68 



Edentata — Megatherium, etc. 



Wall-case, 

 No. 26. 



Great 

 Ground- 

 Sloth.. 



Teeth of 

 Megathe- 

 rium. 



The Megatheriidai, represented by Megatherium, Mylodon, 

 Scelidotherium, Megalonyx, and Gcelodon, present characters inter- 

 mediate between the existing Brady podidse, or Sloths, and the 

 Myrmecophagidas, or Ant-eaters, combining the skull and den- 

 tition of the f orrner, with the structure of the limbs and vertebral 

 column of the latter. Almost all the ancient forms were of 

 g'igantic size, Megatherium being larger than any Rhinoceros. 

 The teeth in Megatherium are prismatic in form (quadrate in 

 transverse section), and composed of hard dentine, softer vaso- 

 dentine, and cementum, so arranged that, as the tooth wears, 

 the surface always presents a pair of transverse ridges, thus 

 producing a dental apparatus well suited, like the molar teeth 

 of Dinotherium, Tapirus, etc., for triturating vegetable food. 

 Megatherium has five such teeth on each side in the upper, and 

 four on each side in the lower jaw, as in the modern Sloth : 

 Gcelodon has one tooth less on each side, both in the upper and 

 lower series. 



Fig. S2.— Lower Jaw of 'Megatherium americanum (Cuvier), showing the double chisel- 

 shaped Molar teeth ; from Pleistocene deposits, Buenos Ayres. 

 £ natural size. 



None of these huge extinct forms were arboreal in habit, but 

 they were probably all phytophagous in diet, subsisting upon 

 the leaves and young branches of trees. 



Although the jaws were destitute of teeth in front, there are 

 indications that the snout and lips were elongated, and more or 

 less extensile, whilst the fore-part of the lower jaw is much pro- 

 longed and grooved (see woodcut, Fig. 82), to give support to a 

 long cylindrical, powerful, muscular tongue, aided by which the 

 great sloth, like the giraffe, could strip off the small branches 

 of the trees which, by its colossal strength, it had broken or 

 bent down and brought within its reach. 



In the Elephants, which subsist on diet similar to that of 

 the Megatherium — the grinding of the food is effected by 

 molar teeth, which are replaced by successional ones as the old 

 are worn away. In the Giant Ground- Sloth only one set of 

 teeth was provided, but these by constant upward growth, and 

 continual addition of new matter beneath, lasted as Jong as the 

 animal lived and never needed renewal. 



