THE ORIGIN OF MAN 73 



and passing into various stocks of more or less 

 narrow-shelled goniatids that finally gave rise in 

 the Carboniferous to many lines of evolution 

 among the primitive ammonids. During the late 

 Permian and early Triassic the greatest variation 

 took place and at the close of the Triassic they 

 mostly disappeared, probably due to a colder cli- 

 mate and oceanic water. In the Jurassic there 

 was another rapid evolution out of two or three 

 stocks only and the height of development was 

 attained at this time. The waning of the am- 

 monids began in the Comanchian and their com- 

 plete extinction came at the close of the Creta- 

 ceous during the critical time of the Laramide 

 Revolution. 



In addition to the ammonids, the rise of the 

 belemnites, the ancestors of the cuttle-fishes, took 

 place during the Mesozoic. The belemnids were 

 very active, highly carnivorous cephalopods, 

 which fed on fish, crabs and molluscs. They had 

 large and fully developed eyes, were devoid of 



