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


  1. Blue
    Posted June 24, 2017 at 3:18 pm | Permalink

    ! W H O A ! .WHOA.WHOA.WHOA.


    • Craw
      Posted June 24, 2017 at 7:00 pm | Permalink

      Well put. Incroyable.

      • Mark Joseph
        Posted June 25, 2017 at 3:54 pm | Permalink

        Yes. This is my favorite fossil thingy since I read about the Titanoboa.

        • Mike
          Posted June 26, 2017 at 7:52 am | Permalink

          Maybe a whole family of them were living in the Burrows? They were big Beasts and no mistake,i doubt they had many Predators, The short faced Bear “Arctotherium ” was possibly one,as they were 11 ft on their hind legs and “Smilodon” could have been another. Wonderful Burrows, we could live in one of those quite

  2. Mark R.
    Posted June 24, 2017 at 3:29 pm | Permalink

    Wow, that is amazing. Maybe they were digging for huge underground insects or grubs or worms?
    Then you mentioned they were herbivores…some type of root? Anyway, I’m thinking the digging could relate to food foraging.

    • infiniteimprobabilit
      Posted June 24, 2017 at 3:40 pm | Permalink

      I don’t even want to think about the size of grubs or worms a 2-ton beastie would be digging for – that’s the stuff of nightmares.


    • Posted June 24, 2017 at 4:41 pm | Permalink

      I think there are few places where you can dig that deep without getting into solid rock, which is not rich at grubs or roots.

      So I guess that the animals “improved” existing caves after all. Still a mystery. After all, the point of becoming 20 feet, 2 ton and armored is to never have to hide in burrows.

    • Zach
      Posted June 24, 2017 at 7:56 pm | Permalink

      Anyway, I’m thinking the digging could relate to food foraging.

      I suspect you’re right, although my guess is they were excavating for some type of nutritious mineral in the rock, a la modern elephants in Kitum Cave.

    • harrync
      Posted June 25, 2017 at 2:09 pm | Permalink

      Maybe they just didn’t know when to stop, like that woodpecker from last Thursday.

  3. infiniteimprobabilit
    Posted June 24, 2017 at 3:36 pm | Permalink

    Hairsplitting here: A VW beetle would weigh closer to one ton than 2, I would hope.

    The armadillo might have been the size of a Beetle but it was much heavier.

    Incidentally, a ton and a tonne are near as dammit the same (within 1%); you couldn’t tell the difference if one parked on your foot. Whereas you could certainly tell the difference if a 2-ton giant armadillo parked on your foot…


    • Ken Phelps
      Posted June 24, 2017 at 5:04 pm | Permalink

      OK, so one of these vintage armadillos was the size and weight of a vintage VW full of modern armadillos.

    • gscott
      Posted June 24, 2017 at 6:22 pm | Permalink

      A metric tonne (1000kg) is within about 1% of a British or long ton (2240 lbs), but those of us in the colonies usually think of short tons which are 2000 lbs. Still couldn’t tell the difference if it was on your foot.

      • infiniteimprobabilit
        Posted June 25, 2017 at 4:20 am | Permalink

        Yes I admit I was thinking of the British long ton (2240 lbs).

        I agree a 10% difference is probably not readily pedally detectable.


  4. GBJames
    Posted June 24, 2017 at 3:41 pm | Permalink


  5. loren russell
    Posted June 24, 2017 at 4:27 pm | Permalink

    A cult of giant sloths did this in response to prophesies of the coming of the bipedal spear-bearers.

    Didn’t work.

    I’m told that most more than $10 million estates in the US are built with bug-out bunkers.

    These probably won’t work either.

  6. Christopher
    Posted June 24, 2017 at 4:38 pm | Permalink

    This made my day. Spectacular. I never could have dreamed that ground sloths would have done such a thing. Yet another reason why I would choose them, rather than the mammoth (essentially just an elephant variation) for “de-extinction (ignoring technology and moral issues, of course).

    • loren russell
      Posted June 24, 2017 at 10:53 pm | Permalink

      Honestly, moral has nothing to do with de-extinction. Has a lot to do with extinction however.

  7. Posted June 24, 2017 at 4:41 pm | Permalink

    Bloody hell amazing… Wouldn’t these burrows have to be that big to fit the family in, especially if used for rearing young?.
    Like, Ok let’s change places, breath in I need to squeeze past..

  8. Torbjörn Larsson
    Posted June 24, 2017 at 5:28 pm | Permalink

    Like some giant sloth machines.

    Maybe the salt hypothesis in the original article comments is viable? Re “strange geographic distribution”.

    • Posted June 24, 2017 at 8:37 pm | Permalink

      Had not read it, but was going to suggest that they were digging to eat dirt, basically.
      Elephants dig to eat salt, for example.

  9. Michael Fisher
    Posted June 24, 2017 at 5:57 pm | Permalink

    The tunnel seems to be horizontal. This to me suggests the mega-mammals are following the line of a buried dry salt lake. I would love to see these tunnels in plan too – are the tunnels as straight as they seem? Perhaps in plan the mammals are digging along a straight ‘fault’ where the digging is easier or where flowing water has begun the job for them?

    • Michael Fisher
      Posted June 24, 2017 at 6:03 pm | Permalink

      This article has plans of tunnels & suggests they were for mating trysts!

      • Posted June 24, 2017 at 9:21 pm | Permalink

        Having a secret tunnel for mating trysts doesn’t sound like a bad idea at all…

        Somewhere, someone is writing an article stating that these tunnels were nuclear bunkers excavated by a super-advanced ancient (and possibly alien) civilization. Those “claw marks” were obviously made by machines!

  10. amyt
    Posted June 24, 2017 at 6:23 pm | Permalink

    Really interesting (amazing cool incredible). Thanks for posting!!

  11. Kevin
    Posted June 24, 2017 at 10:15 pm | Permalink

    This puts some of my landscaping efforts to shame.

  12. Hempenstein
    Posted June 24, 2017 at 10:27 pm | Permalink

    What’s the term for the rubble dislodged in digging a tunnel? Whatever it is, how did they remove it?

    • loren russell
      Posted June 24, 2017 at 10:54 pm | Permalink

      That’s where the glyptodonts come in — they bulldozed it out while the sloths worked the mine face.

    • allison
      Posted June 25, 2017 at 1:18 pm | Permalink

      That’s what I want to know! Claws may be optimal for excavating, but would seem nearly useless for moving soil out of the tunnel (particularly when it was already hundreds of feet long!) Is there a huge mound of soil outside the cave?

    • strongforce
      Posted June 25, 2017 at 11:48 pm | Permalink


  13. Posted June 24, 2017 at 11:01 pm | Permalink

    The ground sloths must have had an affinity for caves, whether they dug them themselves of not. Remains of Shasta ground sloths (including dung accumulations)have often/usually been found in caves, though as far as I know entirely in natural ones. But, maybe someone needs to look closer.

  14. Posted June 24, 2017 at 11:10 pm | Permalink

    Thank you this post. A helpful synopsis of this interesting study.

  15. ThyroidPlanet
    Posted June 25, 2017 at 3:30 am | Permalink

    Never heard of this.

    [ three letter acronyms ]



    Traveling. Can’t react to posts like usual.

    • infiniteimprobabilit
      Posted June 25, 2017 at 4:34 am | Permalink

      Ditto. But it’s a stormy morning in Domegge di Cadore (that’s about 40 miles south of Cortina d’Ampezzo), the Norwegian bikers at the next table are playing some sort of card game, and mine host has a well-stocked fridge of delicious Dolomiti birra.

      (Sorry for the off topic).

  16. infiniteimprobabilit
    Posted June 25, 2017 at 4:25 am | Permalink

    I assume that’s soft rock (barely harder than dry mud) the caves are dug in (since I doubt the diggers had evolved carbide-tipped claws).

    There can only be a limited set of landscapes where the soft-rock strata are (a) thick enough to permit such and excavation and (b) elevated enough above the water table that they didn’t fill with water.


  17. DiscoveredJoys
    Posted June 25, 2017 at 4:53 am | Permalink

    If the burrow digging became associated with sexual display and fitness (males showing off, or females preparing attractive nests, or both) then runaway sexual selection could have resulted in burrows far bigger than ‘necessary’.

    It seems to me that natural, sexual, and artificial selection involve a huge number of trade-offs and sometimes trade-offs stumble into a dead end.

    • Andy
      Posted June 25, 2017 at 10:00 am | Permalink

      I like your explanation!

      I can see a variety of reasons why a burrow would be necessary so it’s not surprising that they got started. Then I can easily imagine mating involving selecting the mate with the biggest, er, burrow…

  18. busterggi
    Posted June 25, 2017 at 9:33 am | Permalink

    Giant sloths – did they attempt migration to China?

  19. Posted June 26, 2017 at 10:24 am | Permalink

    It raises the possibility of ‘burrows’ that collapsed on individuals inside… that would make a brilliant find.

  20. Posted June 26, 2017 at 11:51 am | Permalink

    The “construction works” of non-human animals can be quite astonishing. These are certainly that.

  21. Posted June 26, 2017 at 6:03 pm | Permalink

    What’s truly astonishing is that such creatures so rapidly evolved from their ‘kind’ that Noah had on the ark, and then also so quickly went extinct! I wonder if Ken Ham covers this at the Ark Encounter.

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