Evolution Diary

Seven dino-era feathers found perfectly preserved in amber in western France highlight a crucial stage in feather evolution, scientists report.

The hundred-million-year-old plumage has features of both feather-like fibers found with some two-legged dinosaurs known as theropods and of modern bird feathers, the researchers said.

This means the fossils could fill a key gap in the puzzle of how dinosaurs gave rise to birds, according to a team led by Vincent Perrichot of the Museum für Naturkunde-Berlin in Germany.

The find provides a clear example “of the passage between primitive filamentous down and a modern feather,” said team member Didier Néraudeau of the University of Rennes in France.

The study team isn’t sure yet whether the feathers belonged to a dino or a bird.

But fossil teeth from two dino families thought to have been feathered were excavated from rocks just above the layer that contained the amber, Perrichot said.

“It is entirely plausible that the feathers come from a dinosaur rather than from a bird,” he said.

Perrichot and colleagues described their research last month in the journal Proceedings of the Royal Society B.

Downy Plumes

Paleontologists at the University of Rennes found the tiny feathers encased in a lump of amber, a fossilized tree resin, in a quarry in the Poitou-Charentes region of France in 2000.

Researchers at the European Synchrotron of Grenoble then scanned the amber to reveal the feathers’ fine structures. The plumes’ central shafts, or rachis, are primitive and most closely resemble down feathers, the study team noted.

The feather filaments, or barbs, had yet to become fully fused at the base and—similar to modern down—they lacked hooklets known as barbules to hold the filaments together.

Today’s birds could not fly with such feathers, the team said.

Studies suggest primitive feathers first evolved in flightless dinosaurs that generated heat internally and so would have benefited from the insulation that down can provide.

Feathers later evolved for use in flight, the theory holds, although experts debate whether birds’ immediate ancestors were tree-dwelling, gliding dinosaurs or terrestrial dinos that ran at high speeds and eventually lifted off the ground.

Either way, the amber-encased feathers show for the first time the transition from downy filaments toward an aerodynamic, planar shape that enabled flight, Perrichot said.

“This most critical step in the evolution of feathers” was suggested by evolutionary theories but had never previously been seen in either modern or fossil feathers, he said.

Team member Néraudeau added that this missing link has been “an argument for creationists and others to reject the theropod-birds lineage and to argue in favor of different origins for theropod feathers and bird feathers.”

“First Good Look”

Nick Longrich, of the University of Calgary in Canada, said “this could be our first good look at a dinosaur body feather.”

The bird-fossil expert, who was not involved in the study, noted that the newfound feathers are around 50 million years younger than the first known flying bird, Archaeopteryx, which lived about 150 million years ago.

“Obviously this animal [the feathers came from] isn’t directly ancestral to anything except later dinosaurs, but it’s quite likely that we are seeing aspects of the ancestral [feather structure],” Longrich said in an email.

“So the animal isn’t transitional’ but it may preserve a transitional structure.”

It’s also possible that the simplified structure of the feathers isn’t so primitive, he added.

Modern flightless birds such as ostriches and emus have highly simplified feathers, he said.

More samples from the fossil record are needed to settle the issue, so “hopefully this study will cause more people to look for dinosaur feathers in amber,” Longrich added.

Story reposted from National Geographic