At a market in northern Burma last year, Lida Xing noticed a chunk of amber with a dark blotch inside.

The impurity — plant matter, it seemed at first — made the amber less valuable to the jewellery-makers for whom it was mined. But it made the specimen far more interesting to Xing, a paleontologist from the China University of Geosciences in Beijing.

Xing “noticed the things coming off the side were feathers, and got very excited,” says Ryan McKellar, a colleague of Xing’s and curator of invertebrate paleontology at the Royal Saskatchewan Museum.

Trapped inside the amber was a piece of dinosaur tail, complete with feathers preserved in microscopic detail.

The researchers believe the 3.7-centimetre-long section of tail — eight vertebrae wrapped in skin and soft tissue and covered with pigmented plumage — belonged to a theropod that lived in the mid-Cretaceous, approximately 99 million years ago.

Paleontologists have discovered fossilized dinosaur bones surrounded by compressed feather imprints. They have found full feathers preserved in amber, but unconnected to a particular animal.

“Now we have both in the same piece of amber. That’s what it makes it so spectacular,” says McKellar. A paper describing the find, co-authored by McKellar, Xing and a team of Canadian, Chinese, and U.K. researchers, was published Thursday in the journal Current Biology.

Most scientists now accept that many dinosaurs were feathered, and this discovery will help answer questions about exactly what those dinosaurs looked like and how feathers evolved. But perhaps more than anything else, the find has paleontologists salivating over what’s next.

This is the second piece of amber containing feathered dinosaur-era remains that the researchers have reported this year. In June, McKellar and Xing reported the discovery of a wing from a primitive Cretaceous bird.

These amber specimens are “completely astonishing. They’re just blowing everyone away,” says David Evans, the Royal Ontario Museum’s Temerty Chair and Curator of Vertebrate Paleontology.

The researchers’ first question was what kind of animal this tail belonged to. Because the tail was long and flexible rather than one fused rod, they knew it belonged to a non-avian theropod — a member of a group of dinosaurs that doesn’t include the ancestors of modern birds or transitional species like Archaeopteryx.

“This is a part of the (evolutionary) tree for which we’ve only seen traditional rock compression-type fossils. . . so this is a dream, and a truly beautiful specimen,” says Richard Prum, William Robertson Coe Professor of Ornithology at Yale University.

The team also identified colouration in the theropod’s plumage. The upper side of the feathers appears to be a chestnut brown, while the underside is paler — though the researchers can’t say for sure whether that pigmentation existed in the animal’s life, or whether millennia encased in amber has altered it.

The structure of the feathers fills in some gaps in models of the evolution of feathers. The broad strokes of that evolutionary history have been painted by the fossilized feather impressions, Evans says.

“We’re really filling in the details, and the amber specimens are providing us with amazingly well preserved, three-dimensional detail that we didn’t have before.”

The entire field, Evans and Prum say, is buzzing about what further specimens might emerge from the amber markets in Burma and elsewhere. The fossilized tree resin has long been considered an excellent source of ancient insects and plant matter.

The remains of larger vertebrates like dinosaurs are an unexpected and exciting windfall. Xing was unavailable for an interview because he is currently in Burma.

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“They’re well aware that this is extremely important material,” says Prum. “It keeps coming, so maybe there will be more.”

Prum adds that the 1993 science-fiction blockbuster Jurassic Park is premised on finding dinosaur DNA inside a mosquito trapped in amber — a less far-fetched idea, at the time, than finding an actual dinosaur body part.

“Heck, if Michael Crichton couldn’t have imagined this fossil, how extraordinary is it?”