MORE THAN 10,000 years ago, a woman or young man—a toddler balanced on one hip—set out on a harried trip northward through what is now White Sands National Park, New Mexico. Rain may have pelted the traveler’s face as their bare feet slid on the mud. They paused to briefly set the toddler on the ground before pressing on; a wooly mammoth and giant sloth ambled across their freshly laid tracks. Several hours later, the traveler followed the same route south, this time empty-handed.
Now, a team of scientists have documented nearly a mile of fossilized footprints from the out-and-back venture—the longest human trackway of its age ever found. “I’ve never seen anything quite like it,” says Chatham University’s Kevin Hatala, an evolutionary biologist who was not part of the study team.
The trackway consists of more than 400 human prints, including several tiny child prints, as described in anew study published in Quaternary Science Reviews. By analyzing the shape, structure, and spread of the tracks the research team unveiled an intimate portrait of one ancient person’s walk across the landscape, right down to their toes slipping on the slick surface.
The team also uncovered traces of a mammoth and giant sloth crossing the region after the humans passed. The mammoth seemed unconcerned about possible humans nearby, but the giant sloth likely took notice. The prints suggest it reared back on two legs, possibly to sniff for the human presence, similar to how bears behave today.
“It gives us a sense of humans within their ancient ecosystem,” says study authorSally Reynolds, a paleontologist at Bournemouth University. She points to the sloth’s apparent awareness of humans nearby. “That’s an idea you wouldn’t get from bone.”
The ghost tracks
Fossil footprints are a boon for scientists, preserving stunning snapshots of ancient behaviors that cannot be gleaned from other remains. “Fossils obviously are the backbone of understanding past life,” says paleoanthropologistWilliam Harcourt-Smith of the City University of New York who was not part of the study team. “But footprints sites are special because they’re this moment in time.”
The newfound track site is part of an ongoing effort to document the trove of ancient prints at White Sands National Park—an endeavor driven by the careful observations of David Bustos, the park’s resource program manager. The shallow impressions are tough to spot, only revealed by slight changes in moisture, which cause faint shifts in color.
“He kept noticing these ghost tracks, these footprints, that were coming to light,” Reynolds says of Bustos’ observations.
In 2016, Bustos asked a range of specialists about the tracks, including the first author of the new study,Matthew Bennett, a geologist at Bournemouth University in England. Bennett and his colleagues have since made multiple trips to White Sands, documenting the array of prints—both human and animal—in each section of the park.
The prints of the new study are pressed into fine sand, and a thin crust of salt is all that holds their shape together, Reynolds says. The team carefully excavated 140 of the tracks, using a brush to reveal the delicate structures. Yet such fragile forms quickly break down once uncovered, so the team recorded each print with a series of photographs to construct a three-dimensional model, a technique known as 3D photogrammetry.
Source: National Geographic