194 LAND MAMMALS IN THE WESTERN HEMISPHERE 



attained by European geologists and palaeontologists." Ac- 

 cording to Osborn's arrangement, there are three principal 

 successive Pleistocene faunas, two of which appear to have 

 coincided with interglacial stages, and the third with the last 

 reestablishment of glacial conditions on a grand scale. Re- 

 garding the details of these faunas, there still remains much 

 uncertainty, and consequently there will be no attempt made 

 here to do more than discriminate between the general Pleis- 

 tocene assemblage, on the one hand, and that of the last cold 

 period, on the other. It must be emphasized that we are as 

 yet unable to assert that all of the animals listed together were 

 actually living at the same time. 



It is probable that the Pleistocene fossils already obtained 

 give us a fairly adequate conception of the larger and more 

 conspicuous mammals of the time, but no doubt represent 

 very incompletely the small and fragile forms. With all its 

 gaps, however, the record is very impressive; "the early and 

 mid-Pleistocene life of North America is the grandest and 

 most varied assemblage of the entire Cenozoic Period [i.e. 

 era] of our continent " (Osborn). There is the^ further ad- 

 vantage that the fossils have been gathered over a very great 

 area, extending from ocean to ocean and from Alaska to Central 

 America. Thus, their wide geographical range represents 

 nearly all parts of the continent and gives us information con- 

 cerning the mammals of the great forests, as well as of the great 

 plains. 



Those divisions of the early and middle Pleistocene which 

 enjoyed milder climatic conditions had an assemblage of mam- 

 mals which, from one point of view, seems very modern, for 

 most of the genera, and even many of the species, which now 

 inhabit North America, date back to that time. From the 

 geographical standpoint, however, this is a very strange fauna, 

 for it contains so many animals now Utterly foreign to North 

 America, to find near relatives of which we should have to go 

 to Asia or South America. Some of these animals which 



