140 A NATURALIST IN TASMANIA ch. 



Australia is due to an independent and convergent 

 process of evolution. 



Again, if we examine the extinct Marsupial fauna 

 of Patagonia, preserved for us in the Miocene beds 

 of Santa Cruz, we find a number of types closely 

 similar to those which exist in southern Australia at 

 the present day. There is the Proihylacinus, which 

 is in all essentials identical with the Tasmanian 

 Tiger (Thylacinus), and a number of small Mar- 

 supials (the Microbiotheriidae), which form a con- 

 necting-link between the American Opossums and 

 the Australian Dasyures. Thus the further south 

 we go in the western hemisphere, the more types 

 we find in common with the Australian Marsupials, 

 while in Europe we have nothing but the Opossum 

 (Didelphys) and a number of very ancient types 

 which show no close affinity to existing forms. This 

 is, of course, the exact converse of what we should 

 expect to find on the hypothesis that the Marsupials 

 spread eastwards from Europe to populate Aus- 

 tralia. 



There is also another way of testing this hypo- 

 thesis. If the Marsupials entered Australia through 

 Asia and the Malay Region, it is natural to suppose 

 that the most numerous and the most generalized 

 types would be found in the north of Australia and 

 the most highly specialized in the south, being the 

 latest point reached. But what are the facts ? 

 The tropical regions of Queensland and the Austro- 

 Malay Islands are poorly stocked with Marsupials, 

 and among them are some of the most highly 



