Large animals started going extinct at the end of the Pleistocene, just as both climate change and a new predator — Homo sapiens — arrived on the scene. But despite humans’ brutal legacy of killing other species, it’s been hard to tease out which extinctions were really our fault. For a long time, the giant ground sloth was thought to be a victim of a changing environment. But butchered bones, described in a Science Advances study published Wednesday, once again point an accusing finger at our species.

Before this study, the prevailing theory was that the giant ground sloth survived the mass extinction at the end of the Pleistocene in some places and lived into the beginning of the Holocene, which began about 11,800 years ago. But the new research, first-authored by Gustavo Politis, Ph.D., a professor of archaeology at the National University of Central Buenos Aires, presents direct evidence that humans were butchering giant ground sloths nearly 1,000 years before the Pleistocene gave way to the Holocene.

The paper makes the case that a fossilized giant ground sloth found at the Campo Laborde archaeological site in the Pampas region of Argentina was slaughtered by humans around 12,600 years ago. By demonstrating that humans butchered a giant ground sloth, and using radiocarbon dating to establish when the slaughter occurred, the researchers “cast doubts on other published Holocene ages for Pleistocene fauna in the Pampas.”

This finding, say the researchers, changes the way archaeologists understand the relationship among humans, large mammals, and climate change as the Earth was transitioning out of the last ice age.

Giant ground sloth bones at the Campo Laborde site in Argentina. Gustavo Politis and Pablo Messineo

Previous research has shown that Pleistocene-era humans probably hunted giant sloths in the western US, but evidence of humans killing the animals in South America is rare. Complicating the picture even more are previous dating analyses showing that extinct megafauna, like giant ground sloths, survived the Pleistocene extinction and lived into the Holocene. With these dates, there was no reason to suspect that humans had played a major role in their extinction.

Cut marks on a giant ground sloth rib indicate that humans killed and butchered the animal. Pablo Messineo. INCUAPA-CONICET, Facultad de Ciencias Sociales (UNICEN)

But the new study used an extremely precise method of dating fossils called accelerator mass spectrometry radiocarbon dating to turn this idea on its head. The results of this analysis showed that this ground sloth had been killed 12,600 years ago — before the beginning of the Holocene.

Reinforcing the idea that the humans killed the sloth and didn’t just scavenge it, broken stone tools, including projectile points, were found nearby. Plus, the fact that the remains were found in what used to be an ancient swamp suggests that ancient humans likely put it there on purpose. “[Driving] prey into a swamp is a frequent hunting strategy,” they write.

Archaeologists suspect these tools, found at Campo Laborde, were used to hunt the giant sloth, as evidenced by the broken projectile point (A). Pablo Messineo. INCUAPA-CONICET, Facultad de Ciencias Sociales (UNICEN)

This finding changes what we know not only about giant ground sloths in that part of South America but also all large mammals in the area.

“These new dates do not support extinct megamammals surviving into the Holocene at Campo Laborde and call into question Holocene survival of megafauna at most, if not all, Pampas localities,” they write.

And since humans were killing giant ground sloths at least a couple thousand years before they went extinct, it seems that humans may have played a not-insignificant role in their eventual extinction. Add one more to the list.

Abstract: The extinction of Pleistocene megafauna and the role played by humans have been subjects of constant debate in American archeology. Previous evidence from the Pampas region of Argentina suggested that this environment might have provided a refugium for the Holocene survival of several megamammals. However, recent excavations and more advanced accelerator mass spectrometry radiocarbon dating at Campo Laborde site in the Argentinian Pampas challenge the Holocene survival of Pleistocene megamammals and provide original and high-quality information documenting direct human impact on the Pleistocene fauna. The new data offer definitive evidence for hunting and butchering of Megatherium americanum (giant ground sloth) at 12,600 cal years BP and dispute previous interpretations that Pleistocene megamammals survived into the Holocene in the Pampas.