A hunter-gatherer who trekked through a desert oasis a hundred centuries ago left the continent’s most lasting impression: the oldest known human footprints in North America.

There are only two of them — one left and one right — but the ancient traveler’s path through mineral-rich sediment in the Chihuahuan Desert allowed them to become enshrined in stone, and now dated, some 10,500 years later.

“To my knowledge the oldest human prints previously reported in North America are around 6,000 years old, so the … prints pre-date these by some 5,000 years,” said Dr. Nicholas Felstead, a geoarchaeologist at Durham University who led a new analysis of the prints. [UPDATE: See prints found in British Columbia that are thought to be more than 13,000 years old: “Ancient Human Footprints Found on Canadian Island May Be Oldest in North America“]

The tracks were first discovered during highway construction in northeastern Mexico, about 300 kilometers from the Texas border, in 1961. They were excavated and taken to a local museum for study, but their precise location was lost to history.

A search for the site in 2006 came up empty, but it did turn up an additional 11 tracks in the general area where the original prints were believed to have been found — a marshy, spring-fed desert refuge known as Cuatro Ciénegas.

“Both sets of prints are ones that have been identified before and are the only reported footprints in the Cuatro Ciénegas Basin, but neither have previously been dated,” Felstead said in an interview.

Felstead and his team were able to date the tracks because they were preserved in travertine, a sedimentary rock that contains minute traces of uranium from the waters in which it formed.

Since uranium decays into the element thorium at predictable rates, the scientists were able to measure the ratio of those materials to determine the specimens’ ages.

Their results showed that the pair of tracks discovered in 1961, now housed at Saltillo’s Museo del Desierto, were about 10,550 years old.

The 11 other prints, which remain where they were found in a Cuatro Ciénegas quarry, dated back about 7,250 years, according to the research.

The difference in age suggests that, while both sets of prints were made possible by the basin’s marshy, carbonate-rich sediments, the 11 recently discovered tracks are not from the same precise location as the pair found in the 1960s.

Although rare, other fossil human footprints have been found elsewhere in North America, from Nicaragua to California. But those tracks are at least a thousand years younger than the newly studied samples, Felstead said.

The oldest known human print in the Western Hemisphere is the tiny track of a child’s foot in Chile dated to 13,000 ago — adding fodder to the ongoing debate about when humans first migrated to the New World.

Though they may not clarify that controversy, the new findings from Cuatro Ciénegas do provide valuable insights into a time and region of North America that’s not very well understood, Felstead said.

The region where the tracks were found is known to have been home to a somewhat amorphous culture known as the Coahuiltecans, a diverse group of nomadic hunter-gatherers that ranged from central Mexico to the Texas plains. [Learn what mummified and bundled bodies found in south Texas reveal about ancient burial practices.]

While many of these bands are known to have frequented Cuatro Ciénegas over thousands of years, the Coahuiltecans left precious little evidence that could be fixed to specific dates.

The oldest previously reported human fossil evidence in the area were coprolites — fossil feces — found in a rockshelter dated to about 9,000 years ago, Felstead said.

“So our reported footprint date is not only the oldest human fossil evidence, but also the oldest archaeological evidence, reported from the Cuatro Ciénegas Basin,” he noted.

What’s more, his team’s analysis of the 7,200-year-old tracks also turned up traces of ancient pollen from trees like pecan and willow, suggesting that the region was cooler and wetter than it is today.

But it also yielded pollen from prickly pear cactus, a staple of the Coahuiltecans in historic times, as recorded by the Spanish when the groups first encountered each other in the 1500s.

Taken together, these clues suggest that the person who left the 11 ancient footprints was traveling through a changing landscape — one that was gradually becoming more arid, and more challenging, requiring adaptations that still persist among native people in the Chihuahuan Desert, centuries after the rest of Coahuiltecan culture itself disappeared.

“As the ancient nomadic hunter-gatherers needed to adapt to the increasingly hostile desert conditions …,” the team writes in its study, “they expanded their ability to find resources, leading to longer cycles of nomadism and possibly the expansion of their unique desert culture right into the 18th Century when they finally become extinct after the arrival of the Europeans.”

Falstead and his colleagues report their findings in the latest issue of the Journal of Archaeological Science.

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Nicholas J. Felstead, Silvia Gonzalez, David Huddart, Stephen R. Noble, Dirk L. Hoffmann, Sarah E. Metcalfe, Melanie J. Leng, Bruce M. Albert, Alistair W.G. Pike, Arturo Gonzalez-Gonzalez, & José Concepción Jiménez-López (2013). Holocene-aged human footprints from the Cuatrociénegas Basin, NE Mexico Journal of Archaeological Science : http://dx.doi.org/10.1016/j.jas.2013.11.010