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 

 (? prepubes) 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. 



1 [For recent morphological and taxonomic treatment of the Crocodilia, see numerous 

 papers by C. C. Mook, 1921-, Bulletin, Amer. Mus. Nat. Hist. — Ed.] 



