How big Jurassic flying reptiles got off ground

[January 08, 2009]  WASHINGTON (AP) -- The Jurassic version of jumbo jets -- huge flying creatures weighing hundreds of pounds -- is a mystery of dinosaur-era flight: How did something so big get off the ground? A Johns Hopkins University biologist thinks he has figured out the answer.

What people think of as "flying dinosaurs" but are technically giant reptiles didn't launch into the air like birds. They leapt into the air off all four legs, said Mike Habib, of the university's Center for Functional Anatomy and Evolution. Only vampire bats do something like that.

The flying creatures are called pterosaurs (the "p" is silent). They were a group of flying reptiles that could weigh more than 500 pounds and have bus-sized wingspans. Last year, researchers tried to figure out how they got off the ground by looking at the largest bird now flying, the albatross. They concluded that anything much bigger couldn't get off the ground the same way.

But Habib said pterosaurs shouldn't be compared to birds.

"The catch is that they are not built like birds," Habib said in a telephone interview.

Habib used CT scans of the bones of 155 bird specimens and a dozen species of pterosaurs and found that they were greatly different in strength, size and proportion. In birds, the hind legs were stronger than the front and in some pterosaurs the front legs were several times stronger than the hind ones.

"It's a lot like a leapfrog," Habib said, describing how he figures the pterosaurs got off the ground. "They kind of pitch forward at first, the legs kick off first, then the arms take off."

That allowed some of the ancient giants to get into the air in less than a second. Habib calculated that the 550-pound pterosaur called Hatzegopteryx thambema launched at a speed of 42 miles per hour.

The ancient flier "accelerates more like a Porsche and less like a Volkswagen," Habib said. "That's really handy if you live in a world filled with tyrannosaurs, which it did."

Pterosaurs first appeared about 230 million years ago and died with the dinosaurs 65 million years ago.

Habib's research -- published in a German journal called Zitteliana -- combines paleontology and flight dynamics.

James Cunningham, a Collierville, Tenn., engineer who once led a National Geographic study team looking at the issue, said Habib's work makes sense from a flight dynamics point of view.

"The biggest pterosaurs didn't have enough muscles to get off the ground from wing flapping," Cunningham said.

Pterosaur expert David Unwin, a paleobiologist at the University of Leicester, praised the study for relying more on physical tests than theory. However, he said he is not quite convinced because the study doesn't look at how launch fits with the rest of the pterosaurs' biology and there aren't any preserved pterosaur tracks that help prove or contradict Habib's explanation. He thinks the critters may not have been so heavy, lessening the mystery of their flight.

But Unwin agrees with Habib that scientists should stop comparing to birds or other living species. They are too different and that's what makes them more interesting, Unwin said.

[Associated Press; By SETH BORENSTEIN]

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