Page:The Osteology of the Reptiles.pdf/232

2. 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 symphysis; presacral vertebrae amphicoelous, or some or all opisthocoelous. No predentary or rostral bones in skull. Postaxial digits reduced. No dermal ossicles.
    1. Theropoda. Carnivorous or secondarily herbivorous, bipedal in gait, the front legs more or less reduced. Triassic to close of Cretaceous.
    2. Sauropoda (Cetiosauria, Opisthocoelia). Herbivorous, quadrupedal, the front legs but little or not at all reduced; limb bones not hollow; neck and tail elongate. Jurassic, Cretaceous.
18. Ornithischia (Orthopoda). Herbivorous, a predentary bone in mandible; pubes composed of a spatulate anterior process not meeting in symphysis, and a more or less elongate posterior process. Postaxial digits reduced.
    1. Ornithopoda. Upright-walking, bipedal. Without dermal bones. Lower Jurassic to close of Cretaceous.
    2. Stegosauria. Quadrupedal, with dermal armor of plates and spines; skull small; bones solid. Jurassic to close of Cretaceous.
    3. 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 procoelous.
    1. Pterodermata (Rhamphorhynchoidea). Wing metacarpal not longer than forearm; tail long. Skull with teeth. Jurassic.
    2. Pterodactyloidea. Wing metacarpal longer than forearm; tail short. Skull with or without teeth. Upper Jurassic to Upper Cretaceous.