Early humans living in South America carved giant sloth bones into decorative ornaments that may have been worn as jewellery. The discovery also provides new evidence that people arrived in central Brazil during or before the end of the last ice age.
Giant sloths larger than polar bears and armoured with bony plates once roamed South America during the Pleistocene Epoch, also called the ice age. Climate warming and hunting by people drove the ground-dwelling sloths to extinction around 10,000 years ago, and some of their remains are preserved in cave shelters inhabited by people, including the Santa Elina rock shelter in Brazil.
Though giant sloth skeletons are largely degraded, thousands of their fossilised bony dermal plates, called osteoderms, are preserved as fossils. Three of these scale-like bones, which are between 16,000 and 27,000 years old, have intrigued scientists for decades because of their unusual shape and smooth texture. The bones had complete or partial holes drilled near the border as if to be threaded on a string.
Archaeologists had speculated that the giant sloth bones were modified by humans using stone tools, says Mírian Pacheco at the Federal University of São Carlos in Brazil, “but the great question is, were those artefacts made by humans during the coexistence of humans and [giants sloths]?”
To find out, Pacheco and her colleagues examined the bones using high-resolution microscopes and x-rays. Their analysis revealed scratches going in different directions and repeated gouges made by early stone tools. The bones’ shape and texture couldn’t be explained by natural erosion or animal bites.
The bones were shaped before being fossilised, suggesting humans arrived in the Americas before the end of the ice age. “It’s really exciting to have this window into how people in the past were engaging with these species that we don’t have around anymore,” says Alexis Mychajliw at Middlebury College in Vermont, who was not involved in the work.
The smoothness of the bones suggests repeated friction, possibly from being worn daily as a personal adornment. If so, this is among the earliest evidence of personal artefacts in the Americas, but more research is needed to determine their significance.
“It would be interesting to see if they [used these bones] for decoration, for fashion, or to show that they were from a specific group,” says Thaís Pansani, part of the team. “But we definitely know that they were using them.”