f 



essru in 



Themselves 



by S, David Webb 



Our team of scuba divers had been 

 working the Withlacoochee River in cen- 

 tral Florida for two weeks when I spotted 

 the hand-sized jaw with its strange, 

 warped teeth in a dark depression below 



the main channel. Other fossils gathered 

 from this rich green clay pocket thirty feet 

 below the surface indicated a deposition 

 date of about seven million years ago. The 

 identity of the animal to which the teeth 



belonged was unmistakable: the last of the 

 four teeth in the jaw had a long figure- 

 eight crown and very tall sides, diagnostic 

 features of a mylodont sloth. An hour later, 

 nearing the end of my air supply, I fanned 

 the clay away from a mandible about the 

 size of a human's. It contained the nearly 

 square-crowned teeth and elongate chin 

 "spout" of a small megalonychid sloth. 

 These finds astonished me. Two kinds of 

 sloths had apparendy lived in Florida in 

 the mid-Miocene. 



While plenty of sloth remains had been 

 found at La Brea and other Pleistocene 

 sites, the Horida fossils were at least three 

 times as old as the earliest Pleistocene 

 sloths. Two million years ago, many South 

 American groups had already entered 

 North America via the Panamanian land 

 bridge in a mass movement known as the 

 Great American Interchange {see page 



50 Natural History 4/94 



