ENVIRONMENT AND EVOLUTION OF VERTEBRATES 27 



pouched creatures known as Marsupials. Animals similar to 

 these in essential respects once ranged over the rest of the 

 world but long ago, being less adaptable to the changing en- 

 vironment, became extinct and were replaced by the rising 

 group of placental Mammals. In Australasia the Marsupials 

 still remain relatively unhampered until recent years by the 

 annoyance of powerful rivals. New Zealand has been an island 

 since before the time when Mammals first appeared and none 

 existed there until brought by Man. There are then two types 

 of island, continental like Japan and oceanic like New Zealand ; 

 upon the former we expect to find a fauna very similar to that 

 of the neighboring continent whereas upon the latter the animal 

 life will have developed special local adaptations or peculiari- 

 ties. The connection of an island with a neighboring conti- 

 nent has an important bearing upon the nature of its fauna. If 

 the intervening sea is shallow its breadth is unimportant; if it 

 has been recently nonexistent there will be no marked differ- 

 ence between the island fauna and that of the main land ; if 

 the sea has existed for a great period of time independent 

 evolution will have taken place in the island fauna and great 

 differences between it and the continental animals will now be 

 apparent. 



The anatomy of animals which are now extinct and the his- 

 tory of those which still roam the earth are naturally studied 

 mainly from the bones and teeth, the indestructible portions 

 defying time which are transformed into fossils. These are 

 the skeletons of creatures which have fallen into swamps, into 

 marshes or occasionally into asphalt pools and dying there have 

 been preserved. They are the skeletons of animals over- 

 whelmed by dust or siioav storms and buried. Occasionally an 

 animal has been overtaken by the ice, frozen into a glacier and 

 in this manner preserved until the glacier has melted. Early 

 in the present century we heard of wolves glutting themselves 

 upon the carcass of an age-dead Mammoth newly released from 

 a melting glacier, before the animal Avas obtained for the Petro- 

 grad Museum. The Russian steppes are today occasionally 



