|Fossil Discovery Threatens Theory of Birds' Evolution|
have discovered fossil evidence of the oldest known feathered animal, a
small reptile that probably glided among the trees 75 million years
before the earliest known bird, and they say this challenges the widely
held theory that birds evolved from dinosaurs.
The animal, Longisquama insignis, lived in Central Asia 220 million years ago, not long after the time of the first dinosaurs. It had four legs and what appeared to be feathers on its body. From impressions left in stone, its elongated back appendages had hollow shafts and other characteristics closely resembling those of feathers.
''We can identify certain structures in these fossils that you only find in feathers,'' said Terry D. Jones, a member of the discovery team and the lead author of a report being published today in the journal Science. ''So we're quite sure we're looking at the earliest feather.''
Prior to this, the oldest feather belonged to archaeopteryx, also recognized as the earliest bird. Archaeopteryx lived about 145 million years ago, and its fossils were found in Germany in the 19th century. Scientists who analyzed the Longisquama fossils said the animal had a wishbone virtually identical to archaeopteryx and similar to modern birds.
In the cautiously worded report of the new findings, the scientists referred to the feathers as nonavian -- that is, not related to birds -- and said, ''The exact relationship of Longisquama to birds is uncertain.''
But in interviews and a news release by Oregon State University in Corvallis, one of several universities from which researchers were drawn, members of the discovery team threw down the gauntlet in their dispute with other paleontologists who favor a direct evolutionary link between dinosaurs and birds.
While the new fossil evidence does not conclusively establish that Longisquama was an ancestor of flying birds, John A. Ruben of Oregon State said, it would have lived in the right time and had the right physical structure to have been an ancestor -- and it was clearly not a dinosaur.
Moreover, he and other scientists noted, the advanced development of the newly discovered feathers suggested that feather evolution extended back much earlier, probably before the first dinosaurs appeared on the scene about 240 million years ago.
Paleontologists have long agreed that birds evolved from reptiles. Archaeopteryx itself is a blend of saurian and avian traits. But were the bird ancestors dinosaurs or another reptilian lineage? Beginning with research by John Ostrom of Yale University in the 1970's, evidence seemed to favor a dinosaurian heritage, though a few scientists, Dr. Ruben among them, held out against the emerging orthodoxy.
Storrs Olson, an ornithologist at the Smithsonian Institution who was not on the discovery team but has been skeptical of the dinosaur-bird theory, agreed with the interpretation of the fossils and the implications for understanding bird evolution.
''These extraordinary structures really can be only feathers,'' Dr. Olson said. ''It's extremely important, more important than the discovery of archaeopteryx.''
Mark A. Norell, a paleontologist at the American Museum of Natural History in New York and a leading exponent of a dinosaurian ancestry of birds, said he was not ready to concede that the fossil impressions are of true feathers.
''Even if these turn out to be feathers, they have not established that Longisquama is ancestral to modern birds,'' Dr. Norell said.
The discovery ruffling paleontology's feathers was made by scientists from the University of Kansas, the Russian Academy of Sciences, the University of North Carolina at Chapel Hill, the City University of New York, the College of Charleston, Sonoma State University in California, in addition to Oregon State. Dr. Jones, who participated in the research as a graduate student at Oregon State, is now on the faculty of Stephen F. Austin State University in Nacogdoches, Tex.
The fossils in question were excavated in 1969 in Kyrgyzstan, a former Soviet republic. When the impressions now said to be feathers were first identified as reptilian scales, the specimen was put away in a drawer in Moscow and ignored. But they were retrieved and displayed as part of a touring exhibit of Russian fossils last year. Seeing them, Dr. Jones and Dr. Ruben said they realized immediately that this was a very old animal with feathers.
Other paleontologists and ornithologists were called in for a look. Alan Feduccia of the University of North Carolina, author of ''The Origin and Evolution of Birds'' (Yale University Press), was struck by the hollow shaft covered by a sheath, a characteristic of bird feathers.
''This is a dramatic finding,'' Dr. Feduccia said. ''Everything about the feather points to aerodynamic structure, indicating that the initial function of feathers was in an aerodynamic context.''
A point of contention in the dinosaur-bird debate centers on the initial function of feathers. Dinosaur partisans argue that when some dinosaurs became warm-blooded they developed down as insulation and this led to feathers, which then gave them the ability to fly. Their opponents contend that in some coldblooded reptiles feathers evolved from their scales and were adapted originally for flight.
From an examination of the Longisquama skeleton, scientists inferred that its body feathers would have been adequate for gliding but its musculature would not have supported powered flight. Given more time, though, the muscles could have developed and the feathers could have spread to the forearms, creating wings, the discovery team suggested.
''A point that too many people always ignored is that the most birdlike of the dinosaurs, such as bambiraptor and velociraptor, lived 70 million years after the earliest bird, archaeopteryx,'' Dr. Ruben said in a university statement. ''So you have birds flying before the evolution of the first birdlike dinosaurs. We now question very strongly whether there were any feathered dinosaurs at all.''
June 23, 2000
MORE? (Flying like the Birds)
JOHN NOBLE WILFORD
The New York Times
|[HOME] [AVIATION] [HUMANS] [ORIGINS] [Origin of Flight] [Origin of Language] [Prehistoric Flight] [Atlantis] [Strange finds] [Strange maps] ["Bottleneck"?] [SCIENCE] [WEB LINKS] [SITE MAP] [CONTACT]|