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 New Species of Flying Dinosaur Found in china |
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作者：Anonymous 在 罕见奇谈 发贴, 来自 http://www.hjclub.org
New Species of Flying Dinosaur Found
Predator Lived in Trees, Likely Used Plumage to Glide
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By Guy Gugliotta
Washington Post Staff Writer
Thursday, January 23, 2003; Page A03
Scientists have discovered a new species of flying dinosaur unlike any seen before, a spectacular four-winged predator that lived in trees and probably used its elaborate plumage to glide from branch to branch, research published yesterday said.
The find, in northeastern China's fossil-rich Liaoning Province, significantly boosts the "top-down" theory of the origin of flight: that birds evolved from tree-dwelling dinosaurs that glided through treetops before flapping their wings.
"This time the evidence is overwhelming," said paleontologist Xing Xu, of China's Institute of Vertebrate Paleontology and Paleoanthropology. "It's hard even to imagine how these little animals could have moved around bipedally" -- on their hind legs. Xu led the six-member Chinese team whose findings were reported yesterday in the journal Nature.
The team recovered six specimens of the small predatory raptor that showed nearly complete skeletons as well as the sharply etched outlines of elaborate feathers on the forelimbs, hind limbs and tail. Xu's team called it a four-winged dinosaur -- the first ever found.
University of Kansas evolutionary ornithologist Richard Prum, whose analysis accompanied the research report, called the Liaoning research "the most exciting find on the question of the origin of flight" in the 140 years since the discovery of Archaeopteryx, the 150-million-year-old fossil regarded as the world's first true bird.
But other scientists were reluctant to give the new, four-winged flyer such exalted status. "It's important, certainly," said Brown University vertebrate morphologist Stephen Gatesy. "The first reflex is to say that this is a stage on the way to birds, but for all we know, this could be a quirky side branch."
Regardless of the new dinosaur's ultimate destination in the evolutionary tree, yesterday's report was the second major paper this month on the origin of flight to shake up the century-old debate between the top-down school and the "bottom-up" school, which holds that flight developed among small, land-dwelling dinosaurs that learned to run and flap their winged forelimbs until they achieved liftoff.
Last week University of Montana biologist Kenneth P. Dial proposed an intermediate stage, reporting in the journal Science how seemingly awkward, heavy-legged modern birds -- such as chickens or turkeys -- use their wings as airfoils to gain traction as they run up steep inclines. Dial suggested that small, feathered dinosaurs may have used the same technique to get up into trees.
The two papers "help show that the dichotomy between top-down and bottom-up is false," said Ohio University evolutionary biologist Lawrence Witmer. "These finds from China demonstrate that there are a lot of tiny predatory dinosaurs" that likely had reason to want to get off the ground. Although the majority appear to have been primarily ground-dwellers, he added, "I don't see how you keep them out of the trees."
The newly discovered animal measures about 30 inches from its head to the tip of its long tail, but the body is about the size of a large pigeon. It is a predatory carnivore belonging to the same dinosaur group as Tyrannosaurus rex and the smaller raptors. Xu's team dubbed the new discovery Microraptor gui.
The Xu team unearthed the specimens in the Liaoning fossil fields, where an entire ecosystem appears to have been suddenly buried, perhaps by volcanic ash, 130 million years ago.
Over the past few years, Liaoning has produced unprecedented discoveries of fossils of small therapods that clearly show the outlines of feathers. These animals, fast runners with "killer claws" on the second digit of their hind limbs, were basically two-legged land-dwellers. Bottom-up advocates theorize that these animals' weak forelimbs eventually developed into wings as they made the evolutionary transition to birds.
M. gui also has "killer claws," but its hind limbs contrast sharply with those of most other small raptors, because -- like the forelimbs -- they are thickly carpeted with functional feathers. Xu's team suggested the plumage made it impossible for M. gui to be nimble on the ground. Instead, the team theorized that it lived aloft, gliding among branches like a tree squirrel. Witmer noted that even though M. gui is not as old as Archaeopteryx, it could be a descendant of a shared ancestor.
"It has many of us scratching our heads," Witmer added. Although the new discovery is the first documented flying -- or gliding -- raptor, the feathered hind limbs almost certainly didn't "flap," and there is no conclusive evidence on whether M. gui could splay its hind limbs in a wing-like pose.
The hind limbs' heavy feathers may have been for "display purposes" rather than flight, he added: "Animals will endure all kinds of deficits in their lives if it gives them more and better mates," Witmer said.
Brown's Gatesy said, "What's so, so wonderful is that it's clear that this is what it looked like. Now we have to figure out what it did. I don't know what's going on with the rear end. We need somebody who knows hips."
?2003 The Washington Post Company
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作者：Anonymous 在 罕见奇谈 发贴, 来自 http://www.hjclub.org |
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