The fossil of a strange dinosaur with four feathery wing-like appendages, unearthed in China, could provide clues to the origins of birds, scientists said.
Unearthed at a dinos' graveyard in the northeastern province of Liaoning, the astonishingly-preserved fossil is that of a 125-million-year-old predator the size of a small but slim turkey.
Dubbed Changyuraptor yangi, the creature sports a full set of feathers over its entire body, which measured 1.3 metres from its beak to the tip of its super-long tail.
"At a foot (30 centimetres) in length, the amazing tail feathers of Changyuraptor are by far the longest of any feathered dinosaur," said Luis Chiappe at the Natural History Museum in Los Angeles.
The raptor, believed to be an adult that probably tipped the scale at around 4.5 kilograms, is the biggest so-called "four-winged" dinosaur ever found.
These dinos, known as microraptorines, had long feathers attached to all their legs and arms, although how well they used the skies is a matter of big debate.
The new discovery suggests that in the case of Changyuraptor a form of flight or gliding was quite possible. The super-long tail feather may have existed to give aerodynamic control, ensuring that the critter made a safe landing.
If so, that calls for a rethink of the theory that birds evolved just from small, feathery theropods, or two-footed dinosaurs.
"The new fossil documents that dinosaur flight was not limited to very small animals but to dinosaurs of more substantial size," said Chiappe in a press release.
"Clearly, far more evidence is needed to understand the nuances of dinosaur flight, but Changyuraptor is a major leap in the right direction."
Dating the origin of birds has been a source of wrangling among palaeontologists.
For decades, the title of "first bird" went to the 150-million-year-old Archaeopteryx, 11 specimens of which have been found in German limestone quarries.
But the picture became muddied a few years ago with the emergence of 160-million-year-old fossils in China that appear to be older relatives of Archaeopteryx.
Changyuraptor's tail contributes to the debate by showing one of the long evolutionary paths that led to the first bird.
"Numerous features that we have long associated with birds in fact evolved in dinosaurs long before the first birds arrived on the scene," said fellow investigator Alan Turner of Stony Brook University in New York.
"This includes things such as hollow bones, nesting behaviour, feathers... and possibly flight."
The study appears in the journal Nature Communications.