A number of huge tunnels that were discovered in South America at the turn of the century may have been made by giant sloths. At the turn of the century, professor of geology, Heinrich Frank, spotted a strange hole on a highway in Brazil, and crawled inside. There, he realised the tunnel was 4.5 meters (15 feet) long. He also found a collection of giant claw marks on the ceiling. “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, adding he's "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.” Sign up to our free Indy100 weekly newsletter The tunnel, along with many others that he and others discovered in Brazil and Argentina, are thought to be made by extinct giant sloths 8-10,000 years ago that were around the size of an African elephant. In the Rio Grande do Sul area, Frank and his team found over 1,500 tunnels made by these sloths beasts, with the longest stretching for 609 meters (2,000 feet) and standing at 1.8 meters (6 feet) tall. Goodness. Have your say in our news democracy. Click the upvote icon at the top of the page to help raise this article through the indy100 rankings.