The fossilized bones of a giant, extinct armored mammal provide the latest clue about when humans arrived in South America. At the time, in the late Pleistocene, numerous large animals inhabited the harsh, cold landscape, including giant sloths, mastodons, and saber-toothed cats. Humans were well-adapted to drought and resource scarcity, able to move along dry riverbeds in search of pools and the prey that grazed around them. The authors call this a “blue highway” that operated during the harshest periods.
Scientists have long debated when humans first set foot on the South American continent because “the evidence is so thin,” says Miguel Delgado, an archaeologist at the National University of La Plata in Argentina. For a while, he says, that suggested a time around 13,000 years ago — but a slow accumulation of research is pushing that date back further.
Now, in a study published in PLOS One, Delgado and his colleagues have used new fossil fragments of an armored glyptodont to support other work that places humans in South America at least 21,000 years ago. That was during the late Pleistocene, when they would have had to navigate a planet in a rapidly changing climate.
The Last Glacial Maximum occurred about 20,000 years ago, after which glaciers began to retreat around the world, including in southern South America. If humans were present on the continent then, says Alia Lesnek, a geologist at CUNY Queens College who was not involved in the study, “that could tell us about a really long history around climate change” and their resilience in the face of it.
“For me,” she says, “it opens up a lot of new questions about the relationship between how people traveled, their migration routes and their settlement patterns, and how that relates to glaciers and climate change.”
The Reconquista River runs through the western outskirts of Buenos Aires, Argentina. In 2016, a bulldozer dug up the riverbank to widen the channel. Shortly after the work was completed, Guillermo Jofre, a paleontologist at the Repositorio Paleontológico Ramón Segura, went for a walk there.
That’s when he stumbled upon a handful of exposed fossil bones that belonged to an ancient armadillo-like mammal called a glyptodont. “This animal was heavily armored,” Delgado says. “They had big tails and short limbs.”
Glyptodonts were giant, armadillo-like, shell-covered mammals that went extinct about 10,000 years ago. The study suggests that notches on a glyptodont fossil in South America may have been made by humans just over 20,000 years ago. Daniel Eskridge/Stocktrek Images/Science Source
Finding these bones was a happy accident, because when Joffrey looked closely, he saw something unexpected: small marks on the bones. These marks could have been left on the bones by rocks or other bones that scraped them, or by rodents or carnivores that bit or scratched them, or perhaps by prehistoric people who did something to them.
To find out, Delgado and his colleagues excavated the site and found a variety of fossilized glyptodont bones, including fragments of the hard outer shell, tail, vertebrae, and pelvis.
Back in the lab, they analyzed the samples, looking at them under a microscope, analyzing the chemistry of the sediments, and taking detailed measurements of the cut marks, rendering them as 3D models. The results were unmistakable, Delgado says.
“We realized,” he says, “that the shape of these marks was very similar to cuts made experimentally by humans.” In other words, Delgado believes that the V-shaped cuts were made when the animal was butchered with stone tools by ancient humans.
“The most important piece of evidence is the placement of the marks themselves,” he says, “in the areas of the bone where the flesh is denser.” These are areas of concentrated meat, the places where people would want to cut up and eat the animal. “So it shows us a logical sequence of butchering.”
This isn’t the first glyptodont fossil to be found with these markings, but it’s certainly one of the oldest. When the team dated the fossils, they found that the animal lived about 21,000 years ago.
This means that if humans were responsible for the cuts, they must have been present at the time. “So this is one of the oldest pieces of evidence of human presence here in South America,” Delgado says.
At the time, the late Pleistocene, numerous large animals inhabited the harsh, cold landscape, including giant sloths, mastodons, and saber-toothed cats (all of which shared the Earth with humans until about 10,000 years ago). Delgado says prehistoric humans living then may have contributed to the extinction of these species. And dramatic changes in the environment as glaciers retreated did not prevent the animals from going extinct.
“I think it’s a really exciting step forward,” Lesneck says. “But I think there’s a little more work that needs to be done to fully confirm the conclusions that they’re making — because they’re really bold conclusions — to make sure that, yes, it was humans and not some other process that created the cuts.”
She says future work should focus on additional dating to “solidify” the age estimates of the fossils and looking for human artifacts along the riverbank. “Find things like stone flakes or charcoal,” she says. “Really unambiguous indications of human presence, in addition to cut marks.” (Delgado agrees with that assessment and is already planning further analysis and excavations with his colleagues.)
Scientists from the USA and Ethiopia have studied a Homo sapiens site in East Africa. And they have made a number of significant discoveries that could change our understanding of the ancient history of Homo sapiens. In 2002, during a survey of the tributaries of the Blue Nile in northwestern Ethiopia, scientists discovered an archaeological site that was designated Shinfa-Metema-1, after the name of the river on whose ancient terrace the site is located.
Excavations have shown that humans lived here for a very long time during the Middle Paleolithic (74,000 years ago), leaving behind layers of tens of thousands of stone flakes and plates, as well as huge quantities of animal and fish bones with signs of butchering.
Ancient craftsmen processed basalts, slates, quartz, chalcedony, cutting off the excess and obtaining symmetrical pointed tools. The nature of the damage suggests that these were penetrating weapons – most likely arrowheads.
This is an amazing discovery, since the first convincing evidence of the use of onions appears twenty thousand years later, in France (Mandrin Cave, 54 thousand years old).
Similar points have been found in Africa before, but they were thought to be parts of darts or spears. Now the birthplace of archery may have to be reconsidered.
Blue Nile Survey Project. Stone tools found at Shinfa Metema 1. Scientists believe they are arrowheads.
The inhabitants of Shinfa-Metema-1 ate a varied diet. They hunted mainly small ungulates, less often warthogs and giraffes. Also on the menu were monkeys, guinea fowl, rodents, rabbits, small birds, snakes, lizards and frogs. They got ostrich eggs and, judging by the burnt shells, cooked them over a fire. At some point, the meat diet was replaced by a fish diet – many catfish bones and mollusk shells were found in the sediments. Scientists wondered what prompted people to adjust their diet.
Now Shinfa and other tributaries of the Blue Nile are seasonal, that is, full-flowing only during the rains. The rest of the time they dry up, leaving only small puddles and oxbow lakes. Weather fluctuations affect the structure of the teeth of animals drinking from these bodies of water. For example, if the air is dry, the content of the heavy isotope oxygen-18 in the enamel increases.
topographic-map.com Open Database License (ODbL) v1.0. Shinfa-Metema-1 Archaeological Site in Ethiopia
This helped to find out that the climate was dry at that time. When the main riverbed dried up, people looked for small lakes and backwaters. Animals came to the watering place – there they were probably shot with a bow. Fish were caught by hand in small bodies of water, as local residents still do.
To clarify the age of the site, they turned to cryptotephra. This is a set of methods that allow for precise dating of deposits if they contain eruption products. At Shinfa-Metema-1, scientists discovered microscopic inclusions of volcanic glass. Analysis of the chemical composition showed that these droplets were from the Toba supervolcano, located on the island of Sumatra. Apparently, they got here by air during the largest eruption, which occurred 74 thousand years ago.
Racheal Johnsen. Volcanic glass fragment from the Toba eruption at Shinfa-Metema-1
The volcano then ejected a huge amount of ash and greenhouse gases into the atmosphere. Some scientists believe that the ancient cataclysm led to a “volcanic winter” that could have brought humanity to the brink of extinction. In search of food, people left Africa and spread across the planet.
It is unclear whether the inhabitants of Shinfa-Metema-1 could be our ancestors. Scientists from the US and Ethiopia, led by John Kappelman, doubt it. Their article with the results of many years of research was recently published in Nature. Most likely, the exodus to Eurasia was later carried out by another group of Homo sapiens. However, the site shows how this could have happened.
Traditionally, it has been thought that people migrated from Africa during favorable periods of moisture, when rivers flowed and food could be found in the desert. It is now clear that this was not necessarily the case.
Blue Nile Survey Project. Excavations at Shinfa-Metema-1
Humans adapted well to drought and resource scarcity, and could move along dry riverbeds in search of puddles and the prey grazing around them. The authors call this a “blue highway,” which operated during the harshest periods.
The constant pressure of the environment made people more flexible, encouraged them to look for new habitats and thus launched the process of exploration of Eurasia. But new discoveries are needed to support the idea of the “blue highway”.