Mammals, like other animals, sometimes develop a body shape or lifestyle that is very similar to that of an unrelated animal living in exactly the same environment.
Dolphins, for example, have a very similar body shape to sharks and to the extinct marine reptile ichthyosaurus, because they inhabit the same environment and have a very similar way of life. In the same way, kangaroos have adapted to a similar lifestyle to antelopes and sheep, grazing in open grasslands. This process is called parallel evolution, and it demonstrates how animals develop in the same way, in order to fit in with the available living space and food supply.
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