GEOGRAPHICAL DISTRIBUTION OF ANIMALS
This brief outline will show the great complexity of the conditions to which mammals were compelled to adapt themselves and will help to explain their present arrangement on the surface of the earth, but, it must be insisted, this explanation becomes meaningless if we deny the theory of evolution. 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 bewildering 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 constitute a most peculiar and characteristic assemblage of mammals, such as are found nowhere else in the world.
Mingled everywhere with these strange tropical creatures
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