Of all the longstanding controversies in archaeology, few scholars pull more than the question of when humans arrived in the Americas. For much of the last century, the prevailing theory was that about 11,500 years ago big-game hunters from Asia trudged to North America across a land bridge that spanned the Bering Strait, wandered right through a corridor between glaciers and, in less than a millennium, reached the tip of South America.
Over the past three decades, however, archaeological research has made it increasingly clear that hunters were preceded by much earlier cultures that colonized the Americas between 24,500 and 16,000 years ago.
This week a new academic study he upended those migration timings as well by proposing that what is now west-central Brazil was settled as early as 27,000 years ago, a finding that bolsters the theory that our ancestors inhabited the continent during the Pleistocene epoch, which ended about 11,700 Years ago. The period is also called the Ice Age due to its many cycles of glacial formation and melting.
The conclusions of the article, published in the journal Proceedings of the Royal Society B, are based on an analysis of an unlikely source: three bones of an extinct giant sloth. Excavated 28 years ago in the Santa Elina rock shelter, the fossils — similar to the hard, scaly plates called osteoderms that line the skin of modern armadillos — showed signs of having modified into primordial pendants, with notches and holes that the researchers said that could only have been created by people.
“This is a really significant study because it adds to a growing body of data on early human occupation in the Americas,” said April Nowell, a paleolithic archaeologist at the University of Victoria who was not involved in the project. “It also shows the importance of personal adornment.”
The giant ground sloth first appeared in South America 35 million years ago. Some species were as heavy as modern elephants and, rearing up on their hind legs, stood over 10 feet tall. The enormous herbivore, a distant relative of today’s much smaller tree sloth, had massive jaws and powerful clawed limbs, and may have served as the inspiration for the mapinguari, a mythical beast that, in Amazonian legend, had a nasty habit of tearing apart the heads of men and devouring them. The giant sloth disappeared from the continent about 11,000 years ago, but fossil remains abound.
Three dating methods, applied to three layers of sediments, osteoderms and carbon particles at Santa Elina, indicated that humans first made their mark on the oldest, deepest layer between 27,000 and 23,000 years ago. Since then, people have occupied the refuge at different times: 17,000 to 13,000 years ago in the middle layer and after 6,000 years ago in the upper layer, the researchers say. “The big question is: Were those artifacts made by humans during their coexistence with sloths?” said Mirian Liza Alves Forancelli Pacheco, an author of the study and an archaeologist at the Federal University of São Carlos in Brazil.
Shaped like triangles and teardrops, the three distinctive sloth bones found in the deepest layer appeared to have been smoothed and drilled. “The full or partial holes were clearly drilled near the edges, as if they were designed to be threaded through a string,” Dr. Pacheco said.
Microscopic signs suggested that the osteoderms, and even their holes, had been smoothed out by human hands. Neither natural abrasion nor animal bites could explain their texture and shape, said Thais Rabito Pansani, a paleontologist at the Federal University of São Carlos and lead author of the paper. Further analysis revealed scratches going in different directions and stone tool gouges made a few days to a few years after the sloths died, but before the bones had fossilized.
“In our view, the early humans who lived in the shelter fashioned the bones into personal ornaments, perhaps pendants, that wore away over time from heavy use,” said Dr. Pansani. This would make them the oldest known unearthed jewelry in the Americas and the only trinkets in the archaeological record known to have been made from a giant sloth bone.
“The authors show very convincing evidence of anthropogenic modification of sloth bones,” said Mercedes Okumura, an archaeologist at the University of São Paulo. “Such a study may help shed light on early Americans’ use of ornamentation, as well as the interaction between past humans and megafauna in the Americas.”
For thousands of years, Dr. Nowell noted, the human body has been a place for the creation and expression of individual and group identity, and relics such as giant sloth trinkets play a vital role in this process. “I love that these beads are heavily worn from being strung on or rubbing against skin, fabric, or other beads,” he said. “This speaks to the value of these objects; suggests that they have been worn for a long time.