The species, or Microraptor gui, was the earliest dinosaur able to fly among those studied so far, said a noted Chinese researcher Xu Xing, who had led the research project. The reptiles were completely covered with feathers and their limbs had evolved into wings.

Scientists held that the four-winged structure had never been found in other vertebrates.

The latest issue of Nature magazine published Xu's research finding as its cover article, together with an independent commentary citing this as the most vital breakthrough in researches into flight origins and would make paleontologists re-evaluate some classical work.

The new finding makes the definition of birds even more difficult. Two identifying characteristics of birds -- having wings and the ability to fly -- no longer apply. Before this, another identifying characteristic of birds -- having feathers -- was also done away with by the finding of feathered dinosaurs, according to Xu, a noted researcher with the Institute of Vertebrate Paleontology and Paleoanthropology at the Chinese Academy of Sciences.

The new species climbed up trees using their four limbs and glided between branches, posing an intermediate stage before active, flapping flight, Xu explained.

Paleontologists have long debated how the ancestors of birds learned to fly. The prevailing hypothesis says that dinosaurs learned to fly through their activities on the ground, like running and the other hypothesis says they acquired flight from an arboreal lifestyle.

The new finding is crucial to proving the latter theory, providing evidence that some small-sized dinosaurs developed the ability to fly from living in trees, including falling and gliding.

The fossils were discovered in western Liaoning province, northeast China, in rock strata dating from the early Cretaceous Period approximately 110 million to 120 million years ago. The strata also yielded other rare fossils of dinosaurs and primitive birds.

Mircrocraptor gui was some 77 cm long with peaked and curved claws and a fairly long tail. Except for its relatively short forelimbs, all the reptile's features were more closely related to modern birds and it could fly more strongly than the archaeopteryx, the most primitive bird found in Germany in 1860.

The new species Microcraptor gui is named in honor of Gu Zhiwei,an established Chinese paleontologist as well as an academician of the Chinese Academy of Sciences.

The research is funded, among others, by the China National Natural Science Foundation, the Ministry of Science and Technology and the Chinese Academy of Sciences.

(Xinhua News Agency January 23, 2003)