Giant “paleoburrows” dug by extinct mammals

In the last few years, geologists have been finding—mostly in Brazil—large “paleoburrows” that were almost certainly dug by large, extinct mammals such as giant ground sloths. These burrows can be up to 3000 feet long (!) and 5 feet wide, though the very long ones were surely dug by many individuals over many generations. The shape of the burrows, and the fact that they bear distinct claw marks, are sure signs they were dug rather than being natural caves (the beasts could also have “improved” existing caves, but geologists think that’s unlikely).

Here’s what the excavations look like, from a summary of paleoburrows in Discover Magazine (captions from the site):

Looking into a large paleoburrow in Brazil. (Courtesy: Heinrich Frank)

Inside the first paleoburrow discovered in the Amazon. It’s nearly twice as large as the second-largest known burrow, located elsewhere in Brazil. (Credit: Amilcar Adamy/CPRM)

Here’s evidence that these are the products of animal activity: claw marks:

Claw marks are clear signs from the engineers who dug the tunnel. (Courtesy: Heinrich Frank)

A close-up of the scratches (sadly, there’s no scale, but you can see from the above that the animals must have been BIG.

A closer look at those claw marks. (Courtesy: Heinrich Frank)

The caves are at least 8,000 to 10,000 years old, which is when the suspected excavators went extinct. And those suspects are both giant ground sloths (Megatherium) and giant armadillos (glyptodonts). The sloths, one of the largest land animals that ever lived, were this big (below) and, at least according to Wikipedia, could weigh up to 4000 kilograms (4 “tonnes”) and stretch 20 feet from head to tail. Some were as big as modern elephants, and, like the pachyderms, they were herbivores:

Another candidate, the giant armadillos, or glyptodonts, were also huge, weighing about 2 “tonnes” (2000 kg) and extending about 11 feet: they were the size and weight of a VW Beetle. Here’s one:

But the caves with scratches on the roof were probably made by sloths, which could rear up on their hind legs. Based on the shape of the excavations, Heinrich Frank, a Brazilian geologist, thinks they were made this way:

But why did they need these caves, particularly such long ones? It’s still a mystery:

. . .  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.”

You tell me! It’s cool enough that we have fossil habitats like this.

h/t: Michael