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?

What people think of as "flying dinosaurs" didn't launch into the air like birds. They leapt into the air off all four legs, said Mike Habib, of the Johns Hopkins University's Center for Functional Anatomy and Evolution.

The flying creatures are called pterosaurs. They were a group of flying reptiles that could weigh more than 500 pounds (225 kilograms) 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.

But Habib said pterosaurs shouldn't be compared to birds because their body structures are completely different.

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. "[The pterosaurs] 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.

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."