Findings clip the wings of missing-link prehistoric 'bird'

Last update: October 10, 2009 - 5:50 PM

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Archaeopteryx, the 150-million-year-old fossil that for a century and a half has been considered to be the first bird, was probably only a feathered dinosaur that had great difficulty getting off the ground, researchers reported last week.

Discovered in 1860, only a year after Charles Darwin published "On the Origin of Species," the magpie-size Archaeopteryx generally was assumed to show evolution in action. It had some traits of modern birds, such as feathers and a wishbone, 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 paleontologist Gregory Erickson of Florida State University and the American Museum of Natural History and his colleagues show that it was much less bird and far more dinosaur than had been believed. Their findings were reported in the journal PLoS One.

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. While a bird matures to full size in a few weeks, Archaeopteryx would be nearly as slow-growing as any other dinosaur, requiring at least 2 1/2 years to reach full size -- about that of a modern raven.

All of the 10 known 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 formation in China that did not appear until 20 million years after Archaeopteryx.

"Archaeopteryx had comparable metabolism to the closely related Velociraptor," paleontologist Mark Norell of the American Museum of Natural History, a co-author, 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."

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