (Dl) et un détail de la surface
de ganoïne (D2). Toutes les échelles métriques sont en \xm ("UM”).
— 481 —
200UI1
seouM
500UM
20KU MO* 17MI1
— 482 —
Plate III. — Vertebrate microremains from bed 95 at La Serre, trench E’ (Montagne Noire, Hérault, France), lowermost Car-
boniferous, Siphonodelîa sulcata conodont zone, upper part of middle member of Griottes Formation. A, Ctenacanthidae gen.
et sp. indet., scale CVUL 10, coronal view. Anterior margin faces up. B, Thrinacodus ferox, isolated tooth CVUL 11, latéral
view. C, Protacrodus sp., tooth CVUL 12, coronal view. Labial margin faces up. D, Symmorium sp., broken tooth CVUL
13, coronal view. Labial margin faces up. Ail scale bars are in p.m (“UM”)-
Microrestes de Vertébrés du banc 95 de La Serre, tranchée E’ (Montagne Noire, Hérault, France), niveau le plus bas du
Carbonifère, zone de conodontes à Siphonodelîa sulcata, partie supérieure du membre moyen de la Formation des Griottes.
A, Ctenacanthidae gen. et sp. indet., écaille CVUL ÎO, vue coronale. Le bord antérieur est tourné vers le haut. B, Thrinacodus
ferox, dent isolée CVUL II, vue latérale. C, Protacrodus sp., dent CVUL 12, vue coronale. Le bord labial est orienté vers
le haut. D, Symmorium sp., dent cassée CVUL 13, vue coronale. Le bord labial est orienté vers le haut. Toutes les échelles
métriques sont en [Im (“UM").
— 484
Plate IV. — Vertebrate microremains from bed 99 al La Serre, trench E’ (Montagne Noire, Hérault, France), lower Carboniferous,
kockeli-dentilineatus conodont zone, upper part of middle member of Griottes Formation. A, Thrinacodus ferox, isolated
tooth CVUL 14. nearly coronal view. B-C, Symmorium sp., isolated teeth CVUL 15 and 16, coronal views. Labial margins
face up. D-F, Stethacanthus? sp., isolated teeth CVUL 17, 18, 19, coronal views. Labial margins face up in D-E and down
in F. Note the wom surfaces of most cusps. Central cusp in E was broken after préparation. G-H, Phoebodus cf. R australiensis,
isolated teeth CVUL 20 and 21, coronal (G) and labial (H) views. I, Protacrodus cf. P. vetustus, two associaled teeth CVUL
22. coronal view. J. Elasmobranchii gen. et sp. indet. Type A, isolated branchial denticle CVUL 23, coronal view. K, Elasmo-
branchii gen. et sp. indet. Type B, isolated scale destroyed during préparation, coronal view. AH scale bars are in pm (“UM”).
Microrestes de Vertébrés du banc 99 de La Serre, tranchée E’ (Montagne Noire, Hérault, France), Carbonifère inférieur,
zone de conodontes à kockeli-dentilineatus. partie supérieure du membre moyen de la Formation des Griottes. A, Thrinacodus
ferox, dent isolée CVUL 14, vue presque coronale. B-C, Symmorium sp., dents isolées CVUL 15 et 16, vues coronales. Les
bords labiaux sont tournés vers le haut. D-F, Stethacanthus? sp., dents isolées CVUL 17, 18, 19, vues coronales. Les bords
labiaux sont orientés vers le haut en D-E et vers le bas en F. Les surfaces de la plupart des cuspides sont usées. La cuspide
centrale en E a été cassée en cours de préparation. G-H. Phoebodus cf. P. australiensis, dents isolées CVUL 20 et 21, vues
coronale (G) et labiale (H). I, Protacrodus cf. P. vetustus, deux dents imbriquées CVUL 22, vue coronale. J, Elasmobranchii
gen. et sp. indet. Type A, denticule branchial isolé CVUL 23, vue coronale. K, Elasmobranchii gen. et sp. indet. Type B,
écaille isolée détruite pendant la préparation, vue coronale. Toutes les échelles métriques sont en \im (“UM").
Bull. Mus. natl. Hist. nar., Paris, 4^ sér., 17, 1995
Section C. n” 1-4 : 487-511.
Upper Givetian and Frasnian ichthyoliths
from Bas-Boulonnais (Pas-de-Calais, France): preliminary records
by Claire DERYCKE, Denise BRICE, Alain BLIECK and Nicolas MOURAVIEFF
(Conlribution lo IGCP 328 "Palaeozoic Microvertebrates”)
Absiract. — New finds of Upper Givclian and Frasnian fishes fmm Hmilonnais coninbute lo project IGCP
328 which aims lu creaie a data base oF mieroremains l'or biostratigraphical. pulaeoccological and palaeobiogeo-
graphical corrélations. Morphological and histological data are prcsented to intégrale the ichthyoliths in a sys-
tematic framc. The compc'silion of the fauna is typical of Upper Devonian tunes coinprising Symmorium? sp.,
Cienacanthux sp, and oiher chondrichihyan éléments; acanihodians are présent with Puvnacanthus'.' sp. and Acan-
thodes sp. An infcrognathal of Rhynvlwdm.'/ ,sp. is identified. Actinopterygians are repiesenicd by Mnythoimisia
sp., and sarcopterygian remains intTude an undeterinined Onychodontida. undel. Porolepifonnes and Spodichthys?
sp. AU the previousiy ptiblishcd and ihe newiy described i.ixa are sittiated in ihc Givetian lo Famcnnian strati-
graphical scale of the Ferques inlier. The richest assemblages corne from F) the middie Givetian. lower Ulacoiirt
Formation. 2) the uppermo.sl Givetian-lowermost Frasnian (lowermosl and lower Polyanaihus axymmciricus con-
odont zones), lower Beaulieu Formation, and .') ihe uppei Frasnian (upper P- axymmtiritus and Artcyroxmiihus
trkmgularix zones). Ferqtie.s Formation. The Blacouri Formation a.ssemhiage is duminated by placoderm.s. The
newiy described lower Beaulieu Fontialion as.semblage is muth poorer ir placoderms but riçlKr in chondrichthy-
ans. acanthodians, actinopterygians and sarcopterygians. The Ferques Forniaiion assemblage on the contrary seems
to be devoid of sarcopterygians. but placoderms, chondrichthyans, actinopterygians and acanthodians do occur.
Keywords. — Ichthyoliths. Upper Pevonian. Boulonnais (France), biostraiigraphy. palaeogeography, histo-
logy. systemalics, placoderms, chondrichthyans, acanthodians, actinopterygians, sarcopterygians.
Ichthyolilhes du Givétien supérieur et du Frasnien du Bas-Boulonnais (Pas-de-Calais, France) :
données préliminaires
Résumé. — Une nouvelle microfaune de pnisson.s en provenance du Givétien supérieur et du Frasnien du
Boulonnais est présentée dans le cadre du projet PICG 328 qui vise ù mettre en place une banque de données
à usages biostr.itigraphique. paléoécologique el paléobiogéographique, Les informations morphologiques et his¬
tologiques sont utilisées conjointement afin d’intégrer les ichthyolilhes dans un cadre systématique. La composition
de la faune est typique du Dévonien supérieur puisqu'elle comprend Symmorium'? sp., Cwnaianthus sp. et d'autres
éléments de Chondrichlhyens. les Acatiihodiens Ptumacanüntsl sp. et Acimthodes sp Un inférwgniuhal de Rhm-
chndusl sp. est identifié Les Aciinnptéryglens sont représentés par Moydnimuski sp. Finalement, quelques restes
de Sarcoptérygiens sont figurés : un Onychodontida et des Porolépi formes indéterminés ainsi que Spodklithys?
sp. L'ensemble des taxons déjà publiés et de nouvelles découvertes sont situes dans l'échelle siraiigtaphique du
Givétien au Famennien du massif de Ferques. Les niveaux les plu.s riches proviennent I) de ht partie inférieure
de la Formation de Blucoun d'âge givétien moyen ; 2) de la partie inférieure de la Formation de Beaulieu d'âge
givétien lerniinal- frasnien basal (zones de conoduntes basale et inférieure à Palygnatliiis (ixymmeiricux) : 3) de
la Formation de Ferques d'âge frasnien supérieur (zones à P. asymmeiricus supérieure et à Ancyrognathus trian-
gularis). La faune des niveaux ( est dominée par les Placodennes. Celle des niveaux 2 est beaucoup plus pauvre
en Placodennes mais plus riche en Chondrichlhyens, Acanthodiens, Actinoptérygiens et Sarcoptérygiens. Enfin
la faune des niveaux 3, apparemment dépourvue de Sarcoptérygiens, renferme des Placodermes, des Chondrich-
thyens, de.s Actinoptérygiens et des Acanihodicn.s.
Mots-clés. — Ichihyolithes, Dévonien supérieur. Boulonnais (France), biostratigrapliie, paléngéographie,
histologie, systématique. Placodennes, Chundnchthyens. Acanthodiens, Actinoptérygiens, Sarcoptérygiens.
C. Derycke, A Bueck. Université des Siienies et Technologies de Lille, URA 1365 du CNRS, Sciences de la Terre, 59655
Villeneuve d'.Ascq Cede.y. h rance.
D. Brice, Laboratoire de paléontologie .siratigiaphique, F.U.P.L.. UR.A 1365 du CNRS. 13 rue de Tout, 59046 Lille Cedex, France.
N. Mouraviffr, Inslilul géologique. Mercator, 3 place Louis Pasteur, Université catholique de Loiivain-la-Neuve, 1348 Louvain-
la-Neuve. Belgique.
— 488 —
Introduction
In noithern France, a zone of Palaeozoic outcrops is found in Boulonnais-Artois-Ardenne
along Hcrcynian linéaments. The Midi Fauli, ihe most important overthrust of the région, divides
it in two. The Boulonnais inlier is part of the northern parautochthonous unit (including the
Brabant Massif and the Namur Synclinorium) whereas the southem Artois inliers and the Ardenne
Massif are pans of the allochthonous unit (including the Dinant Synclinorium). In the Parau-
tochthon, the Middie Devonian to Westphalian D layers, which are wiihout schistosity, are con-
formable on the schistous Cambro-Silurian substratum of Brabant (Raoult et al., 1984, 1985;
Raoult & MEtLLlEZ, 1986, 1987; RaouLT, 1986; Khatir et al., 1989). Jurassic and Cretaceous
levels overlay the Palaeozoic. By meatis of érosion and tectonic movements, Devonian and Car-
boniferous rocks outcrop in the Ferques Inlier (Fig. 1).
Six lithological units are defined in the Devonian of Ferques (Brice et al., 1979). The
fauna cornes from four of them; Blacourt, Beaulieu, Ferques and Hydrequent Formations, dated
uppermost Givetian to Frasnian and corresponding to the Polygnathus ensensis to Ancyrognathu.^:
triangularis conodont zones (BRICE, 1988a: we hâve not compared this zonation with ZiECLER
& Sandberg's (1990) one). These formations are famous for their abondant invertebrate fauna
composed of brachiopods, rugose and tabulate corals, conodonts, bryozoans. bivalves, trilobites,
crinoi'ds, slromatoporoids, as well as vertebrates and plant romains (Brice, 1988b).
The Blacourt Formation is interpreted as a platform deposil. The fauna from the Beaulieu
Fomiation indicates an open marine, shallow littoral, perirefal environment in its middie part
(Noces Member). The F'erques Foimation corrc.sponds to a shallow marine environment and was
deposited under variable and sometimes strong energy conditions (tempestites), essentially in a
brachiopod-rich level of the Bois Member. The upper part of the Hydrequent Formation présents
a concentratc sédimentation (BRtCE, 1986, 1988a-b).
Few ichthyofaunal remains hâve been recorded so far in the Boulonnais, since MURCHISON’s
(18401 attribution of Devonian levels on the basis of a fish scale and an “ichthyodorulite". They
correspond to placodcrms, acanthodians, actinopterygians and sarcopterygians. For the first time,
chondrichlhyans are described from the Devonian of Boulonnais. The biostratigraphical distribu¬
tion of some species is uncertain. Biostratigraphical and biogeographical comparisons were made
with Scotland and the Baltic States (Lelièvre et al, 1988).
MATERIALS
The material was collected during a Palaeontological Association field meeting in November
1976 by one of us (N. M.) studying conodonts. They corne mainly from shaly carbonate rock
samples. They are registered in the collection of vertebrates of the University of Lille (CVUL).
Below is the list of samples with their geographical and stratigraphical origins (Fig. 2).
Blacourt Formation
Couderousse Member, nodules in a grey mari, Caffiers-Ferques railway eut, sample BLN19
(Upper Givetian, upper-middle varcus zone).
— 489 —
Fig. 1. — Geological seiting of ihe Boulonnais (squarcd) al ihe wesicm end of ihe northem French Hercynian belt (sub-Mesozoic
geology iifter Kuatik. I‘î90).
Abbr.: h. Carboni ferons: d+dms, Dinantian and Middle + Upper Devonian; di, l.ower Devonian; pzi, Lower Palaeozoic.
Cadre géologique du Boulonnais (encadré) à l'extrémité ouest de la structure hercynienne du nord de la France (écorché
inframésozoïque d'après KhaTIR. 1990).
Abrév. : h. Carbonifère : d + dms, Dinantien et Dévonien moyen et supérieur; di, Dévonien inférieur: pzi, Paléozoïque inférieur.
Beaulieu Formation
Cambresèque Member, “La Cédule limestoiie”, upper part of the SW way of the Banc Noir
quarry (BLNI. 111, IB; uppermost Givetian, lowermost usymmetricus zone).
Cambresèque Member, SW eniry of the Griset quarry (BLN3) and SW way at entry of the
Banc Noir quarry (BLN4 and 5) (lower Frasnian, lower asymmetricus zone).
Upper Noces Member, unit “p”, Caffiers-Ferques raiiway eut (BLN20; lower Frasnian,
middle asymmetricus zone).
Ferques Formation
Bois Member. Bois quarry, Ihick brachiopod-bearing bed (BLN16) and La Parisienne quarry
(BLN7-17) (Frasnian. upper asymmetricus zone).
La Parisienne Member, upper Hexagonaria level, La Parisienne quarry (BLN9; Frasnian,
upper asymmetricus zone).
Fig. 2. — Location of sariiples afier Brice (l98Sa, b, c, Fig. 1 modified). A, Boulonnais. B, Palacozoic inlicr of Ferques. C, quarries and railway cuts with (1
to 20) location of samples BLNI to BLN20.
Abbr.; F is for Formation.
Localisation des échantillons d'après BricE (1988a, b. c. Fig. 1 modifiée). A, Boulonnais. B, massif paléozoïque de Ferques. C, carrières et tranchées de
chemins de fer avec (là 20) localisation des échantillons BLNl à BLN20. Abrév. : F correspond à Formation.
490
— 491 —
Upper part of the Ferques Formation (Gris Member or La Parisienne Meniber) at the bottom
of La Parisienne quarry (BLN8, not in situ) and uppermost bed of the Bois quarry near the
Briqueterie quarry (BLNIO) (Frasnian, upper P. asymmetricus and Ag. triangularis zones).
Hydrequent formation
Thick dolomilic bed. Briqueterie quarry (BLN15; Frasnian, Ag. triangularis zone). Another
sample from this formation (H214; A. Lefrançois, pers. comm.) bas yielded a few broken teeth.
Most samples were studied morphologically using a S.E.M. Cambridge Stereoscan 240; how-
ever, samples BLN19 and 3-4 were so rich in microremains that it was possible to make thin
sections for histological study.
SYSTEMATICS
The new fossil assemblages discovercd in Boulonnais are the first abundant records of fish
microfaunas in the Devonian of France. They are composed of scales, teeth and lepidotrichia
of gnathostomes, that is possible placoderms and numerous chondrichthyans, acanthodians and
osteichthyans. no agnathan remains having been found. However, précisé taxonomie détermina¬
tion to species rank is rarely possible and open nomenclature at the generic rank is employed.
As ail higher groups of gnathostomes are concerned, we are faced with a huge problem of
taxonomy and classification We thus decided to follow one recent consensus about the phylo-
genetic relationships of higher groups as exemplified by SCHULTZE (1990, Fig. 7), with the pla¬
coderms. chondrichthyans, acanthodians and osteichthyans as classes. For each class. we follow
Denison’s (1978) classification of placoderms, Zangerl's (198 G classification of chondrichthy¬
ans (slightiy rnodified according to DERYCKE et al.. 1995), and Denison’s (1979) classification
of acanthodians. Osteichthyans brought us a more difficull problem mainly because of the sar-
copterygian phylogeny and classification which are not stabilized. A number of discussions oc-
cured in recent years on this matler wiihout any consensus (sec, e.g. Forey, 1987; Schultze,
1987, 1991; Vorobyeva & SCHULTZE, 1991; Forey et al., 1991), except in the proposais of
Janvier (1986), Ahlberg (1991) and Cloutier (1991a-b) [see Gee, 1990]. So we refer to the
latter.
Class PLACODERMl Mc Coy, 1848
Order PTYCTODONTIDA Gross, 1932
Family PtYCTODONTIDAE Woodward, 1891
Genus RHYNCHODUS Newberry. 1873
Type species. — R. secans Newberry, 1873; Middle Devonian (Eifelian), USA.
Rhynchodus? sp.
(PI. II, B)
Referred material. — eVUL 37 from BLN5.
— 492 —
Description
The specimen seems to be a lower left gnathal plate or inferognathal in which the shearing
edge is worn and the latéral lamina is broken. It is comparable with the Rhynclwdns sp, published
by Belles-Isles ei al. (1987) from the Givelian of Ferques. At first glance, the most évident
différence is the length. The Frasnian inferognathal from BLN3 (PI. II. B) is millimelric whereas
the Givetian superognathal is centimeiric. There is no groove visible in the lingual view which
is just a progressive curvature of the lamina. It is the only recognized piece of Placodermi in
our material. As ofien, the placoderms which are the dominant remains in fish macrofaunas for
the Devonian both in number of généra and families (YOUNG, 1990; Long, 1993) are not well
represented in microremains.
Class CHONDRICHTHYES Huxley, 1880
Subclass ELASMOBRANCHII Bonaparte, 1838
Order SYMMORIIDA Zangerl, 1981
Family Symmoriidae Dean, 1909
Genus SYMMORllJM Cope, 1893
Type species. — S. reniforme Cope, 1893 (redescribed by Williams, 1985); Carboniferous, Nonh America.
Symmorium? sp.
(Fig. 3a-b; PI. I, D)
Referred material. — CVÜL 27 from BLN8.
Description and discussion
The cladodont tooth CVUL 27 shows a kidney-shaped base with a slight concavity below
the main cusp, This not well pronounced charader permits us to compare our specimen to Sym-
murium (WILLIAMS, 1985: 103). A crown view shows the main broad cusp and the two pairs
of latéral cusps settled along the labial margin of the base. The former one has an 8-sided section
delimited by ridges on the surface; the labial flattened sidc and the lingual convex side are
separated by a cutting edge. Contrary to the central cusp, the latéral ones hâve a labio-lingually
directed greaier length, with an ellipiic shape in cross section. An aboral view shows a line of
foramina in a dépréssion parallel with the labial side (Fig. 3a). Some other little foramina are
dispersed: three at the lingual margin of the ba.se and two on the lingual face under the latéral
cusps. A very extended boss exists lingual ly on the base (Fig. 3b). Its labial face is characterized
by a concavity. Il seems lhat the characters of Symmorium are in this specimen not so pronounced;
for instance, the two lacets described by ZlDEK (1992) as a character of Symmorium are not so
évident here. This is the first occurence of a symmoriid at so early a level, the genus Symmorium
having been described in the upper Famennian of northern Thailand (Long, 1990), the Lower
Carboniferous of North America (Williams, 1985; Zangeri., 1981), Germany (Mader &
SCHUI-TZE, 1987), France (Derycke et ai.. 1995), and up to the late Pennsylvanian of New
Mexico, USA (ZiDEK, 1992).
— 493 —
I »
d
Fig. 3. — Chondrichthyan (a-d) and acanthodian (e) microremains from the Devonian of Bas-Boulonnais. France, a-b, Symmohum?
sp., toolh CVUL 27 from BLN8, Ferques Formation, Frasnian, in aboral (a) and lingual (b) views, same as pl. I, d. c-d,
Chondrichthyes gen. et sp. indet. Type A, denticle CVUL 24 from BLN4, Beaulieu Formation, Frasnian, in latéral (c) and
aboral (d) views, same as pl. I. A; e, Piomacanlhus? sp., looth-whorl CVUL 31 From BLN3, Beaulieu Formation, Frasnian,
in latéral view, same as pl. I, H.
Microrestes de Chondrichtbyens (a-d) et d'Acanthodiens {e) du Dévonien du Bas-Boulonnais, France, a-b Symmorium? sp.,
dent CVUL 27 de BLN8, Formation de Ferques, Frosnien, en vues aborale (ou basale, a) et linguale (b), même spécimen
que pl. l. D. c-d. Chondrichthyes gen. et sp. indet. Type A, denricule CVUL 24 de BLN4. Formation de Beaulieu. Frasnien,
en vues latérale (r) et aborale (ou ha.sale. d), même spécimen que pl. /, A. e. Ptomacanihus ? sp., spirale dentaire CVUL 31
de BLN3, Formation de Beaulieu, Frasnien. en vue latérale, même spécimen que pl. J, H.
— 494 —
Superorder EUSELACHIl Hay, 1902
Order CTENACANTHIFORMES Nelson, 1976
Superfamily CTENACANTHOIDEA Dean, 1909
Family Ctenacanthidae Dean, 1909
Genus CTENACANTHUS Agassiz, 1835
Type species. — Ctenacanthus major Agassiz, 1835; Lower Carboniferous, England.
Ctenacanthus sp.
(PI. I, B-C)
Referred material. — CVUL 25 (PI. I, B) and CVUL 26 (PI. I, C) from BLN8.
Description
These two ctenacanthid scales sensu Reif (1978) présent some common characteristics, that
is a base separated from the crown by a gently pronounced neck and a convex crown towards
the front. In CVUL 25 (PI. I, B), six broad ridges separating deep grooves form the crown,
whereas the crown of CVUL 26 (PI. I, C) is made of three strong ridges. The surface of the
broadest ridge (PI. 1, C) is traversed by a longitudinal groove in its basal part. The former scale
(PI. I, B) only has a forecrown whereas a notch exists in the middle of the labial basal rim of
the latter (PI. 1, C).
CHONDRICHTHYES gen. et sp. indet.
Type A
(Fig. 3c-d; PI. I, A)
Referred material. — CVUL 24 from BLN4.
Description
This element présents a crown separated from the base by a little marked neck. The crown
is made of little sharp spikes directed towards the rear of the animal (Fig. 3c). These spikes
are smaller anteriorly and détermine a polarity. The base shows a large concavity (Fig. 3d). This
seems to be a chondrichthyan scale or perhaps a complex mucous membrane denticle with nume-
rous cusps.
Type B
(PI. L E)
Referred material. — CVUL 28 from BLN3.
Description
This specimen is composed of two rows of two imbricated teeth showing cutting edges.
The two teeth in the foreground are not strictiy in the same plane, they seem staggered and
divergent. This composed element perhaps represents non-functional teeth.
— 495 —
Type C
(PI. I, F)
Referred material. — CVUL 29 from BLN3.
Description
The scale CVUL 29 has a centrifugal growth with smaller fiat peaks in the centre. The
scale has been growing in four directions but with different rates, and the more anterior part of
the Crown would be the left one on the SEM micrograph where two files do exist.
Type D
(PI. I, G)
Referred material. — CVUL 30 from BLNl.
Description
The microremain CVUL 30 is characterized by three bud-shaped cusps which constitute a
high Crown with a deeply grooved ornament drawing a circle-arch. The two extemal cusps show
a pentameric symmetry whereas the less prominent central one has a tetrameric symmetry. The
ornamentation is similar to that of Arauzia federicoi Mader (1986, PI. 6, Fig. 6a) from the
Lower Devonian of Spain.
Class ACANTHODII Owen, 1846
Order CLIMATIIDA Berg, 1940
Family Climatiidae Berg, 1940
Genus PTOMACANTHUS Miles, 1973
Type species. — Ptomacanthus anglicus Miles, 1973; Lower Devonian, England.
Ptomacanthus? sp.
(Fig. 3e; PI. I, H)
Referred material. — CVUL 31 from BLN3.
Description
This specimen seems to be an acanthodian tooth-whorl arranged in a single row. It is com-
posed of six cu.sps with the smallest at the anterior part and covering the older just behind it
(Fig. 3e). As in Ptomacanthus, the row is made of fiat blade-like teeth (Miles, 1973). If it is
a symphyseal tooth-whorl, the cusps should be directed posteriorly or lingually; it could be a
pharyngeal tooth.
— 496 —
Order ACANTHODIDA Berg, 1940
Family Acanthodidae Huxley, 1861
Genus ACANTHODES Agassiz, 1833
Type species. — Acanthodes bronni Agassiz, 1833; Lower Permian, Germany.
Acanthodes sp.
Type A
(Fig. 4; PI. I. 1, L)
Referred MATERiAL. — CVUL 32 (PI. I, I) and CVUL 35 (PI. I, L) from BLN19.
Description
In the sample BLN19, there are more than one hundred minute acanthodian body scales.
They are typically rhomboidal with a fiat smooth crown. A little concavity exists at the top of
denllne layers of crown
prlmordlum
dentine canallcuti
dentine cenallcull
Sharpey's fiber
prlmordlum
Omit of dentine lamolla
B
dentine layers of crown
Sharpeys fiber
dentine cenallcull
acellular bone
FKi. 4. — Histology ol Aatnihudes sp. Type A seules from BI,N19 (BUcour! Formation. Coudcrouï^sc Menihcr, Upper Givetian).
A*B. transverstf ihin scoiinns. C-D, .sagiilul tliin sections. The ubscncc of cell spaces contlrms the Acttnrhoiics type sensu
Cross 1 1947) and 0RVig (1951 ). The wclJ preserved structures show deniiiie cunaliculi. Sharpc>’.s tiben» and growih conceniric
zones.
Htstofogie d’êcotlles f/'AcatMhodes sp. Type A de BLN (9 {Fornutîion de Blannirt, Metnbn' de Coudenmsse. ütviUien supéheur).
A-8, lames minces de coupes trunsversûle.^. C D. hmes minces de coüpe.s sagittales. L'ahsenre d’espaces cellulaires confirme
l'appartenance au type Acanthodes sensu Gmoss 11947} et 0f<viG (I95JI. U\\ structures bien conservée.s montrent de^s ca-
nalicuics de dentine. des fibres de Sharpey et des wnes concentriques de croissance.
— 497 —
the surface. Forwards, the crown is a little bit round and behind it forms an acute angle. The
neck separating the convex base from the crown is narrow but well-defined.
Histology
Thin sections through these scales corroborate the détermination based on the morphology.
As a malter of fact, the absence of cell-spaces (Fig. 4) confirms the Acanthodes type sensu
Gross (1947) and 0rvig (1951). Moreover dentine canaliculi and Sharpey’s fibers are visible
in the base (compare to Heyler. 1969). Transverse thin sections (Fig. 4A-B) show the continuons
concentric zones in the crown and the base around the primordium (Denison, 1979). The crown
is made of concentric well drawn, true dentine layers. Those growth marks may illustrate rhythms
of the animal.
Discussion
The genus Acanthodes, generally recorded from Carboniferous and Permian levels, seems
to be representcd by Devonian spccies but they make a systematic problem, Zidek ( 1976) indeed
considers Acanthodes as a nomen dubium while, for Denison (1979), ail the Devonian scales
attributed to Acanthodes “are surely not Acanthodes” and, for WANG & Turner (1985), “the
whole family is in need of révision”. We thus teniatively déterminé the new material from BLN19
as Acanthodes sp.
Type B
(PI. I, J-K)
Referred material. — eVUL 33 from BLN8 (PI. I, J) and CVUL 34 from BLN17 (PI. I, K).
Description
This typically rhombic-crowned scale has a clearly constricted neck. Forwards, the crown
does not overhang the base and there is a gap between the crown and the base. Posteriorly, the
crown présents a projection ovcriapping the base. As generally in the family Acanthodidae, the
scale is smooth (Denison, 1979).
Acanthodii gen. et sp. indet.
(PI. II, A)
Referred material. — CVUL 36 from BLN4.
Description
This tooih plate présents few rows of striated teeth. Each tooth is orientated lingually and
présents a wide pulp cavity. The labial row consists of seven teeth which are more acute in the
middie part. A bigger cusp, located at the left in the second plane of the SEM micrograph (PI.
II, A), had existed but is broken.
— 498 —
Class OSTEICHTHYES Huxley, 1880
Subclass ACTINOPTERYGII Klein, 1885
In our sainples. nunierous actinopterygian microrcmains hâve been préparée! from BLN4
and BLN3, in the Beaulieu Formation, and some others from BLN8-10 and 16-17 in the Ferques
Formation (Fig. 5). They comprise flank scale.s, ventral scales and .seules front the upper part
of the lail of the types previousiy dctailed by JESSEN (1968). Our material is not particularly
well preserved but. as Long (1988) already noticed, “in the world few Devonian actinopterygians
are wcll-known". So any iicw record has to be mentioned. Osorioicluhys CASIER (1952, 1954)
was the firsl actinopterygian to bc described from the Late Devonian of Belgium and, later,
Lelièvre et ni. (1988) Figured fcw microrcmains from the Givetian of Boulonnais. They were
ail attributed to palaeoniscoid taxa.
This point needs a short comment. Among actinopterygians, LEHMAN ( 1966) considers that
“Chondrostei"’ do not really exlst and Gardiner ( 1967) thinks ihat "the Chondro.stei. the Holostei,
the Halecostomi and the Teleostei... represent grades of evolutionary development rather than
natural subdivisions" (see aiso Lauder & LiEM, 1983), In their classifications, Palaeoniscoidei
are thus considered as a paraphyletic eroup (Gardiner, 1984. 1986). Our specimens are ideniified
at the generic level only or are considered undetermined, and do not allow a revjew of the
“palaconiscoids”. .So we provisionally use Gardiner's (1967) classification. Our material is re-
presenled, as ail actinopterygians, by ganoid-type scales with three superpo.sed layers; a ganoin
external one above dentinc and bony layers (sec LEHMAN. 1966). The onion-skin grovvth of the
ganoin is visible on some of the thin sections (Fig. 5B). The base of the seules is made of bone
with many cell spaces and Sharpey’s fibers for attachment (Fig. 5A-D). The crown is thin with
regard to the bony base. The hemilepidotrichium fin-ray has a pyramidal section (Fig. 5E).
Order “PALAEONISCIFORMES”
Suborder “PALAEONISCOIDEI”
Family STEGOTRACHELIDAE Gardiner, 1963
Genus MOYTHOMASIA Gross, 1950
Type species. — Moythomasia perj'orata Gross. 1950: Upper Devonian (Frasnian). Germany and Western
Australia.
Moythomasia sp.
(PI. Il, C-E)
Referred material. — eVUL 38 from BLN8 (PI. II, C), CVUL 39 from BLN3 (PI. II, D) and CVUL 40
from BLN4 (PI. II. E).
Description
The scale CVUL 38 (PI. II, C) shows the peg and socket articulation between scales which
is characteristic of advanced actinopterygians. The peg (which faces right on PI. II, C) is a
dorsal process and the smooth overlap surface (which faces up) is frontal. So we can orientate
— 499 —
Fig. 5. — Hi.slology of undetemiined actinoplerygian microremains from BLN4 and 3 (Beaulieu Formation, Cambreseque Member,
Frasnian). A-D. Ihin sections of scaies from BLN3. E, thin section of a heniilepidotrichium from BLN4.
Histologie de microrestes d'Actinoptérygiens indéterminés de BLN4 et 3 (Formation de Beaulieu, Membre de Cambreseque,
Frasnien). A~D, lames minces d’écaitles de BLN3. E, lame mince d'un hémilépidotriche de BLN4.
— 500 —
this tnicroremain as a lefl flank scale. The antero-veniral angle equals about I35“. The surface
is worn but we can see ripples of ganoin. This diamond-shaped scale cornes probably from the
ventro-lateral flank of the animal. One rectangular scale (PI. II. D) is ornamented by a layer of
perforated ganoin whose pores are aligned in curve directions. Its posterior margin is serrated
with three denticulations in the prolongation of the direction of its diagonal axis. It seems to
represent a right flank scale on which we can define an antero-ventral angle between the overlap
antenor surface (which laces right on PI. II. D) and the ventral margin (which faces down)
opposite the pcg. This antero-ventral angle is obtuse ( 125“). The shape of the third figured scale
CVUL 40 recalls a ventral scale. Ils anterior part, which represents the overlap area, faces left
on PI. Il, E. The antero-ventral angle is approximaiely 11°. Such an acute angle is also found
in the ventral scales of Howqualepis (LONG, 1988, Fig. 26). The anterior and dorsal margin of
the shiny part is finely striated. An oblique line of pores crosses the exposed surface.
Actinopterygii gen. et sp. indet. AB
Type A
(PI. II. F)
Referred material. — CVUL 41 from BLN5.
Description
A tooth plate CVUL 41 (PI. Il, F) is composed of more than twenty cusps. Each cusp is
ornamented with dashed cristae; Schultze (1977) interpreted this structure as ganoin. Two of
them exhibit an acrodin cap. Ail cusps are gently constricted around their point of insertion.
Type B
(PI. II, G)
Referred material. — CVUL 42 from BLN8.
DESCRIPTION
The tooth CVUL 42 (PI. H, G) is slightly curved with a tip of acrodin. Dashed cristations,
the ornamentation of ganoin (Schultze, 1977), are converging at the top of the tooth and some
diverge from the lingual part towards the labial face. A large pulp cavity is noticeable at the
base.
Type C
(PI. II, I)
Referred material. — CVUL 44 from BLN5.
Description
The absence of ganoin cover in CVUL 44 is surprising. However, it seems to be an acti-
nopterygian left flank scale because of its rhombic shape and the presence of three serrations
— 501 —
at its posterior margin (which faces up on PI. II, I). The ornamentation is peculiar with five
parallel brokeii lines of pores, and, in the middle, two triangles of the cover butting into the
transverse ridges.
Type D
(PI. II, K)
Reff.rred material. — CVUL 46 from BLN3.
Description
The microremain CVUL 46 is divided into two parts. Its anterior one is shiny and covered
by finely striated ganoin whereas the posterior one is bony. This element seems to correspond
to a fin ray like ihose which hâve been interpreted as dorsal fin rays by SCHULTZE & Bardack
(1987, Fig. I3A). It also corresponds to half a lepidotrichium, the latter consisting of two opposite
éléments placed like parenthèses; so this is a hemilepidotrichiiim. As on the most proximal
lepidotrichia of brachyopterygians (Polypteridae) and of Lepisosleidae, an incomplète ganoin
cover is l'ound on CVUL 4f> (PI. U, K, refs in Francillon-Vieielot el al., 1990).
Subclass SARCOPTERYGII Romer, 1955
Order ONYCHODONTIDA Andrews. 1973
ONYCHODONTIDA gen. et sp. indet.
(PI. II, L)
Referred material. — CVUL 47 from BLN4.
Description
This specimen is a portion of the external face of the anterior covered part of a scale. It
bears typical horse-shoe-shaped tubercles. This ornamentation is found in holoptychiids and ony-
chodontids. The convexity of the tubercles indicates the posterior part of the animal (it faces
up on PI. 11. L). Their base is oval and their top surface is sharpiy concave and spoon-like. The
tubercle surface is shiny and probably formed of enamel. When compared to onychodontids, the
ornamentation of CVUL47 dilïers from lhat of Holoptychius. On Glyptolepis. the tubercles seem
more acuie. However, il is suggestive of Onychotlas (0RVic, 1957), a genus aiready represented
by teeth in Boulonnais (Lelièvre et al., 1988). A similar ornamentation occurs in Gro.i.ùus
aragonen.'ii.y ScHULTZE (1973, PI. 33) and Heinienia eiLti.'i 0RVIG (1969, Fig, 6). Two générations
of tubercles arc in fact represented on CVUL 47: one central line of three. a littlc taller and
wider tubercles, Hanked by latéral, more irregular lines. Diagonal alignments seem to be super-
imposed to that pallern, Another unfigured fragment of scale, with the same tuberculate ornamen¬
tation, also shows sinuous ridges. However, a comparable ornamentation lias recently been
described by SCHULTZE (1992) on scales of a dipnoan species, and it seems that spoon-like
tubercles are a plesiomorphic character for Sarcoplerygii (Cloutier, pers. comm ).
— 502
Order POROLEPIFORMES Jarvik, 1942
POROLEPIFORMES gen. et sp. indet.
(PI. II, J, M)
Referred material. — CVUL 45 (PI. II, J) and CVUL 48 (PI. II, M) from BLN4,
Description
The fragmentary specimen CVUL 48 is characterized by well marked sinuous and approxi-
mately parallel branching ridges. It resembles the external view of seules figured by JarvIk
(1949: PI. 8, I) who compared them with seules of Glyptokpis. Tlie piece of bone CVUL 45
(PI. II, J) shows no évident organizaiion but the general pattern of its ridges and iniermediate
pores look like that of CVUL 48 and both fragments are attribiited to Porolepiformes (cf. 0RV1G,
1957; Jarvik, 1985).
Order RHIZODONTIDA Andrews & Westoll, 1970
Family Rhizodontidae Traquair, 1881
Genus SPODICHTHYS Jarvik, 1985
Type species. — Spodichthys buetleri Jarvik, 1985; Middie-Upper Devonian, Greenland.
Spodichthys? sp.
(PI. Il, H)
Referred material. — CVUL 43 from BLN4.
Description
On this fragment of bone, horizontal ridges are connected by short regularly spaced cross
ridges. They form alignments of rectangles or lozenges.This specimen reminds us of seules pub-
lished by JARViK (1985, Fig. 35).
SUMMARY AND CONCLUSIONS
This is a preliminary report of new microvertebrate material from the upper Middle-lower
Upper Devonian of northern France. Part of the samples is presented, the rest being treated in
a Ph. D. thesis defended by one of us (C. D.). As vertebrate microremains hâve been proved
usefui in biosiratigraphy, one of the aims of this work is to settle their stratigraphical ranges in
the Palaeozoic orogen of northern France-southern Belgium. However, only a few of the ichthyo-
liths figured here can be placed in settled taxonomie groups, so this paper may raise more prob-
lems than it solves, LELIÈVRE et al. (1988) hâve mainly studied the macrofauna of the
LA
O
U)
Fig. 6. — Compilée! straiigraphical diMiibution of ihe Devonian vertchrates ot Boulonnais. T he difterem points indicate ihe stratigraphical location of the specimens
figured by Dutertki. 11930, grcy ciicics). Belles-Iles #•/ ul. (1987. black circlcs) and LiïLIÈVRE ei al. (1988. white circles); some of the stratigraphical
levels aie uncerlain. Oiir reporred m.iterial* grcy squares.
Distribution strati^riiphiiiue synlhèiiifuc des Vertèbres du Dévonien du Boulonnais. Les différents points indiquent la localisation stratigraphique des spécimens
Jigufvs par Di'TLRTHl-: cercles gris). HPlLES'flFS el uJ ll9S7. cercles noirs) et LfuI^HF et al. (79^^, cercles blancs). Quelques localisations strali-
graphtques .sont incertame.s. Le matètici (fue nous décrivons ici correspond aux carrés gris.
— 504 —
Givetian-Frasnian of Boulonnais with jusl a few microremains from the Givetian lower Blacourt
Formation. Here uppermost Givetian-Frasnian microfaunas are outlined. Acanthodians, chon-
drichthyans, actinopterygians and sarcopterygians are well represented. the placoderms are very
rare. Some rock samples are particularly rich in ichthyoliths as BI.NI9 (uppermost Givetian,
upper Blacourt Formation) which yielded a mass of acanthodian .scale.s, or BLN3 and BLN4
(lowermost Frasnian. lower Beaulieu Formation) which gave numerous actinoptcrygian scales.
We ai.so .show the first occurrence of Palaeozoic chondrichthyans in Boulonnais. Among them.
the presence of Symmoriidae is one of the oldest recorded examples of ihis family.
Among acanthodians, the Accmthotks type has been recogm/ed in thin sections; however,
the taxonomie attribution of this material has to be revised bceause the Devonian "Acanthades"
seem to differ froin the genus as defined in younger levels. One evidence only of the presence
of Placodemii has been found, i.e. an inferognathal belonging to the Ptyciodoniidac. In our
samples, the actinopterygians are the second group well represented in number of microremains,
with scales of Moythamasia. This genus lias been many times described in the Upper Devonian
of Germany (GrosS, 1930; JnsSEN. 1968) and of Australia (GarDINER. 1984). The other acti¬
noptcrygian scale.s, con.sidered undetennined, hâve no ganoin cover, which is surprising because
classically ganoin ridges intercalatcd with bony grooves characterize Lower Devonian actinopte¬
rygians (ScHULTZE, 1968, 1977), although younger actinoptcrygian scales hâve a continuous
ganoin cover (JANVIER & DE Melo, 1987). Among sarcopterygians, the Porolepiformes are com-
pared with généra from the Middic Devonian of Norway, the Frasnian of Québec and the Middle-
Upper Devonian of Greenland (J.ARViK, 1949. 1985: 0RVlCi. 1957).
In conclusion, we give a compiled stratigraphical distribution of ail previous records of
Devonian fishes in the Boulonnais, including the new ones (Fig. 6). It shows clearly that few'
levels hâve a diversified fauna:
I ) onc in the Givetian lower Blacourt Formation (LELIÈVRE et ai, 1988) in which placoderms
are prédominant;
2) samples from the lower Frasnian. lower Beaulieu Formation (this record) in which ail
gnathostome higher taxa are represented (from placoderms to sarcopterygians);
3) samples in the Frasnian Ferques Formation (this record) with mainly chondrichthyans
and actinopterygians. The marine nature of ail these levels is undeniable by the occurrence of
a large array of invertebrates (Brice. 1988b).
When compared to approximately contemporary ichthyofaunas. different conclusions are
drawn. The Givetian fauna of the Blacourt Formation is close to those from Scotland and the
Baltic (LELIEVRE et al., 1988). On the contrary. the lower Frasnian fauna of the Beaulieu For¬
mation has no vertebrate élément in commun wilh, for example, the fauna of the Escuminac
Formation of Quebec (see, e.g. SCHULTZE & CI.OUTIER. 1991), This différence may be owing
to taphonomical condition.s and sampling bias (with mainly microremains in Boulonnais and
macrofaunas in Quebec), or to cnvironmental différences (wilh less saline conditions in Quebec),
or both. These conclusions are thus in disagreement with ihe classical view of cosmopoliian
Late Devonian faunas (YOUNG, 1987). They are aiso in disagreement with the conclusions of
Brice (1988a-b) who has shown thaï some généra of tabulale corals, brachiopods. cchinoids,
oslracodes of Boulonnais are related to or close to North American ones, implying marine com¬
munications between both areas. The European taxa being stratigraphically younger than the
— 505 —
North American ones, this also leads to hypothesize migrations from west to east, which cannot
be concluded from the microvertebrate faunas.
Acknowledgnients
Thanks to M. Carjdroit (University of Lille) for great Help in operaiing lhe Scanning Electron Mi¬
croscope and to J. Carpentier for processing of SEM micrographs. R. Cloutier (Univ. Lille), H. -P.
ScHULTZE (Kansas Univ., Lawrence), S, Turner (Queensland Muséum, Brisbane) and R. Lund (Adelphi
Univ., N. Y.) gave us helpful remarks on the manuscript and material.
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Plate I. — Chondrichthyan and acanlhodian microretnains from the Devonian of Bas-Boulonnais, France. Ail scale-bars equal
200 pm. A. ClwnJrichthyes gen. et .sp. indet. Type A. Denticle CVUL 24 from BLN4. Beaulieu Formation, Frasnian, crown
view. The crown cusps arc directcd tüwards the rcar of the animal and lace Icft. B-C. Cteiuicanihiis sp. Seules CVUL 25
(B) and CVUL 26 (C) from BLN8, Ferques Formation. Frasnian. crown IB) and front (C) views. Tlie convex sides indicate
the front directions which face down. D, Syiiimorium ? .sp. Tooth CVUL 27 from BLN8, Ferquc.s Formation. Frasnian. occlusal
view. The lingual sidc is indieated by the concavity trf the cu.sps and faces dow'n. E. Chotulrtrhlhves gen. et sp. indet. Type
B. Imbricated teeth CVUL 28 from BLN3. Beaulieu Formation, Frasnian. lingual view F. Chimtlrirluliyes gen. et sp. indet.
Type C. Scale CVUL 29 Iront BLN'3, Beaulieu Formation. Frasnian, crown view. G. Chondriehihyes gen. et sp. indet. Type
D. Seule CVUL 30 from BLNI. Be.nilieu Formation. La Cednie limesione, upper Givetian. crown view. H. Pummcanihus?
sp. Tooth-whorl CVUL 31 from BLN3. Beaulieu Formation. Frasnian. crown view. I. L. Acanihodes sp. Type A. Typical
rhombuidal scales with fiat smooth crowns CVUL 32 tl) and CVUL 35 (I.) from BLNI9. Blaeouri Formation. Upper Givetian.
basal (I) and crown (L) views. J. K.. Acmihoiles sp. Type B. Scales with higher neck CVUL 33 (J) from BLN8 and CVUL
34 IK) from BLNI7. Ferques. Formation. Frasnian. frontal (J) and hitero-lrontal (K.) views.
Miemresle.s île rhnnilrielilhyens et d'arunthnilieni du Dévonien du Bus-Bon! onnais. pruiwe. Toule.s les échrlles métriques
correspondent à 2(X) pm. .4. Chondriehihyes gen. et sp. indet. Type A. Denlinile CVUL 24 de III.N4. Fonnation de Beaulieu.
Ftasnien, vue lurtmale. U-.\ t uspides de ta coumnne sont dirigées vers la partie postérieure de l'uniimd. vers la gauche.
B-C. Ctenacanihus sp Ecailles CVUL 25 (B) and CVUL Ift fO de BLNB, Fonnation de Ferques Feasnien. vues eoronale
IB) et fnmtale (C). Les côtés conveses indiquent les faces aniérteiires qui sont dirigées vers le lias. LL Symmorium ? sp.
Dent CVUL 27 de BLNB, Formation de Ferques, Frasnien. vue ocelusale. Le cillé lingual est indiqué par la concavité des
cuspides. orientée vers le bas. E. Chondrichthyes gen. et sp. indet. Type B. Dents imbriquées CVUL 2S de BLNJ, Formation
de Beaulieu. Frasnien. vue linguale. F. Chondrichthyes gen. et sp. indet. Type C. Ecaille CVUL 29 Je BI.NJ. Formation de
Beaulieu. Frasnien. vue corotuilc. G. Chondrichthyes gen. et sp. indet. Type D. Ecaille CVUL 30 de BLNI. Fonnation de
Beaulieu, calcaire de la Cédule. Givétieii supérieur, vue eoronale. H, Ptoniacanthus ? sp. spirale dentaire CVUL 31 de BLN3,
Fonnation de Beaulieu. Frasnien. vue eoronale. L L Acanthodes sp. Type A. Ecailles rbomhiques typiques à couronnes lisses
el plates CVUL 32 II) et CVUL 35 (L) de BLNI9. Formation de Blaeouri. Gtvetien supérieur, vues basale U) et eoninale
IL). J. K, Acanthodes sp. Type B. flrailles à collel plus bout CVUL 33 IJ) de BLN8 et CVUL 34 iK) de BLNI7. Formation
de Ferques. Fra.snien, vues Jronialc iJ) et latéro-fnmiole (K).
— 510 —
Plate II. — Acanihodian, placoderm and osteichthyan microrertiains from the Devonian of Bas-Boulonnais, France. AU scale-bars
equal 200 |im. A, Acanthodii gen. et sp. indet. Toolh Plate with few rows of striated leeth CVUL 36 from BLN4, Beaulieu
Formation, Frasnian, labial view. B, Rhynchodus? sp. Inferognathal CVUL 37 from BLN5, Beaulieu Formation, Frasnian,
lingual view. C-E, Moyfhonmsia sp. Scales CVUL 38 from BLN8 (C), Ferques Formation, CVUL 39 from BLN3 (D), and
CVUL 40 from BLN4 (E), Beaulieu Formation, Fra.snian. The front of the .scale CVUL 38 (C) faces up and ils dorsal side
faces right. The front and the dorsal sides of CVUL 39 (D) face right and up respectively. The front of CVUL 40 (E) faces
left and its dorsal side up. F, Actinoplerygii gen. et sp. indet. Type A. Tooth Plate CVUL 41 from BLN5, Beaulieu Formation,
lower Frasnian. G, Actinopterygii gen. ci sp, indet. Type B. Tooth CVUL 42 from BLN8, Ferques Formation, Frasnian. H,
Spodichthys? sp, Scale CVUL 43 from BLN4, Beaulieu Formation, Frasnian. 1, Actinopterygii gen. et sp. indet. Type C.
Scale CVUL 44 from BLN5, Beaulieu Formation, lower Frasnian. J. M, Porolepiformes gen. et sp. indet. fragments of bone
CVUL 45 (J) and CVUL 48 (M) from BLN4, Beaulieu Formation, Frasnian. K, Actinopterygii gen. et sp. indet. Type D.
Hemilepidolrichium CVUL 46 from BLN3, Beaulieu Formation, Frasnian. The covered part of the hemilepidotrichium faces
down. L. Onychrîdontida gen. et sp. indet. Scale CVUL 47 from BLN4, Beaulieu Formation, Frasnian.
Microrestes d'Acanthodiens, de Plarodermes et d'Ostéichthyens du Dévonien du Bas-Boulonnais, France. Toutes les échelles
métriques correspondent à 200 \xm. A, Acanthodii gen. et sp. indet. Os avec quelques rangées de dents striées CVUL 36 de
BLN4. Formation de Beaulieu, Frasnien. vue labiale. B. Rhynchodus ? sp. fnférognathal CVUL 37 de BLN5, Formation de
Beaulieu, Frasnien, vue linguale. C-E. Moythomasia sp. Écailles CVUL 38 de BLN8 IC). Formation de Ferques, CVUL 39
de BLN3 (D), et CVUL 40 de BLN4 iE), Formation de Beaulieu, Frasnien. îm partie antérieure de t'écaille CVUL 38 (C)
est tournée vers le haut et son côté dorsal est orienté vers la droite. L'avant et la partie dorsale de CVUL 39 (D) sont
tournés vers la droite et le haut respectivement. Im partie antérieure de CVUL 40 (E) est tournée vers ta gauche et son côté
dorsal vers le haut. F. Actinopterygii gen. et .sp. indet. Type A. Plaque denticulée CVUL 41 de BIJ45. Formation de Beaulieu.
Frasnien inférieur. G. Actinopterygii gen. et sp. indet. Type B. Dent CVUL 42 de BLN8, Formation de Ferques, Frasnien.
H, Spodichthys? sp. Écaille CVUL 43 de BLN4, Formation de Beaulieu, Frasnien. l. Actinopterygii gen. et sp. indet. Type
C. Écaille CVUL 44 de BLN5, Formation de Beaulieu, Frasnien inférieur. J. M, Porolépiformes gen. et sp. indet. Fragments
d’os CVUL 45 (J) et CVUL 48 (M) de BLN4, Formation de Beaulieu. Frasnien. K. Actinopterygii gen. et sp. indet. Type D.
Hémilépidotriche CVUL 46 de BLN3, Formation de Beaulieu. Frasnien. La partie recouverte de l'hémitépidotriche est tournée
vers le bas. L, Onychodontida gen. et sp. indet. Écaille CVUL 47 de BLN4, Formation de Beaulieu, Frasnien.
Bull. Mus. natl. Hist. nat., Paris, 4® sér., 17, 1995
Section C, n" 1-4 ; 513-529.
Early Silurian microvertebrates of eastern Canada
by Susan TURNER and Godfrey S. Nowlan
(Contribution to IGCP 328 “Paleozoic Microvertebrates”)
Abstract. — Early to Late LIandovery platlormal strata from lhe Clemville, Weir, Anse aux Gascons, and
Anse à Pierre-Loiselle Formations, Chaleurs Bay, Gaspé Peninsula. Quebec; Armstrong Brook and Limestone
Point formations of northern New Brunswick; and limestone bloclts from a fault zone at .School Brook Cove,
Nova Scotia. hâve yielded veriebrate microfossils associaied with conodonts. Scales of loganiid ihelodonis are
relatively common comprising Loganellm sentira type, toganellia sp. cf. L. sihiricn, as well us a new form, a
possible kaioporid, Valvtihpis crisia n. g., n. sp. The latter is restricled to the lower LIandovery Clemville For¬
mation. Rare .seules resembling those of Helennlepis Karatajule-Talimaa, 1978 are présent. Other scales and or-
namented bonc.s or plaielets might be derived from chondrichthyans. an anaspid, or a gnathostomc, either
aeanthodian or placoclerm. The ncw assemblages share a close re.semblance with those of the Late Ordovician
and LIandovery of Timan-Pechora and Siberia and hâve features in common with faunas from lhe LIandovery
elsewhert jn OreenlanU, Britain, the Ballic and Tuva.
Keywords. — Vertebrata, Agnatha, Thelodonti, -Silurian, Canada, systematics, biostratigraphy.
Microvertébrés du Silurien inférieur du Canada oriental
Résumé. — Des microrestes de Vertébrés associés à des Conodontes ont été extraits de séquences marines
de plateforme du LIandovery inférieur à supérieur des formations de Clemville, Weir, Anse aux Gascons et Anse
à Pierre-Loiselle. dans la Baie des Chaleurs. Gaspésie. Québec, de.s formations de Armstrong Brook et de Lime¬
stone Point du nord du Nouveau-Brunswick; et des blocs calcaires de la zone faillée de School Brook Cove,
Nouvelle-Écosse. Les écailles de Tliélodontes loganhdes sont as.sez communes, avec les espèces Lnganellki scotica
et Loganelita sp. cf. L sihirica, ainsi qu'un possible katoporidc nouveau. Valyalepis i risla. Celte dernière espèce
est restreinte à la formation de Clemville (LIandovery inférieur). De rares écallie.s ressemblant à celles d'Hete-
notepis Karatajute-Talimaa, 1978 sont présentes. D'autres écailles ain.si que des os ornemenrés cl de petites plaques
o.sseuse.s semblent correspondre à un Chondrichthyen. un Anaspide ou un Gnathostome (Acanthodien ou Placo-
derme). Les nouveaux assemblages sont très proches de ceux de l'Ordovicien supérieur et du LIandovery de
Timan-Pechora et de Sibérie, et ont des formes en commun avec les faunes du LIandovery du Groenland, de
Grande-Bretagne, des Pays Baltes et de Tuva.
Mots-clés. — Vertebrata. Agnatha, Thelodonti, Silurien, Canada, systématique, biostratigraphie.
S. TuRNbK. Queenstund Mu\eurn, P.O. Box 3300, S. Brishane, Qd 4J01. Anstratia,
G. S. Nowlan, Institute of Sedimentary and Petroleum Geology, Geologicol Survey of Canada, 3303-33rd St. N.W., Calgary, Alberta,
Canada T2L 2A7.
Introduction
Vertebrate remains hâve been known from the Silurian of eastern Canada for .some time.
Isolated occurrences of thelodont scales in the Silurian of eastern Canada hâve been reported
during this century (Gardiner, 1966; TuRNER, 1976; Blieck & Janvier, 1991). Most of those
— 514 —
cited along with some of the new Lower Silurian material discussed here corne from the Mas-
carene and Arisaig zones (Williams, in press) in the complex Appalachian orogenic belt of
eastern North America. New Lower Silurian material here described from Quebec is from the
Chaleur zone (WILLIAMS, op. ciL) and material from the Ludlow-Pridoli rocks of Newfoundland
(FÂHRAEUS in Blieck & Janvier, I99l) cornes from the Clam Bank zone (WILLIAMS, op. cit.).
Thelodont scales hâve aiso been reported, but not yet verified, from the important key Lower
Silurian succession of .^nticosii Island (S. POHLER & C. Barnes, pers. comm. 1991).
In 1928 StETSON described new articulaled thelodont material from New Brunswick as
Thelodus “mctcimoshi” . Re-examination of these specimens by Turner (1984, 1986) indicated
that this material included large individuals of Thelodus parvidens as well as a loganellid and
an acanthodian. The Early Silurian date Llandovery) âge of the fish-bearing beds in the Long
Reach Formation is still disputed but there is Utile doubt that the beds are pre-Ludlow in âge
(Turner, 1986; in press).
The Late Silurian to Early Devonian succession in the Arisaig zone of Nova Scotia is par-
ticularly rich in vertébrale romains thaï arc closcly related or idenlical to ihose in the Welsh
Borderland, suggesting close proximily of these areas at the lime (e.g. Turner, 1970; BLIECK
& Janvier, 1991). 0rvig seems to hâve examined the first ihclodonts to be found in the Arisaig
succession (in BOUCOT et al.. 1974). Hc identified thclodontidid scales of “Thelodus parvidens
kind” assoeiaied with Noswlepis and Gomphonchus acanthodian scales and spines. BOUCOT et
al. (1974) used the evidence of the fish fauna to give an Upper Silurian (Ludlow) date to the
upper part of the Moydait Formation. We hâve not yet seen this material, but from what is
already known of the range of Thelodus parvidens in the eastern Canada-western European région,
the âge of the Moydatl could be as old as Wenlock and as young as early Pridoli. However.
graptoliles from the underlying formation are Ludlow in âge (Boucot et al., 1974). More recently,
Goujet (e.g, Bouyx & Goujet. 1985; in Blaise et al., 1991) identified Thelodus parvidens in
the White Rock Formation of the Bear River région of norlhern Nova Scotia (Annapolis zone
of WlLLlAM.S, in press) daling these formations as of laie Ludlow-early Pridoli,
Other Silurian vertebrate microremains hâve bcen found in horizons from Nova Scotia. Le-
GAULT(1968) described acanthodians from the laie Silunan Stonehouse Formation ofeast Arisaig.
Some of the scales were referred by Drnison (1979) to Machaeracanthus, typically a Devonian
genus, and some resemble ihose of No.stolepis. Further material from the Arisaig section is cur-
rently being studied and will be the subject of another paper.
This report briefly ouilines new material discovered in Lower Silurian strata which is cur-
rcntly under detailcd sludy. A summary of the new material is presented and a detailed description
is provided for a new form from the lowest Silurian Clemville Formation on Gaspé Peninsula,
Quebec.
GEOLOGY
Bourque (1975), Bourque & Lachambre (1981) and Nowlan (1981, 1983) hâve outlined
the geology of that part of the Gaspé Peninsula of Quebec from which one suite of samples
came (see Fig. 1). The sites that yielded microverlebrates are on the Clemville River near Port
— 515 —
Fig. 1. — Map of castem Canada shnwing main outerops wilh Luwer Silurian strata stippled. Thnse régional géologie zones of
Williams (in pre.s.s) that are nieniioned in the texl are shown bounded by dashed Unes. Dots indicate spécifie sections
mentioned in the text and Appendix I: A, Ari.saig Coastal section (Boücot ei al.. 1974); C, Petit Port Daniel River section,
near Clemville (BouRQiiK & Lachambre, 1981); Cu. Cunniiighanvs Brook loeality (Turner, 19861; D, sections al Dickie
Point. Dickie Cuve and Raxor Cove (LEE. & NOBIE. 1977); F. Flanagans section (Noble, 1976); G. road and railroad eut
sections ea.sl of Anse aux Ga.scons (Bourque & LachaMbre. 1981); L. Limesione Point secimn (Noble, 1976); S, Sehool
Brook Cove fault zone (Khl’PlE. 198(1). Modified from .Nowi AN (1981).
Carte du Canada otiental ni'Vitrani les principaux affleutements . Silurien inferieur en gri.w. f.e.t cane.t gêtilogii/ues rêgitmales
de Wluj.AM.s l'.rou-v pre.xsel tfUt .\anf inentiannPe.'i dans te texte .tant timilfes par une ligne en pointillé. Les points indiquent
les coupes particuUirex mentionnées dans le texte et l'Appendice I t .4, coupe côtière d'Arisaig tSOliCnr et al. 19741; C.
coupe de Petit Port Daniel Hher. ptis de Clemville tBoVRtfVU & LxrH.MUHHt;. IVSI) : Cu. localité dt Ciinninghain.s Brook
(Turner, 1986); D, coupes de Dickie Point. Dickie Cove et Razor Cove (LEE et NOBLE, 1977); F, coupe de Flanagans
(Noble. 1976) ; G, coupes de la route et du chemin de fer à l'Est de F Anse aux Gascons (Bourque <4 LacHambre, 1981);
L. coupe de Limestone Point (NOBLE. 1976) ; S. zone /aillée de Sehool Brook Cove (Keppie, 1980). Modifié d’après Nowlan
(1981).
Daniel (Nowlan, 1983, Fig. 5, sites 2 A, B and C). The Clemville Fonnation is al the base of
the Chaleurs Group and contains a good Llandovery A brachiopod zone fauna and conodonts
comparable with those of the lowermost Silurian of Anticosti Island. There are also forms as¬
signable to the Icriodella discrela-deflecta conodont zone of Britain CRhuddanian to early
Fronian). BOURQUE (1975) inierpreted the sédiments as shallow water "plalformal’ deposits. The
Weir Formation vertébrales came from two calcarenite horizons within sandstone units on the
north flank of the Clemville anticline. The brachiopod and conodont assemblages in the Weir
Formation suggest an early Fronian âge. The overlying Anse aux Gascons and Anse à Pierre-
Loiselle Formations span the late Llandovery (C4-6) (see Nowlan, 1983, Fig. 2).
— 516 —
Flü. 2. — Sumniaiy t)t' gculogicul furmations unü niicroveriebraie assemblages Irom easlern Canada reported herein.
Synthèse des formations géologiques et des assemblages de microvertéhrés du Canada oriental décrits ici.
Noble (1976) and Lee & Noble (1977) hâve described the sections in northern New Bruns¬
wick from which additional verlebrate material has beeu derived. Nowlan (1983) has sum-
marized the conodont biostratigraphy of the Llandovery strata of this région. The microvertebrates
were recovered from the uppermost part of the Armstrong Brook Formation and that part of the
Limestone Point Formation that correlates best with the Anse à Pierre-Loiselle Formation across
Chaleurs Bay lo the north.
Keppie (1980) discussed the unnamed limestones from the School Brook Cove, Nova Scotia,
which are also placed within the early Llandovery (upper Idwian-lower Fronian B1 to Cl -2).
Nowlan (in Keppie, 1980) identified biostratigraphically diagnostic conodonts and made a pre-
liminary identification of scales of “LoganiaT and “Thelodus species” from two horizons in
early Llandovery limestone blocks from the east side of School Brook Cove, Cape George, Nova
Scotia (Fig. 1, and see Keppie, 1980, Fig. 1 for detailed location). A summary of the geology
and âge of the new material is given in figure 2 and further details of the sites can be found
in the Appendix 1.
— 517 —
NEW MATERIAL AND METHODS
This study prnvides the first evidence of lhe earliest Silurian vertebrates in eastern Canada
and the first Silurian remains from Quebec. The exposed sections near Port Daniel, Quebec,
provide good continuous successions from which to get information on both conodont and thelo-
dont biostratigraphy for the Early Silurian.
The thelodont scales and other microvertebrates reporled here were first discovered in the
late 1970s to early 1980s following treatment of lhe Early Silurian limestoncs for conodonts
using the acetic acid technique (e.g. RtxON. 1976). The new assemblages corne from the Lower
Silurian Chaleurs Group in lhe Llandovery strata of Gaspé Peninsula; from the Amisirong and
Limestone Point Formations, New Brunswick; and from unnamed limestones in the School Brook
Cove area. Nova Scoiia. Ail microvertebrate remains were sent to the senior authoi for further
examination. Here wc présent a prcliminary account of the fish romains as outlined by one of
us (Turnrr, 1991b) ai the Studies on Early Vertebrates Symposium held at the Parc de Miguasha,
Quebec. in June 1991. This report includes the first formai description of a new genus announced
at the sympo.sium and named in honour of a key worker in Early Silurian microvertebrate studies,
Dr Valentina N. KARATAJUTE-Talimaa of Lithuania.
RESULTS: SUMMARY OF NEW MICROVERTEBRATE ASSEMBLAGES
Thelodonti
Loganiida
Loganellia sibirica Karatajute-Talirnaa, 1978 from lhe Clem ville and Weir Formations, Que¬
bec; School Brook Cove blocks. Nova Scotia. These scales closely resemble the scales of Lo-
ganellia sibirica from Tunguska, Siberia (Karatajute-Talimaa, 1978, tab. XX, Figs. 3-12).
LogttneUiu sp. cf. L. sibirica (L sibirica type 2 in Fig. 2) from the An.se aux Gascons and
Anse à Pierre-Loiselle Formations, Quebec, and possibly the Limestone Point Formation, New
Brunswick.
Loganellia scotica (Traquair 1898) from the Clemville and Weir Formations, Anse aux
Gascons, Anse à Pierre-Loiselle Formations, Quebec; Limestone Point Formation, norlhem New
Brunswick. Talimaa & Melikov (1987) placcd together a group of closely-related scales from
the Early Silurian of Russia which presumably .share features in common with L. scolica: they
referred them to "L. ex group scotica".. Certainly scales of L. scotica type are typical of the
Early Silurian in Scotland; lhe type locality is lhe ./amnytius horizon of the Patrick Burn For¬
mation, Lesmahagow (RiTCHiE, 1963; Tl'RNER, 1984); in the Kilbride Formation of Ireland
(Turner, pers. obs,); in Timan-Pechora and northern Siberia (KARATAJUTE-TALIMAAi 1978); and
in England (Aldridge & Turner, 1975; Turner, in Blieck & Janvier, 1991). We place .some
of the scales from eastern Canada in lhe L. scotica group and some as L. scotica sensu stricto
(see Fig. 2).
Loganellia ex gr. cuneata from the Clemville région, Quebec and the School Brook Cove
beds. Cape George. Nova Scotia. The presumed headscales of L cuneata, called L. cruciformis
— 518 —
by Gross (1967) occur in lhe Anse à Pierre-Loiselle Formation, Clemville River section, Quebec.
This group of thelodont scales which superficially resemble L. cuneata (Gross, 1967) is in need
of révision. Scales of this type hâve been reported from the Early to Late Silurian of Siberia,
Tuva and the Baltic région (e.g. KARATAJUTE-Talimaa, 1978; MÀRSS, 1986a). The .scales from
eastern Canada are rather slender and resemble those from Siberia. L cruciformis is now some-
times listed as the cruciform scale type if found in association with L. cuneata scales (e.g.
MÂRSS, 1986a).
Helenolepid?
A fcw scales of a possible new taxon of Helenolepis-Mkc scales corne from the left bank
section of Petit Port Daniel River, west of Clemville, Quebec, Uppcr Llandovery Anse aux Gas¬
cons Formation, Chaleurs Bay Group. These .scales appear closesl lo Helenolepis Karatajute-
Talimaa, 1978 known from the Pridoli of Tuva. Talimaa (1990) has also reported helenolepid
scales from the Upper Llandovery of Siberia. A decision on their désignation will hâve to wait
until more is known about the Siberian forms and until more material is available for histological
analysis.
Katoporida?
Scales of Valyalepis crista n. g., n. sp., described below, occur throughout the Clemville
Formation. Quebec. Details of localities which yielded the new taxon are given in Appendix I.
Thelodontida?
Thehdusl sp. indet.: Only two scales hâve been found from the upper 2m of the Clemville
Formation and 12.7m above the base of the Weir Formation. One scale in the Anse à Pierre-
Loisclle Formation resembles Thelnilus admirabilis Marss, 1982. These scales are outwardiy typi-
cal of Thelodus (see e.g. GROSS. 1967, taf. I ) but hâve small notches in lhe anterior crown rim,
a feaiure which séparâtes thein from most known Thelodus specics. They might also be spécial
cephalo-pectoral or oral scales of a loganiid, which cornmonly resemble scales of Thehdus (e.g.
Turner, I99la). A decision on their désignation will hâve to wait until more material is available
for histological analysis.
Thelodus sp. cf. T. parvidens: One scale from the Limestone Point Formation of northern
New Brunswick resembles those of the type thelodont. Alternatively, it might be a scale of
Thelodus laevis.
Anaspida?
A few ridged scales in the Limestone Point Formation might belong to a birkeniid anaspid
(cf. Marss, 1986a. tab. XXVI). NOREORD (1972) has reported possible Lower .Silurian anaspid
remains from Greenland; ThorsteinSSON (pers, comm.) has new articulated anaspids from the
basal Wenlock of Cornwallis Island. Arctic Canada; and anaspids occur in the late Llandovery
of Scotland (RrrcHiE, 1963).
Gnathostomes
These remains are still being studied and will not be discussed in detail here but investigated
in a future paper. Scales and bone fragments occur in the Clemville and basal Weir Formations
— 519 —
and in the Anse à Pierre- Loisel le Formation; some appear to be acanthodian and some might
belong to an acanthodian or a shark; one scale in the latter formation resembles those of Pilolepis
margaritifera Thorsteinsson, 1973.
A few scales in the Limestone Point Formation might belong to primitive sharks. These
scales are rounded with rhomboid bases bearing a basal pulp cavity and neck openings. Other
scales and ornamented bone might belong to an acanthodian or placoderm.
SYSTEMATIC PALAEONTOLOGY (S. Turner)
Class THELODONTl
Order KATOPORIDA? Karatajute-Talimaa, 1978
Family Katoporidae? Karatajute-Talimaa, 1970
Genus VALYALEPIS n. g.
Type sPECtES. — Valyalepis crista n. g., n. sp.
Diaonosis. — As for type and only speeies (see below).
Remarks. — These scales are characterized by a distinct médian raised ridge which may or may not bifurcate
towards the anterior margin of the Crown and an otherwise relatively smooth crown surface, a combination of
which is considered, at ihis time,. to be a feature of generic importance not found in other thelodont scales except
to a more advanced level perhaps in phlebolepid scales (see e.g. Màrss, 1986a, b).
Etymology. — Named in honour of Dr Valentina (Valya) N. Karatajute-Talimaa for her pioneer work on
Palaeozoic microvertebrates, and front lepis - scale.
Valyalepis crista n. sp.
(Figs. 3-6)
1991b. new genus: Turner, p. 45.
Diaonosis. — Thelodont with small scales less than Imm in length. Simple, elongate, diamond or rounded
leaf-shaped outline with a small posterior point and one or more pairs of latéral indentations possible; rare latéral
lappets. Crown larger than the ba.se. Most body scales hâve a distinctive crown ornement of a single, raised
médian rib which usually bifurcates just posterior to the anterior rim; trifurcation is possible. Neck low and
smooth. Base oval and annular. Basal growth with deepening can occur. Large, oval. shallowly-concave pulp
cavity. Hisiology of kaioporid type isensii Gross, 1967; Turner, 1991a); numerous dentine tabules open directiy
into the pulp cavity. A short canal, which is slightiy thicker than the tabules, either single or double, i.s picsent
in the posterior pulp cavity m .some spccimcns. Crown rim can hâve minoi cienulations. Scales in cro.ss-.scction
resemble a ridged roof. Oral or anterior head scales smaller, low anleriorly with .scalloped crown edge rising to
a smoother posterior point; posterior neck higher than anterior. Cephalo-pectoruI .scales moue elongate with scal¬
loped crown margin and wcaker médian rib.
Hoi OTVPE — Gcological .Survey of Canada - CiSCllB67l from GSC loc. 0-96428 (Fig. 3G-I)
Referred material. — 5 scales (GSC 103667-103670. 103684. 103686) from the type locality (Figs. 3A-F,
4M, O) and 58 scales (GSC 103672-103683, 103685, 1 03690- 1 037 1 6 and 108940-108953) from GSC localities
0- 98049, 0-98060-63, 98065-70 (Figs, 4, 5, 6). Other material has heen used for histological examination The
specimens are reposited in the National Collection of Type Invertebrate and Plant Fos.sils at the Geological Survey
of Canada. Ottawa ).
Type LOCAirrY. — Measured section in Clemville Formation (between 85.5m above the base up to 2m
below the top of the formation). Petit Port Daniel River, west of Clemville, Quebec, eastern Canada (C. Fig. 1;
see Appendix 1 for details).
Type horizon. — 2 ni below' the top of the Clemville Formation. Chaleurs Group (Distomodus keniuckyensis
zone, lower LIandovery (A3-4 brachiopod zones), Lower Silurian).
Ety.molocy. From evista meaning a ridge, in allusion to the shape of the cro.ss .section of most scales.
— 520 —
Fig. y. — Valyaieffis rrista n. g., n. sp,: lepresentailve scales Irom localily GSC loc ()-96428. uppcr 2nî of Clcmviilc Formation.
A-B. CSC 1036O7: A. tlorsu) (crown) view; B. veniral {basai) view; C. sketch diagram of cinss section oï irunk scale (not
lu scalc); D. GSC l()366H; F. GSC 103669; F. GSC 103670; D F. ail in dorsal view; G-l. holotype GSC 10.^671; G, latéral
view; H. dorsal view; I, ventral •vie.w Scale bar. 0.2 njm.
Valyalcpis crisu ti. g., n. sp. : rvailles rvpréu'niomt^s de la localité OSC loc. ü-96428, 2/n du som/tier de la formation de
Clemville. A^B, GSC I<)J667 ; 4, vue dorsale ivnronale) , B. vue ventrale ihu.\alv}; C, schê/mi d'une toupe ti travers u/ie
rcfï/7/f du tronc (p^js à f‘éi‘helU'i ; O, G.SC ■ B G-SC /0d66i/: /•' GSC 10J670 : D-f'i toutes en vue dorsale; G-J,
holotype GSC 103671 ; G, vue latérale ; H. vue dorsale ; I, vue ventrale. Echelle : 0,2 mm.
— 521 —
Description
Scales mostly 0.5mm in length (range 0.4- just less than 1mm). Most scales are low, almost
fiat with the prominent mid rib especially seen in the body scales (Figs. 3D-I, 4, 5). Bases are
very shallow in mosi scales (ail are probably from indtviduals with scales from the same growth
génération); deeper rounded bases are rarely seen (Fig. 5.31).
Oral or anlerior head scales are small (less than U.5mm)i and generally rounded (Figs. 5.1-7).
Some head scales exhibit typical raised posterior point and minor scalloping on anterior crown
rim. Rounded head scales can bc wider than long (e.g. Fig. 5.6).
Transitional scale.s aiso usually hâve a strong médian rib with three to four pairs of coarse
latéral ribs (e.g. Figs. 4. 5.9, 22-23). The anterior bifurcation of the midrib can extend half way
back along the crown and a pair of tly-away posieriorly-pointing latéral wings can be présent
(e.g. Figs. 4, 5.15). One large transitional (cephalo-pecloral) scalc has two pairs of deepiy in-
dented scallops and a prominenl bifurcaled anterior rim (Fig. 5.17).
In many scales the central pair of crown ribs converges in the midiine at a point less than
one third, up to one half of the way along the crown, producing a tnangulat rnid-section (e.g.
Figs. 4, 5.21). One or two pairs of anterior notches can be seen. The scales are characlerized
by a pagodu-like cross-section which resuUs from the high médian rib on the crown (Fig, 3C).
Figure 5 shows the range of variation and details of variety in crown ornament and shape in
the Clemville scales. Possible placement into oral, cephalo-pectoral and postpectoral (sensu
MÀRSS, 1982; 1986a, b) is indicated. Différentiation into the pinnal, and precaudal scale groups
of MÀRSS (op. cit.) could not be decided.
Histology
The scales are generally thin and not altered. The histological structure was discerned using
anise oil application (KarATAJUTE-TamMàA, 1978) and by making a few thin sections of a few
broken scales. The small size and thinness of the scales, however, makes the former technique
more successful; no diagnostic thin sections are yet available. Most scales are young in the
growth sériés, having shallow bases, sometimes with only a thin annular ring, and a large open
pulp cavily (Fig. 6B). The pulp cavity can be oval. elliptical or mushroom-shaped (Figs. 3B, 1,
5.25, 6A-C). As noted ahove. vei7 few' scales exhibit the older stage with deeper basal growth.
In ventral view, the numerous dentme tubules or canals can be seen opening directly into the
pulp cavity (Figs. 3B, 1; 5.25, 6A-C). Thcy arc scaitered evenly over the inner surface although
the shape of the pulp cavity can be mushroom-shaped with the “stalk" anteriorly and thus the
tubule or canal openings can form a rcstricted pattern wiihin the cavity (e.g. Figs. 3B, 6A, C).
In the postero-ventral point ol’ the pulp cavity a slightiy larger opening can be seen which scems
to be the opening of a wider dentine canal or a short, narrow pulp canal (e.g. Fig. 6A). This
short canal, direcled back into the distal point of the crown, can be .seen in a few of the transparent
scales.
Discussion
The style of histology seems closest to the “Katoponis" type of Gross (1967). Valyalepis
thus may be the oldest katoporid recognised to date. However, from the fineness of the tubules
— 522 —
— 523 —
Fig. 5. — Vulyuli-pis cnna n. g., n. sp, skelche,'. showing range ol vaiiaiion in morphology of scales based un .specimens from
GSC localities from the Clemville Formation. Scale bar: O.Snim. Specimens 1-5; GSC 1 03690- 10.%94, 6: GSCI03672; 7-29:
GSC 103695- 1037 16; 30: GSC I0367S; 3l-)4: GSC 108940-10^953. Sample Iwaliles: GSC loc. 0-98049 - 20. 26-29; GSC
loc. 0-98060 - 1-3. 8. 14. 17, 21-22. .30. 32-33. .34-35. 42; GSC loc. 0-98061 - 4, 15-16. 43: GSC loc 0-98062 5. 19.
23, 31. 37. 44; GSC loc. 0-98063 - 39; G.SC loc. 0-98065 - 7, 11-12. 40-41; GSC loc. 0-98066 -6; GSC loc. 0-98068 -
9-10. 13. 18. 25; GSC loc. 0-98070 - 24. .38.
ValyalcpiN cnsia n. g., n. sp. ; dessins monimnl le domaine ae variatiivi morphologique des écailles, Jondés sur des spécimens
des hcalilé.\ GSC de ta Fvrniulion de Clemville. Échelle: 0.5 mm. Spérimens 1-5: GSC I0J690-IOJ694 : 6: GSCI03672 :
7-29. GSC 10.1695-103716 : 30: GSC I0367H: 31-19: CSC HmdO- 108953. üxiililés d’échaiiiilUmnage : GSC hc. 0-
98049620. 26-29: GSC lue. 0-98060 1-3. 8. 14. 17. 21-22. 30. 32-33. 34-35. 42: GSC loc. 0-98061 - 4. 1.5-16. 43: GSC
loc. 0-98062 - 5, 19. 23, 31, 37. 44. GSC loc. 0-98063 - 39. GSCIor 0-98065 - 7. 11-12. 40-41: GSC hc. 0-98066 - 6:
GSC Inc. 0-98068 ■ 9-10. 13. 18. 25: GSC lue 0-98070 - 24. 38.
Fig. 4. — SEM photographs of scalcs of Valyalepis crisia n. g., n. sp. A. possible oral .scale, GSC 103672; B. posi-pectoral
trunk scale, G.SC 103673; C. ceplialopeeloral seule. GSC 103674; D, cephalopecloral scale. GSC 103675; E. po.ssible caudal
scale, GSC 103676, F, posl-pecloral trunk scale. GSC 103677; G, cephalopccbiral scale in latéral view, CSC 103678; H,
GSC 103679: I, posl-pecloral trunk scale, GSC 10.3680; J. basal view to .show aarrow pulp cavity, GSC I036SI, K, latéral
view', GSC 103682; L, basal Vicw, GSC 103683; M, basal view showing widc pulp cavily, GSC 103684; N, basal view,
GSC 103685; O. basal view, GSC 10,3686. Scale bar for ail: 100 pm. escepi K: 200 jjm.
Photographies um microscope éleeimiiique à holayage d'écaiUes de Valyalepis crista n. g., ii. .\p. A. écaille orale possible,
GSC 10.5672, B. écaille posl-petloraU- ilu Ironc. GSC 103673 : C. écaille céphaloperlorole, CSC 103674 : O, écaille cé-
phalopeilnrale, GSC 103675: E, écaille caudale possible. CSC 10.3676; t. écaille posi peciorale du ironc. GSC 103677: G.
écaille léphalofieciorale en vue latérale. GSC 103678: H. CSC 103679 : 1. écaille posi-peciorale du inmc. GSC 10.3680 :
J, vue basale inmiiruni lu cavité pulpairr éiroiie. CSC 103681 : K. vue lalérale. CSC 103682 : L, vue hiisiile. GSC 103683;
M, vue hasale monirani la large rnvilé piilpiiire. GSC 103684 : N. vue basale. GSC 103685 : 0. vue htmle. GSC 103686.
Échelle : 100 pm, sauf Ë : 200 pm.
— 524 —
Fig. 6. — Skelches ol ihc base of three seales of Vahatepis crisui il. g., n. sp. to show the structure of the pulp eavity and
dentinal mbule/canal openings. A-B. GSC 103687-103688 fnim GSC loc. 0-98070; C, GSC 103689 from GSC loc. 0-98066.
Scale bar: 0.2 mm.
Dessins de ta hase de Irais écailles de Valyalepis crista n. g., n. sp. montranl ta structure de la cavité pulpaire et des
ouvertures des canaux/tuhules de dentine. A-B, GSC 103687-103688 de la loc. GSC 0-98070 : C, GSC 103689 de la loc.
GSC 0-98066. Échelle : 0.2 mm.
il is possible that these could be interpreted as dentine tabules and not canals and thus Valyalepis
might be regarded as a relalively advanced or specialised loganiid (.sensu TURNER, 1991a). Head
and transilional seales. if identified correctly as such, do not differ greatly from some loganiid
seales. However, in the general style of the trunk seales with a médian ridge on a thin crown
and almost no base the seules of the new genus resemble those of Phleholepis. considered by
mosi to be an advanced kaloporid (e.g. Karauuuif.-Tai.imaa, 1978). Thus it is possible that
Valyalepis is a close, plesiomorphic relative of Phleholepis.
SUMMARY AND CONCLUSIONS
Previous to this account, Early Llandovery thelodonts had been found in North Timan, Si-
beria and Tuva (ex Tuvainska A, R.) (e.g. MoSKALENKO, 1968; ICxRAT.vtUTE-TALlMAA, 1978;
VaLIUKF.VICIUS et ai, 1983; VLADIMIRSKA et ai. 1986;. Tai.IMAA & Melikov, 1987). There
had been spéculation that thelodonts originated in the Siberian or Tuvan régions (Angaraland)
(Blieck & GOUJET, 1978; Turner & TarLING, 1982). The fauna reported here adds a new
dimension to ilie pieture of the évolution of the earliest thelodonts with the présence of several
loganiid species and a new. possible primitive katoporid. Valyalepis crista, as well as other fish
in eastern Canada in the former Chaleur zone, contemporary, if not older than remains from
elsewhere. Upper Ordovician thelodonts hâve been reported from Timan-Pechora (e.g. in Marss,
1989) and may occur in Canada (Barnes, Spjf.ldnae.s, in Blieck & Janvier, 1991), but neither
— 525 —
find has yet been documented. Talimaa (1991, pers. comm.) bas indicated the close similarity
of one of the Late Ordovician forms from Russia to Valyalepis. Talimaa (1990) reported the
presence of L ex gr. scotica in the Late Ordovician of Russia. Now, there is a strong suggestion
of doser links bctwcen the Chaleur zone and Timan-Pechora/westem Sibcria to allow for the
dispersai of lhese primarily shallow-water marine forms.
The presence of a possible thelodontidid in Ihe Clemville Formation of Quebec (Chaleur
zone), if confirmed. is the earliest record for the group. Thelodus species appear definitely in
the late Llandovery of Europe and in the Long Reach Formation (possible late Llandovery-Wen-
lock) of Southern New Brunswick within the Mascarene zone. They occur commoniy in the
Arisaig and Annapolis zones by Ludlow-Pridoli times.. A possible scale of Thelodus parvidens
in the Limestone Point Formation hinls at the eontemporaneity of part of this formation w'ith
the Long Reach Formation of Southern New Brunswick and the Early Silurian appearance of
this species. The similarity of Lof^unelliu sibirica group .scales in the Anse à Pierre-Loi.selle and
Limestone Point Formations confirms that the latter is of laie Llandovery (C5-6) âge.
The eastern Canadian lhelodonts found in the Chaleur. Mascarene and Arisaig zones in the
Early Silurian closely resemble those from Timan-Pechora and parts of Siberia (e.g. Karata-
jute-Talimaa. 1978; Talimaa, 1990). By late Llandovery. however. a similar ihelodont fauna
is more widespread. being found in the Chaleur zone. .Southern Britain, and in lhe Irish-Scot-
tish-Norwegian belt (Midland Valley terrane) (TURNF.R pers. obs.). The earliest Silurian Clemville
Formation fauna appears to contain endemic éléments and to be distinct front the others recorded
here. If Valyalepis proves to be a primitive katoporid then that group of thelodonts is présent
in the eastern Canadian région (Chaleur zone) as well as probably in Timan-Pechora.
Tlie exposed sections on the Gaspc Peninsula, Québec, providc good polenlial for a delailed
conodont and microvertebrate biostratigraphy of the Lower Silurian. The thelodonts found there rep-
resent some of the oldest known to date and the other microvertebrates comprise anaspid?, shark?,
placoderm? and acanthodian? remains, some of which are the oldest records for gnathostomc fishes.
Acknowledgnients
S. Turner is happy to acknowledge graiils from the linesco-I.U.G.S. Internai ional Geological Cor¬
rélation Programme, the I.G.C P committees of Australia and Canada, the J, B, Tyrrell Fund of the Geo¬
logical Society of London, and to thank the Instiiute of Sedimentary and Petroleum Geology, Geological
Survey of Canada, for Iinancial a.ssistance, ail of which eniihled her to visit Canada in 1991 and work on
the specimens in Calgary, to attend and give a paper at the highiy succe.ssfui Miguasha symposium, as
well as visit some of the Silurian localities in eastern Canada; her work in general is currently financed
by a grani front the Australian Research Council. The scanning électron micrographs were taken by Jenny
WoNG and printed by Bill ,SharmaN both of the Institute of Sedimentary and Petroleum Geology. Dr Alain
Blieck kindly refereed lhe manuscript and we thank him for his useful commeni.s.
LITTERATURE CITED
Aldridge, R. J. & S. Turner, 1975. — Britain’s oldest agnaihans. Genl. Mag.. 112: 419-420.
Blaise, J., E. BoUYX, D. GOUJET, J. LE MENN & F. PARIS, 1991. — Le Silurien supérieur de Bear River (zone
de Meguma, Nouvelle Écosse) : faune, biostratigraphie et implications paléogéographiques. Geobios, 24 :
167-182.
— 526 —
Blieck, a. & D. GOUJET, 1978. — A propos de nouveau matériel de Thélodontes (Vertébrés, Agnathes) d’Iran
et de Thaïlande : aperçu sur la répartition géographique et stratigraphique des Agnathes des “régions gond-
waniennes” au Paléozoïque moyen. Ann. Soc. Céol. Nord. 17 ; 363-372.
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APPENDIX
Detailed localities are provided only for the illustrated material of the new taxon erected
in this paper; ail are in the Clemville Formation, Chaleurs Bay Group. The localities identified
by letters on figure 1 are described below by province and formation. For summary corrélation
chart see Nowlan (1983, Fig. 2).
QUEBEC
Clemville Formation
Locality C on figure I : the samples from the Clemville Formation ail corne from sections
along the Petit Port Daniel River, just west of the village of Clemville near Port Daniel, on the
— 528 —
Gaspé Peninsula. A sketch map of the locality has been published by BouRQUE & Lachambre
(1981. Fig. 16). The l'orination is 110m thick and is exposed on either side of an anticline cored
by the unconformably underlying Mictaw Group. Rhuddanian to Aeronian Stricklandia typica
phylozone (Llandovery A3-4) and /. discreta-I. dejlecta conodont zone. For details of conodont
ranges see Nowlan (1981. Fig. 5).
G.SC loc. 0-96428. 2m below top of formation, north flank of Clemville anticline, latitude
48"10'42”N, longitude 65'’0r34’'W : 22 specimens (Turner, 1984) — V. cristata\ Laganellia
sibirica, L. sp?, Thelodus sp’, indeterminate bone?
GSC loc. 0-98049. 3m below top of formation, below power transmission line, latitude
48'M0'36"N. longitude 65'’0r29"W; 14 specimens - V. iriskv, iMganellia sibirica, L. ex gr.
scotica, acanthodian? scale. shark scale?
GSC loc. 0-98060 72m above base of formation, south tlank of Clemville anticline. latitude
48"10’33”N. longitude 65"0ri3’'W: 30 specimens - V( crisia', Loganellia sibirica. L. sp. cf. L
scoiica. indeterminate thclodont? scale.
GSC loc, 0-98061, 72.5m above base of formation, south flank of Clemville anticline, lati¬
tude and longitude as for 0-98060. 10 specimens - V. crista: Laganellia sibirica, L. ex gr. scotica.
GSC loc. 0-98062 73.8m above base of formation, south flank of Clemville anticline, latitude
and longitude as for 0-98060 ; 32 specimens - V crista', Laganellia sibirica, L. sp. cf, L. .scotica,
L. ex gr. .scotica. thelodont or acanthodian? scale, phyllocarid.
GSC loc. 0-98063 75m at)Ove base of forrnation. south flank of Clemville anticline. latitude
and longitude as for 0-98060: 12 specimens — V. crista‘, Laganellia sibirica, phyllocarid.
GSC loc. 0-98064 - 77m above base of fomialion. south llank of Clemville anticline, latitude
and longitude as for 0-98060: 1 specimen - thclodont? (missing).
GSC loc. 0-98065 -79m above base of formation, south llank of Clemville anticline, latitude
and longitude as for 0-98060: 39 specimens — V. crista: Laganellia sibirica, L. sp. cf. L. scotica,
L. ex gr. scotica, I small indeterminate scale?
GSC loc. 0-98066 - 80ni above base of formation, south flank of Clemville anticline, latitude
and longitude as for 0-98060: 12 specimens - V. crista: Laganellia sibirica, L. sp. cf. L. scotica,
L. ex gr. .scotica, I picce bone?
GSC loc. 0-98067 81m above base of formation, south flank of Clemville anticline, latitude
and longitude as for 0-98060: 22 specimens - V. crista: Loganellia sibirica, L. sp. cf. L. .scotica,
L. ex gr. .scotica, 1 acanthodian? scale,
GSC loc. 0-98068 82m above base of formation, south llank of Clemville anticline, latitude
and longitude as for 0-98060: 30 specimens - V crista: Loganellia .sibirica, L. sp. cf. L. scotica,
L. ex gr. scotica, indeterminate bone?
GSC loc. 0-98069 83.8m above base of formation, .south llank of Clemville anticline, latitude
and longitude as for 0-98060: 13 specimens - V. crista: Loganellia sibirica.
GSC loc. 0-98070 85.5m above base of formation, .south flank of Clemville anticline, latitude
and longitude as for 0-98060: 19 specimens - V. crista: Laganellia sibirica, I bone?
Weir Formation
Locality C as described above under Clemville Formation.
— 529 —
Anse aux Gascons Formation
Locality C as described above under Clemville Formation.
Anse à Pierre-Loiselle Formation
Locality C as described above under Clemville Formation.
Locality G: Roadcut on Highway 132 near Gascons, Southern Gaspé Peninsula, latitude
48°12’20”N, longitude 64"49’30'’W; railway eut 500m southeast of highway section, latitude
48°12’13”N, longitude 64°49’05”W (see BOURQUE & Lachambre, 1981, Figs. 2, 12).
NEW BRUNSWICK
Armstrong Brook Formation
Locality L: Coastal exposure at Limestone Point, northern New Brunswick, latitude
47‘’48’54"N, longitude 65‘’43’34‘’W (see Noble, 1976, Figs. 1, 2).
Limestone Point Form.ation
Locality D; Dickie Cove Brook and Dickie Point, west of Jaquet River, northern New Brun¬
swick. latitude 47“57'07”N. longitude 66‘’07’45’'W (see Lee & NOBLE. 1976, Figs. 1, 2).
Locality F; Coastal exposure at Flanagans, west of Quinn Point, northern New Brunswick,
latitude 47"55’06”N, longitude 65‘’57’18"W (see Noble, 1976, Figs, 1, 2).
Locality L as described above under Armstrong Brook Formation.
Long Reach Formation
Locality Cu: Cunninghams Brook locality, Southern New Brunswick, approximate latitude
45°24’N, longitude 66'’19’W (see Stetson, 1928; Turner, 1986).
NOVA SCOTIA
Arisaiü Group
Locality A: Arisaig coastal section west of Arisaig; long section starting at latitude
45°45’20”N, longitude 62‘T0’36”W and ending at latitude 45"44’09”N, longitude 62°12’40”W
(see Boucot et al., 1974 for details).
Formation uncertain
Locality S: School Brook Cove fault zone, latitude 45°53’00”N, longitude 61°55’06”W (see
Keppie, 1980 for detailed locality).
LOUIS-JEAN
avenue d’ Embrun, 05003 GAP cedex
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Dépôt légal : 594 - Juillet 1995
Imprimé en France
Date de distribution : 1'^'^ septembre 1995
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51 Gavet, M., 1986. “RcmuiUichthys" Gayel, du Cénomanien inférieur marin de Ramallah (Monts
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52 RUS.SEL1,, D.E. & R. Zhai, 1987. The Paleogene of Asia : Mammals and stratigraphy. 490 p., 232
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53 RnsSElx, D.E., J.P. Santoro & D. Si(:o(;neau-Ri)SSEEE (Eds), 1988. Teeth revisited :
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nombreu.x/numerou.s figs. & tabl. ; 34 article.s/papers FF 650.00.
54 VÉRAN, M., 1988. Les éléments accessoires de l’arc hyoïdien des poissons téléostomes
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55 BLIS.SON, (L, 1988. Évaporites et hydrocarbures. 140 p., 50 figs, 3 tabl., cartes/maps FF. 187.20
56 Saint Martin, J.-P., 1 990. Les formations récifales coralliennes du Miocène supérieur d' Algérie
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164 Broutin, ,I. et al. 1995. La Flore fossile du Bassin houiller de Saint-Étienne.
165 Mar-SHALE, L.G., Ch. de Miüzon & D. Si{;o(;neaii-Ri!S.seei,, 1995. Pueadelphys andinus
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Bulletin du Muséum national d’Histoire naturelle
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