FOSSIL LAND MAMMALS AND WESTERN NEARCTIC FAUNA 107 



Texas, from the world-famous White River group of the northern 

 Great Plains, from Montana, and from Saskatchewan. 



Late Cenozoic assemblages are widely scattered through the 

 middle latitudes of western North America. Every western state 

 claims several local faunas representing the last 30 million years of 

 land mammal history on this continent. Pliocene Ncarctic mam- 

 malian assemblages have been discovered as far south as Honduras 

 (Olson and McGrew, 1941). Pleistocene localities would make a 

 dense, stippled pattern for many areas on the map of Fig. 2 and 

 have consequently been omitted. Some of the more important 

 Pleistocene localities in the West include stream and lake deposits 

 of the Great Plains and Texas, cave and shelter accumulations in 

 the Southwest and Mexico, "mucks" and gravels in Alaska, and 

 breas in California. This suite of samples forms the biostratigraphic 

 basis for conclusions as to the origin and affinities of land mammals 

 in western Nearctica. 



SIGNIFICANCE OF FOSSIL LAND MAMMAL SAMPLES 



Since at least the day of Madison Grant's (1904) essay on the 

 origin and relationships of the large mammals of North America, 

 such statements as the following have appeared in the literature: 

 . . . the poverty of animal life which lived in Y area . . . , or . . . in 

 the X beds of corresponding age, a similar but more limited fauna is 

 found. These statements, usually based on little more than pre- 

 liminary surface collecting in newly discovered fossiliferous areas, 

 should have been carefully qualified as pioneer generalizations, but 

 were not. The authors made no evaluation of the factors of ac- 

 cumulation, preservation, discovery, and collection; and the printed 

 conclusions, in light of present knowledge, are no more than facile 

 verbiage. It is no secret that paleontologists yet lack raw data as 

 to the density and relative numbers of individuals, population size, 

 species associations and the like in the once living biocenoses. 

 Surprisingly, the more common a given fossil is in an area, the more 

 likely that there is a poor census for the animal represented. Through 

 the years, the common forms have been kicked aside in the quest 

 for the "remarkably new" exhibition specimens or the perfect 

 study skeleton. Some collectors have been disproportionately in- 

 trigued with the remains of giants (alas, the lust for the mighty 



