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THE AMERICAN MUSEUM JOURNAL 



during the Tertiary Period, when it was an island continent, inaccessible 

 to the contemporary land animals of the northern world. Toward the 

 end of the Tertiary, South America and North xVmerica became united, and 

 the animals of the northern world were enabled to invade South America, 

 where their competition finally resulted in the extinction of all but a rem- 

 nant of the native fauna. The South American Edentates also invaded 

 North America, for the remains of ground sloths and glyptodonts have been 

 found in various parts of the United States. But they were unable to main- 

 tain their foothold here and (except for the little Peba armadillo which ranges 

 as far north as southwestern Texas) there are to-day no living Edentates 

 in the United States or Canada. 



The evolutionary history of the Edentates can be followed through the 

 successive formations of the Tertiary Period in South America, just as that 

 of the horse, camel or elephant can be traced through the successive Tertiary 

 formations of the northern continents. Just as we find the horse, tapir 

 and rhinoceros converging toward a common ancestral stock in the early 

 Tertiar}' of the northern world, so in South America we find the widely 

 different tree sloths, ground sloths, anteaters, glyptodonts and armadillos 

 apparently converging toward a common ancestral stock. The evidence 

 is not so clear or complete, for exploration in South America has not yet 

 progressed so far as in Europe and the United States. Especially in the 

 early Tertiary of South America our knowledge is as yet very fragmentary 

 and incomplete. In the later Tertiary we have much better material, the 

 Santa Cruz formation (Miocene) in Patagonia being an especially rich col- 

 lecting ground. In these Miocene beds we find remains of primitive glypto- 

 donts, ground sloths and armadillos already quite distinct from each other 



Ground Sloth 



Primitive (Irountl Sloth 

 llajjalops 



Cilyptodoiit (Tortoise 

 Armadillo) 



Skulls of Snulh American Edenlalex. Th(! three upper figures arc of living types, i^the 

 lower ones extinct. Hapnlops is much older than the others and is most like the ground sloths, 

 but retains from a common ancestry the small muzzle and rounded occiput of the tree sloths, 

 and in the length of the muzzle there is some suggestion of the antcater 



