Alva Review-Courier -

FLAGSTAFF, Ariz. (AP) — It's something like a modern-day chuckwalla, strolling in sand dunes on an island in what now is the Grand Canyon region.

That's how Steve Rowland, professor emeritus of geology at the University of Nevada, Las Vegas, and his fellow researchers interpret fossil footprints that were revealed in a rock fall near a popular Grand Canyon hiking trail. They estimate the tracks are 313 million years old, give or take a half-million years.

At that age, they'd be among the oldest tracks of animals that lay eggs with a protective hard or leathery shell and the earliest evidence o...