New discoveries could rewrite the history of early Americans – and the 4-ton sloths they lived with

Sloths weren’t always furry, slow-moving tree dwellers. Their prehistoric ancestors were enormous – up to 4 tonnes – and when startled, they brandished huge claws.

For a long time, scientists believed that the first humans to arrive in America quickly killed off these giant ground sloths through hunting, along with many other massive animals like mastodonssaber-toothed cats and dire wolves that once roamed North and South America.

But new research from multiple sites is beginning to suggest that people arrived in America earlier — perhaps much earlier — than previously thought. These findings suggest a remarkably different life for these early Americans, in which they may have spent millennia sharing prehistoric savannahs and wetlands with enormous beasts.

“There was this idea that humans came in and killed everything very quickly – what’s called ‘Pleistocene overkill,'” said Daniel Odess, an archaeologist at White Sands National Park in New Mexico. But new discoveries suggest that “humans cohabited with these animals for at least 10,000 years, without making them extinct.”

Some of the most tantalizing clues come from an archaeological site in central Brazil called Santa Elina, where the bones of giant sloths show signs of handling by humans. Such sloths once lived from Alaska to Argentina, and some species had bony structures on their backs called osteoderms – much like the plates of modern armadillos – that could be used to make decorations.

In a laboratory at the University of Sao Paulo, researcher Mírian Pacheco holds a round sloth fossil the size of a dime in her palm. She notes that its surface is surprisingly smooth, that the edges appear to have been deliberately polished, and that there is a small hole near one edge.

“We believe it was intentionally modified and used by ancient people as jewelry or ornament,” she said. Three similar “dangling” fossils are visibly different from the crude osteoderms placed on a table: they have a rough surface and no holes.

These artifacts from Santa Elina are approximately 27,000 years old, more than 10,000 years before scientists thought humans arrived in America.

Initially, researchers wondered whether the artisans were working on already ancient fossils. But Pacheco’s research strongly suggests that ancient people carved “fresh bones” shortly after animals died.

His findings, along with other recent discoveries, could help rewrite the story of how humans arrived in the Americas – and the effect they had on the environment they discovered.

“There is still a big debate,” Pacheco said.

“Really compelling evidence”

Scientists know that the first humans appeared in Africa, then moved to Europe and the Asia-Pacific, before finally heading to the last continental frontier, the Americas. But questions remain about the latest chapter in the story of human origins.

Pacheco learned in high school the theory that most archaeologists supported 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 coincides with the end of the last ice age, a time when an ice-free corridor likely emerged in North America, providing insight into how early humans entered the continent after crossing the bridge Bering land route from Asia.

And because the fossil record shows the widespread decline of American megafauna beginning around the same time – with North America losing 70% of its large mammals and South America more than 80% – many researchers assumed that the arrival of humans led to mass extinctions.

“It was a great story for a while, when all the time was lining up,” said paleoanthropologist Briana Pobiner of the Smithsonian Institution’s Human Origins Program. “But it doesn’t work very well anymore.”

Over the past 30 years, new research methods – including analysis of ancient DNA and new laboratory techniques – coupled with the examination of additional archaeological sites and the inclusion of more diverse scholars across the Americas, have upended the old narrative and raised new questions, particularly about timing. .

“Anything older than 15,000 years is always under scrutiny,” said Richard Fariña, a paleontologist at the University of the Republic of Montevideo, Uruguay. “But really compelling evidence from older and older sites continues to come 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 his team to analyze when the sluggish osteoderms were likely modified.

“We found that the osteoderms were sculpted before the fossilization process” in “fresh bones,” that is, a few days to a few years after the sloths died, but not thousands of years later.

His team also tested and ruled out several natural processes, such as erosion and animal gnawing. The research was published last year in the journal Proceedings of the Royal Society B.

One of his collaborators, paleontologist Thaís Pansani, recently based at the Smithsonian Institution, is analyzing whether the same-aged sloth bones found at Santa Elina were charred by human-caused fires, which burn at temperatures different from those of natural forest fires.

His preliminary results suggest that fresh sloth bones were present at human campsites – it’s not clear whether they were deliberately burned while cooking or simply nearby. It also tests and rules out other possible causes of black marks, such as natural chemical discoloration.

“A giant ground sloth”

The first site widely considered older than Clovis was at Monte Verde, Chile.

Buried beneath a bog, researchers discovered 14,500-year-old stone tools, pieces of preserved animal skins, and various edible and medicinal plants.

“Monte Verde was a shock. You’re here at the end of the world, with all this preserved organic material,” 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.

One of the oldest sites is at Arroyo del Vizcaíno in Uruguay, where researchers are studying apparent human-made “cut marks” on animal bones dating to around 30,000 years ago.

In White Sands, New Mexico, researchers discovered human footprints dating between 21,000 and 23,000 years ago, as well as tracks of giant mammals of the same age. But some archaeologists say it’s hard to imagine humans passing through a site repeatedly without leaving stone tools behind.

“They made a strong case, but there are still some things about this site that puzzle me,” said David Meltzer, an archaeologist at Southern Methodist University. “Why would people leave prints for a long time, but never leave artifacts?”

Odess at White Sands said it expects and welcomes such challenges. “We didn’t set out to find anything older – we just followed the evidence where it led us,” he said.

Although the exact timing of humans’ arrival in America remains controversial – and may never be known – it seems clear that while the first humans arrived earlier than previously thought, they did not immediately decimated the giant beasts they encountered.

And the White Sands footprints preserve a few moments of their first interactions.

According to Odess’s interpretation, a series of tracks shows “a giant ground sloth moving on four legs” when it encounters the footprints of a small human that recently scurried over. The enormous animal “stops and rears up on its hind legs, moves around, then starts off in a different direction.”