1 8 INTRODUCTORY. [CHAP. 



of their existence, so that the full extent of their range, if they be 

 surviving forms, can now never be ascertained. 



To quote the words of Dr Wallace, it is evident that in the 

 present day we live in an impoverished epoch, so 



Extinction 



of the larger iar as the larger mammals are concerned, as com- 



pared with the Plistocene era ; this being true not 

 only as regards the northern half of the Old World, 

 but likewise North and South America, as well as Australia. 

 From the northern half of the Old World have disappeared the 

 mammoth, the elasmothere, the woolly and other species of 

 rhinoceros, the sabre-toothed tigers, etc.; North America has lost 

 the megalonyx and the Ohio mastodon ; from South America the 

 glyptodonts, mylodons, the megalothere, and the macrauchenia have 

 been swept away ; while Australia no longer possesses the dipro- 

 todon and various gigantic species of kangaroos and wombats. 

 In the northern hemisphere this impoverishment of the fauna has 

 been very generally attributed to the effects of the glacial period, 

 but although this may have been a partial cause, it can hardly be 

 the only one. The mammoth, for instance, certainly lived during 

 a considerable portion of the glacial epoch, and if it survived thus 

 far, why should it have disappeared at the close? Moreover, all 

 the European mastodons and the southern elephant (Elephas 

 meridionalis] died out before the incoming of glacial conditions ; 

 and the same is true of all the extinct elephants and mastodons of 

 southern Asia. Further, a large number of English geologists 

 believe the brick-earths of the Thames valley, which contain 

 remains of rhinoceroses and elephants in abundance, to be of 

 post-glacial age. As regards the southern hemisphere, it can 

 hardly be contended that glacial conditions prevailed there at the 

 same time as in the northern half of the world. 



It is thus evident that although a very great number of large 

 mammals were exterminated (perhaps partly by the aid of human 

 agency) at the close of the Plistocene period, when the group 

 had attained its maximum development as regards the bodily size 

 of its members, yet other large forms had been steadily dying 

 out in previous epochs. And it would seem that there must 

 be some general deep-seated cause affecting the life of a species 

 with which we are at present' unacquainted. Indeed, as there 



