Massive Tunnels That Were Dug By A Giant Sloth That Lived 10,000 Years Ago

A cave in the state of Rondonia explored by geologist Amilcar Adamy from the Brazilian Geological Survey. It is the largest known palaeoburrow in the Amazon, and is twice the size of the second largest palaeburrow in Brazil. Adamy couldn't think of any natural process that would create such a deliberate-looking structure. Frank found his first tunnel in the early 2000s and learned that another scientist had coined the name palaeoburrows for them. When he couldn't come up with an explanation for their existence, this made him look for further tunnels to eventually figure out the truth. As of today, Frank and other researchers have found over 1,500 tunnels in the state of Rio Grande do Sul alone, as well as hundreds more in Santa Catarina. Image credit: Heinrich Frank