This depiction of the newly described dinosaur Xiaotingia zhengi shows what it might have looked like.  © 2011 Xing Lida and Liu Yi

"Hardly any recent discovery shows more forcibly than this how little we as yet know of the former inhabitants of the world."

Charles Darwin wrote these words a few years after the discovery of Archaeopteryx, the so-called "first bird." He might say the same thing today because, in a groundbreaking discovery, paleontologists from China report that the world's most famous feathered fossil species was most likely not a bird.

That's right. Despite what science textbooks and scores of natural-history-museum exhibits say, Archaeopteryx was not a bird.

In a paper published today in Nature, four authors led by Xing Xu, a renowned expert on the origins of birds whom USA Today called "the world's most prolific dinosaur hunter," describe a new species of feathered bird-like dinosaur from northeastern China that dates to about 155 million years ago — approximately five million years older than Archaeopteryx.

Named Xiaotingia zhengi, the dinosaur was about the size of a chicken and weighed approximately 1.8 pounds (820 grams), slightly less than a Swainson's Hawk.

After obtaining the fossil from a dealer, Xu analyzed Xiaotingia to establish its place in the dinosaur family tree. The effort led him to the conclusion that Xiaotingia, four-winged Anchiornis, and Archaeopteryx belong in the Deinonychosauria, a diverse group of bird-like dinosaurs. A separate group known as the Avialae — the one in which Archaeopteryx had been placed until now — makes up the predecessors of modern birds.

It contains species such as Epidexipteryx, Jeholornis, and Sapeornis, all of which were named in the past decade.

"In other words," says anatomist and paleontologist Lawrence Witmer in an accompanying news article, "Archaeopteryx was no longer a bird."

This painting of Archeopteryx by Heinrich Harder dates from about 1916.

One of the differences Xu describes is the shape of the skull. The eye socket of deinonychosaurs is noticeably larger than that of avialans. And the deinonychosaurs' snout is shallow while in avialans, it's deep and short. Consequently, deinonychosaurs are believed to have been carnivores while avialans were most likely plant-eaters.

The finding, Witmer says, is bound to generate controversy among scientists.

"It may mean that much of what we thought we knew about the origin and early evolution of birds will need to be re-evaluated," he writes.

Witmer calls the ancestors of birds and the animals that simply looked like ancestors of birds as "this fuzzy tangled knot" and suggests:

"Perhaps the time has come to finally accept that Archaeopteryx was just another small, feathered, bird-like theropod fluttering around in the Jurassic." —Matt Mendenhall, Associate Editor