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Branching out

作者:路漩    发布时间:2019-03-08 06:14:00    

By Jeff Hecht A NEW look at a fossil discovered a decade ago has added weight to the idea that bats evolved from flightless creatures that hung from tree branches by all four legs. Most palaeontologists now believe that birds evolved from small ground-dwelling dinosaurs that had developed feathers for another purpose. But the origins of bats have been a puzzle. Even the earliest bat fossils, from about 50 million years ago, have wings that closely resemble those of modern bats. Their anatomy suggests kinship with the cat-sized flying lemurs of southeast Asia, which—like many bats— hang upside down from trees by all fours. Three years ago, Nancy Simmons of the American Museum of Natural History in New York suggested that bats and flying lemurs had a common ancestor that hung from branches by all fours, before evolving the ability to glide and eventually to fly. But there was no fossil evidence. Now Mark Hamrick of Kent State University in Ohio may have found the missing link. Hamrick was studying Phenacolemur, a mouse-sized flightless animal that lived around the same time as early bats. He found that bones originally thought to come from its hand actually came from the rear foot, and resembled those that flying lemurs use to hang from trees. “Nobody had realised this was hanging from its hind feet before,” says Hamrick, who reported the results last week at a meeting of the Society for Vertebrate Paleontology in Snowbird, Utah. He believes the animal climbed by hanging underneath branches from all four legs because it was the easiest way to reach the fruit, nectar and insects at their tips. Hamrick concludes that bats and Phenacolemur share a common ancestor. However, it may be difficult to find an intermediate form that shows how bats evolved their wings. Fossils of small mammals rarely survive, Simmons says, and intermediate forms would have existed only briefly. “Once powered flight began to evolve, it was such an important feature that evolution proceeded very rapidly,

 

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