62 STEPPE FAUNAS AND TEMPERATE 



horns are shed annually and are branched. The con- 

 trast between the hving, or recently exterminated, 

 ungulates of the Old and New Worlds is the more 

 remarkable when we find that America has many fossil 

 horses, though no living ones. 



In proof of the statement just made as to the resem- 

 blance between the steppe rodents in the Old and New 

 Worlds, we may note that marmots occur in both 

 regions, that the susHks of Asia are represented by the 

 forms called gophers in America, which belong to the 

 same genus, and that the jumpmg mouse of the American 

 prairies takes the place of the jerboas and their allies 

 in the Old World. As the adaptation to steppe life is 

 similar, we shall refer chiefly in the following descrip- 

 tion to the rodents of the Asiatic steppes. 



The susliks (Spermophilus) are related to the squirrels, 

 but the common steppe form {8. citilliis) differs in the 

 very short tail and the minute ears, both adaptations 

 to the terrestrial and burrowing habit, and markedly 

 contrasted with the long tail and large tufted ears of 

 the common squirrel. Like other steppe rodents the 

 sushks are social and burrowing animals, hibernating in 

 winter, but storing in autumn a large collection of roots, 

 seeds, berries, &c., for winter use. Like the squirrels, 

 they are not averse to a certain amount of animal food, 

 taking small birds and their eggs when occasion offers, 

 and also small rodents belonging to other genera. 



The marmots (Arctomys) form an interesting genus, 

 with representatives both on moimtains and in the 

 steppes. We shall see later that it is not unusual to find 

 relationships between steppe and mountain animals, 

 a fact which has a double significance. In the first 

 place, just as the tundra forms oeppe because it is 

 too remote from the Equator for txee growth to occur, 



