# The Osteology of the Reptiles/Chapter 11

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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 centra. Numerous parasternal ribs. Scapula fan-shaped; a single coracoid; 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 specialized in the scapular girdle with its single coracoid, the earliest 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.
Fig. 175. Skeleton of Mesosaurus (Proganosauria). After McGregor. About four tenths natural size.
​Family Mesosauridae. Lower Permian. Stereosternum Cope (Notosaurus Marsh), Mesosaurus Gervais, Brazil. Mesosaurus Gervais (Ditrichosauruus 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 ​propodial and epipodial bones, hyperphalangy, and often hyperdactyly. Premaxillae long; maxillae short. A parietal foramen; free paroccipitals, 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, postfrontal, and tabular (supratemporal). No lateral opening. Vertebrae short, deeply amphicoelous, without persistent dorsal intercentra. Scapulae small; a single coracoid; clavicles and interclavicle present. No sternum, but numerous parasternals. Pelvis more or less plate-like with small pubo-ischiatic vacuity. Prearticular bone of mandible distinct.
The ichthyosaurs were exclusively marine reptiles, more perfectly adapted to aquatic life 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 holocephalous. 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 Shastosauridae. Body more elongate. Cervical ribs dichocephalous. Tail distinctly expanded and decurved distally. Chevrons Y-shaped. Epipodials relatively long. Feet tetra- or tridactylate.
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, Shastosaurus Merriam, Phalaradon Merriam, California, Nevada. Pessosaurus Wiman, Spitzbergen.
Fig. 177. Skeleton of Ichthyosaurus. After Dreverman.
Fig. 178. Skeleton of Cymbospondylus, a Triassic ichthyosaur. After Merriam. One sixty-second natural size.
​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 presents, however, numerous minor modifications that might justify its division.
Family Ophthalmosauridae. Differs from the more typical Ichthyosauria in the more reduced teeth, the presence of three epipodial 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). ? Ophthalmosaurus Seeley.
? ORDER OMPHALOSAURIA
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 themselves 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 essentially the same horizon in Spitzbergen similar teeth have been described by Wiman, which seem to pertain to the same kind of ​reptiles. Somewhat doubtfully associated with those remains are others of ichthyosaur-like bones that the describer provisionally associated with the Ichthyosauria, bearing possibly a like relation to the known Ichthyosauria that Globidens does to the typical Pythonomorpha.
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 limited, 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 Rhynchocephalia, 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, hollow-boned reptiles of less than eighteen inches in length, with long legs and long tail. The broad lateral temporal region is formed apparently of a single bone, here identified as the squamosal, the quadratojugal absent. The dermosupraoccipital is apparently large. Lacrimal vestigial or absent. A parietal foramen. All cranial bones paired. Palatal bones with teeth. At least seven cervical vertebrae, 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.
Fig. 179. Skeleton of Araeoscelis (Protorosauria). About one fourth natural size.
Fig. 180. Restoration of Araeoscelis.
​arboricolous, insectivorous, lizard-like reptile from the Lower Permian of Texas. Of Kadaliosaurus, unfortunately, the skull is unknown. 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-like, with probably a small pubo-ischiatic vacuity. Ribs single-headed, articulating with centrum, those of the cervical region very slender. Epipodials 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.
Fig. 181. Skeleton of Protorosaurus (Protorosauria), modified from Seeley. About one tenth natural size.
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 skull was the same. The numerous known specimens of Protorosaurus differ so much from each other that it is not at all improbable 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 ​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 reptiles about two feet in length. Skull with a single temporal opening, the quadrate fixed and the lateral temporal region moderately broad. No postfrontals; 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 Rhynchocephalia. 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 quadratojugal 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.
Fig. 182. Skeleton of Saphaeosaurus (Protorosauria). After Lortet. One fourth natural size.
​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 sacrals, and more than seventy caudals. Vertebrae amphicoelous, cervical intercentra hypapophysial. Ribs single-headed, articulating as in the Squamata. Numerous slender, parasternal ribs.
Pleurosaurus, the only certainly known genus of the family, was long supposed to be a member of the Rhynchocephalia, though it has also long been known to have but a single upper temporal opening. Its remarkable adaptation to aquatic life 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 Pleurosaurus, 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 probability the real squamosal.
Uppermost Jurassic. Pleurosaurus v. Meyer (Anguisaurus Münster, 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, streptostylic, 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 septum not ossified. Teeth acrodont or pleurodont, often attached to palatine and pterygoid. Prearticular fused with articular. Ribs single-headed, articulating with centrum.
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 proötics more or less membranous. Lacrimals small or vestigial. Posterior arcade sometimes absent. Mandibles usually united by suture. Vertebrae procoelous, except in the Geckonidae and Uroplatidae; not more than two sacral vertebrae. Clavicles 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 between 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 provisional. 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 characters 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 postoptics ("alisphenoids," "postorbitals"). However, in the Amphisbaenia even this character is doubtful, and in the mosasaurs a distinct descending plate from the parietals resembles that of the snakes, ​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 epipterygoid 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 pentedactyl, 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, comprising 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 ​supported by the elongated hyoid bones. Some are subaquatic in habit. The Moloch lizard, much like a "Horned Toad" in appearance, has long dermal spines.
Oligocene. France [Agama].
Pleistocene. Chlamydosaurus, Australia.
Family Iguanidae. Arboreal, terrestrial, burrowing, or sub-aquatic, reaching a length of six feet. Teeth pleurodont. No dermal 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 fifty genera are known of this family, almost exclusively American in distribution, including our largest and some of our most common lizards,—the Basilisc lizards. Iguanas, "Horned Toads," etc. The large Galapagos lizard, Amblyrhynchus, 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, North America. Proiguana Filhol, France.
Family Anguinidae. With well-developed, pentadactyl limbs, or limbs vestigial. Body covered with dermal ossicles beneath corneous scales. Temporal opening roofed over by dermal bones. Teeth pleurodont. A parietal foramen.
This family, common to Europe and America, comprises about fifty species. Most noteworthy are the "Glass Snakes" and the "Slow Worms," with vestigial limbs or wholly without them.
Miocene. Anguis, Diploglossus, France.
Family Helodermatidae. 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. No parietal foramen. 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 ​famous "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 America. Placosaurus Gervais, France.
Oligocene. Helodermatoides Douglass, North America.
Family Lacertidae. Quadrupedal, terrestrial lizards. Upper surface of skull with numerous dermal bones. Temporal opening roofed over by the postfrontal extending back between parietal and squamosal, 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 attaining 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. Oligocene, 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 crushing teeth.
Lower Cretaceous (Neocomian). Ardeosaurus Meyer.
Eocene. Cadurcosaurus Filhol, France.
​Oligocene. Dracaenosaurus Gervais, Protrachysaurus Stefano, France.
Pliocene. Didosaurus Günther.
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 Aigialosauridae, 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 terrestrial lizards. Unlike most lizards, they have a long protrusible tongue.
Eocene. Saniva Leidy, North America. Paleovaranus Filhol, Proganosaurus Portis, France.
Pliocene. 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 ​vertebrae, slender cylindrical body of twenty-six or twenty-seven vertebrae, two sacrals, and a long flattened tail. Zygosphenes present. Legs relatively small, the front ones smaller than the hind. Pleurodont.
The dolichosaurs, 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 life 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 propelling, and but little other, use in the water. Pleurosaurus, an allied reptile of similar form, has a short neck. In all probability the dolichosaurs 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 mandible 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, Carsosaurus Kornhuber, Opetiosaurus Kornhuber, ? Mesoleptos Cornalia, Europe (Dalmatia).
Fig. 183. Skeleton of Adriosaurus (Lacertilia). Three fourths natural size. After Seeley.
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 subterminal 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 proötic. 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 lizards 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 dorsals, the tail with a pronounced subterminal dilatation, zygosphenes, a well-ossified carpus, and only slight hyperphalangy, of which Mosasaurus and Clidastes are types; a deeper-sea type with proportionally 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 protections 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 families. The mosasaurs were clothed with small Varanus-like scales, of which impressions have been often found. The bones, especially of the deep-diving forms, were soft, doubtless impregnated in life with fat.
​Family Mosasauridae. Teeth conical, pointed.
Upper Cretaceous. Mosasaurus Conybeare, Clidastes Cope, Platecarpus Cope, ? Sironectes Cope, Macrosaurus Owen, Brachysaurus Williston, Baptosaurus Marsh, North America. Plioplatecarpus Dollo, Prognathosaurus Dollo, Hainosaurus Dollo, Mosasaurus Conybeare, Europe (England, France, Belgium, Russia). Taniwhasaurus Hector, New Zealand.
Family Globidentidae. Teeth spheroidal, rugose. Imperfectly known.
Upper Cretaceous. Globidens, Gilmore, Europe and North America.
Fig. 184. Skeleton of Platecarpus as mounted in the Palaeontological Exhibit, Walker Geological Museum.
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 pterygoids; squamosals and tabulars indistinguishable; no postorbitals, lacrimals, or jugals; the nasals large. No parietal foramen. Brain-case in front partly enclosed by plates from frontals. Palate without openings back of the nares. Stapes short and stout. Vertebrae procoelous.
A curious group of burrowing lizards, moving by vertical rather than lateral undulations. The solid skull with the palate firmly fixed, the immovable 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, ​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, Hyporhina Baur (a postorbital arch). Cremastosaurus Cope, Platyrhachis Cope, North America.
Tribe Rhiptoglossa
Small, arboreal, perching lizards. Arches complete, the quadrate slender. Postfrontals indistinguishable; premaxillae small or vestigial; 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 elongated. 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 Madagascar, 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 Stefano, France.
Genera Incertae Sedis
Triassic. ? Paliguana Broom. South Africa.
Jurassic. ? Saurillus Owen. Jura, England.
Eocene. Enigmatosaurus Nopcsa (de Stefano), Europe. Naocephalus Cope, North America.
Upper Cretaceous. Coniosaurus Owen, Saurospondylus Seeley, England. ? Tylosleus Cope, North America.
Pleistocene. Notiosaurus Owen, ? Patricosaurus Seeley, England.
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 limbs or pectoral girdle. There are no temporal arches, no squamosals, jugals, epipterygoids, 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 interrupted by the coalescent optic foramina. Proötics largely visible. The pterygoids and usually the palatines have teeth. The premaxillae are small and often edentulous; maxillae rarely edentulous. Teeth acrodont. Parietals fused, no parietal foramen. The mandibles are united in front by ligaments 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, sometimes to the caudals with a more or less prominent hypapophysis. No chevrons, but more or less of the caudals with a descending process 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 terrestrial 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 altogether; and of them with very few exceptions their fossil remains are few and fragmentary, and their taxonomic relations very doubtful.
​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 (Symoleophis 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 (Pythonidae). Ectopterygoid and coronoid present. 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 limbs 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.
Pliocene. 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. Maxillae 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.
​Uppermost Cretaceous. ? Coniophis Marsh, North America.
Eocene. ? Helagras Cope, North America.
Oligocene. Neurodromicus Cope, North America.
Miocene. Vipera Laurenti, Germany.
Pleistocene. Crotalus Linné, North America.
Family Elapidae. Ectopterygoids present. Maxillae horizontal, not erectile, their anterior teeth deeply grooved or hollowed. Caudal hypophyses 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 practically unknown as fossils. Cobras (Naja Laurenti) have been reported from the Pleistocene of France, but doubtfully.
Family Colubridae. Ectopterygoid present, the coronoid absent. Maxillae horizontal, with solid teeth. Tabular present. Postorbital 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 Linné, Europe and North America [ = ] Bascanion Baird and Gerard, North America.
* ↑ [Much further evidence for this view is given by von Huene in his memoir Die Ichthyosaurier des Lias und ihre Zusammenkänge, 1922, 4to, Berlin.—Ed.]
* ↑ [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 Ichthyosauria.—Ed.]
* ↑ [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.]
* ↑ [Rarely procoelous. See G. K. Noble, 1921, Amer. Mus. Novitates, No. 4.—Ed.]
* ↑ [Except Liolepis.—G. K. N.]
* ↑ [A postorbital arch is present.—G. K. N.]
* ↑ [Varanus komodoensis Owens, of the Dutch East Indies, reaches a length of thirteen feet.—H. C. Raven.]
* ↑ [Occur also in Asia and Malaysia.—Ed.]