The Massive Tunnels in Brazil Dug by Ancient Mega-Sloths

The world is full of mysteries. And sometimes the most amazing discoveries come from something as simple and every day as a construction project. Just such a find recently came to light with the disclosure that part of what will soon become one of South America’s longest road tunnels was dug not by modern construction equipment, but by an extinct species of a giant sloth.

Ancient Mega-Sloths
Photo: Amilcar Adamy/CPRM

Mega-sloths, as these creatures are called, were the elephantine mammals of the Pleistocene epoch. They weighed in at over a ton and could measure up to 10 feet from head to toe. And their propensity for lounging about in mud baths left their fossilized footprints all over the place. The enormous tunnels dug by giant prehistoric creatures are known as paleoburrows, and these massive tunnels may be up to 2,000 feet long and six feet tall. The presence of these caverns was previously largely unknown until a Brazilian geologist noticed something from the road.

Ancient Mega-Sloths
Photo: Robert Bruce Horsfall

Professor Heinrich Frank of the University of Rio Grande do Sul was driving by a construction site when he noticed something intriguing. The excavators had exposed a strange hole, and Frank couldn’t help but wonder where it went. A few weeks later, he returned to the scene and descended into the 15-foot-deep hole. He saw claw marks on the cave ceiling as he crawled down the 15-foot tunnel.

Given his background, he was confident that no natural occurrence would produce a cave with those features. And while he’d never heard of a paleoburrow before, he was certain it had been excavated by a large animal.


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When Professor Frank discovered one tunnel, he went looking for more and was shocked to discover over 1500 paleoburrows utilizing Google and other people’s photographs.

The next step was to determine when it had been dug. After carbon dating a few of the sloth bones he found in the tunnel, Frank determined that the tunnel was about 15,000 years old—the same age as the bones. This made it one of the oldest paleoburrows in the world.

Ancient Mega-Sloths
Heinrich Frank

The Palaeotocas Project has been a personal project of Frank’s since it began. It aims to document as many of these tunnels as possible and also raise public awareness about the importance of preservation.

How these mega-sloths managed to dig these massive tunnels is still something of a mystery, but scientists have a few theories. It’s possible that they used their claws to dig, or that they employed their large tails for support.

Whatever the case may be, this new discovery is a fascinating glimpse into the ancient world. And it’s just one more reminder that there are still plenty of secrets to be revealed about our planet.

More info: Projeto Paleotocas

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