Learn all about South America’s underground caves built by extinct giant sloths

Deep in Brazil’s landscapes lies an extraordinary archaeological mystery: the paleonore megafauna. Attributed to the activity of ancient giant mammals, these massive underground tunnels fascinate scientists and adventurers alike. Their size, structure and origin provide insight into a prehistoric world dominated by creatures much larger than those seen today.
Already in the 1930s, when the first paleonora was discovered, it was believed to be some kind of archaeological object. However, in 2010, the situation changed when geologist Amilcar Adamy of the Brazilian Geological Survey decided to investigate rumors of a strange cave in the state of Rondônia. When Adamy got there, he knew that the cave had been created too deliberately to be a natural process.

Representative image

A few years later, Brazilian scientist Heinrich Frank noticed these unusual structures after encountering his first paleonorva near Novo Hamburgo. Since that first discovery, Frank has identified over 1,500 tunnels throughout Brazil. Some of these burrows extend hundreds of feet in length. One of the tunnels that had branches was about 2,000 feet long. Scientists have found that they are at least 8,000 to 10,000 years old.
Heinrich found his first clue when he started exploring the caves himself. While examining the ceilings of the tunnels, Heinrich Frank noticed a striking detail that indicated their origin: distinct grooves carved into the weathered surfaces of granite, basalt and sandstone. These marks, which he identified as the claw marks of a massive prehistoric creature, provided a key clue.

“Most of them consist of long, shallow grooves running parallel to each other, apparently formed by two or three claws,” Frank and his team described in a 2016 research paper. Most of the caves were smooth, but some were irregular, formed by claws. Given the size of the tunnels and the distinctive claw marks on their walls, researchers are now certain that they are megafauna burrows. They identified the likely creators as giant ground sloths and giant armadillos.

Representative image

Despite these massive creatures reaching up to 4.6 meters (15 ft) in length and weighing approximately 2,590 kg (5,709 lb), a single ground sloth would likely devote a significant portion of its life solely to digging tunnels as extensive and complex as paleonorves. But why such huge caves existed remains a mystery, as much smaller burrows would have been more than enough for their needs to escape the climate, predators and humidity.