110 THE THEORY OF EVOLUTION 



Another family, the history of which is far more 

 fully recorded, but much more difficult to decipher 

 and understand, is that of the rhinoceroses. The 

 difficulty arises from the number of divergent 

 branches and parallel series which developed within 

 the family and the local forms which arose in the 

 various regions to which they migrated, for, with the 

 exception of South America and Australia, every 

 continent has had its rhinoceroses. Strange to say, 

 the available evidence points to North America as 

 the region of their origin, though the proof of this is 

 not entirely conclusive. At all events, the family has 

 been traced farther back in time here than in any 

 other region. At a very early stage, the family 

 divided into three strongly divergent branches, two 

 of which were short-lived, lasting only from the 

 middle Eocene through the lower Oligocene, while 

 the third, that of the true rhinoceroses, has persisted 

 to the present day, but is confined to the warmer 

 parts of Africa and southern Asia. The brief series 

 of the cursorial rhinoceroses was exclusively North 

 American and differed from the other branches of the 

 family in being quite defenceless, having neither 

 horns nor tusks, and entirely dependent upon speed 

 for their safety. They were lightly built and slender, 

 long-necked, long-legged and narrow-footed, with 

 three-toed feet before and behind. There is much 

 about these curious animals that suggests relation- 

 ship to the horses, but the likeness is superficial 

 and due to cursorial habits, for every tooth and every 



