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- 

 colus. 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 Kiver, 

 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 two 

 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 



