Evidence from Fossil Land Mammals on the 

 Origin and Affinities of the 

 Western Nearctic Fauna 



Donald E. Savage 



Museum of Paleontology, University of Calif or?iia, 



Berkeley 



1 he living nonmarine mammal fauna of Ne- 



arctica is divided into 9 orders. These orders are subdivided into 

 about 28 families, about 100 genera, and a minimum of about 175 

 species. Approximately 75% of its orders, 60% of its families, 30% 

 of its genera, and 1-6% of its species are also found in the parts of 

 eastern Asia not occupied by tropical rain-forest. 100% of its orders, 

 about 65% of its families, 15% of its genera, and 3% of its species 

 occur in the parts of South America not occupied by tropical rain 

 forest. But these imposing numbers and their graphic demonstration 

 in Fig. 1 do not afford a satisfactory basis for concluding whether the 

 mammals of North America have closer affinity with those of eastern 

 Asia or with those of South America. The number of taxonomic 

 units in the living ensemble and the taxonomic percentage com- 

 parisons are figures that serve only as a crude index of the total 

 characteristics and affinities. Living mammals are but a small part 

 of the total land mammal fauna of this continent, for many more 

 lived here in the past, and the exterminated forms must also be 

 studied if our knowledge of origins and affinities is to be complete. 

 Beginning in force with Sclater, Darwin, Wallace, and Lydekker, 

 with tremendous propulsion from Osborn (1910) and Matthew 

 (1915), and with recent thorough refinement by Simpson (1947, 

 1953), we see the development of our present knowledge of mam- 

 malian biogeography, involving millions of years of history. Bio- 

 geography "must reckon with time as well as with space" (Hesse, 

 Allee, and Schmidt, 1937, 1951, p. 121). The attributes of a living 



97 



