246 A BOOK-LOVER S HOLIDAYS 



of mammalian life, developing from little beasts 

 the size of woodchucks into the largest and 

 most stately creatures of their kind that ever 

 trod the earth s surface, all at once disappeared 

 to the very last individual. Ground-sloths and 

 elephants vanished likewise. The bigger forms 

 of bison also died out, although one species 

 remained. Many causes of extinction have 

 been suggested. Perhaps all of them were more 

 or less operative. Perhaps others of which we 

 know nothing were operative. We cannot say. 

 But as regards certain of the formidable, 

 but heavy rather than active, beasts of prey 

 it is possible to hazard a guess. Compared to 

 agile destroyers like the cougar and the timber- 

 wolf, the sabretooth and the big-headed, small- 

 legged giant wolf were strong, heavy, rather 

 clumsy creatures. Predatory animals of their 

 kind were beasts of battle rather than beasts 

 of the chase. They were fitted to overcome 

 by downright fighting strength a big, slow, 

 self-confident quarry, rather than to run down 

 a swift and timid quarry by speed or creep up 

 to a wary and timid quarry by sinuous stealth. 

 So long as the heavy herbivores were the most 

 numerous these fighting carnivores were dom 

 inant over their sly, swift, slinking brethren. 

 But when the great mass of plant-eaters grew 



