The Rise of the Mammals 



noceros, the earliest members of the pig family, 

 and the first undeniable rodents, or gnawing 

 animals ; so that this stage marks a great ad- 

 vance for the mammals. 



The first trace of the horse family is found 

 in middle Eocene deposits, and the animal re- 

 joices in the long name, Protorohippus venti- 

 coins. The generic name means ^'before the 

 mountain horse," and the specific name is a 

 joke of Professor Cope's, which will be readily 

 recognized as " dog-Latin " for Wind River, 

 the locality where the specimen was found. 

 The Eocene horse was so small and so different 

 from the horse of to-day, that did we not have 

 the links in the chain which connect the tw^o 

 the relationship might be unsuspected. The 

 story of the horse is now so well known that it 

 need not be dwelt on in detail."'^ It naturally 

 impresses us, because the horse is familiar to 

 every one ; but the line of descent of the cam- 

 els and rhinoceroses is almost as well known as 

 is that of the horse. The largest of the Eocene 



* Those not familiar with it will find the ancestry of the horse 

 given at some length in Animals of the Past. 



227 



