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 https://markgelbart.wordpress.com/2011/04/15/the-extinct-pleistocene-giant-tortoise-hesperotestudo-crassicutata-must-have-been-able-to-survive-light-frosts/).

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.

Reference:

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 https://markgelbart.wordpress.com/2011/03/30/does-a-species-of-giant-ground-sloth-still-exist-in-the-amazon-rain-forest/

And https://markgelbart.wordpress.com/2012/08/19/is-the-9-banded-armadillo-dasypus-novemcinctus-a-dwarf-mutation-of-the-pleistocene-species-dasypus-bellus/

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Does a Species of Giant Ground Sloth still exist in the Amazon Rain Forest?

I’m not impressed with the science credentials and logic of most cryptozoologists such as Loren Coleman.  Bigfoot is a man in an ape suit.  The famous film footage shot in the 1960’s is not of some unknown species of ape, but rather of a Hollywood stuntman in an ape costume.  The stuntman, Bob Heironimus, took a lie detector test on a television talk show, and the test showed he was telling the truth when he confessed to being the man filmed in the ape costume.  Still, Bigfoot believers (like Christian fundamentalists who believe in a literal translation of the bible despite the facts) refuse to accept that the film is a fake.  There may be a great deal of wilderness left in the Pacific northwest but it’s not so remote that a population of a gigantic species of ape could survive undetected following expedition after expedition.  However, the same can’t be said for parts of the Amazon jungle where there are still whole Indian tribes yet to be contacted by Western civilization.

The Amazon rain forest is so vast  there is  a remote possiblity that a large mammal species unknown to science may still live here.  Photo from google images.

I’m skeptical that a large mammal is yet to be discovered here, but it’s much more plausible than the existence of Bigfoot in the Pacific northwest.  The locals description of an animal they refer to as Mapinguari sounds just like a 3-toed giant ground sloth.  They say it is large, has long arms, red fur, long claws, and leaves foot prints with 3 toes.  Pat Spain of the National Geographic Series, The Beastmaster, interviewed a man who even claims to have shot and killed one, and his description of the event is consistent with what one would expect from an encounter with a ground sloth.  The hunter reported that his gun shots to the body had no effect, but eventually he killed it with a shot to its head.  This makes sense (if it actually happened) because ground sloths had armor, like their close relatives the armadilloes, under thick fur that could perhaps protect them from bullets to the body.  Pat showed the hunter pictures of various mammals, and the hunter pointed out an illustration of a giant ground sloth as the animal he killed.  However, he didn’t save any part of the animal because supposedly it smelled horrific, making his story doubtful in my opinion.  A poor Indian would surely understand the value of an unusual animal, particularly the monetary reward he could get by selling it to science. 

Illustration of Harlan’s ground sloth from google images.  The creatures the natives in Brazil describe sounds like a mylodon type of giant ground sloth.  Harlan’s ground sloth was the species of mylodon sloth that lived during the Pleistocene in southeastern North America.  Without positive physical evidence I remain doubtful that it is still extant even in the Amazon rain forest.

If the locals are telling the truth though, some interesting characteristics of giant ground sloths have come to light that we could never gain from just their skeletal remains.  Apparently, giant ground sloths move together with herds of the vicious white lipped peccary.  Perhaps, they forage on the same plant species and mutually attack predators for the Indians claim the sloth is the peccary’s protector.  Fruits and leaves brought down by the sloths when they tear trees apart may be a convenient source of food for the peccaries as well.  The sloths also have an odor that is said to be incapacitating, making for an additional defense mechanism besides their size, armor, and claws.  If it exists, it is probably a mylodon species of sloth related to Harlan’s ground sloth which used to inhabit southeastern North America during the Pleistocene.

Pat suggested stories among the natives of the Mapinguari may be legends passed down from actual encounters their ancestors made with this animal thousands of years ago.  The native people living in this region have had a continued existence here for thousands of years, and perhaps this animal only became extinct 2-3 thousand years ago rather than 11 thousand as science assumed. (See my blog entry entitled “CSI: Pleistocene Alaska.”)  And in fact, scientists know that dwarf ground sloths living on Carribean Islands survived until at least 4 thousand years ago, becoming extinct shortly after human colonization.

Photo of the Chacoan peccary from google images.  This South American species was unknown to science until 1970 and was thought to be extinct for 10 thousand years.

New recent discoveries of mammal species in South America would not be unprecedented.  Scientists found a population of Chacoan peccaries (Catagonus wagneri), a species thought to be extinct for 10 thousand years, in 1970, though the local natives had been hunting them for millenia and reporting about it to Westerners for years.  In the past decade scientists have discovered 10 new species of monkeys in the Amazon.  Maybe that’s why a real scientist, ornithologist David Oren, risked his reputation searching for this possibly extant species of ground sloth.  If it exists, it is likely in grave danger of extinction because natives from uncontacted Indian tribes still probably hunt them with no restrictions.

A review of The Beastmaster (National Geographic Channel Fridays 9:00 pm)

I like Pat Spain, host of The Beastmaster, because he’s a real scientist (a marine biologist) who seeks rational explanations first before succumbing to the possibility that a reported creature is an animal unknown to science.  On one episode for example he traveled to the Congo to investigate reports that a dinosaur-like creature inhabited a remote jungle.  He showed  pictures to the natives of various large animals, including those of long-necked sauropods.  The natives identified a sauropod as the creature called Mkobe Mkembe.  But Pat demonstrated that an elephant swimming across a deep river with only its head and trunk showing, closely resembled a sauropod, the trunk looking very much like a long neck, the head having the appearance of an animal’s upper body. 

On another episode Pat investigated reports of sea serpents off the coast of British Columbia.  He suggested a rare fish knowns as an oarfish, Agrostytichthys (sp.), may be the sea serpent of myth.

3 men holding an oarfish.  Photo from google images.  This creature may be the sea serpent of myth which means the sea serpent is not actually a myth.  They grow larger than this.

Pat leaves the door slightly open  for the possibility that a giant species of ground sloth still roams a remote region of the Amazon.

Pat’s great uncle was Charles Fort, the founder of Cryptozoology and the study of all unnatural phenomena, but the host of The Beastmaster says that he became interested in strange creatures long before he knew he was related to Fort.