SUCCESSIVE MAMMALIAN FAUNAS 



237 



Lower Miocene age." The upper division is referred to the 

 Miocene without question by any one, but for the purposes of 

 this rapid sketch it will be best to treat the two faunas to- 

 gether. This many-named formation, for which the term 

 Arikaree is here employed, as having priority, is found over 

 extensive areas of South Dakota, northern Nebraska and 



Fig. 128. — Most ancient American Antelope {Wromomeryx antilopina), middle 

 Miocene. Restored from specimens in the Carnegie Museum and Princeton 

 University. 



central Wyoming. The fauna was almost entirely a develop- 

 ment from that of the North American Oligocene, with very 

 little admixture of foreign elements, so that the land com- 

 munication with the eastern hemisphere must have been 

 difficult. In this, as in most of the Miocene formations, the 

 smaller mammals are not fairly represented, and it is evident 

 that much remains to be learned with regard to them ; this is 

 especially true of the upper division of this stage. 



The rodents, which were fairly numerous, were directly 

 continuous with those of the upper Oligocene and included 

 forms which were more or less distantly connected with the 



