1296 



CLASS MAMMALIA. 



America ; the typical M. americanum (fig. 1 165) of the former region 

 being fully equal in bulk to the largest species of Rhinoceros. The 

 teeth (fig. 1 166) consist of square prisms, wearing into transverse 

 ridges through the presence of two vertical plates of hard dentine 

 intercalated between softer dentine and cement ; they are similar in 



Fig. 1 166. — Megatherium americanum. — Oral surface of the mandible ; from the 

 Pleistocene of Buenos Ayres. Reduced. 



structure, and are all in contact. The feet are provided with power- 

 ful and huge claws, the third digit in each foot being the longest ; 

 and the humerus has no foramen. 



There are indications that the snout was prolonged, and more or less 

 flexible ; and the tongue was probably prehensile. From the characters 

 of the molar teeth it is certain that the Megathere was purely herbivorous 

 in its habits ; and from the enormous size and weight of the body it is 

 equally certain that it could not have imitated its modern allies, the 

 Sloths, in the feat of climbing, back downwards, amongst the trees. It 

 is clear, therefore, that it sought its sustenance upon the ground, and it 

 was originally supposed to have lived upon roots ; but by a masterly 

 piece of deductive reasoning, Sir R. Owen showed that this great 

 Ground-sloth lived upon the foliage of trees, like the existing Sloths — 

 but with this difference, that instead of climbing amongst the branches, 

 it actually uprooted the tree bodily. In this tour de force, the animal sat 

 upon its huge haunches and mighty tail, as on a tripod, and then grasp- 

 ing the trunk with its powerful arms, either wrenched it up by the roots 

 or broke it short off above the ground. Marvellous as this may seem, it 

 can be shown that every detail in the skeleton of the Megathere accords 

 with the supposition that it obtained its food in this way. 



A smaller but allied form from the Pleistocene of South America 

 has been named Oracanthus, but since this term is preoccupied by 

 a genus of Palaeozoic Fishes, it should be changed. The genus 

 Scelidotherium (fig. 1167), which may be taken to include Platy- 

 onyx, and likewise occurs in the South American Pleistocene, com- 

 prises a number of species, and has characters in some respects 

 intermediate between the preceding and the following genera. The 

 teeth in the upper jaw have an irregularly oval section, while those 

 of the mandible are usually subtriangular ; the whole of the series 

 are in contact, and their crowns do not wear into ridges. The 



