Kevin Holden Platt in Beijing
for National Geographic News
for National Geographic News
January 16, 2009
A fossil of a primitive feathered dinosaur uncovered in China is helping scientists create a better model of how dinosaurs evolved into modern birds.
The winged dinosaur is still in the process of being dated, and might have lived toward the end of the Jurassic period, which lasted from 208 to 144 million years ago. The protobird is "very close to the point of divergence" at which a new branch of winged dinosaurs first took flight, said Xu.
The new species, called Anchiornis huxleyi, was discovered in the ashes of volcanoes that were active during the Jurassic and Cretaceous (144 to 65 million years ago) periods in what is now northeastern China.
(Read about the prehistoric world.)
Anchiornis, which is Greek for "close to bird," measured just 13 inches (34 centimeters) from head to tail and weighed about 4 ounces (110 grams).
The dinosaur's body and forelimbs were covered with feathers, and it "might have had some aerial capability," Xu said.
"Anchiornis is one of the smallest theropod dinosaurs ever uncovered," Xu explained. Theropods were a group of carnivorous dinosaurs that walked on two legs.
Taking Wing
The fossil provides new clues about how feathers, wings, and flight progressively appeared among theropods, along with evidence that certain types of feathered dinosaurs decreased in stature even as their forelimbs became elongated.
The compact structure of Anchiornis "reinforces the deduction that small size evolved early in the history of birds," Xu explained.
"[Anchiornis] exhibits some wrist features indicative of high mobility, presaging the wing-folding mechanisms seen in more derived birds," he said.
"The wrist is a big part of the formation of wings, and pivotal to flight," Xu added. "During flight, steering and flapping greatly depend on the wrist."
Despite this protobird's relatively advanced feathers and wrist, it is unclear if Anchiornis could actually engage in powered flight.
"Behavior and biomechanics are very difficult to determine solely from the fossil record, and perhaps flight is impossible to determine," said Mark Norell, chairman and curator of the division of paleontology at the American Museum of Natural History in New York.
"Feathers have lots of functions, and probably evolved as thermoregulators," said Norell, who closely examined the fossil during a trip to Beijing.
"Dinosaurs might have used feathers for sexual display or to make themselves appear bigger, or as camouflage to avoid predators," he said.
Patterns of spots and bars evident on one species of feathered dinosaur from China might have functioned as a camouflage defense, Norell added.
(Related: "First
Prehistoric Paradise
Xu said that the region in northeastern China where most of the world's feathered dinosaurs, including Anchiornis, have been discovered is a virtual paradise for dinosaur hunting.
"This area has three circles of volcanic activity," with eruptions that intermittently covered and preserved entire biospheres starting from the early Jurassic.
"Volcanos periodically killed the animals and plants and preserved them perfectly in volcanic ash," he said.
"Sometimes the volcanic ash even preserves soft tissues, leaving behind an exceptional 3-D fossil."
Source
No comments:
Post a Comment