Earlier bird steals Archaeopteryx's worm

Fossil of a pheasant-size animal dates to about 10 million years before that of the creature with the title of earliest bird known to science

PUBLISHED : Friday, 31 May, 2013, 12:00am
UPDATED : Friday, 31 May, 2013, 5:10am

A prehistoric creature the size of a pheasant has become a contender for the title of oldest bird to stalk the earth.

The small, feathered "Dawn" bird lived about 160 million years ago in what is now China, about 10 million years before Archaeopteryx, which holds the official title of earliest bird known to science.

The species, which scientists have named Aurornis xui, had claws and a long tail, with front and hind legs similar to those of Archaeopteryx, but some features of its bones were more primitive. It was 50 centimetres from its beak to the tip of its tail.

Encased in sedimentary rock, the fossil preserved traces of downy feathers along the animal's tail, neck and chest, but the absence of larger feathers suggests it was not able to fly. When scientists reconstructed the evolutionary tree of similar creatures using data from their skeletons, A. xui appeared on the bird lineage, but closer to the base of the tree than Archaeopteryx.

"It's an important fossil," said Gareth Dyke, a palaeontologist involved in the study at Southampton University, England. "Aurornis pushes Archaeopteryx off its perch as the oldest member of the bird lineage."

Archaeopteryx holds a prized position in evolutionary history. The fossil, discovered in Germany in 1861, proved that modern birds evolved from dinosaurs, and was the first fossil to support Darwin's theory of evolution, which had been published only two years earlier.

Researchers named the new species Aurornis xui because it marks the earliest days of the evolutionary path that led to modern birds. Aurornis combines aurora, the Latin for dawn, and ornis, the Greek for bird. The second part of the name, xui, honours Xu Xing, a Chinese palaeontologist, according to a report in Nature.

Scientists at the Yizhou Fossil and Geology Park in northeast China bought the remains from a fossil dealer, who claimed they had been unearthed in Yaoluguo, western Liaoning , where sedimentary rock was laid 153 million to 165 million years ago.

It is not uncommon for scientists to work with fossil dealers, but it can be a risky business. Unless experts can confirm where a fossil came from, it can be impossible to gauge their age.

When it was bought, the latest specimen was only partially prepared, but further work by Pascal Godefroit and others at the Royal Belgian Institute of Natural Sciences in Brussels revealed the intricate details of the skeleton. They saw no signs of forgery and said the chances of it being a fake were low.

Analysis of the sediments proved that the fossil came from the Tiaojishan formation, as the dealer claimed, and not more recent deposits nearby.

Though the remains themselves are stunning, scientists are more interested in what the new species means for the evolution of birds and bird flight.

In 2011, Xu Xing claimed that Archaeopteryx was not an ancient ancestor of modern birds after all. The latest study overturns that claim, and returns Archaeopteryx to the avian lineage.

"This work makes Archaeopteryx a bird again, and given that we have the original specimen here in London, we're very pleased to have it reinstated," said Paul Barrett at the Natural History Museum. "It makes life simpler. If Archaeopteryx was an early bird, we only have to worry about one origin of flight."

Dawn is only the latest small-bodied, bird-like creature from the Jurassic to be unearthed by fossil hunters. The picture emerging is of a time when scores of bird-like dinosaurs and dinosaur-like birds lived side by side, with only minor differences separating one species from another.

"This emphasises how grey the dividing line is between birds and dinosaurs. There's such a gradation in features between them that it's very difficult to tell them apart. It only takes relatively small changes in our knowledge of these to flip around some of the evolutionary relationships between them," Barrett said.