“When more than one adaptive radiation appeared to have occured in an isolated geographical area one can call this convergent evolution”. How one can call this convergent evolution ???

A number Australian marsupials and placental mammals each different from the other have evolved from an ancestral stock with in Australian island continent. 

This is a type of convergent evolution, because more than one adaptive radiation occurred in isolated geographical area.

Detailed answer:

Australian marsupials and placental mammals. A number of marsupials, each different from the other evolved from an ancestral stock, but all within the Australian island continent. 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 (e.g., Placental wolf and Tasmanian wolf). 

Convergent evolution : This is because, more than one adaptive radiation has occurred in isolated geographical area