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Challenge to dino-bird evolution theory not dead yet
Feb. 10, 2010
Courtesy Oregon State University
and World Science staff
Although most scientists accept that birds descended from dinosaurs, challenges to the idea aren't dead yet. A 1915 drawing by naturalist William Beebe suggests a hypothetical view of what early birds may have looked like, gliding down from trees.
The picture bears a striking similarity, some scientists say, to a fossil discovered in 2003 that is raising new doubts about whether birds descended from ground-dwelling theropod dinosaurs. (Photo courtesy Oregon State University)
A study just published in the research journal Proceedings of the National Academy of Sciences provides yet more evidence against the theory, according to
some.
The analysis was done of an unusual fossil discovered in 2003 called “microraptor.”
Three-dimensional models were used to study its possible flight potential. The
assessment concluded this small, feathered species must have been a “glider” that came down from trees.
The research is solid and consistent with a string of studies in recent years that pose increasing challenge to the birds-from-dinosaurs theory, said John Ruben, a professor of zoology at Oregon State University who authored a commentary in the journal
on the new research.
A long list of commonalities between birds, reptiles and certain dinosaurs—including similarities in bone structures at both the microscopic and visible levels—have drawn
most paleontologists toward the conventional view of dinosaur-bird evolution.
In it, birds descended from theropod dinosaurs, a great lineage of
ground-dwelling meat-eaters with strong hind legs and short forelimbs.
Yet some are drawing totally different conclusions.
The weight of the evidence is now suggesting that not only did birds not descend from dinosaurs, Ruben said, but that some species
thought to be dinosaurs may have descended from birds. “We're finally breaking out of the conventional wisdom of the last 20 years, which insisted that birds evolved from dinosaurs and that the debate is all over and done
with,” Ruben said. “This issue isn't resolved at all.”
Almost 20 years of research at Oregon State on the forms of birds and dinosaurs, along with other studies, Ruben said, are much more consistent another view: that birds may have had an ancient common ancestor with dinosaurs, but they evolved separately on their own path.
After millions of years of separate evolution, according to this view, birds also gave rise to the raptors, which “look quite a bit like dinosaurs but they have much more in common with birds than they do with other theropod dinosaurs such as Tyrannosaurus
[Rex],” Ruben said.
“We think the evidence is finally showing that these [raptors]
which are usually considered dinosaurs were actually descended from birds, not the other way
around,” Ruben added. Small animals such as velociraptor that have generally been thought to be dinosaurs are more likely flightless birds, he said.
Another study last year from Florida State University raised similar doubts, Ruben
noted.
In the newly published work, University of Kansas scientists examined a fossil that
showed feathers on all four limbs, somewhat resembling a bi-plane. Glide tests based on its structure concluded it would not have been practical for it to have flown from the ground up, but it could have glided from the trees down, somewhat like a modern-day flying squirrel. Many researchers have long believed that gliders such as this were the ancestors of modern birds.
“This model was not consistent with successful flight from the ground up, and that makes it pretty difficult to make a case for a ground-dwelling theropod dinosaur to have developed wings and flown
away,” Ruben said. “On the other hand, it would have been quite possible for birds to have evolved and then, at some point, have various species lose their flight capabilities and become ground-dwelling, flightless animals – the raptors. This may be hugely upsetting to a lot of people, but it makes perfect
sense.”
The study appeared in the Proceedings early online issue for
the week of Jan. 25, whereas Ruben’s commentary was published
in early online issue for the week of Feb. 8.
“Pesky new fossils... sharply at odds with conventional wisdom never seem to cease popping
up,” Ruben wrote in his article.
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Although most scientists accept that birds descended from dinosaurs, challenges to the idea aren't dead yet. A new study just published in the research journal Proceedings of the National Academy of Sciences provides yet more evidence against the theory, according to its authors. The analysis was done of an unusual fossil specimen discovered in 2003 called “microraptor,“ in which three-dimensional models were used to study its possible flight potential. The study concluded this small, feathered species must have been a “glider“ that came down from trees. The research is solid and consistent with a string of studies in recent years that pose increasing challenge to the birds-from-dinosaurs theory, said John Ruben, a professor of zoology at Oregon State University who authored a commentary in the journal accompanying the new research. A long list of commonalities between birds, reptiles and certain dinosaurs—including similarities in bone structures at both the microscopic and visible levels—have drawn the majority of paleontologists toward the conventional view of dinosaur-bird evolution. Yet some are drawing totally different conclusions. The weight of the evidence is now suggesting that not only did birds not descend from dinosaurs, Ruben said, but that some species now believed to be dinosaurs may have descended from birds. “We're finally breaking out of the conventional wisdom of the last 20 years, which insisted that birds evolved from dinosaurs and that the debate is all over and done with,“ Ruben said. “This issue isn't resolved at all.“ Almost 20 years of research at Oregon State on the forms of birds and dinosaurs, along with other studies, Ruben said, are much more consistent another view: that birds may have had an ancient common ancestor with dinosaurs, but they evolved separately on their own path. After millions of years of separate evolution, according to this view, birds also gave rise to the raptors, which “look quite a bit like dinosaurs but they have much more in common with birds than they do with other theropod dinosaurs such as Tyrannosaurus,“ Ruben said. Theropods were a lineage of meat-eating dinosaurs with strong hind legs and short forelimbs. “We think the evidence is finally showing that these animals which are usually considered dinosaurs were actually descended from birds, not the other way around,“ Ruben added. Small animals such as velociraptor that have generally been thought to be dinosaurs are more likely flightless birds, he said. Another study last year from Florida State University raised similar doubts, Ruben said. In the newly published work, scientists examined a remarkable fossil that had feathers on all four limbs, somewhat resembling a bi-plane. Glide tests based on its structure concluded it would not have been practical for it to have flown from the ground up, but it could have glided from the trees down, somewhat like a modern-day flying squirrel. Many researchers have long believed that gliders such as this were the ancestors of modern birds. “This model was not consistent with successful flight from the ground up, and that makes it pretty difficult to make a case for a ground-dwelling theropod dinosaur to have developed wings and flown away,“ Ruben said. “On the other hand, it would have been quite possible for birds to have evolved and then, at some point, have various species lose their flight capabilities and become ground-dwelling, flightless animals – the raptors. This may be hugely upsetting to a lot of people, but it makes perfect sense.“ “Pesky new fossils... sharply at odds with conventional wisdom never seem to cease popping up,“ Ruben wrote in his commentary. “Given the vagaries of the fossil record, current notions of near resolution of many of the most basic questions about long-extinct forms should probably be regarded with caution.“