Hiker, paleontologist follow 300-million-year-old fossil footprints to a breakthrough

From a chance glance by a hiker on a storied Grand Canyon trail, a paleontologist and colleagues managed to trace the footsteps of an animal that lived more than 300 million years ago, and unearth a previously unknown — and surprising — evolutionary quirk.

It was even more fortuitous that the hiker happened to be a geologist himself, and a friend of professor Steve Rowland of the University of Nevada – Las Vegas (UNLV), a leading expert in the study of footprint fossils.

“He knew I was interested in fossil footprints,” Rowland said of his friend, professor Alan Krill, who first spotted the two tracks on the Bright Angel Trail, a geologically well-mapped area of the canyon. Rowland then took time out from a family vacation to study the prints further.

In a paper published this month, Rowland and his co-authors detailed their findings following a four-year study of the two footprints: one well formed, the other merely the claws of a creature. The researchers discovered that the tracks were made by a vertebrate and an amniote, egg-carrying or laying creatures. The footprints are the oldest discovered in what was a sand dune, desert environment. Older ones have been discovered, but in marshy landscapes.

With help from other experts, Rowland now concludes that the creatures likely walked the same trail within hours or days of each other and were lizard-like in appearance, akin to the marine iguana of the Galapagos Islands, and about a foot long.

“There are no body fossils at all at this level in this formation,” said Rowland of the Pennsylvanian Manakacha Formation, a well-documented interval in history because its carbon-rich environment was therefore forensically studied by geologists, and linked to the oil industry.

“There was a Nova Scotia body fossil of the same type, but that was found in marshy, carbon-heavy land,” said Rowland. “That dated to 314 million years ago and we believe that it is just a little bit older than the ones in the Grand Canyon, which we believe are around 313 million years old, give or take half a million years.”

One of the big takes from the study, Rowland said, was that this group of amniotes adapted to a sand dune environment.

“We know lizards and snakes were very comfortable in this environment, but did not know when, and this shows it was very early,” the paleontologist said.

But what came as a real surprise, one that fell out of the study, said Rowland, was the way one of the creatures walked up what was undoubtedly a steep incline. It walked almost sideways but, more important, it did so in a lateral walking gait, right rear first, followed by front on the same side, then the other side.

Almost all animals, including humans, walk diagonally, right leg, left arm, right front, left rear, and vice versa. It is a much faster gait. And it comes from way back, as fish move in the same way.

Rowland cites the example of cats, including big ones, and dogs, walking laterally, slowly and deliberately. It is much more stable; three feet are always on the ground and it is done when hunting or otherwise when the animal needs to be cautious and careful, but only at times. In contrast, camels walk laterally all the time, their gait allowing for a smoother ride, but also providing an extraordinary ability to conserve energy, and not need water, in the toughest environments.

 The team concluded that, at some point in the animal's evolutionary history, this quirk of a gait was learned in order to adapt to the environment, in this case the ability to navigate a steep, potentially treacherous sand dune, and possibly other hazards. The claw tracks reveal the second animal was walking diagonally. If both animals were the same species, as the scientists believe, this creature had developed the ability to walk both laterally and diagonally hundreds of millions of years ago.