An international team of scientists believe they have found the strongest evidence yet that birds evolved from dinosaurs: fossils of two turkey-sized animals with strong legs, stubby arms and down-covered bodies.
Phil Currie, curator of the Royal Tyrrell Museum of Paleontology in Canada, said Tuesday that the fossils, found in China, are of dinosaurs capable of running swiftly, flapping feathered wings and fanning out impressive tail feathers. But the animals could not fly.Currie said the fossils, dated at 120 million to 136 million years old, are absolute proof that birds evolved from dinosaurs, a theory that has been hotly contested for more than 20 years.
"It is a historic moment when a controversy is resolved," Currie said at a news conference. "This shows that dinosaurs are not extinct, but are well-represented by 10,000 species of birds."
Fossils from the earliest known bird, called Archaeopteryx, have been dated at 140 million to 150 million years old.
The new fossils closely resemble Archaeopteryx in some ways, but the new discoveries lack the precise form of true birds, particularly the length of wing and design of individual feathers. For this reason, the researchers believe the fossils represent true dinosaurs that are the immediate ancestors of the first birds.
Currie, Mark Norell of the American Museum of Natural History and Ji Qiang and Ji Shu-An of the National Geological Museum of China describe the fossils in studies published this week in the journal Nature and in a National Geographic cover story.
Both fossils were removed by Ji Qiang and his Chinese colleagues from rock formations beneath an ancient lake bed in the Liaoning Province in northeast China. The area has gained fame in recent years for containing rich deposits of dinosaur remains.
Alan Feduccia, an evolutionary biologist at the University of North Carolina, Chapel Hill, said the Chinese discoveries "are very interesting," but he said they do not provide immediate and final proof that birds evolved from dinosaurs. He said that the new fossils are dated after those of the first bird. This suggests, he said, that the fossils could be either feathered dinosaurs or primitive birds that just happened to resemble dinosaurs.
"The age dates for these things are still unresolved," said Feduccia. He said if the new fossils represent ancestors of early birds, why are they younger than the early birds?
Qiang, speaking through an interpreter, said that while he believes the fossils strongly support the theory that birds evolved from dinosaurs, it is no longer clear where the division line is between the two animal groups.