80 Darwin- Wallace Celebration, 



land-connection with North America permitted the immigration of 

 dogs, large cats, bears, llamas, deer, peccaries, tapirs, horses, masto- 

 dons, and other northern mammals for none of these originated in 

 South America. Only the sloths, armadillos, anteaters, rodents, 

 monkeys, and certain small marsupials withstood the invasion and' 

 survived until the present day. 



The land-area of the South American region when the early 

 Tertiary mammals arose, may perhaps have been more extensive- 

 than it is now. It may even have formed part of a great Antarctic 

 continent, which included also Australia. The discovery of the large 

 extinct horned tortoise, Miolania, both in Queensland and in 

 Patagonia, is supposed to favour this hypothesis ; and there are- 

 other discoveries which admit of interpretation in the same way. 



The Edentata are clearly shown by fossils to have originated in 

 South America, and they can be traced upwards from small ancestors 

 to the gigantic ground-sloths and armadillos, which seem to have 

 become extinct just before European man reached the continent. 

 They wandered into the warm regions of North America as soon as 

 the land -bridge of Panama was established, but they are probably not 

 connected in any way with the so-called Edentata of the Old World. 

 Strange Ungulates (Toxodontia, Typotheria, and Litopterna), which 

 in some respects resemble Rodents, can also be traced through the 

 rocks from small beginnings to gigantic representatives (e. g. Toxodon 

 and Macrauchenia} which lived just before the race died out. Some 

 of the Litopterna were one-toed, and were curious mimics of the 

 horses of the northern hemisphere. Rodents were always numerous, 

 and some of them became as large as cattle when the great ground- 

 sloths flourished. Most interesting are the associated Carnivores, 

 whose skeletons are so closely similar to those of the existing Thy- 

 lacines of Tasmania, that they are often regarded as true Marsupials 

 genetically connected with the Australasian forms. These animals 

 became extinct when the dogs, cats, and bears invaded South 

 America from the north. Monkeys seem to have originated early 

 and changed little with the lapse of time. 



During recent years the most active students of the extinct South 

 American mammals have been Dr. Florentine Ameghino of Buenos 

 Aires, Prof. W. B. Scott and his colleagues in Princeton (U.S.A.), 

 and the veteran Prof. Albert Gaudry of Paris. Their writings may 

 be consulted for an exact account of our present knowledge of the 

 subject. 



