Washington, Jan 7 (ANI): Scientists have come across evidence which suggests that pterosaurs, ancient flying reptiles, used four legs to take flight.

The evidence was found by Michael B. Habib, of the Center for Functional Anatomy and Evolution at the Johns Hopkins University School of Medicine, who compared bone strength in the limbs of pterosaurs to that of birds and concluded that pterosaurs had much stronger arms than legs.

Weve all seen birds take off, so thats whats most familiar, said Habib. But with pterosaurs, extinct 65 million years and with a fossil history that goes back 250 million years, whats familiar isnt relevant, he added.

From their research, the scientists concluded that to take flight, pterosaurs required the use of four limbs.

Two were ultra-strong wings, which, when folded and balanced on a knuckle, served as front legs that helped the creature to walk and leap.

The wings of these hairy reptiles, most notably those of Quetzalcoatlus northropi, which spanned to an impressive 35 feet when the creatures were aloft, propelled the creatures into the air during take-offs that Habib describes as leap-frogging long-jumps.

Pterosaurs had long, huge front limbs, so no partner was required. Then, with wings snapping out, off theyd fly, he said.

Using computer scans to obtain cross-sectional images and geometric data for 155 bird specimens representing 20 species, Habib calculated the strengths of bones in bird limbs and compared these to three species of pterosaurs, the bones strengths of which he calculated using measurements from previously published sources.

Structural strength, taking into account length and diameter, among other things, is a measure of how much force a bone can take before it fractures.

Habib also spent time crunching the numbers using the old, bipedal launch model and simply couldnt find a mathematical solution that would enable the largest of the pterosaurs using hind legs alone to launch at all.

But using all four legs, it takes less than a second to get off of flat ground, no wind, no cliffs, he said.

This was a good thing to be able to do if you lived in the late Cretaceous period and there were hungry tyrannosaurs wandering around, he added. (ANI)