Salutations, PauLO Not all sloths were fuzzy, slow-moving creatures that lived in trees. They had enormous claws when they were startled, and their prehistoric ancestors weighed up to four tons.
Along with many other large species that previously roamed North and South America, such as mastodons, saber-toothed cats, and dire wolves, scientists have thought that the first people to arrive in the Americas quickly drove off these huge ground sloths through hunting.
However, recent studies from a number of locations are beginning to imply that humans arrived in the Americas far earlier than previously believed. These discoveries suggest that these early Americans led a very different life, possibly coexisting with massive animals for millennia on prehistoric wetlands and savannas.
According to Daniel Odess, an archaeologist at White Sands National Park in New Mexico, there was a theory that people soon wiped everything out, a phenomenon known as Pleistocene overkill. However, recent findings indicate that humans coexisted with these species for at least 10,000 years without causing their extinction.
The bones of enormous ground sloths at the Santa Elina archaeological site in central Brazil contain some of the most intriguing hints of human manipulation. In the past, sloths like these lived from Alaska to Argentina. Some species had osteoderms, which are bony projections on their backs that resemble the plates of contemporary armadillos and may have been utilized as decorations.
At the University of São Paulo, Brazil, on September 2, 2024, researcher Marian Pacheco holds a round, penny-sized sloth fossil that dates to approximately 27,000 years ago. He notes that, in contrast to most other specimens, the surface is surprisingly smooth, the edges seem to have been purposefully polished, and there is a tiny hole near one edge. (Photo by Christina Larson for AP)
A spherical, penny-sized sloth fossil is held in the palm of researcher Marian Pacheco at a lab at the University of Sao Paulo. She observes that there is a little hole close to one edge, the surface is astonishingly smooth, and the edges seem to have been purposefully polished.
According to her, we think that ancient people purposefully changed it and used it as jewelry or ornament. Unworked osteoderms on a table, which have rough surfaces and no holes, are clearly distinct from three identical pendant fossils.
These Santa Elina artifacts date back to 27,000 years, which is more than 10,000 years before experts previously believed that people had reached the Americas.
At first, scientists questioned whether the artisans were working on fossils that were already quite old. However, it appears from Pacheco’s research that ancient people were carving fresh bones soon after the animals died.
The story of how humans first arrived in the Americas and how they affected the ecosystem they found there may be altered by her findings and other recent discoveries.
According to Pacheco, there is still a lot of disagreement.
Researchers have shared this image of prehistoric artwork at the Santa Elina excavation site in Brazil’s Mato Grosso state. (via AP) Gueda Vilhena Vialou, Denis Vialou
Scientists know that the first humans emerged in Africa, then moved into Europe and Asia-Pacific, before finally making their way to the last continental frontier, the Americas. But questions remain about the final chapter of the human origins story.
Pacheco was taught in high school the theory that most archaeologists held throughout the 20th century. What I learned in school was that Clovis was first, she said.
Clovis is a site in New Mexico, where archaeologists in the 1920s and 1930s found distinctive projectile points and other artifacts dated to between 11,000 and 13,000 years ago.
This date happens to coincide with the end of the last Ice Age, a time when an ice-free corridor likely emerged in North America giving rise to an idea about how early humans moved into the continent after crossing the Bering land bridge from Asia.
And because the fossil record shows the widespread decline of American megafauna starting around the same time with North America losing 70% of its large mammals, and South America losing more than 80% many researchers surmised that humans’ arrival led to mass extinctions.
It was a nice story for a while, when all the timing lined up, said paleoanthropologist Briana Pobiner at the Smithsonian Institution s Human Origins Program. But it doesn t really work so well anymore.
Tha s Pansani holds a giant sloth rib bone from central Brazil dated to about 13,000 to 15,000 years ago, which is thought to be burned by human-made fire, in the Smithsonian’s National Taphonomy Reference Collection in Washington, on July 11, 2024. (AP Photo/Mary Conlon)AP
In the past 30 years, new research methods including ancient DNA analysis and new laboratory techniques coupled with the examination of additional archaeological sites and inclusion of more diverse scholars across the Americas, have upended the old narrative and raised new questions, especially about timing.
Anything older than about 15,000 years still draws intense scrutiny, said Richard Fari a, a paleontologist at the University of the Republic in Montevideo, Uruguay. But really compelling evidence from more and more older sites keeps coming to light.
In Sao Paulo and at the Federal University of Sao Carlos, Pacheco studies the chemical changes that occur when a bone becomes a fossil. This allows her team to analyze when the sloth osteoderms were likely modified.
We found that the osteoderms were carved before the fossilization process in fresh bones meaning anywhere from a few days to a few years after the sloths died, but not thousands of years later.
Her team also tested and ruled out several natural processes, like erosion and animal gnawing. The research was published last year in the journal Proceedings of the Royal Society B.
One of her collaborators, paleontologist Tha s Pansani, recently based at the Smithsonian Institution, is analyzing whether similar-aged sloth bones found at Santa Elina were charred by human-made fires, which burn at different temperatures than natural wildfires.
Her preliminary results suggest that the fresh sloth bones were present at human campsites whether burned deliberately in cooking, or simply nearby, isn t clear. She is also testing and ruling out other possible causes for the black markings, such as natural chemical discoloration.
The first site widely accepted as older than Clovis was in Monte Verde, Chile.
Buried beneath a peat bog, researchers discovered 14,500-year-old stone tools, pieces of preserved animal hides, and various edible and medicinal plants.
Monte Verde was a shock. You re here at the end of the world, with all this organic stuff preserved, said Vanderbilt University archaeologist Tom Dillehay, a longtime researcher at Monte Verde.
Other archaeological sites suggest even earlier dates for human presence in the Americas.
Among the oldest sites is Arroyo del Vizca no in Uruguay, where researchers are studying apparent human-made cut marks on animal bones dated to around 30,000 years ago.
At New Mexico s White Sands, researchers have uncovered human footprints dated to between 21,000 and 23,000 years ago, as well as similar-aged tracks of giant mammals. But some archaeologists say it s hard to imagine that humans would repeatedly traverse a site and leave no stone tools.
They ve made a strong case, but there are still some things about that site that puzzle me, said David Meltzer, an archaeologist at Southern Methodist University. Why would people leave footprints over a long period of time, but never any artifacts?
Odess at White Sands said that he expects and welcomes such challenges. We didn t set out to find the oldest anything we ve really just followed the evidence where it leads, he said.
While the exact timing of humans’ arrival in the Americas remains contested and may never be known it seems clear that if the first people arrived earlier than once thought, they didn t immediately decimate the giant beasts they encountered.
And the White Sands footprints preserve a few moments of their early interactions.
As Odess interprets them, one set of tracks shows a giant ground sloth going along on four feet when it encounters the footprints of a small human who s recently dashed by. The huge animal stops and rears up on hind legs, shuffles around, then heads off in a different direction.
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