January 28, J 9] 6] 



SCIENCE 



121 



the position of its eyes, ears and nostrils, 

 it was probably aquatic, like the Dugong 

 and Manatee, to which it is also allied." 

 Darwin's scanty materials led him to ex- 

 aggerate the size of this extraordinary 

 beast and his views as to its diverse rela- 

 tionships are not tenable from the modern 

 point of view, but his brief description 

 brings out the strangeness of structure in 

 a vivid way. Toxodon ranged as far north 

 as Nicaragua, but, so far as is known, did 

 not enter North America proper. 



Somewhat distantly related to Toxodon 

 was the equally strange Typoiherium, an 

 animal of moderate size, which was the 

 last of a very long series of native develop- 

 ments. Its permanently growing, chisel- 

 like incisors are so similar to those of the 

 rodents that the genus was long referred lo 

 that order. Typotheres were extremely 

 numerous in the Santa Cruz times, but de- 

 clined rapidly in relative importance after 

 that and disappeared completely at the 

 end of the Pleistocene. 



Of all the many bizarre animals which 

 swarmed in Pleistocene South America, 

 none was more extraordinary than Mac- 

 rauchenia, which, like Toxodon, was one 

 of Darwin's discoveries, when he was on 

 the memorable voyage of the Beagle. Mac- 

 rauchenia was somewhat like a large camel 

 in proportions, but of much heavier build. 

 The head was relatively small and must 

 have had quite a long proboscis, which 

 added much to the grotesque appearance 

 of the creature. The neck was very long, 

 suggesting that the animal browsed upon 

 trees, which is also indicated by the char- 

 acter of the teeth; the legs were long and 

 heavy, the feet short and each provided 

 with three toes. This was the last of the 

 Litopterna, an exclusively South American 

 group which had for a long period played 

 a very conspicuous role in that continent, 

 but, like the typotheres, had begun to de- 



cline in numbers after the Santa Cruz 

 epoch. 



The rodents of the South American 

 Pleistocene do not offer much that is of 

 particular interest. The presence of 

 North American types of meadow-mice, 

 which no longer exist in the southern con- 

 tinent, is a noteworthy fact, as is also the 

 occurrence of Megamys, an extinct repre- 

 sentative of one of the indigenous families. 

 This was the largest of all known rodents, 

 living or fossil, and rivalled the rhinoceros 

 in size — for a rodent, a veritable monster. 



From this comparison of the North and 

 South American faunas, as they are re- 

 vealed in the geological succession, certain 

 facts stand out saliently. (1) It is evident 

 that North America contributed much 

 more extensively to the southern fauna 

 than South America did to the northern. 

 Even in the Pleistocene, when the move- 

 ment of intermigration had reached its 

 maximum and there were more mammalian 

 types common to the two continents thai^ 

 at any other period, before or after, the 

 number of Notogaean types found in North 

 America was really very small; opossums, 

 a few rodents, ground-sloths and glypto- 

 donts complete the list. Of these only the 

 opossums and the short-tailed porcupines 

 have survived to modern times. On the 

 other hand, the list of northern forms 

 which, before or during the Pleistocene 

 epoch, had invaded the southern continent, 

 is very much longer; bears, cats, saber- 

 toothed tigers, weasels, otters, skunks, rac- 

 coons, dogs of many kinds, rabbits, squir- 

 rels, rats, mice, horses, tapirs, peccaries, 

 deer, antelopes, llamas and mastodons, all 

 found their way into South America and 

 most of them still inhabit that region. 

 The short-faced bears, saber-toothed tigers 

 and the mastodons became extinct every- 

 where; the horses died out completely in 

 the western hemisphere, while the ante- 



