438 the age of mammals 



Faunal Divisions of the Quaternary 



The study of the mammals of the Quaternary has by no means progressed 

 so far in America as in Europe; it will be many years before the faunistic 

 succession can be worked out with such chronologic accuracy and precision 

 as has at last been attained by European geologists and palaeontologists. 

 The principal difficulty which confronts us in the study of the life of Pleis- 

 tocene times in America is that the richest deposits of fossil maimnals lie 

 to the south of the great terminal moraine, or farthest advance of the glacial 

 cap. In two localities only, the Afton of Iowa and the Toronto Formation 

 of the Don Valley, has it been possible to locate a mammalian fauna between 

 two great series of glacial deposits. Other such localities will doubtless be 

 discovered. Neither are the stages of human culture available, as in the 

 Old World, to supplement and check the time stages of evolution of the 

 mammals. In the meantime, the student must depend upon the following 

 four lines of evidence to mark the progress of Pleistocene time: 



First, the survival of characteristic Pliocene types, such as the saber- 

 tooths, or machaerodonts. 



Second, the gradual extinction or emigration of these older types, in- 

 cluding the greater part of the indigenous large fauna of North America. 

 Thus the saber-tooths, the tapirs, the camels, the horses one by one dis- 

 appear. Among animals of South American origin the giant sloths and 

 the glyptodonts also gradually vanish. Among forms of Old World origin, 

 the elephants and mastodons gradually disappear. These extinctions, when 

 understood (p. 500), will give us a series of dates. 



Third, the gradual arrival of types new to America but long resident in 

 the Old World (p. 436-7). Thus we notice the successive arrivals or first 

 records of such Eurasiatic mammals as the moose (Alces), the bison (Bison), 

 the mountain goat (Oreamnos), the musk ox (Ovibos moschatus), the true 

 red deer (Cervus), the bear (Ursus), the reindeer (Rangifer), the latter three 

 forms appearing late in Pleistocene times. These arrivals will in time also 

 furnish a series of time divisions. 



Fourth, the comparison of the climatic adaptations of New World groups 

 with those which prevailed during the four grand zones of mammalian life 

 in Europe which we have described above. Such comparison enables us 

 to give a preliminary outline in somewhat hypothetical form of four great 

 faunistic periods or life zones, broadly analogous to those in Europe, as 

 shown in the following table. 



These zones are not sharply distinguishable chronologically at present ; 

 they partly overlap and are partly successive. 



Hypothetical Division into Four Zones or Faunas, I -IV 

 The lines of separation between these zones are by no means clearly de- 

 fined at present, and will depend in the future upon the more accurate 

 definition of species. 



