FOSSIL MAMMALS 371 



ghino's * arguments in favour of this union of South America 

 and Africa are not founded on any palaeontological resem- 

 blance between these two continents, but rather on the affinity 

 of the fossil mammals of South America to those of Europe, 

 Asia and North America. Since I have shown that until 

 about Oligocene times southern Europe was connected by 

 land with western South America, by way of the West Indies 

 and part of Central America, there does not seem to be any 

 necessity for a second land bridge further south in order to 

 account for the mammalian affinities existing between South 

 America and Europe as well as Asia and North America. 

 Professor Osborn does not recognise the existence of any 

 former land bridge during the age of mammals between South 

 America and the Old World except by way of North America. 

 Mr. Lydekker f argues that the only marked community 

 between the Ethiopian and Neogaeic( South American) faunas 

 as regards mammals, relates to the hystricomorphous rodents, 

 but he thinks this community is a very marked one and diffi- 

 cult to explain on any other hypothesis than that of a land 

 connection between the two areas. The Hystricomorpha are 

 a section of the rodent mammals, well distinguished by mor- 

 phological characters from the other sections of that order. 

 It is of the greatest importance to note that this hystrico- 

 morphous section is now confined to Africa and America, 

 with the exception of a couple of genera which range into 

 southern ^Europe and Asia. The centre of distribution is 

 no doubt South America. If they had passed from there to 

 Africa, we .should expect them to be found in Brazil and 

 western Africa. Let us examine the two closely related 

 families of Octodontidae and Ctenodactylidae, which are in- 

 cluded in the section Hystricomorpha. The first is con- 

 fined to South America, the other to Africa. Of the former 

 it is the sub-family Octodontinae which is nearest related 

 to the Ctenodactylidae, and almost entirely confined to 

 Argentina and the west coast of South America. Only a few 

 species like Ctenomys brasiliensis and Ct. minutus really 

 enter Brazil. The extinct species are all but one confined to 



* Ameghino, F., " Formations s6dimentaires," pp. 281 287. 

 t Lydekker, B., " History of Mammals," p. 127. 



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