The process of evolution of different species in a given geographical area starting from a point and literally radiating to other areas of geography is called adaptive radiation .
Small black birds later called Darwin's finches were original seed-eating features , later many other forms with altered beaks arose, enabling them to become insectivorous and vegetarian finches.
Another example is Australian marsupials . A number of marsupials each different from the other evolved from an ancestral stock , but all within the Australian island continent .
When more than one adaptive radiations appeared to have occurred in an isolated geographical area one can call this convergent evolution .
Placental mammals in Australia also exhibit adaptive radiation in evolving into varieties of such placental mammals each of which appears to be similar to a corresponding marsupial .
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