Largest solitary animal burrows ever

The largest animal burrows are palaeoburrows (produced in prehistoric times) believed to have been created at least 8–10,000 years ago by now-extinct giant animals that can be found in their hundreds within South America but most commonly in southern Brazil. Some burrows are so huge that they were once thought to be caves, but no natural geological process is known that can create structures like these. One spectacular example that was discovered in southern Brazil by Heinrich Frank, a professor at Brazil's Federal University of Rio Grande, measures some 600 metres (1,970 feet) long. It is approximately 1.5 metres (5 feet) tall and varies from 1 to 1.3 m (3 feet 3 inches-4 feet 3 inches) in width. Confirming that they were created by animals is the presence of numerous claw marks on their inner wall surface, left behind by their creators. The precise vertebrate species responsible for these gigantic burrows is/are presently unknown. Giant ground sloths are the most popular identity suggested, but some researchers have speculated that gigantic armadillos or armadillo-like beasts called glyptodonts, also long extinct like the ground sloths, may have created at least some of them.

The precise species of mammal responsible for these gigantic burrows is/are presently unknown. Giant ground sloths are the most popular identity suggested, but some researchers have speculated that gigantic armadillos or armadillo-like beasts called glyptodonts, also long extinct like the ground sloths, may have created at least some of them.

The largest burrows made today by a single animal are the maternity dens made by polar bears (Ursus maritimus), which they dig into the snow banks during the Arctic winter to shelter their cubs from the harsh conditions outside. Their burrows are roughly 3 m (10 ft) long, 1 m (3 ft) high and over 2.5 m (8 ft) wide, with up to three oval rooms and a narrow entrance tunnel.