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Phoenix666 writes:

Discover Magazine:

A few years earlier, and about 1,700 miles to the southeast, another Brazilian geologist happened upon a different, equally peculiar cave. Heinrich Frank, a professor at the Federal University of Rio Grande do Sul, was zipping down the highway on a Friday afternoon when he passed a construction site in the town of Novo Hamburgo. There, in a bank where excavators had eaten away half of a hill, he saw a peculiar hole.

Local geology doesn't yield such a sight, so Frank went back a few weeks later and crawled inside. It was a single shaft, about 15 feet long; at its end, while on his back, he found what looked like claw marks all over the ceiling. Unable to identify any natural geological explanation for the cave's existence, he eventually concluded that it was a "paleoburrow," dug, he believes, by an extinct species of giant ground sloth.

"I didn't know there was such a thing as paleoburrows," says Frank. "I'm a geologist, a professor, and I'd never even heard of them."

[...] Until the early 2000s, in fact, hardly any burrows attributed to extinct megafauna had been described in the scientific literature. That's especially curious because, after his chance discovery in Novo Hamburgo, Frank caught the burrow bug and began finding them in droves.

[...] In his home state of Rio Grande do Sul, in the far south of Brazil, Frank has documented at least 1,500 paleoburrows so far. In Santa Catarina, just to the north, he's found hundreds more and counting.

[...] It wasn't until 2015 that Amilcar Adamy of the CPRM [*] had an opportunity to return to that strange cave in Rondonia. It turned out to be the first paleoburrow discovered in the Amazon, which is notable, but not the coolest part. It also turned out to be one of the largest ever measured, with branching tunnels altogether tallying about 2,000 feet in length. The main shafts – since enlarged by erosion – were originally more than six feet tall and three to five feet wide; an estimated 4,000 metric tons of dirt and rock were dug out of the hillside to create the burrow.

[...] 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."

[*] CPRM in Portuguese: Companhia de Pesquisa de Recursos Minerais roughly translated would be "Brazilian Geological Survey".

More background on paleoburrows at Wikipedia.

Well, knock me over with a feather--Tremors had it right?

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