It's just a few centimetres across, but it's one of the most incredible fossil discoveries of 2016: part of the tail of a tiny dinosaur, nestled inside a small, golden chunk of 99 million-year-old amber. The find is beautifully preserved, with bones inside and remnants of soft tissue outside – and most exciting of all, it's totally covered in feathers! What's more, these feathers are unlike any we've ever seen before.

The full piece of amber with the dinosaur tail inside, plus trapped insects and plant bits. Image: Royal Saskatchewan Museum (RSM/ R.C. McKellar) 

At a quick glance, the fossil might easily be mistaken for some sort of plant, and that's exactly what happened when it turned up for sale at the amber market in Myitkyina, Myanmar. It was palaeontologist Lida Xing from the China University of Geosciences who realised the object was something special – and insisted it be purchased by the Dexu Institute of Palaeontology. This is the same market where Xing famously found amber containing ancient bird wings.

Close-up of the feathers covering the dinosaur's tail. Image: Royal Saskatchewan Museum (RSM/ R.C. McKellar) 

You might think a feather-coated tail must belong to a bird, but many two-legged dinosaurs from a group known as the coelurosaurs are known to have sported feathers.

This piece of amber, however, holds only a small part of what was clearly a very long tail, and that length – along with other features of the bones and feathers revealed by microscopy and CT-scanning – leads researchers to suspect that the fossil comes from a non-bird coelurosaur dinosaur. This would make it the first ever non-bird dinosaur discovered in amber.

Identification is difficult, though, since so little of the animal is preserved. What's more, this individual was a juvenile when it died, and therefore not fully developed.

Feathers have been discovered on dozens of dinosaur species – but this fossil is unique. "This specimen shows us a new feather morphology that we have not seen before in the fossil record, and that may not have been recognisable if it was preserved anywhere other than in amber," notes Ryan McKellar of the Royal Saskatchewan Museum. 

If you look closely at a bird feather, you'll see a central shaft (the rachis) with many branches coming off (called barbs), and even tinier branches between the barbs (called barbules). This dinosaur's feathers, on the other hand, feature barbs covered in barbules, but no distinct rachis in the middle. "[This] points to an evolutionary pathway in which barbs with barbules were developed before the rachis. This fine-tunes our understanding of feather evolution," says McKellar.

Extreme close-up of the barbs and barbules of the feathers. Image: Royal Saskatchewan Museum (RSM/ R.C. McKellar) 

These were not feathers for flying. Instead, they may have been useful for keeping warm – or for display. Within the amber, the feathers appear to be dark on top and white underneath, and according to the scientists, their flexible structure is reminiscent of ornamental feathers seen in some modern birds.

But how exactly did this animal's tail end up in its golden capsule? Amber is fossilised tree resin, and Burmese amber can often contain tiny trapped creatures, from ants and scorpions to lizards. Visible alongside the dinosaur tail are the trapped ants and beetles commonly found living near the bases of trees. "It seems most likely that the resin was released low down on the tree that produced it, and that the juvenile feathered dinosaur got stuck in the resin or came into contact with it shortly after death," explains McKellar. 

A small coelurosaur dinosaur approaching a resin-covered tree branch. Image: Chung-tat Cheung

"This is one of those fossil finds that makes you go, 'cool!' Who would have thought that a feathered dinosaur tail could be preserved in amber?" says Stephen Brusatte of the University of Edinburgh, who wasn't involved in this study. "Most feathered dinosaur fossils are skeletons on flattened slabs of rock, so it's difficult to say much about the 3D arrangement of the feathers. This fossil is preserved in 3D and you can see how feathers cover all of the tail."

Brusatte is excited by what this fossil tells us about feather evolution, but he isn't totally on board with the researchers' identification. "I am not completely convinced that it couldn't be the tail of a primitive bird. Primitive birds still had long tails, unlike the birds of today, which have reduced their tails to a stub."

The feathers may be the research focus on this fossil, but beneath them await other surprises. Tightly surrounding the bones are the remnants of soft tissue – a thin film left behind from the dried-out and decomposed skin or muscle that used to be there. There's no DNA (sorry, Jurassic Park fans), but chemical analysis did find traces of iron left over from the dinosaur's long-since-decomposed blood.  

The research is published in the journal Current Biology.

Dinosaur Skeleton Related Content 2016 02 24