Huge tunnels discovered in Brazil and Argentina that were not made by humans or geology

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Deep under the hills of southern Brazil and northern Argentina, scientists found huge tunnels that appear to be cut into solid rock. They say no human or geological process created them.

They do not follow river channels, they show no signs of mining, and they look nothing like normal caves.

Many of the passages are longer than 600 yards (550 meters) and tall enough for an adult to walk through without bending.

The leading idea is that giant, extinct ground sloths dug these colossal shelters, turning parts of South America into a maze of underground homes.

Over the past decade, a detailed study mapped more than 1,500 giant burrows across southern and southeastern Brazil.

These tunnels can reach several hundred feet in length. They branch into side passages, and display long, parallel claw marks etched into their walls.

The work was led by Heinrich Frank, a geologist at the Federal University of Rio Grande do Sul in Brazil. His research centers on paleoburrows – fossil tunnels carved by large, extinct animals that once reshaped the landscapes of southern South America.

Many passages appear in consolidated sands, sandstone, or weathered volcanic rock. These materials are hard for machines to excavate, and harder for humans with simple tools.

Collapsed ceilings and overlapping tunnels show that some routes were widened and reused, a pattern outlined in a chapter on Cenozoic tunnels

Geological processes such as landslides, joints, and natural caves rarely create long, nearly circular tunnels that slope up and down or branch like these.

Frank notes that the tunnel walls are packed with claw marks, sometimes in three parallel grooves, right where a digging limb would bite into rock.

Similar tunnels crop out along road cuts in Argentina, where they intersect and crisscross in dense clusters on some hillsides.

Taken together, the layout looks less like an accident of erosion and more like a network of shelters dug and maintained over long periods.

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