Fossil muddies the origin of birds

A birdlike fossil that dates to roughly 155 million years ago is ruffling the feathers of some paleontologists. At issue is whether the fossil is a dinosaur, an early bird or something in between.

“This new animal is the most primitive bird in the world,” says paleontologist Pascal Godefroit of the Royal Belgian Institute of Natural Sciences. He and an international team of colleagues describe the new specimen May 29 in Nature. The fossil comes from northeastern China’s Tiaojishan formation and is named Aurornis xui.

Not everyone agrees with Godefroit’s interpretation. “This is very birdlike, but it is not yet a bird,” says paleontologist Luis Chiappe of the Natural History Museum of Los Angeles County.

If Aurornis is in fact a bird, the specimen may have implications for scientists’ view of Archaeopteryx, the most famous birdlike dinosaur (or dinosaur-like bird). A controversial 2011 paper argued that Archaeopteryx and two other specimens were feathered dinosaurs, not birds. But Godefroit’s team proposes that Archaeopteryx is evolutionarily younger than the newly discovered Aurornis. So if Aurornis is on the bird lineage, as Godefroit argues, then Archaeopteryx should be, too.

There isn’t any well-preserved plumage on the new specimen, but Godefroit says that the shapes of bones in the fossil’s pelvic region are part of what make him think the animal was a bird.

Still, the fossil’s forelimb is much shorter than that of true birds, Chiappe says. That detail, he says, along with the fossil’s longish reptilian tail and several skull features, suggest it is a dinosaur.