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A Pterosaur Comes In for a Landing
19 August 2009 (All day)
About 150 million years ago in what is today southwestern France, a flying reptile swooped down on a beach, landed on the damp sand, and walked off, maybe to find dinner. Now scientists have uncovered the fossilized tracks of this pterosaur, providing the first glimpse of how these flying creatures touched down.
Pterosaurs, a group that includes pterodactyls, ranged in size from a sparrow to a small airplane. Fossilized footprints indicate that pterosaurs walked on all fours, using their feet and the hands on their wings. But how did they take off and land?
Paleontologist Kevin Padian of the University of California, Berkeley, and colleagues uncovered a major clue on "Pterosaur Beach." Today, the site is a rock quarry near vineyards that lie between the cities of Bordeaux and Toulouse in France, but during the late Jurassic period about 150 million years ago, it was a lagoon with gentle tides that would have barely disturbed the beach's sand. These calm conditions helped preserve prints left by animals.
Among the pterosaur tracks at the beach, one set of four prints stood out. Unlike pterosaur walking tracks, in which the prints of the left and right feet are staggered, Padian and colleagues found that the first two foot impressions were side by side. In addition, the first pair's toe prints were longer than the toes in the rest of the track, suggesting they had been dragged forward. The pattern suggests a landing from the air, with the pterosaur touching down simultaneously with both feet and dragging its toes with the forward momentum. The creature then hopped to make a second pair of side-by-side prints, planted its hands in the sand, and finally started walking off to the left, the team speculates online today in the Proceedings of the Royal Society B. "It's a little Jurassic moment in time that got recorded," Padian says.
The researchers point out that these landing tracks resemble those of living birds like the merganser duck, which adjusts the way its wings flap to slow down enough to land on both feet. Padian and colleagues believe that these print similarities imply that pterosaurs could also stall during a landing, supporting the hypothesis that pterosaurs were extremely capable fliers, like modern birds.
Paleontologist David Unwin of the University of Leicester in the U.K. isn't convinced that Padian's team has found an ancient runway, however. "Personally, I'd love them to be landing marks, but I don't think you can rule out they're swimming marks," he says. He suggests that a swimming pterosaur could have made the first parallel prints when it planted its feet as it reached shore. Padian counters that this would have produced sloppier prints. Paleontologist Martin Lockley of the University of Colorado, Denver, agrees that a pterosaur touchdown is the best explanation. "I think it's very convincing," he says. "Even if there are other possible interpretations, I can't think of anything compelling."