EVOLUTION 



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the marsupials of Australia and those of America are very different. 

 If these fundamental Hkenesses, which make them all marsupials, indi- 



cate a common ancestry, their differences require an explanation. Evo- 

 lution offers that explanation. The ungulates (hoofed animals) do not 

 appear as fossils until after Mesozoic time, and until after AustraHa was 



23 



