Dinosaur fossil may be link to modern birds

The top image shows the complete fossil slab (the head is in the upper left, looking backward, and the tail is stretching across to the right). The enlarged view below shows the hind limbs that appear to be heavily feathered.

NEW YORK (CNN) -- The clearest evidence ever of the missing link between dinosaurs and birds has been found in a newly discovered "feathered" fossil in northeastern China, claim scientists writing this week in the British journal Nature.

The question of whether certain dinosaurs were the ancestors of modern-day birds has been hotly debated. Supporters point to bird-like bone structure, including wishbones and hollow bones, in theropods, a suborder that includes Tyrannosaurus Rex and other dinosaurs that walked on two legs.

Evidence of feathered theropods has been fuzzy, but the scientists writing in Nature say the new fossil makes the picture clearer.

"The feather structure is unmistakable. You see a central shaft, and then veins or barbs coming off the side. It is identical to a modern bird feather," said Mark Norell, paleontologist at the American Museum of Natural History and co-author of the Nature article. "It was even obvious to my 3-year-old daughter."

Norell and a team of Chinese and American scientists discovered the fossilized dromaeosaur last fall in northeastern China's Liaoning Province, an area that has yielded a wide variety of fossils from the late Jurassic and early Cretaceous periods -- approximately 125 million years ago.

The specimen was found embedded in a large slab of rock, in what scientists think was a former lake or pond. It is the third dromaeosaur ever discovered.

"It is the third to be found, but the first one that has shown feathers identical to the ones in modern birds," Norell said. "They were probably present on some of those in the past, but the feathers weren't preserved well enough to be able to see the fine structure. On this latest one, feathers are found all over the fossil, and they are best preserved on the back edge of the forearms and hind limbs."

Detractors weigh in

Theories linking dinosaurs with birds are not without detractors.

"How is an animal going to have flight feathers on its thighs that are half the length of its tail? How could it run or do anything with flight feathers sticking out of the back side of its leg?" said John Ruben, a zoologist at Oregon State University. "It is borderline ridiculous."

Norell said that some modern birds such as certain kinds of hawks have big feathers sticking out of the back of their limbs, and claimed Ruben is really reaching in his attempt to "shoot down" Norell's study.

Ruben also questioned the authenticity of the specimen, calling for a CAT scan to determine whether the entire fossil slab comes from the same source.

"There is no reason to CAT scan this specimen, because clearly it's not pieced together," Norell said. "It is preserved on one large slab, and we have both part and counterpart." Part and counterpart refers to both the top and bottom, or both sides, of the fossil slab.

Norell dismissed Ruben's assertions as "silly pseudo science."

Ruben in 2000 found a fossil that he said showed a reptile-like animal with feathers about 220 million years ago. He said the fossil proved that feathers evolve well before the dinosaurs that had been linked to birds.

In October 1999, National Geographic released a controversial article on what was purported to be a feathered dinosaur called archaeoraptor. Authenticity was called into question and critics claimed that only one side of the slab had been studied. Critics also said that pieces of the fossil could have been cobbled together and that the specimen included more than one animal.