This illustration provided by researchers depicts a person carving an osteoderm from a giant sloth in Brazil about 25,000 to 27,000 years ago.
Credit: Júlia d'Oliveira via AP
Sloths weren't always slow-moving, furry tree-dwellers. Their prehistoric ancestors were huge—up to 4 tons (3.6 metric tons)—and when startled, they brandished immense claws.
For a long time, scientists believed the first humans to arrive in the Americas soon killed off these giant ground sloths through hunting, along with many other massive animals like mastodons, saber-toothed cats and dire wolves that once roamed North and South America.
But new research from several sites is starting to suggest that people came to the Americas earlier—perhaps far earlier—than once thought. These findings hint at a remarkably different life for these early Americans, one in which they may have spent millennia sharing prehistoric savannas and wetlands with enormous beasts.
"There was this idea that humans arrived and killed everything off 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 were existing alongside these animals for at least 10,000 years, without making them go extinct."
Some of the most tantalizing clues come from an archaeological site in central Brazil, called Santa Elina, where bones of giant ground sloths show signs of being manipulated by humans. Sloths like these once lived from Alaska to Argentina, and some species had bony structures on their backs, called osteoderms—a bit like the plates of modern armadillos—that may have been used to make decorations.
Credit: Martín Batallés via
In a lab at the University of Sao Paulo, researcher Mírian Pacheco holds in her palm a round, penny-sized sloth fossil. She notes that its surface is surprisingly smooth, the edges appear to have been deliberately polished, and there's a tiny hole near one edge.
"We believe it was intentionally altered and used by ancient people as jewelry or adornment," she said. Three similar "pendant" fossils are visibly different from unworked osteoderms on a table—those are rough-surfaced and without any holes.
These artifacts from Santa Elina are roughly 27,000 years old—more than 10,000 years before scientists once thought that humans arrived in the Americas.
Originally researchers wondered if the craftsmen were working on already old fossils. But Pacheco's research strongly suggests that ancient people were carving "fresh bones" shortly after the animals died.
In a lab at the University of Sao Paulo, researcher Mírian Pacheco holds in her palm a round, penny-sized sloth fossil. She notes that its surface is surprisingly smooth, the edges appear to have been deliberately polished, and there's a tiny hole near one edge.
"We believe it was intentionally altered and used by ancient people as jewelry or adornment," she said. Three similar "pendant" fossils are visibly different from unworked osteoderms on a table—those are rough-surfaced and without any holes.
These artifacts from Santa Elina are roughly 27,000 years old—more than 10,000 years before scientists once thought that humans arrived in the Americas.
Originally researchers wondered if the craftsmen were working on already old fossils. But Pacheco's research strongly suggests that ancient people were carving "fresh bones" shortly after the animals died.
Credit: AP Photo/Mary Conlon
Her findings, together with other recent discoveries, could help rewrite the tale of when humans first arrived in the Americas—and the effect they had on the environment they found.
"There's still a big debate," Pacheco said.
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.
Her findings, together with other recent discoveries, could help rewrite the tale of when humans first arrived in the Americas—and the effect they had on the environment they found.
"There's still a big debate," Pacheco said.
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.
Credit: Águeda Vilhena Vialou, Denis Vialou via AP
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.
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.
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