Scientists have found evidence of cut marks on the back of an ancient armadillo, suggesting humans were in South America 20,000 years ago – earlier than many researchers thought.
SCOTT DETROW, Host:
When did people first arrive in South America? It’s a matter of some debate, but strange tracks carved into an ancient shellless mammal suggest that humans may have roamed the continent thousands of years earlier than scientists once thought. Here is science reporter Ari Daniel.
ARI DANIEL, BY: The Reconquista River flows through the western suburbs of Buenos Aires. In 2016, a bulldozer excavated the river bank to widen the canal. Shortly after completing this work, one of Miguel Delgado’s colleagues, a paleontologist, went for a walk there.
MIGUEL DELGADO: While walking across the banks of the river, he found exposed fossil bones.
DANIEL: A handful of small, fossilized bones belonging to an ancient armadillo-like mammal—something called a glyptodont.
DELGADO: This animal was heavily armored.
DANIEL: Delgado is an archaeologist at the National University of La Plata in Argentina. Anyway, his colleague was there mid-walk when he just discovered these bones.
DELGADO: It was an accident.
DANIEL: But a very accidental accident, because when he looked closer, he saw something unexpected.
DELGADO: Different kinds of marks in the bones.
DANIEL: These marks could have been chipped into the bones by rocks or other bones scraping them, or maybe they were bitten or scratched by rodents or carnivores, or maybe prehistoric people did something to them. To figure it out, Delgado and his colleagues excavated part of the site and discovered various fossilized glyptodont bones, including pieces of the hard outer shell…
DELGADO: Tail, vertebrae and pelvis.
DANIEL: Back in the lab they analyzed the samples and measured the cut marks in detail and rendered them as 3D models. The results, says Delgado, were unmistakable.
DELGADO: We realized that the shape of these marks is actually very similar to cutting marks created experimentally by humans.
DANIEL: In other words, Delgado believes that the V-shaped cut marks were caused to this animal when ancient people butchered them with stone tools.
DELGADO: The most important piece of evidence is the location of the birthmarks themselves – in the parts of the bones with denser flesh.
DANIEL: Would you cut the animal where there is a lot of meat, cut into it to eat it?
DELGADO: Yes. Yeah. That’s the idea.
DANIEL: This isn’t the first fossilized glyptodont to show up with these kinds of marks, but it’s certainly among the oldest. When the team dated the fossils, they found that the animal lived about 21,000 years ago. So if humans were responsible for the cut marks, they must have been there too.
DELGADO: So it’s one of the oldest evidences of human presence here in South America.
DANIEL: That would be towards the end of the Pleistocene, when all sorts of large animals were trampling across the harsh and freezing landscape.
DELGADO: There are giant sloths, mastodons, saber-toothed ones too.
DANIEL: They all shared the Earth with humans until 10,000 years ago. The findings are published in the journal PLOS One. Alia Lesnek is a geologist at CUNY Queens College who was not involved in the study.
ALIA LESNEK: I think it’s a really exciting step forward.
DANIEL: But she says more work needs to be done to really reveal that people made these cut marks, including looking for artifacts along the riverbank.
LESNEK: You know, finding things like stone flakes or charcoal – really clear indications that people were present in addition to the cut marks.
DANIEL: Lesnek says this work adds to a slowly growing body of evidence that humans inhabited South America earlier than we once thought. It’s not a settled matter at all. But if true, it places humans in the Americas during the Last Glacial Maximum, before the vast ice sheets began to recede.
LESNEK: So it can tell us about a really long history that humans have with climate change.
DANIEL: And as he says, people’s resilience in the face of that change.
I’m Ari Daniel for NPR News.
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