July 28, 2011

Archaeopteryx Not World’s First Bird: Study

Archaeopteryx, once believed to be the world's earliest bird, may actually have been just another feathered dinosaur, according to a report published Wednesday in the journal Nature.

Researchers in China, led by Xing Xu of Linyi University, carried out a phylogenetic analysis combining a newly discovered fossil with other similar dinosaurs and early birds, and concluded that the species should no longer be considered a fully developed bird.

If confirmed, the controversial hypothesis would be a blow to researchers who have long viewed the evolution of birds and feathered flight through the lens of Archaeopteryx since the species was discovered in 1861.

If Archaeopteryx was a dinosaur, it would mean flight evolved at least four times in vertebrates -- in reptiles, birds, dinosaurs, and most recently in bats.

"There has been growing unease about the status of Archaeopteryx as, one by one, its "Ëœavian' attributes (feathers, wishbone, three-fingered hand) started showing up in non-avian dinosaurs," wrote Lawrence Witmer, a paleontologist at Ohio University in Athens, in a related opinion article.

"Perhaps the time has come to finally accept it as 'just another small, feathered, bird-like theropod'," Bloomberg News quoted him as saying.

With Archaeopteryx dismissed as the world's oldest bird, more recently discovered fossils, including epidexipteryx, jeholornis and sapeornis, now become leading candidates for the distinction, Witmer said.

However, he cautioned that the next feathered fossil unearthed in China could easily restore the premier status of Archaeopteryx.

"The overall picture of birds being descended from meat-eating dinosaurs is now very firmly established," said dinosaur expert Paul Barrett with the Natural History Museum in London.

"This is an argument over a relatively small rearrangement of some of the twigs on the evolutionary tree close to the origin of birds," he told The Guardian.

"It doesn't affect much of our big picture view of how birds came from dinosaurs, but some of the minutiae: the small changes that are important to the biology of the animals."

"This part of the evolutionary tree is very sensitive to small changes in how we interpret the anatomy and the combination of anatomical features we see in these animals as they are discovered," he said.

"As a result, the structure of that evolutionary tree is very unstable and can flip around."

"Maybe archaeopteryx wasn't on the direct ancestral line to birds, but was part of an early experimentation in how to build a bird-like body."

The study was published online July 28, 2011, in the journal Nature. 


On the Net: