No. 480] EXTINCTION OF MAMMALIA 851 



manifested itself in herbivorous animals, has frequently led di- 

 rectly to their destruction. This is the tendency to increase in 

 size through the double influence of abundance of food and little 

 waste of tissue through exertion. In the sluggish grass-eaters, 

 dwelling on plains covered with rich herbage, or leaf and twig 

 eaters in tropical forests, the nutritive agencies are in excess of 

 those of waste, and these animals seem always to have tended to an 

 increase in size, until those of least exertion and greatest powers of 

 obtaining food became enormous in dimensions. An example of 

 the same kind among the Carnivora is the Greenland whale, which, 

 while feeding on minute forms, obtains them in enormous quan- 

 tities with little muscular exertion, and has in consequence become 



Bulk not Intrinsically Fatal. — (1) The extinction of a large 

 quadruped attracts more attention but we recall the fact (a) that 

 the small Condylarthra became extinct before the large Ambly- 

 poda, (b) that many families of relatively small Artiodactyla 

 and Perissodactyla became extinct at the same period as the 

 very large Titanotheres; (c) that the relatively small ^Vlylodon 

 disappeared as early as the large Megatherium; (d) that the 

 extinction of the mammoth in the northern hemisphere during or 

 after the glacial epoch attracts attention because of the animal's 

 large size, but as shown, many other quadrupeds vastly inferior 

 in size disappeared at the same time. 



(2) The survival of animals which have been constantly in- 

 creasing in size from the Eocene to the present time may be cited 

 as proof that bulk is not a cause of elimination per ,se. The wild 

 horses, rhinoceroses, many ruminants, bears, and probably the 

 wiiales have now attained the maximum size. The African ele- 

 phant is practically as large as any of the extinct species. IJotii 

 the elephant and the white rhinoceros (which would have survived 

 in large numbers but for the purely accidental interfereiu c with 



respects. ... 



(3) Bulk is fatal under certain changes ot eiivironment where 

 not correlated with an adeciuate feeling inechani.Mn. with a.!c<|uate 

 ■<iefensive powers, adecpiate fertility, and aile(inate deteiisj^ and care 

 €i{ the young. 



