By DAVID WILLIAMSON
UNC-CH News Services
CHAPEL HILL -- By studying fossils newly found in northeast China, scientists have discovered that Archaeopterx -- the famous link between birds and reptiles -- did not give rise to modern birds some 150 million years ago as most experts had thought.
Instead, modern birds appear to have descended from a different, unknown ancestor, one that near the time of Archaeopteryx had many characteristics of birds still inhabiting the earth today, said Dr. Alan Feduccia, a University of North Carolina at Chapel Hill biologist.
"The classic view of bird evolution was that we had this sort of half-bird, half reptile from the late Jurassic period ," Feduccia said. "That was Archaeopteryx with its long reptilian tail and three clawed fingers for climbing up tree trunks, which gradually evolved into the modern birds we know.
"Now, however, we have found strong evidence for a fundamental split in early bird evolution. Contrary to the popular view, it appears that Archaeopteryx represented an evolutionary dead end."
A report on the discovery appears in the Nov. 15 issue of the journal Science. Besides Feduccia, authors are Dr. Lianhai Hou of the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing and Dr. Larry D. Martin and graduate student Zonghe Zhou of the University of Kansas' Natural History Museum.
Last year the team reported in the journal Nature discovery of complete fossilized skeletons of Confuciusornis, a close, somewhat younger relative of Archaeopteryx with clawed fingers for climbing, beaked jaw and short tail. Like its more famous cousin, Confuciusornis probably also was cold blooded.
In the new work, the researchers report discovery of so many specimens of Confuciusornis that they conclude that the bird lived in large colonies, which is the first evidence of social behavior in birds. They also found that that it was the first fully feathered bird yet identified and that its flight feathers were asymmetric, meaning that it too could fly.
More important, Feduccia said, they have found fossils of a modern-type, probably warm-blooded bird they call Liaoningornis together with Confuciusornis. Unlike the latter, the former had a keeled sternum, which is the earliest evidence of that distinctly bird-like structure, one that acted as a pump for air sacs in the lungs and facilitated longer flights. All modern flying birds show that keeled breastbone.
"We would expect that the common ancestor of the two groups -- which we call `Sauriurine' for reptile-like and `Ornithurine' for bird-like -- predates Archaeopteryx and that we may reasonably search for birds in Middle Jurassic and older beds," Feduccia said. "This exacerbates one of the most obvious conundrums facing the theory that birds descended from dinosaurs. The dinosaurs thought to be most like birds are primarily Late Cretaceous in age and are younger than Archaeopteryx by more than 76 million years."
That paradox, he said, has even led some dinosaur experts to argue that birds gave rise to certain late Cretaceous dinosaurs.
The scientist believes that birds suffered cataclysmic extinctions at the end of the Cretaceous period just as the dinosaurs did. Those that survived, chiefly a small group of shore birds, evolved "explosively " into most modern bird groups in only 5 million to 10 million years, a period he calls "bird evolution's big bang." He also believes flight evolved from trees downward -- as tree-climbing reptiles sought food and escape from predators -- rather than from the ground upward.
"This has probably been the most contentious issue in vertebrate paleontology for the past 30 years -- whether birds are derived from earth-bound dinosaurs or whether they are derived from antecedents of the dinosaurs," Feduccia said. "In the 1970s, paleontologists began to view birds simply as modified feathered dinosaurs. Once you do that, you are pretty much stuck with the `ground-up' origin of flight, but it is impossible to explain how flight could have evolved from heavy earth-bound creatures with short forelimbs. Besides making no sense biophysically, that theory also appears to ignore the geologic record."
Most bird-like dinosaurs lived 80 million or so years after the first known birds appeared, he said. All dinosaurs disappeared about 65 million years ago, possibly because a huge meteorite struck Earth.
Feduccia, an evolutionary biologist and ornithologist, is S.K. Heninger professor of biology, author of numerous books and scientific articles and a frequent source for stories about birds, dinosaurs and evolution for various publications. His most recent book, published last month by Yale University Press, was "The Origin and Evolution of Birds."
- 30 -
Note: Feduccia can be reached at (919) 962-3050 (w) or 942-3377 (h). Contact: David Williamson