THE ORIGIN OF MAN 75 



most characteristic ones were the Sauropoda de- 

 scribed above. The flesh eating dinosaurs of this 

 period were also large and terrible, but neither so 

 large nor so ferocious as those of the next period. 

 Also it is interesting to note that the oldest Amer- 

 ican frogs made their appearance during this 

 period, but as they were very small they appar- 

 ently were not of much significance in the animal 

 world of their time. The ammonids were still 

 plentiful though less so than in the Jurassic. In 

 the Comanchian they began to show a great loss 

 of vitality, in that only a few stocks arose, while 

 old ones were evolving toward a loss of characters 

 and an unwinding of the shell. The belemnids 

 were still abundant and flourishing. As to the 

 other invertebrate life of the sea, the sea urchins 

 were very varied and prolific in the warmer seas 

 while the heart urchins here and in the Cretaceous 

 attained their climax of evolution. Among the 

 bivalves, the ribbed oysters and the oyster-like 

 Gryphaeas were very abundant. In the equa- 



