# The Osteology of the Reptiles/Chapter 8

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CHAPTER VIII
THE SUBCLASS ANAPSIDA
Temporal region of skull wholly roofed over, or secondarily emarginated from the sides, not perforated.
1. ORDER COTYLOSAURIA
Temporal roof complete, not emarginated: skeleton primitive. An order of reptiles, not only the oldest geologically, but more primitive in structure than any other; probably the ancestral stock of all later Amniota. They were very variable in size, structure, and habits: as known, subaquatic, lowland, or marsh reptiles, never cursorial or climbing; invertebrate feeders for the most part, varying in size from less than one to about ten feet in length. The body was never slender, nor the legs long; the neck was always short. Dermal ossifications of any kind are known in but a few genera, Diadectes, Pantylus, and the Pariasauridae; the body was probably covered with horny plates or scales. The earliest known member of the order dates from the Middle Pennsylvanian, the latest from the Middle Triassic.
None has all the primitive characters given in the list, but the losses or modifications in any form are few. They may be discussed under three groups, which include their chief evolutional modifications.
1. Carboniferous and Lower Permian
Fig. 161. Eosauravus: Part of skeleton, from above. Enlarged. Specimen in National Museum.
​moderate or considerable length. Two centralia pedis are doubtfully known only in Labidosaurus. Dichocephalous ribs are known only in Seymouria and Pantylus. The cleithrum is vestigial in some.
Fig. 162. Skeleton and life restoration of Cotylosaurs: A, Diasparactus. After Case. One twentieth natural size. B, Seymouria. About two feet long.
Family Seymouriidae. Primitive, terrestrial, insectivorous reptiles less than three feet in length. Teeth conical in a single row on jaws and dentaries. Cleithrum vestigial or absent. Vertebral spines vestigial, the vertebrae with broad arches.
Seymouria Broili (? Conodectes Cope). United States.
Family Sauravidae. Slender reptiles about one foot in length. Skull and intercentra unknown.
Eosauravus (Middle Pennsylvanian). United States.
Sauravus. Thevenin, France.
Family Gymnarthridae. Small reptiles six to eight or ten inches in length, insectivorous or invertebrate feeders. Teeth obtusely ​pointed. Parasphenoid large and broad. Appendicular skeleton unknown, and the skull imperfectly known.
Gymnarthrus Case, Cardiocephalus Broili, United States.
Family Diadectidae (Diadectosauria). From about five to about eight feet in length. Skull short and high. Teeth incisiform in front, transversely molariform posteriorly. Vertebrae with hyposphene and hypantrum. Cleithrum rather large.
Diadectes Cope, Animasaurus Case and Williston, Bolbodon Cope, Chilonyx Cope, Desmatodon Case, Diadectoides Case, Diasparactus Case, United States.
Family Bolosauridae. Teeth subconical, cuspidate. Small reptiles. Teeth and part of skull only, known. Bolosaurus Cope, United States.
Family Captorhinidae (Labidosauria). From one to three feet in length; invertebrate feeders. Dermosupraoccipitals confined to occiput. No supratemporals and, in Labidosaurus, no tabulars. Teeth obtusely flattened, conical, in two or more rows on maxillae, one or more on mandible. Cleithrum vestigial. Spines of vertebrae short, their arches broad. Parasternal ribs present.
Captorhinus Cope, Pleuristion Case, Labidosaurus Cope, United States.
Family Pariotichidae. Small terrestrial reptiles about one foot in length, insectivorous or invertebrate feeders. Teeth obtusely pointed, in one or more rows. Imperfectly known.
Pariotichus Cope, Ectocynodon Cope, Isodectes Cope, Puercosaurus Williston, United States.
Family Stephanospondylidae. Maxillae with two rows of transverse teeth. Cleithrum large. Skull short, imperfectly known, as also the skeleton.
Stephanospondylus Stappenbeck, Phanerosaurus Meyer, Saxony, Germany.
Genera Incertae Sedis: Chamasaurus Williston, Archeria Case, Bathyglyptus Case, Helodectes Cope, United States.
Family Limnoscelidae. Elongate, subaquatic or marsh reptiles seven or eight feet in length. Teeth conical, recurved in single rows.
Fig. 163. Skeleton of Labidosaurus (Cotylosauria) from the side. One fourth natural size.
Fig. 164. Limnoscelis, a subaquatic cotylosaur, from the Permocarbnoniferous of New Mexico. One twelfth natural size.
​Skull elongate and compressed in front. Cleithrum small, tail elongate.
Limnoscelis Williston, United States.
Family Pantylidae (Pantylosauria). Terrestrial reptile less than two feet in length. Skull low, short, flat, with palatal and coronoid teeth; a single row of short teeth in [upper] jaws and mandible. Skeleton imperfectly known. No parietal foramen. Body covered with small bony scutes.
Pantylus Cope (? Ostodolepis Williston), United States.
2. Middle and Upper Permian
Family Pariasauridae (Pariasauria). Large lowland cotylosaurs reaching nine or more feet in length. Skull with protuberances, broad and short, its intimate structure not well known. Teeth in a single row, convex on the outer side with six or seven cusps arranged around their borders. Scapula with acromion and screw-shaped glenoid fossa. Phalangeal formula of front feet unknown. Astragalus and calcaneum fused; centrale and fifth tarsale unknown, possibly absent. Phalangeal formula believed to be 2, 3, 3, 4, 3 in one genus, primitive in others. Body with several rows of bony dermal scutes.
Pariasaurus Owen, Propappus Seeley, Anthodon Owen, Bradysaurus Watson, Embrithosaurus Watson, Pariasuchus Haughton and Broom, South Africa. Pariasaurus or an allied genus, Russia.
3. Lower and Middle Triassic
Family Procolophonidae (Procolophonia). Small reptiles a foot or more in length. Skull triangular, relatively smooth. Teeth in front conical, behind transverse, in a single row. Orbits very large, elongate anteroposteriorly. Parietal foramen large. Dermosupraoccipitals small or vestigial. Tabulars large, including between them and the squamosal a large otic notch. No supratemporals. Post-temporal openings of considerable size. Ectopterygoids distinct. Spines of vertebrae small. Two or three sacrals. Coracoids free in maturity. No cleithrum. Astragalus and calcaneum sometimes fused. Radiale and fifth carpale unossified, also centrale and fifth tarsale, so far as known. Lacrimals small, sometimes excluded from nares. Parasternals sometimes present.
​Procolophon Owen, Saurosternon Huxley, Thelegnathus Broom, South Africa. Koiloskiosaurus Huene, Leptopleuron Owen (Telerpeton Mantell), Sclerosaurus Meyer, Europe.
Family Elginiidae. Skull triangular, broad behind, with long horns in tabular region and numerous conical protuberances. Orbits not elongate. Crowns of teeth denticulate. Intimate structure and skeleton unknown.
Elginia Newton, Scotland.
2. ORDER EUNOTOSAURIA
Primitive terrestrial reptiles with reduced dorsal vertebrae, expanded ribs, and an incomplete carapace of dermal bones.
The skull is doubtless wholly roofed over; the palatine is primitive, with numerous teeth. Maxillae and premaxillae with a single row of small teeth. External nares terminal. Vertebrae slender, notochordal, with vestigial spines; capitular attachment of ribs on anterior part of centrum, the second to ninth ribs with a vestigial tubercle, progressively broadened, contiguous at their borders. Pectoral and pelvic girdles primitive. Tail probably small. Femur slender, sigmoidally curved; feet unknown. Dorsal region strongly convex, covered with dermal ossifications, apparently in median and lateral rows.
This group at present is known by a single species, Eunotosaurus africanus Seeley, from the Middle Permian of South Africa, represented by incomplete specimens which have recently been described by Watson, from whom the above characters are taken. That the genus is intermediate between the true Cotylosauria and the Chelonia seems very probable, as Watson has urged. To locate it with either order will require many modifications in their definitions. For that reason it may be left in an independent position until further discoveries furnish more details regarding the skull, limbs, and carapace. The known characters ally it more closely with the Cotylosauria than with the Chelonia.
Middle Permian. Eunotosaurus Seeley, South Africa.
3. ORDER TESTUDINATA OR CHELONIA
Temporal region of skull usually exposed by the emargination of the roof bones, the supratemporals, dermosupraoccipitals, and tabulars absent. Eight cervicals. Ten dorsal vertebrae enclosed in a more or less complete carapace; an ossified plastron. A single coracoid; pelvis with large openings. Phalangeal formula always reduced.
No order of reptiles is so unequivocally distinguished from all others as the Chelonia, the turtles and tortoises. Jaws are always [beaked], and except in Stegochelys of the Trias they are wholly toothless; a short, broad body, a rather short skull, a flexible neck of eight vertebrae, and an osseous carapace and plastron.
In addition to the bones mentioned above, the postfrontals and ectopterygoids and usually the lacrimals are absent, the temporal region, when roofed over, covered by the large postorbitals, jugals, squamosals, and quadratojugals. The prevomers are united; there is no interpterygoidal opening, and there may be an incipient secondary roof to the palate. The prefrontals meet in the median line, the nasals are often absent; the stapes is slender. The pectoral girdle is composed of a furcate scapula and a single coracoid, usually without a supracoracoid foramen. The carpus and tarsus are much modified, and the phalangeal formula is always reduced, to 2, 3, 3, 3, 3 or 2, 2, 2, 2, 2, with the fifth toe usually still more so. Because of the inflexible carapace the structure and posture of the limbs are much modified. The forearm is so twisted upon the humerus that the foot is brought more or less directly forward in walking. As in the dinosaurs there is a greater or less reduction of the postaxial fingers and a strengthening of those on the other side of the feet. Only rarely, in certain aquatic types, have the outer fingers of the hand more than three phalanges, probably because of an incipient hyperphalangy.
Regarding the general classification of the Chelonia there is still dispute. According to Cope, Dollo, and Hay there are two chief divisions or suborders, the Athecae and Thecophora, dependent upon the character of the carapace, the former with but a single living species, the latter with more than two hundred. The more generally accepted classification recognizes four suborders, the Cryptodira ( ​including the Athecae), the Pleurodira, Amphichelydia, and Trionychoidea. The definitions of the Athecae and Thecophora given by Hay are as follows:
Athecae. Turtles which retain the primitive dermal armor, with at least traces of the subdermal expansions connected with the ribs. A single living species, Dermochelys coriacea.
Thecophora. Turtles in which the primitive dermal armor is obsolete or abolished, the carapace formed by expansions of the ribs, neural plates, and usually peripheral plates.
Evidences of this primitive external series are found as vestiges, perhaps, of various Cretaceous Thecophora, but they have been accounted for in other ways. If however, the interpretation of the characters of Eunotosaurus, as given on a preceding page, is correct, this theory is much strengthened, since the Eunotosauria have both the expanded dermal ribs corresponding with the ordinary carapace of the turtles, and an overlying carapace composed of rows of plates like those of Dermochelys.
A. Suborder Amphichelydia
Mesoplastra present. Nasals and lacrimals distinct. Skull wholly roofed over. Neck short, not retractile, the cervical vertebrae amphicoelous or concavo-convex.
Family Proganochelydidae. Vomer and parasphenoid with small teeth. Nine dorsal ribs (costals) and seven cervical vertebrae, with ribs. Neck with free dorsal plates. Scapular girdle with short proscapular process or acromion; coracoid short, more or less fused with scapula; a supracoracoid foramen. One sacral vertebra. (Jaekel.)
Upper Trias. Stegochelys Jaekel, Proterochersis Fraas, Proganochelys Baur, ? Chelyzoum Meyer, Germany.
Family Pleurosternidae. Cervical vertebrae amphicoelous. Skull elongated; coracoid distally expanded. Carapace united to plastron by narrow buttresses.
Upper Jura. Platychelys Wagler, Pleurosternum Owen, Europe.
Cretaceous. Glyptops Marsh, North America. Helochelys Meyer, Germany.
​Family Baënidae. Carapace united to plastron by strong buttresses. Skull short. Cervical vertebrae for the most part with but one end concave.
Lower Cretaceous. Probaëna Hay, Naomichelys Hay, United States.
Upper Cretaceous. Baëna Leidy, Eubaëna Hay, Boremys Lambe, ? Neurankylus Lambe, Thescelus Hay, Charitemys Hay, ? Polythorax Cope, United States.
Eocene. Baëna Leidy, North America.
B. Suborder Pleurodira
Peripheral bones of carapace present. Neck withdrawn laterally. Mesoplastra absent or present. Temporal roof of skull complete or much emarginated. Pubes and ischia suturally united with plastron. Pterygoids not separating quadrates from basisphenoid.
Family Pelomedusidae. Mesoplastron present. No nasals. Vomers present or absent.
Upper Cretaceous. Bothremys Leidy, Taphrosphys Cope, Amblypeza Hay, Naiadochelys Hay, North America.
Eocene. Podocnemis Wagler, Europe, Africa. Stereogenys Andrews, Africa.
Pliocene. Sternothaerus Bell, Pelomedusa Wagler, Africa.
Family Chelydidae. No mesoplastron. Vomer distinct, the prefrontals separated.
Eocene. Hydraspis, India. Recent South America.
Pleistocene and Recent. Chelodina Fitzinger, Australia.
Family Miolanidae. Skull roof complete with horn-like protuberances. Very large turtles.
Uppermost (?) Cretaceous. Miolania Owen, South America.
Pleistocene. Miolania, Australia.
C. Suborder Cryptodira
Head withdrawn in a vertical flexure. Carapace with marginal plates. Pelvis not united with plastron. Epiplastra in contact with hyoplastra. Pterygoids separating quadrates and basisphenoid.
​Family Thalassemyidae. Temporal region of skull more or less over-roofed. Neck short. Plastron loosely connected with carapace, usually with one or more fontanelles. Ambulatory turtles.
Upper Jura. Eurysternum Wagler, Thalassemys Rütimeyer, Europe.
Upper Jura and Wealden. Tropidemys Rütimeyer, Pelobatochelys Seeley, Europe. Chitracephalus Dollo, Europe.
Upper Cretaceous. Osteopygis Cope, Catapleura Cope, Lytoloma (Rhetechelys, Erquelinnesia) Dollo, North America. Erquelinnesia (Pachyrhynchus) Dollo, Europe, Africa.
Eocene ? Lytoloma Cope, Europe.
Family Toxochelyidae. Temporal region largely over-roofed. Palatines entering into internal nares. Plastron loosely articulated. Carapace with shields. Subaquatic, at least two claws on front feet.
Cretaceous. Toxochelys Cope (? Cynocercus Cope), Porthochelys Williston, North America.
Family Desmatochelyidae. Skull almost wholly roofed over. Internal nares far forward. Small palatine foramen. Nasals present. Plastron loosely connected with carapace. Limbs paddle-like, aquatic.
Upper Cretaceous. Desmatochelys Williston, Neptunichelys Wieland, Atlantochelys Agassiz, North America.
Family Protostegidae. Marine turtles of large size, the limbs paddle-like without claws. Carapace greatly reduced, the plastron loosely attached. Skull large; temporal region wholly roofed over. Internal nares far forward, not under-roofed.
Upper Cretaceous. Protostega Cope, Archelon Wieland, North America.
Family Cheloniidae. Marine turtles with paddle-like limbs and elongate fingers. Skull mostly roofed over. Head not retractile. Plastron loosely united to carapace.
Upper Cretaceous. ? Allopleuron Baur, North America. Allopleuron Baur, Europe. Peritresius Cope, North America.
Eocene. Lembonax Cope, North America. Argillochelys Lydekker, Eosphargis Lydekker, Eochelone Dollo, Europe.
Miocene. Scyllomus Cope, Procolpochelys Hay, North America.
Oligocene. Chelyopsis Beedin, Europe.
​[Family Dermochelyidae. Leathery turtles. Marine turtles, with mosaic of small, polygonal, bony plates, in the dermis of the back, not ankylosed to the ribs.
Eocene. Psephophorus, Egypt, North America.
Recent. Dermochelys.]
Family Chelydridae. Marsh and river turtles, with reduced plastron loosely joined to carapace, the skull incompletely roofed. Entoplastron T-shaped. Caudals mostly opisthocoelous. Feet elongate, webbed.
Upper Jurassic. Tretosternum Owen (Peltochelys Dollo), Europe.
Eocene. Gafsachelys Stefano, Europe.
Miocene. ? Acherontemys Hay, North America. Chelydra, Europe.
Pleistocene and Recent. Macrochelys Gray, Chelydra Schweiger, North America.
Family Dermatemyidae. Temporal region not roofed. Plastron suturally united to carapace. No parietosquamosal arch. Caudals procoelous. Marsh turtles, the carapace well ossified.
Upper Cretaceous. Adocus Cope, Homorophus Cope, Zygoramma Cope, Agomphus Cope, Compsemys Leidy, Basilemys Hay, North America.
Eocene. Anosteira Leidy, Baptemys Leidy, Pseudotrionyx Dollo, Kallistira Hay, Notomorpha Cope, Alamosemys Hay, Basilemys Hay, Hoplochelys Hay, North America.
Oligocene. Xenochelys Hay, ? Anosteira Leidy, North America. Anosteira Leidy, Europe.
Trachyaspis Meyer, Eocene, Miocene, Europe, Africa.
Family Emydidae. Temporal region not roofed. Neck retractile. Carapace low-arched. Subaquatic, the feet webbed. Middle digit rarely reduced. Marsh tortoises.
Upper Cretaceous. ? Gyremys Hay.
Eocene. Paleotheca Cope, Echmatemys Hay, North America. ? Chrysemys, Emys, Europe.
Oligocene. Graptemys Agassiz, North America. ? Clemmys Gray, Europe.
​Miocene. Trachemys Agassiz, Clemmys Ritgen, North America.
Pliocene. Terrepene Merrem, Trachemys Agassiz, ? Clemmys Ritgen, Deirochelys Agassiz, Pseudemys Gray, North America.
Pleistocene. Terrepene Merrem, Chrysemys Gray, Clemmys Ritgen, ? Pseudemys, North America.
Ptychogaster Pomel, Oligocene, Miocene, Europe.
Family Testudinidae. Temporal roof reduced. Neck retractile. Plastron suturally united with the highly arched carapace. Phalanges not more than two in number. Small to very large tortoises, herbivorous, terrestrial.
Eocene. Hadrianus Cope, Achilemys Hay, North America. Testudo, Africa.
Oligocene. Testudo Linné, Stylemys Leidy, North America.
Miocene to Recent. Testudo Linné, North America, Europe, Asia, Africa.
D. Suborder Trionychoidea
Skull and neck as in the Cryptodira, the basiphenoid separating the pterygoids. Plastron ligamentously united with carapace, which lacks the peripheral bones and is covered with a leathery skin only and is flattened. More than three phalanges in third digit. River and lake turtles, the neck long.
Family Plastomenidae. Hyoplastra, hypoplastra, and xiphiplastra closely united. Legs unknown.
Uppermost Cretaceous and Lower Eocene. Plastomenus Cope, North America.
Family Trionychidae. Openings between hyoplastra, hypoplastra, and xiphiplastra. Three claws only, feet elongate.
Uppermost Cretaceous. Helopanoplia Hay, North America.
Eocene. Conchochelys Hay, Axestemys Hay, Aspideretes Hay, Amyda Oken (= Platypeltis Fitzinger), North America.
* ↑ [=Triassochelys Jaekel.—Ed.]
* ↑ [Many genera omitted.—G. K. N.]
* ↑ [Many modern taxonomists unite the Emydidae with the Testudinidae, as the former grade into the latter.—Ed.]