Get Lost in Mega-Tunnels Dug by South American Megafauna

By Andrew Jenner | March 28, 2017 1:39 pm
paleoburrow1

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

It was in 2010 that Amilcar Adamy first investigated rumors of an impressive cave in southern Brazil.

A geologist with the Brazilian Geological Survey (known by its Portuguese acronym, CPRM) Adamy was at the time working on a general survey of the Amazonian state of Rondonia. After asking around, he eventually found his way to a gaping hole on a wooded slope a few miles north of the Bolivian border.

Unable to contact the landowner, Adamy couldn’t study the cave in detail during that first encounter. But a preliminary inspection revealed it wasn’t the work of any natural geological process. He’d been in other caves nearby, formed by water within the same geology underlying this particular hillside. Those caves looked nothing like this large, round passage with a smooth floor.

“I’d never seen anything like it before,” said Adamy, who resolved to return for a closer look some day. “It really grabbed my attention. It didn’t look natural.”

Galerias-paleotoca

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)

A few years earlier, and about 1,700 miles to the southeast, another Brazilian geologist happened upon a different, equally peculiar cave. Heinrich Frank, a professor at the Federal University of Rio Grande do Sul, was zipping down the highway on a Friday afternoon when he passed a construction site in the town of Novo Hamburgo. There, in a bank where excavators had eaten away half of a hill, he saw a peculiar hole.

Local geology doesn’t yield such a sight, so Frank went back a few weeks later and crawled inside. It was a single shaft, about 15 feet long; at its end, while on his back, he found what looked like claw marks all over the ceiling. Unable to identify any natural geological explanation for the cave’s existence, he eventually concluded that it was a “paleoburrow,” dug, he believes, by an extinct species of giant ground sloth.

“I didn’t know there was such a thing as paleoburrows,” says Frank. “I’m a geologist, a professor, and I’d never even heard of them.”

Rise of the Burrow

Until the early 2000s, in fact, hardly any burrows attributed to extinct megafauna had been described in the scientific literature. That’s especially curious because, after his chance discovery in Novo Hamburgo, Frank caught the burrow bug and began finding them in droves.

paleoburrow-3

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

Surveying a 45-mile stretch of highway construction near the city of Porto Alegre, for example, Frank and his students identified paleoburrows in more than 70 percent of road cuts. Although many are completely filled with sediment, they remain readily apparent, standing out like dark, round knots in a dirt bank. Others are still open, like the one that first attracted Frank’s attention.

When Frank found a suitable passage, he squeezed through an elliptical shaft roughly four-feet wide, 65-feet long and lined with claw marks. Extrapolating from the original size of the hill sliced away for the highway, he calculated that the original burrow was about 250 feet long, not counting for twists and turns that it surely once included.

“There’s no geological process in the world that produces long tunnels with a circular or elliptical cross-section, which branch and rise and fall, with claw marks on the walls,” says Frank. “I’ve [also] seen dozens of caves that have inorganic origins, and in these cases, it’s very clear that digging animals had no role in their creation.”

paleoburrow-4

Outside the entrance to a paleoburrow. (Courtesy: Heinrich Frank)

In his home state of Rio Grande do Sul, in the far south of Brazil, Frank has documented at least 1,500 paleoburrows so far. In Santa Catarina, just to the north, he’s found hundreds more and counting.

“In these burrows, sometimes you get the feeling that there’s some creature waiting around the next curve – that’s how much it feels like a prehistoric animal den,” he says.

The First in the Amazon

It wasn’t until 2015 that Amilcar Adamy of the CPRM had an opportunity to return to that strange cave in Rondonia. It turned out to be the first paleoburrow discovered in the Amazon, which is notable, but not the coolest part. It also turned out to be one of the largest ever measured, with branching tunnels altogether tallying about 2,000 feet in length. The main shafts – since enlarged by erosion – were originally more than six feet tall and three to five feet wide; an estimated 4,000 metric tons of dirt and rock were dug out of the hillside to create the burrow.

“This wasn’t made by one or two individuals,” says Adamy. “It was made by many, over generations.” Frank describes it as an exciting, though not particularly surprising, discovery.

“We knew that there could be burrows this big,” he says. “This huge one in Rondonia simply confirms that they do exist.”

In Rio Grande do Sul, Frank has found burrows that were originally several hundred feet long. More than 1,000 total feet of tunnel have been measured in another burrow in the Gandarela Mountains, far to the north in the state of Minas Gerais. Though he has yet to investigate, Frank’s received reports of one burrow more than 3,000 feet long in Santa Catarina.

Prehistoric Engineers

Frank believes the biggest burrows – measuring up to five feet in diameter – were dug by ground sloths. He and his colleagues consider as possibilities several genera that once lived in South America and whose fossil remains suggest adaptation for serious digging: Catonyx, Glossotherium and the massive, several-ton Lestodon. Others believe that extinct armadillos such as Pampatherium, Holmesina or Propraopus, though smaller than the sloths, were responsible for even the largest burrows.

paleoburrow-digging

Regardless, 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.”

Dating the burrows also remains guesswork at best—animals don’t dig holes after they go extinct. However, they had to have been dug at least 8,000 to 10,000 years ago, when South America’s giant ground sloths and armadillos vanished. Dating organic material found in burrow sediments – which has yet to be done – would reveal when sediments washed in, but not necessarily when the burrow was dug. Frank says that speleothems, or mineral deposits, growing on burrow walls could be used to calculate an age, although that hasn’t been tried yet either.

Another head-scratcher is the strange geographic distribution of paleoburrows. While common in the southern Brazilian states of Rio Grande do Sul and Santa Catarina, they are, so far, almost unknown just to the south in Uruguay (though some of the first ever described were found even further south in Argentina). Likewise, very few have been found farther north in Brazil, and Frank is aware of just a tiny handful of possible burrows in other South American countries.

scratch-marks

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

He doesn’t think he’s biased because he happens to live and work in the heart of burrow country. Frank has colleagues who have searched extensively elsewhere in Brazil and come up mostly empty. He’s also done sleuthing using Google, searching for images of caves posted by others. In the south of Brazil, he frequently identifies paleoburrows by details unwittingly captured in photos, like one of a smiling troop of Brazilian boy scouts posing in front of a cave wall covered with claw marks. In other parts of the country and continent, people post pictures of caves that they visit, but practically none of them look like they were originally dug by animals.

A South American Thing

Though North America was also once home to giant ground sloths and giant armadillos, you won’t find paleoburrows here.

“The fact that we don’t have them here could simply be that we’ve overlooked them,” says Greg McDonald, a Bureau of Land Management paleontologist who studies extinct South American sloths. “[Or] it may be that we had them up here but didn’t have the right types of soils that allowed them to survive for a long time.”

Here, too, unanswered questions are raised by absence of paleoburrows. The beautiful armadillo, Dasypus bellus, an extinct creature about twice the size of today’s nine-banded armadillo, was widespread in Pleistocene North America and had forelimb morphology very similar to that of modern armadillos, which are enthusiastic burrowers. Beautiful amardillo remains are frequently found in caves, but not ones scientists have ever thought were actually dug by the animal.

Megatherium_americanum

In South America, giant sloths—some the size of elephants—roamed the surface, and were, perhaps, expert tunnel diggers. (Credit: Wikimedia Commons)

Another possibility, McDonald allows, is that paleoburrows are found in North America, but no one has paid them any attention, as was the case in South America until quite recently.

“Something can be out there and they’re so common and people just take them for granted,” he says. “And [no one knows] till somebody with a little bit of curiosity takes a closer look and says, ‘What’s forming these?’”

For the handful of scientists in South America studying paleoburrows, there’s a long list of research projects to design, all revolving around the same basic questions: who, why, what, where and when?

At the top of Frank’s list is to better describe patterns emerging from observations he’s collected studying paleoburrows for the past decade. Some are simple shafts; others are complicated works of underground engineering, with branching tunnels that twist and turn and rise and fall to form a network with more than one entrance. Some occasionally open up into much larger chambers. There are relatively small ones. Then there are the enormous ones.

“We need to figure out the patterns. We’re starting to understand this better,” Frank says. “And from there, we’ll be better able to infer what kinds of different animals were digging them.”

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  • Mike Richardson

    They do remind me of super-sized armadillo burrows. Maybe giant ground sloths are contenders for these tunnels, but I wouldn’t rule out the some of the larger prehistoric Amarillo species either.

  • Wendy McNally

    Maybe they aren’t tunnels dug by animals.

    Maybe giant trees from the past pushed their long, round roots…spiraling and twisting…creating smooth curving tunnels as they attempted to reach water sources.

    Perhaps the succulent tender ends of the roots were clawed and eaten by large animals.

    Are there any signs of growth rings along the insides of the tunnels?

    Wendy

    • femmebot

      Wouldn’t root systems create a Fibonacci-like pattern?

    • Ian Collins

      How would you explain the claw marks?

      • Danygalw

        I agree.

      • Richard

        As Wendy stated: “Perhaps the succulent tender ends of the roots were clawed and eaten by large animals.”

        • wendy king

          but Richard, those claw marks are way inside the tunnels and up on the ceiling. No large animal could reach in that far. There would be some indication of plant matter somewhere if nibbling roots were the answer to the tunnels. I think the giant armadillo scenario seems more reasonable than giant sloths. Sloths don’t dig, armadillos still do. (And don’t touch or eat them, they cause leperosy!) I still like the idea of a movie for this story…. (grinning!)

      • wendy king

        from claws? roots don’t have claws.

    • Danygalw

      They said there are claw marks along the insides of the tunnels.

    • RabbleRabbleRabble

      I honestly think it would be easy (especially for local geologists) to judge if this were made by a plant versus an animal. The pattern and size of the branching tunnels, plus any indication of root behavior like foraging for water would be noted and easy to recognize. There would almost certainly have to be some sign of wood print and even some degree of plant material on the walls. There would be little reason for the roots to grow with a rounded top, but flat bottom like these tunnels are shaped, and plants are mostly shaped in response to stresses/influences in their environment. There has also been no evidence found so far of any trees larger than the largest giant sequoia, and if you google a pic of a sequoia’s root system, you’ll see that even though these trees are taller than the Statue of Liberty, their roots wouldn’t even come close to making tunnels this :)

  • rollie nelson

    There are possible “paleoburrows” in del norte county in northern California. In Lake Earl and around the Klamath river estuary. Although local tribal oral history associates them with a water serpent. The stories usually place the entrances underwater as they were used by the serpent to travel underground great distances between bodies of fresh water. Many of the “known” tunnel locations are buried in silt build-ups created by the dams on the river. My tribe considers it to be an evil being due to the numerous deaths attributed to it in the past.

    • CptDavenport

      There is a tunnel around here, south Brazil, near the sea with the same local folklore: water serpents.

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      • wendy king

        So here are two clues as to how Nessie gets from one lake to another! The old myths are founded on truth. They could also just be natural caves systems used by the ‘monster’ since they occur along a fault line as in Scotland, and in karst topography.

        • rollie nelson

          “Kay’moss” was known to be active within the last hundred and fifty years.

          I believe it was not a spirit. It was considered a real thing back then. While the Yurok had a very complex religion, Kay’moss not a part of that. It was part of the real world. And it really killed people.

  • Matias Taglioretti

    Xenarthran paleoburrows were investigated and first time reported in Argentina. Good paleoburrows expositions are preserved in Mar del Plata sea clift (Buenos Aires, Argentina). https://uploads.disquscdn.com/images/e46ad682691fc957f23bb6e9d3873aaa3f3984b6a9462d4c2d4bad8e7448df13.jpg

  • Erik Bosma

    Time to start calling in the archaeologists. Let’s find some bones, boys and girls. Although I think they’re probably a shared burrow begun by one animal and then enlarged and reformed by later generations of the same and different animals. Possibly even paleo-Brazilians had a hand in them too. Check for smoke residue, firepits, etc.

    • DPenhead

      Paleontologists. Though, needing archaeologists would be even cooler!

  • (((kired)))

    Maybe the creatures that dug them migrated to South America for mating or another reason, and some of the larger tunnels were communal.

  • Steve Mumford

    Glyptodons and Deodicurus seem much more likely to me than ground sloths. Modern sloths don’t burrow, whereas modern armadillos do.
    Most of the ‘caves’ are tight. Ground sloth remains in North American caves are in large caves, spacious, not burrow-like.

    • Toby James Irving

      Modern sloths are really weird as sloths go though.
      The extinct ground sloths were for a start entirely comfortable on the ground, and they also didn’t poop a third of their bodyweight once a week as far as we know (can you imagine the size of the coprolites we’d find if they did?). Ground sloths were terrestrial, unlike modern sloths and the extinct aquatic sloths, so I don’t think you can rule out burrowing because the highly specialised arboreal sloths of today don’t.

      • wendy king

        Has anybody ever found giant poops of any ancient species? We find nests and eggs and know there were a lot in one area in Mongolia, but nobody writes about finding giant fosilized poop, sorry, craprolites?. Im just curious as to why?

        • faile13

          They actually do, and study it.

        • Paul Block

          I have a coprolite in my hand, as it happens. Now I have put it down so that I can type. I found it on a beach facing the North Sea so it could have come from anywhere, along with the amber and fossilised wood which I collect.

    • wendy king

      Good observation!

  • Gabriel Fortune

    maybe there was some now-extinct predator they were protecting themselves from. I don’t know much about prehistoric S American mammals – I understand that at some point the main predators were sabre-toothed marsupials?

    • Steve Mumford

      No, these would have likely dated to after humans arrived. Most paleontologists believe that humans played some role in the extinction of the megafauna, about 12,000 years ago.
      At that time, the Americas were connected by the Panamanian land bridge. There were lots of big predators including lions, smilodon, homotherium, bears, wolves, jaguars, etc. Even the big sloths would have needed some protection.

  • Pete Wagner

    Would explain how the Amazon women seen by the Spanish explorers got there from and then returned to the inner world.

  • Jackson Landers

    Great article, awesome photos, good writing, I am jealous.

    But that graphic you included. Seriously, what is that? What information do you think that even conveys? The sloth did some digging, then rested, then dug some more. And then the tunnel gets a nickname? How much vodka went into the design of that graphic?

    • Electronic Yogi

      info-graphic could be better perhaps. The stage-digging however can be clearly seen in the A, B and C photos. You haven’t looked very carefully.

    • Blue_Oak

      Haha, I had a similar unease about that graphic but hadn’t had my coffee yet. This might be what happens when geologists, for whom I have great respect, stretch outside their area of expertise.

    • RicardoB

      It shows the characteristic shape of a series of domes rather than a straight tunnel and the hypothesis of why that shape formed. Most burrowing animals do it all at once leaning a straight shaft but also don’t burrow as far.

  • bwana

    The extinct giant ground squirrel is probably responsible for a fair number of these burrows… :) :)

    • wendy king

      The plot thickens! Giant squirrels??? Really???

      • bwana

        Either that or sasquatches :) :)

  • Rainald Koch

    I wonder why nobody addresses the hypothesis that the paleoburrows have been excavated by humans.

    Other idea: I remember salt-mining elephants in Africa.

    • Danygalw

      Because of the claw marks.

      • Maia

        And the scooped segmentation of the walls.

        • Rainald Koch

          A weak argument given the far-fetched explanation for the segmentation.

          • faile13

            I find the segmentation arcs of the tunnel to be fascinating….if those animals had not paused creating those ridges, the tunnel would’ve collapsed. The natural arcing supported them for thousands of years by distributing the weight.

      • Rainald Koch

        I expect claws consisting of more than one finger and miss the corresponding pattern on the cave walls. A singly-pointed (human) tool would match the presented images. Just an idea that I miss being discussed.

        • faile13

          Look at the claws of the sloth, tightly spaced, unlike tiger or bear. More like multiple buckets on an excavator, but scraped – not shoveled. I think humans would’ve used wider tools like shells or pieces of wood or bone. Narrower to start a section or work around a problem area, but broader for overall volume. Human tool were pretty diversified and specialised.

  • J.YOUNG

    What is the point of these studies? Of any prehistoric studies? Just really something to do. A lot end up as mere guesses anyway. Better to
    allocate time/resources for modern flora/fauna challenges.

    • Christopher Spence

      Well, as the saying goes, “if you don’t know I can’t tell you”- and it begs the question- why comment on an article that doesn’t interest you? You must have alot of time on your hands-so chop!chop! J. Young-add something to the wonderful rich story of the planet Earth and its inhabitants- living or dead!

    • Electronic Yogi

      Well, these tunnel systems begs for a coherent description and understanding.

      Do you seriously believe that these dudes would study modern flora/fauna challenges if they weren’t trying to understand these phenomena? And – actually – describing and understanding pre-historic flora/fauna is heavily linked to understanding modern flora/fauna. You would know if you knew anything about flora/fauna at all.

      And a question: Which specific parts of “modern flora/fauna” do you feel is being neglected or underfunded?

      • J.YOUNG

        Never said anything neglected. Still say these studies useless. How does knowing. Tell me how knowing what/how/why these tunnels were built is relevant today?
        They extinct anyway, which means to say natural selection say they are irrelevant.

        • Vincent J.

          Much science is driven by the personal curiosity of the scientist. Note that the article opens with a guy who took the time to crawl into a curious-looking hole. I doubt that this required a government grant, and I doubt that it took any time away from his day job. If somebody were to tell him that he’s wasting his time and is not allowed to do such things, it’s unlikely he’ll be interested in those things which you find important.

        • skyfaller

          So as soon as you’re dead, everything you did was irrelevant, yes? Especially if you didn’t leave any children behind, meaning that your life was genetically irrelevant.

          • Steve Kellmeyer

            As a complete sidenote, I find it fascinating that most vociferious proponents of evolution have two or fewer children: they don’t even reach replacement fertility with their own genes. It’s almost like they don’t believe their own theories.

            Charles Darwin had 10 children – he backed theory with action. Modern evolutionists? Yeah, no.

          • skyfaller

            It’s possible to believe that natural selection exists, while simultaneously not caring about your genes achieving world domination. You might try to spread your memes instead, for example.

            I think my genes are pretty decent but they’re far from my highest priority in life.

          • Steve Kellmeyer

            Well, since evolution likewise teaches there are no good nor bad genes, but only what survives, then no evolutionist would be upset with the movie “Idiocracy” or the use of Brawndo.

            An evolutionist would only note that people so stupid that they voluntarily choose not to have children are actually the ones who are not viable.

          • faile13

            You have proof that Darwin had 10 children to back his theory of evolution? I hardly think that was foremost in his mind😄. Reminds me of Monty Python and the Meaning of Life:
            Protestant Husband: “The Catholics, everytime they have sex, they have to have a child!”
            Protestant Wife: “Well that’s right, dear. We have two.”

          • Steve Kellmeyer

            Well, I give Darwin the benefit of the doubt. If you want to argue that Darwin was a hypocrite just like the other evolutionists, feel free.

        • faile13

          But the work lives on without collapsing for 10,000+/- yrs….look at the pictures of the natural arc created by the digging process and tell me what you learn about weight disbursement? If you don’t learn from what you observe and pass it on, then you will become extinct. Each discovery and understanding it builds off the last. Which is why we are communicating this way instead of by grunting and pantomime. How can you use modern technology at all and say all these studies are useless? Or do you still tear raw meat with your teeth?

        • Steve Mumford

          Yes, J. Young, better to ignore these ‘useless’ things that can’t effect anything here and now. Also, the history of evolution. Also most art & literature, which, when you think about it, is pretty ‘useless’, especially the old stuff that only a few losers read or look at.
          Say, pass me the bong, will you?

  • ButILikeCaves

    As for the absence in Florida, once home to many sloths, I attribute that to the plethora of caves we have. Ready made burrows, and many giant ground sloth fossils have been found in them. In all my caving years, I have never come across something like these tubes.

    • wendy king

      How does it happen that ‘many’ ground sloths died in their caves? How did they die inside their caves? How? Why? You would think they would be safe inside their cave and die outside of it.

      • ButILikeCaves

        Died in their sleep?

        • wendy king

          Maybe the skeletons were babies that died?

      • Paul Block

        No one is safe from old age. I have seen my cats retire to a quiet corner when they knew their time was up. We need some work to find skeletal remains in these burrows or high concentrations of phosphates to indicate faeces. I would love to know what geology pertains here. Did these beasts actually carve a way through rock or was it soil that has since become impacted? The subject is fascinating.

      • http://www.wendymcnally.com Wendy Mcnally

        Any numbers and types of animals may have died in these tunnel caves due to disease, old age, starvation or predation.

        Even human skeletons might be found but, it doesn’t mean that any of the creatures found dead in these caves were responsible for making the caves.

  • Pete Wagner

    Wow, of all the crazy stories to explain away the inner Earth under world (to include journeys down depicted in ancient texts), this one is high on the list. So these big sloths didn’t spend much time eating? Is the movie coming?

  • Taco Cat

    graboids!

  • http://dragonflypower.com/index.html BillCornelius

    ground sloth coprolites gave been found in lava tunnels in Nevada and (I think) California.

  • tuna_MEOW

    Have any of their bones been found?

  • StanChaz

    That Star Trek episode!

  • thaidude

    I can visualize a sloth clawing away to make a tunnel…but how could they remove tons of dirt from a horizontal hole hundreds of feet long?

  • Vincent J.

    Aliens dug these tunnels. Yeah, that’s it. It was the Greys. That’s it. That’s the ticket.

  • Shelley Williamson

    Maybe they were after salt or other minerals in the rocks. Elephants carve large caves digging for salt with their tusks.

  • Wendy Mcnally

    The stop and start pattern is why I think tunnels were made by mega flora…persistent roots of vines snaking along forming the rounded pushing effect of continuous but, not consistently effortless forward growth.

    The flat bottoms of the tunnels are probably from centuries of water and soil erosion…and, GRAVITY.

    NO ALIENS HERE!!!

  • wendy king

    Wouldn’t this story make a great movie? A bunch of eleven year old boys go exploring, find tunnel with monster sloth living at the bottom?!!! Who doesn’t attack them but grabs all of them in a giant paw and clutches them to its furry chest, rolls over, falls asleep and snores!!

  • faile13

    I’m wondering if these tunnels weren’t the products of more than one species, say, giant worms (takes care of the dirt removal, as well as addressing the serpent legends), then sloths or something come along and forage or scavenge? Nutrients in the walls? Growth of fungal or plant matter? I have no clue. Also, can’t the scientists who deal with ancient fauna estimate the size of the animals based on the spread and length of the claw marks? That would be helpful in determining if perhaps more than one animal was responsible for the tunnels, animals rarely create spaces larger than what they need. Were the giant ground sloths known for creating burrows to live in? Or were they more likely to dig a tunnel following prey? Chasing large, protein laden worms or other burrowing critter…or following a network of delicious roots?

    • Only Some Stardust

      Some animals have disproportionately huge claws for their size.

  • https://vehiclepad.com/ Audi A3

    How would you explain the claw marks?

  • Capn Jack

    Oh No! Giant Prairie Dogs

  • Juliet E. Morrow

    Very cool, thanks for posting this. I’ve been telling my students for years about the potential damage done by megafauna digging in the pleistocene, but I did not know that Giant sloths were diggers.

  • Ron

    Giant ground sloth skeletons have been found in the Eastern U.S., almost exclusively in natural caves. The presence of these extensive and abundant caves might mean that they didn’t have to dig tunnels. They just used the caves that were already available.

  • Joanne Ballard

    In the photo captioned “Outside the entrance to a paleoburrow. (Courtesy: Heinrich Frank)”, is that modern graffiti on the outside of the cave?

  • donlawler

    not claw marks – tool marks. Think a minute about the incredible wear that tunneling through stone would put on the claws and teeth of any megafauna creature.

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