Bats are unmistakable.
No mammals other than bats have true wings and flight. Bat wings are modified forelimbs, much as are bird wings, except in the case of bats the flight surface is covered with skin and supported by four fingers, while in birds the flight surface is provided mostly by feathers and is supported by the wrist and two digits. The flight membrane usually extends down the sides of the body and attaches to the hind legs. Bats are the second-most speciose group of mammals, after rodents. In some tropical areas, there are more species of bats than of all other kinds of mammals combined.