Bats are the only mammals that are capable of true flight. Several other mammals are capable of gliding for considerable distances.
Bats are efficient flyers, although their wings have developed very differently from those of birds. A bat’s wing is like an outstretched hand with very long fingers, connected by thin skin. Other mammals, such as squirrels and marsupials, are able to glide by means of sheets of skin stretched between their front and back legs. They use these sheets to travel from tree to tree. These animals are not closely related and yet they have developed the ability to fly quite separately, so this is an example of parallel evolution.
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