50 WATER REPTILES OF THE PAST AND PRESENT 



hundred species of six or seven groups, and at least two orders have 

 been described. Of these the Cotylosauria are the continuation 

 of the American order, but include more speciahzed forms, the 

 Pareiasauria and the Procolophonia, all of them, like the more 

 primitive American forms, characterized by the imperforate 

 temporal region. The Therapsida, likewise, seem to be the con- 

 tinuation of the American Theromorpha, so closely allied to them 

 that it is difhcult to draw a distinguishing hne between them. 

 On the other hand, these African reptiles merge through the 

 Theriodontia into the mammals in the Triassic. They are all 



Fic. 27. — Restoration of Labidosaiini.s, a cotylosaur reptile from Texas, about 

 three feet long. 



terrestrial, crawling reptiles, except a few which are described 

 on a later page under the Anomodontia. 



The records of the lower part of the Triassic period are scanty 

 everywhere in the world, save perhaps in Africa. Before the close 

 of the period, however, probably every important group of cold- 

 blooded air-breathing animals had made its appearance in geological 

 history, if we except the snakes; even the mammals had appeared, 

 and possibly the birds. The Cotylosauria, Theromorpha, and 

 Therapsida disappeared, the latter giving birth to the mammals; 

 the nothosaurs and plesiosaurs, the ichthyosaurs, dinosaurs, croco- 

 diles, phytosaurs, rhynchocephalians, lizards, and turtles have all 

 left records of their existence in Upper Triassic rocks; and the 

 pterodactyls had also, in all probability, begun their career, 

 though none is surely known till the Jurassic. 



