an ancient order of mammalia dating to the early Eocene, including the bats. They are nocturnal mouselike mammals having four toes of each of the anterior limbs elongated and connected by a web, so that they form membranous wings that can be used in flying. They also have anatomical adaptations, including large ears, for echolocation, by which they navigate and in some cases find insects. The order includes the suborders Megachiroptera (the fruit bats) and Microchiroptera (insectivorous bats). See Bat. Previously spelled cheiroptera.