The ferocious Velociraptor, made famous in the movie Jurassic Park, was probably covered in feathers.
A re-assessment of a fossil forearm unearthed in Mongolia in 1998 has revealed an array of small bumps.
In modern birds, such "quill knobs" are the locations where secondary feathers, the flight or wing feathers, are anchored to the bone with ligaments.
The American Museum of Natural History and the Field Museum of Natural History report their study in Science magazine.
Quill knobs on living bird species are most evident in strong flyers. Those birds that primarily soar or that have lost the ability to fly entirely, however, typically lack signs of quill knobs, the research team says.
"A lack of quill knobs does not necessarily mean that a dinosaur did not have feathers," explained Alan Turner, from the AMNH and Columbia University, New York, US.
"Finding quill knobs on Velociraptor, though, means that it definitely had feathers. This is something we'd long suspected, but no one had been able to prove."
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The Mongolian Velociraptor specimen's short arms indicate that the creature itself could not fly; but its feathers may have been useful for display, to shield nests, for temperature control or to help it manoeuvre while running, the team says.
The latest study will undoubtedly alter the perceptions some people have built up of the beast thanks to the successful movie franchise.
The real creature belonged to the Dromaeosauridae, a family of small to medium-sized, lightly built and fast-running dinosaurs from the Cretaceous Period (146 million to 65 million years ago) who appear from the fossil record to have been very effective predators.
There is even evidence some, such as Deinonychus, hunted in packs; but their reputation has been somewhat overstated, say scientists.
The animal in the AMNH/FMNH study weighed about 15kg and was some 1.5m long - a far cry from the giant presented in Jurassic Park.
Like other dinos in its family, Velociraptor had a distinctive sickle-shaped claw on the second toe which many have assumed was employed to disembowel victims.
But recent research has indicated this fearsome-looking appendage was probably used just to hang on to prey.