VERTEBEATA 73 



The LoEiCATA includes three suborders, as follows : 

 Posterior nostrils opening in front of palate ; 

 nasals very short; premaxillary very 

 large ; external nostrils posterior, nasals 

 short ; Parasuchia. 



Nasal bones very long, separating the small 

 premaxillaries ; external nostrils an- 

 terior ; Pseudosuchia. 

 Nareal canal underroofed to behind larynx ; 

 no clavicle ; pubis excluded from acetab- 

 ulum ; external nostrils anterior ; Eusuchia. 



The Parasuchia and Pseudosuchia are restricted to the 

 Trias of both continents. The most important family of 

 the Parasuchia is the Belodontidfe (Fig. 24). The Pseudo- 

 suchia include the Aetosauridae, the members of which 

 were completely incased in an armor of bony plates. To 

 the Eusuchia belong the true crocodiles. They commence 

 in the Jurassic with the Teleosauridse and Goniopholididse, 

 which are followed in the Cretacic by the Crocodilidse (Fig. 

 25) and Gavialidse, which still exist. 



The Rhynchocephalia include two suborders : 

 Vertebrae amphicoelous ; axis undivided ; Sphenodontina. 

 Vertebrae amphiplatyan ; dentatum of axis 



separate ; Choristodera. 



To the Sphenodontina belong the Protorosauridae and 

 Paleohatteriidae, from the European Trias, the Homoeosauri- 

 dae, from the European Jurassic, and the Sphenodontidae, 

 which are represented by one species now living in New 

 Zealand. They are all of terrestrial habit, and of small or 

 medium size. The only family of the Choristodera is that 

 of the Champsosauridae, which is found in the Postcretacic 

 of North America and the Eocene of Europe. The 

 species were aquatic, and reached the size of some of the 

 modern caymans. The dentine is inflected at the base of 

 the teeth, and the limbs were paddle-like. This order fur- 

 nishes the starting point for the great Archosaurian series. 



