78 THE ORIGIN OF MAN 



narrow, while some forms had a long, rudder-like 

 crest extending backward from it two feet. They 

 soared over the sea and, diving like ospreys, 

 picked out of it the fishes on which they fed. The 

 seas of this period continued to be dominated by 

 reptiles. The ichthyosaurs were vanishing but as 

 to the plesiosaurs, they attained their culmination 

 during this period. The most interesting of the 

 newly appearing animals were the scaled reptiles 

 known as mosasaurs which were confined to the 

 Cretaceous. They were gigantic in size, car- 

 nivorous, marine lizards ranging in length up to 

 twenty-three feet, with their limbs modified into 

 swimming paddles. In the early Cretaceous, 

 oceans began to spread over the continents and 

 it is therefore interesting to note that there was 

 great opportunity for expansive evolution, but 

 few new marine stocks appeared. But it was 

 a time of death instead to many characteristic 

 ones. In the late Cretaceous, ammonids, belem- 

 nids, rudistids and other stocks of molluscs dis- 



