![prehistoric sloth prehistoric sloth](https://cf.myheritageimages.com/records/thumb/newspapers/pa/the_mount_washington_news/1938/04/08/issue1/page_0008_96x_5b41b3d4.jpg)
"Most consist of long, shallow grooves parallel to each other, grouped and apparently produced by two or three claws," Frank and his team explained in a 2016 paper.
![prehistoric sloth prehistoric sloth](https://vignette.wikia.nocookie.net/cryptidarchives/images/4/44/Giant_Ground_Sloth_by_Hermann_Trappman.jpg)
When he looked up at the ceiling, he got his first big clue about what could be behind their construction - distinctive grooves in the weathered granite, basalt, and sandstone surfaces, which he's identified as the claw marks of a massive, ancient creature. It wasn't until Frank started climbing inside them that he realised the extent of these tunnels, which can extend for up to 100 metres, and occasionally branch off into separate chambers.
![prehistoric sloth prehistoric sloth](https://www.museum.zoo.cam.ac.uk/sites/www.museum.zoo.cam.ac.uk/files/styles/page_content/public/content/20d.2.i_i_giant_ground_sloth_angela_wade_resized.jpg)
There are now more than 1,500 known palaeoburrows that have been found in southern and southeastern Brazil alone, and there appear to be two different types: the smaller ones, that reach up to 1.5 metres in diameter and the bigger ones, that can stretch up to 2 metres in height and 4 metres in width. Once he knew what to look for, he found hundreds of them scattered across the Brazilian landscape. It didn't look natural."Ī few years later, Frank found his own strange cave, thousands of kilometres away in the town of Novo Hamburgo. "I'd never seen anything like it before," Adamy told Jenner. The structure was huge, and according to Jenner, it's still the largest known palaeoburrow in the Amazon, and is twice the size of the second largest palaeburrow in Brazil.Īdamy had gone to investigate the tunnel, determined to attribute it to some kind of geologic process, but once he saw it with his own eyes, he couldn't think of any natural process that would create such a deliberate-looking structure. Researchers have known about these tunnels since at least the 1930s, but back then, they were considered to be some kind of archaeological structure - remains of caves carved out by our ancient ancestors, perhaps.įast-forward to 2010, when geologist Amilcar Adamy from the Brazilian Geological Survey decided to investigate rumours of a peculiar cave in the state of Rondonia, to the north-west of the country. "I'm a geologist, a professor, and I'd never even heard of them." "I didn't know there was such a thing as palaeoburrows," lead researcher behind the latest study, Heinrich Frank from the Federal University of Rio Grande do Sul in Brazil, told Andrew Jenner at Discover. But then there's the massive claw marks that line the walls and ceilings - it's now thought that an extinct species of giant ground sloth is behind at least some of these so-called palaeoburrows. Turns out, they're far more ancient than they look, estimated to be at least 8,000 to 10,000 years old, and no known geologic process can explain them.