262 PROCEEDINGS OF THE ACADEMY OF [1895. 



tropical lowlands; but these were not suitable habitats for the horse, 

 which could only thrive on the firm and grassy uplands, and which 

 may in consequence have become extinct at this time in North 

 America. 



This explanation, however, fails to account for the disappearance 

 of the South American horse, or of its huge contemporaries, the 

 megatherium, megalonyx,, mylodon and glyptodon. The disap- 

 pearance of the last named animals, in view of their sluggishness and 

 stupidity, is not inexplicable, since it may have been due to a cause 

 similiar to that we have adduced in the case of the cretaceous reptiles— 

 the destruction of their young by more agile and cunning animals. 

 To this it may be objected that in such a case they would probably 

 have disappeared early, and never attained their wide distribution. 

 But this by no means follows. Intelligent animals may rapidly 

 develop new methods of attack. Unintelligent animals are not 

 likely to develop new methods of defence with similar rapidity. If 

 some active carnivorous animal, therefore, began to attack and 

 destroy the young of the giant sloths in a new and covert manner, the 

 parents may have proved quite incapable of guarding against this 

 suddenly developed danger, and the coming generations of these 

 creatures may have been fatally reduced. 



We must, however, in considering the problem of the disappear- 

 ance of the animals in question, take into account a hostile agency 

 which did not exist at any earlier period — that of Man. A new 

 lord of the earth had appeared, and one with powers of destruction 

 never before possessed in the animal world. Within quite recent 

 times several species of animals have become extinct through human 

 aggression. Others may have become extinct in the past. We know 

 that the early savages of Europe killed the horse and other large 

 animals for food, and the early Americans may have done the same. 

 Man may have played an active part in the extinction of the giant 

 sloths and the glyptodon — it they persisted till the human period — 

 by destroying their young, even if he did not attack the mature 

 animals — and have thus cut off these specially dull and slothful 

 species. 



Such an explanation will not account for the extinction of the 

 South American horse, nor does any hypothesis — even of an unsatis- 

 factory character — suggest itself. It is true that some entertain 

 the idea that the South American horse did not become extinct. 



