AXCESTRY OF THE EDENTATES 303 



but of much smaller size and not so widely divergent as their descendants . 

 In succeeding Pliocene formations we find remains of species intermediate in 

 size and character connecting them with the giants of the Pleistocene Epoch 

 of the age of early man. 



The American Museum and Princeton Museum obtained during the 

 years 1898 to 1900 splendid collections from the Patagonian Miocene, which 

 have been studied and described by Professor W. B. Scott. Among the 

 skeletons in this Museum is one of Hapalops, which has recently been 

 mounted by Mr. Albert Thomson under the direction of the curator. It is, 

 according to Professor Scott, a collateral ancestor of the giant groimd sloths, 

 and illustrates very well what their direct ancestors were probably like. 



From the study of the construction of the animal in order to discover 

 its probable habits as a guide to its pose, we concluded that like the ant- 

 eaters, it was partly arboreal and partly terrestrial. The living anteaters, 

 when the}^ are walking along the branches of trees, step upon the palm of 

 the fore foot and sole of the hind foot, as do most qtuidrupcds, but when they 

 walk on the ground the large claws of the fore foot are in the way, so they 

 are apt to walk upon the knuckles, although the hind foot with its smaller 

 claws rests flat. Arboreal apes very commonly walk on the ground in 

 the same way, partly from the difficulty of bending the hand backward 

 into an unusual position, partly to protect the delicate tips of the 

 fingers. 



It seemed probable that the Hapalops with its large front claws would 

 find it most convenient to walk in this manner when on the ground. This 

 position habitually taken would tend in the course of time in a terrestrial 

 descendant to be modified by resting on the outer side of the hand, and in 

 this way the peculiar twist in the fore foot of the giant ground sloths is very 

 exactly accounted for. The hind foot also l)ecame twistefl inward, but 

 from a position resting on the sole of the foot, and this again explains how 

 various peculiarities in the hind foot construction of the great ground sloths 

 arose. The general resemblance in the construction of the hind foot in 

 Hapalops to that of the anteaters ga\e reason to believe that it was equally 

 limited in its motion, so that the animal stepped off the ends of the toes 

 without much bending of the foot at the ankle and first row of phalanges. 



We see then in this ancestral ground sloth a very marked approach 

 toward the common ancestor of ground sloths, tree sloths and anteaters. 

 It does not show any notable approach toward the glyptodonts and 

 armaflillos. But when we obtain a more complete knowledge of the early 

 Tertiary, ancestors of the Edentates, we shall hope to confirm what the 

 fragmentary renuiins known to us seem to indicate, that all these Edentates 

 were derived from a conunon ancestral source. 



