This undated photo provided by Grand Canyon National Park shows park employees Klara Widrig, left, and Anne Miller examining a rock that revealed fossilized footprints at the Grand Canyon in northern Arizona.
Some researchers have estimated the footprints are 313 million years old, among the earliest found at the Grand Canyon.
(Grand Canyon National Park via AP)FLAGSTAFF, Ariz. It's something like a modern-day chuckwalla, side-stepping sand dunes on an island in what now is Grand Canyon National Park.
Still, the paper raises interesting questions, said Mark Nebel, the paleontology program manager at the Grand Canyon.
The Grand Canyon has talked about creating a trail-side display or flying the rock out and into a museum, which would be costlier, Nebel said.