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This telltale tail shows dinosaur feathers in ‘exquisite detail’ after 99 million years

The tip of the dinosaur tail, preserved in amber. (R.C. McKellar/Royal Saskatchewan Museum)

Ninety-nine million years ago, a small nib of dinosaur tail was dipped in resin, the honey-thick liquid that plants ooze to defend against insects. Perhaps the little dinosaur died before resin enveloped its teeny extremity. If so, it was a fortuitous death for paleontologists, allowing the tail to stay in place long enough for the resin to harden into amber.

The amber hunters who dug up the segment in Burma (Myanmar) assumed the encased remains were vegetation, making the amber valuable when carved into jewelry. It probably did not occur to them that their discovery could be a dinosaur tail with secrets to tell. But a Chinese paleontologist named Xing Lida, perusing a Burmese amber market in 2015 for objects of scientific interest, recognized the amber’s true value.

“With the new specimen from Myanmar, we finally get that association between identifiable bones and feathers preserved in exquisite detail,” said Ryan McKellar of the Royal Saskatchewan Museum in Canada, a paleontologist and an author of the study, in an email to The Washington Post. Lida, McKellar and their Chinese and Canadian colleagues published an analysis of the tail on Thursday in the journal Current Biology.

This was not the first time that paleontologists examined feathers trapped in Cretaceous amber. But without underlying body parts, doubt remained that the plumage once sprouted from dinosaurs. This amber held eight vertebral segments as well as soft tissues. Beneath the feathers were, McKellar and his co-authors wrote, “presumably muscles, ligaments, and skin” — rarities in a discipline historically reliant on fossilized bones. (Chemical analysis even found traces of iron oxides in the tail, suggesting dino blood contained hemoglobin.)

“If the authors can safely establish the authenticity of this fossil — and I have no doubts that they can — this is a truly amazing find,” Gerald Mayr, an expert on fossilized birds at the Senckenberg Research Institute in Frankfurt, Germany, who was not involved with the study, told The Post via email.

X-ray images revealed that no ancient bird grew this tail. The tail tip belonged to a two-legged dinosaur called a theropod. “We can tell that this specimen came from a theropod dinosaur because the tail is flexible and the vertebrae articulate with each other, instead of being fused together to form a solid rod — which is a characteristic of modern birds and their closest relatives,” McKellar said. Specifically, the researchers hypothesized the animal was a type of dinosaur called a coelurosaur, and likely a juvenile.

Coelurosaurs included the famous giants like Tyrannosaurus rex, but these theropods were a diverse bunch. The remains captured in amber were tiny — at just 1.4 inches, the preserved tail segment was as long as a watch face is wide. “If we extrapolate total body size from this,” McKellar said, “the whole animal would have been about the size of a sparrow.”

Examining the tail with microscope and CT scanner, the scientists could observe how dino feathers were arranged on the body and make out tiny, 3-D structures. It also gave the paleontologists a sense of feather pigments, plus larger-scale color patterns.

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“We can see general color patterns in the tail,” McKellar said. “These consist of pale or white feathers on the underside of the tail, and chestnut brown feathers on top of the tail.” This coloration, however, comes with a 99-million-year-old caveat. The resin may have altered the feathers’ iridescence, or changed its chemistry to “knock out” certain colors.

The feather structures themselves offered a glimpse into the evolution of plumage. “What strikes me particularly is the presence of such short, modern-type feathers on a long tail,” Mayr said.

McKellar described the feathers as “fairly similar to modern bird feathers.” That is, they were shaped like the feathers on modern birds’ bellies and heads, which protect their insulative layers. The fossil feathers were not quite like flight feathers. “Flexible” and “fuzzy,” in McKellar’s words, they did not have a strong central shaft. (The coelurosaur feathers lacked a thick hollow rod — you’d struggle to stick these feathers in your cap or hold them as a quill.) The dinosaur plumage suggested that, on an evolutionary scale, the side branches of feathers developed before this main shaft.

The find was the latest in a string of high-profile discoveries involving ancient plumage. As The Post reported in November, Chinese scientists recently identified microscopic pigment-containing flecks in a 130-million-year-old bird. That specimen, too, was purchased in an Asian flea market.

In this case, the ancient remains included trapped insects, which McKellar was happy to describe. “Funny enough, I mostly work on fossil wasps, and the feathers are one of those side-interests that keep me out of trouble,” he said. “There are two ants in the piece of amber that belong to an extinct group (called Sphecomyrminae) which is only known from the Cretaceous. There are also the remains of a cockroach and a lucanid beetle in the amber piece.” The insect species within the amber, he told The Post, indicate the resin leaked from a section of tree close to the forest floor.

Considering the pace of spectacular fossils pulled from Burmese amber mines, Mayr told The Post he would not be surprised if the future held even more intriguing finds. “I cannot think of what a wealth of anatomical information,” he said, “an amber-preserved skull of these animals would provide.”

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