The mysterious tunnels dug by giant sloths – 12/02/2023 – Science

In 2009, a farmer was driving his tractor through his corn field in southern Brazil when he felt the vehicle suddenly sink into the ground and tilt to one side.

The tractor shuddered to a stop. The farmer got out and saw that the wheel had sunk deep into the dry ground.

Much to his surprise, the tractor had broken down over what appeared to be the top of an underground cavity.

Researchers soon learned about this unusual discovery and went to the farm to investigate what happened. They were surprised to discover a tunnel about 2 meters high, almost 2 meters wide and about 15 meters long, which crossed the land, passing directly under the farmer’s house.

And there was more: deep claw marks on the walls of the tunnel indicated that its last inhabitants were not human beings.

The farmer had come across an intriguing topic in paleontology, still in development. He discovered a paleoburrow – a prehistoric tunnel excavated in the rock by giant animals.

Geologist Luiz Carlos Weinschutz, one of the scientists who visited the farm, concluded that the tunnel was the work of a giant sloth, or a giant armadillo, excavated at least 10,000 years ago.

One scientific study described giant ground sloths as “elephant-sized hamsters,” a far cry from the slow-moving sloths that live in trees today.

They grew up to four meters in length and walked on all fours, although research indicates that some were able to stand and walk like bipeds.

Almost 100 different species of sloths populated the American continent between 10,000 and 15 million years ago, alongside car-sized giant armadillos that also excavated long tunnels through the rocks of Brazil.

I first heard about paleoburrows in 2015, when the press reported the discovery of a 100-meter-long tunnel, excavated by giant sloths in the state of Rondônia. It was the first paleoburrow found in the Amazon region.

But it was on vacation that I spent years ago, in the South and Southeast of Brazil, that I had the chance to visit a paleotoca in person.

During the trip, I visited the Caminhos dos Cânions do Sul Geopark, between the states of Santa Catarina and Rio Grande do Sul. The park is home to several paleo caves.

After an hour of walking through a forest-covered canyon in Santa Catarina, I reached my destination – a two-meter-high tunnel excavated in a large weathered rock.

Its interior was cold and dark. Their curved surfaces have been roughened by the hairs of giant sloths rubbing against them over thousands of years.

Unmistakable marks of long claws scratch the walls. It feels like I’m going down a giant rabbit hole.

Heinrich Theodor Frank, a geologist by profession and expert on paleoburrows at heart, states that when you enter one of these tunnels, “you find an open book. You look, you feel that this was not done by human beings.” He’s right.

Discovery and preservation

Today, most paleoburrows are filled with sediment, but some have remained clean, in whole or in part, like the one I visited and the tunnel the farmer found in the corn field.

The 2009 discovery came as interest in paleoburrows began to grow, after hundreds of them were identified in the South and Southeast of Brazil.

In the last 15 years, more than 1,500 paleoburrows have been found in the region, which is now recognized as having the largest concentration of paleoburrows built by giant animals in the world.

No one knows for sure why there are so many paleoburrows in the South and Southeast of Brazil. The majority are in Santa Catarina and Rio Grande do Sul, but there are notable examples also in Minas Gerais, such as a group of six tunnels 40 meters long that lead to chambers 10 meters wide and 4 meters high.

And, in June this year, the Minas Gerais court ordered the protection against human activity of a 340-meter-long paleo cave in Serra do Gandarela (metropolitan region of Belo Horizonte). It is the largest paleoburrow ever found in the state.

While numerous paleoburrows can be found in South America, none have been recorded in North America.

“It’s something that has no logical explanation, as megafauna roamed the entire continent. There should be tunnels in other places”, according to Frank.

Some experts claim that the high concentration of paleoburrows in the South and Southeast of Brazil is simply due to the fact that the region is a center for paleontological research. But others disagree, indicating that geographic evolution influences the different behaviors between species across the American continent.

At the time of megafauna, the temperature in the Americas was up to 10 °C lower than current levels. And the continent was also much drier.

Between myths and legends

Researchers and local residents believed for many years that the tunnels were constructions left by past civilizations. And that the claw marks were actually from pickaxes.

Some paleoburrows contain rock art, such as Toca do Tatu, in Santa Catarina. The design inscribed on the walls appears to show the Sun emitting its rays and groups of triangles representing mountains.

But, as the art is engraved on the rocks and not painted, its dating is almost impossible, according to archaeologist Lizete Dias de Oliveira. No one knows for sure who made the marks on the rock and what they mean.

Regional indigenous communities probably knew about the existence of paleoburrows before they were scientifically identified, as indicated by references to tunnels in their oral tradition.

A legend of the Kaingang people, originally from Rio Grande do Sul, tells that a huge flood caused their ancestral parents to swim to the mountain peaks, where they excavated a path in search of shelter.

Other stories of the Kaingang people indicate that they were aware of the burrows built by megafauna. A popular legend for children tells the story of a family who went down an armadillo hole to enjoy the abundance of food inside. But a white man cut the rope where they descended and took their land, with the family trapped underground.

The exact plot of the myths varies. But for the Kaingang people, accuracy is not as important as the story itself.

“For the Kaingang people, there are no myths, as everything that is told by the older indigenous people is considered true”, as researcher Cláudia Aresi wrote in her master’s thesis at the Federal University of Rio Grande do Sul, about cultural transformations and the territory of the Kaingang people.

Another theory related to paleoburrows stated that the tunnels hid riches that would have been left by the Jesuits. This possibility led treasure hunters to search the caves in search of the supposed fortune, but nothing was found other than dust and sediment.

“Treasure hunters are a horror for archeology,” says Oliveira. “They harm and invert the soil, causing the newest to become older and the oldest to become newer.”

Oliveira highlights that this makes it difficult to study the sediments in search of new indications that could bring revelations about the tunnels.

Animal work

The claw marks eventually led scientists to conclude that the tunnels were built by ancient local megafauna, particularly giant armadillos and giant sloths.

“We analyzed the bones of animals that lived in this region over the last two million years,” explains Frank. “Animals like horses, saber-toothed tigers and elephants don’t dig. You have to look for animals that have claws, so there are only two options: giant sloths and giant armadillos.”

Weinschutz is now mapping Santa Catarina’s paleoburrows in 3D, to try to find patterns in the tunnels that could reveal the biomechanism of excavation of these large constructions. He also looks for traces of ancient fur to help identify the species that built them.

“This study is still new, we have years and years of research ahead of us in this area,” he says excitedly.

The results of the studies may clarify some of the reasons that led animals to build such large tunnels.

Most scientists argue that its purpose was to care for young, regulate body temperature or even hibernate, but the exact reason remains a mystery. And experts suspect that each of the tunnels would have taken centuries or even thousands of years to build, suggesting that the sloths and armadillos lived in family social groups.

“Each generation went a little further, and after all those years, they created a big cave,” explains Frank.

The megafauna (both armadillos and sloths) must have “developed absurd strength in their arms” to be able to cut through the rock and rigid sediments that even a pickaxe would have difficulty piercing, according to Weinschutz.

Intrigued by the process of building the dens, I visited the Earth Sciences Museum, in Rio de Janeiro. I was then able to observe the skeleton of a fossilized sloth and get an idea of ​​its size.

Its elongated skeleton was the size of a horse and its curved claw covered my outstretched hand.

As I held that claw, my thoughts went to the paleoca that I visited, with its deeply scratched walls – the true treasure of those ancient homes.

The armadillos and giant sloths of the past may have long disappeared, but their stories remain, forever marked in southern Brazil. They are a portrait of a world that remains a mystery to us, even today.

How to visit the paleoburrows

The Caminhos dos Cânions do Sul Geopark houses several paleoburrows open to the public. The tunnels are signposted and it is possible to walk to them:

– The Engenho Velho paleo cave complex is located in the Santa Catarina municipality of Jacinto Machado, an hour and a half walk (round trip).

– Toca do Tatu, where visitors can observe rock art, is in the municipality of Timbé do Sul, also in Santa Catarina, on the trail called Portal do Palmiro. Along the same route are the Três Barras paleoburrows, in the municipality of Morro Grande (SC). It’s a four-hour walk, round trip.

To make the visit, it is important to hire an experienced guide who can provide safety equipment, such as helmets, protective clothing, masks and gloves. Contact the park for more information.

This text was originally published here.