308 OEIGIN AND DISTEIBUTION OF MAMMALS 



and the complete extinction of the Dasijuridae, Palaeothentinae and Abderitinae. 

 Only one caenolestid — Zygolestes — and Didelphys are recorded from the Plio- 

 cene. Toxodontinae, Macrauclieniidae, edentates and rodents form the main 

 part of the fauna. Among the rodents also we often find forms which, like 

 the representatives of the other groups just mentioned, are distinguished from 

 their predecessors by a considerable increase in bodily size, such as Megamys of 

 the subfamily Chinchillinae. The still existing genera, Myopotamus, Lagostomus 

 and Hydrochoerus, also appear. The Gravigrada and Glyptodontia are in part 

 already represented by genera of the Pampas formation, although the Dasypoda 

 became poorer in the number of genera and species. True Carnivora — 

 Cyonasua, Ardothermm and Canis — are also said to make their appearance. 



An important and interesting fauna is that of the Tarija valley in Bolivia. 

 It is at all events of essentially greater age than that of the Pampas formation, 

 and contains in addition to the previous South American faunal elements — 

 Gravigrada, Glyptodontia, Dasypoda, Caviinae, Ododontmae and Capromyinae — a 

 number of forms which had hitherto been restricted to the northern hemisphere 

 or even to North America. These neAvly appearing types are Mastodon, Tapiriis, 

 Equidae — Hippidium — Cervicornia, Camelidae, Felidae — Smilodon, Felis — Ursidae 

 — Ardotlierium — and dogs. Mustelidae — Mephitis — Frocyonidae, Leporidae and 

 Hesperomtjinae, as well as Dicotyles, also reached South America at the end of 

 the Tertiary, and then formed an important part of the South American 

 mammal fauna in the Pleistocene. The original fauna became gradually poorer 

 except in the long-established types of rodents, but the still surviving Toxodontia, 

 Gravigrada, Glyptodontia and Litopterna of the family Macraudieniidae attained a_ 

 very large size of body and often also extreme specialisation. In the older 

 Pampas formation — Monte Hermoso — there are still Typotheria — Pachyrucos 

 and Typofherium, as well as Froterotheriidae — Epitherium. The extinction of 

 these small or only moderatelj^ sized forms may doubtless be ascribed to 

 competition with the much better and serviceably organised mastodonts, artio- 

 dactyls, and perissodactyls, as well as to the activity of the immigrant beasts 

 of prey. Gradually this competition and the ravages of the larger Felidae 

 exterminated also the Macraucheniidae, Toxodontidae and the giant Edentata. 

 If man, who arrived ver}'^ late in South America, took part in the disappearance of 

 these animals, he can only have exterminated the very last remnant of the old 

 indigenous fauna. That he was really contemporary at least with one ground 

 sloth, the Glossotherium, is certainly proved by the discoveries in the Eberhard 

 cave on the ^ulf of Ultima Esperanza. 



While the mammal faunas hitherto discovered in the South American 

 Tertiary are confined to Patagonia, and the older Pleistocene faunas are hitherto 

 known only from the Tarija valley in Bolivia and from Monte Hermoso, that 

 of the later Pleistocene, the so-called fauna of the Pampas formation, has a 

 much wider distribution. The principal localities in which it is found are still 

 the northern parts of Argentina, but remains of species of the Pampas forma- 

 tion are also known from Chili and Brazil, while fragmentary remains of giant 

 edentates are met Avith in the caves of Minas Geraes, Brazil, and also in the 

 volcanic tufts of Ecuador, although here in diminishing number compared with 

 the horses and auchenias. 



