Grzegorz Niedzwiedzki /U. of Warsaw and Institute of Paleobiology

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ScienceShot: An Earlier Start for Dinosaurs?

The cat-sized, three-toed creature that may have given rise to Tyrannosaurus Rex, Velociraptor, and other fearsome dinosaurs loped across the earth nearly 10 million years earlier than previously thought. In the Holy Cross Mountains of southern Poland, researchers have found tracks, like the one shown above, indicating that animals called "stem dinosaurs" first appeared about 250 million years ago—only a couple of million years after the great Permian-Triassic extinction, a catastrophic event that wiped out over 90% of all marine species and over 75% of land creatures on the planet. The team will report online tomorrow in the Proceedings of the Royal Society B that the 2-centimeter-long footprints belonged to Prorotodactylus, which walked on four feet. Each foot had only three prominent toes, however, meaning that sooner or later these creatures probably evolved into the theropod dinosaurs, the three-toed, upright-walking beasts that would dominate the planet for the next 150 million years or so—until another catastrophic event wiped them out.

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