256 THE WOKLD OF LIFE 



large animals lived there must have been much more woody 

 vegetation than there is now. During the voyage of the Beagle, 

 Darwin collected a large quantity of these interesting fossils, 

 as described in his JSTaturalist's Voyage round the World (chap, 

 v.). The skeleton and outline figure of a Mylodon shown in 

 Fig. 90 was 11 feet in total length, but other species were 

 larger. 



A remarkable extinct genus, Scelidotherium, of which the 

 complete skeleton is shown in Fig. 91, was about 10 feet long, 

 and has less massive limbs than the Megatherium or Mylodon, 

 and more elongated jaws. In some respects it approached the 

 ant-eaters, and was probably, like them, terrestrial in its habits. 

 About twelve distinct genera of these ground-sloths are now 

 known, comprising a large number of species. They ranged 

 all over South America and into the warmer parts of North 

 America, and before the immigration of the horse and the 

 sabre-toothed tiger in Pleistocene times, they must have con- 

 stituted the larger and more important portion of the mam- 

 malian fauna of South America. 



Extinct Mammals of Australia 



The existing Australian mammals, although of varied form 

 and structure, are almost all marsupials, the only exceptions 

 being the aerial bats, and small rodents allied to rats, which 

 latter might have entered the country by means of floating 

 timber or trees from the nearest islands. These two orders 

 are therefore of little importance geographically, although by 

 counting the species it may be made to appear that the 

 higher mammals (Placentalia) are nearly as numerous as the 

 lower (Marsupialia). The wild dog, or dingo, is also appar- 

 ently indigenous, but it may have been introduced by early 

 man, as may some of the rodents. It is unfortunate that the 

 deposits of Tertiary age in Australia seem to be very scanty, 

 except recent gravels and alluvial muds, and none of these 

 have produced fossils of Mammalia except in caves and dried- 

 up lakes, which are all classed as of Pleistocene age. These, 



