568 



SCmNGE. 



[N. S. Vol. XI. No. 276. 



The third migration into ISTeogsea estab- 

 lished its links with Australia, bringing in 

 Marsupials,, both polyprotodont and dipro- 

 todonts. The fourth was from the north, 

 Arctogfea, and is positively known ; it oc- 

 curred at the end of the Miocene, and 

 brought in the northern Carnivora, Bears, 

 Wolves, Cats, and Sabre-tooth Tigers, Eac- 

 coons and Mustelines, the Artiodactyla, 

 deer and camels, the Pei'issodactyla, horses 

 and tapirs, three types of Eodents, the 

 Squirrels, Mice and Hares or Eabbits and 

 the Mastodon. The ISTotogseic types, as 

 well as the animals of the first invasion, in 

 the meantime had largely died out, and the 

 introduction of more vigorous Arctogseic 

 types, especially the carnivores, together 

 with a change of climate, exterminated a 

 further portion of the autochthonous Neo- 

 gseic fauna. At the same time, that is of 

 this second invasion, many of the South 

 American forms entered North America; 

 they seem to have reached this continent 

 in the upper Pliocene. 



We now turn to ARCTOGiEA. In the Eo- 

 cene period we find in Europe and North 

 America what may be considered the pure 

 or Autochthonous fauna of the Holarctic re- 

 gion, in the absence of all knowledge of 

 Asia. Southern Asia is an absolute terra 

 incognita the earliest known deposits in this 

 region being in the Upper Oligocene in 

 which the fauna is remarkably similar to 

 that of Europe. Northern Asia is un- 

 known paleontologically until the Pleisto- 

 cene — here is a region for explorers. How- 

 ever, we may consider it as part of a broad 

 Eurasiatic land area — extending from the 

 Eocky Mountain Eegion to Great Britain. 

 The faunal relations are astonishingly close, 

 between the new and old worlds at this 

 time. Every year's discovery increases the 

 resemblance and diminishes the differences 

 between Europe and the Eocky Mountain 

 region. Distinguishing North America, 

 however, are the Tylopoda, this sub-order 



includes the peculiar Artiodactyla of the 

 Camel-llama tribe ; these Professor Scott in 

 a recent paper considers as including all 

 the early types of American ruminants 

 which we have been vainlj' endeavoring to 

 compare with European types. The radia- 

 tion of the Tylopod phylum into a great 

 variety of types is quite conceivable and it 

 is thoroughly consistent with the funda- 

 mental law of adaptive radiation which we 

 find operating over and over again. 



In Europe there are in the upper Eocene 

 two classes of animals, first those which 

 have their ancestors in the older rocks. 

 The second class includes certain highly 

 specialized animals which have no ances- 

 tors in the older rocks — among these, per- 

 haps, are the peculiar flying rodents or 

 Anomaluridce, now confined to Africa, and 

 secondly the highly specialized even-toed 

 ruminant types — the Anoplotheres, Xipho- 

 donts and others, the discovery of which 

 in the Gypse near Paris — Cuvier has made 

 famous. It is tempting to imagine that 

 these animals did not evolve in Europe but 

 that they represent what may be called the 

 first invasion of Europe by African types 

 from the Ethiopian region. 



It is a curious fact that the African con- 

 tinent as a great theater of adaptive radia- 

 tion of Mammalia has not been sufficiently 

 considered. It is true that it is the dark 

 continent of paleontology for it has prac- 

 tically no fossil mammal history but it by 

 no means follows that the Mammalia did 

 not enjoy an extensive evolution there. 



Although it is quite probable that this 

 idea has been advanced before — most writ- 

 ers speak mainly or exclusively of the in- 

 vasion of Africa by European types. Blan- 

 ford and Allen it is true have especially 

 dwelt upon the likeness of the Oriental and 

 Ethiopian fauna but not in connection with 

 its antecedent cause. This cause I believe 

 to have been mainly an invasion from south 

 to north correlated with the northern ex- 



