584 PALEONTOLOGY 



the modern mammals suddenly appear in the Lower Eocene (as distin- 

 guished from the basal Eocene, in which the Cretaceous mammals 

 are found), and second, they enjoy a more or less independent evolu- 

 tion and radiation on each of the four great continents. There thus 

 arose the four peculiar or indigenous continental faunae of South 

 America, of North America, of Europe and Asia or Eurasia, and of 

 Africa. Of these South America was by far the most isolated and 

 unique in its animal life. North America and Eurasia were much the 

 closest, and Africa acquired a halfway position between isolation and 

 companionship with Eurasia. 



South America. The most surprising result of recent discovery 

 is that the foreign element mingled with the early indigenous South 

 American fauna is not at all North American, but Australian. 1 The 

 wonderful variety of eight orders of indigenous rodents, hoofed 

 animals, edentates, and other herbivores were preyed upon by carni- 

 vores of the marsupial radiation from Australia, which apparently 

 came overland by way of Antarctica. There are possibly here also 

 some South African foreigners. The South American radiation more 

 or less closely imitated that of the northern hemisphere. Late in 

 Tertiary times North America exchanged its animal products with 

 South America, practically to the elimination of the latter. 



Eurasia and North America. Each of these continents contained 

 four orders of mammals in common with South America, namely, 

 the Primates (monkeys), the Insectivores (moles and shrews), the 

 Rodents (porcupines, mice, etc.), and the Edentates (armadillos, 

 etc.). From some early Tertiary source North America, Eurasia, and 

 Africa also acquired in common four great orders of mammals which 

 are not found at all in the indigenous fauna of South America. These 

 are the Carnivores (dogs, cats, etc.), the Artiodactyls (deer, bo vines, 

 camels, and pigs), the Perissodactyla (horses, rhinoceroses, and 

 tapirs), and the Cheiroptera (bats). Migration and animal intercom- 

 munication between North America and Eurasia was very frequent. 

 The history of these nine orders of mammals in North America and 

 Eurasia developed as follows: Certain families indigenous to North 

 America both evolved and remained here, others finally migrated 

 into Europe and South America. Similarly Eurasia had its continu- 

 ous evolution into forms which remained at home as well as into 

 those which finally migrated into North America and even into 

 South America. 



Africa. The most astonishing and gratifying feature of recent 



1 For a series of monographs on the South American fossil faunas, see Reports 

 of the Princeton University Expeditions to Patagonia, 1896-99, 4to, Princeton, 

 N. J. For the Australian element in the South American faunas see Moreno, 

 Note on the Discovery of Miolania . . . in Patagonia, Nature, Aug. 24, 1899, p. 

 396; H. F. Osborn, Science, N. S., vol. xi, April 13, 1900, pp. 564-566. Sinclair, 

 W. J., The Marsupial Fauna of the Santa Cruz Beds, Proceedings of the American 

 Philosophical Society, vol. XLIX, 1905, pp. 73-81. 



