Hundreds of hikers each day pass by the fallen boulder along the Bright Angel Trail in Grand Canyon National Park.
It might otherwise go unnoticed except for the 28 indentations 鈥 sloping footprints left behind by a small, reptile-like creature about 310 million years ago 鈥 that cover the rock鈥檚 expansive surface.
鈥淚t鈥檚 the oldest trackway ever discovered in the Grand Canyon in an interval of rocks that nobody thought would have trackways in it, and they鈥檙e among the earliest reptile tracks on earth,鈥 said Steve Rowland, 性视界传媒 professor of geology who is studying the fossil trackways.
Rowland, who presented his findings at the recent annual meeting of the Society of Vertebrate Paleontology, said he鈥檚 not prepared to say that they鈥檙e the oldest tracks of their kind ever discovered, but it鈥檚 a possibility, as he鈥檚 still researching the discovery.
鈥淚n terms of reptile tracks, this is really old,鈥 he said, adding that the tracks were created as the supercontinent Pangaea was beginning to form.
Rowland was first alerted to the tracks in spring 2016 by a colleague who was hiking the trail with a group of students. The boulder ended up along the trail after the collapse of a cliff.
A year later, Rowland studied the footprints up close.
鈥淢y first impression was that it looked very bizarre because of the sideways motion,鈥 Rowland said. 鈥淚t appeared that two animals were walking side-by-side. But you wouldn鈥檛 expect two lizard-like animals to be walking side-by-side. It didn鈥檛 make any sense.鈥
When he arrived home, he made detailed drawings and began hypothesizing about the 鈥減eculiar, line-dancing gait鈥 left behind by the creature.
鈥淥ne reason I鈥檝e proposed is that the animal was walking in a very strong wind, and the wind was blowing it sideways,鈥 he said.
Another possibility is that the slope was too steep, and the animal sidestepped as it climbed the sand dune. Or, Rowland said, the animal was fighting with another creature, or engaged in a mating ritual.
鈥淚 don鈥檛 know if we鈥檒l be able to rigorously choose between those possibilities,鈥 he said.
He plans to publish his findings along with geologist Mario Caputo of San Diego State University in January. Rowland also hopes that the boulder is soon placed in the geology museum at the Grand Canyon National Park for both scientific and interpretive purposes.
Meanwhile, Rowland said that the footprints could belong to a reptile species that has never yet been discovered.
鈥淚t absolutely could be that whoever was the trackmaker, his or her bones have never been recorded,鈥 Rowland said.
