HISTORY OF THE EDENTATA 



609 



No dermal armour has yet been found in association with 

 any of the genera, and, so far as the predominant fMegalo- 

 nychidai are concerned, of which so many skeletons have been 

 collected, this negative evidence must be allowed great weight. 

 But the material of the other two families is so rare and in- 

 complete, that the failure to find dermal ossicles is of no value 

 in determining the question; probably, the fmylodonts pos- 

 sessed them. 



These small Santa Cruz fground-sloths were not so clumsy 

 and slow-moving as their gigantic successors of the Pampean, 

 and must have been inoffensive plant-eaters, 

 some of them perhaps more or less arboreal 

 in habits, but they could defend themselves 

 with their long, sharp claws. 



It would require far too much space and 

 lead us into a labyrinth of anatomical techni- 

 calities to point out all the many resem- 

 blances to other edentate suborders which 

 are to be noted in the skeleton of the Santa 

 Cruz fGravigrada, which thus justified their 

 position as the most nearly central group of 

 the entire order. Not only was the skeleton 

 of these Miocene fground-sloths very much 

 less specialized than in their Pleistocene suc- 

 cessors, but they were much closer to the anteaters than 

 were the latter. Aside from the skull, all parts of the 

 skeleton displayed this resemblance in so marked a manner 

 that the common derivation of the two suborders seems hardly 

 open to question. Different as was the skull in the two groups, 

 the differences were not such as to preclude the origin of both 

 from the same type. Even more closely connected were the 

 fground-sloths and the tree-sloths; the resemblance was 

 most clear in the teeth and skull, but there were also many 

 points of likeness throughout the skeleton. In the tree-sloths 

 the entire bony structure has been profoundly modified in 

 2r 



Fig. 291. — Left pes 

 of ]H(ipalops, Santa 

 Cruz. Princeton 



University Mu- 



seum. Letters as 

 in Fig. 290 and 

 scale of reduction 

 the same. 



