WHY DO ANIMALS BECOME EXTINCT? 221 



back to the little Eocene Hyracothere. So in 

 a general way it may be said that much of 

 what at the first glance we might term extinc- 

 tion is really the replacement of one set of 

 animals by another better adapted to surround- 

 ing conditions. 



Again, there are many cases of animals, and 

 particularly of large animals, so peculiar in 

 their make up, so very obviously adapted to 

 their own special surroundings that it requires 

 little imagination to see that it would have 

 been a difficult matter for them to have re- 

 sponded to even a slight change in the world 

 about them. Such great and necessarily slug- 

 gish brutes as Brontosaurus and Diplodocus, 

 with their tons of flesh, small heads, and feeble 

 teeth, were obviously reared in easy circum- 

 stances, and unfitted to succeed in any strenu- 

 ous struggle for existence. Stegosaurus, with 

 his bizarre array of plates and spines, and huge- 

 headed Triceratops, had evidently carried spe- 

 cialization to an extreme, while in turn the 

 carnivorous forms must have required an abun- 

 dant supply of slow and easily captured prey. 



Coming down to a more recent epoch, when 



