アメリカ自然史博物館のインスタグラム(amnh) - 10月15日 08時30分

It's #FossilFriday! Birds have hollow bones, and most scientists assumed this trait evolved along with flight: lighter bones should make it easier to fly. But studies have shown that Allosaurus, a fairly primitive theropod, also had hollow bones. Allosaurus was a big animal with tiny arms, so it wasn’t flying anywhere—like so many other bird traits, hollow bones appear early in the dinosaur family tree.

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