National Geographic News
Photo of a giant sloth bone.

A giant sloth bone might hold the key to the peopling of the Americas.

Photograph by Martin Batalles

Map of Uruguay Arroyo by NGM Maps.

Helen Thompson

for National Geographic

Published November 20, 2013

When did people get to the Americas? The answer remains a subject of fiery debate.

Most scientists agree that humans began arriving in the Americas between 13,000 and 15,000 years ago, and the Clovis people of North and Central America are generally considered the "first Americans."

But new fossil evidence from a streambed in southern Uruguay could challenge such theories.

Results published November 19 in Proceedings of the Royal Society B suggest the presence at the site of human hunters who may have killed giant sloths and other megafauna. That itself isn't odd, but the site, called Arroyo del Vizcaíno, has been radiocarbon dated to between 29,000 and 30,000 years old—thousands of years before people were thought to be there. (Also see "Photos: Speared Mastodon Bone Hints at Earlier Americans.")

"That's pretty old for a site that has evidence of human presence, particularly in South America," said study co-author Richard Fariña, a paleontologist at Uruguay's Universidad de la República.

"So, it's strange and unexpected."

What's the controversy?

Giant sloths, saber-toothed cats, oversize armadillos, and other large mammals once roamed the Americas—a diversity that would easily rival an African savannah today. (Watch a saber-toothed cat video.)

But by 11,000 years ago, many of the species had disappeared, likely due to climate change or the arrival of human hunters in the New World. But when exactly humans got here, and how they arrived, remains unknown.

What's new?

In 1997, severe drought forced local farmers to drain a lagoon in Arroyo del Vizcaíno, which exposed a mysterious bed of gigantic bones.

After a series of bureaucratic roadblocks, paleontologists excavated the site in 2011 and 2012, unearthing over a thousand fossils. "From the paleontological point of view, that is absolutely marvelous in itself," Fariña said.

Many of the bones belong to three extinct ground sloth species, mainly Lestodon armatus. Weighing in at up to four tons, the animals "were the size of smallish elephants," he said.

Photo of dig site where sloth bones were found.
Photograph by Martin Batalles
The giant sloth bones were uncovered at a dig site dated at 29,000 to 30,000 years old.

Fossils from other common South American megafauna turned up in the mud as well: three species of glyptodonts, or armadillo ancestors; a hippo-like animal called a toxodon, which has no living relatives; a South American saber-toothed cat (Smilodon populator); and an elephant-like stegomastodon, among others. (Learn more about extinct animals that could possibly be revived.)

Some of the bones bear telltale markings of human tools, which suggests the animals were hunted for food. The team also found a potentially human-made scraper that could have been used on dry animal hides, and stone flakes.

Why is it important?

Clues from the site point to a human presence at Arroyo del Vizcaíno much earlier than accepted theories of migration. Fariña and his team are both excited and cautious about their results.

Fariña said the strength of the new evidence lies in the team's methodology and the fact that two of the bones they tested for dating also bore markings similar to those made by human tools. "The association can't be closer than it is," he said.

The date of Arroyo del Vizcaíno may make some archaeologists cringe: South America's earliest human settlement at Monte Verde in Chile dates to only 14,000 years ago. (Also see "Clovis People Not First Americans, Study Shows.")

What does this mean?

The study certainly does not prove definitively that humans were killing giant sloths 30,000 years ago in South America.

The fossils found at Arroyo del Vizcaíno might simply be a product of nature mimicking human tools, and the authors acknowledge that possibility.

"South America played an exceptionally important role in the peopling of the Americas, and I'm pretty sure we have some significant surprises waiting for us," Bonnie Pitblado, an archaeologist at the University of Oklahoma who was not associated with the study, said in an email. (Read a National Geographic magazine story on the peopling of the Americas.)

"Maybe people killing sloths at [the Arroyo del Vizcaíno site] 30,000 years ago is one of them, maybe it's not—but it certainly isn't going to hurt to have it on our collective radar screen as we continue to contemplate the peopling of the New World."

What's next?

The Uruguayan team has further excavations and environmental reconstruction studies planned for the site.

Fariña estimates that it could yield a thousand more bones, and they plan to build a local museum to house the site's many fossils.

29 comments
Edward Williams
Edward Williams

It is reassuring that the authors are not rushing to make exaggerated claims; as they point out there could be a natural origin for the marks (teeth or claw marks of a predator, for example) or for some reason the C14 dates could be uncertain.  Examination of Ice Age drowned sites along the Pacific coast of N and S America (technically possible but extremely costly) could help considerably in determining how early homo sapiens reached the new world.

Brian M.
Brian M.

I am not the first to say it, but it definitely applies to this discovery:


If EVERYONE KNOWS there were no humans in America before 12,000 ago, archeologists just don't waste their time looking for evidence of humans in geological strata older than 12000 years. And we seldom find what we are not looking for if we're certain it does not exist, even when we find it.

So with this evidence out there, many archeologists will now look more closely in areas once thought a waste of time. And more than a bit of that looking will be at materials excavated at sites previously examined which included anomalous data.

It will be very interesting to see what comes of that scrutiny.

Stephen Mumford
Stephen Mumford

This is remarkable, but readers should take it with a grain of salt! It more than doubles what the current evidence says abount how long humans have lived in the Americas. In science, such outlier finds happen regularly, and are often never backed up with further finds or evidence and eventually get relegated to accidental causes. One should remain skeptical, although open-minded. Even the investigators admit that they cannot rule out that the marks in question might be naturally occurring.

That said, it's certainly not impossible that this find could lead to others that open up the field to a radical new view of Pleistocene human habitation of the Americas.

Michael Shea
Michael Shea

lower right corner of bone is a animal head map  , carved into it.

Patrick Conley
Patrick Conley


did giant sloths evolve into today's couch potatos? 

Cristina Caporale
Cristina Caporale

IT´s really amazing!! These tool marks in animal bones show lots of our conjetures. I agree with you like an studient of antropology. I´ve always though people had been here more years ago. Cientist that are mindclose will ask themselves¿and this? ¡oh god! ¿Where is Uruguay? They try to don´t respet us. ARRIBA URUGUAY Y SUS PROFES, ESTUDIANTES, Y QUE CON  POCOS RECURSOS AÚN PODEMOS!!!!

CLINTON A.
CLINTON A.

Poorly worded title. I thought that giant sloths were killing people.

Tom Carberry
Tom Carberry

Archaeology and anthropology, much like astronomy, assume a steady state progression of human evolution.  But the evidence doesn't back up this view.

For the last 100,000 years or so, the earth has gone through various stages of a massive ice age.  Giant sheets of ice covered much of the northern hemisphere.  

These sheets of ice destroyed anything they slid over, so if human habitations existed before the ice sheets came, we will never know.

I believe the earth has suffered massive world wide catastrophes within living human memory and that most of the catastrophes came from space.

Much of human mythology supports this view.  Hittite and Greek mythology (Greeks took a lot from the Hittites) talk about wars between the gods and these people identified the planets as the gods.

When they talk about Venus arising out of the shoulder of Zeus, most historians and scholars take that metaphorically.  Or when Hesiod talks of the earth running molten, people accept it as part of a story, but not as a description of an historical event.

Our ancestors should have had better technology and societies than we have, because they had much bigger brains and bodies than we have.  Yes, the human brain on average has shrunk well over 10% since the dawn of agriculture.  And human bodies have shrunk even more, although in industrial societies people have started to re-coup body size (not just in obesity, but in height).  

People should all look like NBA players, not like knights in dwarf armor (go to Germany and look at the suits of armor for the tiny sociopaths who ruled back then).  

Unfortunately, most people still eat terrible diets based on survival foods from long ago disasters, rather than reverting back to today's readily available healthier foods.

M. Waters
M. Waters

We often dismiss the myths and legends of indigenous people, who claim they have been there since the beginning.  I hope scientists are big enough to put aside their enormous ego's and take a serious look at these findings.  This is not the only site that appears to show humans were in the America's 30-40 thousand years ago.  There is a dig in Colorado that appears to show meat caching and tool marks on animal bones!

Edward Ogle
Edward Ogle

It’s an excellent and exciting speculation, we now know that there were cities in Europe/Asia that have been aged to 30,000 years.  These cities were discovered but recently, and it seems to prove there is much we still don’t know about the ability of our ancestors.It is fact that many established “experts” have always resisted, some adamantly, new claims or discoveries.Should I live so long, I look forward to learning this to be fact since it has been my belief for decades.  They had the same brain they we have today, and even though some people today don’t always use that gift is not relevant.

Kevin S.
Kevin S.

This is amazing! Quite fascinating

Juan Bergamin
Juan Bergamin

Felicitaciones a Fariña y su equipo por su maravilloso trabajo! 

craig hill
craig hill

The land bridge itself has been proven by, of all people, the descendants of Indians themselves, who detail in their stories handed down how their ancestors arrived by boat. When you think it through, boat makes much more sense than land bridge as vehicle.

There is also a cave in Brazil with human bones of Africans long predating Asian settlements. CLEARLY peoples from all directions, like the Vikings, were on the water and either caught in currents or intentionally acted as their own Columbus. As the Viking settlements and DNA shows, all non-Asian explorer/immigrants died out  (This is not rocket surgery.) The groups that stayed for good came in large numbers, by boat, down the Pacific coast, from Asia, preceding the next large wave from Europe, the destroyers, by 15-20,000 years.  

Rodney Harrison
Rodney Harrison

Watched a show on history or discovery some time ago where cave drawings in South America were alleged to show humans slaughtering humans, rather than hunting animals. DNA of a very few  surviving individuals indicated Aboriginal origins, predating the last ice age, of the first humans in South America, who were later wiped out by the humans crossing the ice bridge and into Central and South America. Their timeline seems to agree with these findings, insofar as human presence in the area is concerned.

stan moeller
stan moeller

Does this 30,000 year old find help support the theory the Americas were first reached by boat or raft, rather than a land bridge from Siberia?

Nikolaos George Pargas
Nikolaos George Pargas

@Tom Carberry I agree with much of what you say, however, in spite of your good intentions, the point should be stressed that one should be more regardful before, unthankfully, demotes a superordinate civilization, like the Greek, to apism, merely to be led by unremarkable cultures.

The Greek civilization exhibited all the elements a true civilization ought to exhibit and more. This was well understood by the emerging Europeans when they, conscientiously, envisaged all Hellenism in its splendour, so much so, that they were stunned by it, at the beginning and they thought it to be exogenetic .

As for the human brain, it is my opinion that, nowadays, it is not brains we lack - on the contrary - but the ability to properly analyze what we, so smartly, discover, losing, altogether, that which should, naturally, follow next: WISDOM.

For the reasons above and for the reasons our Intelligentsia, securely, hold as conclusive - and not as an anagogy in Truth - I express my concern for the total human progress, for, before one should, readily, accept in faith, one should first, eagerly, prove in reason and reconsider, at length, his habitual mode of regarding other theories, unfairly, sometimes, as being in the sphere of pseudology, as a possible object of knowledge, at least, otherwise he condemns to default, by chance-medley, these things which might add, decisively, to what's missing from the true picture of our past, including the theories about the prehistoric habitation of the Americas, which, to the minds of our Brilliants, the obvious did not occur, that is, that these battered lands, were ALWAYS peopled by the same processes that peopled the rest of the world.

When, soon, finally, the whole Earth story emerges, in front of a staggered world, most of our scientists will rush to malign it, while a few, with, still, some form of dignity cowering inside them, will perpetrate intellectual self-murder for being so, persistently, obtuse, in the hour of their triumph.

Vladimir Garcia
Vladimir Garcia

@Tom Carberry Tom you have no idea what your talking about. First you state "they had much bigger brains and bodies than we have". False bigger brain does not mean high intelligence, and bigger body does not mean more likely to survive. Second you state "I believe the earth has suffered massive world wide catastrophes within living human memory and that most of the catastrophes came from space". MOST CATASTROSPHES DID NOT CAME FROM SPACE.

Lauren Dawson
Lauren Dawson

@Tom Carberry I have to agree with @Efren Matrtinez. You very clearly have little understanding, if any at all, of anthropology, archaeology, palaeontology, geography, etc. The list goes on. 

Sincerely, 

An Anthropologist

Efren Martinez
Efren Martinez

@Tom Carberry  Wow, your post contributes nothing to the article.  It is clear you have no clear understanding of anthropology or archaeology and most, if not everything, of what you say is pure conjecture.  

Nikolaos George Pargas
Nikolaos George Pargas

@M. Waters Righting the misaffections of our well-concerted errorists of science, is a task worth taking, at last.

Your view holds uncontested truth.

In fact, the American continent is the site of a megacosmic destruction, inflicted with unproportionable and irrevocable misfortune,  swept all past evidence, ominously dragging the rest of the world under

- a world edging its future prospect with imminent catastrophe.

Ken Truitt
Ken Truitt

@craig hill 

"This is not rocket surgery"

 That statement is meaningless.  You can get a rocket surgery degree in two years from my local community college.

terry wofford
terry wofford

@craig hill Many tribes histories say they came from the east, not west, so your statement is wrong

Sean Carlisle
Sean Carlisle

@craig hill

"The land bridge itself has been proven by, of all people, the descendants of Indians themselves, who detail in their stories handed down how their ancestors arrived by boat."

This statement doesn't make any sense. How does their oral tradition, telling of travel by boat, prove the existence of the land bridge?


Keenan Sutherland
Keenan Sutherland

@stan moeller yes a find like this would give more support to that theory, although a journey across an open ocean is extremely hard to track archaeologically. Unless someone finds a totally isolated 30,000 year old site on a tiny South Pacific island somewhere..

The method of colonization could also have been in small boats along the ice bridge in the North, rather than across open ocean. So rather than walking across an unfrozen land bridge, it seems plausible that people may have been travelling by boat along the coast of what would become an eventual land bridge. 

Bruce Parsons
Bruce Parsons

@Sean Carlisle @craig hill Well for example the Maori of New Zealand claim they settled the island with about 400 people, and genetic studies support this.  This is just one well documented case where the stories of aboriginal have been borne out by science.  It gives credence to all such stories.  Try to remember that these people had to be very smart to have survived this, so why doubt their intelligence cd also preserve such ancestral knowledge

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