6oo SCIENCE PROGRESS 



We have seen that at some epoch which we should describe 

 as Late Cretaceous or Early Paleocene there was a dispersal 

 of Placentalia throughout the five continents. The land- 

 bridges may not all have existed actually contemporaneously, 

 but they existed at about the same time. We infer, then, the 

 existence of a period of general union. In the Paleocene rocks 

 of Europe and North America we find five orders of archaic 

 placental mammals. Four of those orders reached South 

 America. The fifth order is the Creodonta, the group of primi- 

 tive beasts of prey. These animals teemed in North America, 

 but apparently never reached South America. We infer, 

 therefore, that South America was separated at a date prior 

 to the formation of the oldest known Paleocene rocks, and at 

 a time when four of the Paleocene orders, but not the Creodonta, 

 had been evolved. This is rather a pretty result. The Creo- 

 donta would naturally be evolved later than the herbivores 

 on whom they preyed. From this point onwards till the 

 Pliocene, South America has a history totally distinct from the 

 rest of the world. 



We know much less about the fossil mammals of Africa 

 than about those of South America ; indeed, until the present 

 century, we knew practically nothing about them. We do 

 not meet the fauna until the Middle Eocene of Egypt. Here 

 we find a fauna distinct from that of the northern continents, 

 but less distinct than that of South America. There were 

 Creodonta in Africa. Also certain rodents, chiefly of the 

 Hystricomorph (Porcupine) group. Also certain Artiodactyla 

 (even-toed ungulates), including swine and a primitive extinct 

 group, the Anthracotheriidae. All these groups flourished in 

 northern lands, where they had apparently been evolved since 

 the severance of South America. But there were no Peris- 

 sodactyla (odd-toed ungulates), nor true Carnivora in Africa, 

 although these abounded in Eocene Europe ; and there was 

 a similar absence from Egypt of certain groups now extinct 

 which were characteristic of the Eocene of the north. On the 

 other hand, there were primitive Proboscideans and primitive 

 Hyracoidea in Africa, both these groups being absent from the 

 Eocene of Europe. In addition, there were in Africa repre- 

 sentatives of two other quite peculiar orders of ungulates, the 

 Embrithopoda (the genus Arsinoitherium) and the Barytheria. 

 Hence it is usually inferred that these latter four orders 

 were evolved in Africa. In regard to the Creodonta and 

 Artiodactyla possessed in common by Europe and Africa, it 

 is difficult to know whether these are all ancient animals dating 

 back to the original connection, or whether some of them may 

 have made their way southwards across the seas, perhaps by 

 chains of islands. The correct interpretation of the evidence 



