They have two incisors in the upper and lower jaw, which grow continually and are kept short by gnawing.
The order Erinaceomorpha contains a single family, Erinaceidae, which comprise the hedgehogs and gymnures.
The bats' distinguishing feature is that their forelimbs are developed as wings, making them the only mammals capable of flight.
They are the mammals most fully adapted to aquatic life with a spindle-shaped nearly hairless body, protected by a thick layer of blubber, and forelimbs and tail modified to provide propulsion underwater.
Even-toed ungulates' weight is borne about equally by the third and fourth toes, rather than mostly or entirely by the third as in perissodactyls.