THE PROGRESS OF LIFE 83 



short glance at them will, however, be sufficient ; 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 Rhynchocephalia ; but 

 in the upper Trias, and during the rest of the Mesozoic 

 era, we find marine forms, including the long but 

 stiff-necked Plesiosaicrus, which sometimes attained a 

 length of thirty feet. The turtles (Chelonia) are re- 

 lated 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 im- 

 possibility of their going ashore to lay their eggs, as 

 no doubt the other marine reptiles did. Their affinities 

 are doubtful ; but they appear to be most nearly 

 related to the early Ehynchocephalians. That they 

 were descended 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 related 

 to the Khynchocephalians. Lizards are first known in 

 the Jurassic, and snakes in the upper Cretaceous. The 

 branch called Pythonomorpha were large, snake-like 

 marine animals, swimming by means of four paddles 

 Some of them attained the enormous length of seventy 

 feet. They were cretaceous only. The Ornithosauria, 



