386 LAND MAMMALS IN THE "WESTERN HEMISPHEEE 



two groups were converging back to a common ancestry. This 

 may be discovered in the Bridger, but it seems more probable 

 that these forms were immigrants. Another fact concerning 

 the Uinta genus, which is important, is that the upper molars 

 possessed the fifth or unpaired cusp which also occurred in the 

 contemporary foreodonts, as well as in the fanthracotheres 

 and other Old World families. 



Suborder Tylopoda. Camels and Camel-like Animals 



Existing Tylopoda are all included in a single family, the 

 Camelidse, and by several authorities no other family, even of 

 extinct forms, is admitted to the suborder. My own prefer- 

 ence, however, is to refer the problematical little fbypertrag- 

 ulids to this group, as will be shown subsequently. 



6^ Camelidce. Camels and Llamas 



Under modern conditions, no mammals could seem more 

 completely foreign to North America than those of the camel 

 family, which, now restricted to two well-defined genera, in- 

 habit central Asia and the colder parts of South America. 

 Yet, as a matter of fact, this family passed through nearly 

 the whole of its development in North America and did not 

 emigrate to the other continents before the late Miocene or 

 early Pliocene, and it is this North American origin of the 

 family which explains its otherwise inexpUcable distribution 

 at the present time. To all appearances, the whole family 

 had completely disappeared from this continent in the later 

 Pleistocene, but in the middle and earlier portions of that 

 epoch both true camels and large llama-like animals were very 

 abundant on the Great Plains and in California, while they 

 seem to have avoided the forested regions. 



In order to appreciate the changes through which the 

 camels and llamas have passed, it will be necessary to consider 

 briefly the skeletal and dental structure which characterizes 



