A rock tumble at the Grand Canyon revealed fossil footprints that researchers say are among the oldest in the park.
Steve Rowland is a geology professor at the University of Nevada, Las Vegas, and recently published his findings. He says the creature that made the tracks is something like a modern-day chuckwalla that sidestepped sand dunes in a coastal plain more than 300 million years ago. Not everyone is convinced the footprints were created by a single, four-legged animal, moving laterally. Or, that the footprints are those of animals that lay hard-shell eggs. But officials at the Grand Canyon say the research raises interesting questions.