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Geologist Allan Krill was hiking along the Grand Canyon National Park’s Bright Angel Trail with a group of students in 2016 when he spotted it: a fallen boulder lying just off the side of the trail, with curious markings that resembled footprints. Krill, who was visiting the University of Nevada, Las Vegas (51³Ô¹ÏºÚÁÏ) from Norway, sent photos of his find to an old friend and colleague, Stephen Rowland, a 51³Ô¹ÏºÚÁÏ paleontologist.

A new research paper led by paleontologist Steve Rowland at the University of Nevada, Las Vegas analyzes this chance find of two sets of footprints (also called trackways) on the same rock that are potentially both from the same unknown species.

It's something like a modern-day chuckwalla, side-stepping sand dunes on an island in what now is Grand Canyon National Park.

A rock tumble at the Grand Canyon revealed fossil footprints that researchers say are among the oldest in the park.

It’s something like a modern-day chuckwalla, side-stepping sand dunes on an island in what now is Grand Canyon National Park.

It’s something like a modern-day chuckwalla, side-stepping sand dunes on an island in what now is Grand Canyon National Park.

Footprints found in the Grand Canyon, Arizona, reveal the journey that two creatures took when they walked up the sand dunes approximately 313 million years ago. The footprints were discovered when a huge boulder fell down in the Pennsylvanian Manakacha Formation, revealing the imprinted tracks.

On a day about 313 million years ago, a four-legged animal took a stroll up the slope of a sand dune, leaving only footprints behind.