PRESENT PROBLEMS OF PALEONTOLOGY. 241 



these prototypes connect with the modern mammals. This fauna is 

 found in the Cretaceous and basal Eocene of Europe, North America, and 

 possibly in Patagonian beds of South America (Ameghino), and while 

 giving rise to many dying-out branches, by theory furnished the original 

 spring from which the great radiations of modern mammals flowed. 

 But practically again we await the direct connections and the removal 

 of many difficulties in this theory. In fact, one of the great problems 

 of the present day is to ascertain whether this radiation of Cretaceous 

 mammals actually furnished the stock from which the modern mam- 

 mals sprang, or whether there was also some other generalized source. 



The Tertiary, or Age of Mammals, presents the picture of the dying 

 out of these Cretaceous mammals in competition with the direct ances- 

 tors of the modern mammals. I use the word modern advisedly, be- 

 cause even the small horses, tapirs, rhinoceroses, wolves, foxes and other 

 mammals of the early Tertiary are essentially modern in brain develop- 

 ment and in the mechanics of the skeleton as compared with the small 

 brained, ill-formed and awkward Cretaceous mammals. 



Whatever the origin, two great facts have been established: first, 

 the modern mammals suddenly appear in the Lower Eocene (as distin- 

 guished from the basal Eocene, in which the Cretaceous mammals are 

 found), and second, they enjoy a more or less independent evolution 

 and radiation on each of the four great continents. There thus arose 

 the four peculiar or indigenous continental faunas of South America, of 

 North America, of Europe and Asia or Eurasia and of Africa. Of 

 these South America was by far the most isolated and unique in its 

 animal life. North America and Eurasia were much the closest, and 

 Africa acquired a half way position between isolation and companion- 

 ship with Eurasia. 



South America. — The most surprising result of recent discovery 

 is that the foreign element mingled with the early indigenous 

 South American fauna is not at all North American but Australian. 

 The wonderful variety of eight orders of indigenous rodents, hoofed 

 animals, edentates and other herbivores were preyed upon by carnivores 

 of the marsupial radiation from Australia, which apparently came 

 overland by way of Antarctica. There are possibly here also some 

 South African foreigners. The South American radiation more or 

 less closely imitated that of the northern hemisphere. Late in Ter- 

 tiary times North America exchanged its animal products with South 

 America, practically to the elimination of the latter. 



Eurasia and North America. — Each of these continents contained 

 four orders of mammals in common with South America, namely, the 

 Primates (monkeys), the Insectivores (moles and shrews), the Rodents 

 (porcupines, mice, etc.), and the Edentates (armadillos, etc.). From 

 seme early Tertiary source North America, Eurasia and Africa also 

 acquired in common four great orders of mammals which are not found 



