'I've seen dozens of caves that have inorganic origins, and in these cases, it's very clear that digging animals had no role in their creation.'īelow is a summary of how the various tunnel diameters match up to known species of ancient armadillos and sloths:

'There's no geological process in the world that produces long tunnels with a circular or elliptical cross-section, which branch and rise and fall, with claw marks on the walls,' Frank told Discover. The discovery seemed to answer one of the long-standing questions in palaeontology regarding the ancient megafauna that roamed the planet during the Pleistocene epoch, from about 2.5 million years ago to 11,700 years ago: Where were all the burrows?Īs Frank and his colleagues explain, it's estimated that about half of the mammalian species on Earth right now are classified as semi-fossorial - meaning they spend some time inside burrows, but have to go outside to feed. 'These grooves are mostly smooth, but some irregular ones may have been produced by broken claws.' '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. 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.

Giant sloth