Archaeopteryx indeed flew into history

Findings: Somehow, it had the brains to take wing.

August 05, 2004|By Dennis O'Brien | Dennis O'Brien,SUN STAFF

It's one of the great mysteries of evolution: When and how did birds first take to the skies?

In a study released yesterday, scientists examining the brain of the world's oldest-known bird moved closer to an answer.

Archaeopteryx, they say, could indeed fly.

The prehistoric animal flapped through the air 147 million years ago, with a thimble-sized brain that gave it the same ability to see, hear and control its flight as that of modern birds, scientists said.

The crow-sized creature has been intensively studied over the years - researchers have had latex casts of its brain since the 1980s - because the animal is a unique historical hybrid.

The claws on its wings, its teeth and long bony tail belong to a dinosaur. The feather arrangements and body resemble those of modern birds.

"It's a kind of window into where birds come from," said Alan Gishlick, an expert on the origins of avian flight at the National Center for Science Education, a California organization that defends the teaching of evolution in public schools.

Brain size matters

In the study released yesterday, a team of U.S., British and Spanish scientists said that computer images created from CAT scans of a fossil found in 1861 show the Archaeopteryx brain was three times the size of the brains of comparably sized reptiles.

Archaeopteryx also had optic centers and an inner ear - keys for maintaining balance in flight - akin to those of modern birds.

"While it may not have been the best flier, we feel sure that it most certainly could fly," said Richard Ketcham, the University of Texas researcher who performed the scans and is a co-author of the study, published in the journal Nature.

Brain size turns out to be a key indicator of flight capability.

"The sophistication of the brain has to be much greater to go from two-dimensional space, which is what land-based animals move around in, to moving around in the three-dimensional world of flight, with all of the disturbances you get with winds and things like that," said Kevin Padian, a paleontologist at the University of California, Berkeley.

Experts say a brain with the sophistication of Archaeopteryx's didn't evolve overnight - so birds of some kind were probably flying long before Archaeopteryx first took to the skies.

"What the study shows is that the problem of bird origins is far more difficult than anyone could have imagined," said Alan Feduccia, an evolutionary biologist at the University of North Carolina.

X-ray vision

The study also confirms long-held assumptions that Archaeopteryx could fly and provides the first detailed X-ray examination of the creature's brain.

"We always looked at the wing structure and the feathers. But no one ever looked at whether it had the brain, the neural capacity, to manage itself in the air," said Lawrence Witmer, a paleontologist at Ohio University who wrote an accompanying article in Nature. He called the report a landmark study.

Scientists say that fossils of wishbones, skeletons, feathers and breastplates found over the years show birds have been flying for at least 150 million years.

But they admit that the fossil evidence is sketchy.

"We're only looking at a fossil record that is one-tenth of 1 percent of whatever was around back then," Gishlick said.

Exactly how birds first took to the skies remains a mystery. Some paleontologists believe that flight evolved from the "ground up" as birds used wings to lift themselves in the air for an advantage in escaping predators or chasing after prey.

Others argue that flight began in the trees, as birds sought refuge to nest their young, then gradually developed an ability to glide from tree to tree, like flying squirrels.

"If flight did evolve from the ground up, it's a unique case among vertebrates," said Feduccia, who supports the tree origin theory.

Although it might be the oldest known bird, Archaeopteryx wasn't the first creature to take to the skies. Pterosaurs, a class of flying reptiles that included pterodactyls, dominated the skies 240 million years ago before dying off in the same extinction that wiped out the dinosaurs 65 million years ago.

Scientists agree that the 15,000 species of modern birds are the descendants of reptiles that began sprouting feathers millions of years ago. But beyond that, avian origins are open to debate.

Differing views

Most paleontologists believe that the birds' ancestors were dinosaurs. But a minority say birds might have evolved from a different type of reptile. To support their arguments, both sides cite recent discoveries of feathered dinosaurs that lived in China 120 million years ago.

"We all agree that birds and dinosaurs are related. The question is, at what level," said Feduccia, who favors the minority view.

Archaeopteryx was plucked from a limestone pit in 1861, two years after Charles Darwin published his Origin of Species, so its discovery supported early arguments for evolution

Six other fossilized samples of the ancient bird have been found since then, all recovered from the same massive Solnhofen limestone formation in Germany. They remain scattered around the world among collectors and museums.

Fossil in a box

The sample used for the Nature study was the first fossil found and remains one of the prized possessions of the Museum of Natural History in London.

For the tests, museum researcher Angela C. Milner carried the fossil in a box in her shirt pocket from London to the University of Texas for the tests, according to Witmer.

"That was apparently the safest way to transport it," Witmer said.

Experts who have studied Archaeopteryx say the study doesn't address how skilled the creature was as an aviator.

"Whether it stayed up in the air very long, we don't know," Padian said. "It may not have been as maneuverable as birds we see today, or as strong a flier. But it was capable."

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