15,600-Year-Old Footprint Reveals New Details About the Oldest Americans

“This story is not finished here. It’s just the start."

Flickr / kasio69

Around 15,600 years ago, a man sludged through the mud, leaving his footprint etched in the earth. He lived in a southern Chile quite unlike the one that exists today: His neighbors were primitive elephants and llamas, and his home was fenced in by huge glacial sheets. While trekking through the mud was just one part of a very ordinary day for him, in the context of human history, the moment was extraordinary: His footprint, scientists announced in Plos One, is now the oldest ever found in the Americas.

The discovery described in the study contributes to our growing understanding that we barely know anything about the ancient humans who became the first to cross over from Eurasia into the Americas. It stokes the flames of an ongoing debate about how they got here in the first place.

“This story is not finished here. It’s just the start,” lead author Karen Moreno, Ph.D. tells Inverse. Her discovery supports a theory of ancient human migration into the Americas that has gained traction in recent years.

For a time, researchers were fairly confident about how the Americas became populated by humans, betting that the “Clovis First” theory was the correct one.

A photograph taken of the print after its discovery in 2010.

Karen Moreno et. al. 

Moreno is a lecturer and paleontologist with the Austral University of Chile and argues this footprint is further evidence of a pre-Clovis South America. The Clovis were people who lived across North America 13,000 years ago, named for Clovis, New Mexico, where evidence of their settlements were first found. When these remains were discovered in the 1930s, they became regarded as the first human inhabitants of the “New World.”

Since then, new discoveries pointing to even older remains have challenged the theory, and today there are many competing theories circling the how and when of the first Americans. The Clovis First theory was linked to humans traveling through the ice-free Bering Land Bridge, which then extended from northern Eurasia into North America. But more recently, a coastal route theory posits the first Americans migrated down Pacific Rim shorelines down to South America. While it’s certainly possible that humans traveled along both routes at different times, the Chilean footprint’s existence adds credibility to the coastal-route theory.

“The original passage from Asia was supposed to be through the Bering Strait, through North America, and then South America,” Moreno says. “But in North America, evidence of human appears to be younger than what we have here. We don’t have the evidence that proves that they navigated yet, but maybe the south of Chile might provide some more answers in the future.”

Artist rendering of the event.

Karen Moreno et. al. 

Moreno, meanwhile, is a specialist in footprints of all fauna and when she first learned of this print, she had her doubts that it truly belonged to a man. The idea was so radical that she set out to prove, with various methods, that it actually didn’t belong to a human being.

“I am very, very excited about this discovering but, in the beginning, I was very skeptical about the idea,” Moreno says. “So actually, my main role was to try to find out why this footprint wasn’t actually a human footprint. When I couldn’t do that, then I was convinced we could move on with the research.”

It was first found in 2010 by Leonora Salvadores, at that time a biology undergraduate student. Salvadores was helping out an excavation at a site called Pilauco, near the city of Osorno. The site is in northwestern Patagonia, near Monte Verde, site of the famous discovery of a settlement suggesting humans occupied South America at least 18,500 years ago. That claim pushed back the peopling of the Americas by 4,000 years and is contested by some scientists.

Archeologists have found megafauna remains and lithic flakes at Pilauco before. This time, as Salvadores methodically worked through layers of dirt, she felt a difference in the consistency of the sediments. She decided to change the way she excavated and dug around the inconsistency instead of continuing to cut through layer by layer, which is more typical of archeology. In that way, she saved the footprint.

The star marks the mystery point on the footprint.

Karen Moreno et. al. 

The footprint itself was odd. It looked like it belonged to a human, but there was a strange raised point near the ball of the foot — something like an inverted miniature mountain. Salvadores, Moreno, and their team got to work trying to recreate the footprint-making situation experimentally. They mixed different amounts of water with sediments, recruited people who could leave a similar print, and had them step in their own mud. Meanwhile, Moreno evaluated whether any sort of other animals could have left a similar mark.

In the end, they discovered that at a certain stickiness level, a bit of the mud stuck to the man’s toe then plopped back into the print as he lifted his foot. That explained the small mountain.

Radiocarbon dating of the sediment layer and the artifacts found around the same layer revealed that human activity happened in Pilauco at least 15,600 years ago. Moreno suspects there were once other footprints at the site but were perhaps destroyed on accident during other excavations. Here, a young student took a chance, and a bit of history emerged.

“We have to keep looking for and at the ways humans might have come here,” Moreno says. “Some of that data might be under the sea, where water levels were lower on the coasts during the glacial period.”

The present study describes the discovery of a singular sedimentary structure corresponding to an ichnite that was excavated at the paleo-archaeological site Pilauco (Osorno, Chile). The trace fossil is associated with megafauna bones, plant material and unifacial lithic tools. Here we present a detailed analysis of the Pilauco ichnite and associated sedimentary structures, as well as new radiocarbon data. The ichnological analysis confidently assigns the trace to the ichnospecies Hominipes modernus—a hominoid footprint usually related to Homo sapiens. Some particular characteristics of the Pilauco trace include an elongated distal hallux, lateral digit impressions obliterated by the collapsed sediment, and sediment lumps inside and around the trace. In order to evaluate the origin of the ichnite, trackmaking experiments are performed on re-hydrated fossil bed sediments. The results demonstrate that a human agent could easily generate a footprint morphology equivalent to the sedimentary structure when walking on a saturated substrate. Based on the evidence, we conclude that the track-maker might well have been a bare-footed adult human. This finding, along with the presence of lithic artifacts in the same sedimentary levels, might represent further evidence for a pre-Clovis South American colonization of northern Patagonia, as originally proposed for the nearby Monte Verde site.

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