Image: Science

The origin of birds remains a controversial topic among dinosaur researchers, and new findings on feathers may stir things up once again. Until the 1970s, most scientists thought that birds were descendants of reptiles. Since then, however, the view has gradually shifted. Today, most believe that about 150 to 180 million years ago, birds evolved from theropods, a group of dinosaurs that includes, among others, the well known Tyrannosaurus rex. Proponents of both theories based their arguments on similarities between the skeletal structures of birds and reptiles or dinosaurs.

Now two researchers from the Chinese Academy of Sciences in Bejing describe another intriguing physical feature in a study of Protopteryx fengningensis, one of the earliest birds ever found. The starling-size animal lived about 120 million years ago and is a member of the Enantiornithine family of birds. Fucheng Zhang and Zhonghe Zhou, who published their results in the December 8th issue of Science, found that the wing bone and muscle structure of Protopteryx was very similar to that of modern birds. At the same time, the animals still had a single claw (the equivalent of a thumb in humans) on their wings, which has disappeared in modern birds.

Although the reduced claw puts Protopteryx closer to modern birds than earlier creatures such as Archaeopteryx, its feathers were apparently more primitive. According to Zhang and Zhou, these plumes had many scale-like qualities, leading them to believe that feathers developed from scales. They supposedly evolved in stages: Initially, scales became elongated and developed a central shaft. This shaft then sprouted barbs on each side, which grew increasingly fine until they became feathers. Protopteryxs own fluff seems to fall somewhere in the middle of this evolution.

Supporters of the reptile-origin theory see these findings as an indication that birds evolved from reptiles, whereas supporters of the dinosaur-origin theory see the emergence of feathers as unrelated. Whatever the case, Protopteryx's fate, at least, is well known: The Enantiornithine family of birds died out during the mass extinction 65 million years ago. And their demise gave an opportunity to the Ornithurae family, ancestors of modern birds.