Bats are the only mammals with true powered flight
Bats (order Chiroptera) stretch skin over elongated finger bones to fly with more agility than most birds. They are the second-largest mammal order after rodents—about twenty percent of mammal species, with at least 1,500 named. Folklore loves and fears them in equal measure.
A bat's wing is a hand. The order name Chiroptera joins Greek words for hand and wing, and the membrane stretches across enormously long fingers whose bones are flattened and grow less mineralised toward the tips. That lengthening comes from stepped-up activity of the gene BMP-2 in the embryo's forelimbs. The results range from Kitti's hog-nosed bat, 29 to 33 millimetres long and about 2 grams, to the flying foxes, and the Mexican free-tailed bat has been clocked at 160 kilometres per hour over the ground.
Their fragile skeletons fossilise poorly; only about 12 percent of bat genera that ever lived are thought to be known. The oldest finds, around 55 to 56 million years old, are isolated teeth. Onychonycteris finneyi, found in 2003 in Wyoming's Green River Formation and about 52 million years old, had claws on all five fingers and short broad wings, and it suggests bats could fly before they could echolocate. Genomic work has killed the flying primate idea that megabats evolved flight separately; all bats share one ancestor, and they sit in Laurasiatheria alongside carnivores and hoofed mammals.
Linnaeus lumped the seven bats he knew into the primates in 1758, and Johann Friedrich Blumenbach gave them their own order about twenty years later. The old split into fruit-eating megabats and microbats has given way to two new suborders, Yinpterochiroptera, which includes the megabats, and Yangochiroptera. That rearrangement implies echolocation by the larynx either evolved twice or was lost in megabats, some of which later reinvented it with tongue clicks. Teeth vary too, from 38 in small insect-eaters down to 20 in vampire bats.
English once called them flittermice, like German Fledermaus; the word bat appeared around the early 1570s. People mine their dung as guano fertiliser, rely on them to eat crop pests, visit roosts as tourists and, in parts of Africa, Asia, the Pacific and the Caribbean, eat them.
Source: Bat
