This Massive Tunnel in South America Was Dug by Ancient Mega-Sloths

Researchers have found several colossal burrows in South America that are so huge and neatly constructed, you'd be forgiven for thinking humans dug them as a passageway through the forest. Turns out, they're far more ancient than they look, estimated to be at least 8,000 to 10,000 years old, and no known geologic process can explain them.

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