Mammoth bones and “ghost” footprints from ancient peoples are the latest evidence in a scientific debate about when the first humans arrived in the Americas.
Fossilized bones, in particular, may suggest that people lived in North America tens of thousands of years before the generally accepted date for the arrival of the first Native Americans of around 10,000 BC.
The researchers say radiocarbon dates of chemicals in mammoth bones, from a mother and her calf, indicate that the animals lived about 37,000 years ago in what is now New Mexico. Patterns of fractures in the bones show that they were butchered by humans, who must therefore have lived there at the same time, the researchers added. But the findings are disputed by some other scientists, who say the fractures may have been caused naturally.
The latest “ghost” footprints, meanwhile, were found a few weeks ago in an Air Force missile range in a Utah desert. Scientists think they are around 12,000 years old, but this is only the second time such footprints have been found, and they support last year’s discovery of ghost footprints in New Mexico that are believed to be at least 21,000 years old — although this one discovery, too, is disputed.
Mammoth bones at what is called the Hartley site in northern New Mexico, in rocks above a tributary of the Rio Grande, are hailed as the most conclusive evidence yet that humans arrived in the Americas as late as 50,000 years ago by walking on a “bridge land” between what is now Siberia and Alaska.
The researchers say they are confident in their dating and interpretation that the fractures were caused by repeated impacts with sharp objects during deliberate culling. They also say there is evidence that fire was used selectively to cook many of the bones.
“I think it’s a solid radiocarbon date,” said paleontologist Timothy Rowe, a professor at the Jackson School of Geosciences at the University of Texas at Austin. “Sceptics will put everything under the microscope, but I think we’ve checked all the boxes.”
Rowe is the lead author of a study of mammoth bones published last month in the journal Frontiers in Ecology and Evolution.
He said the fractures and tiny splinters of bone caused by the butchering process are also distinctive and seen in similarly aged butcher sites in Europe and Asia: “If this site was in northern Siberia, no one would be blinking.”
The idea that mammoths were butchered by early humans is supported by other recent discoveries, including human footprints in New Mexico’s White Sands National Park and what are said to be stone tools made 33,000 years ago in a cave in the north. from Mexico.
But the idea and the evidence are disputed by other scientists. The dating of the White Sands footprints has been questioned, and some scientists think the objects from Mexico are not tools but naturally sharp rocks.
And they dispute that the fractures in mammoth bones can only have been done by humans; rather, they may have been caused by a landslide or other natural event.
“The fracture patterns in these mammoth bones at that location could definitely be caused by humans,” said anthropologist Andre Costopoulos, a professor at the University of Alberta in Edmonton, who posted a detailed online examination of the latest research. “But they are not necessarily diagnostic of a human presence.”
“We don’t have clear evidence yet, because there are other possible explanations that need to be ruled out first, and they weren’t,” he said.
The absence of distinctive stone tools at the Hartley site is also an issue. The researchers say the people who killed the mammoths may not have used sophisticated stone tools, but only primitive tools indistinguishable from natural bone or rock.
But other scientists say there is no evidence for this, and that even early humans at this point may have better tools.
Archaeologist Ben Potter, formerly at the University of Alaska Fairbanks and now at Liaocheng University in China, said there is evidence from Africa, Europe and the Far East that Homo sapiens used complex stone tools starting around 47,000 years ago, and so its absence from the local Hartley is significant.
He said in an email that he is not convinced by the latest research on mammoth bones and the idea that it shows that people arrived in the Americas a long time ago. “Anything is possible. However, we just have to have evidence to support the claim,” he said. “I don’t think they have enough evidence yet, and certainly not on this site.”
Some other scientists are more convinced, however, and suggest that others may be reluctant to face the possibility that some humans arrived in the Americas 50,000 years ago.
“The research looks very complete,” said Spencer Lucas, curator of paleontology at the New Mexico Museum of Natural History and Science. “When will the archaeological community wake up and smell the coffee? There is so much evidence,” he said.
“I’m not saying this is the final proof… but you have the footprints of White Sands, and the [Mexico] local – there’s all sorts of accumulating evidence that points to human occupation of the New World before 20,000 years ago, and I don’t understand why this idea is even worth discussing.”