262 NATURAL SCIENCE [October 
Typotheria, 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 he 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 
the 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 
Rodents 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 find 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 Tozodon, whose representatives attained the size of 
large rhinoceroses. The Megatheria and Glyptodons reached the 
