452 



THE AGE OF MAMMALS 



1. Early and Mid-Pleistocene Mammals of the Plains Regions. 

 The First or Equus Zone Fauna 



This is chiefly a plains, desert, and river-border fauna, including some 

 very large mammals, but less varied in type than that of the Megalonyx 

 Zone. It begins in early and extends into mid- and perhaps late Pleistocene 

 times. 



The life of the plains and mountain regions, or of what may be called 

 the Equus-Camelus-Mylodon Zone, is known in numerous and widely scat- 

 tered deposits in the Great Plains, in the mountain region, and along the 



Fig. 



195. — The Upper Pliocene or Lower Pleistocene imperial mammoth (Elephas imperator). 

 Model by Charles R. Knight in the American Museum of Natural History. 



coast of Florida. Some of these local river or wind-drift deposits have 

 received distinct formation names, such as the 'Sheridan' of Scott, the 

 'Rock Creek' of Gidley. 



As we should expect in deposits bordering on great grassy plains and 

 uplands, one of the most abundant mammals is the horse; consequently 

 these formations have come to be knowm collectively as 'Equus Beds' 

 (Marsh) or the ' Equus Zone.' It is not shomi that they are all of the same 

 age; on the contrary, they probably represent a very long period of time. 

 Some may have been deposited near the beginning of the Pleistocene; 

 others may be mid-Pleistocene. We may, therefore, distinguish the ' early ' 

 and the 'late' Equus Zone; distinct zonal names will in time be applied. 



