Archaeopteryx, believed for 150 years to have been the first bird, was probably only a feathered dinosaur that had great difficulty getting off the ground when it lived 150 million years ago, researchers reported this week in the journal PLoS One.
Discovered in 1860, only a year after Charles Darwin published his famous "On the Origin of Species," the raven-sized archaeopteryx was generally assumed to show evolution in action. It had the feathers and wishbones of birds, but it also retained the teeth, tail and three-fingered hands of dinosaurs.
But new studies of its bones and those of other fossils, by a team led by paleontologist Gregory M. Erickson of Florida State University and the American Museum of Natural History, show that it was much less bird and far more dinosaur than had been believed.
Examining microscopic chips of bone, the team concluded that the bones were very dense and slow-growing, while those of birds are porous, light and fast-growing. Birds mature to full size in a few weeks, but archaeopteryx would have taken at least 2 1/2 years to reach its full size, the scientists reported. That's nearly as slow a growth rate as that of dinosaurs.
All of the 10 known fossil specimens of archaeopteryx, the scientists concluded, are juveniles. And the creatures' bones would be so heavy that they could perform only very limited aerial maneuvers.
Examining other early fossils, they concluded that modern bird physiology did not begin to appear until Confuciusornis, a toothless bird from the Yixian geological formation in China that did not appear until 20 million years after archaeopteryx.
"Archaeopteryx had comparable metabolism to the closely related velociraptor," coauthor Mark Norell, an American Museum of Natural History paleontologist, said in a statement. "We knew that they are a kind of dinosaur, but we now know that the transition into true birds -- physiologically and metabolically -- happened well after archaeopteryx."