THE CRETACEOUS PERIOD 



765 



forms persisted for a while. Their bills resembled those of mod- 

 ern birds. 



Terrestrial birds existed, but the fossil record of them is meager. 

 There were some curious aquatic forms, which will be mentioned 

 in connection with the sea. life. The mammals thus far recovered 

 from the Cretaceous indicate little advance upon those of the 



Fig. 517. A Cretaceous pterodactyl, Nyctosaurus gracilis Marsh, about 

 Vw natural size, from Niobrara Cretaceous, Kansas. (Restored by 

 Williston.) 



Jurassic. Mammals appear to have played a very inconspicuous 

 part in the fauna of the period. 



The Sea Life 



Vertebrates. The ichthyosaurs and plesiosaurs which had dom- 

 inated the Jurassic sea lived on into the Cretaceous. The former 

 dropped into an insignificant place soon after the beginning of the 

 period, but the plesiosaurs attained their highest development and 

 perhaps their greatest size, during the period. The American types 

 of plesiosaurs indicate lack of intermigration between this continent 

 and Europe. 



The aquatic branch of the scaled saurians (Squamata) attained 

 great importance as veritable sea serpents. The long-necked, 

 lizard-like reptiles of the Comanchean period were the forerunners 



