If it dives like a duck, has webbed feet like a duck and flies like a duck, is it a duck?

Maybe not, but Chinese and US scientists do believe the long extinct Gansus may be an ancestor of the modern duck.

Talking to reporters in Washington, DC yesterday, the scientists said the Gansus (Gansus yumenensis), a loon-like ancient bird, was one of the oldest members of the lineage leading to modern birds.

The team have excavated five well-preserved Gansus fossils in the town of Changma, Northwest China's Gansu Province, about 2,000 kilometres west of Beijing.

And the new fossil specimens, reported in today's issue of the journal Science, help fill in the avian family tree.

Living about 110 million years ago, the amphibious avian suggests that early birds may have been waterfowl.

The fossils include nearly complete skeletons consisting of three-dimensional, mostly uncrushed bones. Several of the specimens even contain appreciable carbonized remains of feathers and webbed feet.

According to a release from You Hailu, a scientist with the Chinese Academy of Geological Sciences and the primary author of the Science article, details in the hind legs and feet of the Gansus show that the bird was probably a foot-propelled diver like today's grebes, loons and many ducks, although the species might not have been as good at diving as its modern counterparts.

"It must have been much smaller than the modern chicken, based on the fossils," co-author Jerry Harris, director of paleontology of Dixie State College in Utah, said in a telephone interview.

But scientists failed to find a skull during the excavation, which is crucial in tracing back what the bird fed on, Harris said.

"Without the skull, we could not tell the skeletal shape of its beak," he said.

However, scientists unearthed some fossils of plants, fish and insects. In combination with its diving habit, the bird probably dined on what lived under water, Harris suggested.

Harris said the discovery was significant as the anatomy of the specimens has shown that the Gansus was very close to modern birds, and no other similar findings so far have been "quite that advanced or old (in the lineage)."

The Gansus belongs to a lineage of early birds called the Ornithurae, which includes all modern birds (Neornithes) and their immediate fossil ancestors.

The Gansus is not a member of the Neornithes, but it is the oldest known ornithuran.

Besides the Gansus, several other ancient ornithuran birds also show they adapted to an aquatic lifestyle, but "they were pretty (much) towards the end of the evolution, and there was a gap between the trend," Harris said. "The finds add new information."

About 80 per cent of all fossils they discovered in Changma belonged to Gansus, which contradicts previous discoveries. Previously, fossils of "opposite birds" dominated, he said.

These opposite birds, whose shoulder joint was reversed compared with that of modern birds, were another type of ancient bird that disappeared along with all non-avian dinosaurs at the end of the Cretaceous period, leaving no descendants.

Ornithuran birds probably arose in the Early Cretaceous, between 110 million and 140 million years ago, when enantiornitheans, or opposite birds, ruled the skies.

"The finds will help us understand the important switch in bird evolution, which is now at the forefront of our following research," Harris said.

He explained that in earlier fossil sites such as the famous deposits in Liaoning Province, which yielded the first "feathered dinosaur" specimens a decade ago few were found that were related to modern birds.

But the Changma deposits are only a few million years younger than those at Liaoning, so they may assist researchers in their probe into how and why ornithurans rose to dominance over the opposite birds.

You Hailu said environmental changes may have played a role in the switch, "but it's hard to answer this question just based on bird fossils. We need more information on the paleoclimate."

The Gansus' fossils are preserved in rocks that were deposited in an ancient lake, whose quiet environment helped preserve soft tissues.

To find the fossils, the paleontologists split open countless slabs of mudstone from the lake "like turning the pages of a book," co-author Matthew Lamanna of the Carnegie Museum of Natural History, located in Pittsburgh, Pennsylvania, said in the press release.

The first dig was conducted in 2003 and followed by another in 2004.

Lamanna says the Changma finds may be very significant since they provide a rare glimpse into what happened with land ecosystems around 110 million years ago, shortly after the period of history that the find at the Liaoning deposits had implied.

"It may represent not only the next chapter in bird evolution, but the next phase in the evolution of a lot of different types of organisms," he said.

Harris added that no other discoveries have been quite similar, although a fossilized partial hind leg of Gansus was found in 1981 in Changma.

"In England, they found one from 100 million years ago," he said, "but it is obviously not as advanced as our finds."

(China Daily 06/16/2006 page1)