206 TYPES OF ANIMAL LIFE 



lived which had toes in various degrees of reduction 

 as to number. Thus a creature known as Hipparion, 

 which existed in Europe, Asia, and North America 

 during Pliocene times, instead of having but a single toe 

 to each foot had three ; but the two lateral ones were 

 quite minute and rudimentary, and in an Indian variety 

 the lateral toes seem to have disappeared. It was of 

 about the size of a donkey. In the lower Pliocene of 

 North America another species with three digits was 

 also found and was named Protohippus by Prof. Leidy. 

 Prof. Cope has suggested that this latter kind was the 

 ancestor of the American horse, and that Hipparion was 

 the ancestor of the Old World horse. Should this opinion 

 be verified it would be a complete demonstration that 

 similar forms may have an independent origin, since the 

 horses of America which became extinct closely resembled 

 the horses of the Old World. A fossil beast from a 

 lower formation, that of the Miocene, has been named 

 Anchitherium. It was of about the size of a sheep and 

 had three toes to each foot, whereof the lateral ones 

 were less diminutive than in the two kinds last noticed. 

 Sometimes it had in addition a rudimentary middle-foot 

 bone, though with no digit attached to it. 



From yet lower rocks, those of the middle and upper 

 Eocene, a still smaller animal has been indicated which 

 has been named Pachynolophus, which not only had a 

 large median digit with a smaller one on either side of it, 

 but had also another and still smaller external digit. 

 Lastly, in the lower Eocene remains of yet another beast 

 have been found. It has been named Phenacodus, and 

 had five digits to each foot. It has been regarded as the 

 lowest root of that genealogical tree along which the 

 modern horse has been supposed to have been evolved. 



