DISTRIBUTION. 181 



becoming extinct in the cretaceous. The first mammals appear in 

 the triassic, the birds in tlie Jurassic. Among the invertebrates 

 the ammonites, which appeared in the Devonian, reached their 

 greatest develojiment and became extinct in tliis era. 



(«) 



(J) 



In the tertiary all of the now living orders of mammals and 

 birds appeared, among them man, whose remains have been traced 

 with certainty to the pleistocene. 



