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Planet Earth

Dead Dinosaurs Walking

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Gazing at a set of petrified footprints, Stephen Gatesy has conjured up an animated vision of the predatory dinosaurs that sloughed through mudflats in eastern Greenland more than 200 million years ago. The smudgy steps they left behind show that the ancestors of T. Rex stomped about much like giant turkeys.

Gatesy, a biologist at Brown University, has puzzled over these dinosaur tracks since he and his colleagues discovered them a decade ago. Some prints clearly belonged to birdlike, carnivorous dinosaurs called theropods; others looked unfamiliar. He wondered if the sticky ground made the animals step awkwardly and leave the odd markings. So he videotaped turkeys--living relatives of the dinosaurs--barreling down a series of muddy runways in his lab. The deep impressions closely resembled the tracks from Greenland.

Just like the live birds, the dinosaurs stepped right into the muck, sank down a few inches, and drew their toes together while they plucked out their feet. "We were stunned," says Gatesy. "Both the ancient and the modern forms were doing the same thing." But unlike birds, the dinosaurs did not have a backward-facing first toe, and their tracks bore impressions of their heels. The heel print shows that walking dinosaurs depended more on rotation about the hip, like humans and reptiles, rather than at the knees, like ambling birds.

The deep Greenland footprints brought to life details of dinosaur motion that fossilized skeletons alone can never reveal. "No matter how strong inferences may be from the bones," says Gatesy, "it sure is nice to see concrete evidence."

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