GEOGRAPHICAL DISTRIBUTION OF ANIMALS 



This brief outline will show the great complexity of the 

 conditions to which mammals were compelled to adapt them- 

 selves and will help to explain their present arrangement on 

 the surface of the earth, but, it must be insisted, this explana- 

 tion becomes meaningless if we deny the theory of evolu- 

 tion. If each individual species represents a separate act 

 of creation, then there can be no relationship between 

 species other than that of an ideal plan. On the other hand, 

 if species are really related by community of descent, and 

 new forms arise by the modification of older ones, then many 

 of the facts of distribution are simply and naturally explained 

 as due to changes in geography and climate, of which we 

 have such clear and indisputable evidence. 



If we study the mammals of South America of to-day we 

 at once see that they fall naturally into two groups. Those 

 of one group are very peculiar and are limited almost 

 exclusively to the Neotropical region; those of the other are 

 closely related to the mammals of North America. Confined 

 to South America and Central America are a group of 

 strange, bizarre creatures (the Edentata), such as the ant 

 bear, the tree ant eaters, the sloths and armadillos, and, if 

 we include the Pleistocene epoch in our purview, a bewil- 

 dering variety of two extinct edentate groups, the immense 

 groundsloths and the glyptodonts, or giant armadillos, the 

 remains of which have been found buried in the Pampas of 

 Argentina in astonishingly great number. In South America 

 we find also the platyrrhine monkeys and marmosets and a 

 host of peculiar rodents, cavies, agoutis, tree porcupines, the 

 water hog (the largest living rodent), chinchillas, spiny rats, 

 and many opossums, as well as another type of marsupial, 

 which distantly resembles those of Australia. These consti- 

 tute a most peculiar and characteristic assemblage of mam- 

 mals, such as are found nowhere else in the world. 



Mingled everywhere with these strange tropical creatures 



[87] 



