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Mega-tunnels dug by ‘mega-mole’

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Deep inside Brazil, there are tunnels large enough for a person to walk through. They are neatly symmetrical—too neat to have been caused by any known geologic process. And they are lined with claw marks, reported Popular Mechanics.

These megatunnels are probably the handiwork of giant ground sloths—humongous "paleoburrows" that no longer walk the Earth. But tens of thousands of years after these megafauna did their digging, those tunnels still dot this part of South America. Discover has a great feature up about it.

“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,” says Brazilian scientist Heinrich Frank. “I’ve [also] 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.”

“This wasn’t made by one or two individuals,” says Adamy. “It was made by many, over generations.” Frank describes it as an exciting, though not particularly surprising, discovery.

In Rio Grande do Sul, Frank has found burrows that were originally several hundred feet long. More than 1,000 total feet of tunnel have been measured in another burrow in the Gandarela Mountains, far to the north in the state of Minas Gerais. Though he has yet to investigate, Frank’s received reports of one burrow more than 3,000 feet long in Santa Catarina.

Regardless, the sheer size of the burrows is something that Frank and his colleagues are still trying to explain. Whether prehistoric sloths or armadillos were responsible, the burrows are far larger than would be necessary to shelter the animals that dug them from predators or the elements.

The giant armadillo, the largest living member of the family, weighs between 65 and 90 pounds and is found throughout much of South America. Its burrows are only about 16 inches in diameter and up to about 20 feet long.

“So if a 90-pound animal living today digs a 16-inch by 20-foot borrow, what would dig one five feet wide and 250 feet long?” asks Frank. “There’s no explanation – not predators, not climate, not humidity. I really don’t know.”

Dating the burrows also remains guesswork at best—animals don’t dig holes after they go extinct. However, they had to have been dug at least 8,000 to 10,000 years ago, when South America’s giant ground sloths and armadillos vanished.

At the top of Frank’s list is to better describe patterns emerging from observations he’s collected studying paleoburrows for the past decade. Some are simple shafts; others are complicated works of underground engineering, with branching tunnels that twist and turn and rise and fall to form a network with more than one entrance. Some occasionally open up into much larger chambers. There are relatively small ones. Then there are the enormous ones.

“We need to figure out the patterns. We’re starting to understand this better,” Frank says. “And from there, we’ll be better able to infer what kinds of different animals were digging them.”

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