SUCCESSIVE MAMMALIAN FAUNAS 199 



and even throughout the table-land of Mexico. The areas 

 of the two species overlapped along the northernmost United 

 States, but are elsewhere distinct. 



A third species was the huge flmperial Elephant {E. \i7npera- 

 tor), the largest of American forms, to which Osborn's calcula- 

 tions give the almost incredible height of 13 ft. 6 in. This 

 great creature was characterized not only by its enormous 

 stature, but also by the proportionately very large size of its 

 grinding teeth, and was a survivor from the preceding Pliocene 

 epoch ; it is not known to have passed beyond the middle Pleis- 

 tocene and was thus the first of the species to become extinct. 

 In geographical range, the flmperial Elephant was a western 

 form, extending from the Pacific coast almost to the Mississippi 

 River, east of which it has never been found, and from Ne- 

 braska southward to the City of Mexico. The meaning of this 

 distribution is probably that this elephant shunned the forests 

 and was especially adapted to a life on the open plains. Over 

 most of its area the winters were severe, and this fact makes 

 it likely that the animal was clothed with hair, but nothing is 

 definitely known on this point. 



Many other hoofed animals, far more than now inhabit 

 North America, are found in this Pleistocene fauna. The 

 Perissodactyla were represented by horses and tapirs, but not 

 by rhinoceroses ; it might seem superfluous to say that there 

 were no rhinoceroses, but, as a matter of fact, that family had 

 a long and varied American history and became extinct only 

 during or at the end of the Pliocene epoch. The horses were 

 extremely numerous, both individually and specifically, and 

 ranged, apparently in great herds, all over Mexico and the 

 United States and even into Alaska. All the known species 

 (at least ten in number) belong to the genus Equus, but the 

 True Horse {E. caballus), to which all the domestic breeds are 

 referred, is not represented. The smallest known member of the 

 genus is the pygmy E.^tau of Mexico. E .]fraternus , likewise 

 a very small species, is found especially in the southeast, but 



