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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Top Ten Pleistocene Animals I would bring back to the Present, if I could

(Warning: I’m jumping on my soapbox for this blog entry.)

Merry Christmas?  I say bah humbug!  Christmas is an ancient pagan holiday celebrating the winter solstice–the shortest day of the year–with a festival of artificial lights.  The Romans knew how to party, and they turned this festival into a drunken orgy known as Saturnalia.  They gave toys to their kids to distract them, so the children wouldn’t be aware that their parents were engaged in a little joyful wife and servant swapping.  The Catholic Church gained political power in the 4th century, but the hierarchy was unable to stop the alcoholic sex-crazed fun.  Instead, they incorporated the holiday and falsely claimed it to be the birthday of Jesus, the invisible Jewish rabbi who the psychotic founders of Christianity believed was the son of God, after God supposedly deposited his sperm into Mary’s vagina without breaking her hymen.

Pious Christians tried to break the real spirit of what the winter solstice should be about, but they haven’t ruined it nearly as much as the oppressive rulers of today’s American society have.  Big corporations and monstrous merchants have transmogrified this glorified sex orgy into a psychological compulsion for working class people to waste money on a bunch of junk they don’t need, so that wealth is transferred from the poor to greedy merchants.  Clueless economists make the ridiculous claim that this is good for the economy.  In reality it’s only beneficial for credit card-owning banks who for the rest of the year use this expensive spending orgy to drain working class people’s money, like vampires sucking the blood of sheep.

I’m not interested in material objects, but I do have a Christmas wish that a magic Santa could transport live specimens of extinct Pleistocene animals to the present so scientists could study the beasts, and zoos could display them.  Here’s my top ten wish list:

Photo of a replica skeleton of Ermeotherium that I took at the Skidaway Island museum.

1. Eremotherium laurillardi–a giant ground sloth.  There’s nothing like this beast living today.  Diminutive South American tree sloths are the closest living relative, but c’mon, there’s just no comparison.  This massive beast lived on Georgia’s coastal plain until about 30,000 years ago which is the time the last glacial maximum began.  The climate became too cold for them in North America, but they persisted in South America until about 11,000 years ago.

2. Smilodon fatalis–the saber-toothed cat.  There’s nothing like this alive today either.  Maybe we could lead a horse or cow into its cage and solve the mystery, once and for all, how it killed its prey.

3. Glyptotherium floridanum–Glyptodont.  A mammal built like a turtle and the size and shape of a Volkswagon.  Who wouldn’t want to see this in person?

4. Mammut americanum–Mastodon.  I’d pick mastodon over mammoth.  Mammoths are closely related to extant living Asiatic elephants, but mastodons were much more primitive and were related to an ancient order close to the evolutionary foundation of elephant-like animals.

5. Megalonyx jeffersonii–Jefferson’s ground sloth  This was a smaller ground sloth about the size of an ox.  For ecological reasons I believe this was the most common kind of ground sloth found in Georgia during most of the Pleistocene.  It preferred forested environments and was better adapted to colder temperatures, living as far north as Canada.

6.  Glossotherium harlani–Harlan’s ground sloth. Co-existed with Jefferson’s ground sloth, but apparently preferred open meadows as opposed to the forested conditions frequented by the other.

7. Mammuthus colombi–Columbian mammoth.  An elephant adapted for living in a temperate region.  Definitely unique enough to make my Christmas wish list.

8. Dinobastis serum–Scimitar-toothed cat.  Not as famous as Smilodon but equally as fascinating.  Got to give it the edge over other mammals left off the top ten list such as the Pleistocene vampire bats, extinct javelinas, and extinct llamas.  Though interesting, those other species do have similar living relatives, but there are no species of fanged cats left on the planet.

9. Terratornis sp.–The terratorn.  It’s a condor with a 14 foot wingspan.

10. Hesperotestudo crassicutata–This giant tortoise lived on Georgia’s coastal plain during warm interglacials and interstadials.  It grew as big as modern day Galapagos Island tortoises, but was closely related to extant gopher tortoises.

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The nature lover in me did get a real gift this year in time for Christmas.  The state of Georgia is going to purchase 15 square miles of Oaky Woods in Houston County.  Currently, it’s being managed as a wildlife management area, but real estate developers were threatening to destroy it.  Oaky Woods is a unique wilderness.  It’s the last stand of the black bear in the piedmont region of Georgia, and it’s home to 4 state record trees.  The landscape consists of mature stands of mixed pine and oak as well as rare remnants of blackbelt prairie, a probable relic habitat dating back to the Pleistocene.  Moreover, there is some good fossil-hunting ground there.  Eocene marine fossils are commonly found on this piece of land.

See www.saveoakywoods.com

Augusta radio talk show host, Austin Rhodes, suggested I go live in a tree when I brought this subject up on the Augusta Chronicle message board.  What a jerk!  The site is now protected, however, no thanks to shmucks like him.

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My next entry will be about ice berg keel scours off the coast of South Carolina. 

Cool.