AND ITS INHABITANTS 135 



stupid compared with the shrewdness of their modern sup- 

 planters (Fig. 26). 



Incursion of the modernized mammals. The archaic mam- 

 mals barely survived the Eocene, only one group, the hyaeno- 

 donts, being found in Oligocene rocks. Early in the Eocene, 

 however, are seen the vanguard of an army of invaders, none 

 of which seem directly related to the native mammals. Their 



Fig, 26. — Restoration of the creodont, Dromocyon. After Osbom, from 

 Lull's "Org^ic Evolution," published by the Macmillan Company. 



simultaneous appearance in North America and Europe 

 points to a contiguous center of evolution somewhere to the 

 north, either a circumpolar land or the northern part of wfiat 

 is now Asia. Here they underwent their primal evolution and 

 here they were endowed with the highest potentialities along 

 the three directions wherein the archaic mammals failed. 

 Climatic oscillation in the north In the early Tertiary drove 

 these modernized mammals south along the three continental 

 radii, not all at once, but in a series of drives, until the competi- 



