The fossil of a "bizarre" feathered dinosaur from the era before birds evolved has been discovered in China.
Epidexipteryx was very bird-like, with four long ribbon-like tail feathers - probably used in display.
But the pigeon-sized creature shows no sign of the flight feathers seen in other bird-like dinosaurs, according to a report in the journal Nature.
The discovery highlights the diversity of species present in the Middle to Late Jurassic, just before birds arose.
The fossil was described by a team of palaeontologists led by Fucheng Zhang and Xing Xu, of the Chinese Academy of Sciences.
Dr Angela Milner, associate keeper of palaeontology at the Natural History Museum, London, said: "This exquisitely preserved fossil is an exciting and totally unexpected find.
"It shows that feathers were likely being used for ornamentation for many millions of years before they were modified for flight.
"It provides fascinating evidence of evolutionary experiments with feathers that were going on before small dinosaurs finally took to the air and became birds."
Air of mystery
The discovery adds yet more complexity to the early history of the era when small meat-eating bipedal dinosaurs evolved into birds.
Many feathered dinosaurs have been unearthed at the now famous fossil site in Liaoning Province in China. These include the squirrel-sized creature called Microraptor, which is thought to be a key discovery in the story of how dinosaurs led to birds. Microraptor used the long feathers on all four of its limbs to glide or parachute from tree to tree, scientists believe.
Epidexipteryx, on the other hand, was a primitive, flightless member of the avialae clade.
It was discovered at the Daohugou beds, in Nincheng County, Inner Mongolia, in sediments which have been dated to around 168-152 million years ago.
Phylogenetic analysis suggests the species is a member of a "bizarre lineage" known as the scansoriopterygidae (meaning "climbing wings").
The authors also note that it displays "an unexpected combination of characters" seen in several different groups of theropods - the bipedal dinosaurs which eventually gave rise to birds.
It had a fluffy, down-like covering and sprouted two pairs of enormously long, ribbon-like shafted tail feathers. These were almost certainly used for display - making it the oldest known species to possess these.
But its limbs lacked contour feathers - a feature common to most modern birds.
Dr Zhang said: "Although possessing many derived features seen in birds... [Epidexipteryx] shows some striking features... not known in any other theropod.
"The bizarre appearance... indicates that morphological disparity... close to the origin of birds is higher than previously assumed.
"The absence of... limb feathers suggests that display feathers appeared before aerofoil feathers and flight ability.
"It underscores the importance of Jurassic theropods for understanding avian origins."
Dr Graham Taylor, of Oxford University's Animal Flight Group, said: "This fossil is the latest in a string of feathered dinosaurs emerging from China, but is especially exciting for two reasons.
"Firstly, whereas other feathered dinosaurs date from after the appearance of the first known bird, this fossil appears to be much closer in age, so it opens a new window on the evolutionary events at the critical transition from dinosaurs to birds.
"Secondly, it has an exquisite set of ornamental tail feathers, suggesting that feathers were used in show even before they were used in flight."