Brazilian paleoburrows?

Aliens, secret military operations or megafauna?

Adam Hennessy
8 min readFeb 1, 2022


Something a little different today, but something I found really intriguing.

We will be delving (pun intended) into the underground ‘tunnels’ in Brazil that have been found winding beneath the Amazon.

What are they?

I parenthesised the word ‘tunnel’ as while colloquially correct the actual term given to these structures is paleoburrow.

Defined a paleoburrow is an

“burrow formed by an animal of the ancient past.”[1]

Wikipedia goes a little deeper and a better functional definition is that a paleoburrow is

“an underground shelter (tunnel, burrow, lair, etc.) excavated by extinct paleo-vertebrate megafauna (i.e., giant mammals, such as ground sloths) that lived in the prehistoric era.”[2]

Generally, these burrows are small (large compared to their modern equivalent, but nonetheless overall quite small. However, what brings us here today is a particular system of tunnels discovered by Amilcar Adamy a geologist working for Brazilian Geological Survey (known as CPRM [its Portuguese initialisation]) in 2010 and explored in 2015.

Credit: Amilcar Adamy/CPRM

This burrow system is massive.

It has a main entrance with branching tunnels totalling around 2,000 feet in length. The main shaft (pictured above) is larger today than it was when dug, due to erosion, but even at the time best estimates place it at over 6 feet 3–5 feet wide. This equates to about 4,000 metric tons of dirt and rock that was excavated to create the burrow.

4,000 metric tons is 4 million kilograms or 8,818,490 pounds.

Credit: Amilcar Adamy/CPRM

Where are they?

The large site mentioned above is beneath the Amazon in Brazil in a place called Rondonia, a few miles north of the Bolivian border.

Curiously they are littered (not as large as this) throughout the South of Brazil (even as far south as Argentina) but are non-existent to the north of Brazil.

The most prolific researcher and paleoburrow hunter is Heinrich Frank, a professor at the Federal University of Rio Grande do Sul, who has documented over 1,500 paleoburrows across Brazil.[3] Most of his finds are smaller burrows that do not extend as far into the earth and are not as expansive as the Rondonian burrow.

Heinrich Frank

Digging around these paleoburrows are not unique to South America.

In Victoria, Australia in an outcrop of the Otway Group (Albian) three structures are thought to show the first evidence of dinosaur burrows outside of North America.[4] A semi-circular burrow, the size here is much smaller a constant diameter of around 1 foot and around 7 feet long with a slow and gradual decent.

In North America we have a burrow in eastern Pennsylvania, in the Mississippian Mauch Chunk Formation. This formation is believed to date to 345–320 million years ago. The burrow is semi-circular around 1.5–2 feet in diameter with a maximum height of 0.6 feet.[5]

You can see from the images that these burrows are fossilised and far less exciting than their Brazilian counterparts and this has to do with age.

When did all this digging happen?

The Brazilian paleoburrows are thought to be around 10–12,000 years old. So relatively recent in the scheme of Earth’s history and are seemingly without comparison anywhere in the world. The issue with the two sites (North America and Australia) is age the Australian site is from Late Cretaceous period 100.5–66 million years ago and the North American site is thought to be from much earlier 345–320 million years ago.

Therefore, the Brazilian burrows are a historical anomaly.

So, what made the paleoburrows?

While the focus is on the Brazilian burrows, lets just quickly look at the Australian and the North American for a moment.

It is thought, even though separated by time both burrows were created by a form of Tetrapod.

The Australian burrow is based of some prints in the greater area and by a process of elimination. The North American site the engineer was discovers based on its actual tracks fossilised at the site of the burrow.[6]

Spencer G. Lucas et al
Spencer G. Lucas et al

I raise this just to show how comparatively benign this creature is compared to what is believed to have constructed the Brazilian tunnels.

Giant sloths!

Yes you read that right it is believed that the largest burrows were dug by ground sloths. There are three fossilised suspects that researchers looked at.

1. Catonyx

Was a large ground sloth thought to have roamed the forests of Brazil until around 10,000 years ago. Its weight has been estimated at around 1,640kg[7] (3616lb). You can see below the claws of this beast — perfect for digging.

Eduard Solà

2. Glossotherium

These ground sloths are slightly smaller than the Catonyx with a length of about 13 feet snout to tail-tip and weighing around 1,480kg[8] (3263lb). They are thought to have become extinct around 12,000 years ago.

3. Lestodon

The biggest of the suspects standing around 15 feet tall and weighing in at 2,590 kg (5710lb). While the first thought might be this has to be the excavator these creatures were believed to have died out around 15,000 years ago.
Green is the Glossotherium, blue is the Lestadon and red is the Catonyx. Credit: artbyjrc

4. There are some researchers who believe an extinct armadillo (Pampatherium) was the architect of the burrows, but they are small compared to the sloth’s cited above. Below there is a wonderful artistic depiction of some of the creatures mentioned heretofore.

Interestingly there have been paleolithic cave paintings depicting giant sloths from around the time of their extinction found which offer evidence of their existence at the time and evidence of their scale.


This pictograph depicts a giant land sloth and the humans at the time, while there may well be artistic licence the dimensions do seem to match a 15-foot-tall mega-fauna creature.

We know there were giant ground sloths, from depictions at the time and from fossils, but did they dig the burrows?

Here are some theories.

No- they are human made.

The burrows/tunnels (the largest ones) were dug by ancient peoples as a means to escape predators and the environment. They could be fortified, and they could fit large collectives and act as a base for hunter, gatherer culture. The issue with this is two-fold. Tools at the time may not have been sophisticated enough to be able to achieve the dimensions we see and there is not art depicted within any given tunnel system. If history has shown us anything, when we make a home, we decorate.

While there are marks which could indicate tools, they are currently theorised to have been made by the claws of the sloths.

Heinrich Frank

Earliest form of D.U.M.B

Ok so this is a silly one I wanted to throw in.

Common conspiracies in modern day are that government, often in league with extra-terrestrials have deep underground military bases (D.U.M.B’s) in which they research advanced tech and conduct a myriad of experiments.

Could these tunnels be the openings of an ancient alien version of this, and we are yet to find the way deeper?

No — ok moving on.

Sloth burrows

This seems to be the most logical conclusion.

The timing is right, the size seems close enough (although there is some conjecture that they are oversized for need based on current burrowing), but little is known of the family structure of these early sloths, it could be they lived in family groups, after all fossil remains are often grouped.

I believe that our mega-fauna created paleoburrows and we are yet to fully appreciate the amount we have on our earth.

Here in Australia, we had many mega-faunas so it is a matter of when not if we discover our own, so hit the trail and start exploring.

Keep hunting for the truth.




[3] Jenner, Andrew (March 28, 2017). “Get Lost in Mega-Tunnels Dug by South American Megafauna”. Discover. Kalmbach

[4] Anthony J. Martin, Dinosaur burrows in the Otway Group (Albian) of Victoria, Australia, and their relation to Cretaceous polar environments, Cretaceous Research, Volume 30, Issue 5, 2009, Pages 1223–1237.

[5] Lauren Storm, Mattathias D. Needle, Casey J. Smith, David L. Fillmore, Michael Szajna, Edward L. Simpson, Spencer G. Lucas,

Large vertebrate burrow from the Upper Mississippian Mauch Chunk Formation, eastern Pennsylvania, USA,

Palaeogeography, Palaeoclimatology, Palaeoecology,Volume 298, Issues 3–4,2010,Pages 341–347.

[6] Spencer G. Lucas, David L. Fillmore & Edward L. Simpson (2010) The Mississippian Tetrapod Footprint Ichnogenus Palaeosauropus: Extramorphological Variation and Ichnotaxonomy, Ichnos, 17:3, 177–186

[7] Boscaini Alberto, Iurino Dawid A., Mamani Quispe Bernardino, Andrade Flores Rubén, Sardella Raffaele, Pujos François, Gaudin Timothy J. Cranial Anatomy and Paleoneurology of the Extinct Sloth Catonyx tarijensis (Xenarthra, Mylodontidae) From the Late Pleistocene of Oruro, Southwestern Bolivia. Frontiers in Ecology and Evolution. Vol 8 2020.

[8] Boscaini Alberto, Iurino Dawid A., Mamani Quispe Bernardino, Andrade Flores Rubén, Sardella Raffaele, Pujos François, Gaudin Timothy J. Cranial Anatomy and Paleoneurology of the Extinct Sloth Catonyx tarijensis (Xenarthra, Mylodontidae) From the Late Pleistocene of Oruro, Southwestern Bolivia. Frontiers in Ecology and Evolution. Vol 8 2020.