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 a new 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 author Sally 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 paleoanthropologist William 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.
“The minute we expose them, the race is really on to record them before they ... just disappear,” Reynolds says.
By studying the shape, size, and distribution of the footprints, the researchers attempted to piece together what happened during the ancient walk across the muddy ground. The primary track maker could have been either a woman 12 years or older, or possibly a young man, based on a comparison of the footprint lengths to modern humans. In at least three points along the way, tiny footprints join the main trackway, evidence of a child less than three years old.
The spacing of the tracks suggests the person was traveling around 3.8 miles an hour. While not a jog, this would have been a hasty pace considering the muddy conditions and heavy load, Hatala notes.
In a few spots, the traveler's strides were unusually long, as if they were stepping or leaping over an obstacle. “It could be puddles." Reynolds says. "It could be wet mammoth poo."
The child, however, was carried only one way. During the northbound trip, the tracks of the left foot are slightly larger, which may be the result of carrying the toddler on one hip. Among the northbound tracks, there are also instances of the trekker’s toes sliding on the muddy surface, the foot dragging to create a banana-shape print. Yet in the southbound return, this size difference in tracks is not apparent, and the slippage much less frequent, suggesting the walker was unencumbered.
Researchers had previously suggested that differences in right- and left-footed prints could be evidence of carrying a load, but it was often speculation. The new study offers a bit more evidence: “In this particular case, you see the footprints of a child suddenly appear partway through,” Hatala says.
The animal tracks helped the team estimate when the adventurer trekked across the land. After the northbound trip, the mammoth and giant sloth stepped across the fresh trackway, while the human’s southbound prints cut into those of the animals. This overlay shows that all the prints were set down within a few hours before the mud completely dried. The presence of these now extinct creatures alongside humans suggests that the ancient adventure took place at least 10,000 years ago.
‘Just like us’
In 2017, Reynolds, who is married to Bennett, was home pregnant when Bennett called her with news about the long series of footprints. “He was over the moon,” Reynolds recalls. They were particularly smitten with the ancient child brought along for the ride. “These tiny little footprints were just so unexpected,” she says. They called the tracks “Zoe’s trail” the name they planned to give their still unborn daughter.
Much remains unknown about the ancient adventurer. Where was the track maker going? What was the purpose of the trek? What happened to the child?
The track maker seemed to know the route well, Reynolds says, perhaps following a path to the camp of another family or hunting group. “There was no dithering around, getting lost,” she says. But the journey’s endpoint remains unknown, since the prints head off into what is now the White Sands Missile Base, which is inaccessible to the researchers.
The behavior recorded in the trackway is perhaps not surprising, Harcourt-Smith says. One might expect humans to carry children: “All cultures do it; ape relatives do it,” he says. But at the same time, there’s a certain relatability to the find.
“It’s a reminder that these people were just like us,” he says. “Maybe different individual daily stresses—we don’t have mammoths walking around—but they’re walking around the landscape in the same way we would.”
The research team continues its work at White Sands National Park, piecing together a nuanced look at the region’s former residents. “These are little snapshots into ancient life and attitudes to other animals and landscapes that we just never thought we could get,” Reynolds says. With time, more stories—and certainly more mysteries—will be uncovered.