500 



THE AGE OF MAMMALS 



exist in North America, but that convincing proof of the fact from the 

 standpoint of physical anthropology still rc^mains to be produced. 



Auriferous gravels. — The most recent review of this question is that 

 of Sinclair,^ in which the following conclusion has been reached: "A review 

 of the evidence favoring the presence of the remains of man in the auriferous 

 gravels of California compels one to regard it as insufficient to establish the 

 fact. It has been shoAvn either that there have been abundant opportunities 

 for the relics in question to be mixed Avith the gravels accidentally, or that 

 the geological conditions at the localities are such as to render it impro])able 

 that the implements and bones have been associated in the gravels to the 

 extent supposed." 



Mercer ^ reached a negative conclusion in his survey of the Trenton 

 gravels: "Nor has anything yet been found any\vhere else in the valley to 

 corroborate the alleged antiquity of the chipped blades from Trenton." 

 The Trenton case has been somewhat weakened by the appearance among 

 the drift specimens of several blades of common Indian pattern. 



Causes of Pleistocene Extinction ^ 



Certainly the most direct instance of widespread extinction of quadrupeds 

 contemporaneous with a secular change of climate was that of the Glacial 

 Period in the entire northern hemisphere. 



As we have seen, the beginning of the Pleistocene found North America 

 peopled with the following kinds of great quadrupeds, all of which disap- 

 peared during or shortly after the Ice Age: 



Artiodactyla 

 Perissodactyla 

 Proboscidea 

 Edentata 



Camelidse 



Equidse 



TapiridiE 



Mastodontinse 



Elephantinse 



Gravigrada 



Glyptodontia 



Camels 

 Llamas 

 Horses 

 Tapirs 



Mastodons 



Elephants 



Giant Sloths 

 Megalonyx 

 Megatherium 

 Paramylodon 



Glyptotherium 



It would be natural to assume that extinction was directly brought about 

 by the profound changes of temperature and moisture, accompanied by 



1 Sinclair, Wm. J., Recent Investigations bearing on the Question of the Occurrence of 

 Neocene Man in the Auriferous Gravels of the Sierra Nevada. Univ. Cal. Publ., Amer. Archceol. 

 Ethnol., Vol. VII, no. 2, 1908, pp. 107-131. 



2 Mercer, H. C., The Antiquity of Man in the Delaware Valley. Repr. fr. Publ. Univ. Pa., 

 Vol. VI, 1897, pp. 1-85. 



' Osborn, H. F., The Causes of Extinction of Mammalia. Amer. Natural., Vol. XL, 

 DO. 479, Nov., 1906, pp. 769-795, no. 480, Dec, 1906, pp. 829-859. 



