3 14 CLASSIFICATION OF VERTEBRATES. 



\ 



teeth or are toothless, and occasionally teeth occur on the ossi- 

 fied palatines (Fig. 171). The feet are either fitted for walking 

 or for swimming. 



SUB-ORDER i. SPHENODONTINA. 



Small terrestrial forms with amphicoelous vertebrae. Here belongs the 

 living Sphenodon. The fossil forms, Hom<zosaurus, Hyperodapedon, Pro- 

 terosaurus, Paloeohatteria, Telerpeton, etc., have been found only in 

 Europe. 



SUB-ORDER 2. CHORISTODERA. 



Aquatic reptiles with flattened vertebras ; teeth on the palatines and 

 pterygoids. Large forms from the upper cretaceous of North America 

 (Champ os aurus^) and lower eocene of Europe \Simcgdosaurus). 



ORDER VI. DINOSAURIA. 



Extinct, mostly terrestrial reptiles, frequently of enormous 

 size, with long tail, ambulatory feet, and a skin either naked or 

 covered with large dermal spines, plates, and ossicles. Vertebrae 

 solid or hollow ; flat, amphicoelous, or opisthocoelous, the latter 

 predominating ; sacrum of 3 to 6 vertebrae ; ribs bicipital ; ab- 

 dominal ribs occasionally present ; quadrate fixed ; supra- and in- 

 f ratemporal fossae present. Teeth in alveoli or alveolar grooves ; 

 no episternum or procoracoid ; sternum partially ossified ; ilium 

 elongate in front of and behind the acetabulum, the acetab- 

 ulum itself open ; pubis with frequently a well-developed post- 

 pubic branch ; toes with claws or hoofs. 



As the name implies, the dinosauria were enormous reptiles, 

 remains of which have been found in all continents except Aus- 

 tralia, but which were especially developed in western America. 

 In many respects they resemble the lizards ; in others some 

 were decidedly bird-like. In size they varied between forms a 

 yard in length up to giants over a hundred feet long. Some 

 were herbivorous, some carnivorous, and they were largely in- 

 habitants of swampy places ; some, like Amphicoelias and the 

 Megalosaurs, having bones so hollow and light that it seems as 

 if they could only support the weight of the body when it was 

 immersed in water. 



An exoskeleton occurred only in some orthopoda, and pos- 



