Which came first: the feathers or flight?

New Archaeopteryx fossil shows feathers evolved before flight
One of the best-preserved fossils of the world’s first bird reveals thatArchaeopteryx sported feathered “pants” that weren't suited to flying - adding weight to the theory feathers evolved before flight.

Archaeopteryx was a small crow-sized creature that lived around 150 million years ago in the late Jurassic period, and is widely considered one of the first birds. Studying its fossils - which share many characterises of both dinosaurs and modern birds, including feathers - has helped scientists find out more about the link between feathered dinosaurs and birds.

But a long-standing mystery still remains. Which came first - the feathers or flight?

Now the discovery of one of the best preserved Archaeopteryx fossils might help put an end to the debate.

Previous fossil discoveries had shown that Archaeopteryx had pennaceous feathers - the kind found in modern birds - on its wings that were adapted for flight - they were asymmetrical and overlapped in a way that made them aerodynamic, as Tim Wogan writes for Science. But the presence of pennaceous feathers on its hind legs had confused researchers - was the species a four-winged glider? Or were the leg feathers simply for decoration or warmth?

The new fossil, uncovered in Bavaria, Germany in 2011 by palaeontologists from Ludwig Maximilians University in Munich, clearly shows for the first time an imprint of all ofArchaeopteryx’s feathers, including the 4 to 4.5-cm-long feathers on its hind limbs and the up to 11.4-cm-long tail feathers.

The hind limb feathers, however, were asymmetrical on either side of their stems, unlike aerodynamic feathers which have one narrow side and one longer side (a little like a wing).

"These results contradict the hypothesis that the flapping flight of modern birds was preceded by a four-winged gliding stage," the study authors wrote in their new paper in Nature.

The early bird’s tail feathers, which were more than half the length of the tail bone, however, were asymmetrical, which means they could have been involved in flight.

To investigate further, the paeoleontologists Christian Foth and Oliver Rauhut, along with photopgrapher Helmut Tischlinger, examined other recently discovered primitive bird fossils, mainly from China, and found that the presence of feathers on these early birds was extremely varied and inconsistent across species.

Many of the animals with feathers wouldn’t have been able to fly due to short arms, others simply had feathers in unpractical places for flight.

Writing in Nature, the researchers propose a new theory - that after feathers evolved, they became adapted for a range of different reasons, such as to attract a mate, for camouflage, or for insulation. And then when animals began to fly, they evolved further to become more aerodynamic.

This theory suggests that there was not one single origin of bird flight, but that it potentially evolved in species several different times.

"This indicates that the origin of flight in avians was more complex than previously thought and might have involved several convergent achievements of aerial abilities," the authors wrote.

The new discovery “fills in a lot of blanks,” as palaeontologist Mark Norell of the American Museum of Natural Hiostry in New York told Science, but the jury is still out on the role of these leg feathers.

Norell believes that they evolved for mating displays, whereas vertebrate palaeontologist Nick Longrich of the University of Bath in the UK told Science they could be airfoils that aided flight. ”They're really long, they overlap the same way flight feathers do, and the fact that they curve is a characteristic flight feather feature,” he explained.

The feathers could also be remnants from ancestors that had previously flown.

One thing is clear - the more Archaeopteryx specimens we find, the more we’re learning about early birds and the evolution of flight. And it’s a fascinating story to follow.