DISCOVERY DISPUTES DINOSAUR-BIRD LINK.

Byline: John Noble Wilford The New York Times

In an analysis of new fossil discoveries in northeastern China, American and Chinese researchers have found evidence that they say casts serious doubt on the widely held theory that birds are direct descendants of dinosaurs.

The findings suggest that archaeopteryx, a reptilian bird that lived 145 million to 150 million years ago, and its close kin were not direct links between reptiles and today's birds, but evolutionary dead ends. By the time of archaeopteryx, another bird lineage with perhaps much more ancient origins existed. That lineage seems to have led to modern birds.

The strongest clue, scientists said, comes from the fossils of a bird the size of a sparrow, called Liaoningornis, which was uncovered by a farmer in Liaoning Province. In one test, volcanic rocks associated with the bones have been dated at 137 million to 142 million years old, which in evolutionary terms would make the bird a virtual contemporary of archaeopteryx.

But the specimen is considerably more modern looking than the primitive archaeopteryx, having foot bones and a keeled breastbone that resemble those of birds today. It offers the earliest evidence of such a distinctly birdlike structure as the keeled breastbone, which is essential for flight. (It is not clear whether archaeopteryx, which did not have one, was capable of more than gliding downward from cliff tops.) The bones also suggest that this bird was probably warm-blooded, like modern birds and unlike reptiles.

In a report published Friday in the journal Science, the researchers concluded that this and other discoveries indicated a much more ancient avian history, extending perhaps to reptilian ancestors even before the age of dinosaurs, which began more than 200 million years ago.

``This exacerbates one of the most obvious conundrums facing the theory of a dinosaurian origin of birds,'' the scientists wrote. ``The dinosaurs thought to be most like birds are younger than archaeopteryx by more than 76 million years.''

This time paradox, the scientists suggested, has led some to speculate that birds gave rise to certain dinosaurs in the late Cretaceous geologic period, rather than the reverse. The Cretaceous ended 65 million years ago, the time of the mass extinction that wiped out dinosaurs and most birds. Those that survived, mainly shore birds, then evolved rapidly into the bird groups known today.

In any event, one of the scientists, Alan Feduccia, an ornithologist at the University of North Carolina, at Chapel Hill, said the fossils offered ``strong evidence for a fundamental split in early bird evolution'' long before archaeopteryx. ``This raises an interesting question about whether archaeopteryx and all of the other recently discovered early birds may be a sideline of avian history,'' he said in a telephone interview.

Feduccia wrote ``The Origin and Evolution of Birds,'' published this fall by Yale University Press. The other contributors to the Science report are paleontologists: Lianhai Hou of the Institute of Vertebrate Paleontology, in Beijing; Larry D. Martin of the University of Kansas, at Lawrence; and Zhonghe Zhou, a graduate student at Kansas.

Their interpretation of the new fossils is certain to ruffle feathers among paleontologists, most of whom embrace the theory that birds evolved from dinosaurs, though fewer and fewer still think that archaeopteryx was the direct ancestor. Ornithologists, on the other hand, have long disputed the dinosaur-bird link, contending that dinosaurs and birds probably shared an ancestor among predinosaur reptiles.

As Feduccia said: ``This has probably been the most contentious issue in vertebrate paleontology for the past 30 years - whether birds are derived from earthbound dinosaurs or whether they are derived from antecedents of the dinosaurs.''