AQUATIC REPTILES 



205 



BAPTANODON 



CRETACEOUS 



CYMOOSPONDYLUS 



the body cavity of the mother, resulting in the young ichthyo- 

 saurs being born in the water fully formed and able to take 

 care of themselves immediately after birth like the young of 

 modern whales and dolphins. When this viviparous habit 

 finally released the ichthyosaurs from the necessity of return- 

 ing to land for breeding they developed the extraordinary 

 powers of migration which car- 

 ried them into the Arctic seas 

 of Spitzbergen, the Cordilleran 

 seas of western North America, 

 and doubtless into the Antarc- 

 tic. So far as we know this 

 viviparous habit was never de- 

 veloped among the seafaring 

 turtles, which always return 

 to shore to deposit their eggs. 

 While the ichthyosaurs vary 

 greatly in size, they present a 

 reversed evolution from the ter- 

 restrial, quadrupedal type into 

 the swift-moving, fusiform body 

 type of the fishes, which is 

 finally reduced in predaceous 

 power through the degeneration of the teeth, as observed in 

 the Baptanodon, an ichthyosaur of the Upper Jurassic seas of 

 the ancient Rocky Mountain region. 



While the continental seas of Jurassic time were favorable 

 to this remarkable aquatic marine phase of the reptiles, still 

 greater inundations both of North America and of Europe 

 occurred during Upper Cretaceous time. This was the period 

 of the maximum evolution of the sea reptiles, the ultimate 

 food supply of which was the surface life of the oceans, the 



Fig. 82. 



Restorations of Two Ich- 

 thyosaurs. 



Cymhospcmdylns, a primitive ichthyosaur 

 from the Triassic seas of Nevada (after 

 Merriam), and the highly speciahzed 

 Baptanodon, a Cretaceous ichthyosaur 

 of the seas of that period in the region 

 of Wyoming, in which the teeth are 

 greatly reduced. Restorations for the 

 author by W. K. Gregory and Richard 

 Deckert. 



