Fossil hunters in China have discovered what may be one of the weirdest prehistoric species ever seen — a four-winged dinosaur that apparently glided from tree to tree.

The 128-million-year-old animal — called Microraptor gui, in honor of Chinese paleontologist Gu Zhiwei — was about 2 1/2 feet long and had two sets of feathered wings, with one set on its forelimbs and the other on its hind legs.

Exactly where the creature fits into the evolution of birds and dinosaurs is not clear. But researchers speculated that it developed around the same time as or even later than the first two-wing, birdlike dinosaur, Archaeopteryx, which is believed to have flown by actually flapping its wings.

Paleontologists were intrigued by the discovery. They have seen gliding dinosaurs before, but never one with feathers. And they have never seen a four-winged dinosaur before.

“It would be a total oddity — the weirdest creature in the world of dinosaurs and birds,” said Luis Chiappe, a paleontologist at the Natural History Museum of Los Angeles County who did not participate in the dig.

Scientists said the fossils — discovered in the Chinese province of Liaoning, northeast of Beijing, at a site that has yielded several important specimens in recent years — revive a debate between two theories of how dinosaurs might have evolved into birds.

One theory holds that some of these apparent bird ancestors learned to flap their wings to power flight while they were gliding from tree to tree. The other theory suggests they learned to fly by increasing their running speed with their wings and taking off from the ground.

The latest find tends to support the gliding-in-trees theory.

“It’s a phenomenal find,” Chiappe said. “We don’t have anything that resembles this in the whole dinosaur and bird spectrum.”

Details of the fossils appear in Thursday’s issue of the journal Nature.

Paleontologist Xing Xu of the Institute of Vertebrate Paleontology and Paleoanthropology at the Chinese Academy of Sciences described six fossils with leg feathers arranged in a pattern similar to wing feathers in modern birds.

“They are long and some have asymmetrical vanes like flight feathers,” Xu said.

The feathered legs amount to rear wings, Xu said. He speculated they could have represented an intermediate stage of development before the emergence of true flight powered by flapping the wings. Or, the feathered legs could have been an evolutionary dead end, other researchers said.

Scientists believe Microraptor gui probably did not fly by flapping its wings, because of the way the rear legs are set in the hip sockets and because the rear legs probably would have encountered turbulence from flapping front wings. That suggests instead that both sets of wings were used just for gliding, Chiappe said.

Other scientists said the fossils add diversity to the story of flight, even if they do not immediately provide answers.

Ken Dial, head of a biological flight laboratory at the University of Montana, said there is room for both gliding and flapping dinosaurs in evolutionary history.

“Gliding represents a splendid example of convergent evolution,” Dial said. “We should not be surprised to unearth gliding dinosaurs as we have numerous living-day examples of gliders in nearly all the vertebrate groups — reptiles, mammals, birds and even parachuting amphibians.”

Last week, Dial reported in the journal Science that the way young birds such as turkeys and quail use their wings suggests ancient birds eventually learned to fly by running and flapping.

Paul Sereno, a University of Chicago paleontologist, said the best way to determine whether Microraptor gui was an intermediate stage in bird evolution or a dead end is to find other dinosaur fossils with feathered legs.

Sereno called the Xu study a landmark paper but added: “Whether this represents an intermediate form that all birds passed through is a question that’s going to be hotly debated.”