Page:Darwinism by Alfred Wallace 1889.djvu/417

 the tree-kangaroos of New Guinea; a large wombat as large as a tapir; the Diprotodon, a thick-limbed kangaroo the size of a rhinoceros or small elephant; and a quite different animal, the Nototherium, nearly as large. The carnivorous Thylacinus of Tasmania is also found fossil; and a huge phalanger, Thylacoleo, the size of a lion, believed by Professor Owen and by Professor Oscar Schmidt to have been equally carnivorous and destructive. Besides these, there are many other species more resembling the living forms both in size and structure, of which they may be, in some cases, the direct ancestors. Two species of extinct Echidna, belonging to the very low Monotremata, have also been found in New South Wales.

Next to Australia, South America possesses the most remarkable assemblage of peculiar mammals, in its numerous Edentata—the sloths, ant-eaters, and armadillos; its rodents, such as the cavies and chinchillas; its marsupial opossums, and its quadrumana of the family Cebidae. Remains of extinct species of all these have been found in the caves of Brazil, of Post-Pliocene age; while in the earlier Pliocene deposits of the pampas many distinct genera of these groups have been found, some of gigantic size and extraordinary form. There are armadillos of many types, some being as large as elephants; gigantic sloths of the genera Megatherium, Megalonyx, Mylodon, Lestodon, and many others; rodents belonging to the American families Cavidae and Chinchillidae; and ungulates allied to the llama; besides many other extinct forms of intermediate types or of uncertain affinities. The extinct Moas of New Zealand—huge wingless birds allied to the living Apteryx—illustrate the same general law.

The examples now quoted, besides illustrating and enforcing the general fact of evolution, throw some light on the usual character of the modification and progression of animal forms. In the cases where the geological record is tolerably complete, we find a continuous development of some kind—either in complexity of ornamentation, as in the fossil Paludinas of the Hungarian lake-basins; in size and in the specialisation of the