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UNLV geologist Stephen Rowland discovered that a set of 28 footprints left behind by a reptile-like creature 310 million years ago are the oldest ever to be found in Grand Canyon National Park. (Photo/Stephen Rowland)

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Tiny footprints, big discovery: 28 small reptile tracks oldest ever found in Grand Canyon

Hundreds of hikers each day pass by the fallen boulder along the Bright Angel Trail in Grand Canyon National Park.