This image, courtesy of the US Department of Energy's SLAC National Accelerator Laboratory, shows a fossil of Archaeopteryx. File picture: Pete Larson, US Department of Energy's SLAC National Accelerator Laboratory, via AFP

Washington - Since its first fossil was unearthed in Bavarian limestone in 1961, Archaeopteryx - the original early bird - has been a palaeontological rock star.

Not only is it considered Earth's oldest-known bird but its blend of primitive dinosaur traits with characteristics seen in modern birds has long fascinated scientists. However, none of the specimens found over the years had given a comprehensive view of its plumage, leading some experts to question whether Archaeopteryx was a capable flier - or could even fly at all.

That has all changed. Scientists on Wednesday described the best-preserved fossil of Archaeopteryx ever found, revealing the whole plumage in great detail including a feather arrangement fully capable of flight and curious “feather trousers” on the legs.

The level of preservation is due to the fossil's fine-grained limestone, formed in an ancient lagoon. It was found by a private collector in northern Bavaria in Germany.

Archaeopteryx lived 150 million years ago, but its plumage in many ways resembled today's birds.

The fossil showed that contour feathers - the basic vaned, quill-like feathers of a bird - covered its entire body up to the head as in modern birds. The shafts of the wing feathers were comparable in strength to those of modern birds. And the plumage of the hind limbs looked like that of modern birds of prey like falcons and eagles.

“Since its first discovery in the 1860s, Archaeopteryx has been the object of many debates in relation to bird evolution, especially flight and feather evolution. There were debates if it was ground-dwelling or arboreal, if it could fly or not,” said paleontologist Oliver Rauhut of the Bayerische Staatssammlung für Paläontologie und Geologie in Munich.

Paleontologist Christian Foth of the same institution said some scientists had suggested the vanes of its feathers were too weak to support flight, but the new fossil backs the idea Archaeopteryx was completely capable of flying.

“It retains its status as the Urvogel,” Foth said, using the German word meaning “original bird”.

Birds arose during the Jurassic Period from small feathered bipedal dinosaurs. They were not alone in the skies, which were dominated by flying reptiles known as pterosaurs.

Archaeopteryx was a crow-sized bird with primitive traits like teeth, a long bony tail and the absence of a bony, keeled sternum where flight muscles attach.

The feathers on its legs were quite long but were restricted to the thigh and shank, looking like “feather trousers”. They may have been used for display and to stabilise flight during landing.

Feathers appeared in dinosaurs millions of years before the first birds and initially had nothing to do with flight. In fact, full-fledged contour feathers have been found dinosaur species that did not fly.

“The original feathers were simple filaments or down feathers, and probably used for body insulation, camouflage, but also display,” Foth said.

“This probably was also true for the first contour feathers. However, once contour feathers were evolved, they could be easily recruited for aerodynamic functions,” Foth added.

The study was published in the journal Nature. - Reuters