Some Giant Ground Sloths Dug Long Burrows

Many interesting habits of the extinct species of Pleistocene megafauna will remain unknown to science because dead fossil specimens inadequately represent the complete behavior repertoire of once living animals.   For example no scientist would have ever guessed that some species of giant ground sloths dug long underground chambers.  Sure, they had big claws and were anatomically built for digging, but scientists assumed they merely dug for roots and tubers.  The surprising discovery of paleoburrows dug by 2 different species of extinct ground sloth reveals a habit no zoologist would have predicted.

Glossotherium, also known as Harlan’s ground sloth.  It lived in North and South America.  It’s 1 of 2 species that we know for sure dug burrows.  Other species probably did as well.

Scelerodotherium, also known as Darwin’s ground sloth.  It lived in South America and also dug burrows.

Since 1928, scientists have discovered 42 paleoburrows dug by giant ground sloths in the Mar del Plata region of Argentina.  These sites are near the Atlantic coast not far from Buenos Aires and are located on floodplains next to or directly in sea cliffs.  They range in age from Pliocene to late Pleistocene.  The tunnels are from 2-4 feet wide and as much as 70 feet long, and they are multichambered.  Some are filled with collapsed sediment while others are still intact.

Photos of giant ground sloth tunnels dug into sea cliffs located in the Mar del Plata region of Argentina.  Click to enlarge.  The photos are from the below referenced paper.

A geologist discovered the first ground sloth burrow known to science in 1928, but it was a minor footnote ignored by paleontologists for 70 years.  This burrow contained the skeleton of a Scelerodotherium and was filled with volcanic ash.  Scelerodotherium was a 1600 pound ground sloth with a skull resembling that of an anteater.  Vertebrate paleontologists at first rejected the idea that ground sloths dug burrows because they thought the animals were too big to be fossorial creatures.  The largest extant burrowing mammal is the African aardvark which grows to 200 pounds.  However, the authors of the below referenced paper determined that these burrows were dug by ground sloths.  The claw marks on the sides and roofs of the tunnels match those of 2 different species of ground sloths–Scelerodotherium (Darwin’s ground sloth) and Glossotherium (Harlans’s ground sloth).  Scelerodotherium was restricted to South America, but Harlan’s ground sloth lived in South and North America, including what’s now Georgia where its fossil remains were unearthed in Yarbrough cave, Bartow County and a few coastal sites.  Harlan’s ground sloth grew to 2400 pounds and was the larger of the 2 species.  Both species had long claws, well developed triceps muscles shaped for digging, and the ability to balance on 2 limbs–all characteristics that enabled them to dig tunnels.  Paleoburrows of armadilloes and pampatheres (extinct giant armadilloes) have also been discovered in the Mar del Plata region.

Ground sloths probably dug their long underground chambers for 2 reasons.  When not feeding, they could retreat into their burrows to avoid predation.  With their backs protected on 3 sides by dirt walls, they could easily defend themselves from a frontal attack by using their long claws.  More importantly, the tunnels provided the sloths with some protection from the elements.  The edentates–the order including sloths, anteaters, and armadilloes–are primitive mammals with poorly developed thermoregulatory systems.  During extremly cold or hot weather, ground sloths could stay in their underground chambers and remain well insulated.  This adaptation explains how some species of ground sloths survived in cold climates.  Fossils of Jefferson’s ground sloth have been found as far north as Alaska and the Canadian Northwest Territories.  Although there’s no direct evidence Jefferson’s ground sloth dug burrows, I think we can safely assume it did based on its fossil distribution.

If we could travel back in time to visit the Pleistocene, ground sloths might be a rare site, even when they were common.  They likely stayed in their burrows through most of the winter, emerging only during warm days to feed.  During hot months, they probably were nocturnal, feeding in the darkness and returning to their burrows shortly after the sun rose.  Their preference for fossorial living explains why their fossils are so often found in caves.  Caves are ready made burrows that provided protection from the elements.

Many extinct and extant organisms used or even depended upon ground sloth burrows.  The fossil remains of a glyptodont were found in 1 ground sloth burrow.  Glyptodonts were physically incapable of digging their own.  Giant tortoises too probably made use of sloth burrows, possibly explaining how this frost sensitive species survived as far north as Bartow County, Georgia during the Ice Age. (See

Extant gopher tortoises dig burrows that provide habitat and refuge for dozens of other vertebrate and invertebrate species.  There’s no telling how many animals made use of ground sloth burrows.


Vizcaino, Sergis; et. al.

“Pleistocene Burrows in the Mar del Plata area (Argentina) and their Probable Builders”

Acta Palaeontologica Polonica 46 (2) 2001 pp. 280-301

See also



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15 Responses to “Some Giant Ground Sloths Dug Long Burrows”

  1. James Robert Smith Says:

    I had absolutely no idea! Amazing!

    When I was in Yellowstone I took photographs of a very large adult grizzly bear that had either modified part of a collapsed river bank, or dug a trough itself, for sleeping. The entire time I was there to take photos (from a very great distance, thanks), he continued to sleep the sleep of a top predator completely assured of his safety.

    At the time, there were fly fishermen moving toward the bear from opposite directions. I didn’t wait to see what happened, but always assumed the fellows were aware of the bear’s presence. At any rate, I did not subsequently hear of two people being mauled and eaten in the Park that day.

    HEREis a photo of the bear. I cropped the image from a photo I took with my most powerful lens. (Sometimes I think I was still too close.) Taken on the Lamar River in Yellowstone National Par where the Pleistocene still partially exists.

  2. markgelbart Says:

    Thanks for the neat photo.

    Grizzly bears do dig their own dens. Black bears, however, use pre-existing dens dug by other animals or tree hollow for hibernating.

  3. Mark LaRoux Says:

    This might explain a lot of ‘cavelets’ (for lack of a better description) that people find on hillsides and near old riverbeds in soft soil. I’ve seen these near the Red river, the Tennessee, and the Black Warrior…interesting implications. Wonder how they interacted with jaguars.

  4. markgelbart Says:

    Hmm, I wonder, if there are paleoburrows in southeastern North America. I would think in a forested landscape that most of them became filled with organic material and have vanished.

    I would guess “cavelets” near rivers are probably formed by river erosion.

    Adult ground sloths were probably too tough for jaguars to take on. Today, even giant anteaters are usually able to defend themselves from jaguars, though not always.

  5. Evidence Humans Butchered a Jefferson’s Ground Sloth in Ohio 13,700 years ago « GeorgiaBeforePeople Says:

    […] 13,700 years ago, the Laurentide Glacier had retreated northward from Ohio and Lake Erie was young, and recently filled with glacial meltwater.  The climate was rapidly warming but still quite cold during winter.  But as I wrote  in a previous blog entry, these  beasts with neotropical origins could survive cooler climate because they dug deep underground burrows. […]

  6. The Extinct Corkscrew Beavers of the Miocene | GeorgiaBeforePeople Says:

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    […] Or they utilized burrows dug by giant ground sloths. (See also:  If there were no freezing temperatures on the Atlantic coastal plain during the Ice Ages, […]

  8. Heinrich Frank Says:

    Many hundreds of tunnels, many tens of meters long…. 60 m are common…branching…. forming saloons….claw marks everywhere on the walls…sometimes more than 3,000….tunnel heights of up to 2 m, widhts of up to 4 m… in southernmost Brazil. We work routinely inside them. Tomorrow I will do fieldwork again….See our website: .

    • markgelbart Says:


      I’m going to write a new blog entry about this.

      I think this burrowing habit explains how some species of giant ground sloths were able to colonize colder regions of North America.

      I also think giant tortoises may have used these tunnels, also explaining how they could live in regions with winter frosts.

  9. New Studies of Giant Ground Sloth Burrows in Brazil | GeorgiaBeforePeople Says:

    […] wrote about ground sloth burrows a few months ago (See:  At the time I was unaware of more recent studies of newly discovered paleoburrows in Brazil.  […]

  10. Giant Ground Sloths Used Bipedal Locomotion | GeorgiaBeforePeople Says:

    […] ability to dig deep underground burrows enabled some species to colonize Alaska and Canada (See: )  I think ground sloths were so unique, that if I was able to bring just 1 species of extinct […]

  11. Did Eremotherium laurillardi Supplement its Diet with Sea Weed? | GeorgiaBeforePeople Says:

    […] Eremotherium laurillardi, a species of giant ground sloth, apparently was abundant along the Georgia coast during the Sangamonian Interglacial (~132,000 BP-~118,000 BP).  Fossils of this species have been found at 7 of the 9 known coastal fossil sites of Pleistocene Age. It was really a spectacular beast growing as large as 18 feet long and weighing 6000 pounds.  When it sat on its haunches, it was even taller than a mammoth.  It disappeared from the state when the climate turned colder, probably some time between ~75,000 BP-~30,000 BP.  The fossil record is too incomplete to determine exactly when this species succombed to the cold in this region.  Eremotherium continued to exist in South America until the end of the Pleistocene.  Two other species of ground sloths  were better adapted to the cold and likely lived in Georgia as recently as 11,000 BP.  Jefferson’s ground sloth (Megalonyx jeffersonii) and Harlan’s ground sloth (Paramylodon harlani) were able to survive subfreezing temperatures by denning in underground burrows. (See: […]

  12. The Presence of the Extinct Pleistocene Giant Tortoises (Hesperotestudo sp.) is Evidence of Open Environments but not of Warmer than Present Day Climates | GeorgiaBeforePeople Says:

    […] burrows dug by ground sloths and pampatheres.  Their burrows dotted the landscape as well.  (See: […]

  13. The Largest Saber-toothed Cat, Smilodon populator | GeorgiaBeforePeople Says:

    […] as a kind of strategy to defend themselves from S. populator.  These burrows still exist.  (See: )  A ground sloth in a burrow with its back protected would have been impossible for a Smilodon to […]

  14. w Says:

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