U'a<'i '.» ^.^.''^i'i icJ Ji;:t!;<: :?''J5J "jUik .Ko'h3A£^ "Bi t 3^ Boston Public Library book ]'=; to ^e returned to the on c last staniT' Digitized by the Internet Archive in 2010 with funding from Boston Public Library http://www.archive.org/details/osteologyofrepti1925will THE OSTEOLOGY OF THE REPTILES LONDON : HUMPHREY MILFORD OXFORD UNIVERSITY PRESS THE OSTEOLOGY OF THE REPTILES BY SAMUEL WENDELL WILLISTON M.D., Ph.D., Sc.D., N.A.S. Late Professor of Palaeontology in the University of Chicago \ ARRANGED AND EDITED BY WILLIAM KING GREGORY, Ph.D. Associate in Vertebrate Palaeontology American Museum of Natural History, New York Professor of Vertebrate Palaeontology Columbia University CAMBRIDGE HARVARD UNIVERSITY PRESS 1925 COPYRIGHT, 1925 BY HARVARD UNIVERSITY PRESS PRINTED AT THE HARVARD UNIVERSITY PRESS CAMBRIDGE, MASS., U.S.A. FOREWORD In this book we have the chief results of WilHston's half-century of exploration and research in the field of vertebrate palaeontology. Here we find the gist of his earlier researches upon the mosasaurs, plesiosaurs, and pterosaurs of the marine Cretaceous of Kansas, the substance of his later and fundamental discoveries among the primi- tive reptiles of the Permian of Texas, and the epitome of his last, comprehensive survey of the evolution of the Reptilia as a whole. The writing of this book was thus the culminating effort and achieve- ment of his inspiring career.^ Death overtook him before the final revision and completion of this work, but happily not before he had finished the greater part of the text and had made for it with his own pen a large series of new and excellent line-drawings. In accordance with WilHston's wishes the writer undertook to put his last work in shape for the publisher and to see it through the press. For the long delay since 191 8 there have been too many causes to be profitably set forth in detail. The University of Chicago Press, which had published Williston's earlier books, repeatedly found itself unable to accept this one notwithstanding its good will, and private publishers proposed conditions that were not accept- able, either to the Williston Memorial Committee, or to Professor Williston's family. After much unsuccessful correspondence in vari- ous directions, the sad plight of Williston's still unpublished work came to the notice of Professor Thomas Barbour of Harvard Uni- versity, and through his good offices the Harvard University Press now has the honor of publishing the ''Osteology of the Reptiles." The new drawings that Williston made for this book have been supplemented by many other illustrations, mostly from Williston's earlier works, which were needed to illustrate the present text. The University of Chicago Press has courteously loaned many of these cuts, while others have been copied from the original publications of the authors to whom they are credited. The American Museum of ^ For an excellent account of Williston's life and work see Henry Fairfield Osborn's article, "Samuel Wendell Williston, 1852-1918," Journal of Geology, Vol. xxvi, 1918, pp. 673-689. vi FOREWORD Natural History, with the cordial approval of President Osborn, has at all times given indispensable support in the work of making ready this book for the press. Special acknowledgment is due to Mrs. E. H. Fink and Mrs. C. P. Meadowcroft of the Museum. Dr. G. K. NoblCj Curator of Herpetology, has supplied critical notes on the sections dealing with recent reptiles. Every effort has been made to keep intact the spirit and letter of the original text, and in the few places where corrections or emenda- tions seemed necessary they have been placed in square brackets, as have also the footnotes that record some of the more conspicuous discoveries and advances since 19 18. W. K. G. CONTENTS PART I THE SKELETON OF REPTILES INTRODUCTION PAGE The Primitive Skeleton of Reptiles o. . 3 The Primitive Skull of the Reptilia 6 The Primitive Postcranial Skeleton 7 CHAPTER I The Skull of Reptiles 9 External Appearance, Excrescences, Chief Openings 9 The Skull Elements . 13 The Mandible 27 The Skull of the Cotylosauria ^:i Chelonia 44 Theromorpha 46 Therapsida 52 Nothosauria 56 Plesiosauria 56 Placodontia 59 Ichthyosauria 60 Protorosauria 62 Squamata 65 Lacertilia or Sauria 66 Ophidia or Serpentes 72 Rhynchocephalia 74 Pseudosuchia 77 Pelycosimia 77 Phytosauria 79 Crocodiha 83 Dinosaurs (Saurischia, Ornithischia) 87 Pterosauria 88 CHAPTER II The Vertebrae 90 CHAPTER III The Ribs and Sternum 112 viii CONTENTS CHAPTER IV The Pectoral and Pelvic Girdles 124 The Pectoral or Shoulder Girdle 1 24 The Pelvic or Hip Girdle 142 CHAPTER V The Limbs 155 The Propodials 158 The Epipodials 165 The Mesopodials 169 The Metapodials and Phalanges 195 PART II THE CLASSIFICATION AND RANGE OF REPTILES CHAPTER VI The Problem of Classification 205 CHAPTER VII A Synoptic Classification of the Reptilia 210 CHAPTER VIII Subclass Anapsida 215 Order Cotylosauria 215 [Suborder Seymouriamorpha] Family Seymouriidae 217 [Suborder uncertain] Family Sauravidae 217 [Suborder uncertain] Family Gymnarthridae 217 Suborder Diadectosauria 218 Family Diadectidae , 218 Bolosauridae 218 Suborder Labidosauria 218 Family Captorhinidae 218 Pariotichidae 218 Stephanospondylidae 218 Genera incertae sedis 218 [Suborder uncertain] Family Limnoscelidae 218 Suborder Pantylosauria 220 Family Pantylidae 220 Suborder Pariasauria 220 Family Pariasauridae 220 CONTENTS IX Suborder Procolophonia 220 Family Procolophonidae 220 [Suborder uncertain] Family Elginiidae 221 Order Eunotosauria 221 Order Testudinata or Chelonia 222 Suborder Amphichelydia 223 Family Proganochelydidae 223 Pleurosternidae . 223 Baenidae • 224 Suborder Pleurodira 224 Family Pelomedusidae 224 Chelyidae 224 Miolanidae • • 224 Suborder Cryptodira 224 Family Thalassemyidae . . . '. 225 Toxochelyidae 225 Desmatochelyidae 225 I Protostegidae 225 Cheloniidae 225 [Dermochelyidae] 226 Chelydridae 226 Dermatemyidae 226 Emydidae 226 Testudinidae 227 Suborder Trionychoidea 227 Family Plastomenidae 227 Trionychidae 227 CHAPTER IX Subclass Synapsida 228 Order Theromorpha 228 Suborder Pelycosauria 233 Family Sphenacodontidae 233 Suborder Edaphosauria 233 FamUy Edaphosauridae 233 Suborder Poliosauria 233 Family Poliosauridae • • • 233 Ophiacodontidae 233 Suborder Caseasauria 233 Family Caseidae 233 Suborder uncertain • 236 Family Paleohatteriidae • 236 Genera incertae sedis 236 Order Therapsida 236 Suborder Dinocephalia 237 Family Tapinocephalidae 238 Deuterosauridae 239 X CONTENTS Rhopalodontidae 239 Titanosuchidae 239 Suborder Dromasauria 239 Family Galechiridae 239 Galeopidae 239 Macroscelesauridae 239 Suborder Anomodontia 239 Family Dicynodontidae 240 Suborder Theriodontia . 240 Tribe Gorgonopsia 242 Family Gorgonopsidae 242 Ictidorhinidae 242 Burnetidae 242 Tribe Bauriasauria 242 Therocephalia 243 Family Scylacosauridae 243 Ictidosuchidae 243 Lycosuchidae 243 Scaloposauridae 243 Alopecopsidae 243 Whaitsidae 243 Genera incertae sedis 243 Tribe Cynodontia 244 Family Nythosauridae 244 Cynosuchidae 245 Cynognathidae 245 Diademodontidae 245 Theriodontia (?) incertae sedis 245 CHAPTER X Subclass Synaptosauria 246 Order Sauropterygia 246 Suborder Nothosauria . 247 Family Nothosauridae 247 Suborder Plesiosauria 248 Family Plesiosauridae 248 Pliosauridae 248 Cryptocleididae 250 Elasmosauridae 250 Polycotylidae 250 Brachaucheniidae 251 Genera incertae sedis 251 Order Placodontia 251 Family Placodontidae 252 CHAPTER XI Subclass Parapsida ...................... 253 Order Proganosauria 253 CONTENTS XI Family Mesosauridae « 255 Order Ichthyosauria • • • 255 Family Mixosauridae 256 Shastosauridae 256 Ichthyosauridae 256 Ophthalmosauridae 258 ? Order Omphalosauria 258 FamUy Omphalosauridae 258 Order Protorosauria 259 Family Araeoscelidae 259 Protorosauridae 261 Saphaeosauridae 262 Pleurosauridae • 262 Order Squamata 264 Suborder Lacertilia (Sauria) 265 Tribe Kionocrania 266 Family Geckonidae 266 Euposauridae 266 Agamidae 266 Iguanidae 267 Anguinidae • 267 Helodermatidae 267 Lacertidae 268 Tejidae • 268 Scincidae 268 Tribe Platynota 269 Family Varanidae 269 Dolichosauridae 269 Aigialosauridae 270 Tribe Pythonomorpha (Mosasauria) 272 Family Mosasauridae 273 Globidentidae 273 Tribe Amphisbaenia 273 FamUy Amphisbaenidae 274 Tribe Rhiptoglossa 274 Family Chameleontidae 274 Genera incertae sedis 274 Suborder Ophidia (Serpentes) 275 Family Typhlopidae 276 Boidae (Pythonidae) 276 Paleophidae 276 Viperidae • 276 Elapidae . 277 • Colubridae 277 CHAPTER XII Subclass Diapsida 278 ? Order Proterosuchia 278 xii CONTENTS Order "Eosuchia" 278 Family Younginidae 278 Superorder Diaptosauria . , 279 Order Rhynchocephalia . 279 Suborder Rhynchosauria . 279 Sphenodontia (Rhynchocephalia vera) 281 Choristodera 283 ? Suborder Thalattosauria 283 Superorder Archosauria 284 Order Parasuchia 284 Suborder Pseudosuchia 284 Family Aetosauridae 285 Ornithosuchidae 285 Scleromochlidae 285 Suborder Pelycosimia 285 Suborder Phytosauria 286 Family Phytosauridae 286 Stagonolepidae 286 [Suborder Desmatosuchia] 286 Order Crocodilia [Loricata] 287 Suborder Eusuchia 288 Family Teleosauridae 288 Pholidosauridae 288 Atoposauridae 288 Goniopholididae 289 Dyrosauridae 289 Hylaeochampsidae 289 Gavialidae 289 Tomistomidae 289 Crocodilidae 290 Genus incertae sedis 290 Suborder Thalattosuchia 290 Family Metriorhynchidae 291 [Dinosauria] : • • 291 Order Saurischia 291 Suborder Theropoda 291 Family Plateosauridae 291 Anchisauridae • • • 292 Suborder Sauropoda (Opisthocoelia, Cetiosauria) 292 Family Cetiosauridae 293 Camarasauridae 293 Atlantosauridae 293 Diplodocidae 293 Genera incertae sedis 293, Order Ornithischia [Orthopoda, Predentata] 294 Suborder Ornithopoda (Predentata) 294 Family Nanosauridae . 294 Hypsilophodontidae 294. Iguanodontidae 295, CONTENTS xiii Trachodontidae (Hadrosauridae) ........ 295 Suborder Stegosauria 295 Ceratopsia 295 Order Pterosauria 296 Suborder Pterodermata (Rhamphorhynchoidea) . 296 Family Rhamphorhynchidae 298 Suborder Pterodactyloidea 298 Family Pterodactylidae 298 Ornithocheiridae 298 Pteranodontidae 298 Nyctosauridae . 298 Genera incertae sedis . 298 PART I THE SKELETON OF REPTILES INTRODUCTION THE PRIMITIVE SKELETON OF REPTILES That the reptiles were evolved from the Amphibia, and more spe- cifically from that order known as the Temnospondyli, seems now assured. The earliest as also the most primitive reptiles that we know belong to the order called the Cotylosauria. With the excep- tion of Eosauravus from the middle Pennsylvanian of Ohio, of which, unfortunately, the skull is unknown, our knowledge of them goes no further back than the late Carboniferous and early Permian. At that time there was a considerable diversity of known forms, belong- ing to at least four well-differentiated groups and twenty or more families; from which we may very properly conclude that their earli- est ancestors, the beginning of their stock, lived much earlier, cer- tainly at the beginning of the Upper Carboniferous, and very prob- ably in Lower Carboniferous times. We therefore never can expect to find in the rocks of the Permian any real connecting link between the two classes. Both the reptiles and the amphibians had changed in this interval, an interval perhaps of millions of years, retaining in varying degrees their ancestral characters, while losing or adding others in various ways. The reptiles, by the acquirement of a new mode of life, the loss of gills in their youth and entire emancipation from the water, became more progressive than the amphibians, and their evolution was more rapid. Characters that are common to many amphibians became more and more rare among the reptiles, and the amphibians, handicapped by inherited habits, were restricted more and more to subordinate roles, and only a few of the more progressive continued to develop. They, for the most part, lost those characters and adap- tations that brought them into immediate competition with the rep- tiles, and by the close of Triassic times had become restricted to habits and habitats no longer invaded by them. The modern toads, frogs, salamanders, and blindworms differ far more from the higher amphibians of Paleozoic times than did the latter from their con- temporary reptiles. Fig. I, Primitive Cotylosaur Seymouria, from nearly complete specimen, from above. A little less than one third natural size. INTRODUCTION Nevertheless, there were still so many inherited characters among both the amphibians and reptiles of early Permian times that nothing distinctive of either class can be found in the skeleton, except in the atlas and feet, with a considerable gap in the structure of their ver- tebrae. In the vertebral column there was a general change among the Temnospondyli from the embolomerous to the rhachitomous type, that is, from the more simply divided centrum of two disks to the tripartite centrum composed of wedges; while all reptiles had ac- quired a reduced embolomerous form with one disk, the centrum, and one wedge, the intercentrum. Doubtless all amphibians of Lower Carbonif- erous times had embolomerous verte- brae, but only a very few of their stock persisted as late as the Per- mian. In general literature the Am- phibia are distinguished from the Reptilia by the possession of two occipital condyles. The earliest am- phibians doubtless all had a single occipital condyle, an inheritance from their ancestral fishes — all that we know from the Lower Carboniferous had — of which only one known de- scendant with that character survived to the Permian. The reptiles, how- ever, retained the single condyle until the beginning of their evolution into mammals, when they too de- veloped a double condyle. We relied, until recently, upon the widely open palate of the Amphibia as a final distinguishing char- acter of their class, but we now know that some, if not all, of the earliest amphibians had a [closed] palate like that of the [earliest] rep- tiles, but of these none is known at the beginning of Permian times. In other words, a single condyle and a closed palate are more prim- itive characters of the tetrapods than those we had assumed as characteristic of the Amphibia. We know no amphibians with as many bones in the digits as the early reptiles possessed, and no rep- tiles with as many bones in the tarsus as the early amphibians had, Fig. 2. Seymouria (Cotylosauria). A, from above; B, from side. One third natural size. 6 THE OSTEOLOGY OF THE REPTILES but doubtless when we discover the feet of the earliest reptiles we shall find them not different from the feet of the contemporary am- phibians. Every known bone in the skull of the Temnospondyli, except the interfrontal of a very few, has been found in the skull of early rep- tiles, and all, indeed, in a single genus Seymouria (Figs. 1,2) from the Lower Permian of Texas. And there is no bone in the skeleton of reptiles that is not known in these same amphibians, except the preparietal of the Anomodontia, the supraorbitals of various Squa- mata and the predentary and rostral bones of certain dinosaurs, and doubtless the last two, if not all, are simply dermal bones which be- came temporarily attached to the skull. The girdles and limbs of the two classes are distinguishable only by minor characters. And thus, while we do not know from these later rocks, and probably never shall from rocks later than the Lower Carboniferous, all of the characters common to the two classes in any one animal, from the comparison of all it is not difficult to decide what were the primitive characters of the reptilian skeleton in almost every detail. They may be summarized as follows: The Primitive Skull of the Reptilia Rugose, with five openings in roof : A. Paired, divided, terminal nares. B . Paired orbits beyond middle [i.e.,m front of the middle of the skull] . C. Median parietal (pineal) foramen. An emargination of the occipital border, between tabular and squamosal, for the ear [the "otic notch"]. Seventeen pairs of roof bones; four pairs of palatal bones; eight pairs of cranial bones; eight pairs of mandibular bones; three unpaired cranial bones; one unpaired palatal bone — seventy-eight in all. A. Paired Bones I . PremaxiUae {px) 2. Maxillae {mx) / 3. SeptomaxiUae {sx) Nasal bones 4. Nasals {no) ^' T> ^. , , V^ N ' \ Median roof bones 0. Parietals [pa) 7. Interparietals {ip) INTRODUCTION Mandible 8. Lacrimals {la) 9. Prefrontals ipr) 10. Postfrontals (^/) j" Surrounding orbits 1 1 . Postorbitals {po) 12. Jugals 0') 13. Intertemporals {it) 14. Supratemporals {st) 15. Tabulars {t) j, Temporal bones 16. Squamosals {sq) 17. Quadrato jugals {qj) 18. Dentaries {d) , 19. Coronoids {cor) , 20. Splenials {sp) 21. Postsplenials {psp) 22. Angulars {an) 23. Prearticulars {pa) 24. Surangulars {sa) 25. Articulars {art) 26. Prevomers {pv) 27. Palatines {pi) 28. Pterygoids {pt) 29. Ectoptery golds {ec) 30. Quadrates {qu) Articulation of mandible 31. Exoccipitals {eo) 32. Paroccipitals {poc) 2,2)- Prootics {pc) 34. Postoptics (a/) \ Cranial bones 35. Stapes {stp) 36. Epipterygoids {ep) 37. Ethmoids {se) Palatal bones, dentigerous A A. Unpaired Bones 38. Parasphenoid {ps) Palate 39. Supraoccipital {so) 40. Basioccipital {ho) j. Cranial bones 41. Basisphenoid {hs) The Primitive Postcranial Skeleton A. Membrane Bones, Exoskeletal 1. Sclerotic plates in orbits. 2. Paired clavicles, cleithra and elongate interclavicle 3. Dermal plates or scutes. THE OSTEOLOGY OF THE REPTILES AA. Cartilage Bones, Endoskeletal 1. Notochordal vertebrae; two or three cervicals, about twenty- three pre- sacral; one sacral; moderately long tail; proatlas; atlas embolomer- ous; all vertebrae to tenth or twelfth caudal with free, holocephalous ribs, articulating continuously with intercentrum and diapophysis. 2. Intercentra between all vertebrae. 3. Slender and numerous parasternal ribs. 4. Scapular girdle composed of paired scapulae, procoracoids and meta- coracoids, fused in adult life, the three forming the glenoid socket; a supracoracoid and a supraglenoid foramen. 5. No sternum. 1 6. Pelvis plate-like with small obturator foramen only; acetabulum formed by the three bones, closed. 7. Legs short and stout. 8. Humerus dilated at extremities, with entepicondylar foramen. 9. Carpus with four bones in proximal row; two (three?) in middle row; five in distal row; all well ossified. 10. Hand pentadactylate, the fourth finger strongest and longest; phalan- geal formula 2, 3, 4, 5, 3. 1 1 . Tarsus composed of nine bones : two in first row ^ ; two in second ; five in distal row; all well ossified. 12. Feet pentadactylate, the fourth toe strongest and longest; phalangeal formula 2, 3, 4, 5, 4. 1 [But see footnote i, on page 122 below. — Ed.] ^ [But see footnote on page 187 below. — Ed.] CHAPTER I THE SKULL OF REPTILES External Appearance, Excrescences, and Chief Openings The skull of reptiles, as of other vertebrates, has undergone many changes in adaptation to food, offensive and defensive habits. It has lost not a few bones in various forms, and others have united or formed new associations; to such an extent, indeed, that there are several in later reptiles about whose homologies there has been and yet is dispute. It has developed excrescences or horns for defense or offense, or has been covered at times with a solid armor of skin bones; but it has gained permanently no new bones, though a few have been added temporarily from the exoskeleton. The skull of carnivorous reptiles (Figs. 7,7,, 45) is more or less elongate, like that of a wolf; in- sectivorous reptiles may have a more slender skull (Fig. 52 b); while those reptiles using the jaws to crush invertebrates always have a short and powerful skull (Fig. 49). The face of aquatic, lish-eating reptiles (Fig. 58) is always long, sometimes very long (Fig. 67), as in the modern gavials. Excrescences or horns on the skull have been developed in not a few. The earliest known is that of the cotylosaurian Chilonyx, with excrescences, and the theromorph Tetraceratops, with large protu- berances. Some of the later Cotylosauria, like Elginia, had horny protuberances at the back part. A few carnivorous dinosaurs have a median facial and supraorbital rugosities, as though for the support of horns or spines. In the Ceratopsia (Fig. 70 a) the development of horns and spines was carried to a remarkable degree, not only on the face but also along the posterior margin of the greatly extended skull. Perhaps of all reptiles none has surpassed some of the modern cha- meleons in the development of facial horns (Fig. 55 d), though not a few other lizards, like the horned lizards and moloch lizards, have many sharp protuberances and horny excrescences, which, were they magnified to the size of dinosaurs would be equally imposing. Even some turtles, like the southern Miolania, have horns upon the skull. Usually the median unpaired facial horn is borne by the lO THE OSTEOLOGY OF THE REPTILES nasals, as in the mammals, but in the chameleons it is formed by the maxillae. The paired facial horns are borne by the prefrontals or postorbitals. The frontals and parietals are sometimes developed into enormous crests in the dinosaurs, the supraoccipital in ptero- saurs. Doubtless all such horns or protuberances were covered in life with a horny sheath. The external nostrils {external nares) vary greatly in position. Primitively located near the extremity of the face (Figs. 2,3, etc.), each was surrounded by the premaxilla, maxilla, nasal and lacrimal, and they almost always have the same relations with the first three of these bones, wherever located. Well separated by the premaxillae and nasals in the older reptiles, they are often confluent in later ones (Figs. 31, 32, 59, 68). They are surrounded by the maxillae in the chameleons (Fig. 55), by the nasals in the phytosaurs (Fig. 66); the nasals are often excluded from them, and the lacrimals have lost all relations with them since Permian times. In most aquatic reptiles they have receded toward the orbits, or rather the face has grown away from them, often for a long distance, as in the ichthyosaurs (Fig. 50), plesiosaurs (Fig. 46 a), proganosaurs, thalattosaurs (Fig. 61), and phytosaurs (Fig. 67). In the very slender-faced amphibious CrocodiHa (Fig. 68) and Choristodera (Fig. 63), however, the nostrils retain their primitive position at the extremity of the face. They are located far back from the extremity in the volant pterodactyls (Figs. 71, 72) as in most birds. The internal nares, or choanae, normally situated almost immedi- ately below the external (Fig. 55), are carried back by a respiratory canal, formed by the undergrowth of the maxillae and palatines as a secondary palate, to a greater or less extent in the Cynodontia and Crocodilia (Fig. 69) ; in the former and in the early kinds of the latter, to the posterior border of the palatines; in the later crocodiles even into the pterygoids. A similar respiratory canal, probably separated from the cavity of the mouth by a membrane only, is character- istic of the Phytosauria (Figs. 66, 67). A partial secondary palate, formed by the union of the palatines or maxillae, with the opening only a little way back, occurs in some Chelonia and Anomodontia. In those reptiles in which the external nares are situated posteriorly, the internal nares are also (e.g., Figs. 61,66). In the plesiosaurs only (Fig. 46), there may be a partial reversion of the respiratory THE SKULL OF REPTILES II canal, with the internal opening in front of the external. The in- ternal nares, primitively (Figs. 6, 21, 47) divided by the prevomers and surrounded by the premaxillae, maxillae and palatines, may sometimes (Figs. 49, 71 c) lie between the prevomers and palatines. The parietal or pineal foramen, very large in certain shell-eating cotylosaurs (Fig. 22), had become inconstant even in that order. It is present, so far as known, in all the Theromorpha (Figs. 33-42), and in the Therapsida (Figs. 43-45), with the exception of a few forms; in the Proganosauria, Ichthyosauria (Fig. 50), Sauropterygia (Fig. 48), the Diaptosauria (Figs. 60-62), and most lizards (Figs. 55 A, 56), but is absent in some true lizards, the chameleons, and all snakes (Fig. 59). It has been reported in certain doubtful Pseudo- suchia and more or less doubtfully in a few phytosaurs and dinosaurs, but with these possible exceptions appears to be absent in all the Archosauria (Figs. 65 b, 66 b, 68, etc.) as also the Chelonia (Figs. 30, 31, 32). Usually located between the parietals anteriorly (Figs. 22, 2)2), 43, 44, 45, 46, etc.), it may occur between the frontals pos- teriorly (Fig. 55). In the Anomodontia and Gorgonopsia (Fig. 43) there is a separate bone, the preparietal, a small unpaired element of doubtful homologies, absent in other reptiles, in front of or surround- ing the foramen. The orbits, directed upward sometimes in aquatic animals (Fig. 32), but usually laterally, were primitively (Figs. 2, 3, 22, 23, 33, 43, 44, 65) surrounded by the prefrontal, postfrontal, postorbital, jugal, and lacrimal. The frontal usually forms a part of the upper margin, the maxillae sometimes below (Figs. 30, 48, 49, 55, 56, 59). In snakes (Fig. 59), only the prefrontal and postorbital may be left. Sometimes the postorbital bar is incomplete in lizards (Fig. 56), snakes (Fig. 59), and therapsids (Fig. 45 d). The prefrontal is ex- cluded in some dinosaurs, the postorbital in Araeoscelis (Fig. 52) and Hyperodapedon (Fig. 62 d), leaving not a single element invari- ably associated with the orbit. Antorhital or preorhital vacuities are very characteristic of the Archosauria, occurring in all phytosaurs (Figs. 66 b, 67 a) and true pseudosuchians (Fig. 65 b, d), most Saurischia (Fig. 70 a, b) and Pterosauria (Fig. 71) and some Croco- diha. Usually there is but one, but there may be two or even three on each side in certain Theropoda (Fig. 70 a). 12 THE OSTEOLOGY OF THE REPTn.ES Openings through the skull rooj} back of the orbits, are character- istic of all reptiles save the Cotylosauria (Figs. 2, 4, 19, 22) and Chelonia. The upper opening, the supratemporal, arose primitively by the separation of the postorbito-squamosal bar (Fig. t,^ a) from the parietal (Fig. 53 c). The lower or lateral temporal opening ap- peared primitively (Figs. ^^, 53 a) between the squamosal and the jugal. It is bounded above by the postorbito-squamosal arch, below by the jugal, to which was added, in some of the double-arched forms, the quadrato jugal (Figs. 62, 64, 65, 70 a, b). Either the upper or the lower opening may occur independently, or both to- gether. In the Cynodontia (Fig. 45) and some other Theriodontia, with a lower temporal opening (Figs. 44 f, 45 d), the squamosal may fail to meet the postorbital above the opening, permitting the parietal to form the upper boundary in part; and this is the condition in mammals. In not a few of the Therapsida, the Dinocephalia especially (Fig. 44 b), the jugal is excluded from the lower margin by the union of the squamosal and postorbital. All known forms of the Sauropterygia (Figs. 46, 47, 48) and Placo- dontia (Fig. 49) have the single opening bounded below by the squamosal and postorbital, above by the sides of the parietal, that is, it is like the upper one of those reptiles with two temporal openings. It is usually considered to be what it really appears to be, the upper temporal opening only; and its certain nature will not be determined until more is known of their terrestrial antecedents. The intertemporal vacuity. The single temporal opening of the Squamata (Figs. 55, 54), when complete, the Ichthyosauria (Fig. 50), and certain other forms here grouped under the Parapsida, Hes between the postorbito-squamosal arch and the parietal, but has, in most if not all, an additional bone helping to form its posterior or outer border, the supratemporal or tabular, for there is doubt as to its real homology. (See pages 61-69 below.) The post-temporal opening is situated on the occipital aspect of the skull, a vacuity between the parietal, or parietal and squamosal, and the paroccipital on each side. It is present in some Cotylosauria 1 [In addition to the openings noted by the author, paired subtemporal openings occur in all reptiles in the palatal aspect of the skull; they are bounded medially by the pterygoids and the basis cranii, laterally by the lower temporal bar, if present, or by the dermal covering of the temporal region, as in Squamata. — Ed.] THE SKULL OF REPTILES 1 3 (Fig. 21 b), and Theromorpha (Fig. 45 g), and is generally present in later reptiles though absent or vestigial in the CrocodiHa. The cranial region thus exposed by these various openings has been exposed to a greater or less degree in most Chelonia (Figs. 30- 32) in a different way: by the emargination of the roof bones from behind or from behind and below, until, in some forms like the terepenes, the whole temporal roof is lost. Posterior palatine or suborbital openings occur in most reptiles (Figs. 55, 63, 66, 69, 72) since the Theromorpha, but are absent in some turtles. They are situated between the palatines and maxillae posteriorly, and are usually also bounded in part by the ectoptery- goids. They do not occur in the Cotylosauria (Figs. 6, 21 a, 24, 29) or Theromorpha (Figs. 40 c, 42 c), though present in many Therapsida. The Skull Elements The primitive relations of the skull elements may be discussed seri- atim, with their chief modifications in later reptiles. Premaxillae (px). Primitively short (Figs. 2,3,4, 19, 22, 33, 43), articulating with maxillae, nasals and pre vomers, the posterior process forming a partial division between the nasal chambers. They form the anterior boundary of the external and internal nares. Four or five teeth in each. Elongate in the strictly aquatic reptiles (Figs. 46, 47) and in the Pterosauria. In the plesiosaurs (Figs. 46, 47), pterosaurs (Fig. 72 a), some lizards (Fig. 56), and thalattosaurs (Fig. 61), a median pro- longation separates the nasals, articulating directly with the frontals, in the first group (Fig. 46) sometimes directly with the parietals, separating the frontals. Edentulous in the chameleon lizards (Fig. 55), they take no part in the boundary of the nares. They are also edentulous in the turtles (Figs. 30-32), anomodonts (Fig. 44 c), some dromasaurians, the later pterodactyls (Fig. 72), most orni- thischians (Fig. 700,0), the chameleon lizards, and many snakes. Teeth, when present, are in a single row and rarely exceed five or six in number in each, though there are as many as twenty-three in some phytosaurs (Fig. 66) and even more in ichthyosaurs, where the dentigerous border is greatly elongated. The dentigerous part is short in the long-faced plesiosaurs (Fig. 48 c) . They are often fused (Fig. 72), and sometimes united with the nasals (Fig. 54 c). 14 THE OSTEOLOGY OF THE REPTn.ES Maxillae (mx). Primitively (Figs. 2 b, 3, 4, 6, 19, 21, 22, 33, 43), articulating anteriorly with premaxillae, above with septomaxillae and lacrimals, posteriorly with the jugals, ectopterygoids, and post- orbitals internally, forming the outer boundary of both external and internal nares in part. In most reptiles since Permian times they also articulate with the nasals above {e. g., Figs. 2,3, 43, 44); in the crocodiles (Fig. 69 b) with each other on the palate, as also in many Anomodontia and Theri- odontia. They are edentulous in the Chelonia (Figs. 30-32), later Pterosauria (Fig. 72), some Anomodontia (Fig. 44 c), Dromosauria, Ophidia, Saphaeosaurus, Ornithomimus, etc. The teeth may be in single or numerous rows. Fig. 3. Pantylus (Cotylosauria), from side. Three fourths natural size. Septomaxillae {sx). Small bones, the so-called turbinals of reptiles, located partly within the nasal chamber, but appearing more or less on the outer side at the back part of the external nares. (Figs. 32), 44 A, B, F, 45.) Present probably in all the earliest and most early reptiles, and in most Squamata (Fig. 59); they are absent in the Chelonia (Figs. 28-32) and Crocodilia (Figs. 68, 69). In some Dro- masauria they extend back on the face to meet the lacrimals. Little can be said about them in other extinct reptiles. Nasals (na) . Articulating with premaxillae, f rontals, prefrontals, and lacrimals, forming more or less of the partition between the ex- ternal nares. Except in most Cotylosauria (Figs. 2, 3, 22, 23, etc.), some Thero- morpha and Therapsida, they also articulate with the maxillae on the sides. They are absent in many Chelonia (Figs. 28-32) ; either absent THE SKULL OF REPTILES 15 or fused with the premaxillae in the Mosasauria (Fig. 54 c) ; sepa- rated by the premaxillae in the plesiosaurs, pterosaurs (Fig. 72), and some lizards (Fig. 56), and probably absent in some of the former (Fig. 46). They do not enter into the formation of the nares in the Rhiptoglossa (Fig. 55 d), but surround them in the Phytosauria (Figs. 66, 67). Very large in the Ichthyosauria (Fig. 50), they also articulate with the large postfrontals. They are often fused in the midline. Frontals (fr). Primitively (Figs. 2, 4, 22, 23, etc.) articulating with nasals, prefrontals, postfrontals, parietals, and ethmoids, often form- ing the middle of the upper margin of the orbits. Always present and not varying much in their relations. In the plesiosaurs (Fig. 46), pterodactyls (Fig. 72), and some lizards, they articulate directly with the premaxillae (Fig. 56), and in some of the former are separated externally in the middle. Often fused in mid- line (Figs. 68, 69). Parietals (pa). Primitively (Figs. 2, 4) articulating with frontals, postfrontals, inter temporals, supratemporals, tabulars, and inter- parietals; below with the supraoccipital, epiptery golds, postoptics, and prootics. In the absence (e. g., Figs. 31 b, 33, 44, 45, etc.) of the intertem- poral and supratemporals, the parietals articulate directly with the squamosals and postorbitals; in the Chelonia (Fig. 30) and Croco- dilia, also directly with the pterygoids. Fused in most late reptiles {e.g., Figs. 69, 72). Interparietals (ip). Primitively (Figs. 2 a, 4, 22) back of the parietals on the superior surface of the skull, articulating with pari- etals, tabulars, and supraoccipital. In the later Cotylosauria (Fig. 9), most if not all Theromorpha (Figs. ;^Sj 42 d), some Therapsida (Figs. 44 A, d, g), they are situated on the occipital surface and are usually unpaired. A vestige, sup- posed to be these bones, occurs in some Crocodilia, originally named dermosupraoccipitals. They do not help form any part of the cere- bral wall. Unknown or doubtful in other reptiles. Lacrimals (la). Primitively (Figs. 2 b, 3, 22, 23, etc.) large, ex- tending from orbit to nares, articulating with prefrontals, nasals, septomaxillae, maxillae, and jugals. In the latest Cotylosauria (Procolophon) , most Theromorpha 1 6 THE OSTEOLOGY OF THE REPTILES (Fig. ss) and Therapsida (Figs. 43, 44, 45), and all other reptiles, they are excluded from the narial margin. They are small or vestigial in the Squamata, and absent in most Chelonia and in Sphenodon (Fig. 60 a) . They are of extraordinary size in some Theropoda (Fig. 70 a) , articulating posteriorly with the postorbitals. It has been urged by Jaekel and Gaupp that these bones are not the homologues of the mammalian lacrimal, and should be called by another name, for which postnasal and adlacrimal have been proposed.^ Fig. 4. Pantylus, from above. Three fourths natural size. Prefrontals (pr). Primitively (Figs. 2, 4, 22) at the upper anterior border of the orbits, articulating with lacrimals, nasals, frontals, and postfrontals, and by a descending process with the palatines. Never absent, though much reduced and excluded from the orbital margin in the Theropoda (Fig. 70 a). Sometimes (Fig. 70 c) they articulate with the postorbitals or postf ronto-orbitals when the post- frontals are absent as discrete bones. Below, they articulate with the prevomers in the Chelonia (Fig. 30 b), with the palatines and ptery- goids in the Crocodiha (Fig. 69 d). Excluded from the frontals in the 1 [The cumulative evidence against the views of Gaupp and Jaekel, with regard to the reptilian homologue of the mammalian lacrimal, has been set forth in the Bulletin of the American Museum of Natural History, vol. xlii, pp. 99, 131-135. — Ed.] THE SKULL OF REPTILES 17 Ichthyosauria (Fig. 50). Thought by some to be the homologues of the mammaHan lacrimals, and so called. Postfrontals (pf). Primitively (Figs. 2,4, 22) at the upper posterior border of the orbits, articulating with prefrontals, frontals, parietals^ the intertemporal or supratemporals when present, and with the postorbitals. In the Chelonia (Figs. 30 a, 31 b, c, 32 a), Crocodilia (Figs. 68^ 69), many mosasaurs (Fig. 54), lizards (Fig. 56) and the snakes (Fig. 59), the Pterosauria (Figs. 71, 72), Dinosauria (Fig. 70), and many Therapsida (Figs. 44 d, 45), they are absent or fused with the postorbitals which take their place. Sometimes they (Fig. 46 c, 49 a) help form the anterior boundary of the upper temporal opening. They extend forward to the nasals in the Ichthyosauria (Fig. 50). Postorbitals (po). Primitively (Figs. 2, 3,4, 5, 22) at the upper back part of the orbits, articulating with post- frontals, jugals, and squamosals. A descending process also articulates with the maxillae or ectopterygoids. In the absence of the intertemporal and supratemporal, the postorbital Fig. 5. p««/y/«.f. Cotylosaur skull: , ,. T , •,1,1 • , 1 /T^' left temporal region, from without. also articulates with the parietal [r IgS. Three fourths natural size. 28, 30, 33, 43). In the absence of the postfrontal it takes its place, often extending forward to meet the prefrontal (Figs. 30, 45 b), or even the lacrimal (Fig. 70 a) in the Theropoda. It still retains its connection with the maxillae [sic] ^ in certain Chelonia (Fig. 31 b) and most snakes (Fig. 59), but not in most other reptiles. Rarely in the lizards (Fig. 56) it does not meet the squamosal. In the Crocodilia (Fig. 69) it is large, and may ar- ticulate with frontal, parietal, jugal, quadratojugal, and squamosal. It extends far back in the Chelonia (Figs. 30, 31 a), forming a large part of the temporal roof, articulating with the quadratojugal, the latter also in the Ichthyosauria (Fig. 50). It is extensive also in some of the Dinosauria (Fig. 70), supporting the paired horns of the Ceratopsia (Fig. 70 d) . Jugals iju). Primitively (Figs. 2 b, 3, 5, 22, 33) large, forming the under boundary of the orbits, articulating in front with lacrimals 1 ["Maxillae" — a lapsus calami for "parietal"? — Ed.] 1 8 THE OSTEOLOGY OF THE REPTILES and maxillae, above with postorbitals, and, by an extensive over- lapping suture, with the squamosals and quadra tojugals ; on the inner side perhaps with the ectopterygoids. Absent in some Ophidia (Fig. 59 b) and some lizards (Fig. 56). In the lizards (Fig. 55) they may not articulate with the squamosals. Intertemporals {it) . An amphibian bone known only in Seymouria (Figs. 2, 19) of the Cotylosauria, intercalated between the post- frontal, parietal, supratemporal, and postorbital. Supratemporals {si). Primitively (Figs. 2, 4, 19) articulating at the sides of the parietals with the postfrontal and postorbital an- teriorly, the tabulars behind, and the squamosals on the outer side; interrupted by the otic notch in Seymouria (Figs. 2, 19). Absent in the more specialized Cotylosauria, probably all Thero- morpha, and all other reptiles save possibly the Ichthyosauria (p. 62) and Squamata (p. 65). Generally known as the posterior bone of the arch in the Squamata (Fig. 55 a, to). [But see tabular below.] Tabulars (/). Primitively (Figs. 2, 4, 22) on the dorsal surface of the skull in the Cotylosauria, as in the Amphibia, at the outer side of the interparietals, articulating with the squamosals and supra- temporals, with the upper end of the quadrates and the outer end of the paroccipitals, whence the name " paroccipital plates" given to them by Baur. They are known to be absent in but a single genus of Cotylosauria; are probably present in most Theromorpha (Figs. 33 B, 42 d) and Therapsida (Fig. 44 g), and some " Pseudosuchia " (Fig. 65 c). The tabular has been identified by the author as the posterior bone of the arch in the Squamata (p. 62), and Ichthy- osauria (p. 62), usually and perhaps correctly called the supra- temporal. It is unknown in other reptiles. Squamosals {sq). Primitively (Figs. 2, 4) articulating with tabu- lars and supratemporals above, in the absence of the latter directly with the parietals (Figs. 33 a, 53 a). Below, they cover the posterior part of the temporal region, extending back of the quadrate to articu- late with the pterygoids (Fig. 7), overlapping extensively the quadra- tojugals on the sides (Fig. 33 a), and articulating in front with jugals and postorbitals. In later reptiles the squamosal has undergone many changes, but is always present, though sometimes vestigial in the Chelonia, THE SKULL OF REPTILES 1 9 Squamata, and Ichthyosauria. Only in the Cotylosauria and some Theromorpha does it articulate with the pterygoids. In later forms it articulates with the paroccipital to a limited extent, supporting the head of the quadrate. In many Therapsida (Figs. 43, 44 b), but not in the more primitive Theromorpha (Fig. 33 a), it may articulate with the postorbital below as well as above the temporal opening. Its relations with the quadratojugal are also inconstant, lost in the Crocodilia (Fig. 69 c) and Predentata (Fig. 70 c). On the other hand, it may extend forward to unite with the maxillae in some plesiosaurs (Fig. 46 b). In the Squamata (Fig. 55 a), as most recent authors identify the squamosal, it articulates with the bones usually called the supratemporal and the postorbital (rarely excluded from it) and usually with the jugal. Quadratojugals {qj). At the outer posterior side of the temporal region (Figs. 2 b, 3, 22, 33), overlapped by the squamosals, articu- lating in front narrowly with the jugals, behind with the quadrates. The quadratojugals are relatively large in the primitive skull, sometimes forming a part of the articular surface for the mandible (Fig. 21 b). In the single-arched skull the quadratojugal tends to disappear. It is probably present in all Theromorpha, but is often confined chiefly to the posterior side of the quadrate (Fig. 42 d). It is absent in most Therapsida,^ the Sauropterygia and the Squamata. It enters into the boundary of the lower temporal opening only in the Crocodilia (Fig. 69), Phytosauria (Fig. 66 b), Pseudosuchia (Fig. 65), Pterosauria, Theropoda (Fig. 70 a), and some Predentata (Fig. 70 d), excluded in many Predentata (Fig. 70 c), as in all the other double-arched reptiles. It is very large in some Chelonia (Fig. 30 a), articulating with the postorbitals, as is also the case in the Crocodilia (Fig. 69 c). Prevomers (pv). Paired bones on the palatal surface, articulating with the premaxillae in front, the pterygoids and palatines behind separating the internal nares; dentigerous (Figs. 6, 40 c). Only in the Chelonia (Fig. 32 b) are the prevomers single, though sometimes fused in the Rhiptoglossa, Theropoda, and Theriodontia (Figs. 43 c, 44 e). They are edentulous in all known reptiles except the Cotylosauria (Fig. 6), some Theromorpha, perhaps, certain "Pseudosuchia," Diaptosauria (Fig. 63), and Squamata. Poste- 1 [But see footnote, p. 52. — Ed.] 20 THE OSTEOLOGY OF THE REPTILES riorly in the Squamata (Figs. 55 c, 56 b) they articulate with the palatines only, as also in some Chelonia (Figs. 31 a, 32 b) and Plesiosauria (Fig. 46 b) . Generally believed not to represent the un- paired vomer of the mammals. Palatines {pi). Primitively (Figs. 6, 21) forming the posterior boundary of the internal nares, articulating with the prevomers and pterygoids on their inner sides, the maxillae on their outer, and with the descending process of the prefrontals above. More or less denti- gerous. Fig. 6. Pantylus. Cotylosaur skull: from below. Three fourths natural size. Teeth are still present in the Theromorpha (Figs. 40 c, 42 c) and some Therapsida, but are lost in other reptiles except the Rhyn- chocephalia (Figs. 62 e, 63 b) and most Squamata (Fig. 54 b). They may join in the middle in the Chelonia (Figs. 31 b, 32 b) and in the Crocodilia (Fig. 69 b) below the prevomers. Pterygoids (pt). (Figs. 6, 7, 21, 40 c.) Bones of the posterior part of the palate, articulating with the prevomers in front, the palatines and ectopterygoids laterally, the basisphenoids on the inner sides, the quadrates and squamosals posteriorly. Dentigerous. As stated above they do not articulate with the prevomers an- teriorly in the Squamata and many Chelonia and Plesiosauria, but do articulate with the parietals in many Chelonia. Their connection THE SKXJLL OF REPTILES 21 with the prevomers is lost in some Cynodontia (Fig. 43 c) and Rhiptoglossa. Teeth are generally present in the Theromorpha, Rhjoichocephalia, and Squamata, and in some Therapsida and "Pseudosuchia." In the early reptiles (Figs. 6, 21, 24 c, 40 c) they are more or less loosely articulated with the basipterygoid process of the basisphenoid, as in most modern reptiles, but are fixed in the Therapsida (Fig. 43 c) and not a few others. There is an interptery- goidal space between them partly filled with the parasphenoid ros- trum in the early reptiles (Figs. 6, 21 a), as in the Plesiosauria (Fig. 47 p), Rhynchocephalia, most Squamata (Fig. 55 c), etc. In some Therapsida (Fig. 43 c), Notho- sauria (Fig. 47 e), Placodontia (Fig. 49 b), they unite along the whole middle line. There is a theory that the pterygoids are the real homologues of the mam- malian alisphenoids.^ Ectoptery golds {ec). The ecto- pterygoids (transpalatines) have V not yet been certainly demon- scu--.:* strated in the early Cotylosauria, though perhaps present; they are certainly absent in some of the Temnospondyli. They have been recognized in all other orders ex- cept the Ichthyosauria and Chelonia, connecting the pterygoids with the posterior end of the maxillae, back of the palatines; sometimes also with the jugals in the Squamata (Fig. 55 c). Most remarkable are their relations in Pteranodon (Fig. 72 c) of the Pterosauria, where they pass above the palatines to unite with the pterygoid. The ectopterygoids are believed by some to be the homologues of the pterygoid process of the alisphenoid of the mammals. Epiptery golds (ep). A pair of bones articulating below with the pterygoids, above with the parietals (Fig. 8). They have been ob- served in the Temnospondyli, various genera of the Cotylosauria, Theromorpha, and Therapsida, and are probably generally present in reptiles, though absent in the Crocodilia, many Chelonia, the Fig. 7. Parity lus. Cotyiosaur skull: left quadrate region, with section of mandible through condyle. En- larged one half. ^ [Watson has shown that this view is untenable. — Ed.] 22 THE OSTEOLOGY OF THE REPTn.ES Ophidia, Amphisbaena, Rhiptoglossa of the Squamata. In the Chelonia (Fig. 30 b) they have been identified with a plate of bone intercalated between the descending plate of the parietal and the basisphenoid of many forms. Their real homologues are yet doubt- oc so PR Fig. 8. Latidosaurus hamatus Co'pt. Cotylosaur skull: A, right quadrate from below; B, the same from above; C, posterior basicranial bones from above. Fig. 9. Labidosaurus hamatus Cope. Cotylosaur skull: from behind. ful; by some they have been identified with the alisphenoid of the mammals. Supraoccipital {so). (Figs. 9, 21 b, 42 d.) Unpaired, articulating with the parietals and interparietals above, the exoccipitals, par- occipitals, and prootics, and including a part of the semicircular canals formerly believed to be in a separate bone called the epi- otic, but which has never been demonstrated in any air-breathing THE SKULL OF REPTILES 23 animal. Primitively more or less excluded from the margin of the foramen magnum. Only in certain plesiosaurs is the supraoccipital paired, by the ex- tension of the large foramen magnum to the parietal roof. In most reptiles save the Ophidia and Crocodilia, it enters more or less into the boundary of the foramen magnum. Exoccipitals (eo). Primitively (Figs. 21 b, 42 d) small, forming the larger part of the boundary of the foramen magnum, approximated to each other both above and below, closely articulated with the basioccipital only. Primitively the exoccipitals took but little part in the formation of the occipital condyle, but in many later reptiles they form a large part, as in the Chelonia (Fig. 3 1 b) , or even the whole, as in the Am- phisbaenia (Fig. 56 b) ; or, by the recession of the basioccipital, the double condyles of the Cynodontia and mammals. Paroccipitals (po). (Figs. 9, 21 b.) Only in the Cotylosauria primi- tively do the paroccipitals exist as distinct bones in the adult, articu- lating with the exoccipitals, supraoccipital, prootics, stapes, tabulars, and quadrates. On the inner side they help form, with the supra- occipital and prootics, the otic capsule. In the Theromorpha, so far as known, the paroccipitals are fused with the supraoccipital, sutur- ally or loosely articulated with the exoccipitals. In the Chelonia (Fig. 31 B, op), only of modern reptiles, are they separate bones in the adult, intercalated between the exoccipitals, supraoccipital, prootics, squamosal, and supporting the head of the quadrate. Among other reptiles they are known to be free only in the Ichthy- osauria (Fig. 51), articulating with the basioccipital, exoccipitals, stapes, and so-called supratemporal. In other reptiles they are indis- tinguishably fused with the exoccipitals in the adult. Prootics (pc). The prootics (Figs. 8, 10, 11, 30, 59, 69) are a con- spicuous part of the brain-case, intercalated between the supra- occipital, paroccipitals, basioccipital, basisphenoid, and, when present, the postoptics, and containing a part of the internal organ of hearing. Their relations are yet poorly known in the primitive reptiles. They usually have foramina perforating them for the pas- sage of the third and sixth nerves, and form' the posterior boundary of the foramen for the fifth nerve; posteriorly for the eighth, ninth, and tenth nerves. They form a large part of the brain-case exteriorly in 24 THE OSTEOLOGY OF THE REPTILES the snakes (Fig. 59) and amphisbaenian lizards; in the mosasaurs (Fig. 57) their outer extremity extends to the outer extremity of the Fig. 10. A,^, Edaphosaurus. Theromorph skull: occipital complex, from without and within, natural size; C, genus indet. basisphenoid, from below; D, the same from above; E, the same from side, natural size. V , G,Yi, Eryops. Temnospondyl skull: basicranial bones, longitudinal and transverse sections; so, supraoccipital; po, paroccipital; eo, exoccipital; bo, basioccipital; pc, prootic; bs, basisphenoid; ps, parasphenoid; st, stapes; ep, epipterygoid. paroccipital, articulating with the so-called supratemporals, or, as the author believes, the tabulars. Postoptics (as, at) , (laterosphenoids, otosphenoids, " alisphenoids") . Variable and yet doubtful bones in the reptiles, apparently not THE SKULL OF REPTILES 25 homologous with the mammalian alisphenoid, though usually so called. Imperfectly known in the early reptiles, they have been recog- nized in the Temnospondyli, Cotylosauria, and Theromorpha, ar- ticulating as in the Crocodilia (Fig. 69) below with the basisphenoid, Fig. II. A, B, C, D, Dimetrodon. Pelycosaur skull: occipital complex: A, from below; B, the same from above; C, obliquely from behind; D, the same from in front. Temno- ■ spondyl skulls: E, Eryops, section through parasphenoidal rostrum, near front part of orbit; F, Eryops, section through parasphenoidal rostrum near base; G, Cacops, section through parasphenoidal rostrum at middle of orbit. above with the parietal, back of the optic foramen, whence the name postoptics given to them by Cope. Between them and the prootics is the foramen for the fifth nerve. They form the lateral brain-case in the Crocodilia, but are absent in the Chelonia and snakes. In the lizards they are imperfectly ossified, and are usually lost in prepared specimens. They are present in the Rhynchocephalia and most other reptiles. 26 THE OSTEOLOGY OF THE REPTILES Fig. 12. Pantylus. Cotylosaur skull and mandible: immature animal, from below. Natural size. Basisphenoid (bs). (Figs. lo, ii d, 30.) Forming the floor of the brain-case in front of the basioccipital, continuous with the para- sphenoid in front (Fig. 12), which is closely fused with its under side, ar- ticulating in front above with the postoptics (Fig. 69 d), behind above with the prootics (Figs. 30, 69 d),. externally above with the stapes (Fig. II c), and externally below with the pterygoids. It lodges in front the fossa or depression for the pituitary body (Fig. 69 d). Stapes (st). (Fig. lie, D.) The stapes in all early reptiles is a large bone, articulating over the auditory opening, or foramen ovale, between the paroccipital and basisphenoid, and extending toward or touching the quadrate. It is perforated near its proximal end by the foramen for a perforating artery. It is also large in the Ichthyosauria and Plesiosauria, but in most other reptiles is slender, without a perforating foramen. It is stout and short in the Amphisbaenia (Fig. 56). Parasphenoid (ps). (Figs. 6, 10 c, d, 21 A.) A membranous, unpaired bone, firmly fused in the adult with the under side of the basisphenoid, and never a separate bone.^ It extends far forward as a narrow rostrum in the temnospondyls (Fig. 1 1 e-g) and some cotylosaurs (Figs. 6, 21 a) quite to the pre vomers, forming the floor to the ethmoidal cavity. This seems to be the rule in the early reptiles, though in some {Lahidosaurus sp) it 1 [It is separate in at least some geckos. — G. K. N.] Fig. 13. Pantylus. Cotylosaur skullr internal cranial bones. Natural size. A, basioccipital; B, basisphenoid; C, section at front of basisphenoid; D, section of rhinencephalic chamber op- posite hind margin of orbits; E, out- line of same at extreme front end of parietals; F, same in front of orbits; pal, prevomer. THE SKULL OF REPTILES 27 may not extend in front of the basisphenoid. It has been homolo- gized by Broom with the median vomer of mammals, whence the name prevomers for the paired bones in front, the so-called vomers. Ethmoid {eth) or Sphenethmoid. In the temnospondyl amphibians (Fig. II e-g), between the orbits and in front of the optic foramina^ there is a pair of thin bones lying closely below the frontals and united with the parasphenoid below, enclosing an undivided cavity for the olfactory lobes, opening into the nasal and paranasal cavities in front of the orbits. Similar bones have been observed in various cotylosaurs (Fig. 13) and theromorphs, and are probably constant among early reptiles. They have been called sphenethmoids, though they have no immediate relation to the sphenoid. Probably the median ethmoidal plate arose from the fusion of these bones. There was no median ossified interorbital septum in these reptiles, and not probably any median septum. A cartilaginous interorbital septum is present in most modern reptiles but is ossified in none. Skull Elements — Synonyms Ectopterygoid = Transpalatine, Transverse. Interparietal = Dermosupraoccipital, Dermooccipital, Postparietal. Postoptic = Laterosphenoid, Otosphenoid, "Alisphenoid." Paroccipital = Opisthotic. Prootic = Petrosal. Prearticular = Goniale. Postsplenial = Preangular. Splenial = Opercular. Supratemporal = Supramastoid, Suprasquamosal. Squamosal = Prosquamosal. Tabular = "Epiotic," Postparietal [sic] K The Mandible The mandible of reptiles was composed primitively of eight, possibly nine, separate bones, differing from that of their temnospon- dyl antecedents (Figs. 14, 15) only in the loss of one or two slender bones along the inner margin of the teeth, the precoronoid and inter- coronoid. All of these, except the postsplenial, known in a single cotylosaur (Fig. 18), have persisted to modern times, though never all in the same reptile, none having more than six, and some but five. The relations of these bones will be seen in the accompanying 1 [Possibly "paroccipital plate" was intended. — Ed.] 28 THE OSTEOLOGY OF THE REPTILES figures (16-18) and do not require a detailed description. The den- tary (d) is always present and dentigerous, except in all Chelonia (Fig. 31 B, e), some Anomodontia (Fig. 44 c) and Dromasauria, some Theropoda, and the late Pterosauria (Fig. 71 e), Saphaeosau- rus, etc. The coronoid (cor), extending along the inner margin of the teeth from near the symphysis to the hind end of the dentary on the inner Fig. 14. Trimerorhachis alleni Case. Temnospondyl skull and mandible: A, right man- dible, inner side; B, the same, outer side; C, D, E, sections of mandible as designated; F, skull and mandible, left side; psp, postsplenial; cor, coronoid; icor, intercoronoid; pcor, precoronoid. side, possibly composed of two bones in some of the earliest reptiles (Fig. 18), has been restricted to a place at the posterior end of the dentary in later forms {e. g., Fig. 55 b), and may in some cases be absent. In the Plesiosauria (Fig. 2 5 a) it still retains its ancient character, even entering into the symphysis in some cases. In the Dinosauria, or some of them at least, it also extends far forward, or there may perhaps be a distinct bone in front, the intercoronoid THE SKULL OF REPTILES 29 or precoronoid. Primitively (Fig. 18) it often bore teeth, as in many temnospondyls, but no such teeth are known in later reptiles. The sur angular (sa) , always present in reptiles, though sometimes indistinguishably fused with the articular, forms the upper margin of the mandible back of the coronoid, and the outer margin of the Fig. 15. Trimerorhachis insignis. Temnospondyl mandible: A, right ramus from below; B, the same from above. Meckelian orifice (Figs. 15-18). In some it may take part in the articular surface for the quadrate. The angular {an) , on the inferior border posteriorly, articulating with the dentary in front, the prearticular, articular, and surangular behind, and extending to the hind angle of the jaw, is always present (Figs. 15-18). In the crocodiles (Fig. 69 c, d) it helps form the inner border of the Meckelian orifice. Fig. i6. A., Dimetrodon incisivus Cope. Pelycosaur: left mandible, outer side. B, Dimetrodon incisivus Cope. Pelycosaur: left mandible, inner side. C, Dimetrodon incisivus Cope. Pelycosaur: right mandible, inner side. D, Labidosaurus hamatus Cope. Cotylosaur: right mandible, inner side. E, Labidosaurus hamatus Cope. Cotylosaur: right mandible, outer side. THE SKULL OF REPTILES 31 The splenial {sp), entering into the Meckelian symphysis primi- tively (Figs. 15-18), extending back to the posterior inferior Meckel- ian foramen, articulating with the dentary, coronoid, prearticular. Fig. 17. Diadectes {Nothodon). Cotylosaur: left mandible, from within. One half natural size. Fig. 18. Pantylus. Cotylosaur: A, right mandible from inner side; B, the same from above; C, the same from below; D, sections corresponding to letters. and angular, is not infrequently absent. In Pantylus (Fig. 18) only, so far as known, the postsplenial corresponds to its posterior part as in the known Stegocephalia (Fig. 15). It [the splenial] never bears 32 THE OSTEOLOGY OF THE REPTn.ES teeth and is more or less inconstant, absent in Sphenodon and most Chelonia. It is a thin bone and forms the cover to the Meckelian groove, whence the name opercular often given to it. Primitively (Figs. 15-18) it formed a large part of the inferior border of the man- dible anteriorly, appearing on its outer face, but in all late reptiles it is restricted to the inner side. It enters into the mandibular sym- physis in most long-jawed reptiles, probably an acquired character. The prearticular (goniale) {pa), recognized only within recent years, is a thin bone, articulating with the articular behind, the angu- lar below, the coronoid and splenial in front, forming the hind border of the posterior inferior foramen and the lower margin of the Meckel- ian orifice. It was present in all early reptiles (Figs. 16-18), and re- mains a separate bone in the modern turtles (Fig. 3 1 e) and young Sphenodon (Fig. 60). It was present in the Dinosaurs, Plesiosauria (Fig. 25 a), where it was first named, Ichthyosauria, and doubtless many other extinct reptiles. It is fused with the articular in the Squamata (Fig. 55 b), extending far forward in the mosasaurs (Fig. 58), ensheathed by the united angular and coronoid, splenial and dentary. It is apparently wholly absent in the CrocodiHa (Fig. 69) . The articular, the only cartilage bone of the mandible, forms the cotylus, in whole or part. Distinct in all early (Figs. 16-18) and many later reptiles, it may be indistinguishably fused with the pre- articular or surangular. Believed to be the malleus of the mam- malian ear. Openings in the mandible Aside from the large opening for the entrance of nerves and blood- vessels [and jaw muscles] at the posterior upper part of the man- dible (Figs. 16-18), there are in the early reptiles one or two smaller openings through the inner wall : the posterior one just in front of and below the anterior end of the large orifice, between the coronoid, angular, prearticular, and splenial, is still present in the crocodilians (Fig. 69 d). a large perforation of the outer wall of the mandible, between the angular, surangular, and dentary, is very characteristic of most Crocodilia (Fig. 69 c), Theropoda (Fig. 70 a), Phytosauria, and Pseudosuchia (Fig. 65 a, e). A foramen posteriorly, between the prearticular and angular, is for the passage of a track of the chorda tympani nerve. THE SKULL OF REPTILES 33 The Skull of the Cotylosaurl^ (Figs. 1-9, 12, 13, 16 D, E, 17-24, 25 B, C, 26-29) Fig. 1 9. Seymouria baylorensis. Cotylo- saur skull: from above. One half natural size, n, nasal; /, lacrimal; pf, prefrontal; pof, postfrontal; /;-, frontal; it, intertem- poral; St, supratemporal; do, dermoocci- pital; t, tabulare. Fig. 20. Seymouria bay'lorensis. Skull and pectoral girdle: from the side. One half natural size, pm, premaxilla; m, maxilla; /, lacrimal; n, nasal; pj, prefrontal; j, jugal; po, postorbital; sq, squamosal; qj, quadratojugal; cl, clavicle; ic, inter- clavicle; sc, scapula; c, coracoid. But few modifications of the primitive characters of the skull are known in this order. The parietal foramen is absent in one or two 34 THE OSTEOLOGY OF THE REPTn.ES genera, the supratemporals and tabulars in a few others. Teeth may occur on the coronoids. The postsplenial occurs in but one known genus [Pantylus], as also the intertemporal [Seymouria]. The inter- parietals are reduced and posteriorly placed in a few, and in the latest genera may be vestigial. The lacrimal in Procolophon is small, not reaching the nares. The teeth are usually conical throughout; in some genera they are obtuse and cuspidate; in the Diadectidae the posterior ones are transversely molariform; in no known forms are they sectorial. Doubtless with future discoveries other modifications of the primitive structure will be found. D.SOc Qu. Pf B^ROcFxaBOcfmOv QuJ. Fig. 21. Cotylosaur skull: Seymouria. After Watson. A, from below. Two thirds natural size. B, occipital view. Two thirds natural size. 35 Fig. 22. Cotylosaur skull: Diadectes, from the side and above. One half natural size. 36 Fig. 23. Limnoscelis paludis. Cotylosaur skull: A, from the side; B, from above, fm, premaxilla; «, nasal; /, lacrimal; m, maxilla; /, frontal; pj, prefrontal; poj, postfrontal; po, postorbital; pa, parietal; do, dermooccipital; /, tabulate; j, jugal; sq, squamosal; qj, quadrato- jugal; q, quadrate; d, dentary; sur, surangular; an^, angular. 37 Fig. 24. Limnoscelis paludis. Cotylosaur skull: from below. Two fifths natural size, sp^ splenial; pa, prearticular; st, stapes (?). 38 Fig. 25 Fig. 27 Fig. 25. A, Trinacromerum osborni Williston. Plesiosaur: left mandible to sym- physis, inner side, after Williston, 1903; B, Captorhinus aguti Cope. Cotylosaur: left mandible, from within; C, the same, outer side. Fig. 26. Limnoscelis paludis. Cotylosaur. Outline of back of skull. Two fifths natural size. Fig. 27. Cotylosaur. Inner side of mandibles. A, Limnoscelis paludis; B, Labi- dosaurus hamatus. One half natural size, ar/, articular; 9, quadrate; J«r,surangular; cor, coracoid; pa, prearticular; ang, angular; sp, splenial. 39 Fig. 28. Labidosaurus hamatus Cope. Cotylosaur skull: from above. Two thirds natural size. 40 B Fig. 29. Labidosaurus hamatus Cope. Cotylosaur skull: A, from below, B, from the side. Two thirds natural size, a, articular; an, angular; bs, basisphenoid; ep, epiotic; ex, exoc- cipital; pp, postparietal; pt, pterygoid; q, quadrate; st, stapes. 41 Fig. 30. Pleurodiran skull: Macrochelys, from the side and hemisection. One half natural size. 42 Fig. 31. A, Pleurodiran skull: Podocnemis, from below. B, the same, from the side. One half natural size. C, Trionychoid mandible Platypeltis, from the inner side. Three halves natural size. D,Cryptodiran skull, T^rt/awofWjj, occiput. One half natural size. E, Cryptodiran skull, Colpochelys, from above. One half natural size. 43 44 THE OSTEOLOGY OF THE REPTILES The Skull of the Chelonia (Figs. 30-32) The skull of the Testudinata or Chelonia is never elongate, though relatively slender in some of the more predaceous kinds. It always lacks the septomaxillae, postfrontals, supratemporals, dermosupra- occipitals, tabulars, ectopterygoids, ethmoids, and the parietal fora- men. The nasals are usually absent, and the lacrimals are present Fig. 32. ■ Trionychoid s^nW: Platypeltis. Natural size. A, from above; B, from below; C, atlas of same from the si^de. Note abnormal proatlas. only in some ancient forms. The prefrontals are large, meeting in the middle line. The prevomers are single and sometimes obsolete; they usually articulate above with the prefrontals. The para- sphenoid has been lately recognized as a distinct bone in certain forms. There is no postoptic, but its place is taken, except in Dermo- chelys, by descending plates from the parietals to the pterygoids, sometimes with an intercalated epipterygoid, which, however, is usually absent. The quadrate may or may not reach the basisphe- noid. The palatines often meet in the middle line be;tween the pre- THE SKULL OF REPTILES 45 vomer and the pterygoids. The pterygoids also usually meet in the middle, though separated in the Trionychoidea by the basisphenoid. The palatines also often meet for a short distance below and in front of the internal nares, forming a rudimentary secondary palate. The temporal region primitively was wholly roofed over, and yet is, in some marine turtles, by the large postorbital, quadratojugal, and squamosal. Usually it is more or less exposed by the emargination of the roof from behind or below, or from both sides; and the squamo- sals and quadratojugals may even become vestigial in the process as in the terapenes. The quadrate is always large, its ear-cavity some- times wholly surrounded by bone. The stapes is slender. The con- dyle is largely formed by the exoccipitals, in some wholly so. It re- mains cartilaginous in the Dermochelyidae, as in some cotylosaurs. The paroccipital remains free throughout Ijfe. The mandibles have a large, free prearticular, usually but incor- rectly called the splenial; the splenial is rarely present (Emydura, Toxochelys, etc.) . Both upper and lower jaws are encased in a cutting horny sheath, and are without teeth. Small teeth on the palatal bones are known to occur only in Stegochelys, a Triassic genus. 46 THE OSTEOLOGY OF THE REPTn.ES The Skull of the Theromorpha (Figs. lO A-D, II A-D, l6 A-C, 32-42) More modifications of the skull structure are found in this order than in the Cotylosauria, as would be expected. The interparietals and tabulars are probably sometimes absent, and they are always confined to the occipital surface when present, the former usually, if not always, unpaired. The supratemporals are doubtfully present in any. The quadratojugal is smaller and never extends far forward. Fig. 3a bis. Theromorph skull: Ophiacodon mirus Marsh, lateral view, pa, parietal; ^0, postorbital; ^, prefrontal; /, lacrimal; 7, jugal; 9^, quadratojugal; y, quadrate. The lacrimals seldom extend to the nares. The teeth are often want- ing on the prevomers and are sometimes present on the coronoids. There is a lower temporal opening, bounded by the jugal, postorbital, and squamosal. In the Edaphosauridae only may it possibly extend to the parietal. The teeth of jaws and mandibles are more variable, often markedly anisodont, conical, obtuse, or compressed and sectorial. Fig. 33. Theromorph skull: Sphenacodon, A, from the side; B, from above. One third natural size. 47 Fig. 34. Theromorph skull: Glaucosaurus megalops, from the side and from above. Natural size. Fig. 35. Theromorph skull: Mycterosaurus, from the side. Natural size. Fig. 36. Theromorph skull : Varanosaurus brevirostris Williston, from the side. Two thirds natural size. Fig. 37 Fig. 38 Fig. 37. Theromorph skull: Varanosaurus brevirostris Williston, from above. Two thirds natural size. Fig. 38. Theromorph skull: Varanosaurus acutirostris Broili, from above. Two thirds natural size. After Broili. Fig. 39. Theromorph skull: Mycterosaurus, from above. Natural size. 49 Fig. 40. Theromorph skull: Naosaurus claviger. A, from the side; B, right mandible, from inner side; C, skull from above; D, the same from below. Two fifths natural size. 5° Fig. 41. Theromorph skull: Casea broilii Williston, from above. Natural size. Fig. 42. Casea broilii Williston: A, skull, from the side; B, left mandible of same, from inner side; C, skull, from below; D, from behind. Three fifths natural size, pm, pre- maxilla; m, maxilla; po, postorbital; j, jugal; d, dentary; sa, surangular; ang, an- gular; sp, splenial; art, articular; pa, pre- articular; c, coronoid; poc, paroccipital; pa, palatine; bs, basisphenoid; bo, basioccipital; pt, pterygoid; q, quadrate; st, stapes; eo, exoccipital; so, supraoccipital; ds, dermo- supraoccipital. SI 52 THE OSTEOLOGY OF THE REPTH^ES The Skull of the Therapsida (Figs. 43-45) Many more modifications of the skull are found among the reptiles grouped under the name Therapsida or Anomodontia sens. lat. The supratemporals are never present. The postf rontals are often absent ; the quadratojugals are present only in the Dinocephalia and are small. ^ Only in some of the Dromasauria do the lacrimals and septo- maxillae exclude the maxillae from union with the nasals. There is a separate bone in front or surrounding the parietal foramen in the Anomodontia and Gorgonopsia. The parietals may be united in some of the Bauriasauria. The interparietal or dermosupraoccipital is always on the occipital surface of the bone and is unpaired; it is generally present, as also the tabulars. The temporal foramen, usu- ally bounded above as in the Theromorpha, reaches the parietal in theTherocephalia and Theriodontia, the postorbitals and squamosals not meeting. The vomers are fused into a single bone in the Gor- gonopsia, Bauriasauria, and Cynodontia. The pterygoids and pala- tines meet in the middle line in the Dinocephalia. There is a partial false or secondary palate formed by the union of the maxillae in front of the nares in the Anomodontia, a well-formed secondary palate in the Bauriasauria and Cynodontia. The ectopterygoids may be absent or present. Only in some of the Therocephalia are there teeth on the palatal bones. The pterygoids do not meet the small quadrates in the Cynodontia. In the Cynodontia the condyle is essentially dicondylar. The parietal foramen is usually absent. Some Dromasauria and the females of some Anomodontia are edentulous. Other anomodonts may have a single caniniform tooth in each jaw, or canines and molars. The Therocephalia have aniso- dont sectorial teeth, the Cynodontia with real heterodont dentition, the molars sectorial or cuspidate. 1 [Broom, Sollas, Watson, and von Huene have observed a distinct quadratojugal in various Therapsida. — Ed.] Fig. 43. Gorgonopsian skull: Scylacops capensis. A, from the side; B, from above; C, from below. One half natural size. After Broom. 53 Fig. 44. Therapsid skulls: A, B, Mor»zoJ(?«r«j (Dinocephalia) from above and from side. After Watson. One twelfth natural size. C, Dicynodon (Anomodontia) from the side. After Broom. One half natural size. D, Cistecephalus (Anomodontia), from above. After Broom. One half natural size. E, Gorgonops (Gorgonopsia), from below. After Watson. One fourth natural size. F, Scylacosaurus (Therocephalia), from the side. After Broom. Two sevenths natural size. G, Diademodon (Cynodontia), occiput. After Watson. One half natural size. 54 Fig. 45. Therapsid skulls: A, Cynognathus platyceps (Cyno- dontia), from the side. After Broom. One third natural size. B, the same, from above. C, Cynognathus crate- ronotus, upper teeth, from the side. D, Bauria (Bauria- sauria), from above. After Broom. One half natural size. SS 56 THE OSTEOLOGY OF THE REPTILES The Skull of the Nothosauria (Fig. 47) [No manuscript. See pages 211, 246, 247] The Skull of the Plesiosauria (Figs. 46-48, 25 a) The extreme aquatic adaptations of the plesiosaurs have caused certain modifications in the structure and relations of the bones of the skull that are unique among reptiles. The general shape of the skull seems to bear a definite relation to the length of the neck, always shorter in the long-necked forms, slender, sometimes very slender in the short-necked types. The pre- maxillae are always greatly elongated, extending back at least as far as the front part of the orbit, in the long-faced kinds even to articu- late with the parietals, above or between the frontals. The alveolar border also is [short?] shut. The maxillae are much more elongate than in the icthyosaurs and phytosaurs. There are no teeth in the palate. The nasals have never been certainly determined; possibly they are fused with the frontals, which extend as far forward as the external nares, forming the inner border. The prefrontals are small; the lacrimals have been identified in a few forms only; they appear to be absent in some. The postf rentals are probably present in all. The orbits are bounded below by the jugals and maxillae. The quadratojugals are conceded to be absent in all plesiosaurs. The single large temporal opening is bounded below by the postorbitals and squamosal, above by the parietals, which are more or less ele- vated in the middle in a crest. There is a pineal foramen. The squamosals, in some at least, join each other back of the parietals on the upper surface of the skull. There are no interparietals, tabulars, or supratemporals. On the occipital surface the supraoccipital is excavated more or less by the foramen magnum, which may extend to the roof, dividing the bone. The paroccipitals are always fused with the exoccipitals. The brain-case is more or less open in front on the sides, the post- optics either reduced or absent. The stapes is large and stout. THE SKULL OF REPTILES 57 Very great also, are the modifications of the palate. The anterior nares are situated either between the prevomers and the maxillae, Fig. 46. Sauropterygian skulls: A, Peloneustes. After Linder. One ninth natural size. B, Plesiosaurus. After Andrews. One sixth natural size. C, Muraenosaurus. After Andrews. One sixth natural size. Fig. 47. Sauropterygian skulls: A, Nothosaurus, from above. One fourth natural size. B, Simosaurus, from below. After Jaekel. One fourth natural size. C, Thaumatosaurus, from below. After Fraas. One fourth natural size. 58 THE OSTEOLOGY OF THE REPTILES or between them and the palatines, and, like the external ones, are small. There is always a remarkable posterior interpterygoidal vacuity, divided in the middle throughout by the large parasphenoid, the pterygoids meeting in front of and to a slight extent behind them. Fig. 48. Plesiosaur skulls: A, Elasmosaurus, from the side: pm, premaxilla; m, maxilla; po, postorbital; j, jugal. B, Plesiosaurus, from the side. One sixth natural size. C, Trinacromerum, from the side: ang, angular; d, den- ,;' tary; pm, premaxilla; po, postorbital; /, jugal; sur, surangular. An anterior interpterygoidal vacuity, as also posterior palatine and other openings in the palate, may or may not be present. The in- ternal nares are in front, sometimes very much in front, of the ex- ternal nares. The coronoids are elongate bones, extending along the^sides of the teeth internally and meeting each other in some forms in a median symphysis. As usual in long-faced forms, the splenials meet in a median symphysis. THE SKULL OF REPTILES 59 The Skull of the Placodontla. (Fig. 49) The skull of the Placodontia is almost unique among reptiles for the extraordinary development of large, flat, crushing teeth upon the Fig. 49. Placodont skulls: A-D, Placodus. After Broili. One fourth natural size. E, Placochelys. After Jaekel. One half natural size. 6o THE OSTEOLOGY OF THE REPTILES jaws and palatines, in Placodus as few as twenty all told, in Placo- chelys still fewer. In consequence, the palatines are very large, meet- ing each other throughout as do the pterygoids in the median line. The ectopterygoids are very small and the pterygoids are restricted to the posterior part of the palate, widely separated from the pre- vomers. The massive cranium has a large temporal opening bounded above by the parietal, below by the united postorbitals and squamosal, with the postfrontal entering into the anterior border. Except for the postfrontals, the structure here, it is seen, is like that of the Dino- cephalia, and possibly has arisen in the same way. The stout lateral bar below the opening is identified by Jaekel in Plachochelys as composed of the squamosal and quadratojugal, by Huene as the supratemporal and squamosal; both views are probably incorrect, since Broili finds only the squamosal, which is in Placodus the more probable. So, also, Huene believes there is an interparietal, which Broili cannot find. The nasal only of the roof bones is unpaired in Placodus; possibly the prevomers are also single. There is a large epipterygoid. No tabulars have been found. The premaxillae in Placodus are large, each with three incisor-like teeth. The largest skulls of Placodus are about ten inches long. The Skull of the Ichthyosauria (Figs. 50, 51) The skull of the ichthyosaurs, while retaining not a few primitive characters, has been highly and peculiarly modified in many ways. The greatly elongated premaxilla, unlike those of other aquatic reptiles, is broadly separated above by the very large nasal, and bears numerous teeth; the maxillae are short. All bones are paired. The frontals are small. The very large orbits have the usual bound- ing bones, prefrontal, postfrontal, postorbital, jugal, and lacrimal, but their relations are somewhat changed. The prefrontals are long, the postfrontals are extraordinarily large, articulating in front not only with the whole extent of the frontals but also with the nasals and prefrontals, posteriorly with the so-called supratemporals. The postorbitals are long bones forming nearly the whole posterior THE SKULL OF REPTILES 6l boundary of the orbits, with their usual articulations. The jugals are long, articulating with postorbitals, quadratojugals, maxillae, and lacrimals. The relations of the bones of the palate and the boundaries of the nares are primitive ; an ectopterygoid has not been recognized and is probably absent; there are no teeth on the palatal Fig. 50. Ichthyosaur skull: Baptanodon {Ophthalmosaurus) , from the side, from above, and from below. After Gilmore. bones. On the occiput the paroccipitals, unlike all other reptiles since the primitive Cotylosauria, save the Chelonia, are separate. The stapes is a short, stout bone, possibly an acquired, more probably a primitive, character. There are no dermosupraoccipitals. The large parietal foramen is at the front end of the parietals, sometimes be- tween the frontals. Most characteristic of the ichthyosaur skull is the structure of the temporal region, about which there has been dispute from the time of 62 THE OSTEOLOGY OF THE REPTILES Owen to the present. The large temporal vacuity is admittedly the upper one, bounded on the inner side by the parietal, on the outer by the postfrontal and the so-called supratemporal. There is no lateral foramen, and it is quite improbable that a preexistent one was later closed by the encroachment of the orbit. This region, as in the primi- tive skull, has five bones. About three, the postfrontal, postorbital, and quadratojugal, there can be no question of identity. And un- less we accept the wholly improbable theory that new bones have been developed in the temporal region of the ichthyosaurs, the other two must be homologized with the supratemporal, or tabular, and the squamosal. The supratem- poral bone was the first to be lost in the primitive skull, and there is no certain evidence yet forthcoming that it was re- tained in any reptiles after the cotylosaurs. If, however, the supratemporal was persistent f&og in the ichthyosaurs instead of the tabular, by no possibility can it be the bone on the outer side of the squamosal, as some recent writers assert, as a com- parison of the cotylosaur skull will make e.vident. The outer bone, sometimes obsolete in ichthyosaurs, must be the squamosal. The upper, posterior bone completing the upper border of the tem- poral vacuity, the author prefers to believe is the tabular and not the supratemporal, and doubtless is homologous with the bone so recognized in the skull of the Squamata. We cannot conceive of its being anything else, having as it does the same relations with paroccipital, parietal, and quadrate, rarely in the mosasaurs extend- ing forward to articulate with the postorbital. Fig. 51. Ichthyosaur skull: Baptanodon {Ophthalmosaurus) , from the rear. After Gilmore. Ang, angular; bs, basisphenoid; d, dentary;/r-, frontal. The Skull of the Protorosauria (Figs. 52, 53 c-e) In the order here provisionally called the Protorosauria the skull is completely known in none, but best in Araeoscelis, the oldest cer- THE SKULL OF REPTILES 63 tainly-known reptile with a single typical upper temporal vacuity. The roof bones are all paired in all, so far as known. In Araeoscelis, Pleurosaurus, and ^f^i^ohdihly Protorosaurus . there is a parietal foramen, but none in Saphaeosaurus. The lacrimal is small or vestigial in all. The postfrontal is present in Araeoscelis, and only in this genus are there indications of the presence of the dermosupraoccipitals. Prob- ably all have teeth on the palatal bones. Their chief interest lies in the structure of the temporal region. In Araeoscelis the temporal opening is bounded externally by three Fig. 52. Parapsid skulls: A, Pleurosaurus, from the side. Natural size. B, Araeoscelis, from the side. Twice natural size. bones, the postorbital in front, and two bones posteriorly, about which there is doubt because of their evident identity with the cor- responding bones in the lizard skull, which have been the subject of more controversy than any others of the reptilian skull. Aside from the tabular, there are three recognized bones of the primitive tem- poral region, all present in the Cotylosauria and Ichthyosauria, to which the names mastoid, supramastoid, squamosal, suprasqua- mosal, prosquamosal, temporal, supra temporal, and quadratojugal have been applied in almost all possible combinations. Only two of these are present in Araeoscelis, Pleurosaurus and the Squamata, to 64 THE OSTEOLOGY OF THE REPTD^ES which all of these names have been given by different authors. The more general opinion is that the posterior one of the Araeoscelis and ^p>' E Fig. 53. Parapsid, etc., skulls: A, B, Mycterosaurus (Theromorpha), from the side and from above. Natural size. C, Araeoscelis (Protorosauria), from above. Natural size. D, Pleurosaurus (Protorosauria), from above. One half natural size. E, Sauranodon (Protorosauria), from above. Natural size. Squamata arch is the supratemporal, the anterior and outer one the squamosal; some, however, reverse these names, calling the posterior THE SKULL OF REPTILES 65 one the supratemporal or its synonym, the prosquamosal. Yet others both in the past and the present call the outer anterior bone the quadra to jugal. The author has given his reasons for believing that the posterior bone is none of these but the tabular instead, the an- terior one the squamosal, the quadratojugal absent. He believes that the posterior is the tabular because it occupies the primitive position of that bone in its relations to the interparietal, paroccipital, squamosal, and quadrate. The supratemporal is the first bone to disappear in the temporal region of the Cotylosauria, and its pres- ence has never been positively determined in the Theromorpha and Therapsida. It is quite possible, however, that both the tabular and supra- temporal have disappeared in these reptiles, and that the squamosal has usurped their position and functions; the true supratemporal, however, has no relations with the quadrate as has the bone so called in the skull of the lizards. If so, the bone articulating with it in front and forming the outer boundary of the temporal opening may be the quadratojugal, as was formerly believed and yet is by some. It is a fact, however, that the quadratojugal is a very inconstant bone in all single-arched reptiles otherwise. It is very small in the Thero- morpha, is present in only a very few of the Therapsida as more or less of a vestige, and has wholly disappeared in the Sauropterygia. That it should lose its original position at the lower outer side of the quadrate, to form part of the articular surface for its upper end, seems improbable. Furthermore, in the Ichthyosauria (and ? Saphaeosaurus) there is a distinct bone between it and the temporal opening that must be either the squamosal or supratemporal. There is at present no certain solution of the problem. The Skull of the Squamata (Figs. 54-59) The skull of the Squamata is at once distinguished from that of all other reptiles by the movable, streptostylic quadrate, secondarily more or less fixed in some forms. The exoccipitals and paroccipitals are always fused ; the pterygoids never reach the vomers ; the inter- parietals and either the supratemporals or tabulars, or the quadra- tojugals, according to the identification, are absent. The teeth are 66 THE OSTEOLOGY OF THE REPTILES acrodont or pleurodont; the prearticular of the mandibles is always fused with the articular. Other characters are very variable in this extensive order, which is sometimes divided into two or three dis- tinct orders. Sauria or Lacertilia In the lizards (Figs. 55, 56) the quadrate articulates above nor- mally with three bones, the squamosal, paroccipital, and a third bone whose homology is yet disputed, but which is usually called the supratemporal. The squamosal may be absent in those lizards without a temporal arch, and rarely in certain degraded burrowing lizards (Fig. 56) the "supratemporal" may also be absent, the quadrate lying against the brain-case and more or less fixed by the pterygoid. The paroccipital usually but not always helps support the quadrate. As regards the identity of all these bones, there has been great dif- ference of opinion, and there is by no means unanimity at the present time. The tabular, as here identified, has been called the squamosal, supramastoid, supratemporal, and even the paroccipital (opisthotic) . The squamosal as here considered has been called the quadratojugal, supratemporal, paraquadrate, squamosal, and prosquamosal. The reasons for their identification as the tabular and squamosal will be found in the discussion of the skull of the Protorosauria. Below, the quadrate articulates with the pterygoid on the inner side by a rather free joint in most lizards, in some, like the Am- phisbaenia (Fig. 56) by a close sutural joint. On the inner side the usually slender stapes abuts against the quadrate (Fig. 55 c). In the mosasaurs there is an elongated suprastapedial process arching backward and often extending to the lower end, enclosing the au- ditory meatus, as in some turtles. The tabular (Fig. 55 a, /a), or supratemporal, at the distal and under side of the parietal process, forming more or less of the boun- dary of the temporal opening, articulates with the squamosal, par- occipital, and quadrate. In the mosasaurs (Fig. 54 c) only, it has a long internal process, firmly wedged in between the paroccipital and prootic, extending nearly or quite to the semicircular canals. In some lizards the tabular has suffered reduction or has become indistinguishably fused with the squamosal. THE SKULL OF REPTILES 67 The squamosal normally articulates with the tabular and quad- rate posteriorly, anteriorly with the postorbital, and often, both in the lizards and mosasaurs, by a slender prolongation with the tip of Fig. 54. Mosasaur skulls: Upper figure, Clidastes, from the side; mjddle figure, Platecarpus, from below; lower figure, Tylosaurus, from above, an, angular; bs, basisphenoid; c, coronoid; ep, epipterygoid; fr, frontal; _;', jugal; /, lacri- mal; m, maxilla; na, nasal; oc, occipital condyle; pa, parietal, palatine; pm, premaxilla; pf, prefrontal; pt, pterygoid; po, postorbital; q, quadrate; sp, splenial; sq, squamosal; tr, transverse; v, vomer. the jugal; very rarely, as in Uromastix, with the jugal only. In some lizards it has suffered reduction, and is absent in the Geck- onidae, Anniella, and Amphisbaenidae, vestigial in the Heloder- matidae. Fig. sS- Lacertilian skulls: A, Conolophus, from above. Natural size. B, the same, left mandible. Three fourths natural size. C, Varanus, from below. Natural size. D, E, F, Chameleon, from the side, the postoptic, and the upper end of quadrate. THE SKULL OF REPTILES 69 The temporal fossa, normally (Fig. 55 a) bounded above by the parietal, below by the tabular, squamosal, and postorbital, may be wholly absent, as in the Amphisbaenidae (Fig. 56 a), completely Fig. 56. Lacertilian skull: A, B, C, Amphisbaena, from above, below, and the side. Five halves natural size. D, side view of atlas and axis. roofed over by dermal bones, or obliterated by the union of the tem- poral arch with the parietal. The premaxillae may be paired or fused; in the mosasaurs (Fig. 54 c) the united bone is fused with the nasals posteriorly, or the latter may be absent or vestigial. The lacrimals are always small. 70 THE OSTEOLOGY OF THE REPTILES sometimes vestigial or absent. The prefrontals are always large, en- tering into the formation of the nares in the Varanidae and Mosa- sauridae (Fig. 54 a) . They articulate with the palatine by a descend- ing process. The nasals, usually paired, are sometimes fused with the premaxillae or with each other; they are separated from the nares in the Rhiptoglossa (Fig. 55 d). The postfrontals are rarely large in lizards and are often absent; when absent the postorbitals take their place, sometimes (Fig. 55 d) ending forward over the orbit to meet the prefrontal. The postfrontal and postorbital are not rarely found united by suture in the mosasaurs ; usually, however, the two bones are indistinguishably fused or the postfrontal is absent. Posteriorly the postorbitals articulate as usual with the squamosal; below with the jugals. The postorbito-jugal and the postorbito-squamosal arch may be absent in various terrestrial lizards. The jugal is a slender bone bordering the orbit below and extend- ing forward to meet the lacrimal when that bone is present. It articu- lates with the maxilla, ectopterygoid, postorbital, and often with the tip of the squamosal. It may be vestigial or even entirely absent in lizards. The maxilla articulates normally with the premaxilla, sometimes with the nasal and prefrontal, with the jugal, prevomer, palatine, ectopterygoid. It always bears a single row of acrodont or pleuro- dont, pointed or obtuse teeth. On the palate the prevomers are paired or partially fused in the Rhiptoglossa. They articulate in front (Fig. 55 c) with the pre- maxillae, laterally usually with the maxillae, posteriorly with the palatines only. They very rarely bear small teeth. The palatines (Fig. 55 c), unlike those of most other reptiles, are intercalated between the prevomers and pterygoids, articulating on the sides with the maxillae and more or less with the ectopterygoids. They sometimes bear teeth. The pterygoids have the normal articu- lations except that in front they articulate with the palatines only. The posterior palatine opening is usually large. They usually bear teeth. The epipterygoid, a slender rod, is present so far as known in all lizards except the Amphisbaenia and Rhiptoglossa/ articulating in a 1 [Also DibamidK. — G. K. N.] THE SKULL OF REPTILES 71 pit on the upper side of the pterygoids and extending to or toward the parietals. The frontals usually and the parietals always are fused in the mid- line (Fig. 55 a). ^ The parietal foramen, usually present, is absent in many terrestrial lizards and in the Rhiptoglossa. The frontals and parietals may be either paired or unpaired. The frontals in the Varanidae, Helodermatidae, and some others have descending proc- esses of the frontals which meet in the middle below, en- closing a rhinencephalic cham- ber, very much like the prim- itive one of the early reptiles. The brain-case of lizards, as of other reptiles, is formed by the supraoccipital, exocci- pitals, paroccipitals, basiocci- pital, basisphenoid, prootics, and postoptics, but is more or less membranous in front on the sides. The postoptics (Fig. 55 d, al) are small ossifications in the wall membrane, usually lost in macer- FiG. 57. Platecarpus, occ\Y>\t&\\\fw. /^o, basi- occipital; eo, exoccipital; pf, postfrontal; st, stapes; pt, pterygoid; q, quadrate. Fig. 58. Mosasaur mandible: Clidastes, inner side of right mandible, ang, angular; art, articular; cor, coronoid; pa, prearticular; sur, surangular. ation. In the Amphisbaenia (Fig. 56 c) and Mosasauria the sides of the parietals are partially decurved, forming incomplete cerebral walls, but they do not reach, as in the snakes (Fig. 59 b), to the basisphenoid. The mandibles (Figs. 55 b, 58) are composed of the dentary coro- noid, surangular, articular, angular, and splenial, with a long fused prearticular, which in the mosasaurs is more or less ensheathed by the union of the coronoid and angular, strengthening the peculiar ^ [Some geckos have them separate. — G. K. N.] 72 THE OSTEOLOGY OF THE REPTILES joint between the angular and splenial; a similar joint, though less well developed, is found in the monitor lizards. The mandibles are usually united in front by suture but are ligamentously connected in the mosasaurs and some land lizards. As is seen, there are many variations in the skull of the lizards, more than in many other groups of reptiles called orders. Ophidia or Serpentes (Figs. 59 a-e) The skull of snakes differs from that of lizards, especially in the complete closure of the brain cavity in front by descending plates from the parietals and frontals, the former always meeting the basisphenoid below, the latter sometimes interrupted by the coa- lesced optic foramina; in the constant absence of the postoptics, epipterygoids, and squamosals, the quadrate articulates proximally with the tabular only, which may also be absent. The parietals are always fused; there is no parietal foramen. There is no temporal arch, and, rarely, no ectopterygoid. The premaxillae are small and often edentulous, the maxillae rarely edentulous. The pterygoids and palatines usually bear long teeth. The postorbitals may meet the maxillae below, and there is no jugal. The vipers (Fig. 59 e) have but one functional tooth attached to the maxilla. It is hollow, with an opening at its base and another near its apex for the passage of venom. Only the dentary is freely articulated in the mandible, the posterior bones closely fused; the two mandibles are usually united in front by ligament only. There is no ossified interorbital septum, and the prootics are largely ex- posed on the side of the skull. The mandible of Ophidia has the primitive structure, except that the coronoid appears to be absent or fused, the bone usually so called being clearly the prearticular. The long splenial, as usual in reptiles with a long median symphysis of the mandibles, enters into the symphysis. The conical teeth of the premaxillae, maxillae, and dentaries primitively were inserted in sockets, but in the more specialized types are rather loosely lodged in grooves. Fig. 59. Ophidian skulls: A, B, C, D, Python, from above, and from the side, occiput, and palatine bone with teeth. Natural size. E, Crotalus, from the side. Natural size. 73 74 THE OSTEOLOGY OF THE REPTILES The Skull of the Rhynchocephalla (Figs. 60-63) [No manuscript. Some skull characters are noted on pages 20, 21, 25, 213, 279.] Fig. 60. Rhynchocephalian skull: Sphenodon (Tuatera), from the side and above, pm, premaxilla; n, nasal; prf, prefrontal; /, frontal; pf, postfrontal; /), parietal; /)o, postorbital; jy, squamosal; »?, maxilla; _/, jugal; ^r;', quadrato- jugal; q, quadrate; c, coronoid; sa, surangular; art, articular; pa, preartic- ular; d, dentary; an, angular. Fig. 61. Thalattosaur skull: Thalattosaurus, from above and from the side. After Merriam. One eighth natural size. _EiG. 62. Rhynchosaur skulls: A, B, Stenomelopon, from above and from the side. After ^Boulenger. One fourth natural size. C, Hyperodapedon, from the side. After Huxley. D, the same, from above. After Burckhardt. E, from below. After Boulenger. One fourth natural size. 75 Fig. 63. Choristoderan skull: Champsosaurus, from above and from below. After Brown. One half natural size. 76 THE SKULL OF REPTILES 77 The Skull of the Pseudosuchia (Fig. 65 a-e) The skull of the typical Pseudosuchia is very much like that of the Pelycosimia (Fig. 64), in structure. All the bones of the skull roof are present except the dermosupraoccipital, tabular, and supra- temporal ; the lacrimal is small ; there is no parietal foramen ; and the palate bones have the primitive relations. Other forms, however, referred to this group provisionally, have both the dermosupra- occipital and tabular {Youngina, Fig. 64 c), and teeth on the pre- vomers and pterygoids {Proterosuchus). The upper and lateral temporal openings, a large antorbital vacuity and one in the man- dible, are like those of the Parasuchia. The antorbital foramen is large, as are also the orbits. The supratemporal foramen is large and never posterior in position. The Skull oe the Pelycosimia (Fig. 64) The skull of the Pelycosimia differs from that of the Phytosauria chiefly in the position of the external and internal nostrils near the extremity of the face, and at a considerable distance in front both of the orbits and antorbital openings. The face is short in front of the nostrils. There is also no respiratory channel back of the internal nostrils, so characteristic of the phytosaurs. The skull is markedly carnivorous in type. , Fig, 64. Pelycosimian skull: Erythrosuchus , from above. After von Huene. One sixth natural size. 78 THE SKULL OF REPTILES 79 The Skull or the Phytosauria (Figs. 65, 66, 67) The skull of the Phytosauria is nearly uniform in general structure, characterized especially by the elongated face and posterior location of the external nostrils. No bones are fused in the midline, and none, save the primitive dermosupraoccipital, tabulars, and supratem- porals are missing. The paroccipitals, as usual, are firmly fused with the exoccipitals. There is no parietal foramen. The supratemporal openings are more or less depressed below the level of the parietals but retain their primitive boundaries. The well-developed quadrato- jugals enter into the formation of the lateral temporal openings posteriorly. There is a primitive quadrate foramen between the quadratojugal and the quadrate. The stapes is slender. There is a large antorbital foramen bounded by the maxilla, nasal, lacrimal, and jugal. The greatly elongated face is composed chiefly of the premaxillae, which extend back to the anterior ends of the nares, with the septo- maxillae intervening, in the middle. The nostrils are surrounded by the large nasals and are elevated to or above the superior plane of the skull. The bones of the palate retain their primitive relations, and there are small posterior palatine vacuities, larger in the more primitive forms. The pterygoids meet broadly in the median line, forming the roof of a deep respiratory channel between the heavy, underarching palatines, in some almost forming an incipient secondary palate, in the phytosaurs, as in the crocodiles, doubtless caused by the large fiat tongue. The interpterygoidal opening and parasphenoid are small. The elongate prearticular of the mandible is fused with the articu- lar. As usual in slender-jawed reptiles with a long symphysis, the splenial participates in it, an acquired character. The condition of the coronoid is not yet definitely determined, but it is doubtless present, though small. A large foramen, so generally characteristic of the Archosauria, is constant in the outer wall of the mandible be- tween the surangular, angular, and dentary. The teeth are numerous, set in deep sockets and confined, as in other archosaurians, to the premaxillae, maxillae, and dentaries, Fig. 65. Pseudosuchian skulls: A, B, Euparkeria, from the side and from above. After Broom. Five sixths natural size. C, Youngina, from above. After Broom. Three halves natural size. D, E, Ornithosuchus, from above and from the side. After Bou- lenger. One half natural size. 80 THE SKULL OF REPTILES 8i either cylindrical throughout or partly or chiefly flattened and denti- culated. The first two or three teeth on each side, especially above^ Fig. 66. Phytosaur skull: Machaeroprosopus , from above and from below. are cylindrical and much elongated. The dentulous portion of the premaxillae is long, with twenty or more teeth on each side. The chief differences in the skull structure of the various members, of the order are found in the relative position of the external nares,. Fig. 67. Phytosaur skull: Mystriosuchus. /)W, premaxilla; m, maxilla; ««, nasal; /, frontal; p, prefrontal; /, lac- rimal; pj, postfrontal; po, postorbital; pa, parietal; sq, squamosal; qj, quadratojugal; pi, palatine; /, transverse; in, internal nares; en, external nares; pt, pterygoid; bs, basisphenoid; eo, exoccipital. After McGregor. 82 THE SKULL OF REPTILES 83 the extent of the elevated facial carina in front of the nares, and the shape of the teeth, more slender and cylindrical in those with slender jaws, more flattened and compressed in those with a compressed and elevated face, doubtless because of the more dominant fish-eating habits of the former, the more general carnivorous habits of the latter. The Skull of the Crocodilia (Figs. 68, 69) The skull of the Crocodilia invariably lacks the postfrontals, supratemporals, epipterygoids, tabulars, septomaxillae, and parietal foramen, and the paroccipital is fused with the exoccipital. The parietals and frontals are fused in the midline. The supraoccipital is a triangular bone, excluded from the foramen magnum. The quadratojugals take part in the formation of the lateral temporal opening, narrow bones between the quadrates and jugals extending forward to meet the postorbitals. The quadrates are firmly wedged in between the quadratojugals, postorbitals, parietals, exoparoccipi- tals, postoptics, squamosals, prootics, basisphenoid, and pterygoids, an extensive connection. The supratemporal openings are large in the early forms, small in the later ones, and almost [or entirely] obso- lete in some. The lateral temporal opening is separated in the teleo- saurs from the orbits by an unmodified postorbital bar immediately below the skin. In the broader-faced amphicoelian and in all the procoelian types it is a cylindrical bar with a considerable space be- tween it and the skin. The postoptics (Fig. 69 d, as) are fully ossi- fied, extending from the basisphenoid to the frontals. There is no ossified interorbital septum. An antorbital vacuity is often present in the teleosaurs, but only rarely has been found in the early pro- coelian types. The nasals may or may not separate the external nares, connecting with the premaxillae ; they are divided by a carti- laginous septum in life. The nares are always at the extremity of the face, no matter how long and slender it may be. There is a eusta- chian canal connecting with the otic sinuses, in the median line be- tween the basioccipital and basisphenoid. The most important modifications of the crocodilian skull are found in the palate, distinguishing these reptiles from all others. The maxillae meet broadly in the middle line, excluding the prevomers Fig. 68. Crocodilian skulls: A, Teleosaurus, from above. About one fifth natural size. B, Dakosaurus, from above. After Fraas. One twelfth natural size. C, Alligatorellus, from above. After Lortet. One half natural size. D, ^//»g-«/or, occiput. Onehalf natural size. E, Hylaeochampsa, from below. After Andrews. Fig. 69. Alligator skull: one half natural size. 86 THE OSTEOLOGY OF THE REPTn.ES from the palatal surface, except rarely just back of the premaxillae in the caimans, or in front of the pterygoids in the tomistomids. The palatines also meet in the middle line in all, sending up proc- esses for articulation with the postorbital, and forming the floor of the respiratory canals. The pre vomers form a pair of tubes above the maxillae and palatines, articulating posteriorly with a supra- palatal prolongation of the pterygoids; they are separate as usual, and do not often appear on the palatal surface. The pterygoids also meet in the middle line, in all procoelian forms completely surround- ing the internal nares, which may or may not be divided by a median partition, meeting below the nasal tubes in front of them. In the early teleosaurs these openings were at the posterior border of the palatines. In the goniophilids the openings are surrounded by both palatines and pterygoids. The pterygoids articulate posteriorly and externally with the post- optics by a narrow pillar, possibly representing the epipterygoids. There are large posterior palatine vacuities at the sides of the pala- tines, and, in Hylaeochampsa, an additional opening in the palate between the ectopterygoid and maxilla. In the mandible (Fig. 69 d) the splenials meet in a median sym- physis in slender jaws. The prearticular is apparently wholly absent, or fused with the angular. There is a large mandibular foramen be- tween the angular, surangular, and dentary on the outer side, absent in the Thalattosuchia. The Skull or the Dinosaurs (Saurischm, Ornithischia) (Fig. 70) [No manuscript. Skull characters noted, pages 17, 28, 32, 214, 291-296.] "<3 tS 1) 3 o S o "3 O u < . . ^ s s S < g " s < i .0 N The Skull or the Pterosaurl^ (Figs. 71, 72) [No manuscript. Skull characters noted, pages 11, 14, 17, 19, 21, 28, 214, 296-298.] Fig. 71. Pterosaur skulls: A, Rhamphorhynchus, from the side. B, Campy lognathus, from the side. After Plieninger. One half natural size. C, Rhamphorhynchus, front part of palate. After von Huene. One half natural size. D, Ornithodesmus, end of beak. After Hooley. One fourth natural size. E, Pteranodon. About one fourteenth natural .size Fig. 72. Pterosaur skulls: A, Nyctosaurus, from above; B, the same from below. About five eighths natural size. C, Pteranodon, from be- low, after Eaton. About one fourth natural CHAPTER II THE VERTEBRAE The spinal column or backbone of reptiles, as of all other air-breath- ing vertebrates, is made up of a variable number of separate seg- ments called vertebrae. A vertebra (Fig. 73 b) is composed of a body, or centrum, and an arch, or neurapophysis, each ossifying separately and uniting at variable times, the neurocentral sutures more persis- tent than in most mammals, young or aquatic reptiles always (Fig. 87 B, c), adult land reptiles often showing them.^ Fig. 73. Anterior dorsal and cervical vertebrae: A, B, Sphenodon (Rhynchocephalia), anterior dorsal from the side and front; C, D, Iguana (Lacertilia), anterior dorsal from the side and front; E, F, Ophidia, anterior dorsal from behind and in front; G, Pter- anodon (Pterosauria), cervical from the side, after Eaton. Projections from the vertebrae, called processes or apophyses, serve for the attachment of muscles or ligaments, for articulation with adjacent vertebrae, or for the support of ribs, and are often characteristically different in different reptiles. Two pairs of proc- esses springing from the arch, one in front and one behind, are 1 [For the modern embryological viewpoint of the composition of reptilian vertebrae see Schauinsland, in Hertwig's Handhuch der Entwickeliingsgeschichte der Wirbel- tieren, etc., 1906. — Ed.] THE VERTEBRAE 91 known as zygapophyses. The pair in front, the prezygapophyses (az) , always has the flat or concave articular surface directed upward, that is, toward the dorsal side, or upward and inward ; while that of the posterior pair, the postzygapophyses (pz), is turned downward, that is, toward the ventral side, or downward and outward. The zygapophyses may be obsolete or even absent in the posterior part of the column of aquatic reptiles. The vertebrae of all snakes, some lizards, and some mosasaurs, have additional articulations, or rather, extensions of the zygapo- physial articulations about their inner ends, known as zygosphenes (Fig. 73 D, f) and zygantra (Fig. 73 e). The zygosphene is a wedge-shaped process at the anterior end of the arch, above and be- tween the zygapophyses, which fits into a corresponding cavity, the zygantrum, at the posterior end of the next preceding ver- tebra. Zygosphenes and zygantra strength- en the articulations, though restricting ver- tical flexure. They occur, as is seen, only in reptiles with a long, flexible vertebral column,^ and are absent in those mosasaurs in which the column is less elongate and flexuous. Zygosphenes are also known to occur in certain aquatic Stegocephalia with long, slender vertebral columns. In certain other reptiles this arrangement is reversed, in that the wedge-shaped median process, called hypo- sphene (Fig. 74) is below and between the inner ends of the post- zygapophyses, fitting into a cavity, the hypantrum, at the front end of the next succeeding vertebra. Hyposphenes and hypantra are especially characteristic of certain cotylosaurs, placodonts, and dino- saurs, where they were first recognized and described. The later pterodactyls have another pair of articulating processes, called exapophyses (Fig. 73 g), at each end of the cervical verte- brae on the ventral side, their articulating surfaces facing in oppo- site directions to those of the zygapophyses above them. They strengthen the articulations, but limit torsion, and are substitutes Fig. 74. Dorsal vertebra: Diadectes (Cotylosauria) from behind, showing diapophyses, postzygapophyses, and hy- posphene. 1 [Exceptions to this rule occur in recent lizards. — Ed.] 92 THE OSTEOLOGY OF THE REPTH^ES for the peculiar saddle-shaped articulations of the cervical vertebrae of birds. On the dorsal side of the arch, in the middle, is the spine or neura- pophysis, of extremely variable size and length, sometimes rudi- mentary, sometimes very long. As a rule, the spines are longest and stoutest at the beginning of the dorsal series, for the attachment of muscles and ligaments controlling the neck and head. The spines are always short in legless or slender crawling reptiles (Fig. 73 D-r) and are never long or slender in aquatic reptiles, in front at least. The spines of most sauropod dinosaurs in front of the sacrum are broadly divided, V-shaped, doubtless for the lodgment of stout muscles and ligaments used in controlling the long neck. A longer or shorter process on the sides of the arch for the support in part or wholly of the ribs is known as a diapophysis (Fig. 73 b, 75). A like process or facet on the side of the centrum anteriorly for articulation of the head of the rib is called a parapophysis (Fig. 73 r). Either is commonly called a transverse process, and the same term is often applied to a like process on the sides of the caudal vertebrae, of which probably the anterior ones, at least, in all cases are merely coossiiied ribs. A process, paired or single, on the under side of the vertebrae, is properly called a hypapophysis (Figs. 73 e, 75 a). Hypapophyses are characteristic of snakes, often as far back as the tail; in some instances they are developed to serve as a sort of masticatory apparatus for the crushing of eggs in the stomach.^ They also often occur on the cervical vertebrae of lizards, crocodiles, and turtles. Paired hypapophyses (lymphapophyses) are characteristic of the caudal vertebrae of snakes, where they replace the absent chevrons.^ When the ends of the centra are concave, as they are in all early reptiles, nearly all fishes, and most amphibians, the vertebrae are known as amphicoelous (Fig. 74) . If the cavities are deeply concave, communicating with each other through the centrum, the vertebrae are called notochordal; that is, the notochord was continuous in life. And this was the primitive condition found in the Cotylosauria (Fig. 1 [The eggs are cut, not crushed, and in the oesophagus, not the stomach (Fitz- simons) . — Ed.] 2 [The distinctions between l3Tnphapophyses and hypapophyses break down in the embryology of modern lizards. — Ed.] THE VERTEBRAE 93 74) and Triassic Ichthyosauria and continuous to the present time in the living gecko Hzards. More usually, since middle Permian times the cavities are shallow, bowl- or saucer-like, or almost flat (platycoelous) or even quite flat (amphiplatyan) . Until after the middle Jurassic times the vertebrae of all known reptiles were amphicoelous. A ball-and-socket joint appears at that time, so far as we yet know, with the concavity in front, the ball or convexity behind. This kind of vertebra, called procoelous, gradu- ally became the prevailing one, all reptiles since early Eocene times, except the geckos among lizards, the turtles, and Sphenodon, pos- sessing them. Procoelous vertebrae appeared among the Crocodilia in early Cretaceous times (Hylaeochampsa) , amphicoelian types, however, persisting until early Eocene {Dyrosaurus) . The vertebrae of all known snakes (Fig. 73 e, r), dating from Lower Cretaceous, are procoelous, as are also the presacral vertebrae of the Pterosauria, dating possibly from early Jurassic times. The caudal vertebrae of some turtles are procoelous. Procoelous vertebrae, however, are not restricted to reptiles, some modern frogs having them. They doubt- less arose in terrrestrial crawling reptiles with a flexuous column, and it was doubtless from such ancestors that the aigialosaurs and mosasaurs, aquatic reptiles, inherited them. Possibly the ptero- dactyls acquired the ball-and-socket articulations after the attain- ment of flight. The presacral vertebrae of the sauropod, as also the cervical verte- brae of many theropod and orthopod dinosaurs, have the convexity of the centrum at the front end, just the reverse of procoelous. Such vertebrae have been called opisthocoelous, and are doubtfully known in other reptiles, save the cervicals and caudals of certain turtles. They do occur, however, in the cervical region of certain Triassic Stegocephalia, and in some modern fishes and many modern sala- manders. Most remarkable are the cervical vertebrae of the Chelonia. The earliest that we know had amphicoelous vertebrae throughout the column, but most others have an extraordinary combination of all tjT)es, amphicoelous, . procoelous, opisthocoelous, plano-concave, plano-convex, and even biconvex, otherwise known in only the first caudal vertebra of the procoelian crocodiles. Platypeltis {=Amyda) spinifera, a living river-turtle, has opisthocoelous cervical vertebrae, 94 THE OSTEOLOGY OF THE REPTILES and certain pleurodiral turtles have saddle-shaped articulations. In no other order of reptiles are the variations so great as in this. The pleurocoelous (Fig. 75) presacral vertebrae of the sauropod dinosaurs are peculiar in having large cavities in the centra, sepa- rated by a median partition, with an oval or round orifice at each side. Not only is the centrum thus light- ened in these dinosaurs, but the arch is curiously strengthened by plates and but- tresses. Certain other South African rep- tiles (Tamboeria) also have pleurocoelous vertebrae. It is supposed that this hollow- ness and lightness of the cervical and dorsal vertebrae, correlated with the other- wise solid or cancellous skeleton, served to keep the body erect in water, their natural habitat in wading or swimming. Except in the snakes and legless lizards, where but two regions are recognized, the caudal and precaudal, the spinal column of reptiles is divisible into cervical, dorsal, sacral, and caudal regions, and sometimes lumbar also, as in mammals. The cervical region is that in front of the shoulder- girdle, the dorsal that between the shoulder and hip girdles, the sacral that which sup- ports the hip girdle, and the caudal that of the tail. We may hardly venture to guess as to the primitive number of vertebrae in rep- tiles. We are quite sure that there has size. '■ been an increase in number in some, a decrease in others. The land temnospondylous amphibians that we know have but one real cervical vertebra, the so-called atlas, twenty-two to twenty-five dorsals, one or two sacrals, and a short or moderately long tail. Trimerorhachis, an aquatic Lower Permian temnospondyl, has thirty-one precaudal vertebrae and no differen- tiated sacrals. The earliest reptile that we know, Eosauravus, subaquatic in habit, had at least twenty-four or twenty-five pre- FiG. 75. Dorsal vertebra of Diplodocus (Saurischia). After Hatcher. One tenth natural THE VERTEBRAE 95 caudals, two sacrals, and a long tail. In no embolomerous amphib- ian is the number of vertebrae known. The numbers of presacral and sacral vertebrae in reptiles may be tabulated as follows: Presacral Sacral Cotylosauria 23-26 1-3 Chelonia • 18 2-3 Theromorpha 23-27 2-3 Therapsida 25-28 2-7 Nothosauria 40-42 2 Plesiosauria 40""ioS 3~4 Proganosauria 29-34 2 Ichthyosauria 40^65 o Sauranodon (Saphaeosaurus) 22-23 2 Kionocrania (Lacertilia) ' 22-74 0-2 Rhiptoglossa 16 2 Dolichosauria 29 2 Mosasauria 29-42 o Rhynchocephalia 25 2 Rhynchosauria 23-24 2 Choristodera 23-26 2 Pseudosuchia 23-26 2 Phytosauria 26 2 Eusuchia 23-24 2 Thalattosuchia 25 2 Theropoda 23 2-5 Sauropoda 26 4-5 Stegosauria 27 3-4 Trachodontia 3°-34 8-9 Iguanodontia 24-28 4-5 Ceratopsia 24 7 The earliest reptiles had functional ribs and a sacrum, and we may omit the very variable tail in our comparisons. The majority of terrestrial reptiles, it is seen, have between twenty-three and twenty- six presacral vertebrae. In all probability the earliest reptiles were lowland and crawling in habit, and it is legitimately presumable that they had not less than twenty-three nor more than twenty-six verte- brae in front of the sacrum, a single sacral, and not more than sixty caudals, the largest number found in any early reptile, or altogether between eighty and ninety vertebrae in the whole column, as against thirty-five in modern turtles and four hundred and fifty in some modern snakes. The smallest number of presacral vertebrae known in any reptile — sixteen — is recorded for Brooksia, a recent cha- meleon lizard. 96 THE OSTEOLOGY OF THE REPTH^ES Intercentra. The earliest reptiles probably all have a small or vestigial, more or less wedge-shaped bone intercalated between the adjacent ventral margins of the centra throughout the column, to which Professor Cope in 1878 gave the name intercentrum (Fig. 76 e). Intercentra had previously long been known as "interverte- bral" or " sub vertebral wedge-shaped bones," but their significance was ill understood. With the more complete ossification of the ver- tebral centra they began to disappear in the dorsal region, in early or middle Permian times, but have remained to modern times in the gecko lizards and in Sphenodon. They have persisted in nearly all reptiles in the tail as the chevrons, and more or less in the neck, hav- ing been entirely lost as simple intercentra only in the crocodiles and a few other reptiles. The intercentrum of the first vertebra has remained functional in all Amniota as the basal piece or "body" of the atlas. Intercentra are characteristic of deeply amphicoelous or noto- chordal dorsal vertebrae, that is, in the more primitive vertebrae, and never occur in procoelian, amphicoelian, or opisthocoelian reptiles. They occur in many precocious lizards throughout the neck, often in their normal places between the centra but frequently shifted for- ward on the preceding centrum, either loosely attached or coossified with an exogenous outgrowth, forming with it a functional hypa- pophysis. Where they occur between the centra they may be elon- gated into false hypapophyses. A similar condition is known in some Chelonia on the first two to four vertebrae, where they are usually paired. Double intercentra have also been observed in the anterior vertebrae of Procolophon, a cotylosaur, and in the young of certain plesiosaurs. In the Ichthyosauria, though the centra are deeply biconcave, only two to four intercentra have been observed. They have also been found in the anterior vertebrae of some plesiosaurs. It is now universally believed that the undivided or holospondylous vertebrae of reptiles were evolved from divided or temnospondylous vertebrae of the Stegocephalia. It was Cope who first recognized the identity of the parts and his views are now generally accepted, though not by all. Temnospondylous vertebrae are of two kinds, called by Cope embolomerous (Fig. 76 a-c) and rhachitomous (Fig. 76 d). The former are known in only a few amphibians, from the Mississippian, Penn- THE VERTEBRAE 97 sylvanian, and Lower Permian, but best in Cricotus (Fig. 76 a-c) from Illinois and Texas. Rhachitomous vertebrae are much more widely known in numerous forms from the Pennsylvanian and Permian of various parts of the world. An embolomerous vertebra is composed of two subequal, noto- chordal disks, the anterior one the intercentrum, or hypocentrum, bearing the exogenous chevron in the tail; the posterior one the pleurocentrum; and the arch or neurocentrum, resting upon both the intercentrum and pleurocentrum, but chiefly the latter. The artic- ular surface for the head or capitulum of the ribs is chiefly on the intercentrum; the surface for the articulation of the tubercle of the rib, on either the arch or diapophysis. A rhachitomous vertebra (Fig. 76 d) differs in that the intercen- trum or hypocentrum is more or less wedge-shaped, with its base on the ventral line, its apex not reaching the dorsal side; while the pleurocentra behind are paired, with the basal side above and their apices reaching the ventral line only narrowly or not at all. The neurocentrum, as in the embolomerous forms, is borne by all three bones, but chiefly by the pleurocentra. The head of the ribs articu- lates with the intercentrum, the tubercle with the diapophysis of the neurocentrum. The earliest known amphibian vertebrae are embolomerous ; rha- chitomous and holospondylous vertebrae appearing later, so far as our present knowledge goes. And this is one of the reasons why it would seem that the embolomerous type is the more primitive, giv- ing origin directly to the reptilian holospondylous type, as was first suggested by Cope ; that the rhachitomous type was derived from it by the loss of the upper part of the intercentrum and the lower part of the pleurocentrum and the division of the latter into two lateral parts. This reversion of the pleurocentrum to a more primitive onto- genetic condition is the chief objection to this theory, nevertheless it is the more probable. We have seen that the more primitive phylo- genetic condition of the intercentra persists longest in the neck and tail. In the caudal vertebrae of Eryops (Fig. 76 d), and probably other rhachitomous amphibians, there is an intermediate condition between the embolomerous and rhachitomous types, in which the single pleurocentrum is typically embolomerous, that is, disk-like and perforated for the notochord; while the intercentrum bearing 98 THE OSTEOLOGY OF THE REPTH^ES its exogenous chevron is typically rhachitomous, in that it is wedge- shaped. And this very probably represents the real intermediate condition between the embolomerous and holospondylous vertebrae. Evidence that reptilian vertebrae arose in this way is also seen in the dorsal vertebrae of a young Seymouria, the most amphibian-like, Fig. 76. Vertebrae: A, B, C, Cricotus (Temnospondyli), dorsal, basal caudal, and median caudal, from the side and front. D, Eryops (Temnospondyli), caudal, from the side. E, Seymouria (Cotylo- sauria), median dorsal, from the side. F, Dimetrodon (Pelycosauria), dorsal intercentrum from behind and below. G, Trimerorhachis (Temnospondyli), intercentrum from side and below. otherwise, of all known reptiles (Fig. 76 e). The intercentrum is here remarkably large for a reptile, nearly half as long as the notochordal centrum or pleurocentrum. And it is also almost the condition found in the first vertebra of primitive reptiles, the atlas (Fig. 79), as will be shown in the discussion of that bone. Additional evidence is fur- nished by the fact that while truly embolomerous vertebrae occur in fishes, in the modern Amia, for instance, real rhachitomous vertebrae THE VERTEBRAE 99 are known only among amphibians. Certain ancient fishes {Eury- cormus), it is true, with dorsal embolomerous vertebrae, have in the tail pseudo-rhachitomous vertebrae, composed of two half-disks, the one with its base below, the intercentrum, the other with it above, the undivided pleurocentrum. The evolution, then, of the holospondylous reptilian vertebra from the temnospondylous amphibian vertebra seems clear : by the simple increase in size of the notochordal centrum and the progressive de- crease of the intercentrum to a wedge-shaped, subvertebral bone, and its final loss everywhere in the column save in the atlas and chevrons of the tail; and thus the term hypocentrum becomes purely a" synonym of the earlier term intercentrum. The retrogression of the disk-like pleurocentrum into the paired pleurocentra of the Rhachitomi, is paralleled by the separation of the primitively single intercentrum into pairs, observed in Procolophon, many turtles, and some plesiosaurs. Cervical Vertebrae (Figs. 77-81) The number of vertebrae in the neck or cervical region of reptiles is not always easily determinable. In those reptiles having a sternum, the first rib attached to it definitely determines the beginning of the thorax. The distinction is almost as definite in those in which there is a change in the articulation of the rib from the centrum to the arch, as in the Sauropterygia and Archaeosauria. But the early reptiles had no sternum, and free ribs were continuous from the atlas to the sacrum without change in their mode of articulation. In such, the changes in their shapes, with other modifications, may indicate approximately the beginning of the dorsal series. Better evidence, however, is found in the position of the pectoral girdle as found in the rocks. The number is very variable, more so than that of the dorsal verte- brae. The Cotylosauria, like the Temnospondyli, have but one or two vertebrae which may properly be called cervical, since the pec- toral girdle is almost invariably found lying immediately back of the skull, the front end of the interclavicle, indeed, between the angle of the jaws. Primitive reptiles, then, like their immediate ancestors, the Stegocephalia, had practically no neck, and but little motion of the head in a lateral direction. lOO THE OSTEOLOGY OF THE REPTD^ES The Theromorpha have a longer neck, with at least six and prob- ably seven vertebrae (Fig. 77), as shown by the lengths of the ribs, by the diapophyses, and mored efinitely by the position of the scap- ula and clavicles as observed in various specimens. These numbers, six or seven, are those given for the Therapsida, as this order is im- perfectly known, and seven is the number that has remained so per- sistently in their descendants, the mammals. Modern chameleons have but five; true lizards, the Chelonia and Rhynchocephalia, eight; the monitor lizards, Crocodilia, Theropoda, Iguanodontia, and Fig. 77. Notochordal cervical vertebrae, with intercentra, of Ophiacodon, a primitive theromorph: pa, proatlas; an, arch of atlas; o, odontoid; ax, axis. Ceratopsia, nine; the Pterosauria and Phytosauria, eight or nine; the Pseudosuchia, eight to ten; the Trachodontia and Sauropoda, as many as fifteen. It must be remembered, however, that in some cases these numbers are only approximately correct, dependent upon the interpretation of what constitutes a cervical vertebra by different observers. On the other hand, among strictly amphibious or aquatic reptiles there has been an increase or decrease in the number, the latter in the tail-propelling aquatic types. The ancient proganosaurs have ten or eleven; the dolichosaur lizards, thirteen; the nothosaurs, six- teen to twenty-one or twenty- two ; the plesiosaurs, from thirteen to as many as seventy-six; probably also the increase in number among the trachodont and sauropod dinosaurs may be attributed to water THE VERTEBRAE lOI Fig. 78. Ophiacodon. Proatlas, axis, and ribs. habits. The marine crocodile, with a fin-hke tail, lost two, like the mosasaurs and aigialosaurs, having seven; Pleurosanrus probably had but five ; and the ichthyosaurs, the most specialized of all aquatic reptiles, had practically no neck. The first two or three of the cervical vertebrae are markedly differentiated in all reptiles, as in the higher animals. The first of these, the proatlas, is in- constant and vestigial, and has not been included in the numbers above given. The second, the first of our usual nomenclature, is the atlas. The third, more or less closely united with the atlas, is the axis, or epistropheus. The following cervical vertebrae, when present, are differentiated more or less from the dorsal series by their less erect or shorter spines, transverse pro- cesses, or the slenderness and mode of rib articulation. The cervicals of the later pterodactyls have additional ar- ticulations on their ventral sides, as has been described above (p. 91). Proatlas. The proatlas (Figs. 79 c, 80 D, l) is a small, more or less vesti- gial neural arch between the arch of the atlas and the occiput, usually paired. It is believed to be the arch of a vertebra formerly intercalated be- tween the atlas and the skull; by some, homologous with the so-called atlas of the Amphibia; by Baur, as the representative of a vertebra fused with the occiput in the reptiles; by others, as merely the separated spine of the atlas; by others, as the arch of a vertebra whose centrum is represented by the anterior end of the odontoid. Another theory, which has less to commend it, is that of Jaekel, namely, that the Fig. 79. Theromorph vertebrae: A, Dimetrodon, atlas and axis; B, the same atlas, from the front; C, the same proatlas, from the side; D, Sphenacodon, neurocentrum of atlas, inner side, i, intercentrum; o, pleu- rocentrum (odontoid); n, neurocen- trum (arch). I02 THE OSTEOLOGY OF THE REPTn.ES centrum of the proatlas is the so-called intercentrum of the atlas, necessitating the view that the axial intercentrum is merely an ac- cessory or provisional bone developed below the odontoid to fill out what would otherwise be an unoccupied space! Positive evidence of the proatlas has been discovered in several genera of the Cotylosauria, but no complete specimen has yet been discovered ; it is doubtless present throughout the order. It is present in many if not all forms of the Theromorpha and Therapsida. In Ophiacodon (Fig. 78) and Dimetrodon (Fig. 79) of the former group, it is a small bone on each side, articulating in front by a facet on the exoccipital, behind with an anterior zygapophysis on the arch of the atlas, both surfaces looking more or less downward. These articular surfaces appear to be present in all known genera. In the Crocodilia, occurring as far back as Jurassic times, it is a single bone in the adult, roof-shaped, arising from paired cartilages. In Iguanodon (Fig. 80 l), of the predentate dinosaurs, as also in several genera of the Sauro- poda, and the Triassic Plateosaurus of the Theropoda, it is paired, as in the modern Sphenodon (Fig. 80 D),also articulating with the atlas. A roof -shaped, unpaired proatlas has been described in Rhampho- rhynchus, a Jurassic pterosaur. It has also been reported in the cha- meleon lizards and the mammals Erinaceus and Macacus. As an abnormal element it was also found by Baur in a trionychoid turtle {Platypeltis spinifer, Fig. 32), partially fused with the occiput, and articulating with the arch of the atlas in the primitive way, from which he concluded that the real body of this vertebra had become permanently fused with the basioccipital. Probably it will be even- tually discovered in many other extinct reptiles. Atlas (Figs. 78, 79, 80). There is no vertebra in the known amphib- ians which can be homologized with the atlas of reptiles. By some the so-called atlas of the amphibians is thought to be represented by the proatlas; or it may have entirely disappeared. In the earliest reptiles (Fig. 79), the atlas is temnospondylous in structure, that is, composed of a paired arch resting in part upon a large, wedge- shaped intercentrum, in part upon a single large, embolomerous, notochordal pleurocentrum, all of them loosely connected with the axis, the arch of the atlas or neurocentrum articulating in the usual way by zygapophyses. In its highest development, in the mammals, the arch and inter- Fig 8o Atlas, axis, and ribs: A, Trinacromerum (Plesiosauria); B, Platecarpus (Mosasauria); C, 'Baptanodon (Ichthyosauria), after Gilmore; C, Cymbospondylus (Ichthyosauna), after Merriam; \i,Sphenodon (Rhynchocephalia); Y.,Nyctosaurus (Pterosauna); Y,Champsosaurus (Choristodera), after Brown; G, Gavialis (Crocodilia); H, Enaliosuchus (Crocodilia), atter Jaekel; I, J, Diplodocus (Dinosauria), after Marsh; K, Camptosaurus (Dinosauna), atter Gil- more; Uhuanodon (Dinosauria), after Dollo; M, Chrysemys (Chelonia); lcand the atlas, lost in mam- mals. In the primitive Ophiaco- don (Fig. 78) and Dimetrodon (Fig. 79) the condylar cup is formed by the intercentrum and arch, completed in the middle by the front end of the odontoid, that is, the pleurocentrum or true centrum, which has no independent motion whatever, and is not united with the axis. The arch bears a rib upon its diapophysis, and the large odontoid is perforated for the noto- chord, as in the embryonic cartilage of mammals. The pleurocen- trum or centrum, large and notochordal primitively, reaching the ventral side of the vertebra, grew progressively smaller till it finally disappeared wholly from side view in the Pterosauria (Fig. 80 e) , most Dinosauria, and the Squamata (Figs. 80 b, l). In the Rhyn- chocephalia (Fig. 80 d), Choristodera (Fig. 80 r), and Phytosauria it is yet largely visible from the side, but the first and second inter- centra have become contiguous below it. In the Crocodilia (Fig. 80 g) and Chelonia (Fig. 80 m) the pleurocentrum still retains its Fig. 81. Atlas and axis of D//)/oi/o(:«J' (Saurischia). After Holland. One fourth natural size. THE VERTEBRAE 105 primitively large size, reaching the ventral side, doubtless because of the loss, fusion, or great decrease in the size of the axial inter- centrum. In the marine crocodiles (Fig. 80 h) the pleurocentrum is more reduced. Among the Chelonia the atlas may fuse into an independent vertebra, articulating with the axis. At other times the odontoid is more or less united with the axis, with no motion be- tween it and the ring of the atlas. The axial intercentrum may be paired or single, fused with the odontoid or apparently absent. When paired they are more or less elongated, forming pseudo-hypa- pophyses, serving for the attachment of neck muscles. In the Plesiosauria (Fig. 80 a) the odontoid is to a greater or less extent visible from the side, but is much reduced. In both the plesi- osaurs and pterodactyls the atlas and axis are fused, indistinguish- ably so in the adult; both are slender-necked animals with small or vestigial cervical ribs. In the short-necked Ichthyosauria the atlas and axis show a progressive fusion from the earlier forms (Fig. 80 c), in which a complete disk represents the atlas, to those in which the bodies of atlas and axis are imperfectly or indistinguishably fused (Fig. 80 c). Axis (Figs. 78-81). The axis differs from the following vertebrae in its broader and stouter spine, its usually more elongated centrum, and in its relations with the atlas. Its prezygapophyses are small and turned outward at the base of the spine. In the Cotylosauria and Theromorpha the front end of its centrum is deeply concave, the persistent notochord continuous through the notochordal odontoid. In procoelian, opisthocoelian, and platycoelian vertebrae the front end is flattened for sutural or ligamentous union with the odontoid. Its centrum is usually longer and usually bears a rib, though in the modern cocodiles (Fig. 80 g) and the dinosaurs (Fig. 81) its rib has migrated forward. The axial intercentrum is nearly always present, primitively larger than the following intercentra, and is intercalated between the bodies of the atlas and axis in the usual way. Among the crocodiles (Fig. 80 G, h), anomodonts, and some lizards it has disappeared or is represented by the merest vestige. It is small in the dinosaurs and chelonians. io6 THE OSTEOLOGY OF THE REPTILES Dorsal Vertebrae (Fig. 82) The smallest number of dorsal vertebrae known in reptiles is that of the Chelonia, invariably ten. In the chameleon lizards there are as few as eleven; in the pterodactyls about twelve. In the lat- FiG. 82. Ophiacodon mirus Marsh (Theromorpha). Seventh to twentieth vertebrae, from the side. One half natural size. ter order three or more of the anterior ones may be more or less immovably united for the support of the pectoral arch, forming the notarium. In the Chelonia they are fused throughout in the cara- pace. The largest number of dorsal vertebrae in reptiles having a sacrum, forty-one or forty-two, is found in Pleurosaurus, a slender, aquatic Jurassic reptile. About thirty is the usual number in the plesiosaurs. In terrestrial reptiles the number never exceeds twenty- two or twenty-three and is usually about eighteen. In reptiles lack- THE VERTEBRAE 107 ing a sacrum the number between the girdles may be much greater, thirty-five in the mosasaurs, and as many as seventy-four in some terrestrial, legless lizards. As has been said, there is not often the same distinction between thoracic and lumbar vertebrae that there is in mammals. There are, however, even in the Coty- losauria, examples (Fig. 164) of true lumbar vertebrae, that is, vertebrae in front of the sacrum not bearing ribs of any kind. Sacral Vertebrae (Fig. 83) The sacrum of land vertebrates is composed of from one to four or five vertebrae, either fused to- gether or separate, bearing short, stout ribs for the support of the pelvis. Rarely among the am- phibians are there more than one ; certain temnospondyls and mod- ern urodeles^ are known to have two. It is quite certain, however, that reptiles began their career with but a single rib-bearing sacral vertebra, inasmuch as Seymouria of the Cotylosauria is known to have no more (Fig. i). A second vertebra (Fig. 84), however, was soon added from the basal caudal series by the enlargement of the ribs to come in contact with the ilium on each side. And this num- ^ [Also some frogs. — Ed.] sri Fig. 83. Sacrum and caudal vertebrae of Macrochelys (Chelonia), seen from below. THE VERTEBRAE I 09 ber, two, has remained persistent in most reptiles and even most mammals to the present time. A third vertebra, from the cau- dal series, was early united in many Theromorpha and the latest Cotylosauria. Still another, and possibly two, were joined in the Dinocephalia and Anomodontia. The Plesiosauria, purely aquatic animals with propelling legs, have three or four sacrals. From one to three additional vertebrae have been fused with the sacrum in front in the Pterosauria (Fig. 118 d), and some Dinosauria, but they are not true sacral vertebrae. Not only may the sacral vertebrae be closely fused, but their arches and spines may become almost indistinguishably united. Usually, however, the zygapophyses remain visible and are some- times functional. In Iguana, even the zygosphene and zygantrum are present between the two sacrals. The sacrum is lost, not only in the snakes and legless lizards, but also in the mosasaurs and late ichthyosaurs, where hind legs have lost locomotive functions. Caudal Vertebrae (Figs. 76, 83-85) The tail of the earliest known reptile, from the Coal Measures of Ohio (Fig. 84), was long and slender. The Cotylosauria had, for the most part, only a moderately long tail, with not more than sixty vertebrae. The length of the tail, however, depends so much upon habits that it may be extremely variable even in members of the same order. Stumpy- tailed lizards (Trachysaurus) , for instance, have practically no tail, while other skinks have a very long and slender one. Invariably it is long in tail-propelling, swimming rep- tiles; such reptiles move sinuously through the water, preventing much use of the legs as propelling organs. Those with propelling legs, on the other hand, have a broader and flatter body and short tail, of use only as a steering organ. However, sauropod dinosaurs, though supposed to be exclusively water animals, have a very long and slender tail, more or less whiplash-like at the end. As a rule, swift-moving, crawling reptiles have a long and slender tail, while short-tailed reptiles are invariably slow in their movements upon land. The spines of the caudal vertebrae in land reptiles are seldom long; certain chameleon lizards and the basilisc lizard are exceptions ; the no THE OSTEOLOGY OF THE REPTILES vertebrae distally are more slender and the zygapophyses weak. One of the first indications of swimming habits, at least in those rep- tiles with long tails, is the widening and elongation of the caudal spines throughout, [less] at first [anteriorly] and then more distally until a terminal fin is developed with the end of the column in the lower lobe (Fig. 85). The basal caudal vertebrae, from one to six in number, those with- out chevrons but with ribs, are called pygals. They have the ordinary intercentra in those reptiles in which they [intercentra] are persistent throughout; sometimes with rudimentary chevron-like processes > Fig. 85. Tail, scapula {sc), and coracoid {cor) of Geosaurus (Thalattosuchia). After Fraas. The cloaca in the living animal occupies the space below them. The number is more or less reduced in modern reptiles; the Crocodilia have but one, most lizards, two. There is an unossified vertical septum through each caudal cen- trum in many lizards, the Proganosauria Saphaeosaurus and Spheno- don, along which it readily breaks, causing the easy loss of the distal part. This septum was once supposed to represent the division between the primitive component parts of the centrum. It is now thought to be an acquired character, not occurring in the early embryo. Chevrons, or haemapophyses (Fig. 84) for the protection of the vessels on the under side of the tail, really outgrowths from the inter- centra (Fig. 76 d), occur below and between the caudal centra in THE VERTEBRAE III most reptiles. Usually single and Y-shaped — whence the name chevron — they may be paired in the Plesiosauria and Ichthyo- sauria. The medial ones of the Sauropoda have two Y-shaped, broadly divergent branches united at their base. More or less ves- tigial in the turtles, they are absent in snakes, replaced by a pair of vertical hypapophysial-like processes (lymphapophyses) . Chevrons articulate as a rule intercentrally, but sometimes ex- clusively to the distal part of the preceding centrum with which they may be coossified, as in some mosasaurs and lizards, especially those in which the cervical intercentra have migrated forward to articulate or be coossified with the median hypapophysis. Chevrons primi- tively, as in the temnospondyl amphibians, have their branches united above in an intercentrum-like bone, a condition found in the proximal chevrons of Sphenodon. In later reptiles, for the most part, the two branches articulate separately. At the tip of the tail they are vestigial or absent. CHAPTER III THE RIBS AND STERNUM ^ The ribs of reptiles, like those of the amphibians, primitively articu- late with all vertebrae, at least as far back as the middle of the tail. The first to become fixed or closely united with the vertebrae, after the sacral, were the caudal, next the lumbar, and last of all the cervi- FiG. 86. Vertebrae and ribs: A, Clidastes (Mosasauria), posterior cervical vertebra, from behind; B, Cymbospondylus (Ichthyosauria), anterior dorsal vertebra, from the side, after Merriam; C, Ichthyosaurus (Ichthyosauria), middle dorsal vertebra, from the side (after Broili); D, Bimetrodon (Theromorpha), anterior dorsal rib; E, Diadectes (Cotylosauria), anterior dorsal rib. cal. The dorsal ribs are free, except in the Chelonia, some Ptero- sauria, and some armoured dinosaurs. The ribs of the Temnospondyli (Fig. 86) articulate with intercen- trum and arch, usually without differentiation of the articular sur- faces. And this was the original mode among reptiles. With the diminution in size of the intercentrum, the head, or capitulum, joins the adjacent ends of two centra across the intervertebral cartilage, the articular surface, however, continuous to the tubercle, which articulates with the end of the diapophysis. This continuous articu- lation from the intercentral space to the arch was the almost invari- 1 [For the morphology and variation of the ribs, in connection with the segmentation of the vertebrate body, see Biitschli, 1921, Vorlesungen iiber Vergleich Anai.; Kingsley, Compar.-Anat. Cert. — Ed.] THE RIBS AND STERNUM 113 able rule among the Cotylosauria (Fig. 86 e) and occurs occasion- ally in the Theromorpha and even in the recent Sphenodon. Such ribs, though usually called single-headed, are not really so since both capitulum and tuberculum are present, though connected. A better name for them is holocephalous. Soon, however, the articular sur- faces become restricted to the head and tubercle, that is, there is an emargination of the articular surface between them, the so-called neck, and the rib is truly double-headed, or dichocephalous (Fig. 86 d). Strictly speaking, single-headed ribs are those which have lost either the head or the tubercle. This early mode of articulation of double-headed ribs, the head across the intervertebral cartilage, the tubercle to the diapophysis of the arch, has continued through those reptiles [see above] and through the mam- mals. And this is essentially the mode of rib artic- ulation in the Diaptosauria. In many reptiles, however, perhaps in part because of the closer articulation of the vertebrae, the head has migrated backward to articulate with a facet or process on the anterior end of the cen- trum, the parapophysis, and there it has remained in the cervical vertebrae of most reptiles, and in the dorsal vertebrae of the Squamata and their fig. 87. Dorsal vene- allies. In the dorsal region there have been many ^{^^ Thaiattosaurus. " _ -^ (After Mernam.) modifications. In those reptiles which are here classed under the Parapsida, that is, the Ichthyosauria, Progano- sauria, Pleurosaurus , and Squamata (Figs. 80 n, 73 c-f), the tuber- cular part of the articulation has been largely or wholly lost, and the single-headed ribs remained attached more or less wholly to the centrum. In the later Ichthyosauria and later Plesiosauria, it is true,, the ribs are often dichocephalous (Fig. 86 c), both articulations unit- ing with the centrum. There is, however, in such forms no real tubercle. The ribs of Araeoscelis, a Lower Permian reptile, are single-headed and central in the cervical region, imperfectly double- headed in the dorsal region. So also, the ribs are described as single-headed in Pleurosaurus, Protorosaurus, the Proganosauria^ and Thalattosauria (Fig. 87), probably all with a single, typical,, upper temporal opening. The dorsal ribs (Figs. 80 o, 89) of the 114 THE OSTEOLOGY OF THE REPTILES Sauropterygia articulate with the diapophysis (d) exclusively by a single head, the cervical ribs (Fig. 89 r) exclusively with the cen- trum, usually also by a single head. The dorsal ribs of the Archosauria, that is, the Pseudosuchia, Parasuchia (Fig. 88), Crocodilia (Fig. 90), Dinosauria (Fig. 80 p), and Pterosauria, are double-headed, the anterior ones at least, but both articulations are with the arch or diapophysis. And this mode of articulation would seem to exclude their immediate ancestral re- lationship to the birds, in which the head of the ribs articulates with the centrum throughout. Atlantal ribs, present in all early reptiles, have been lost in modern ones, except the Croc- odilia, where they are attached exclusively to the intercentrum, in the ancient Metriorhynchus pz. to both arch and intercentrum. In the Dino- sauria, some of them at least, the first inter- centrum bears a small rib (Fig. 81). Axial ribs are more often present, but are lost in not a few reptiles, particularly the Ptero- sauria (Fig. 80 e) and Chelonia (Fig. 80 m). In early crocodiles the axial rib articulated with diapophysis and parapophysis ; in later croco- diles the diapophysial articulation is lost, though a vestige often remains, and the single- headed rib has migrated forward on the odon- toid. The dorsal ribs of the Eunotosauria and all Chelonia ^ have expanded to meet or fuse with each other, forming more or less of a carapace (Fig. 91). Peculiarly expanded and overlapping ribs in the posterior dorsal series occur in some of the Theriodontia. In Cynognathus the thirteenth to the seventeenth ribs shorten rapidly and project widely with a remark- able expansion near the proximal end, which overlaps the succeed- ing rib in a concavity on its anterior border. In the lumbar series (Fig. 92) they lose the free portion of the shaft, ending in wide, 1 [This leaves out of account the costal plates which enter into the formation of the carapace. See Gadow, " Reptiles and Amphibia," Cambridge Nat. Hist.; Procter, 1923, Proc. Zool. Soc. — Ed.] Fig. 88. Dorsal verte- bra of phytosaur: az, anterior zygapophysis; pz, posterior zygapoph- ysis; d, c, articulations of rib. THE RIBS AND STERNUM 115 interlocking ends. Such ribs gave great strength to the lumbar region, and are perhaps analogous to the greatly expanded trans- verse processes of the crocodiles. The first four to six ribs of the Cotylosauria, and rarely also of the Theromorpha, are progressively flattened and dilated, sometimes, as Fig. 89. Plesiosaur vertebrae: Polycotylus. Cervical vertebrae from the side and behind, and dorsal vertebrae from in front: az, anterior zygapophysis; pz, posterior zygapophysis; r, r, r, cervical ribs; d, articulation of dorsal rib. Fig. 90. Vertebrae of gavial from the side (cervical), and from ,in front (dorsal): az, an- terior zygapophysis; pz, posterior zygapophysis; d, diapophysis; r, cervical rib; c, articu- lation for head; /, for tubercle of dorsal rib. in Diadectes and Limnoscelis (Fig. 95), remarkably so, for the direct support of the short and broad scapula. Not only are these ribs so remarkably dilated in Diadectes, but, continuing the expansion back- ward, there are three flat dermal plates overlying the following ribs. The cervical ribs of the Crocodilia (Fig. 90) and Dinosauria are ii6 THE OSTEOLOGY OF THE REPTILES short and more or less "hatchet-shaped," either fused or more or less closely united to arch and centrum. The free cervical ribs of lizards and mosasaurs begin upon the axis. Only vestiges of ribs re- main in the pterodactyls and turtles; they are nearly always fused. Three or four of the single-headed ribs of the Sauropterygia articu- lating with both centrum and arch are known as pectoral ribs. Fig. 91. Inner side of carapace of Stegochelys (Chelonia). After Jaekel. About one sixth natural size. In certain early cotylosaurs (Figs. 128, 164), four or five verte- brae in front of the sacrum bear no ribs of any kind; in others, Seymouria (Fig. i) for instance, free ribs continue to the sacrum. Many other reptiles have a variable number of the presacral ribs coossified with the centrum, or centrum and arch, so-called trans- verse processes. Sacral ribs. True sacral ribs often retain their primitive attach- ments (Fig. 93), the capitular part articulating more or less inter- centrally with the preceding vertebra, the tubercular part with the Fig. 92. Vertebrae: Cynognathus (Cynodontia), posterior dorsal vertebrae, from above. After Seeley. One half natural size. Fig. 93. Nothodon lentus Marsh (Cotylosauria). Sacral vertebra, from in front. Natural size. 117 Il8 THE OSTEOLOGY OF THE REPTILES arch. Real sacral ribs have been in all cases added from behind, since the caudal ribs have retained more or less in all animals their original attachments, while the lumbar or posterior dorsal ribs have often undergone changes. It is improbable that there has ever been any "migration" of the sacral vertebrae; that is, the first true sacral vertebrae of all animals ^ are identical with the single sacral vertebra of Seymouria. Additional sacral ribs have been due to the gradual elongation of the basal caudal ribs and their articulation with the ilium, as shown in the tail of the alligator snapper turtle. The second and third pairs were added very early in the history of reptiles. Remarkably, in the Lacertilia evidences of sacral ribs have not been found, the ilia being supported by transverse processes, out- growths of the centra (Moodie). Not only are the two sacral ribs of the Crocodilia (Fig. 121) primitive in their attachments, but the centra also have retained their primitively amphicoelous structure. On the other hand, additional vertebrae have joined the sacrum in front, as many as three in some reptiles, but in such cases the ribs have not reverted to their primitive attachments if modified, though they may extend to the ilium. In the Ceratopsia three lumbar verte- brae have been fused with the sacrum, and their diapophyses with the ilium. Indeed in some instances {Monoclonius for instance) a vestigial free rib may remain on the first, so-called sacral vertebra. In the later pterodactyls there are several such sacro-lumbar verte- brae, and also in the Anomodontia (Fig. 119 c), groups that have been accredited with from seven to ten sacral vertebrae. In all these the ilium is greatly prolonged in front of the acetabulum. The pro- jections from the vertebrae have often been called indiscriminately transverse processes, but that term is true only of the sacro-lumbars. Whether or not the dinosaurs acquired the third or the fourth sacral vertebrae after their divergence from their immediate ances- tral stock is perhaps a question. But two are accredited to Hallopus, a primitive type. There can be no question, however, but that the dinosaurs, both the Saurischia and the Ornithischia, descended from reptiles with but two sacral vertebrae, since the allied Crocodilia 1 [But few contemporary morphologists would endorse this view. It certainly does not apply to the Amphibia and is very doubtful for the Chelonia. — Ed.] THE RIBS AND STERNUM 1 19 and Pseudosuchia have but that number, and since doubtless the Diapsida began with but two. Many temnospondylous amphibians have on the hind border of the dorsal ribs an angular uncinate process, like that so characteristic of birds. Such ossifications have never been observed among the older reptiles. They occur in the Jurassic Homoeosaurus and the modern Sphenodon of the Rhynchocephalia ; imperfectly ossified proc- esses also occur in the Crocodilia. In many other reptiles they doubtless remained unossified, and in much probability will yet be found in other reptiles as fused processes or separate ossifications. Ventral or Abdominal Ribs Many, perhaps most, of the Stegocephalia, especially the Branchi- osauria, had on the under side of the body an armature of bony rods, or plates, of various forms, called by Baur gastralia, by Gegenbaur the parasternum, and ordinarily known as ventral or abdominal ribs. They are arranged in a V-shaped pattern with the apex in front, and may sheath the whole under side of the body, extending on the limbs. In some cases, exterior to these a distinct armor of dermal plates has been observed. Among the temnospondylous amphibians they occur more rarely. In Cricotus, an ambolomerous type, they sheath closely the under side of the abdomen, each composed of an unpaired median piece, and numerous lateral ones. Among the Rhachitomi they have been observed in Archegosaurus in the shape of slender rods. They are unknown in the Stereospondyli. Ossified parasternal ribs, in greater or lesser numbers and complex- ity, occur in some members of every chief group of reptiles, though far from constantly in each group. Among the Cotylosauria they are known in three families, the Sauravidae, Captorhinidae, and Procolophonidae ; they are certainly absent in some, if not many, of the known genera of the order. They have been observed in only a few of the Theromorpha, and are certainly absent in some of the families. They are known in Galechirus of the Dromasauria; among the Proganosauria; Protorosaurus, Kadaliosaurus, Pleurosaurus, and Saphaeosaurus of the subclass here called the Parapsida; in Aigialo- saurus and some recent lizards ; in the Choristodera, Homoeosaurus, Hyperadapedon, and Sphenodon of the Rhynchocephalia; in the Pseudosuchia (Scleromochlus) , Phytosauria, Pterosauria, Crocodilia, I20 THE OSTEOLOGY OF THE REPTILES and Theropoda, of the Archosauria; in the Sauropterygia, Ichthyo- sauria, and Chelonia. They are thus, it is seen, characteristic of the Reptilia as a whole, though frequently absent in formS related to those which possess them. No explanation has yet been given of their inconstancy. Fig. 94. Sternum and parasternum : A, Theropleura (Theromorpha). About one half natural size. B, Sphenodon (Rhynchocephalia). Three halves natural size. C, Champsosaurus (Choristodera). One half natural size. D, Lystrosaurus (Anomodontia). One half natural size. E, Nyctosaurus (Pterosauria). Nearly one half natural size. The most primitive parasternals known among reptiles are those of the Cotylosauria and Theromorpha (Fig. 94 a), slender, bony rods composed of several pieces on each side, meeting in a median, unpaired, V-shaped piece. They sheath closely the whole under side of the abdomen from the coracoids to the pelvis, twelve to fifteen times as numerous as the overlying vertebrae, and more than two THE RIBS AND STERNUM 121 hundred in number. Anteriorly they are covered or underlaid by the distal end of the interclavicle. In the modern Sphenodon (Fig. 94 b) there are about twenty-four such rods, each composed of a median, unpaired piece and a lateral splint, every alternate one of the first eleven attached to the end of a dorsal rib. In the Phytosauria they are similar, nineteen or twenty in number. The Choristodera (Fig. 94 c), Plesiosauria, and Ichthyosauria, aquatic reptiles, have larger and stouter parasternals, consisting of a straight or slightly curved median piece, and three or four lateral splints on each side. The Crocodilia (Fig. 121c) have seven or eight pairs, each composed of two slender rods on each side (not joined in the middle) . In earlier members of the order there was a larger number, and some of them, at least, were composed of the usual V-shaped median piece and a lateral splint on each side. The last pair is enclosed in a dense sheath of fascia continuous with the ends of the so-called pubes. Among the modern lizards abdominal ribs are often present, espe- cially in the chameleons, each composed of one broadly V-shaped piece, either connected with the dorsal ribs or free, sometimes paired and usually cartilaginous. Only in a few forms have they been ob- served as slender ossifications. Clearly endoskeletal in origin, they have been supposed to be not true parasternals, and have been called distinctively abdominal ribs. That they are not continuations of the dorsal ribs seems evident from the fact that they are some- times much more numerous than the overlying vertebrae. These lacertilian ribs are located, it is said, in the rectus abdominis muscles. The parasternals of Sphenodon are in the superficial part of the rectus and external oblique muscles, and are united by a dense sheath of fascia. The later pterodactyls have five or six flattened parasternals, the anterior ones broadly V-shaped, the posterior ones paired. In the earlier pterodactyls the unpaired median piece has one or two lateral splints. They have also been observed in various genera of theropod dinosaurs. In the Chelonia they are represented by the posterior three pairs of plastral elements, as usually accepted, but it is possi- ble that these are really dermal elements and [not] true parasternals. The extinct Saphaeosaurus (Sauranodon) had a full armature of ossi- fied parasternals similar to those of Sphenodon. Parasternal ribs have long been considered to be of dermal origin, 122 THE OSTEOLOGY OF THE REPTH^ES skin bones which have sunk into the muscles. The abdominal ribs of the lizards are undoubtedly true endoskeletal bones, and Fiirbringer has suggested that in these animals they are new growths, supplant- ing the dermal parasternals which have long since disappeared, and that they represent the ends of the dorsal ribs, or outgrowths from them. That they and the sternum to which they are supposed to have given origin are really the ends of true ribs is improbable, since no other tetrapods are known in which the dorsal ribs meet on the under side of the body, or even approach each other. It would seem more reasonable that the abdominal ribs of all reptiles are of paren- chymatous or cartilaginous origin, and that the anterior ones fused to form the sternum.^ The so-called sternum of the modern amphib- ians (there was no sternum of any kind in the Stegocephalia) is an ossification of the myocomata, not derived from the dorsal ribs, and is thought not to be homologous with the sternum of reptiles. Sternum The earliest recorded occurrence of a sternum or breastbone in rep- tiles is in the Anomodontia (Fig. 94 d) where, according to Broom, it is generally present and ossified. It is figured in Keirognathus as a small, subquadrilateral bone lying over the posterior extremities of the coracoids and distal end of the interclavicle. Only rarely does it occur as an ossification in other reptiles, the best examples of which are the Pterosauria (Fig. 94 e) where, as a broad, shallow concave bone, it covers the whole under side of the thoracic region with a stout manubrium-like process in front, but without a true keel. On either side of the base of the median anterior protuberance it gives articulation to the elongate coracoid. Its lateral margins have articular facets for four or five, sometimes ossified, sternal ribs. Posteriorly in the middle it is contiguous with the parasternal ribs. In many reptiles the sternum is wholly absent, even as a cartilagi- nous element. There was no space, even for a rudimentary one, in the Ichthyosauria and Sauropterygia back of the united coracoids and in front of the parasternals. It has been thought that its absence in these orders is due to its loss; it is more probable that their an- 1 [For further support of this view, see C. L. Camp, 1923, Bulletin, Amer. Mus. Nat. Hist., vol. XLViii, pp. 389-393-] THE RIBS AND STERNUM 123 cestors never possessed it. There could have been no sternum, even a small cartilaginous one, among the Cotylosauria and Theromorpha^ since in several instances in both these orders the parasternals have been found sheathing the whole abdomen from the coracoids to the pelvis. Probably this was the condition in all the early reptiles; probably also the condition in the early Rhynchocephalia, since Rhynchosaurus had parasternal ribs reaching nearly to the coracoids^ leaving little or no space for a sternum. In the modern Lacertilia (Fig. 99) and in Sphenodon there is a more or less calcified, thin, rhomboidal plate articulating on each side with the coracoid in front and ending in a single or paired continu- ation, the xiphisternum. It gives articulation on each side to from one to four or five, exceptionally more, sternal ribs, also cartilagi- nous. Rarely, no ribs articulate with the sternum, and the sternum itself may be represented by a pair of small cartilaginous plates or may be wholly absent. Sometimes it has single or paired perfora- tions. Similar cartilaginous sterna have been found in the Doli- chosauria and Mosasauria, and doubtless it was present in most of the extinct members of the order. In the Chelonia there is no trace of a sternum. In the living Crocodilia the sternum is a small, oval, cartilaginous plate, contin- ued into a pair of cartilaginous xiphisternal rods to which six or eight dorsal ribs are attached by the intervention of cartilaginous sternal ribs. Nothing is known of the sternum in extinct crocodiles or phytosaurs; probably it was present as a cartilage. The sternum has been found in not a few dinosaurs. Among the Sauropoda it has been recognized in a pair of oval, ossified plates. CHAPTER IV THE PECTORAL AND PELVIC GIRDLES The Pectoral or Shoulder Girdle (Figs. 95-113) Those bones which form the framework for the support of the an- terior extremities in vertebrate animals are collectively called the ^Cledkrumx cbvicue ^Zetacorcicoid irrf-eiclavLcle S u/pr 0/ cor coco id T. Fig. 95. Biadectes (Cotylosauria). Pectoral girdle, right side. pectoral or shoulder girdle. In our own skeleton, as in that of most mammals, there are but two on each side, the scapula, or shoulder- blade, and the clavicle, or collar-bone. A third bone, or possibly two, on each side, are represented in most mammals by mere vestiges, which early unite with the scapula to form the coracoid process. In 124 THE PECTORAL AND PELVIC GIRDLES 125 the lowest living mammals, of which Ornithorhynchus and Echidna are the only examples, there are in addition to the clavicles three well-developed bones on each side, the scapula and two bones articu- FiG. 96. Pectoral girdles: A, Cacops (Temnospondyli), from above. One half natural size. B, ^(jyOTowr/a (Cotylosauria), from below. One half natural size. C, Diadectes (?), from below. One half natural size. D, Varanops (Theromorpha), from above. One half natural size. lating with it at its lower end, the anterior of which, originally named epicoracoid by Cuvier, is generally known as the procoracoid; the posterior one helping to form the articulation for the arm bone, known as the true coracoid. The homologies of these, or rather of 126 THE OSTEOLOGY OF THE REPTILES the epicoracoid, are yet doubtful, and will be discussed later. There is also a median, unpaired bone in these mammals, the inter clavicle, unknown in other mammals. Primitively (Figs. 95, 96), that is, in the oldest known reptiles, the pectoral girdle is composed of eleven separate and distinct bones, at least in early life: the median interclavicle and a clavicle and clei- thrum on each side, all five of dermal origin, together composing the secondary or clavicular girdle; and three bones on each side, the scapula and two coracoids,^ all of endoskeletal origin, composing the primary or scapular girdle. The cleithrum (Fig. 95), a relic from the fishes, disappeared in Triassic times, after long existence as a mere vestige. The posterior of the two coracoids also disappeared in late Triassic times, in rep- tiles at least, though a vestige may possibly be present in our own shoulder girdle. The scapula, clavicles, and anterior one of the two coracoids, the so-called procoracoid, are still present in most reptiles; in snakes only are they wholly absent, though much reduced and non-functional in some lizards. Clavicular Girdle The clavicular girdle is variable among the temnospondyl am- phibians, dependent, as in reptiles and higher vertebrates, upon the habits of the animals. In the aquatic types of all Stegocephalia the clavicles and interclavicles are rugose [on the ventral side], heavy and broad, forming more or less of a pectoral buckler — a peculiar adaptation to their water habits, perhaps in a measure analogous to the plastron of the turtles or the extraordinary development of the coracoids in the plesiosaurs. In such forms also, the cleithrum is re- duced. The girdle in the adult land forms, of which Eryops (Fig. 108) and Cacops (Fig. 96 a) may be taken as types, is almost indistinguish- able from that of their contemporary cotylosaurs, except that the cleithrum is larger and the interclavicle less elongate. They are smooth throughout in Cacops, the more terrestrial form. Cleithrum. The cleithrum so generally characteristic of the Stego- cephalia (Figs. 96 A, 108) was doubtfully ever functional in reptiles, 1 [According to Watson, the coracoid originally was a single piece which never be- came subdivided in the amphibians, cotylosaurs, or ordinary reptiles, the subdivision occurring only in the Theromorpha, Therapsida, and mammals. — Ed.] THE PECTORAL AND PELVIC GIRDLES 127 whatever may have been its function in the amphibians ; and it was never large. It is known only in certain members of the Cotylo- sauria, Theromorpha, Dinocephalia, and Anomodontia, best devel- oped perhaps of all in Diadectes and its alHes of the Cotylosauria (Fig. 95), where its somewhat spatulate upper extremity partly overlies the front, upper border of the scapula, articulating below with the stem of the clavicle. It is vestigial in some forms and seems to be quite wanting in others. Among the Theromorpha it has been observed in Edaphosaurus (Fig. 98) as a rod-like bone at the upper Fig. 97. Clavicles and interclavicle of Ophiacodon (Theromorpha). front border of the scapula. In the Anomodontia and Dinocephalia (Fig. 107 d) it is a feeble splint, clearly a vestige. There have been several theories as to what has become of it, but none is demon- strable. Its vestigial condition in various cotylosaurs indicates its entire disappearance. Clavicles. Clavicles are usually present in reptiles. They are ab- sent in the Crocodilia, serpents, Mosasauria, and some Sauria; more or less vestigial in some lizards ; and either absent or vestigial in the Pterosauria and Dinosauria. In crawling reptiles (Figs. 96 B-99) they are usually curved bones, with a dilated mesial extremity, articulating on the ventral side of 128 THE OSTEOLOGY OF THE REPTILES the end of the interclavicle ; and a more or less slender stem which articulates with the front border of the scapula, or its acromion when present, and also with the lower end of the cleithrum when that bone is present. In modern lizards the clavicles articulate usually with the front border of the cartilaginous suprascapula (Fig. 99). The inner end in some lizards is broad and perforated (Fig. 99 c). Fig. 98. Edaphosaurus novomexicanus (Theromorpha). Pectoral girdle, two fifths natural size: c, cleithrum; cl, clavicle; sc, scapula. The clavicles of the Chelonia are known as the epiplastra of the plastron (Fig. 100). In the Nothosauria (Fig. loi) they are normal but very stout, firmly united with the scapula and with each other. The clavicles of the Plesiosauria (Fig. 102) are remarkable in some respects. Usually they are a pair of thin, triangular bones, lying upon the inner or visceral surface of the proscapular process of the scapula (corresponding to an acromion), of the interclavicle and sometimes also of an anterior process from the coracoid ; they may be absent. In the Ichthyosauria (Fig. 103), they are slender, some- times coossified with each other; nor are they expanded mesially in either the Phytosauria or Choristodera (Fig. 104), and all water rep- tiles. Doubtful vestiges of the clavicles have been reported in the pterodactyls. Fig. 99. Pectoral girdles (Lacertilia): A, B, Iguana; C, Zonosaurus (after Siebenrock). Natural size. Fig. 100. Primitive chelonian pectoral girdle: Stegochelys. After Jaekel. 129 Fig. ioi. Pectoral girdle of Nothosaurus (Nothosauria), from photograph by E. Fraas: id, interclavicle; cl, clavicle; sc, scapula; cor, coracoid. Fig. 102. Pectoral girdle of Trinacromerum (Plesiosauria), from above: ic, interclavicle; cl, clavicle; sc, scapula; c, coracoid. THE PECTORAL AND PELVIC GIRDLES 131 Fig. 103. Pectoral girdle of Ichthyosaur, Baptanoden {Ophthalmosaurus). After Gilmore. Fig. 104. Pectoral girdle of Champsosaurus (Choristodera). After Brown. Interclavicle. The interclavicle in the earliest-known reptiles (Fig. 96 B, c, d) is an elongate bone with a dilated but not T-shaped an- terior extremity. The stem underlies the approxi- mated mesial borders of the coracoids, usually ex- tending beyond them. In a specimen referred to Pantylus (Fig. 105), a primitive cotylosaur, the interclavicle is forked in front and somewhat fan- shaped behind, shaped very much like that of the monotremes. In the later cotylosaurs the front end is more dilated, as usual with all later reptiles. In the known forms of the Therapsida (Fig. 107 c) the shape is usually like that of the Theromorpha and Cotylosauria. It is very short and fan-shaped in Fi«- i°5. Pantylus . -^ (Cotylosauria): inter- Lystrosaurus of the Anomodontia (Fig. 94 d), where clavicle (/^«afO(fo« (Theromorpha). Pelvis. One half natural size. A, from the side; B, from above, pu, pubis; /'/, ilium; is, \ schium. 144 THE PECTORAL AND PELVIC GIRDLES 145 A small opening soon appeared where the four bones meet below in the Theromorpha (Figs. 114 c, 117), and increased in size, till, in Fig. 118. Pelves and sacrum: A, Varanus (Lacertilia), from the right. ^, Erythrosuchus (Parasuchia), from the right. After Broom. One tenth natural size. C, Rutiodon (Phyto- sauria), from below. After McGregor. One eighth natural size. D, Nyctosaurus (Ptero- sauria), sacrum and right innominate bone from within; D , anterior parasternal ribs of same ; D , prepubis of the same from below. Fig. 119. Pelves (Therapsida) : A, Galechirus (Dromasauria). After Broom. Nearly natural size. B, Diademodon (Cynodontia). After Broom. About one half natural size. C, Galepus (Dromasauria). After Broom. Nearly natural size. most reptiles, since Triassic times at least, this pubo-ischiatic open- ing extended on each side nearly to the acetabulum, leaving only a narrow connection between the pubis and ischium (Fig. 118). Later, 146 THE OSTEOLOGY OF THE REPTILES the symphysial ends of the pubis and ischium became connected in many by Hgaments, or cartilage (Fig. 120), and later in some by Fig. 1 20. Pelvis and sacrum. A, Iguana (Lacertilia), pelvis from below; B, sacrum from below. About natural size. C, Dicynodon (Anomodontia), pelvis, from above and from the side. After Broili. Nearly one half natural size. bone, producing a false obturator or thyroid vacuity on each side. A foramen or vacuity homologous with that in mammals, the so-called THE PECTORAL AND PELVIC GIRDLES 147 obturator foramen, that is between the pubis and ischium with which the real obturator or pubic foramen is merged, occurs in the Therio- dontia (Fig. 119), Anomodontia, and later pterodactyls (Fig. 118 d). The formation of a thyroid vacuity in the theriodonts may be due to the gradual increase in size of the pubic or true obturator foramen and its recession backward, as in the Dromasauria, till it finally lies Fig. 121. Pelvic girdle and sternum: Alligator (Crocodilia). A, pelvic girdle, from the right; B, the same, from above, showing sacrum; C, the same, from below, with parasternals; D, sternum and interclavicle. One half natural size. between the two bones, the pelvis still retaining its primitive plate- like character with only a small median pubo-ischiatic vacuity. But this will not explain the thyroid vacuity in Pteranodon and Nycto- saurus of the Pterosauria (Fig. 118), since it is inconceivable that these reptiles had an unbroken descent from forms without a median vacuity. In no reptiles is the pelvis more aberrant than in the Crocodilia (Fig. 121). So characteristic is its structure that it at once distin- 148 THE OSTEOLOGY OF THE REPTILES guishes the order from all others. The ilium is a strong bone firmly united with the two pairs of stout sacral ribs, of which the posterior is the larger. Below, the ilium articulates with the ischium only, to form the acetabulum. In front of the acetabulum it is produced for- ward to join ligamentously with an anterior process of the ischium, enclosing between them a foramen of considerable size for the passage of the obturator nerve. The ischium is a rather long bone, with a thin, spatulate extremity which joins its mate in a median symphysis. Its anterior process, which may be in part the real pubis, articulates in front with the so-called pubis. This bone is slender, with a thin and dilated anterior extremity which touches, or is closely approxi- mated to, its mate only at its inner anterior corner, and is continuous anteriorly, with a thin but strong plate of fascia joined to the para- sternal ribs. With much reason it has long been urged that the an- terior projection of the ischium represents the real pubis. ^ In early life it is largely cartilaginous, but becomes fully ossified in the adult. The so-called pubis is probably homologous with the prepubis of the pterodactyls. It has no pubic foramen. The ilium of the Pterosauria, like that of all bipedal reptiles is pro- duced anteriorly by the sides of the vertebrae, very much so in some forms. The ischium and pubis are closely united into a more or less broad plate, either with a thyroid foramen, as in Nyctosaurus (Fig. 118 d) and Pteranodon, or with a small pubic foramen below the acetabulum, as in Rhamphorhynchus , proving the normal structure of the pelvis, though sutures have not been observed. The prepubes, often called the real pubes, are either paired, as in Pterodactylus, or united in a ventral band, as in Rhamphorhynchus, Pteranodon and Nyctosaurus (Fig. 118 d). They articulated with a tuberosity on the front margin of the pubes and in all probability were continued in front with a ligamentous sheath that enclosed the parasternal ribs. The pubes and ischia meet in a symphysis below, though this has been disputed for some. As remarkable as the pelvis of the crocodiles is that of the Dino- ^ [The pubis of the Crocodilia gives attachment to a series of muscles which as a whole are homologous with these that are attached to the true pubis in Sphenodon and lizards (Gregory and Camp, Bulletin, Amer. Mus. Nat. Hist., 1918; Romer, ibid., 1923, p. 606). If the true pubis of Crocodilia has become vestigial and the prepubis has become the functional pubis, how did the prepubis capture the system of muscle attachments of its predecessor? — Ed.] THE PECTORAL AND PELVIC GIRDLES 149 sauria, or rather of that division called the Predentata, or order Orni- thischia. In the other divisions, the Theropoda (Fig. 122 a) and Sauropoda (Fig. 122 b), the pubes have the normal reptilian struc- ture, though unusually stout and strong, meeting in the middle below Fig. 122. Pelves (Dinosauria) : A, Ceratosaurus (Saurischia). After Marsh. One sixteenth natural size. B, Apatosaurus (Saurischia). After Marsh. One thirty-second natural size. C, Triceratops (Ornithischia). After Marsh. One twenty-fourth natural size. D, Stegosaurus (Ornithischia). After Marsh. One twentieth natural size. E, Trachodon (Ornithischia). One tenth natural size. in a firm symphysis, much elongated in the Theropoda. The sym- physis of the ischia is less strong. The pubes of the Ornithischia (Fig. 122 c-e) have been the sub- ject of much dispute and speculation. Each is composed of two pro- jections or processes : the anterior one, the so-called pr epulis, or pre- 150 THE OSTEOLOGY OF THE REPTILES pubic process, typically flattened and more or less spatulate distally, is directed forward and downward [upward] and does not join its mate in a median symphysis. At times it may be small or even ves- tigial (Ankylosaurus) , but is broad and stout in "the quadrupedal Ceratopsia, where apparently it again functions as the normal pubis. The postpubis, or postpubic process, t5^ically is long and slender, directed backward immediately below the slender ischium and not meeting its mate in a symphysis ; that is, the pelvis is more or less open below, as in birds. The postpubis is vestigial in the heavy quad- rupedal Ceratopsia, which have certainly descended from bipedal forms. It is, however, unusually stout in the quadrupedal Stego- saurus, possibly as a reinforcement to the ischia in the support of the heavily armored body. When this peculiarity of the dinosaurian pelvis was first discovered by Hulke and Marsh it was hailed as a direct proof of the dinosaurian ancestry of birds. It may be, however, merely another of the many parallel characters brought about by similar causes. According to one view, the prepubic process is the real pubis, homologous with the pubis of the Saurischia; the postpubic process an outgrowth from it. According to another view, the postpubic process is the real pubis, corresponding to the pubis of birds, the prepubic process homologous with the prepubis of pterodactyls or crocodiles. There has never been, however, any evidence to show that it is derived from a sepa- rate center of ossification. An analogous but not homologous structure is observed in many running birds, the ostriches, Geococcyx, etc., where, in addition to the normal, slender, posteriorly directed pubis siriiilar to the post- pubic process of the dinosaurs, a more or less prominent pectineal process, arising, however, from the ilium, is directed forward, like that of the dinosaurs. The pubis of birds in its embryonic development turns backward from its normal position. Whence it would appear that the development of the two processes in the dinosaurs has arisen in response to similar causes, and cannot be ascribed to a common heredity, as was once thought. Why the bipedal predentate dinosaurs should have acquired such a remarkable structure of the pelvis, and not the even more bipedal theropods, is not yet entirely clear. It has been ascribed to differences in the posture of the tail in running, but would seem, to the author at least, rather to have been THE PECTORAL AND PELVIC GIRDLES 1 51 due to differences in procreational methods, the open pelvis of the predentates permitting larger eggs to be extruded, as in the birds. It may be added that the acetabulum of all dinosaurs is perforate, as in the birds. The pelvis of amphibious or aquatic reptiles is also modified not a Httle. It lost all connection with the spinal column in the Mosasauria and later Ichthyosauria, but is firmly connected, as usual, in other water animals. The slender ilium of the mosasaurs, like that of the Fig. 123. Pelvis oi Platecarpus (Mosasauria), from below. Fig. 124. Pelvis of A^oMoJflMr«J (Nothosauria). After Andrews. ichthyosaurs, lay loosely in the flesh with its upper end in apposition or ligamentously connected with the end of a transverse process or rib of a single vertebra. The narrow ischia and pubes meet in a sym- physis, and there is a pubic foramen. In the earher ichthyosaurs the broad ischia and pubes were sepa- rated by the broad pubo-ischiatic opening, and the pelvis was con- nected with a sacrum. In the later forms, however, the pelvis was re- duced, the rod-like ilium lay loosely in the flesh, and the pubes and ischia were united without a pubo-ischiatic opening. In the Nothosauria (Fig. 124) the pelvis, of the usual type, shows only a moderate aquatic adaptation in the broad pubes and ischia. 152 THE OSTEOLOGY OF THE REPTILES The ilium is firmly connected with the sacrum, and there is a pubic foramen; the pubo-ischiatic notch is small. In the Plesiosauria (Figs. Fig. 125. Pelvic girdle of Trinacromerum osborni, an Upper Cretaceous plesiosaur. from above: />, pubis; is, ischium; il, ilium. 125, 126), the slender ilium, connected Hgamentously with a sacrum of three or four vertebrae, articulates at its distal extremity with the J Fig. 126. Pelvic girdle oi Elasmosaurus (Plesiosauria) : p, pubis; is, ischium; »7, ilium. Fig. 127. Pelvis: Testudo (Chelonia); A, from below; B, from the side. One half natural size. 153 154 THE OSTEOLOGY OF THE REPTn.ES ischium only, and, like that of the Chelonia, is directed upward and backward. The pubes and ischia, like the coracoids, are very broad and flat, secondarily plate-like, meeting in a more or less horizontal symphysis. There is no pubic foramen, and usually the large pubo- ischiatic vacuity is broadly connected across the median line — prob- ably separated by a ligament in life. In some genera, however, Sthenarosaurus or Thaumatosaurus, for instance, the two bones are secondarily broadly united at their symphyses, producing a false thyroid foramen with which the obturator foramen is confluent, as in mammals. The ischia are triangular or "hatchet- shaped," elongated in the short-necked forms, short in the long-necked. The pelvis of the Chelonia (Fig. 127), like the pectoral girdle, has been modified by its peculiar relations to the carapace and plastron. There is a large pubo-ischiatic vacuity, often divided in the middle by a cartilaginous septum, but broadly ossified in the land tortoises, as in the plesiosaurian Sthenarosaurus. As in the plesiosaurs, there is no separate pubic foramen or notch, rarely absent in reptiles. The ilium, like that of the plesiosaurs, is elongate and is directed upward and backward to the firm sacrum. The pubis is larger than the ischium and has a stout tuberosity which rests upon the plastron, or, in the Pleurodira, is cocssified with it. Usually in crawling reptiles (Figs. 114-118 a) there is no, or only a small, preacetabular process to the ilium, but always a postacetabu- lar one. In upright-walking animals the preacetabular process is al- ways well developed, sometimes at the entire expense of the postace- tabular process. It is unusually long in the Anomxodontia (Figs. 120 c, 119), Ceratopsia (Fig. 122 c, e), and Pterosauria (Fig. 118 d), where it is supported by the united or contiguous diapophyses of the lumbar vertebrae, false sacral vertebrae. The ilium is more or less helmet-shaped in the Saurischia (Fig. 122 a, b) as also in some Coty- losauria, Therapsida (Cynognathus) , and Theromorpha (Casea) — all such forms have short toes; possibly it is due to the greater expansion of the gluteal muscles. The evolution of the reptilian pelvis has been, as we have seen, from the primitive closed and plate-like type, by the progressive de- velopment of a vacuity between the ischia and pubes, by the elonga- tion of the anterior process of the iHum, and by its closer union with additional true sacral or lumbar vertebrae. CHAPTER V THE LIMBS Two pairs of limbs are almost always present in reptiles, composed^ as in mammals, of four analogous segments: the arm and thigh bones, conveniently called propodials; the forearm and leg bones, or epi- podials; the wrist and ankle bones, or mesopodials; the manus and pes, composed of metacarpals and metatarsals, or metapodials ; and a variable number of finger and toe bones, known as phalanges. The limbs are best understood and described as though directed outward from the long axis of the body (Fig. 128), the palms of the hands and soles of the feet turned downward or to the ventral side, the epipodials parallel, the thumb or pollex, and the big toe or hallux y on the anterior or preaxial side, the little finger and little toe on the posterior or postaxial side. The terms outer and inner are often ap- plied to the anterior extremity, as though directed backward in the axis of the body, the thumb on the outer side. The hind extremities are sometimes described as though parallel with the long axis of the body, with the big toe on the inner side. As the hallux is analogous- with the pollex, this nomenclature places them on the opposite sides and should not be used for any vertebrates. The fore and hind limbs of terrestrial reptiles are of approximately equal length, the hind pair the longer. In aquatic reptiles [e.g., ichthyosaurs, mosasaurs] the front pair are often the larger, and usually the longer; in volant reptiles [pterosaurs] they are much longer than the hind pair. In bipedal reptiles [e.g., later Theropoda] or those usually assuming this posture in locomotion, they are smaller or very much smaller. In climbing and cursorial reptiles the lim.bs are more or less, sometimes very much, elongated and slender (Fig. 155). The digits of fleet, crawling reptiles are long; those of the more upright-walking kinds (Figs. 145, 141 i), in which the digits of the two sides are brought more nearly parallel to each other, are short- The articular surfaces of the limb joints of aquatic reptiles (Figs. 149, 158) are poorly developed, unextensive, and more or less carti- laginous. 155 156 THE OSTEOLOGY OF THE REPTILES Swimming reptiles with propelling tails [e.g., ichthyosaurs, mosa- saurs] have short propodials, sometimes very short; on the other hand, the propodials of limb-propelling water reptiles [e. g., plesio- saurs, proganosaurs] are elongated. The epipodials of ordinary ter- restrial reptiles are always somewhat shorter than the propodials. Greater shortening of these bones is indicative of swimming habits, possibly also of burrowing ; and in strictly aquatic reptiles they are always very short; indeed the degree of water adaptation may be gauged by the proportional lengths of the epipodials. On the other hand, in springing, leaping, or volant reptiles, they may be consider- ably longer than the propodials (Fig. 155). The limbs of some Lacertilia and most Ophidia are wholly absent; some snakes have vestiges of the hind pair, and some lizards only vestiges of either pair or the front pair only. All other known reptiles have four functional limbs. Primitively {e. g., Figs, i, 128) reptiles were pentadactylate, with the phalangeal formulae 2, 3, 4, 5, 3 for the front, 2, 3, 4, 5, 4 for the hind pair, the fourth digit the longest and strongest; and most rep- tiles still retain these characters. The first digit to be lost is the fifth, and only in a few dinosaurs is the first digit wholly lost. In the more upright-walking kinds, those in which the feet of the two sides are brought more nearly parallel in walking, the greater strength of the foot passes more to the preaxial side, and both the fourth and fifth digits may be obsolete or lost, and very rarely the third also. This weakening of the postaxial digits is especially noticeable in the dinosaurs (Figs. 141, 156) and turtles (Fig. 154), in which the posture in locomotion is more like that of mammals. The same character is also observed in the Crocodilia (Figs. 140 a, 157), unlike other crawl- ing reptiles, and tends to confirm Huene's contestation that the an- cestors of these reptiles were originally more upright in locomotion than are their descendants. As a rule the hind limbs of terrestrial reptiles, as of terrestrial mammals, are more specialized than the anterior ones; that is, there are fewer bones, and the ones remaining are more developed than those of the front feet. Among aquatic and volant reptiles, on the other hand, where locomotion is chiefly effected by the fore limbs, these are more specialized. In certain lizards (Phelsuma) the first digit has become vestigial, the others are well developed. Fig. 128. C«/»/or^/««j (Cotylosauria) : Skeleton, from below. One half natural size. 157 158 THE OSTEOLOGY OF THE REPTILES Propodials The humerus (Figs. 1 29-131), or first bone of the anterior ex- tremity, articulates in the glenoid fossa of the scapular girdle, usu- ally by a more or less complete, free, ball-and-socket joint, permit- ting rotation. Jn most of the Cotylosauria (Figs. 128, 130, 132) and "racLi/aoc uindT COTld. tesser troch,. ddducior fLbulc Fig. 129. Theromorph limbs: Naosaurui, humerus, dorsal side, femur, ventral side. One half natural size. stouter-limbed Theromorpha (Figs. 129, 131, 134) the articular sur- face is more or less spiral-like, extending around the head from the ventral postaxial to the dorsal preaxial side, permitting movement in an antero-posterior direction with a concomitant partial rotation as the hand, directed forward obliquely, is brought backward in walk- ing. The bone was not depressible below a horizontal plane with- out dislocation. The articular surface of the pterodactyl humerus THE LIMBS 159 (Fig. 141) is saddle-shaped, permitting motion in two planes only — ■ antero-posterior and dorso-ventral. At the upper or proximal end of the bone, near its articular part, are two more or less prominent processes for the attachment of Fig. 130. Seymouria (Cotylosauria). Humerus, femur, tibia. A, right humerus, j (Dinocephalia). After Gregory. One twenty-second natural size. Skeleton in American Museum. always, present. Large clavicles and inter clavicle. No acromion. Pelvis with small pubo-ischiatic vacuity. An entepicondylar fora- men. Legs stout; epipodials and digits short; phalangeal formula unknown, probably primitive. Family Tapinocephalidae. Middle and Upper Permian. Del- phinognathus Seeley, Lamiasaurus'^ Watson, Moschognathus Broom, Mormosaurus Watson, Moschops Broom, Moschosaurus Haughton, Phocosaurus Seeley, Pnigalion Watson, Struthiocephalus Haughton, 1 [This statement refers only to the cheek teeth; the premaxillary teeth and the first three or four in the dentary have a long conical crown, greatly expanded posteriorly at the base, and long roots. — Ed.] 2 [Cranium, Fig. 170. — Ed.] THE SUBCLASS SYNAPSIDA 239 Tapinocephalus Owen, Taurops Broom, Archaeosuchus Broom, Scapanodon Broom, Eccasaurus Broom, South Africa. Family Deuterosauridae. Upper Permian. Deuterosaurus, Eichwald, Ural Mts. Family Rhopalodontidae. Upper Permian. Rhopalodon, Eich- wald, Ural Mts. Family Titanosuchidae.^ Upper Permian. Titanosuchus Owen , South Africa. ''Lamiasaurus'^ [snout]. B. Suborder dromasauria About the size of a rat. Skull short; orbits large; lacrimals con- tinuous to septomaxilla ; temporal opening bounded by postorbital, squamosal, and jugal; possibly the preparietal, and probably the in- terparietal, present; parietal foramen large ; teeth isodont,subisodont, or absent; quadra tojugals obsolete or absent; vertebrae notochordal, intercentra unknown; two or three sacrals, probably twenty-eight presacrals; parasternals present; no acromion and no clei thrum; pelvis plate-like, pubic foramen large; carpus primitive, tarsus with or without a fifth tarsale; phalangeal formula 2, 3, 3, 3, 3. Family Galechiridae. A single row of subisodont teeth. Middle Permian. Galechirus Broom, Galesphyrus Broom, Galepus Broom, South Africa. Family Galeopidae. Edentulous. Middle Permian. Galeops Broom, South Africa. Family Macroscelesauridae. Macroscelesaurus Haughton. C. Suborder Anomodontia From the size of a mouse to that of a tapir, vegetable or inver- tebrate feeders. Large temporal opening bounded by postorbital, squamosal, and jugal. Skull typically short and wide, the face short; quadrates and squamosals large; lacrimals small; quadratojugals small or obsolete.^ Preparietal usually present, in front of, or sur- 1 [A number of new genera of South African Titanosuchidae were described by Broom in 1923 {Proc. Zool. Soc, London). — Ed.] 2 [See page 243, below. — Ed.] 240 THE OSTEOLOGY OF THE REPTn.ES rounding, parietal foramen. An interparietal and small tabulars. Premaxillae fused and always toothless, and in life covered with horny beak. Maxilla usually with an enlarged, permanently growing canine, which, however, is absent in the females of some genera, and generally with a number of small molars often irregularly arranged in more than one series. Molars are always present on the mandible if in the maxilla, but there is never any canine present. Prevomers fused. A rudimentary false palate, no teeth on palatal bones. Stapes large. Occipital condyle tripartite. Dentary, angular, and surangular large; no coronoid. A mandibular foramen. Sclerotic plates in orbits. Vertebrae amphicoelous; no intercentra back of atlas; four to seven sacrals. No parasternals. Legs short and stout,, hands and feet short; an entepicondylar foramen. Phalangeal for- mula 2, 3, 3, 3, 3. A thyroid foramen in pelvis; ilium projecting in. front of acetabulum. An ossified sternum. The shoulder girdle has the coracoid and precoracoid well developed, and a distinct but short acromion. There is a small cleithrum known in Dicynodon and Cistecephalus , and possibly present in most other genera. Family Dicynodontidae. Middle Permian. Dicynodon Owen,. Pristerodon Huxley, South Africa. Upper Permian. Tropidostoma Seeley, Diaelurodon Broom, Pro- dicynodon Broom, Eocydops Broom, Emydops Broom, Diictodon Broom, Emydorhynchus Broom, Emyduranus Broom, Taognathus Broom, Cryptocynodon Seeley, Endothiodon Owen, Cistecephalus Owen, Chelyrhynchus Haughton, South Africa, Dicynodon Owen, South Africa and Russia. Lower and Middle Triassic. Dicynodon Owen, Lystrosaurus Cope,. Prolystrosaurus Haughton, Myosaurus Haughton, South Africa. Upper Triassic. Kannemeyeria Seeley, Gordonia Newton, Geikia Newton, Scotland. Placerias Lucas, Brachybrachium Williston,, Wyoming. D. Suborder Theriodontia Carnivorous Therapsida with more or less differentiated dentition, including at least one pair of upper caniniform teeth; a prominent coronoid. Vertebrae never notochordal; few or no teeth on palate bones. No cleithrum. Manus and pes, so far as known, rarely primitive. 241 242 THE OSTEOLOGY OF THE REPTILES I. Tribe Gorgonopsia Prefrontals and large postfrontals contiguous over orbit. A dis- tinct preparietal in front of small parietal foramen. Temporal open- ing bounded above by united postorbital and squamosal, below by squamosal and jugal or squamosal only. Parietal region wide. A single vomer (? fused prevomers). No secondary palate; an ecto- pterygoid. No acromion on scapula; no cleithrum; coracoids rela- tively small; a large proatlas. Phalangeal formula primitive 2, 3, 4, 5, 3- A group intermediate, according to Broom, between the Thero- cephalia and Anomodontia. Middle and Upper Permian. Family Gorgonopsidae. Gorgonops Owen, Scymnognathus Broom, Cyniscodon Broom, Cerdognathus Broom, Scymnosaurus Broom, Gorgonognathus Haughton, Scylacognathus Broom, Scylacops Broom, Galesuchus Haughton, Ictidomorphus Broom, Aloposaurus Broom, Aelurosaurus Owen, Cynodraco Owen, Tigrisuchus Owen, Arctosu- chus Broom, Ardognathus Broom, Arc tops Watson, Theriodesmus Seeley, Asthenognathus Broom, South Africa. Inostrancevia Ama- litsky, Russia. Family Ictidorhinidae. Middle and Upper Permian. Ictido- rhinus Broom, South Africa. Family Burnetidae. Lower Triassic. Burnetia Broom,^ South Africa. 2. Tribe Bauriasauria A well-formed secondary palate; a median, unpaired vomer; single occipital condyle; the pterygoids extend to quadrates; no post- frontals; squamosal small; quadrate large; parietal foramen present or absent; strong incisors and grinding molars; large posterior pala- tine vacuities. No acromion on scapula. Upper Triassic. Bauria Broom, Micro gomphodon Seeley, Melino- don Broom, Sesamodon Broom, Aelurosuchus Broom, South Africa. 1 [Made the type of a new suborder, Burnetiamorpha, by Broom, 1923. — Ed.] THE SUBCLASS SYNAPSIDA 243 3. Tribe Therocephalia Temporal opening large, bounded below by squamosal and jugal, above by the parietal or the connected postorbital and squamosal.^ No quadratojugals^; quadrates small; a parietal foramen; squa- mosals large; no preparietal. Teeth conical, four or five in pre- maxilla; one or two large upper caniniform teeth, and five to nine smaller ones posteriorly; no secondary palate, or a rudimentary one (? Scaloposaurus) ; prevomers separated or fused {Scaloposaurus) ; an interpterygoidal opening; large posterior palatine vacuities; palate with few or no teeth; postfrontals small or absent; parietal region usually narrow. Mandible with loose symphysis, long dentary, and large coronoid; posterior elements not reduced. Postcranial skeleton largely unknown. Family Scylacosauridae. Middle and Upper Permian. Alope- codon Broom, Pardosuchus Broom, Glanosuchus Broom, Scylacosau- rus Broom, Pristerognathus Seeley, Ididosaurus Broom, Alopecogna- thus Broom, Scylacorhinus Broom, South Africa. Family Ictidosuchidae. Middle and Upper Permian. Ictido- suchus Broom, Arnognathus Broom, Cerdodon Broom, South Africa. Family Lycosuchidae. Middle and Upper Permian. Lycosuchus Broom, Trochosuchus Broom, Hyaenasuchus Broom, South Africa. Family ScALOPOSAURiDAE. Middle and Upper Permian. Scalopo- saurus Owen, Ictidognathus Broom, Simorhinella Broom, Idicephalus Broom, Akidnognathus Haughton, South Africa. Family Alopecopsidae. Middle and Upper Permian. Alopecop- sis Broom, Scymnopsis Broom, South Africa. Family Whaitsidae. Whaitsia Haughton, South Africa. Family doubtful. Middle and Upper Permian. Lycosaurus Owen, Eriphostoma Broom, Lycorhinus Broom, Scymnorhinus Broom, Alopecorhinus Broom, Scylacoides Broom, South Africa. 1 [In typical Therocephalia, as described by Broom, the postorbital and squamosal do not connect with each other. — Ed.] 2 [See page 239, above. — Ed.] 244 THE OSTEOLOGY OF THE REPTILES m 4. Tribe Cynodontia Especially characterized by a heter- odont dentition, a secondary palate, reduced posterior mandibular bones, and two occipital condyles. Dentition composed of from three to five incisors, ■P^ a canine, and seven to nine, rarely thir- 2 teen, molars, secodont or gompho- g gnath or cuspidate. Temporal opening c bounded by parietal and postorbital t above, usually by squamosal and post- ^ orbital only below; frontals small, ex- 0 eluded from orbital margin by the £? union of the prefrontal and postorbital ; ^ postf rentals absent; parietals narrow; ^ a small parietal foramen, but no pre- < parietal bone ; tabular large ; quadrate ^ small; stapes long, stout or slender; the S, pterygoids do not reach the quadrate; i probably a small ectopterygoid; vomer ::^ large, unpaired. Coronoid large. A 1 small acromion on scapula; scapula 1° with reflected anterior border; no clei- j" thrum. Fifth carpale unossified; pha- c langeal formula 2, 3, 3, 3, 3, so far as ^ known. A thyroid foramen in pelvis. '^ Feet imperfectly known, the digits ^ short. Vertebrae amphicoelous; no i dorsal intercentra. Twenty-eight pre- sacrals, four sacrals. Family Nythosauridae. Septo- maxillae on face; molars less cuspidate; ft# posterior mandibular bones less re- duced. Middle Triassic. Nythosaurus Owen, Ictidopsis Broom, Gale- saurus Owen, Platycraniellus v. Hoepen, South Africa. THE SUBCLASS SYNAPSIDA 245 Family Cynosuchidae. ? Middle Triassic. Cynosuchus Owen, South Africa. Family Cynognathidae. Septomaxillae within nares; molars cuspidate; [posterior] mandibular bones more reduced. Upper Triassic. Cynognathus Seeley, Lycochampsa Broom, South Africa. Family Diademodontidae. Upper Triassic. Diademodon Seeley, Gomphognathus Seeley, Trirachodon Seeley, South Africa. ? Upper Triassic Cynochampsa Owen, South Africa. 5. Theriodontia (?) Incertae Sedis Upper Triassic. ? Dromotherium Emmons, North Carolina. Tri- holodon Seeley, Karoomys Broom, South Africa. Lower Jurassic. Tritheledon Broom, Pachygenelus Watson, South Africa. [May be either primitive mammals or cynodonts — too imper- fectly known to enable one to decide. Probably each is the type of a distinct family. — R. Broom.] CHAPTER X THE SUBCLASS SYNAPTOSAURIA 6. ORDER SAUROPTERYGIA A SINGLE, large temporal opening, bounded above by the parietal, below by the postorbital and squamosal. No dermosupraoccipitals, tabulars, or quadratojugals. Quadrate fixed. A parietal foramen. Neck elongated, the tail never long. Vertebrae platycoelous. Cer- vical ribs attached exclusively to the centrum, the dorsal ribs ex- clusively to the arch by a single head. A single, large coracoid on each side. Girdles stout. Pelvis with large pubo-ischiatic opening, or secondarily a thyroid foramen. No sternum. Parasternals stout. There is still much doubt as to the derivation and genealogical relationships of this order of reptiles, chiefly because of the structure of the temporal region. The general characters of the skeleton are more or less modified by aquatic adaptations. The boundaries of the temporal region seem to be those of the upper opening of the diapsid reptiles; and there are many who believe that it really is the upper one, and that the order is nearest related to the Progano- sauria. The opening, it is seen, is bounded quite like that of some members of the Therapsida, especially the Cynodontia; and these reptiles are confidently believed to have descended from theromor- phous reptiles with a typical lower opening. The more general opinion is that the Sauropterygia are related to the anomodont-Hke reptiles. Some, however, would trace their descent directly from the Cotylosauria; others from the Diapsida, by the loss of the lower arch. The author believes that the first of these views is the correct one, but in the present uncertainty they may be left in an independent group. Whatever has been their origin, we must await the discovery of their more terrestrial ancestors in the early Trias. The modifica- tions of structure in adaptation to aquatic life are very pronounced, even in the Nothosauria. The order is clearly divisible into two chief groups, the Nothosauria and the Plesiosauria. THE SUBCLASS SYNAPTOSAURIA 247 A. Suborder Nothosauria Crawling or swimming reptiles from three to seven feet in length, of exclusively Triassic age. Skull depressed, more or less elongate, the orbits situated far forward, looking upward. Nares about mid- way between the orbits and extremity. Lacrimals possibly absent. Palate without openings, except the large internal nares, the vomers and pterygoids meeting in the middle hne throughout. From twenty to twenty-five cervical, twenty-five to thirty dorsal, two to five sacral, vertebrae, and a moderately long tail. Clavicles stout, the interclavicle vestigial. The elongated coracoids meet in the middle line. Epipodials much shorter than propodials. Phalangeal formula primitive, or with the loss of one phalanx in the fourth finger. Digits probably webbed in life. The Nothosauria were all aquatic in habit, but not exclusively so like the plesiosaurs, the feet still retaining terrestrial characters, with but minor aquatic adaptations. The. parasternals, like those of the Plesiosauria, are very stout, apparently also an aquatic adaptation. The body was never slender, though less broad than that of the plesiosaurs, and it is not probable that they were rapid swimmers. They doubtless lived in the shallow waters, as do the crocodiles, com- ing frequently to land, and subsisted chiefly upon fishes and inverte- brates, for the capture of which their slender, curved teeth were well fitted. A pecuhar parallel adaptation to that of the contemporary aquatic Labyrinthodontia is seen in the forward position of the eyes in the flat skull, and also in the unusually stout clavicular girdle of both. Several famiUes have been proposed, based upon minor characters of the skull chiefly. For the present they may all be placed in a single family, the Nothosauridae. Family NoTHOSAURiDAE. Upper and Middle Trias. Anarosaurus Dames, Cymatosaurus Fritsch, Dactylosaurus Glirich, Doliovertebra Huene, Lamprosaurus Meyer, Lariosaurus Curioni, Microleptosaurus Scuphos, Neusticosaurus Seeley, Nothosaurus Miinster, Parthano- saurus Scuphos, Pistosaurus Meyer, Proneusticosaurus Volz, Simo- saurus Meyer. 248 THE OSTEOLOGY OF THE REPTn.ES B. SUBORDER PLESIOSAURIA Marine reptiles from eight to about fifty feet in length, with paddle-like, hyperphalangic limbs. Skull moderately broad to very slender. Nares small, situated remote from the extremity and near the orbits. Orbits with sclerotic plates. No distinct nasals. Internal nares small, situated in front of the external. A pair of posterior in- terpterygoidal openings divided by the parasphenoid always present; other openings variable on the palate. The squamosals meet in the middle line posteriorly. Coracoids very large, contiguous in midline; clavicles and interclavicle small, sometimes vestigial. Ilium rod-like, articulating below with ischium only, above with a well-developed sacrum of three or four vertebrae. An extensive and long-lived group of purely marine reptiles, widely distributed over the earth; as a whole clearly defined, but with many minor modifications. The neck was extremely variable in length, with from thirteen to seventy-six cervical vertebrae. The body was broad, though not nearly so broad as represented in most modern restorations. The most perfect specimen known — and the author has seen most of them in the collections of the world — is that of Thaumatosaurus victor, in the Stuttgart museum, of which a figure copied from a photograph is reproduced here. The body, it is seen, is broadly oval, but not flat, protected below by the extraordinary developments of the pectoral and pelvic girdles and intervening parasternal ribs. Their phylogenetic relationships with the Notho- sauria are incontestable, though the closed palate of the latter indi- cates that no known form could have been actually ancestral to them. Family Plesiosauridae. Skull moderately long. From thirty- five to [seventy-six] cervical vertebrae, the cervical ribs double- headed. Scapulae not contiguous in the middle; no interclavicular foramen; epipodials much longer than broad, no accessory epipo- dials. Coracoids contiguous throughout. Jurassic. Plesiosaurus Conybeare, Thaumatosaurus Meyer, Europe. Family Pliosauridae. Skull long, neck short, composed of about nineteen vertebrae. Cervical ribs double-headed; five pectoral and about twenty dorsal vertebrae. Premaxillae continuous to parietals in middle. Scapulae closely approximate in midHne; coracoids con- Fig. 173. Skeleton of Thaumatosaurus (Plesiosauria). After Fraas. One twentieth natural size. 249 250 THE OSTEOLOGY OF THE REPTH^ES tiguous throughout. Two or three epipodials, as broad as long or broader. Ischia long. Large or very large. Jurassic. Pliosaurus Owen, Peloneustes Lydekker, Europe. Family Cryptocleididae. Very much like the following family, but the neck is shorter, with from thirty- two to forty-four vertebrae; and the coracoids are contiguous throughout. From two to four epipodials, all short. Cervical ribs single-headed. Skull short. Jurassic. Cryptodeidus Seeley, Muraenosaurus Seeley, Tricleidus Andrews, Picrocleidus Andrews, Microcleidus Watson, Sthenaro- saurus Watson, Europe. Fig. 174. Skeleton of Trinacromerum osborni, a Cretaceous plesiosaur, as mounted in the University of Kansas Museum. Family Elasmosauridae. Head short, neck very long, with from more than fifty to seventy-six vertebrae; ribs single-headed. The scapulae meet in midline; no interclavicular foramen. Coracoids broadly separated on their posterior half. Ischia short. Two epi- podials only, short. Upper Cretaceous. Elasmosaurus Cope, Ogmodeirus Williston and Moodie, Leurospondylus Brown, North America. Family Polycotylidae. Skull very slender. Premaxillae articu- lating with parietals. Neck not longer than head, with from twenty- three to twenty-six vertebrae; ribs single-headed. The precoracoidal process separates the scapulae in the midline; an interclavicular fora- men; coracoids contiguous throughout. Ischia elongate. Three or four epipodials, all short. Upper Cretaceous. Polycotylus Cope, Trinacromerum Cragin, ? Piratosaurus Leidy, North America. THE SUBCLASS SYNAPTOSAURIA 251 Family Brachatjcheniidae. Skull long, neck very short, with but thirteen vertebrae, shorter than skull. Cervical ribs singleheaded. Pterygoids not reaching to vomers. Paddles imperfectly known. Upper Cretaceous. Brachauchenius Williston, North America. Genera incertae sedis Triassic. "Plesiosaurus" Conybeare, Europe. Jurassic. Eretmosaurus Seeley, Colymbosaurus Seeley, Tschyrodon Meyer, Liopleurodon Sauvage, Spondylosaurus Fischer, Simolestes Andrews, Europe. Megalneusaurus Knight, Pantosaurus Marsh,, " Muraenosaurus" Seeley, North America. Lower Cretaceous. ^'Plesiosaurus'' Conybeare, North America. Upper Cretaceous. Mauisaurus Hector, New Zealand. Polypty- chodon Owen, Europe. Cimoliosaurus'Leidy,OligosimusL,eidy,Bri'mo- saurusl^eidy,Piptomerus CoY)e, Orophosaurus Cope, Embaphias Cope, Taphrosaurus Cope, Uronautes Cope, "Plesiosaurus^' Conybeare,. North America. 7. ORDER PLACODONTIA Temporal opening bounded by parietal, postfrontal, postorbital, and squamosal. Jaws and palatines with few, very large, fiat crush- ing teeth. A parietal opening. Vertebrae amphicoelous, with hypo- sphene, h3rpantrum. Ribs double-headed. Remainder of skeleton unknown. This singular group of littoral, shell-eating reptiles has long been a problem, because of our ignorance of the skeleton. Some would include them among the Sauropterygia as a separate suborder; others would give to them the same rank among the Therapsida. If the supratemporal and interparietal are really present, as believed by Huene, they would certainly find no place among the Sauro- pterygia. But their presence has been denied. On the other hand, if there should prove to be but a single coracoid on each side in the pectoral girdle, their location among the Therapsida would be im- proper. Placochelys has a carapace of bony plates, both above and below, with isolated ones upon the skull, all of which seem to be wanting in Placodus. Their presence or absence, however, is of no more importance than in the Dinosauria, or Squamata, as examples. 252 THE OSTEOLOGY OF THE REPTILES As might be suspected in such forms, the number of presacral verte- brae is reduced. The temporal vacuity is bounded as in the plesiosaurs, and also in some theriodonts. The maxillae are large, the nares situated rather far back, perhaps an adaptation for grubbing in the mud after in- vertebrates. Possibly there was a moderate adaptation in Placodus for life in shallow water. The placodonts were reptiles of considerable size, perhaps eight or ten feet in length, undoubtedly slow in movement, and with a heavy skull, as have all shell-eating reptiles. Until more is known of the skeleton, the group may remain in an independent position, though there is Uttle in the structure of the skuU that would entitle them to an ordinal rank; shell-eating animals with crushing teeth occur in various orders. Family Placodontidae. Upper Triassic. Placodus Agassiz {Ano- mosaurus Huene), Placochelys Jaekel, Cyamodus Meyer, Europe, CHAPTER XI THE SUBCLASS PARAPSIDA 8. ORDER PROGANOSAURIA Primitive, aquatic reptiles with long neck, body, and tail, two or three feet in length. Structure of skull imperfectly known, probably with a single, upper temporal opening on each side. Face long and slender, the nostril near orbits, the premaxillae elongated. Teeth numerous, long and slender; small teeth on vomers, probably also on other palatal bones. Vertebrae deeply amphicoelous; intercentra unknown; eleven or twelve cervicals, eighteen to twenty- two dorsals, two sacrals and sixty or more caudals. Free ribs on all presacrals except atlas; dorsal ribs stout, single-headed, articulating with cen- tra. Numerous parasternal ribs. Scapula fan-shaped; a single cora- coid; clavicular girdle primitive; pelvis with small pubo-ischiatic vacuity. Humerus with entepicondylar foramen. Propodials long; epipodials short, carpus and tarsus primitive ; phalangeal formula of pes (in Mesosaurus and Noteosaurus at least) 2, 3, 4, 5, 6, the fifth toe elongate. These small reptiles, the first known in geological history with marked aquatic adaptations, retain many primitive characters, though highly speciahzed in the scapular girdle with its single cora- coid, the earhest known. Aside from the Dolichosauria and certain dinosaurs they are the only known aquatic reptiles with both neck and tail elongated. Until the skull is better known, however, doubt remains as to their relationships with other reptiles. By some they have been placed with the double-arched reptiles; by others among the Sauropterygia. Because of the articulation of the single-headed ribs especially, and the probable possession of but a single, upper temporal opening, their natural association seems to be near the ichthyosaurs and lizards.^ 1 [Much further evidence for this \aew is given by von Huene in his memoir Die Ichthyosaurier des Lias und ihre Zusammenhdnge, 1922, 4to, Berlin. — Ed.] 254 THE SUBCLASS PARAPSIDA 255 FvmiLY Mesosauridae. Lower Permian. Stereosternum Cope (Notosaurus Marsh), Mesosaurus Gervais, Brazil. Mesosaurus Ger- vais {Ditrichosaurus Gurich), ? Noteosaurus Broom, South Africa. Fig, 176. Restoration of Mesosaurus. After McGregor. The posture of the hind leg is slightly modified. 9. ORDER ICHTHYOSAURIA Marine reptiles with all aquatic adaptations of the tail-propelling type: elongated face; posterior nares, sclerotic plates, short neck, elongated body, no sacrum, long, flattened or dilated tail, short pro- 256 THE OSTEOLOGY OF THE REPTH^ES podial and epipodial bones, hyperphalangy, and often hyperdactyly. Premaxillae long; maxillae short. A parietal foramen; free paroccip- itals, large stapes; no ectopterygoids or dermosupraoccipitals. Teeth inserted in sockets or grooves, labyrinthine in structure; none on palatal bones. The large upper temporal vacuity is bounded by parietal, postf rontal, and tabular (supratemporal) . No lateral open- ing. Vertebrae short, deeply amphicoelous, without persistent dorsal intercentra. Scapulae small; a single coracoid; clavicles and inter- clavicle present. No sternum, but numerous parasternals. Pelvis more or less plate-like with small pubo-ischiatic vacuity. Prearticu- lar bone of mandible distinct. The ichthyosaurs were exclusively marine reptiles, more perfectly adapted to aquatic Hfe than any other known ones unless it be the plesiosaurs. They varied from about two to about thirty feet in length. Family Mixosauridae. Cervical ribs for the most part holo- cephalous. Tail with a preterminal dilatation, slightly decurved. Chevrons Y-shaped. Epipodials relatively long; feet pentedactylate. Face less elongate. Teeth more or less anisodont, inserted in sockets. Middle and Upper Triassic. Mixosaurus Baur, Spitzbergen,. Switzerland, Germany. Family Shastosaueidae. Body more elongate. Cervical ribs dichocephalous. Tail distinctly expanded and decurved distally. Chevrons Y-shaped. Epipodials relatively long. Feet tetra- or tri- dactylate. Both the Mixosauridae and Shastosauridae, which Merriam gives only sub-family values under the Mixosauridae, are more primitive^ with less perfect aquatic adaptations than the later forms of the Ichthyosauridae, and especially the Ophthalmosauridae. Middle or Upper Triassic. Cymbospondylus Leidy, Toretocnemus Merriam, Merriamia Boulenger, Delphinosaurus Merriam, Shaslo- saurus Merriam, Phalaradon Merriam, California, Nevada. Pesso- saurus Wiman, Spitzbergen. Family Ichthyosauridae. Fewer presacral vertebrae; pelvis more reduced; tail with a broad terminal fin; epipodials shorter; dorsal ribs dichocephalous; chevrons separate or fused; hind limbs 257 258 THE OSTEOLOGY OF THE REPTILES usually more reduced; frequently hyperdactylate. Teeth inserted in grooves. Face longer. Upper Triassic to Upper Cretaceous. Ichthyosaurus Koenig {Proteosaurus Howe), Europe, Asia, Africa, Australia, New Zealand, South and ? North America. A widely distributed genus as it is ordinarily accepted. It pre- sents, however, numerous minor modifications, that might justify its division.^ Family Ophthalmosauridae. Differs from the more typical Ich- thyosauria in the more reduced teeth, the presence of three epipo- dial bones in the front paddles, the more reduced hind paddle, the fusion of the ischium and ilium, in the apparent entire absence of chevrons, and in the more discoidal form of the phalanges. Upper Jurassic. Ophthalmosaurus Seeley (? Baptanodon Marsh), Europe and North America. Cretaceous (Upper Greensand). 7 Ophthalmosaurus Seeley. ? ORDER 0MPHAL0SAURIA2 Family Omphalosauridae. Marine reptiles with a short, shell- crushing skull. Mandibles short, the dentaries united in a strong symphysis, their broad, convex, superior surface beset with several rows of low-crowned, button-like crushing teeth, the largest about fifteen millimeters in diameter. Vertebrae amphicoelous. "Palate plesiosaur-like." Skeleton otherwise unknown. The incompletely known remains of these reptiles, described by Merriam, are very suggestive of a new type of shell-eating aquatic reptiles, but until more is known they are merely suggestive, the ordinal rank and relationships provisional or conjectural. In them- selves the characters are not of ordinal rank, but their associations and their age make it not at all improbable that when fully known they will justify the rank provisionally given to them. From essen- tially the same horizon in Spitzbergen similar teeth have been described by Wiman, which seem to pertain to the same kind of ^ [Von Huene (1922) divides the old genus Ichthyosaurus into several phyletic lines, the evolution of which he traces from the Triassic to the Upper Cretaceous. — Ed.] ^ [Recent authors (von Huene, Nopcsa) class the Omphalosauria with the Ichthyo- sauria. — Ed.] THE SUBCLASS PARAPSIDA 259 reptiles. Somewhat doubtfully associated with those remains are others of ichthyosaur-like bones that the describer provisionally as- sociated with the Ichthyosauria, bearing possibly a like relation to the known Ichthyosauria that Glohidens does to the typical Pytho- nomorpha. Middle Triassic. Omphalosaurus Merriam, Nevada. Pessopteryx Wiman, Spitzbergen. 10. ORDER PROTOROSAURIA Quadrupedal, arboreal, terrestrial, or subaquatic reptiles one to six feet in length, with a single, upper temporal opening between the parietal and the temporal arch, the quadrate fixed. Ribs in part or all single-headed, articulating with centra — a single coracoid, an interclavicle, and clavicles. This order, as here Hmited, is a provisional one, including several reptiles, some of them imperfectly known, which cannot be placed in any other known order. Most of them have hitherto been classified with the RhynchocephaUa, from which they are distinguished by the absence of a lateral temporal opening, so far as known. Perhaps when finally known they will be found to be incoherent. For the present they may be defined as families. Family Araeoscelidae. Very slender, arboreal or leaping, hol- low-boned reptiles of less than eighteen inches in length, with long legs and long tail. The broad lateral temporal region is formed ap- parently of a single bone, here identified as the squamosal, the quad- ratojugal absent. The dermosupraoccipital is apparently large. Lac- rimal vestigial or absent. A parietal foramen. All cranial bones paired. Palatal bones with teeth. At least seven cervical verte- brae, twenty dorsal, two sacral, and a long, slender tail. Vertebrae amphicoelous with persistent intercentra. Cervical ribs, at least, single-headed, the dorsal more or less dichocephalous. Coracoid and scapula closely fused. Humerus with both entepicondylar and ectepicondylar foramina. Pelvis primitive. Phalangeal formula primitive. Calcaneum produced. Araeoscelis, the type of the family, is the earliest definitely known reptile with a single, upper temporal vacuity, bounded as in the lizards, and a fixed quadrate. It was a very slender, leaping or Fig. 179. Skeleton of ^raeoscelis (ProtoTosaurla.). About one fourth natural size. Fig. 1 80. Restoration of Araeoscelis. 260 THE SUBCLASS PARAPSIDA 261 arboricolous, insectivorous, lizard-like reptile from the Lower Per- mian of Texas. Of Kadaliosaurus, unfortunately, the skull is un- known. Its slender bones were less hollow, and it has also numerous parasternal ribs, unknown in Araeoscelis. Lower Permian. Araeoscelis Williston, Texas. Kadaliosaurus Credner, Germany. Family Protorosauridae. Elongate reptiles with long neck and hind legs and hollow bones, from three to five feet in length. Skull imperfectly known, probably with an upper temporal opening only. Sclerotic plates in orbits. Prevomers, palatines, and pterygoid with small teeth. Vertebrae amphicoelous, with persistent intercentra. Seven cervicals, sixteen to eighteen dorsals, two or three sacrals, and a long tail. A single coracoid. Pelvis more or less plate-Hke, with Fig. 181. Skeleton of Protorosaurus (Protorosauria), modified from Seeley. About one tenth natural size. probably a small pubo-ischiatic vacuity. Ribs single-headed, articu- lating with centrum, those of the cervical region very slender. Epi- podials about as long as propodials, the hind legs much longer than the front. Humeri with ectepicondylar (?) foramen; nine or ten carpals, seven tarsals ; phalangeal formula primitive, the digits long. Numerous abdominal ribs. Although the first-described fossil reptiles, the protorosaurs are still imperfectly known in the details of their structure, especially of the skull, pectoral, and pelvic girdles. In the elongation of the neck and the slender legs Protorosaurus very much resembles Araeoscelis, and doubtless had similar habits, whether or not the structure of the skuU was the same. The numerous known specimens of Protoro- saurus differ so much from each other that it is not at all improb- able that they represent different genera. Aphelosaurus is still more problematical, inasmuch as all that is known of it are the trunk and limbs. The limbs resemble those of 262 THE OSTEOLOGY OF THE REPTH^ES Protorosaurus in size, slenderness, and proportions. The single- headed ribs are described by Thevenin as articulating intercentrally. Lower Permian. ? Aphelosaurus Gervais, France. Upper Permian. Protorosaurus v. Meyer, Germany. The nares were described by Seeley as immediately in front of the orbits- — ^an error. There may be a small antorbital foramen, but it is doubtful. Family Saphaeosauridae. Slender, terrestrial or subaquatic rep- tiles about two feet in length. Skull with a single temporal opening, the quadrate fixed and the lateral temporal region moderately broad. No postf rontals ; postorbitals large. No parietal foramen. Maxillae and dentaries edentulous, with cutting edges. Vertebrae procoelous without intercentra; twenty- three presacrals, two sacrals, and fifty or more caudals. Caudal vertebrae with splitting point (?). Ribs single-headed, articulating with anterior part of centrum. Coracoid with two median emarginations. Interclavicle T-shaped, the clavicles slender. Parasternals numerous, composed of a median unpaired pices and a lateral splint on each side. Pubes and ischia broadly separated by pubo-ischiatic opening, the ischia with a stout posterior tuberosity. An ectepicondylar foramen in humerus. Manus and pes pentedactylate, with primitive phalangeal formula. Saphaeosaurus, usually called Sauranodon, has long been classed as a representative of a distinct family of the RhynchocephaUa. The skull, as described by both von Meyer and Lortet, has but a single temporal opening on each side, bounded externally by the postorbital and squamosal (tabular?) . There is no lower temporal opening. The structure of the temporal region as described is doubtful. In much probability the tabular, squamosal, and quadra tojugal are all present. In all its essential characters it is a Lacertilian with a primitively fixed quadrate. The vertebrae, as figured and described by Lortet, are procoelous, perhaps the first known evidence of such in geological history. Upper Jurassic. Saphaeosaurus v. Meyer {Sauranodon Jourdan), France. Family Pleurosauridae. Very slender, snake-Hke, aquatic rep- tiles, with short neck, long body, very long flattened tail, and small pentedactylate legs; attaining a length of nearly five feet. Skull Fig. 182. Skeleton of Sap/iaeosaur us (Protorosaui'ia.). After Lortet. One fourth natural size. 263 264 THE OSTEOLOGY OF THE REPTILES elongate, pointed, the nares remote from end. No postfrontals. A parietal foramen. The single temporal opening is bounded within by the parietal, without by the postorbital and (?) squamosal. A small quadratojugal. Teeth pointed and recurved. Acrodont. Palatal teeth unknown. Five cervicals, forty or forty-one dorsals, two sa- crals, and more than seventy caudals. Vertebrae amphicoelous, cer- vical intercentra hypapophysial. Ribs single-headed, articulating as in the Squamata. Numerous slender, parasternal ribs. Fleurosaurus, the only certainly known genus of the family, was long supposed to be a member of the RhynchocephaHa, though it has also long been known to have but a single upper temporal opening. Its remarkable adaptation to aquatic Ufe is shown in the elongated head, posterior nares, short neck, very slender trunk, very small legs, and enormously elongated tail, with its long chevrons and spines, which in life was surmounted by a thin crest of scales. Acrosaurus is probably only the young of Fleurosaurus, as the author convinced himself by examination of specimens in the Munich museum. In consequence, the ordinal name once proposed for these reptiles, Acrosauria, is inappropriate. The structure of the temporal region still needs confirmation. If there is but a single bone bounding the temporal opening posteriorly, it is in much probabiHty the real squamosal. Uppermost Jurassic. Fleurosaurus v. Meyer {Anguisaurus Miin- ster, Saurophidium Jourdan), Germany, France. } Acrosaurus v. Meyer. Germany. 11. ORDER SQUAMATA With a single temporal vacuity on each side, bounded by parietal, tabular, squamosal, and postorbital, secondarily sometimes roofed over or the arcade obsolete. No lower temporal opening or bar. Quadrate movably articulated, streptostyhc, secondarily sometimes fixed. No supratemporals, dermosupraoccipitals, or quadratojugals. The pterygoids articulate in front with the palatines, never with the prevomers. Paroccipitals fused with exoccipitals. Interorbital sep- tum not ossified. Teeth acrodont or pleurodont, often attached to palatine and pterygoid. Prearticular fused with articular. Ribs single-headed, articulating with centrum. THE SUBCLASS PARAPSIDA 265 A. Suborder Lacertilia (Sauria)^ Subvolant, arboreal, terrestrial, burrowing, subaquatic, or marine reptiles from a few inches to about forty feet in length; quadrupedal, bipedal, or limbless; herbivorous, insectivorous, or carnivorous. Brain-case in front of prootics more or less membranous. Lacrimals small or vestigial. Posterior arcade sometimes absent. Mandibles usually united by suture. Vertebrae procoelous, except in the Geck- onidae and Uroplatidae; not more than two sacral vertebrae. Clav- icles and interclavicle rarely absent. No entepicondylar, but usually an ectepicondylar foramen in humerus. This group is often given an ordinal rank, equivalent to the Ophidia or even to the Pythonomorpha, but the ultimate distinctions be- tween them are almost trivial, as will be seen, and in many legless burrowing lizards the skull structure mimics that of the snakes. More than eighteen hundred species are known, distributed widely throughout the world, usually classed in about twenty families and numerous genera. Because of their predominantly terrestrial habits, but few remains of lizards are found in the rocks, aside from the more aquatic or marine types. Only about fifty genera of extinct forms have been described and less than one hundred species, and the greater majority of those are for the most part fragmentary and incomplete, so much so that their systematic positions are very often uncertain and pro- visional. Doubtless they have had a long and abundant geological history from very remote times, but of the true land lizards almost nothing is known throughout the Mesozoic. But few positive char- acters are distinctive of the group, though many negative ones are. The mandibles are usually suturally united in the middle, but a few forms have them ligamentously attached. The presence of legs is not distinctive, though at least a vestige of the pectoral girdle remains. The more or less open brain-case in front is perhaps the most diagnostic, only partially enclosed by the more or less vestigial post- optics ("alisphenoids," "postorbitals"). However, in the Amphis- baenia even this character is doubtful, and in the mosasaurs a dis- tinct descending plate from the parietals resembles that of the snakes, 1 [For a very comprehensive morphological and taxonomic revision of the Lacertilia, see C. L. Camp, "Classification of the Lizards," Bulletin, Amer. Mus. Nat. Hist., 1923, XLViii. — Ed.] 266 THE OSTEOLOGY OF THE REPTH^ES but does not reach the basisphenoid. The jugals, squamosals, and tabulars may be more or less vestigial, and even the quadrate may be secondarily fixed and immovable. Tribe Kionocrania Terrestrial, burrowing, subaquatic, or subvolant. A slender epi- pterygoid articulates with parietal and pterygoid; no descending plates of the parietals. Palate with large openings, usually with teeth on palatines or pterygoids or both. Feet when present usually pen- tedactyl, with the primitive phalangeal formula, the fifth metatarsal more or less hook-shaped proximally. Eight cervical vertebrae. Family Geckonidae. Vertebrae amphicoelous,^ notochordal, with persistent intercentra. Quadrupedal. Jugal vestigial. No temporal arcade. Parietals paired. Clavicles perforated near mesial end. A family of small lizards widely scattered over the earth, compris- ing nearly three hundred species and about fifty genera. They are of interest because of the persistently primitive condition of the vertebrae. They must have had a long independent history from early Mesozoic times, but no species are known as fossils. Family Euposauridae. Small lizards, from two to four inches in length, of doubtful position; referred to the Anguinidae by Boulenger. Head relatively large and broad, orbits very large, the temporal openings said to be closed. Structure poorly known, twenty-three presacrals. Upper Jurassic. Euposaurus Lortet, France. Family Agamidae. Temporal and postorbital arches complete. A parietal foramen.^ No dermal ossicles [on back]. Teeth acrodont. Quadrupedal. This exclusively Old- World family includes about two hundred known species of about thirty genera, some of them attaining a length of three feet. Perhaps the most noted members are the Flying Dragons (Draco), small lizards with an extraordinary development of the ribs to support a parachute membrane. Chlamydosaurus, one of the largest of the family, has an extraordinary frill about the neck 1 [Rarely procoelous. See G. K. Noble, 1921, Amer. Mus. Novitates, No. 4. — Ed.] 2 [Except Liolepis. — G. K. N.] THE si":bclass pail\psida • 267 supported by the elongated hyoid bones. Some are subaquatic in habit. The Moloch lizard, much like a ''Homed Toad" in appear- ance, has long dermal spines. Ohgocene. France [A go ma]. Pleistocene. Chlamydosaurus. Australia. F.A3IILY Iguaxtd.ie. Arboreal, terrestrial, burrowing, or sub- aquatic, reaching a length of six feet. Teeth pleurodont. Xo der- mal ossifications. Temporal and orbital arches complete. Spines of vertebrae sometimes elongate. A parietal foramen. Zygosphenes sometimes present. Herbivorous and insectivorous. About three hundred species and fdty genera are known of this family, almost exclusively American in distribution, including our largest and some of our most common lizards. - — the Basihsc lizards. Iguanas. '"'Horned Toads." etc. The large Galapagos lizard. Amhly- rhynchus. is a noteworthy herbivorous, aquatic form that seeks its food in shallow water, returning to the land for safety when pressed by enemies; perhaps one of the ways in which terrestrial reptiles acquired water habits. Eocene. Iguanavus Marsh. Xorth America. Proiguana Filhol, France. Family AxGnxroAE. With well-developed, pentadactyl limbs, or limbs vestigial. Body covered "v^ith dermal ossicles beneath corneous scales. Temporal opening roofed over by dermal bones. Teeth pleurodont. A parietal foramen. This family, conmion to Europe and America, comprises about fifty species. Most noteworthy are the ''Glass Snakes"" and the "Slow Worms,"' with vestigial hmbs or wholly without them. Miocene. Auguis. Diploglossus. France. Family HELODERM.A.Tn)Ai:. Poisonous, terrestrial lizards with grooved, slender, pleurodont teeth. A postorbital but no temporal arch, the squamosal absent; prefrontal and postfronto-orbital in contact over orbits. Parietals and frontals fused. X'o parietal fo- ramen. Upper surface of body and skull more or less covered by dermal ossicles. An ossified, subfrontal. rhinencephalic chamber. Quadrupedal. But one genus and two species of this family are known, the fa- 268 THE OSTEOLOGY OF THE REPTILES mous ''Gila Monsters" of Arizona. They are thickset, slow lizards with a club-like tail, reaching a length of about two feet, the only known poisonous members of the suborder. Eocene. Glyptosaurus Marsh, Thinosaurus Marsh, North Amer- ica. Placosaurus Gervais, France. Oligocene. Helodermatoides Douglass, North America. Family Lacertidae. Quadrupedal, terrestrial Uzards. Upper sur- face of skull with numerous dermal bones. Temporal opening roofed over by the postfrontal extending back between parietal and squa- mosal, the arches complete. A parietal foramen. Teeth pleurodont. The family of Lacertidae comprises about one hundred species restricted in distribution to Europe, Asia, and Africa. None is large and some are common throughout England; one, Lacerta vivipara, is the only reptile known to occur in Ireland. Miocene. Lacerta, France. Family Tejidae. Arboreal, terrestrial, or subaquatic lizards at- taining a length of three feet. No postorbito-squamosal arch.^ A parietal foramen. No dermal ossicles. Zygosphenes sometimes present. A family of American lizards including about one hundred species, some, like the Cnemidophorus, common throughout the United States. The teeth of Dracaena are large oval, crushing organs. Uppermost Cretaceous. ? Chamops Marsh, North America. Oligo- cene, Tejus. Family SciNciDAE. Temporal arch complete. Temporal openings roofed over by dermal bones. Body also covered by dermal ossicles beneath the corneous scales. Quadrupedal, bipedal, or limbless; terrestrial, subaquatic, or burrowing. Pleurodont. The large family of skinks comprises about four hundred living species, cosmopolitan in its distribution. Some attain a length of about two feet. Trachysaurus of Australia is peculiar in its stumpy tail and very large scales of the body. Cyclodus has spherical crush- ing teeth. Lower Cretaceous (Neocomian). Ardeosaurus Meyer. Eocene. Cadurcosaurus Filhol, France. * [A postorbital arch is present. — G. K. N.] THE SUBCLASS PARAPSIDA 269 Oligocene. Dracaenosaurus Gervais, Protrachysaurus Stefano, France. Pliocene. Didosaurus Giinther. Tribe Platynota Terrestrial or subaquatic lizards from two or three feet to about thirty in length. Epipterygoid and parietal foramen present. Feet pentadactylate, with the primitive phalangeal formula. Sacrals present. Family Varanidae, Terrestrial or subaquatic, reaching a length of about thirty feet (Megalania). Skull more or less elongate, the nostrils rather far back, broadly open. Premaxillae, nasals, and parietals unpaired. Postorbital arch incomplete. Descending plates from the frontals enclose a rhinencephalic chamber. An imperfect joint between angular and splenial. Large palatal openings. Nine cervical, twenty dorsal, vertebrae. Girdles complete. No dermal bones. This family, exclusively [Australian], African, and Asiatic, includes but one genus, Varanus, with about thirty living species, none more than seven feet in length.^ Some are subaquatic in habit, seeking the water, in which they swim with freedom by aid of the long flattened tail, to escape their enemies. Their structure is so like that of the following forms of the Dolichosauridae, and especially the Aigialo- sauridae, that it would seem very probable they all had a common origin in early Cretaceous times. Megalania, from the Pliocene of India [and Pleistocene of Australia], is the largest of all known ter- restrial lizards. Unlike most Hzards, they have a long protrusible tongue. Eocene. Saniva Leidy, North America. Paleovaranus Filhol, Froganosaurus Portis, France. PHocene. Megalania Owen, India. Pleistocene. Varanus, India. [Megalania, Australia.] Family Dolichosauridae. Slender aquatic lizards, two or three feet in length, with a relatively small skull, long neck of thirteen 1 [Varanus homodoensis Owens, of the Dutch East Indies, reaches a length of thir- teen feet. — H. C. Raven.] 270 THE OSTEOLOGY OF THE REPTH^ES vertebrae, slender cylindrical body of twenty-six or twenty-seven vertebrae, two sacrals, and a long flattened tail. Zygosphenes pres- ent. Legs relatively small, the front ones smaller than the hind. Pleurodont. The dohchosaurs, with their greatly elongated neck and body, have been thought by some to be ancestrally related to the snakes but this is very doubtful, since their flattened tail shows a distinct adaptation to water Ufe and it is improbable that the snakes ever passed through an aquatic stage in their evolution. Aside from' the Proganosauria, they are the only known swimming reptiles with both neck and tail elongated. Just what habits were subserved by this structure is a problem. Because of the snake-like sinuosity of the neck, body, and tail, the small legs must have been of no pro- pelHng, and but Uttle other, use in the water. Pleurosaurus, an alHed reptile of similar form, has a short neck. In all probabiUty the doh- chosaurs were a side branch from the common varanoid ancestral stock of the aigialosaurs and mosasaurs, but not directly ancestral to any later forms. Lower Cretaceous (Neocomion). Acteosaurus Meyer, Adriosaurus Seeley, Pontosaurus Kramberger, Europe (Dalmatia). Upper Cretaceous. Dolichosaurus Owen, England. Family Aigialosauridae. Subaquatic lizards from three to six feet in length. Skull large, mosasauroid. Neck of seven vertebrae; body of twenty-one vertebrae; tail long, flattened. Two sacrals. Legs of nearly equal size, the propodials somewhat shortened. Feet not hyperphalangic, probably webbed. The skull of the aigialosaurs is almost identical in structure with that of the mosasaurs, including the remarkable joint in the man- dible between the angular and splenial, and their ligamentous union in front. The neck is shortened, the body elongated, with the same number of vertebrae found in some mosasaurs. The limbs, however, were terrestrial, with only slight aquatic adaptations. Doubtless the reptiles were amphibious in habit, frequenting the shallow waters for food. Lower Cretaceous (Neocomion). Aigialosaurus Kramberger, Car- sosaurus Kornhuber, Opetiosaurus Kornhuber, ? Mesoleptos Cornaha, Europe (Dalmatia). Fig. 1 83. Skeleton of Adriosaurus (Lacertilia). After Seeley. Three fourths natural size. 271 272 THE OSTEOLOGY OF THE REPTILES Tribe Pythonomorpha (Mosasauria) Large marine lizards with more or less elongated head, shortened neck, elongated body, a long, flattened tail with a more or less sub- terminal dilatation, and paddle-like extremities. From six to about forty feet in length. Temporal and postorbital arches complete, the tabular with a long process wedged in between paroccipital and prootic. Parietal and frontal unpaired; a parietal foramen. Palate with large openings. Teeth with osseous base inserted in shallow pits in premaxillae, maxillae, dentaries, and pterygoids. Nasals and premaxillae fused into a single bone. A true joint between angular and splenial; rami of mandibles united by ligaments. Vertebrae procoelous. Sclerotic plates present sometimes with zygosphenes. Seven cervicals. No clavicles; sometimes a slender interclavicle. A calcified sternum. No sacrum. Legs paddle-like, short, webbed, without claws, hyperphalangic, pentadactylate. The mosasaurs are a group of large marine lizards, of world-wide distribution during Upper Cretaceous times. In all probability they were descended from subaquatic Uzards like the aigialosaurs in late Lower Cretaceous times, differing from them chiefly in the loss of the sacrum and the adaptation of their limbs to purely aquatic uses. Three types of mosasaurs are recognized: the surface-swimming type with elongated trunk composed of as many as thirty-five dor- sals, the tail with a pronounced sub terminal dilatation, zygosphenes, a well-ossified carpus, and only slight hyperphalangy, of which Mosasaurus and Clidastes are types; a deeper- sea type with propor- tionally shorter neck, less elongated trunk with but twenty-two vertebrae, a more uniformly flattened tail, less well-ossified carpus and tarsus, and greater hyperphalangy, with Platecarpus as a type; a diving type, with more elongated head, heavy cartilaginous pro- tections for the ears, a relatively short neck, body with but twenty- two vertebrae, a longer and much flattened tail, the almost entirely cartilaginous mesopodials and highly developed hyperphalangy, and greater size, of which Tylosaurus is the best-known type. And these three groups have been, perhaps rightly, recognized as distinct fam- ilies. The mosasaurs were clothed with small Varanus-\ike scales, of which impressions have been often found. The bones, especially of the deep-diving forms, were soft, doubtless impregnated in life with fat. THE SUBCLASS PARAPSIDA ^n Family Mosasauridae. Teeth conical, pointed. Upper Cretaceous. Mosasaurus Conybeare, Clidastes Cope, Platecarpus Cope, ISironectes Cope, Macrosaurus Owen, Brachysaurus Willis- ton, Baptosaurus Marsh, North America. Plio- platecarpus Dollo, Prognathosaurus Dollo, Haino- saurus Dollo, Mosasaurus Conybeare, Europe (England, France, Belgium, Russia). Taniwha- saurus Hector, New Zealand. Family Globidentidae. Teeth spheroidal, rugose. Imperfectly known. Upper Cretaceous. Globidens, Gilmore, Europe and North America. )/ ^ r w Tribe Amphisbaenia Worm-like or snake-like, burrowing lizards, reaching a length of about one and one-half feet, either legless or with short tetradactyl front limbs immediately back of the skull. Body with numerous rings and without scales, the tail very short and blunt. Eyes minute. No postorbital or temporal arch, the quadrates fixed by the ptery- goids; squamosals and tabulars indistinguishable; no postorbitals, lacrimals, or jugals; the nasals large. No parietal foramen. Brain-case in front partly enclosed by plates from f rentals. Palate without openings back of the nares. Stapes short and stout. Vertebrae procoelous. A curious group of burrowing hzards, moving by vertical rather than lateral undulations. The solid skull with the palate firmly fixed, the im- movable quadrates, and entire absence of arches, together with the vestigial or absent limbs, are characters almost as far removed from the typical lacertilian structure as are those of the snakes, 2 74 THE OSTEOLOGY OF THE REPTILES and seem to be as important in classification as those distinguishing the much more typically lizard-like mosasaurs. No extinct lizards are certainly referable to this tribe, though it is probable that some referred to it will eventually be found to have all the essential characters of the group. Family Amphisbaenidae. With the characters of the group. Oligocene. Rhineura Cope, Aciprion Cope, Diacium Cope, Hy- porhina Baur (a postorbital arch). Cremastosaurus Cope, Platyrha- chis Cope, North America. Tribe Rhtptoglossa Small, arboreal, perching lizards. Arches complete, the quadrate slender. Postfrontals indistinguishable; premaxillae small or vesti- gial; no septomaxillae; parietals and frontals unpaired; no parietal foramen; epipterygoids absent or vestigial; palate with openings. Vertebrae procoelous; five cervicals, from eleven to fifteen dorsals, two sacrals, and slender, prehensile tail, the spines sometimes elon- gated. Clavicles absent or vestigial. Mesopodials much reduced, digital formula 2, 3, 4, 4, 3, the digits in opposable groups of two and three. Abdominal ribs present. A group composed of about fifty living species confined to Mada- gascar, Africa, and India. A curious group of insectivorous tree lizards, long famous for their power to change color, and for their peculiar grasping digits. Our paleontological knowledge of them is vague. Family Chameleontidae. With the characters of the group. Eocene. Chameleo (Leidy), North America. Prochameleo de Ste- fano, France. Genera Incertae Sedis Triassic. ? Paliguana Broom. South Africa. Jurassic. ? Saurillus Owen. Jura, England. Eocene. Enigmatosaurus Nopcsa (de Stefano), Europe. Nao- cephalus Cope, North America. Upper Cretaceous. Coniosaurus Owen, Saurospondylus Seeley, England. ? Tylosteus Cope, North America. Pleistocene. Notiosaurus Owen, ? Patricosaurus Seeley, England. THE SUBCLASS PARAPSIDA 275 B. Suborder Ophidia (Serpentes) Elongated, legless reptiles of from a few inches to thirty feet in length, sometimes with vestiges of hind limbs but never with front Hmbs or pectoral girdle. There are no temporal arches, no squa- mosals, jugals, epiptery golds, lacrimals, postoptics, and sometimes no ectopterygoids. The quadrate articulates loosely with the tabular only; in a few instances even the tabular is absent (Uropeltidae) . The brain-case in front is enclosed by descending plates from the parietals and frontals to the sphenoid, from the latter sometimes in- terrupted by the coalescent optic foramina. Prootics largely visible. The pterygoids and usually the palatines have teeth. The premaxil- lae are small and often edentulous; maxillae rarely edentulous. Teeth acrodont. Parietals fused, no parietal foramen. The man- dibles are united in front by Ugaments only; the posterior bones are often fused, the coronoids sometimes absent, the dentaries loosely articulated. The vertebrae are numerous, sometimes exceeding four hundred in number, divisible into precaudal and caudal, series, the first two or three without ribs, cervical. Always procoelous and always with zygosphenes and zygantra. Anterior vertebrae, some- times to the caudals with a more or less prominent hypapophysis. No chevrons, but more or less of the caudals with a descending proc- ess on each side (lymphapophyses) . This suborder, often considered an order, includes more than eighteen hundred living species widely distributed over the earth. Like so many groups of organisms known in many related forms, there is scarcely a single positive character to distinguish them ; the most decisive, as has been mentioned, is probably the complete bony closure of the brain- case; and there is never a vestige of a pectoral girdle, though several families have vestigial pelvic and hind limb bones. Probably the snakes are the latest group of equivalent rank to be evolved among the Reptilia, and of the snakes the poisonous vipers are probably among the latest. Most snakes are purely ter- restrial in habit; a few are burrowing, and still others are aquatic. And chiefly because of such upland habits they are very scantily represented among fossils, not more than fifty or sixty species alto- gether; and of them with very few exceptions their fossil remains are few and fragmentary, and their taxonomic relations very doubtful. 276 THE OSTEOLOGY OF THE REPTILES Family Typhlopidae. No ectopterygoids or tabulars. Maxillae vertical, toothed; maxillae and mandibles edentulous. Vestiges of pelvis present. The Typhlopidae with but a single living genus and about one hundred species are widely distributed in the tropical regions. They are burrowing in habit. A single extinct form {SymoleopMs Sauvage) from the Cretaceous of France (Senonian) has been referred here; the single known vertebra is more probably that of a dolichosaur lizard. Family Boidae (Py thonidae) . Ectopterygoid and coronoid pres- ent. Maxillae horizontal, reaching premaxillae, with solid teeth, the latter with or without teeth. Tabular long, or short and closely attached to the skull (Illysiidae) . Vestiges of hind Hmbs present. A family of wide distribution comprising about sixty species, some of them attaining a length of nearly thirty feet. Boas, anacondas, pythons, etc. Upper Cretaceous. Dinilysia Woodward, Patagonia. Eocene. Protagaras Cope, Limnophis Marsh, Lestophis Marsh, Boavus Marsh, North America. Oligocene. Paleopython Rochebrune, Scytalophis Rochebrune, France. Paleryx Owen, England. Miocene. Heteropython Rochebrune, Scatophis Rochebrune, France. Aphelophis Cope, Ogmophis Cope, Calamagras Cope, North America. Botrophis Mercer, France. PHocene. Python Daudin, East India. Family Paleophidae. Neural spines elongate; vertebrae with an inferior ridge. Large snakes, probably subaquatic, imperfectly known. Eocene. Pterosphenus Lucas, Paleophis Owen, North America. Paleophis Owen, Europe. Family Viperidae. No coronoids. Ectopterygoids present. Max- illae vertically erectile, articulating with prefrontal, excavated (Crotalinae) or not (Viperinae). Poison fangs perforated. About one hundred living species of these poisonous snakes with erectile fangs are known, widely distributed. Pit vipers (rattlesnakes and copperheads) exclusively in America.^ 1 [Occur also in Asia and Malaysia. — Ed.] THE SUBCLASS PARAPSIDA 277 Uppermost Cretaceous. ? Coniopkis Marsh, North America. Eocene. ? Helagras Cope, North America. OHgocene. Neurodromicus Cope,. North America. Miocene. Vipera Laurenti, Germany. Pleistocene. Crotalus Linne, North America. Family Elapidae. Ectopterygoids present. Maxillae horizontal, not erectile, their anterior teeth deeply grooved or hollowed. Caudal h3^ophyses bifid. Laophis, Salonica. This family of highly poisonous snakes, in its wider sense including the cobras, sea snakes, and the coral snakes of the southern United States, comprises nearly two hundred living species. They are prac- tically unknown as fossils. Cobras {Naja Laurenti) have been re- ported from the Pleistocene of France, but doubtfully. Family Colubridae. Ectopterygoid present, the coronoid ab- sent. Maxillae horizontal, with solid teeth. Tabular present. Post- orbital not produced forward. This family of harmless snakes includes more than half of all living species, none attaining a size of more than seven or eight feet. Their distribution is world-wide. Miocene. Elaphis Aldrich, Tamnophis Rochebrune, Pylemophis Rochebrune, Periops Wagler, Europe. Pleistocene. Coluber Linne, Europe and North America [ =] Bas- canion Baird and Gerard, North America. CHAPTER XII THE SUBCLASS DIAPSIDA Two temporal openings, the upper bounded by the parietal above, the postorbito-squamosal arch below; the lateral by the postorbito- squamosal arch above, the jugal, or jugal and quadratojugal, below. A single coracoid on each side; no cleithra. Pelvis with pubo- ischiatic opening. Quadrate fixed or partly movable, never strep- tostylic. The phyletic unity of this great division of reptiles and their descendants, the birds, admits of Uttle or no doubt. In much prob- ability they were derived from the single- arched type with the lateral opening, by the simple separation of the postorbital and squamosal from the parietal. Until recently it was confidently believed that the most primitive and oldest representative of the subclass was Paleo- hatteria, from the Lower Permian. In all probabiUty, if not cer- tainty, this form did not have the upper temporal opening, and must therefore be included in the more primitive group, the Theromorpha. At present the oldest known form referable to the subclass is Youngina, from the Upper Permian of Africa, an intermediate type peculiar in its retention of certain skull bones lost in all other mem- bers. It is, however, yet very imperfectly known. Doubtless many other forms from the Permian with these and yet other primitive characters await discovery. 12. ? Order Proterosuchia Skull elongate, with palatal teeth; an antorbital vacuity. Skull only known. [Triassic. Proterosuchus Broom, South Africa.] 13. Order "Eosuchia" Family Younginidae. Skull with interparietals and tabulars (? supratemporals). Skull short; no antorbital vacuity^; probably with palatal teeth. Skeleton otherwise unknown. Upper Permian. Youngina Broom, South Africa, 1 [An antorbital vacuity is present, according to Broom. — Ed.] THE SUBCLASS DIAPSIDA 279 A. SUPERORDER DIAPTOSAURIA Teeth on some or all the palatal bones, acrodont or protacrodont. No antorbital opening; no interparietals or tabulars. Vertebrae amphicoelous. Dorsal ribs holocephalous, articulating in part or chiefly to centrum. Two or three sacral vertebrae. Fifth tarsale absent. Phalangeal formula never reduced. Parasternal ribs present. In the absence of more complete information as to the structural details of some of the forms included under this group name, and in the differences of opim'on, as usual, as to the value of the groups, the tribe or superorder Diaptosauria has a present use. Several groups formerly placed under it are now relegated to other divisions. 14. ORDER RHYNCHOCEPHALIA Terrestrial or littoral lizard-like reptiles of small or moderate size. Palate primitive, with teeth on some or all the bones. Pectoral girdle complete. Dorsal ribs holocephalous, articulating in inter- central space and arch. The three groups of reptiles here considered suborders are by some authors given a family rank, by others ordinal. Except the Hving Sphenodon, most of the genera are yet incompletely known. The differences between them seem hardly greater than among the Lacertilia with the inclusion of the Pythonomorpha. A. Suborder rhynchosauria Skull more or less depressed and broad, with a strong, decurved, and edentulous beak, formed by the premaxillae. Temporal open- ings relatively large, their boundaries as in the Sphenodontia. No parietal foramen. Nares undivided. Palate with small interptery- goidal opening. Dorsal intercentra absent or unknown. About seven or eight cervicals and twenty- three presacrals; two sacrals. A small pubo-ischiatic vacuity. Humerus without epicondylar foramina. A small group of terrestrial, perhaps in some cases subaquatic, shore-dwelling and shell-eating reptiles from three to six feet in length. The complete skull, tail, and mesopodials are known in none. In Howesia a distinct intermedium tarsus is figured; if not an 2 8o THE OSTEOLOGY OF THE REPTILES error, it is the only known example among reptiles. The palatal teeth are confined to the palatines in two or three rows, save in Howesia, where they occur on the pterygoids only. However, the Fig. 1 85. Skeleton of Rhynchosaurus (Rhynchocephalia). After Woodward. Five sixteenths natural size. THE SUBCLASS DIAPSIDA 281 anterior part of the skull of this genus is poorly known, and its im- mediate relationships with the other genera are still in doubt. Upper Triassic. Rhynchosaurus Owen, England. Hyperodapedon Huxley, Scotland, India. Stenometopon Boulenger, Scotland. Howesia Broom, South Africa. B. Suborder SpheNodontia (Rhynchocephalia vera) Upper temporal opening bounded by parietal, squamosal, post- frontal, and postorbital. A single row of acrodont teeth on maxillae, dentaries, and palatines. Premaxillae with a decurved beak, usually with teeth. Frontals and parietals paired. No lacrimals. A parietal foramen. Humerus with an entepicondylar foramen, sometimes also with an ectepicondylar foramen. Pelvis with large pubo-ischiatic vacuity. Carpus primitive. Twenty-three to twenty-five presacral vertebrae, the neck with not more than eight. Parasternal ribs present. Two genera only, the living Sphenodon and the Jurassic Homoeo- saurus, can be located with certainty in this suborder. Sphenodon has long enjoyed the reputation of being the most primitive of living reptiles, as evidenced by the persistent dorsal intercentra, deeply amphicoelous vertebrae, and the single-headed ribs of primitive type. So far as known Homceosaurus agrees closely, except that it has no uncinate process on the ribs, a character in which Spheno- don is almost unique among reptiles. Probably it has dorsal inter- centra, but this remains to be determined. It has also no ectepi- condylar foramen present in Sphenodon. Palacrodon and Opisthias are known only from mandibles. The former, however, is said to have teeth quite Hke those of Ardeosaurus which, according to Nopcsa, is a near relative of Acrosaurus. Nor is the temporal region of Ardeosaurus as well known as one could wish. Brachyrhinodon has two temporal arches, but is poorly known otherwise. Of Eifelo- saurus the skull is wholly unknown. Middle and Upper Triassic. ? Eijelosaurus Jaekel, ? Polyspheno- don Jaekel, Germany. Palacrodon Broom, South Africa. Brachy- rhinodon Huene, Scotland. Upper Jurassic. Homceosaurus, v. Meyer, Ardeosaurus v. Meyer, Germany.^ MBut cf. page 268 above. According to C. L. Camp (1923), Ardeosaurus is related to the geckos . — Ed.] 282 THE OSTEOLOGY OF THE REPTILES Lowermost Cretaceous. Opisthias Gilmore, Wyoming. Recent. Sphenodon Gray, New Zealand. Fig, 1 86, Skeleton of /fo>waoJtf«r«J (Rhynchocephalia). After Lortet. Natural size. THE SUBCLASS DIAPSIDA 283 C. Suborder Choristodera Elongate, subaquatic reptiles, with a very slender face, terminal undivided nares, with small teeth on all palatal bones. No parietal foramen. Internal nares posterior. Teeth labyrinthine in structure. Vertebrae shallowly amphicoelous without dorsal intercentra. Twenty-six presacral, two or three sacral, and a long, flattened tail. Dorsal ribs holocephalous, broad, and heavy. Parasternals stout. Pelvis without pubo-ischiatic opening. Humerus with ectepicon- dylar foramen. Mesopodials imperfectly known. This small group of water reptiles, animals reaching a length of eight feet, is of interest because of the retention of several primitive characters, otherwise unknown in the Diapsida, especially the laby- rinthine teeth and the absence of a pubo-ischiatic opening. The ar- rangement of the bones of the temporal region is doubtful. The legs are essentially terrestrial in structure, with but slight aquatic adaptations, but the heavy flattened ribs and the elongate flat- tened tail decisively indicate bottom-crawling aquatic habits. The relationships between the known genera are very close. Uppermost Cretaceous and Paleocene. Champsosaurus Cope {Nothosaurops Leidy), North America. Simcedosaurus Gervais, France, Belgium. D. ? Suborder Thalattosauria Marine reptiles with elongate face, posterior[ly placed external] nares, sclerotic plates, and paddle-like extremities. Premaxillary, anterior, mandibular, and pterygoidal teeth conical; those of the prevomers, and posterior part of maxillae and mandibles low- crowned. A parietal foramen. Vertebrae rather deeply biconcave; intercentra unknown. Dorsal ribs holocephalous, articulating chiefly with centra. Parasternal ribs slender. Humerus short, with- out foramina. These small reptiles of but three or four feet in length are still im- perfectly known; nor is it quite certain that they have two temporal openings. The upper opening occupies a peculiar position. The limbs, so far as known, resemble those of the mosasaurs. The habits of the thalattosaurs must have been similar to those of the mosa- saurs; the dentition intermediate between that of the Mosasauridae and that of the Globidentidae. 284 THE OSTEOLOGY OF THE REPTILES Middle and Upper Triassic. Thalattosaurus Merriam, Necto- saurus Merriam, California. AA. SUPERORDER ARCHOSAURIA Dorsal ribs attached exclusively to the arch, at least anteriorly, by two articulations, the cervicals to arch and centrum. Usually an antorbital vacuity. The quadra to jugal is well developed and usually enters the border of the lateral temporal opening. No parietal fo- ramen, tabulars, or [dermojsupraoccipitals, and doubtfully, [if] ever, the interparietals. Teeth thecodont, confined to jaws, rarely absent. Vertebrae never notochordal, nor the dorsal intercentra persistent. 15. ORDER PARASUCHIA From small to rather large, crawling or leaping reptiles, character- ized especially by the normal pelvis, absence of a secondary palate, and a large antorbital opening. Body usually with dermal armor. Roof bones of skull always paired; postfrontals present. Vertebrae amphicoelous or platycoelous. Clavicles and interclavicle present, the corocoid not elongate. Parasternal ribs generally present. Meso- podials imperfectly known; phalanges not reduced. The Parasuchia in the present sense were long united with the Crocodilia as two suborders, the Parasuchia, sens, str., and the Pseudosuchia or Aetosauria, but the marked differences in skull and pelvis justify their ordinal separation. By some authors the three suborders here recognized are each given ordinal rank. Sclerotic plates are known in a single genus of Pseudosuchia. A. Suborder Pseudosuchia Typically a group of small, slender, climbing or leaping reptiles with more or less elongated hind legs. The external and internal nares are near the extremity of the more or less pointed skull; the lateral orbits are large, as are also the antorbital openings. The epi- podials are long, the clavicles and interclavicle slender. None of the forms referred to this suborder is completely known, and among the known forms there is a considerable diversity of structure, some departing so widely, perhaps, that their location here is provisional. Of the more typical, Sderomochlus has no dermal THE SUBCLASS DIAPSIDA 285 armor, and Euparkeria alone has sclerotic plates ; the latter has been accredited with an interparietal bone. With the inclusion of the doubtful forms there are but few con- stant characters to distinguish the group from the Rhynchocephaha ; typically, however, the absence of palatal teeth, and the attachment of the dorsal ribs are decisive. As a whole, however, the group is one of wide genetic possibiHties and [may] have had a close genealogical relationship with all the other members of the Archosauria, and especially the Saurischia. Nearly every known genus has been ac- credited with family rank. Family Aetosauridae. Twenty-five presacrals; two sacrals. Hu- merus a Httle longer than radius and ulna; hind legs a half longer than the front. Dorsal scutes transversely elongate, covering the whole back; abdomen with small plates. Triassic. Aetosaurus Fraas, Dyoplax Fraas, Germany. Stegomus Marsh, Connecticut. Family Ornithosuchidae. Scapula slender, coracoid short and broad. Legs very slender, the epipodials a Httle longer than the propodials. Two rows of dermal plates, each longer than broad. Euparkeria is accredited with an interparietal, the only member of the group. Triassic. Ornithosuchus Newton, ? Erpetosuchus Newton, Eng- land. Euparkeria Broom, Sphenosuchus Haughton, South Africa. Family Scleromochlidae. Premaxillae united. Twenty-one presacrals, three sacrals. Scapulae slender, coracoid long. Pubes long and slender, expanded at extremity; calcaneum with tuberosity; feet as long as tibia, the epipodials longer than propodials. Slender parasternal ribs. No dermal armor. Triassic. Scleromochlus Woodward, England. B. Suborder Pelycosimia Large, heavily built, terrestrial or marsh reptiles. External and internal nares near extremity of triangular skull. Antorbital open- ings large, the orbits relatively small. Upper temporal opening not depressed below level of [parietals]. Palatines approximated or con- 286 THE OSTEOLOGY OF THE REPTILES tiguous, without respiratory canal. Teeth compressed, curved, and sharply pointed. Legs short and rather stout. This group, proposed as a separate order, is based almost exclu- sively upon Erythrosuchus. In the structure of the skull it is some- what intermediate between the Pseudosuchia and the Phytosauria. Triassic. Erythrosuchus Broom, South Africa. ? Scaponyx Wood- ward, South America. c. SUBORDER Phytosauria Large, crawling, subaquatic reptiles, reaching a length of twenty or more feet, especially characterized by the elongate face, com- posed chiefly of the premaxillae, the posterior nares, and the deep respiratory canal, formed by the underarching of the palatines. Skull rugose, the lateral, temporal, and antorbital openings large, the supratemporal opening small and more or less depressed below the plane of the parietals. Tip of premaxillae decurved, with two or three very long, cylindrical teeth on each. Teeth either cyhn- drical throughout, or the posterior ones more or less flattened and separated. Neck, body, and tail covered with four or more rows of strong dermal bones; the pectoral region and abdomen with smaller, bony scutes. Tail long and flattened, compressed. Feet probably webbed. Vertebrae platycoelous ; two sacrals. Family Phytosauridae. Ilium with postacetabular process; pubis not dilated at extremity. Triassic. Phytosaurus Jaeger, Mystriosuchus Fraas, Mesorhinus Jaekel, Germany. Parasuchus Lydekker, India. Paleorhinus WiUis- ton, Angistorhinus Mehl, Lophoprosopus Mehl, Rocky Mts. Rutiodon Emmons (Rhytidodon) , CaroUna, New York, Connecticut. Family Stagonolepidae. A supracoracoid foramen. Ilium with- out postacetabular process; pubes dilated at extremity. Triassic. Stagonolepis Huxley, England. [D. Suborder Desmatosuchia] [Large, long-tailed reptiles reaching a length of perhaps sixteen feet, especially characterized by the probably secondary absence of the upper temporal opening. Cervical and anterior dorsal bony plates bearing long horn-Uke outgrowths. Skull with large antorbital THE SUBCLASS DIAPSIDA 287 opening and dorsal anterior nares, snout not greatly produced. Teeth thecodont. Distinguished from the Phytosauria especially by the absence of the upper temporal opening, which may have been secondarily lost as in the caimans. Von Huene refers Desmato- suchus to the Phytosauria. Triassic. Desmatosuchus Case, Texas.] 16. ORDER CROCODILIAN [Loricata] Internal nares carried far back in the mouth by the union of the maxillae and palatines, and in the later forms the pterygoids also. Premaxillae never much elongate, the external nares terminal. Ace- tabulum formed by ilium and ischium only, the so-called pubes (Pprepubes) excluded and not meeting in a median symphysis. Phalanges of fourth and fifth digits reduced; calcaneum elongate. Two sacral vertebrae. The Crocodilia are at once distinguished from all other reptiles by the structure of the palate and pelvis. There is not a very great di- versity of structure among the known forms. All are lizard-like in form, with a long, flattened tail, very predaceous, with conical the- codont teeth, and more or less water-loving in habit. In size they vary from less than one foot to about fifty feet in length. The verte- brae were platycoelous in all till about the beginning of the Lower Cretaceous; procoelous in all since the early part of the Eocene. Some have a relatively broad skull ; others a more or less elongated face, sometimes very slender, as in the ancient teleosaurs and the modern gavials. In such forms the nasals do not reach the external nares, and the splenials meet in a symphysis. The upper temporal openings in the modern forms are smaller, very small in the broad- faced types. In the early types the arch between the orbit and lateral temporal opening was covered immediately by the skin; since Wealden times the bar is more cylindrical and more deeply placed. The amphibious crocodiles have a strong dermal, osseous armor along the back and tail, sometimes also on the under side. Both the carpus and tarsus are peculiarly modified, suggesting, v. Huene thinks, a primitive, more upright- walking gait. ^ [For recent morphological and taxonomic treatment of the Crocodilia, see numerous papers by C. C. Mook, 1921-, Bulletin, Amer. Mus. Nat. Hist. — Ed.] 288 THE OSTEOLOGY OF THE REPTn.ES A. Suborder Eusuchia An antorbital opening primitively present but lost in many an- cient and all modern forms. Mandible with an external vacuity posteriorly. Nine cervical vertebrae, twenty-three or twenty-four presacrals. No sclerotic plates in orbits. Body with dermal bones. Feet partly webbed, clawed, not paddle-like. Until within recent years, and still by some authors, the Eusuchia. comprised only those crocodiUans with procoelous vertebrae, am- phicoelian forms comprised in the suborder Mesosuchia. It is now known that the change in the form of the vertebrae was a relatively unimportant one and may have occurred in different lines of descent. Family Teleosauridae. Vertebrae platycoelous. Internal nares large, situated at posterior end of palatines. Face very long and slender. An antorbital opening sometimes present. Postorbital bar not modified. Upper temporal opening large. A nearly complete dermal armor. Front feet much smaller than hind. From two to ten feet in length. Jurassic. Pelagosaurus Bronn, Teleosaurus Geoffroy, Teleido- saurus Deslongchamps, Suchodus Lydekker, Aeolodon Meyer, Cro- codilemus Jourdan, Gnathosaurus Miinster, Europe. Steneosaurus Geoffroy, Europe, Madagascar. Cretaceous. ? Teleorhinus Osborn, Wyoming. Family Pholidosauridae. Vertebrae platycoelous. Internal nares opening in palatines and pterygoids. Face long; the nasals reach to the premaxillae. Upper temporal opening smaller than orbits. Postorbital bar modified. Front legs larger than in the Teleosauridae. Dorsal and ventral armor present. Upper Jura and Lowermost Cretaceous. PhoUdosaurus Meyer (Macrorhynchus) , Pterosuchus Owen, Europe. Family Atoposauridae. Vertebrae platycoelous. Posterior nares not reaching pterygoids. Head short, broad. Upper temporal open- ings much smaller than orbits. Dermal armor composed of two rows of quadrilateral plates, probably extending on tail. Probably no ven- tral scutes. Tail long. Small reptiles from eight to sixteen inches in length. THE SUBCLASS DIAPSIDA 289 Upper Jurassic. Atoposaurus Meyer, Alligator ellus Jourdan, Alligatorium Lortet, Germany. Family GoNioPHOLiDAE. Vertebrae platycoelous. Internal nares bounded by pterygoids and palatines. Face rather broad, not long. Postorbital bar subdermal. A dorsal armor of two or more rows of plates. Lowermost Cretaceous. GoniophoUs Owen, Europe, North and South America. Nannosuchus Owen, Theriosuchus Owen, Machimo- saurus Meyer, Bernissartia DoUo, Europe. Upper Cretaceous. Coelosuchus Williston, TeleorUnus Osborn, Wyoming. Notosuchus Woodward, Cynodontosuchus Woodward, South America. Family Dyrosauridae. Vertebrae platycoelous; internal nares between palatines and pterygoids. Face very slender. Postorbital bar subdermal. From fifteen to eighteen feet in length. Lower Eocene. Dyrosaurus Pomel, Africa. Family Hylaeochampsidae. Vertebrae probably procoelous. Internal nares surrounded by pterygoids. Palate with large foramen between ectopterygoid and maxillae. Skull short, broad. Wealden Cretaceous. Hylceochampsa Owen, ?Heterosuchus Seeley, England. Family Gavialidae. Vertebrae procoelous. Posterior nares sur- rounded by pterygoids. Face very slender. Postorbital bar sub- dermal. Upper temporal openings large. Nasals remote from nares. Dorsal but no ventral scutes. From ten to fifty feet in length. Pleistocene, Recent. Gavialis Oppel, Rhamphosuchus Owen, Paleosuchus Falconer and Cautley, India. Family Tomistomidae. Vertebrae procoelous. Posterior nares surrounded by pterygoids. Face less elongated, gradually merging into cranium. Postorbital bar subdermal. Nasals extend into nares. Sometimes an antorbital opening. From six to forty or more feet in length. Upper Cretaceous. Thoracosaurus Leidy, Holops Cope, United States. Eocene. [Tomistoma, Europe, Africa.] Eosuchus DoUo, Belgium. Plioeene. Tomistoma (?) [Gavialosiichus], Florida. 290 THE OSTEOLOGY OF THE REPTILES Pleistocene. Tomistoma, Hungary. Recent. Tomistoma, Borneo. Tertiary. Leptorhamphus Ameghino, Oxydontosaurus Ameghino, Argentina. Family Crocodilidae.^ Vertebrae procoelous. Posterior nares surrounded by pterygoids, single or divided. Upper temporal open- ings small. Postorbital bar subdermal. Face never slender. Teeth stout, anisodont. Dorsal plates in two or more rows, the ventral armor present or absent. The nasals usually reach the external nares. From four or five to more than forty feet in length. Uppermost Cretaceous. Deinosuchus Holland, Bottosaurus Leidy [Agassiz], Brachychampsa Gilmore, Leidyosuchus Lambe, ? Polydectes Cope, North America. Crocodilus Laurenti, Italy. Eocene. Crocodilus Laurenti, Diplocynodon Pomel, Europe, North America. Limnosaurus Marsh, North America. Oligocene. Caimanoidea Mehl, South Dakota. Miocene. ^'' Crocodilus'^ [?], [Alligator], North America. Pleistocene. Crocodilus Laurenti, Europe, India, Africa, North America. [Alligator, North America.] [Recent. Crocodilus, Osteolaemus, Osteoblepharon, Alligator, Cai- man, Jacare.] Incertae Sedis. Lower Jurassic. Notochampsa Broom, South Africa. B. Suborder Thalattosuchia Marine crocodiles, without bony armor, and with Hmbs more or less modified as paddles, without claws. Vertebrae platycoelous. Face more or less elongated. Nares at posterior end of palatines. Prefrontals large, protuberant. Supratemporal openings large. Bones of skull smooth. Orbits with sclerotic plates. No antorbital or mandibular openings. Seven cervical, twenty-five presacral, vertebrae. Tail long, with distal fin-like dilatation. 1 [Willis ton here includes the genera Alligator and Caiman under the CrocodUidae, and places Tomistoma in a separate family, but Mook {op. cit.) has shown that Alli- gator, Caiman, and Jacare are more distinct from Crocodilus and its allies {Osteolae- mus, Osteoblepharon) than is Tomistoma. — Ed.] THE SUBCLASS DIAPSIDA 29 1 Family Metriokhynchidae. Upper Jurassic. Dacosaurus Quenstedt, Geosaurus Cuvier, Europe. Metriorhynchus Quenstedt, Europe, Patagonia. Lowermost Cretaceous. Neustosaurus Raspail, ? Enaliosuchus Dollo, Europe. [DINOSAURIA] 17. ORDER SAURISCHIA More or less upright-walking reptiles. The normal pubes and ischia meet in a ventral symphysis, the acetabulum perforated. No predentary or rostral bones. One or more antorbital openings. No dermal bones. A. Suborder Theropoda Carnivorous or secondarily herbivorous in habit. More or less bipedal in gait, the hind feet more or less digitigrade, the front legs more or less reduced. Pubes meeting in a long ventral symphysis, with a distal dilatation. Family Plateosauridae. Teeth less compressed, not recurved and somewhat thickened, their anterior and posterior borders den- ticulated. Anterior vertebrae platycoelous; twenty- three presacrals, three sacrals. Front legs a little longer than the femora, preaxonic, their phalangeal formula 2, 3, 4, 5, (?), the first claw large. Hind feet more mesaxonic, the first and fifth toes reduced. Feet digiti- grade or semiplantigrade. Astragalus without ascending process. Upper Triassic. Plateosaurus Meyer, Gressylosaurus Riitimeyer, Pachysaurus Huene, Teratosaurus Meyer, Europe. Euskelosaurus Huxley, Gryponyx Broom, South Africa. This, the most primitive family of the Theropoda, is thought by some to have an ancestral relationship with the Sauropoda. The characters drawn chiefly from Plateosaurus may not and probably do not apply to all the genera listed in the family. The reptiles were clearly bipedal in gait, though of rather heavy build. Jaekel thinks that the hind feet were purely plantigrade, but this was improbable since the mesaxonic structure distinctly indicates the elevation of the ankle from the ground. Plateosaurus attained a length of about fifteen feet. 292 THE OSTEOLOGY OF THE REPTILES Family Anchisatjridae. Smaller and more slender theropods. Vertebrae amphicoelous. Teeth compressed, more or less recurved. Astragalus without ascending process. Upper Triassic. Anchisaurus Marsh, Megadactylus Hitchcock, Ammosaurus Marsh, Connecticut Valley. Thecodontosaurus Riley and Stutchbury, England, Africa, AustraHa. Massospondylus Owen, South Africa. Zanclodon Plieninger, Sellosaurus Huene, Europe. [No MS. was found for (i) the Coelurosauria, containing several families and numerous genera of light-limbed saurischian dinosaurs, including the Ornithomimidae, (2) the Megalosauria group of the Fig. 187. Skeleton of Gorfoj^wrwj (Saurischia). After Lam be. One thirty-sixth natural size. Jurassic, and (3) the Deinodont group of the Cretaceous. For group I see papers by Osborn 191 7 {Bulletin, Amer. Mus. Nat. Hist., vol. XLiii), von Huene 192 1 {Acta Zodlogica, Bd. II) ; for groups 2 and 3 see Matthew and Brown, 1922 {Bulletin, Amer. Mus. Nat. Hist., vol. XLVi). — Ed.] B. SUBORDER SAUROPODA (OPISTHOCOELIA, CETIOSAURIA) Quadrupedal, semiplantigrade, herbivorous dinosaurs, with long neck and tail and small skull. Postfrontal sometimes present. Teeth subcylindrical, with a thickened, spoon-shaped crown, in a single row, and more or less restricted to anterior part of jaws, the premaxUlae with teeth; no predentary. No coronoid process to mandible. The anterior, sometimes all, presacral vertebrae opisthocoelous, with a more or less developed hyposphene-hjrpantrum articulation, and with hollow, lateral cavities in centra. Four or five sacrals, twenty-six or THE SUBCLASS DIAPSIDA 293 twenty-seven presacrals. The pubes are massive and meet in a large ventral symphysis. Carpals and tarsals reduced, feet preaxial. Limb bones cancellous in structure. From about fifteen to about ninety feet in length. Family Cetiosauridae. Spines of dorsal vertebrae simple, not furcate. Front limbs as long as the hind. Scapulae dilated distally. Pubes not constricted. Upper Jurassic. Cetiosaurus Owen {Cardiodon Owen), England. Lower Cretaceous (Morrison). Haplacanthosaurus Hatcher, Bra- chiosaurus Riggs, Rocky Mts. Gigantosaurus Fraas (non Seeley), {? Brachiosaurus Riggs), South Africa. Pelorosaurus Mantell, Europe, Madagascar. Family Camarasauridae. Spines of dorsal vertebrae furcate. Front limbs distinctly shorter than hind. Scapulae distally ex- panded. Ischia slender. Lower Cretaceous. Camarasaurus Cope (Morosaurus Marsh), Pleurocoelus Marsh, North America. Titanosaurus Lydekker, Europe, Madagascar, India. Upper Cretaceous. Titanosaurus Lydekker, France, Patagonia. Family Atlantosauridae. Spines of presacral vertebrae furcate. Front legs much shorter than hind. Scapulae narrow distally. Ischia expanded at extremity. Lower Cretaceous (Morrison). Atlantosaurus Marsh, Apatosaurus Marsh (Brontosaurus Marsh), Amphicoelias Cope, Rocky Mts.^ Family Diplodocidae. Spines of presacral vertebrae furcate. Front legs shorter than hind. Teeth slender, confined to anterior part of jaws. External nares near top of skull, remote from extrem- ity. Ischia not expanded distally, the pubes constricted in middle. More slender sauropods. Lower Cretaceous (Morrison). Diplodocus Marsh, Rocky Mts. Genera Incertae Sedis: ? Jurassic. Dystrophaeus Cope, Rocky Mts. Upper Jura and Wealden. Bothriospondylus Mantell, Chondrosteus Owen, Chondrosteosaurus Owen, Eucamerotus Hulke, Ischyrosaurus ^ [Belongs in Diplodocidae. — Osborn and Mook.] 294 THE OSTEOLOGY OF THE REPTILES Hulke, Nesodon Mousaye, Oplosaurus Gervais, Ornithopsis Seeley^ Europe. Lower Cretaceous (Morrison). Barosaurus Marsh/ Caulodon Cope,^ Elosaurus Peterson and Gilmore, Epanterias Cope, Symphy- rophus Cope, ? Astrodon Leidy, Rocky Mts. Lower Cretaceous. Dinodocus Owen, Hypselosaurus Matheron, Aepysaurus Gervais, Morinosaurus Sauvage, Europe. Algaosaurus Broom, South Africa. Upper Cretaceous. Argyrosaurus Lydekker, Microcoelus Lydek- ker, South America. 18. ORDER ORNITHISCHIA [Orthopoda, Predentata] Quadrupedal or bipedal dinosaurs, especially characterized by the presence of a predentary bone in the mandible and by the structure of the pelvis. Premaxillae rarely with teeth. Antorbital openings small or absent. Vertebrae amphicoelous or amphiplatyan, the anterior ones often opisthocoelous. Pubes not meeting in a median symphy- sis, with an anterior, more or less spatulate, prepubis, and a posterior, usually long, postpubis, underlying the ischium. Front limbs always shorter than hind, never functionally pentadactylate, rarely with as many as four phalanges in any digit. Hind limbs usually function- ally tridactylate, more or less digitigrade. Ungual phalanges short and broad. A. Suborder Ornithopoda Bipedal in habit, digitigrade. External nares near extremity of face, divided. Postpubis complete, slender. Antorbital opening sometimes small. Family Nanosauridae. Premaxillae edentulous. Teeth in a single row, compressed and pointed. Vertebrae amphicoelous; three sacrals. Femur shorter than tibia. Bones very hollow. Of the size of a cat. Lower Jurassic. Nanosaurus Marsh, Colorado. Family Hypsilophodontidae. Premaxillae with teeth. Teeth in a single row. Anterior vertebrae opisthocoelous. Femur longer than 1 [Belongs in the Diplodocidae. — Lull.] 2 [Belongs in the Camarasauridae. — Osborn and Mook.] THE SUBCLASS DIAPSIDA. 295 tibia. Body covered with dermal ossifications. Five sacral verte- brae. Manus with five, the pes with four, digits, the fifth vestigial. Wealden. Hypsilophodon Hulke, England. Family Iguanodontidae. Premaxillae edentulous. Teeth in a single row. Anterior vertebrae platycoelous or opisthocoelous. No dermal ossifications. Four or five sacral vertebrae. Femur longer or shorter than tibia. Four functional fingers, three functional toes. This family has been sometimes divided into three, the Laosauri- dae with platycoelous vertebrae, the Camptosauridae, and Iguano- dontidae with opisthocoelous vertebrae; but the differences seem to be of minor importance. The Scelosaurus, though its teeth are unknown, has been located with the Hypsilophodontidae. Its vertebrae are plano-concave or nearly amphiplatyan. It is the latest of known Ornithopoda and may eventually, perhaps, find its proper location in a distinct family. Lower Cretaceous (Morrison, Wealden). Camptosaurus Marsh, Laosaurus Marsh, Rocky Mts. Iguanodon Mantell, England. Family Trachodontidae. (HADE.osAURiDAE.)Teethinmanyrows, forming a tessellated pavement in use. Premaxillae edentulous. Cranium often with crest. Extremity of face more or less dilated. Cervical vertebrae opisthocoelous, about fifteen in number; seven or eight sacrals. Tail flattened. Femur longer than tibia; phalanges reduced; four functional fingers and three functional toes. Sub- aquatic in habit; sclerotic plates in orbits. Upper Cretaceous. Cheneosaurus Lambe, Claosaurus Marsh, Had- rosaurus Leidy, Hypacrosaurus Brown, Kritosaurus Brown, Grypo- saurus Lambe, Prosaurolophus Brown, Saurolophus Brown, Stephano- saurus Lambe, Corythrosaurus Brown, Trachodon Leidy. B. Suborder Stegosauria [Quadrupedal, with dermal armor of plates and spines; skull small; bones solid. Jurassic to close of Cretaceous. No MS.] c. Suborder Ceratopsia Secondarily quadrupedal dinosaurs, with large skull, armed with horns and protuberances, located on nasal, postorbitals, and the margin of a greatly extended "frill" or extension of the skull over 296 THE OSTEOLOGY OF THE REPTH^ES the neck. Lateral temporal openings small. Teeth with divided roots in a single functional row. No teeth on premaxillae, the upper jaws terminating in a distinct ''rostral" bone. Vertebrae platy- coelous, the first three or four cervicals coossified. Sacrum com- posed of numerous vertebrae. Ilium with long preacetabular and postacetabular process. Ischium slender, curved, the postpubis more or less vestigial. Carpus and tarsus reduced, but two carpalia. Astragalus firmly united with tibia, the calcaneum free; fifth toe vestigial. Uppermost Cretaceous. Anchiceratops Brown, Brachyceratops Gil- more, Ceratops Marsh, Chasmosaurus Lambe, Centrosaurus Lambe, Diceratops Lull, Eoceratops Lambe, Leptoceratops Brown, Mono- clonius Cope, Triceratops Marsh, Styracosaurus Lambe, Torosaurus Marsh, Agathaumas Cope, Western North America. 19. ORDER PTEROSAURIA Volant reptiles with highly ossified, pneumatic skeleton. Skull elongated, more or less pointed, the external nares remote from the tip. No parietal foramen. Orbits with sclerotic plates. Neck elon- gate; eight or nine cervicals, ten or more dorsals, four to ten sacrals, and about twelve to forty caudals; the presacrals procoelous, the caudals amphicoelous. No supracoracoid foramen, clavicles, or in- terclavicle. Sternum large, well ossified; parasternals present. Hu- merus shorter than forearm, with large lateral process; carpus more or less reduced; a pteroid bone articulating with carpus. First three fingers small, with claws; fourth greatly elongated for support of patagium; fifth digit absent. Prepubes articulating with pelvis. Femora shorter than tibia; fibula reduced or absent; first tarsal row more or less fused with tibia; feet long, pentadactylate, the fifth toe more or less reduced. A. SUBORDER PTERODERMATA (RHAMPHORHYNCHOIDEA) Antorbital opening distinct. Jaws with teeth. Prevomers and internal nares distinct. Orbits large. Free cervical ribs sometimes present. Tail long, with a terminal dilatation. Metacarpals less than half the length of the forearm, articulating with carpus. Fibula present; fifth toe complete. Fig. 1 88. Skeleton o{ Rhatnphorhynchus (Pterosauria). One thirc" natural size. 297 298 THE OSTEOLOGY OF THE REPTILES Family Rhamphorhynchidae. Jurassic. Rhamphorhynchus Meyer, Scaphognathus Wagner, Di- morphodon Meyer, Dorygnathus Orpel, Campylognathus Plieninger, Europe. B. Suborder Pterodactyloidea Wing metacarpal, longer or but little shorter than forearm. Tail very short. No cervical ribs. Fifth toe more or less reduced. Family Pterodactylidae. Nares and antorbital vacuity more or less coalescent. Teeth in anterior part of jaws. Anterior dorsal vertebrae not fused. All metacarpals articulating with carpus. Pre- pubes not band-like. Smaller. Upper Jurassic. Pterodactylus Cuvier {Ornithocephalus Sommer- ing, Diopecephalus Seeley, Cycnorhamphus Seeley, Pterodracon Ly- dekker), Europe. Family Ornithocheiridae. Skull more elongate. A supra- occipital crest. Scapula with enlarged distal end articulating with notarium. Jaws with teeth in front. Skeleton imperfectly known. Wealden. Ornithocheirus Seeley, Ornithodesmus Seeley, England. Family Pteranodontidae. Skull much elongated, toothless. A long supraoccipital crest. Orbits small. No antorbital opening. No fibula; fifth toe without phalanges. First three metacarpals splint- like. Upper end of scapula articulating with notarium. Prepubes band-Hke. From twelve to twenty-five feet in expanse of wings. Upper Cretaceous. Pteranodon Marsh, North America. Ornithos- toma (? Pteranodon) Seeley, England. Family Nyctosauridae. Like the Pteranodontidae, but no oc- cipital crest, and the upper end of scapula flat, not articulating with notarium. Eight-foot wing expanse. Cretaceous. Nyctosaurus {N yctodactylus) Marsh, Kansas. Genera Incertae Sedis. Doratorhynchus Seeley, Paleornis Man- tell, England. Lower Cretaceous, Dermodactylus Marsh, Wyoming. Fig. 1 89. Skeleton o( Pterodactylus. Four thirds natural size. Fig. 190. Skeleton oi Nyctosaurus (Pterosauria). One eighth natural size. 299 300 ^ Boston Public Library Central Library, Copley Square Division of Reference and Research Services The Date Due Card in the pocket indi- cates the date on or before which this book should be returned to the Library. Please do not remove cards from this pocket. ,^°STON PUBLIC LIBRARY 3 iiiH^^^^^^^^^^^ 3 9999 06607 Oil 9 -^4: