Is This Iconic Evolutionary Bird Really Not a Bird?

NEW YORK (The Blaze/AP) -- One of the world's most famous fossil creatures -- Archaeopteryx -- widely considered the earliest known bird on Earth, is getting a rude present on the 150th birthday of its discovery: A new analysis suggests it isn't a bird at all. The International Business Times reports:

In subsequent years, theories of the bird species evolution drew heavily on archaeopteryx. But the discovery of several feathered dinosaurs in the past 15 years has led experts to question whether it was really the first bird.

Thus, Chinese scientists are proposing a change to the evolutionary family tree that boots Archaeopteryx off the "bird" branch and onto a closely related branch of birdlike dinosaurs.

Archaeopteryx (ahr-kee-AHP'-teh-rihx) was a crow-sized creature that lived about 150 million years ago. It had wings and feathers, but also quite un-birdlike traits like teeth and a bony tail. Discovered in 1861 in Germany, two years after Charles Darwin published "On the Origin of Species," it quickly became an icon for evolution and has remained popular since.

The Chinese scientists acknowledge they have only weak evidence to support their proposal, which hinges on including a newly recognized dinosaur.

Other experts say the change could easily be reversed by further discoveries. And while it might shake scientific understanding within the bird lineage, they said, it doesn't make much difference for some other evolutionary questions.

Archaeopteryx dwells in a section of the family tree that's been reshuffled repeatedly over the past 15 or 20 years and still remains murky. It contains the small, two-legged dinosaurs that took the first steps toward flight. Fossil discoveries have blurred the distinction between dinosaur-like birds and bird-like dinosaurs, with traits such as feathers and wishbones no longer seen as reliable guides.

"Birds have been so embedded within this group of small dinosaurs ... it's very difficult to tell who is who," said Lawrence Witmer of Ohio University, who studies early bird evolution but didn't participate in the new study.

The proposed reclassification of Archaeopteryx wouldn't change the idea that birds arose from this part of the tree, he said, but it could make scientists reevaluate what they think about evolution within the bird lineage itself.

"Much of what we've known about the early evolution of birds has in a sense been filtered through Archaeopteryx," Witmer said. "Archaeopteryx has been the touchstone... (Now) the centerpiece for many of those hypotheses may or may not be part of that lineage."

The new analysis is presented in Thursday's issue of the journal Nature by Xing Xu of the Chinese Academy of Sciences in Beijing, and colleagues. They compared 384 specific anatomical traits of 89 species to figure out how the animals were related. The result was a tree that grouped Archaeopteryx with deinonychosaurs, two-legged meat-eaters that are evolutionary cousins to birds.

But that result appeared only when the analysis included a previously unknown dinosaur that's similar to Archaeopteryx, which the researchers dubbed Xiaotingia zhengi. It was about the size of a chicken when it lived some 160 million years ago in the Liaoning province of China, home to many feathered dinosaurs and early birds. According to the Guardian, Paul Barrett, a dinosaur researcher at London's Natural History Museum, had the following to say:

"The overall picture of birds being descended from meat-eating dinosaurs is now very firmly established. This is an argument over a relatively small rearrangement of some of the twigs on the evolutionary tree close to the origin of birds. It doesn't affect much of our big picture view of how birds came from dinosaurs, but some of the minutiae: the small changes that are important to the biology of the animals.

This part of the evolutionary tree is very sensitive to small changes in how we interpret the anatomy and the combination of anatomical features we see in these animals as they are discovered. As a result, the structure of that evolutionary tree is very unstable and can flip around. Maybe Archaeopteryx wasn't on the direct ancestral line to birds, but was part of an early experimentation in how to build a bird-like body."

Julia Clarke of the University of Texas at Austin, who did not participate in the study, said the reclassification appeared to be justified by the current data. But she emphasized the study dealt with a poorly understood section of the evolutionary tree, and that more fossil discoveries could very well shift Archaeopteryx back to the "bird" branch.

Anyway, moving it "a couple of branches" isn't a huge change, and whether it's considered a bird or not is mostly a semantic issue that doesn't greatly affect larger questions about the origin of flight, she said. The International Business Times continues:

...the assertion of Xu's study doesn't challenge the scientific community's assumption that birds evolved from dinosaurs. However, they may have to look elsewhere to bestow the title of the oldest known bird fossil. Moreover, the theory of evolution may have lost one of its early icons.

Luis Chiappe, an expert in early bird evolution at the Natural History Museum of Los Angeles County who wasn't part of the new study, said he doesn't think the evidence is very solid.

"I feel this needs to be reassessed by other people, and I'm sure it will be," he said.