49 



The Edentate mammals have long been a puzzle to Zoolo- 

 gists, and up to the present time no clew to their affinities with 

 other groups seems to have been detected. A comparison of 

 the peculiar Eocene Mammals which I have called the Tillo- 

 doniia, with the least specialized Edentates, brings to light 

 many curious resemblances in the skull, teeth, skeleton and 

 feet. These suggest relationship, at least, and possibly we 

 may yet find here the key to the Edentate genealogy. At 

 present, the Tillodonts are all from the lower and middle 

 Eocene, while Mbropus, the oldest edentate genus, is found in 

 the middle Miocene, and one species in the lower Pliocene. 



The Edentates have been usually regarded as an American 

 type, but the few living forms in Africa, and the Tertiary 

 species in Europe, the oldest known, have made the land 

 of their nativity uncertain. I have already given you some 

 reasons for believing that the Edentates had their first home 

 in North America, and migrated thence to the southern 

 portion of the continent. This movement could not have 

 taken place in the Miocene period, as the Isthmus of Darien 

 was then submerged ; but near the close of the Tertiary, 

 the elevation of this region left a much broader strip of land 

 than now exists there, and over this, the Edentates and other 

 mammals made their way, perhaps urged on by the increasing 

 cold of the glacial winters. The evidence to-day is strongly in 

 favor of such a southern migration. This, however, leaves the 

 Old World Edentates, fossil and recent, unaccounted for; but I 

 believe the solution of this problem is essentially the same, 

 namely : a migration from North America. The Miocene rep- 

 resentatives of this group, which I have recently obtained in 

 Oregon, are older than any known in Europe, and, strangely 

 enough, are more like the latter and the existing African types 

 than like any of our living species. If, now, we bear in mind 

 that an elevation of only 180 feet would, as Dana has said, 

 close Behring's Straits, and give a road thirty miles wide from 

 America to Asia, we can easily see how this migration might 

 have taken place. That such a Tertiary bridge did exist, we 



