In 2016, during a hike in Grand Canyon National Park, ancient footprints were discovered that date back approximately 313 million years. These footprints on the side of a boulder that fell off a cliff represent the oldest vertebrate tracks in the Grand Canyon. The discovery is significant because it provides evidence of shelled-egg-laying animals, such as reptiles, and offers insights into the earliest evidence of vertebrate animals walking in dunes.
The footprints were found on the Bright Angel Trail, and if the cliff had not collapsed, the boulder would have remained hidden, and the ancient tracks may have never been noticed. This stroke of luck allowed researchers to study these ancient trackways and gain insights into the type of animal that left them when the rocky surface was a dune slope.
The tracks reveal two sets of footprints left by basal amniotes, early tetrapod vertebrates that may belong to the base of the reptile evolutionary tree. The first set of tracks shows a distinctive sideways-drifting pattern, indicating a lateral-sequence gait in which the legs on one side of the animal moved after the legs on the other. This gait is commonly observed in living species like dogs and cats when they walk slowly. The discovery of this gait in these ancient tracks provides valuable information about the early history of vertebrate animals.
The reason behind the sideways gait remains unclear. However, these tracks demonstrate that basal amniotes inhabited sand dune regions even in ancient times. Also, though it is challenging to determine the exact identity of the animal that left these tracks, they resemble Chelichnus, a set of ambiguous fossil tracks in Scotland dating to the Permian period.
The discovery of these ancient footprints in the Grand Canyon provides valuable insights into the early history of vertebrate animals. It highlights the presence of shelled-egg-laying animals and their ability to navigate sand dunes. The fortunate circumstances of the cliff collapse and the subsequent encounter by hikers allowed scientists to uncover these tracks and learn more about the ancient creatures that once roamed the area. However, the identity of the trackmaker and the complete story of this ancient species remains elusive, as there is no record of their bones in the fossil record.