SCIENTISTS have discovered the fossil of a crow-sized bird that lived in China roughly 150 million years ago and possessed undersized wings that may have made it more of a runner than a flier a discovery that paints a more complicated picture of early avian evolution.

The new Jurassic Period species, Yuezhuornis yangyuanensis, represents one of the earliest-known birds, similar in age to the famous Archaeopteryx from Europe. Yuezhuornis is puzzling for an early bird in that it seems already to have diminished the ability to fly in favour of running on the ground, perhaps somewhat like a roadrunner a fast runner but clumsy flier that rarely takes to the air.

`Yuezhuornis challenges the traditional paradigm that the avian body plan evolved almost exclusively under the selective pressures of flight,` said paleontologist Min Wang of the Institute of Vertebrate Paleontology and Paleoanthropology, part of the Chinese Academy of Sciences, who helped lead the study published on Wednesday in the journal Nature. `So this new fossil just changes our assumption about what a Jurassic bird looks like,` wang said.

Asked if Yuezhuornis may have lived like a roadrunner by mostly running but flying in short bursts when necessary, Wang said, `Yes, that is likely.` The nearly complete fossil was unearthed in Fujian Province in southeastern China.

Birds evolved during the Jurassic from small feathered dinosaurs, but fossils showing precisely when this occurred and howitunfolded arelacking. Archaeopteryx long was the oldest-known bird but a small number of others of similar age like Yuezhuornis have now been found.

Yuezhuornis, which weighed an estimated 1.8 pounds (800 grams), presented a mosaic of anatomical traits combining avian and dinosaurian characteristics.

Its forelimbs were fully developed wings, though they were too small compared to the rest of the body to have allowed forrobust flying. It also had the slender cranial bones of a bird and a bird-like pelvis.

On the other hand, Yuezhuornis had a sickle-shaped claw on its flexible second toe similar to that of meat-eating dinosaurs like Deinonychus, Velociraptor and Troodon a dangerous weapon useful for a terrestrial hunter. In fact, Wang said, Yuezhuornis may have competed for prey with small non-bird dinosaurs. It had relatively large, closely packed and serrated teeth lining its jaws, typically present in certain carnivorous dinosaurs but not birds. In addition, it had a long and bony dinosaurian tail, as all the earliest-known birds did.

Archaeopteryx combined avian and dinosaurian traits, too, but its well-proportioned wings showed it was built for flying.-Reuters