Of all the long-running disputes in archaeology, few roil scholars
more than the question of when humans arrived in the Americas. For much of the
past century, the reigning theory was that in or around 11,500 years ago
big-game hunters from Asia trudged to North America across a land bridge
spanning the Bering Strait, hung a right through a corridor between glaciers
and, in less than a millennium, reached the tip of South America.
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Over the past three decades, however, archaeological research
has made it increasingly clear that the 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 upended even those migration
timelines by proposing that what is now central-west 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
around 11,700 years ago. The period is also called the ice age because of its
numerous cycles of glacial formation and melting.
The conclusions of the paper, published in the journal
Proceedings of the Royal Society B, are based on an analysis of an improbable
source: three bones from an extinct giant ground sloth. Excavated 28 years ago
in the Santa Elina rock shelter, the fossils — similar to the hard, scaly
plates, called osteoderms, that armor the skin of present-day armadillos —
showed signs of having been modified into primordial pendants, with notches and
holes that researchers said could only have been created by people.
“This is a really significant study because it adds to a growing
body of data on the antiquity of 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 ornaments.”
The giant ground sloth first appeared in South America 35
million years ago. Some species were as hefty as modern elephants and, rearing
up on their hind legs, stood more than 10 feet tall. The hulking herbivore, a
distant relative of today’s much smaller tree sloth, had massive jaws and
powerful clawed limbs, and it may have served as inspiration for the
mapinguari, a mythical beast that, in Amazonian legend, had the nasty habit of
twisting off the heads of humans and devouring them. The giant sloth
disappeared from the continent some 11,000 years ago, but fossil remains
abound.
Three dating methods, applied to three layers of sediment,
osteoderms and charcoal particles at Santa Elina, indicated that humans first
left a mark on the oldest and deepest layer around 27,000 to 23,000 years ago.
Since then, people have occupied the shelter at different times: from 17,000 to
13,000 years ago in the middle layer and after 6,000 years ago in the top
layer, researchers say. “The big question is, were those artifacts made by
humans during their coexistence with the 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 peculiar sloth
bones found in the deepest layer appeared to have been smoothed and perforated.
“Complete or partial holes were clearly drilled near the edges, as if they had
been designed to be threaded on a string,” Pacheco said.
Microscopic markings suggested that the osteoderms, and even
their holes, had been buffed 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 first 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 had died,
but before the bones had fossilized.
“In our view, the early humans who lived in the shelter
fashioned the bones into personal ornaments, possibly pendants, that over time
became worn from heavy use,” Pansani said. This would make them the oldest
known jewelry unearthed in the Americas and the only trinkets in the
archaeological record known to have been made from giant sloth bone.
“The authors show very compelling evidence for an anthropogenic
modification of the sloth bones,” said Mercedes Okumura, an archaeologist at
the University of São Paulo. “Such a study can help to shed light on the use of
adornments by the early Americans, as well as about the interaction between
past humans and megafauna in the Americas.”
For thousands of years, Nowell noted, the human body has been a
site for the creation and expression of individual and group identity, and
relics such as giant sloth baubles play a vital role in that process. “I love
the fact that these beads are heavily worn from being strung or from rubbing
against the skin, cloth or other beads,” she said. “That speaks to the value of
these objects; it suggests they were worn for a long time.”
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