214 THE OSTEOLOGY OF THE REPTILES 



B. Thalattosuchia.' Neck shorter; no dermal plates; sclerotic 

 plates in orbits. Vertebrae amphicoelous ; a terminal caudal 

 fin. Front legs reduced, paddle-like. Marine. Jurassic. 



DINOSAURIA. More or less upright-walking reptiles. 



17. Saurischia. Pelvis normal, the pubes meeting in a ventral sym- 

 physis; presacral vertebrae amphicoelous, or some or all opistho- 

 coelous. No predentary or rostral bones in skull. Postaxial 

 digits reduced. No dermal ossicles. 



A. Theropoda. Carnivorous or secondarily herbivorous, bi- 

 pedal in gait, the front legs more or less reduced. Triassic 

 to close of Cretaceous. 



B. Sauropoda (Cetiosauria, Opisthocoelia). Herbivorous, 

 quadrupedal, the front legs but Httle or not at all reduced; 

 limb bones not hollow; neck and tail elongate. Jurassic, 

 Cretaceous. 



18. Ornithischia iOrthopoda) . Herbivorous, a predentary bone in 

 mandible; pubes composed of a spatula te anterior process not 

 meeting in symphysis, and a more or less elongate posterior proc- 

 ess. Postaxial digits reduced. 



A. Ornithopoda. Upright-walking, bipedal. Without dermal 

 bones. Lower Jurassic to close of Cretaceous. 



B. Stegosauria. Quadrupedal, with dermal armor of plates 

 and spines; skull small; bones solid. Jurassic to close of 

 Cretaceous. 



C. Ceratopsia. Quadrupedal. Skull very large with bony 

 horns and a posterior expansion fringed with scutes or 

 spines. Uppermost Cretaceous. 



19. Pterosauria. Volant reptiles, the bones pneumatic. Fourth 

 finger greatly elongated to support patagium. Vertebrae pro- 

 coelous. 



A. Pterodermata (Rhamphorhynchoidea). Wing metacar- 

 pal not longer than forearm; tail long. Skull with teeth. 

 Jurassic. 



B. Pterodactyloidea. Wing metacarpal longer than fore- 

 arm; tail short. Skull with or without teeth. Upper Juras- 

 sic to Upper Cretaceous. 



