The 28 footprints capture an early reptile-like creature’s unusual diagonal gait (Courtesy of Stephen Rowland) Some 310 million years ago, a reptile-like creature with an unusual gait roamed the sandy expanses of the Grand Canyon, leaving a trail of 28 footprints that can still be seen today. As Michael Greshko reports for National Geographic, these unusually well-preserved markers represent the national park’s oldest footfalls—and, if additional analysis links the early reptile to one that left a similar set of prints in Scotland roughly 299 million years ago, the tracks may even earn the distinction of being the oldest of their...