Our past holds the key to our present and future. This’s very same when it comes to our and other species’ evolution on this planet. For millions of years, the dinosaurs had roamed the Earth and then they became extinct leaving us with fossils and clues as to how life was back then. Recently, the scientists have discovered a piece of amber that contained feathered dinosaur’s tail from the mid-cretaceous period which sheds new light on the evolution of bird plumage.

The amber is 99 million years old and belonged to mid-Cretaceous time. The tail is believed to belong to a juvenile coelurosaur, a close relative of birds, and has a chestnut-brown upper surface and white underside. 

Lida Xing from the China University of Geosciences in Beijing and Ryan McKellar from the Royal Saskatchewan Museum in Canada have published a study of the amber fossil on Current Biology. Though it is not new to find feathers in ambers, there has never been a complete part, such as a tail in this case, of a dinosaur preserved in it. The researchers believe that the dinosaur is a juvenile and about the size of a sparrow.

Lida Xing first discovered the fossil at an amber market in Myitkina, Myanmar. For over 2,000 years, Myanmar has been mining ambers and a large number of insects preserved in the deposits has made it a place of interest for scientists studying anthropology for the last 20 years. 

Kachin State of north-eastern Myanmar is a place of interest for both scientists and jewelers due to all the amber being mined there, which also preserves many small species that are unlucky enough to get trapped in the sticky sap of the trees back then.

Though it is a treasure trove for research and there are reports of similar species being found there, the larger pieces of amber often are broken down into smaller pieces during mining, and according to Dr. McKellar, the scientists don’t always get to know how much of the specimen gets missed as the amber is turned into jewelry. By the time Lida Xing found the fossil, it was already polished for jewelry.

The amber fossil is unique in the sense that corpses usually are flattened when fossilized, but this one contained a tail with eight vertebrae surrounded by feathers, and its structure is intact and preserved in 3D. It also preserved the flesh and skin, which would have otherwise easily decomposed or altered, ferritin (a blood cell protein), and even ferrous iron. 

When scientists find skeletons or the remains of dinosaurs as fossils, the features and details are usually lost as they get flattened, and so the three-dimensional structure must be reconstructed through speculation. But, this fossil preserved not just the structural arrangement of the feathers on the tail, but also labile tissues and matter that are difficult to study in other settings. The soft tissue layer around the tailbone retained abundant ferrous iron, which means that there are traces of primary hemoglobin and ferritin trapped in the tail.

The CT scan of the fossil shows how the feathers are attached to the vertebrae of the tail.  

It also shows that the tail vertebrae of this dinosaur are not fused into a rod or pygostyle like in modern birds, proving that it’s not just a prehistoric fossil.

The mapping of flow lines in the amber as seen under UV light.

The researchers found that the feathers did not have well-developed central shaft known as rachis. However, they had barbs and barbules, the two finest tiers of branching in modern feathers, showing that these structures had developed much before the rachis did. 

Barbs are the thin hair-like structures that are attached to the central shaft of a feather. Barbules are the minuscule structures on the barbs that crisscross and lock with the barbules of the next barb to create vane, the part of the feather with no gaps between barbs, which helps the birds during the flight to resist the air.

Xing and McKellar believe that fossils like these would help us understand the evolutionary development of feathers, and also they offer a glimpse into the preservation potential of amber fossils. 

[sources: BBC, cell.com]