THE TRIASSIC PERIOD. 



47 



fornia. These, the Thalattosauria 1 (Fig. 343), were a strange group of 

 true marine reptiles, probable descendants of some early rhyncho- 

 cephalian-like reptile. The skull, though of ichthyosaurian aspect, 

 differed widely from the ichthyosaurian skull in structure, and was 

 remarkable for the possession of numerous teeth on the palate. The 

 group apparently soon became extinct, without descendants. The 

 Thalattosauria were less remotely removed from their ancestors than 

 the well-known ichthyosaurs of the Jurassic period, whose limbs had 



Fig. 343. — Skull of Thalattosaurus alexandrce (side and top), about f natural size. 



(After Merriam.) 



been, for the most part, converted into short broad flipper-like paddles. 

 In the newly-discovered Triassic forms the limb-bones were longer 

 (Fig. 342), and shaped more like those of the walking reptiles; the 

 hind limbs were often as large as the forward ones, while in other 

 characters they were more primitive. 



In many respects the Triassic land life, both plant and animal 

 would fall into its more natural relations if its evolutions in the latter 

 part of the period were united with those of the Jurassic. While the 

 early Trias was closely akin, physically and biologically, to the Per- 

 mian, the later part was little more than the initial phase of the Jurassic. 



1 Recently described by Merriam. 



