Extinct Pleistocene Mammals 421 



Williston of Chicago University, and by Prof. W. J. SincLiir of Prince- 

 ton University, and they concur in the follov/iug statement by Prof. 

 Sinclair: (See plate XI.) 



"They are the lower mciars (2nd right and 3rd left) of two in- 

 dividuals of a large species of Bison, differing in several respects from 

 a specimen of the recent species in our collection. I do not think 

 that it is possible to be certain about the species. Your specimens 

 are quite different from either Cervalces, the wapiti, or the moose." 



These two teeth are quite different from each other. One is not 

 worn at the crown, and appears to have been immature. It is 2^^ 

 inches long and 1% inches wide. The outer incasing enamel em- 

 braces a roughly plano-convex cylindrical area which is loosely occu- 

 pied at the root by two curved enamel lamellae which are hollow, and 

 which give the exterior of the tooth the appearance of being double, as 

 they cause the body of the tooth to be divided into two main longv 

 tudinal parts. The outer side of the tooth has five prominent ridges 

 of enamel separated by four furrows, all caused by undulating folds 

 of the enamel. The inner side of the tooth shows simply the two 

 main, rounded, vertical body-portions. Below the gum is a parasitic, 

 simply tubular tooth, adherent between the two body portions in the 

 outer angle formed by them. The roots are open below. 



The other tooth is not so long vertically but is wider, and has 

 been much worn away on the grinding surface. Its width is 1% 

 inches and its vertical length is two inches. This tooth is divided 

 into three body-parts, but two only have internal lamellae of enamel. 

 The roots are closed at the bottom. 



The only extinct Bison of America, so far as I can learn, is B. 

 latifrons, and to that species these specimens may be provisionally 

 referred until the discovery of more material may correct or confirm 

 it. That was found in the Pleistocene of Texas, and has been sup- 

 posed to be the progenitor of the present Bison. 



These four species are only a part of the fauna of large animals 

 that flourished in the United States in Pleistocene time. Their com- 

 panions embraced extinct species of reindeer, elk, horse, lion, bear, 

 sloth as well as the mastodon, and this fauna was spread apparently 

 over the whole country, though not perhaps contemporary. Great and 

 remarkable as this fauna appears, in contrast with the present, it was 

 but the dwindling remnant of the Vertiary fauna which preceded it. 

 From the Tertiary to the Pleistocene there was a reduction not only 

 in the number of genera but also in the average size and number of 

 individuals, and a similar change has continued to the present time. 

 What may have been the cause of chi;-? extinction of the great mammals 

 is unknown At the present time the agency of man is paramount, 

 but we can hardly appeal alone to that cause in the Tertiary and the 

 Pleistocene, in the dearth of evidence that man flourished cotemporary 

 with these great mammals. The natural and inevitable effect of the 

 Glacial period was certainly to confine some of the great mammals to 

 restricted quarters and to reduced food supply. They probably also 

 combatted each other, the young especially suffering from the attacks 

 of cotemporary carnivores. To the Glacial period is due, probably. 



