6o6 SCIENCE PROGRESS 



the Anthropoidea as a whole, but such an inference is much 

 strengthened by the astonishing character of the geographical 

 separation. These Anthropoidea who were living among 

 primitive and peculiar mammals in Miocene South America — 

 whence did they come, and how long had they been there ? 

 The only really parallel case is that of the Hystricomorph 

 rodents, to which I have already referred. The early Hystri- 

 comorph remains are somewhat older and much more abundant 

 than those of the Platyrrhina. Berryman Scott makes use 

 of his trans-Atlantic bridge to get these animals across from 

 Africa. Matthew evolves the Platyrrhina from hypothetical 

 Paleocene lemuroids, quite independently of the Catarrhina ; 

 as for the Hystricomorpha, he suggests, though with compre- 

 hensible hesitation, that they may have floated across the 

 Atlantic on a raft. One feels that even " Atlantis " is less 

 improbable than such a raft. Abel brings the monkeys across 

 the east-west channel from North America in the Eocene, 

 and apparently Osborn also accepts this theory. The objection 

 to this view which has been felt by many naturalists, is that 

 there is a total absence of both Anthropoidea and Hystrico- 

 morpha from the geological record of North America. But 

 negative evidence of this kind is of doubtful value ; and in 

 the case of the Hystricomorpha it certainly has little weight, 

 for they occur in the Eocene of Europe ; and, since they were 

 therefore on the Mainland, a few of them may well have reached 

 North America. This seems much more plausible than either 

 rafts or trans-oceanic bridges. 



Finally, there is the possibility that certain groups of the 

 higher, as distinct from the archaic, placentals have a greater 

 antiquity than has been supposed, and existed before the barriers 

 to dispersal arose, or when those barriers were less formidable 

 than they subsequently became. This may be true of the 

 Xenarthra, of the Hystricomorpha, of primitive Anthropoidea, 

 and perhaps of certain Artiodactyla. It can hardly be without 

 significance that the same two groups of higher mammals, the 

 Hystricomorpha and Anthropoidea, whose presence in ancient 

 South America puzzles us, are also found associated in ancient 

 Africa. And the two branches of the Anthropoidea resemble 

 one another in too many points for the convergence theory 

 to be probable. Some of the higher groups of mammals may 

 have existed as scarce and inconspicuous elements in the fauna 

 of Paleocene times. 



Apart from these theoretical considerations, I have en- 

 deavoured in the foregoing pages to show how much is clear 

 and how much is at present uncertain in the general stor}?- of 

 the Placentalia, and to indicate the highly mysterious part in 

 that story which is played by the higher Primates, The American 



