Fossils From China Suggest All Birds Had a Common Ancestor
By Kenneth Chang
THE NEW YORK TIMES
Filling a gap in the evolution of birds, scientists have dug up fossils of a bird that lived 110 million years ago and looked remarkably like a small modern-day waterfowl.
One of the new fossils, from northwest China, even preserves the webbing between the toes. The finding, reported Friday in the journal Science, supports the notion that all living birds, from ostriches to ducks to hummingbirds, descended from an ancestor that lived by the shore.
The first fossil of the bird, Gansus yumenensis, was discovered 25 years ago, and it was named after where it was found, near the city of Yumen in the Chinese province of Gansu. But that fossil was just the left foot and part of the ankle, enough to show that the Gansus was small — about the size of a robin — but leaving much unknown.
In 2004, researchers led by Hai-lu You of the Chinese Academy of Geological Sciences returned to the region and found about 40 more fossils of Gansus in an area that was once a lake. The best preserved fossils are nearly complete and even show parts of the feathers, although none include the bird’s skull.
The bones of the upper body suggest that Gansus was able to take flight from the water, much like today’s ducks. Webbed feet and bony knees, which probably anchored strong muscles, show that Gansus could swim.
“We have thought of it as more like a diving duck or a loon,” said Matthew C. Lamanna, an author of the Science paper who is assistant curator of vertebrate paleontology at the Carnegie Museum of Natural History in Pittsburgh. “We see it as a swimmer or a diver.”
Birds first evolved about 40 million years before Gansus lived, but early birds like Archaeopteryx looked more like the dinosaurs that most paleontologists believe birds descended from. Gansus instead possessed skeletal features — for example, the bones in the ankle and upper foot were fused together — that are seen in modern birds.
“All other birds from the early Cretaceous period are not as closely related to modern birds as this one is,” Lamanna said.
At the time Gansus lived, the prevalent birds in most parts of the sky were of a type known as “opposite birds” because some bones in their shoulders and feet were reversed compared with present-day birds. But at the Chinese lake, Gansus appears to have been the most common bird. About 80 percent of the bird fossils found so far have been of Gansus. That might eventually offer some clues of how modern birds later rose to dominance while the opposite birds became extinct along with the dinosaurs 65 million years ago.
In building the family tree of birds, the scientists also noticed that most of the close relatives of modern birds lived in or around water.
“We noticed that a sequence of aquatic birds led up to the modern birds,” Lamanna said.