JANUAKT 28, 1916] 



SCIENCE 



119 



have been a forest-living creature, and, so 

 far as is now known, was confined to the 

 region east of the Mississippi River. The 

 almost equally massive Mylodon replaced 

 it over the Great Plains and on the Pacific 

 coast, particularly fine specimens occur- 

 ring in the wonderful asphalts of Rancho 

 la Brea, which the work of Professor J. C. 

 Merriam has rendered so celebrated. A 

 third genus, Megatherium, of even greater 

 size and heavier proportions, extended into 

 Georgia and South Carolina, but is not 

 known farther north, as it was probably 

 unable to endure a cold climate. Those 

 most grotesque beasts, the Glyptodonts, 

 which were like enormous armadillos in 

 appearance, accompanied the ground-sloths 

 in their migration to North America, but 

 have been found only in the southern 

 states, from Florida to Texas and Mexico, 

 being doubtless limited in their northward 

 range by the barrier of climate. 



The Pleistocene rodents tell a similar 

 story. Practically all of the modern forms 

 were already here and associated with these 

 were certain strange and curious forms, 

 like the giant beaver, of northern origin, 

 but now extinct, and a few South American 

 immigrants, like the short-tailed porcu- 

 pines and the water-hogs, of which only the 

 former have survived. The marsupial 

 group of the opossums had in the Eocene 

 epoch extended over Europe and the 

 Americas, but none have been found in 

 North America in beds later than the 

 Oligocene. Of course such small animals 

 may have merely escaped the collector's 

 eye, but, taking all things into considera- 

 tion, it is probable that the group van- 

 ished completely from the northern hem- 

 isphere and returned with the immigra- 

 tion from South America, where they had 

 continued to flourish without interruption. 



The Pleistocene fauna of South America 

 was likewise much richer and more varied, 



especially in very large mammals, than is 

 the existing one, and is far stranger than 

 the corresponding one of North'- America, 

 differing more radically from that of mod- 

 ern times, for the extinctions swept away 

 not only species and genera, but whole 

 families and orders as well. The pampas 

 of Argentina, the caverns of Brazil and, 

 in lesser degree, areas in Bolivia and Ecua- 

 dor, have yielded a marvelous series of 

 Pleistocene mammals, which give a very 

 striking picture of the life of the times. 

 The same distinction between immigrant 

 and autochthonous types which was noted 

 in the existing fauna of South America 

 was as strongly marked in the Pleistocene. 

 Beside those northern immigrants which 

 have maintained their foothold in the 

 southern continent and are represented 

 there to-day, there are many others which 

 are now extinct, some of those groups 

 which have become altogether extinct, others 

 which have vanished from the western 

 hemisphere, or from South America only. 

 The Pleistocene fauna had substantially 

 all of the mammals which still inhabit 

 Notogffia and it is therefore unnecessary to 

 repeat the names of those which form part 

 of the modern fauna. It may be noted, 

 however, that some of the recent families 

 had representatives much larger in size 

 than any that now exist, such as the 

 monkeys and the raccoons, above all, the 

 armadillos. 



Some of these extinct immigrants were 

 very abundant and conspicuous in the 

 Pleistocene. The great saber-toothed tigers 

 ranged all the way from Pennsylvania and 

 California to the -Argentinian pampas and 

 were accompanied by the short-faced bears. 

 A strange feature was the presence of a 

 wolf which is apparently referable to the 

 same genus {Cyan) as the wild dog or 

 Dhole, of recent India. Horses were very 

 common wherever Pleistocene fossils have 



