Humans and tunnels have a deep historic connection. We have used tunnels for housing, mining, travel, military and for various other purposes since the dawn of history. But some tunnels in South America have recently created a buzz among geologists, researcher, and explorers. Not only are these tunnels created by non-humans, but they also contain huge claw marks. Let’s explore these mysterious mega-tunnels of South America dug by the extinct megasloth.

In the early 2000s, geology professor Heinrich Theodor Frank discovered a mysterious tunnel at a construction site in Novo Hamburgo, Brazil. After close inspection, he found out that it contained claw marks indicating it was created by an extinct megafauna.

Heinrich Frank is a geologist at one of the biggest federal universities in Brazil. He was once driving along the Novo Hamburgo highway. During his drive, he noticed a strange hole at a construction site along the highway. The hole was about one meter in diameter. Since he was in a hurry, he didn’t stop to take a look, but a few weeks later he returned back to the same spot.

Upon reaching the spot, Frank started inspecting the hole. To his surprise he found out that it is actually a tunnel. The tunnel was a couple of meters in length and about seventy cm in height. The interior of tunnel was full of scratches, especially on the ceiling. These scratches were made with huge claws. When he tried to find a geological explanation for the tunnel’s existence, he couldn’t find any. After a lot of research he concluded that it was a “paleoburrow” dug by an extinct species of giant ground sloth.

In 2010 another geologist heard rumors of an impressive cave in the Amazon. After asking around he discovered another paleoburrow on a wooded slope, north of the Bolivian border.

When geologist Amilcar Adamy heard rumors about an unusual cave in southern Brazil, he went there to find out the truth. His search for the cave brought him to a gaping hole located a few miles north of the Bolivian border. At that time he couldn’t contact the landowner. So, it was not possible for him to study it in detail. He had already been to a number of caves near that region which were formed by water. But this one was different as it was larger with a round passage and smooth floor. Later he found out that similar tunnels have been discovered by geologist Heinrich Frank few years earlier.

He returned to the strange cave in 2015. It turns out that the tunnel Adamy saw was the first paleoburrow discovered in the Amazon. It is also the largest paleoburrow ever discovered having a length of 2,000 feet. The main shafts were originally more than six feet tall and three to five feet wide. They have been enlarged since then due to erosion. Approximately 4,000 metric tons of dirt and rock were dug out to create the burrow. According to Adamy, it wasn’t created by one or two creatures but by many generations.

After discovering the first paleoburrow, Frank and his student started searching for more near the city of Porto Alegre. They identified many of them in more than seventy percent of road cuts.

Intrigued by the first paleoburrow, Frank started researching scientific literature to gather more information. But there was hardly any mention of burrows created by extinct megafauna. So, he, along with his students, started surveying a forty-five mile stretch of highway construction near Porto Alegra. They found many paleoburrows but most of them were completely filled with sediment.When Frank found a paleoburrow with a suitable passage, he squeezed through the four-foot wide elliptical shaft. He found the same claw marks he had found before in this sixty feet long tunnel.

So far, Frank has documented 1,500 paleoburrows. Just to the north of Santa Catarina he has found hundreds more and is still counting. Frank says, “In these burrows, sometimes you get the feeling that there’s some creature waiting around the next curve – that’s how much it feels like a prehistoric animal den.”  Frank has received reports of a burrow more than 3,000 feet long situated in Santa Catarina. He has yet to investigate it, but if it’s found to be true it would become the longest paleoburrow ever found, longer than the one situated in Amazon.

According to Frank, the biggest burrows were dug by ground sloth. Others believe that extinct armadillos are responsible for these burrows. Even though there is no known date of its creation, geologists estimate that these paleoburrows must have been dug 8,000 to 10,000 years ago.

The giant armadillos which once roamed the Earth weighed between sixty-five to ninety pounds. They could dig a sixteen inch by twenty-foot burrow. This can make anyone wonder how big those creatures were who dug the paleoburrows which were 250 feet long and five feet wide. According to geologists, it may be giant prehistoric sloths or armadillos. Skeletal remains of armadillos can be found inside these burrows, but these skeletons are of a much smaller animal than those which could have dug these large burrows.

Another question that haunts the geologists is trying to determine just when these burrows were dug. The giant sloth and giant armadillos went extinct 8,000 to 10,000 years ago. So, these burrows must have been dug around or before this period. According to Frank, the exact period can be determined by dating the organic material found in the burrow sediments, but this testing hasn’t been done yet.

Even though paleoburrows are found all over South America, there is no sign of these burrows in North America. Since the discovery of these burrows, the geological preference of their creators has posed another head-scratching question for geologists.

Paleoburrows are common in the southern Brazilian states of Rio Grande do Sul and Santa Catarina. Very few have been found in extreme north of Brazil and in other South American countries. Surprisingly, not even a single paleoburrow has been discovered in North America even though it was once home to giant ground sloths and giant armadillos. According to Greg McDonald, a Bureau of Land Management paleontologist, there is a possibility that the soil of North America is different enough that these burrows couldn’t survive. He also says that maybe there are paleoburrows in North America, but they have been overlooked.

[sources: 1, 2, 3, 4, 5, 6]