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October 17, 2021

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UNLV professor says Grand Canyon reptile tracks among earliest on earth

Las Vegas Paleontologist Stephen Rowland

Christopher DeVargas

UNLV paleontologist Stephen Rowland poses for a portrait at the Richard A. Ditton Learning Lab inside the Las Vegas Natural History Museum, Tuesday Aug. 25, 2020.

Fossilized animal tracks discovered in the Grand Canyon were likely left by a reptile some 313 million years ago, among the oldest found on Earth, a UNLV professor said.

“There are no reptilian-like tracks much older than these tracks,” said UNLV geology professor Stephen Rowland, who has been studying the prints for several years.

Rowland, whose findings were published this month in the scientific journal PLOS One, said the animal that left the tracks was probably similar to the common chuckwalla lizard found in the Mojave Desert. It is a stocky, four-legged lizard with a thick pointed tail.

The tracks, found in 2016 by Norwegian geologist Allan Krill, provide more insight into a major evolutionary development, Rowland said.

They come from an amniote, an animal that lays shelled eggs on land or retains a fertilized egg within the mother.

The group is separate from anamniotes — fish and amphibians that require water to breed.

“The ability to lay an egg with a shell on it was a major breakthrough that allowed them to survive on dry land because the shell kept it safe and moist,” Rowland said.

The discovery also reveals how early four-legged animals were walking in a lateral sequence, which was not previously known, Rowland said.

“I was able to reconstruct how the animal was moving its feet ... We never had evidence prior to this on how early animals were using the lateral sequence gait,” Rowland said.

Most four-legged mammals walk in lateral-sequence where the back legs follow the front legs on the same side.

Other primates walk in a diagonal sequence, where the back legs follow the front legs on the opposite side.

“From this study, we can say that that lateral sequence gait had become a standard gait by more than 300 million years ago. We had no idea about that,” Rowland said.

The fossilized footprints are still in the Grand Canyon, but Rowland hopes his research justifies the expense of removing and preserving the rock.

He said he’s been talking to the National Park Service about putting it in a museum so it’s protected from vandalism and weather.

Rowland said his findings have encouraged him to search for more tracks at the Grand Canyon and the Gold Butte National Monument area northeast of Las Vegas.