TWO decades ago palaeontologists were astonished to discover impressions of feathers in rock around the petrified bones of dinosaurs that had clearly, from the anatomy those bones displayed, been unable to fly when they were alive. Astonishment turned to delight with the subsequent discovery of exquisitely preserved examples of these feathers in the petrified tree resin known as amber. Now, a team led by Xing Lida at the China University of Geosciences, in Beijing, and Ryan McKellar at the Royal Saskatchewan Museum, in Regina, has uncovered something even more impressive. As they report in Current Biology, they have found, again preserved in amber, part of a dinosaur’s feathered tail.

Their fossil comes from the Hukawng valley amber mines in northern Myanmar, already famous for many spectacular specimens of life dating from 99m years ago, during the mid-Cretaceous period. The tail in question was once attached to a carnivorous dinosaur from a group known as the coelurosaurs, the most famous member of which is Tyrannosaurus. The coelurosaur here, though, was no tyrannical giant. Its tail bones are only two millimetres wide, suggesting it was not much larger than a modern sparrow. Whether it was fully grown or still a juvenile remains unknown.

The animal’s feathers appear to have been darkish brown on the top. Underneath, they seem either to have lacked colour altogether or to have been coloured by bright pigments known as carotenoids that degrade quickly after death. As for their structure, their central shafts and the paired barbs branching from these shafts resemble those of ornamental feathers in many bird species alive today. In particular, the bending of some of the barbs within their amber matrix suggests they were flexible in life in a way that flight-feather barbs are not.

Why feathers first evolved has been debated for years. Some suggest for insulation, rather like the hair of mammals. Some argue they were, from the beginning, a way of generating lift—perhaps helping the predatory dinosaurs that sported them to get a better kick with the razor-sharp claws on their hind legs. Others still theorise that they were evolutionary fashion statements, as many still are today. If the feathers on the newly reported specimen did sport carotenoids, it would suggest that the fashionistas are on to something.