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Paleontologists in China have discovered the fossil remains of a four- winged dinosaur with fully developed, modern feathers on both the forelimbs and hind limbs.
The new species, Microraptor gui, provides yet more evidence that birds evolved from dinosaurs, and could go a long way to answering a question scientists have puzzled over for close to 100 years: How did a group of ground-dwelling flightless dinosaurs evolve to a feathered animal capable of flying?
Xu Xing, a paleontologist at the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, China, and colleagues suggest in the January 23 issue of the journal Nature that the species is an early ancestor of birds that probably used its feathered limbs, along with a long, feather-fringed tail, to glide from tree to tree.
They argue that the animal represents an intermediate stage in the evolution of flight, from gliding much as flying squirrels do today to the active wing flapping of modern birds.
Xu's work has long been supported by the National Geographic Society's Committee for Research and Exploration.
The six specimens were excavated from the rich fossil beds of Liaoning Province in northeastern China. They are dated at between 128 to 124 million years old (Early Cretaceous).
"To have fully formed flight feathers on the hind legs is fascinating," said James Clark, Ronald Weintraub Associate Professor of Biology at George Washington University, Washington, D.C.
"There were some interesting speculations about 90 years ago that birds might have had four feathered limbs, but no one has suggested it in recent times, since all living birds use only their forelimbs," he said. "This find broadens the whole scope of thinking about the origins of flight."
The Bird-Dinosaur Connection
Much fossil evidence has been uncovered supporting the idea that birds evolved from a group of bipedal carnivorous dinosaurs called theropods. Within the theropod group, birds are most closely related to dromaeosaurids. Velociraptor, a star in the movie Jurassic Park, is probably the most famous of dromaeosaurs.
Earlier finds in Liaoning suggest that the earliest dromaeosaurs were small, feathered animals with forelimbs similar to those of Archaeopteryx, the oldest known bird at around 150 million years old, and feet with features comparable to modern tree-living birds.
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