262 NATURAL SCIENCE [October 



Typothcria, the Ancylopoda, the Astrapotheria, the Peltateloidea, 

 the Plagiaulacoidea, and the monkeys had disappeared. Of the 

 Sparassodonta and Litopterna few traces remained. On the other 

 hand, the Glyptodons and Megatheria, though in smaller numbers, 

 were represented by forms which frequently attained a gigantic size. 

 The hystricomorphous rodents had increased extraordinarily in 

 numbers and size : the fossiliferous deposits of the Parana contain 

 remains which indicate the former existence of mice of the size of 

 oxen and horses. 



Let us see what was happening meanwhile in the other con- 

 tinents. Since the submergence and disintegration of the Antarctic 

 continent, Australia has remained isolated until our days ; the 

 primitive fauna of the Sparassodonts and Plagiaulacoidea, which 

 were derived from the ancient Argentine continent, continued their 

 evolution independently until they formed the Thylacines, the 

 Dasyures, and the Kangaroos, living and extinct, of the same 

 region. 



South Africa, on the loss of its connection with South America, 

 united itself with Asia, which already formed a continuous land with 

 Europe ; but the Atlantic, which extended over the Sahara as far' as 

 trie Red Sea, opposed a barrier to the direct passage of the faunas 

 of South Africa to Europe, and vice versa. On the other hand, with 

 the continental transformation of the northern hemisphere, lands 

 emerged, which put the Euro-asiatic continent in more or less direct 

 communication with North America. 



The ancient mammals of the Argentine Territory, which by 

 reason of the submergence of the Antarctic continent had remained 

 in South Africa, passed on at once to the Asiatic Continent, where 

 they found conditions favourable to their development and evolution. 

 The Pyrotheria developed into the Proboscidia, the Archaeohyracoidea 

 into the living Hyracoidea, the Notohippidea into horses, the Con- 

 dylarthra into Artiodactyles and Perissodactyles, the Sparassodonta 

 into Creodonts and Carnivora, etc. The remaining South American 

 mammals, such as the Monkeys (Homunculidae), the Hystricomorphous 

 Eodents and the Opossums, invaded the Euro-asiatic continent by 

 the same route. From Asia they passed on to Europe, and from 

 Europe to North America, where they became specialised under 

 different forms, each more bizarre and fantastic. 



We return to South America. We fiud ourselves in the last 

 third of the Cainozoic era at the end of the Miocene period. The 

 mammalian fauna has continued to diminish in number. The 

 Proterotheridea and the large rodents of the previous epoch have 

 disappeared. Of the numerous order of the Toxodonts, there only 

 remains the genus Toxodon, whose representatives attained the size of 

 large rhinoceroses. The Megatheria and Glyptodons reached the 



