The bird calls that filled Jurassic Park.

For more than a century, the lowest branches of the avian family tree seemed a lonely place, occupied by the solitary species Archaeopteryx lithographica, the oldest known bird. But recent fossil discoveries from Asia are filling in the bottom boughs, dramatically altering the picture of early avian history.

In the Oct. 19 Nature, Chinese and U.S. paleontologists describe several new fossils belonging to a bird species that lived roughly 140 million years ago. Called Confuciusornis sanctus, this pigeon-size flier hails from the end of the Jurassic period, making it only slightly younger than the 150-million-year-old Archaeopteryx.

Korean scientists have found another, presumably Jurassic bird fossil, the researchers note, but the Korean group has not yet published a description of the specimen in a scientific journal.

The new findings show that at the time of Archaeopteryx, or even before, birds were evolving in many different directions, says study coauthor Alan Feduccia, an ornithologist at the University of North Carolina at Chapel Hill. "So while we've been concentrating on this ancient bird Archaeopteryx as the key to the whole problem of bird evolution, it may just have been a sideline, [with] many branches of the avian tree evolving almost simultaneously."

The other authors of the Nature study were Lian-hai Hou and Zhonghe Zhou of the Chinese Academy of Sciences in Beijing and Larry D. Martin of the University of Kansas in Lawrence. Hou, Zhou, and another Chinese colleague first announced the discovery of Confuciusornis earlier this year in a Chinese journal.

Found in the northeast province of Liaoning, the Confuciusornis fossils display a patchwork of primitive and advanced features. Like Archaeopteryx, the Chinese fossils have long fingers with large curved claws, a feature absent in almost all later birds. The design of its front limbs, along with the curved claws on its feet, indicates that Confuciusornis could climb trees.

While its body resembles that of the oldest bird, Confuciusornis' skull looks much more modern. Unlike most birds from the age of the dinosaurs, but like all living birds, the Chinese species had a horny, toothless beak. Prior to this discovery, scientists had thought that toothless beaks did not appear until the late Cretaceous period, roughly 70 million years ago, says Feduccia.

The Confuciusornis find has generated excitement among researchers who study avian evolution.

"It's fantastic to have this burst of findings of early birds," says Luis M. Chiappe of the American Museum of Natural History in New York City. However, Chiappe questions the reported Jurassic age of the Chinese bird.

The exact age of Confuciusornis remains unknown. Scientists debate not only the precise age of the fossils, but also the closing date of the Jurassic period. The fossils may fall in the latest part of the Jurassic or the opening of the Cretaceous.

The specimens from Liaoning show evidence that Confuciusornis had feathers along its leg, making this the earliest record of contour feathers, as distinct from flight feathers. Scientists do not know whether Archaeopteryx had such feathers along its body, but it clearly had flight feathers along its wings and tail.

The presence of contour feathers is important because it bears on whether early birds were warm-blooded. Some researchers have speculated that contour feathers arose first among warm-blooded dinosaurs as a form of insulation. Birds would have inherited feathers from their dinosaurian ancestors and later used them for flight.

But a recent study (SN: 3/14/94, p.312) casts doubt on this theory of feather origins. The bones of some Cretaceous birds have growth rings, a feature common among cold-blooded animals. The find suggests that early birds may not have developed a fully warm-blooded physiology.