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Dinosaur tail trapped in amber offers insights into feather evolution - Fragment complete with fossilised bones and traces of muscles, ligaments and mummified-looking skin dates from around 99 million years ago

December 30 , 2016:

by Nicola Davis

A length of fluffy plumage discovered within a piece of amber has been identified as part of a dinosaur tail, offering new insights into the evolution of feathers.
Why palaeontologists are aflutter over new fossil feather finds

Around 3.7cm long, with chestnut-coloured feathers on the top and pale feathers underneath, the tail was found complete with fossilised bones as well as traces of muscles, ligaments and mummified-looking skin.

While researchers say it is not possible to determine the species to which the tail belonged, they say the dinosaur lived around 99 million years ago and was most likely a juvenile, non-avian theropod – a group of dinosaurs that includes velociraptors and tyrannosaurs.

“If you were to hold [an adult] in your hand it would have been about the size of a sparrow,” said Ryan McKellar, co-author of the research from the Royal Saskatchewan Museum, Canada.

Bought in a Chinese market, the fragment is not the first piece of amber found to contain prehistoric feathers. Indeed McKellar and his colleagues have previously discovered wing tips with skeletal remains from a group of extinct primitive birds called Enantiornithes, as well as a wide array of amber-bound feathers which could not be linked to particular animals.

But none, says McKellar, have been clearly linked to a non-avian dinosaur before.

“It is the first time we are seeing skeletal material with feathers coming off of the sides of it and we know for sure that we are dealing with something that is not a bird, it is more dinosaur-like,” he said.

The all-important clues, he adds, lie in the length of the tail, the shape of the vertebrae, and the fact that the vertebrae are not fused into a rod-like structure as they are in birds.

Short, fuzzy, and lacking the stiff central shaft ubiquitous among modern birds, the feathers also suggest the dinosaur was unlikely to have taken to the skies, said McKellar. “The colouration might have played some sort of role in camouflage or visual signalling, but the feathers themselves, because they lack the central shaft or the rigidity, they are not particularly useful for things like flight,” he said.

But the discovery does more than shed light on the creature’s appearance. Published in the journal Current Biology by researchers from Canada, China and Bristol, it offers fresh insights to the mystery of how feathers evolved.

“Modern birds have three tiers of branching to their feathers, they have the rachis – or central shaft – and there are barbs that come off of those and then there are barbules, or these little fine branches, that come off of the barbs,” said McKellar. “One of the big long-standing debates is how we developed those three tiers of branching in modern bird feathers.”

Fossilised dinosaur feathers in the form of carbon films have previously been discovered in rocks, but they offer only limited clues as to the fine details of feather structure. Feathers trapped in amber, on the other hand, are rich in information.

With the newly discovered amber bearing feathers with a very short rachis but boasting both barbs and barbules, the team say the discovery backs up previous evidence suggesting the central shaft evolved after the finer tiers of branching.

Roy Wogelius from the University of Manchester, who has also studied dinosaur feathers but was not involved in the new study, said that the research made a fundamental contribution to our understanding of how feathers evolved.

“One of the big questions in palaeontology is the evolution of flight, and part of that is the evolution of that very, very very special soft tissue that we call feathers,” he said. “Part of the reason why it is under debate is because this kind of soft tissue preservation is so rare.”

McKellar agrees that amber offers unique opportunities to capture a glimpse of the past. “I think the most exciting aspect is how much amber can add to vertebrate palaeontology,” he said. “Even a few small scraps like this, they give you a quality of view where the preservation is so good that you can start to answer bigger questions even though you are not getting the whole animal, necessarily.”



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