Feduccia and his team also examined the way digits formed within the wings and limbs of dinosaurs and extinct and existing birds. Many scientists who support the theory that birds evolved from dinosaurs point to the fact that both share a three-digit system somewhat comparable to the human thumb, index finger and middle finger.

The new study found that birds have more of an index finger, middle finger and ring finger arrangement within their wings and on their feet. Since this "digit identity" is different from what two-legged dinosaurs had, the authors of the new paper say their findings cast additional doubt on the hypothesis that birds evolved from theropods.

Instead, Feduccia supports the theory that birds and dinosaurs shared a common ancestor, but that birds and dinos developed separately on their own evolutionary paths.

"A good candidate for this common ancestor is Lagosuchus, a small, quadrupedal archosaur (ancient reptile) that lived around 220 million years ago in what is now Argentina," he said.

He explained that Lagosuchus had a five-digit hand that could have evolved into the digits found on both birds and dinosaurs.

John Ruben, chair of the Zoology Department at Oregon State University, told Discovery News that the new study is "quite good and presents very carefully researched data."

Ruben said, "There is no question birds and dinosaurs are closely related, but the question is, do birds emerge after the appearance of meat-eating dinosaurs or beforehand."

Ruben, like Feduccia, believes the evidence as it stands now does not support the existence of feathered dinosaurs or the theory that birds evolved from carnivorous theropods.

Frances James, professor emerita in the Department of Biological Science at Florida State University, told Discovery News that she also supported the new study's findings.

"Flight must have evolved from the trees down and not from the ground up," she said. "The ancestor to birds therefore could have been some arboreal archosaur, but we just don't know. The question as to where birds came from is now left open."

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