50 THE LESSON OF EVOLUTION 



for, owing to their extraordinary forms, they have 

 become familiar to most people. 



The Sauropterygia commenced in the Trias with 

 land animals (Nothosaurus) which are connected 

 with both the Anomodontia and the Ehynchocep- 

 halia ; but in the upper Trias, and during the rest of 

 the Mesozoic era, we find marine forms, including 

 the long but stiff-necked Plesiosaurus , which some- 

 times attained a length of thirty feet. The turtles 

 (Chelonia) are related to the Sauropterygians in 

 structure, although widely different in appearance. 

 They are first known in the upper Trias. The 

 Ichthyopterygia, including Ichthyosaurus, range 

 from the upper Trias to the close of the Cretaceous ; 

 and represent in habits and in appearance the whales 

 and porpoises of to-day. They were viviparous ; 

 and this was probably due to the impossibility of 

 their going ashore to lay their eggs, as no doubt the 

 other marine reptiles did. Their affinities are doubt- 

 ful ; but they appear to be most nearly related to the 

 early Ehynchocephalians. That they were des- 

 cended from land reptiles and were not fishes is 

 sufficiently proved by the bones of the shoulder and 

 pelvic girdles, the teeth, and the absence of a bony 

 operculum : the last showing that they did not 

 breathe by gills. 



The Squamata, or scaly reptiles, are closely re- 

 lated to the Ehynchocephalians. Lizards are first 

 known in the Jurassic, and snakes in the upper 

 Cretaceous. The branch called Pythonomorpha 

 were large, snake-like marine animals, swim- 

 ming by means of four paddles. Some of them 



