430 THE SUCCESSION OF THE VERTEBRATE FAUNAS. 



opossums and Caenolestidae of the present day. The only very 

 noteworthy types not found in the later Tertiaries of the 

 countr} 7 are the large Pyrotherium, which seems to have been 

 more or less closely related to the Amblypoda of North 

 America, and the group of carnivorous Sparassodonta, which 

 only appear to differ from the ordinary creodonts in exhibiting 

 a more incomplete change of teeth. The jaguars (Felis), 

 wolves (Canis), tapirs (Tapirus), deer (Cariacus), and llamas 

 (Auchenia), now characterizing South America, also the mas- 

 todons and horses which lived there in the Pleistocene, are, of 

 course, recent immigrants from the north. They passed over 

 the isthmus of Panama as soon as it emerged in the beginning 

 of the Pliocene period, just as the sloths and glyptodonts then 

 wandered northwards. As in other regions, so in South 

 America, the mammals were largest and most numerous during 

 the period immediately preceding the present. 



The Australian Tertiary Fauna. 



So far as can be judged at present, Australia has been 

 separated from all other existing continental areas since the 

 remote epoch when Prototheria and Metatheria were the 

 dominant mammals. All the existing mammals of that island- 

 continent belong to these two sub- classes, except a few small 

 rodents and bats, which may have crossed the sea by accident, 

 and a species of dog (Canis dingo), which may have been 

 brought by the earliest human immigrants. Unfortunately, 

 however, no late Secondary or early Tertiary deposits have 

 hitherto been found in Australia yielding remains of a terrestrial 

 fauna ; and nothing is known of the forerunners of the existing 

 types except from quite recent superficial deposits, in which 

 there is evidence of comparatively large moiiotremes and marsu- 

 pials closely related to those still surviving. Some of the extinct 

 genera, as might be expected, are partly intermediate between 

 certain existing forms ; but the only noteworthy feature of the 

 old fauna, apart from the large size of many of its members, 

 is the presence of ancestral kangaroos in which the dispro- 

 portion in the development of the fore and hind limbs has not 

 yet become very marked. Except in the specialization of the 



