Grand Canyon is an expansive stretch of red rock in the US and finding fossil footprints is not unusual.

But a discovery made by a geology professor turned out to be a bigger deal than he could have imagined. He found the oldest vertebrate fossil tracks ever found at Grand Canyon National Park — about 313 million years old, reported CNN.

According to a news release this week from the park, a visiting professor from Norway at the University of Nevada, Las Vegas (UNLV), Geologist Allan Krill came across a boulder marked with set of fossil footprints while on a hike with students in 2016. 

After the hike, Krill sent a photo to colleague Stephen Rowland, a paleontologist at UNLV. Rowland and a team of colleagues documented the discovery in a paper published Wednesday in the journal PLOS One.

“These are by far the oldest vertebrate tracks in Grand Canyon, which is known for its abundant fossil tracks,” Rowland said in a statement. “… They are among the oldest tracks on Earth of shelled-egg-laying animals, such as reptiles, and the earliest evidence of vertebrate animals walking in sand dunes.”

According to the researchers, the footprints show two separate animals passing on the slope of a sand dune.

The researches said that the pattern of the footprints revealed a distinctive gait that scientists did not know about in early animals. Called a lateral-sequence walk, it involves the rear leg and the front leg on one side of the animal moving together, alternating with those legs on the other side moving together.