Fossils Challenge Origin Theory

WASHINGTON - The fossil of a small lizard-like, flying reptile with a complex set of feathers challenges the theory that birds evolved from dinosaurs, a new study says.

Researchers say the feathered reptile lived about 220 million years ago, proving that feathered animals evolved millions of years before the appearance of the dinosaurs that most experts say are the ancestors of modern birds.

The fossil has been called Longisquama and is thought to be an archosaur, a member of a reptile group that later gave rise to dinosaurs, crocodiles and birds. The first known bird, Archeopteryx, appeared about 145 million years ago, some 75 million after the date for Longisquama.

``Here you've got an animal that isn't a bird and it isn't a dinosaur, and yet it has feathers,'' said Nicholas R. Geist, paleobiologist at Sonoma State University and co-author of a study appearing Friday in the journal Science.

``It is going to be a major monkey wrench in the theory about the dinosaurean origin of birds,'' he said. ``It is going to cause some people to take a real good second look at their data.''

However, Jacques Gauthier of Yale University, an expert on the evolution of dinosaurs, said that Longisquama is a poorly preserved specimen that is important only ``if you allow your imagination to run wild.''

``There is a huge body of data that show birds evolved from dinosaurs,'' said Gauthier. ``This (the Longisquama study) is way over the top.''

Gauthier said that a single specimen is not enough to dismiss a theory that is supported by many studies that point to the dinosaur ancestry of birds, including evidence that some dinosaurs had feathers.

The Longisquama fossil includes the head, forelegs and part of a torso of a lizard-like animal. Along its back are a series of appendages that Geist and his co-authors say are feathers.

Longisquama was found in Kyrgyzstan, in central Asia, in 1969, and was stored for years in a drawer in Moscow. The specimen provoked little interest until it was included as part of a traveling exhibition and spotted at a shopping mall in Kansas by Oregon State University paleontologists John Ruben and Terry Jones, co-authors of the study in Science.

Ruben and Jones said they identified the appendages on the back of the small fossil as feathers and began a long study of the small critter.

Jones said that the feathers along the back of Longisquama are fully developed and very ``birdlike.''

``The skeleton is also very birdlike,'' said Jones. ``It has a birdlike head, shoulders and a wishbone. The wishbone is almost exactly like that of Archeopteryx.''

Geist said the feather structure of Longisquama was well preserved in hardened mud because the animal apparently sank to a lake bottom after it died.

He that Longisquama probably had muscle control of the feathers and that it used them to glide from trees. The animal was not able to achieve true flight as do modern birds, said Geist.

``These feathers emerge from a follicle the way feathers do in modern birds,'' said Geist. ``They had a quill-like structure that was hollow.''

Geist said that feathers are very complicated structures and that it is unlikely that feathers would have evolved twice -- once among the early reptiles and then later among the dinosaurs.

Ruben said that other researchers have identified dinosaurs as having feathers and as being birdlike. But he said two of the most birdlike dinosaurs, Bambiraptor and Velociraptor, lived 70 million years after the earliest known bird.

Longisquama, however, he said, lived at the right time and had the feathers that suggest it could have been an evolutionary ancestor of birds.

Jones said that the feathers on Longisquama are so well developed that it is likely that the first feathers appeared on reptiles many generations before Longisquama came along.

But Gauthier said the study is going to have little effect on the theory that birds evolved from dinosaurs, an idea that can be traced back through the work of hundreds of scientists over many decades.

Accepting a Longisquama as the first bird ``would be like saying suddenly that humans are not primates or even mammals,'' said Gauthier. He said more evidence than Longisquama would be needed to disprove a theory that has been long accepted by the majority of paleobiologists.

Source:
http://www.popsci.com/news/06222000_fossils.shtml

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