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"Process of evolution of different species in a given geographical area starting from the original species for getting adapted in the new habitats is called Adaptive Radiations". 

Placental mammals show adaptive radiations in Australia island continent mammal have involved in the different habitats. These species of placental mammals appear similar to corresponding Marsupial species of the same habitat. Eg- Marsupial Tasmanian wolf and Placental wolf 2 Marsupial Tasmanian flying cat and Placental Bobcat 3 Marsupial Flying Phalanger and Placental Flying Squirrel 4 Marsupial spotted cuscus and Placental Lemur 5 Marsupial mouse and placental mouse 6 Marsupial mole and placental mole

An adaptive radiation is a rapid evolutionary radiation characterized by an increase in the morphological and ecological diversity of a single, rapidly diversifying lineage
example is the evolution of a fourth cusp in the mammalian tooth