66 



THE WHITE RIVER BADLANDS 



Just as individuals suffer distress and destruction so, 

 sometimes, entire animal groups battling for position in 

 life's long race and gaining for a time supremacy in their 

 field are in turn oppressed and in the end obliterated by the 

 contending forces. Of the animals described in this book 

 several groups are wholly extinct, no relatives of any rea- 

 sonable nearness being found living today. Notable among 

 such are the Titanotheres, the Oreodons and the Moropus. 

 Reference to the extinction of others is given in connection 

 with their description. 



Often extinction is apparent rather than real and the 

 seeming obliteration may be only the normal expression of 

 constant change. For example, in the horse, camel, rhin- 

 oceros and other families the consecutive changes may be 

 traced through a long continued series of replacements by 

 the process of gradual development. Again the seeming 

 extinction may be only a migration from the locality in 



Figure 16 — Land areas of the world during Late Cretaceous and 

 Basal Eocene time. Period of extinction of the great Reptilia. 

 A time of elevation, favoring an interchange of archaic life be- 

 tween South and North America, also between North America 

 and Europe. South America probably united with Australia via 

 Antarctica, allowing an interchange of carnivorous and herbi- 

 vorous marsupials. A partial community of fauna between 

 North America and Eurasia with Africa. Rearranged from W. 

 D. Matthew, 1908. H. F. Osborn: The Age of Mammals in 

 Europe, Asia, and North America, 1910. Published by The Mac- 

 millan Company. Reprinted by permission. 



