August 20, 2009

Fossil Tracks Show How Ancient Flying Reptiles Landed

Scientists have discovered a small strip of land found frozen in time in petrified mud where a pterosaur once landed in search for food 140 million years ago.

When the ancient reptile touched down, its feet pressed into soft mud leaving behind prints that fossilized and have now been identified.  After examining the preserved footprints, scientists determined that the pterosaur stalled in the air shortly before touching down, a technique also used by many modern birds.

Scratch marks left behind from the reptile's claws reveal that the speed of its approach was too fast to reach an immediate stop, and that it made a small, clumsy hop before coming to a halt. The ability to stall its flight to control the landing shows the pterosaurs were "strong, maneuverable flyers" that had mastered a skill still employed by birds today.

The discovery marks the first time scientists have identified footprints made by the pterosaurs as they made a landing. The tracks were among hundreds left behind by pterosaurs, dinosaurs, invertebrates and other Jurassic animals at Crayssac in France.

An international team of researchers analyzed the tracks, and realized that one set of prints belonged to a creature making a landing.  The prints revealed how the flying reptile would have moved -- touching down safely, folding its wings and turning slightly before wandering off in search of a meal, the scientists believe.

"It's pretty cool," said researcher Kevin Padian, professor of integrative biology and curator of paleontology at the University of California, Berkeley.

The size of the prints indicates the pterosaur had a wingspan of about 3 feet, he said.

"We think they were perambulating the beach looking for invertebrates to feed on," he told the Independent.

Using its wing arms as a pair of front legs, the pterosaur could walk in a way more similar to birds and mammals than to modern lizards.

Of particular interest to scientists was the short distance, less than 10 inches, the reptile required to come to a complete stop.  This suggests the pterosaur had lost most of its speed before touching down on the ground.

"The elongated claw impressions... and the absence of tracks behind this preserved series indicate quite strongly that the animal was landing," wrote the researchers.

"The short distance between the first and second sets of pes [rear] prints recalls a short and immediate 'stutter step', perhaps a simultaneous hop with both feet. At this point the animal stopped and rested its forelimbs on the ground."

"The arrangement of prints excluded the possibility of a running landing, such as some ducks and seabirds prefer today, but supported the idea that most of the forward motion had been lost in an aerial stall. We infer that, like most birds, these pterosaurs used their wings to stall before landing," they concluded.

A report about the finding was published yesterday in the journal Proceedings of the Royal Society B.


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