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Dinosaur-bird missing link
possibly found
Feb. 21, 2005
Special to World Science
Researchers say they have found a partial fossil of a feather-footed creature possibly similar to the direct dinosaur ancestor of birds.
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Evidence is starting to emerge that birds
originated in Laurasia, a supercontinent made up of present-day Eurasia,
Greeland and North America, shown here as it would have looked 200
million years ago. (Courtesy U.S. Geological Survey)
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The newfound fossil might come from a
relative of Archaeopteryx, the first known bird, researchers say.
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Although it’s not the first fossil of a bird-like dinosaur
ever found, it seems more closely related than the others to the actual dinosaur
species that evolved into birds, the researchers said.
That’s because the previously unearthed fossils seem to come from dinosaurs that lived slightly later than the first
birds. These might thus have been “irrelevant” to the dinosaur-bird transition, explained the researchers.
They reported the findings in the Feb. 1 issue of the research journal
Naturwissenschaften (Natural Sciences).
The newfound fossil appears to be older than those previously discovered, and may predate the birds, said Xing Xu,
one of the authors.
“This is significant because [of] both its relatively early age and its appearance,”
Xu, of the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences, Beijing,
wrote in an email. “We are beginning to find more bird-like dinosaurs, or even very bird-like dinosaurs from earlier rock.”
The findings help to confirm a theory—believed by most, but not all paleontologists—that birds evolved from dinosaurs, he said. It could also reveal more about how bird flight originated and precisely which type of dinosaur gave rise to the bird lineage.
For one thing, the researchers said, the findings suggest birds originated in Laurasia, an ancient super-continent composed of present-day Eurasia, North America and Greenland. The available evidence “perhaps tentatively supports an Asian origin” of birds, they wrote.
The new specimen, from a fossil-rich bed of rock near the village of Daohugou, China, comes from an animal apparently slightly shorter than 1 meter (about 1 yard) long, said the researchers. The fossil shows only a leg with long, lush, bird-like feathers.
The rock beds, called the Daohugou beds, seem, based on the fossils in them, to have formed during the middle or later part of the Jurassic period, the researchers said. The Jurassic is a period between 208 million and 146 million years ago, when birds and flowering plants are believed to have evolved, and when many dinosaurs flourished.
The Jurassic period is of course the time period referred to in the Steven Spielberg movie Jurassic Park. Birds are in fact believed to be closely related to one of the dinosaur stars of that movie, the fleet-footed Velociraptor.
Velociraptor—which looks something like a little Tyrannosaurus Rex that may have made up in zippiness what it lacked in size—was a member of a family of smart, vicious dinosaurs called dromaeosaurs. The previous findings of bird-like dinosaur fossils, announced in 2003, were identified as particularly small representatives of this group. They were most remarkable in that they had four wings. Both their front and hind limbs had each developed into a pair of wings.
These creatures were dated at around 115 million years old, younger than the oldest known bird, Archaeopteryx, which lived around 150 million years ago. Thus, they lived to late to have been bird ancestors.
The new finding might not have that drawback, according to the researchers who made both discoveries, Xu and his colleague Fucheng Zhang. They said the newly discovered creature, dubbed
Pedopenna daohugouensis (“the feather-footed one from Daohugou) is a primitive member of a family of dinosaurs called eumaniraptora.
This group, they added, is both larger and older than the dromaeosaurs, but includes and gave rise to both them and the birds. Eumaniraptora also includes the troodontids, a family of long-legged, fast dinosaurs thought to have had large brains and excellent sight, hearing and hand coordination.
If this picture is correct, then, birds would have evolved from a creature similar the common ancestor of all the eumaniraptora, an animal not unlike
P. daohugouensis.
Moreover, the finding adds to a trend: the most primitive examples of the various members of eumaniraptora and their relatives come from eastern Asia, the researchers wrote. This is what suggests, to them, that birds originated in this area, which at the time was part of the supercontinent of Laurasia.
The discovery also adds to evidence, which also appeared with the 2003 findings, that birds’ dinosaur ancestors had feathers both on their front and hind limbs, according to the researchers. Since this feather arrangement forms a structure ideal for gliding, the way flying squirrels move among trees, it supports a hypothesis that the most primitive birds learned to fly this way, the researchers added.
However, P. daohugouensis has shorter leg feathers than the previously described specimens, the researchers said. Thus it might represent an evolutionary stage in which the birds’ ancestors were already losing their leg feathers and shifting to an arrangement in which only the front limbs handled the task of flying.
—EJL
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