A new theory proposed by researchers suggests that a series of mysterious ancient Amazon caves were not created by ancient humans as previously thought, but instead may have been dug out of the Earth by massive ice age beasts that have since become extinct.
The Armadillo’s Den in southern Brazil is among the most studied of the mysterious ancient Amazon caves. Known as Toca do Tatu in Portuguese, this enigmatic formation has baffled scientists who couldn’t readily determine who or what dug it into the sandstone bedrock. Although local legend suggests that the Armadillo’s Den was used by Jesuit missionaries to hide gold several centuries ago, no gold has been found.
More recently, a group of researchers proposed that Armadillos Den and several of the 1,500-2,000 mysterious ancient Amazon caves found in the region were created by giant sloths weighing nearly two tons. If correct, the theory could solve a decades-old mystery while identifying the largest such tracks left by any ancient organism ever discovered.
Mysterious Ancient Amazon Caves Only Found Locally
In an article published in Nature, several researchers proposing the giant sloth theory discussed the evidence supporting that conclusion.
First, many researchers cited note that most of the known examples of ancient sandstone caves are concentrated within Brazil, with the remaining few in Argentina. This alone means they are less likely to represent a natural formation.
According to Heinrich Frank, a retired geologist formerly at the Federal University of Rio Grande do Sul in Porto Alegre, Brazil, the majority of the larger caves, which can reach 2 meters in height and 4 meters in width, were filled with rubble, making them hard to find.
“We often find them when a company is doing some earth-moving work for construction,” Frank explained.
Early 20th-century scientists assumed Indigenous ancient humans carved the caves due to many of the older inscriptions found on the cave walls and ceilings. When taking tourists through Armadillo’s Den, local guide Vadevino Alano highlights a peculiar zig-zag carving on the wall left behind by archaic humans.
“This line puzzled many explorers who came here in the past,” Alano says. “But what it most certainly shows is an ancient map of the Rocinha River that flows nearby.”
“Past Indigenous groups could have used it to orient themselves in the region,” says Alano, a descendant of one of the Indigenous groups that could have made the enigmatic carving.
While many of the inscriptions are made by humans, the larger scratches found on the walls and ceilings of several of the mysterious ancient Amazon caves have baffled researchers for decades.
Giant Ice Age Beats May Have Dug the Caves Over 10,000 Years Ago
Sergio Vizcaíno, head of the vertebrate paleontology department at the La Plata Museum in Argentina, first proposed in 2001 that the mysterious ancient Amazon caves be attributed to animals instead of humans. In that study, Vizcano and colleagues suggested that the large claw marks discovered in many of the caves match perfectly with the claws of giant sloths that roamed the area thousands of years ago before going extinct.
In 2012, Frank and Francisco Buchmann, a paleo-oceanographer at São Paulo State University in São Vicente, Brazil, were part of the first group to describe the Armadillo’s Den. Like Vizcaino, the researchers determined that giant sloths may have dug out the caves.
Scientists classify these tracks, tunnels, and other markings left by ancient organisms, including sloths, as ichnofossils. The most extended researchers have adequately described lies within Pará state in the Amazon region. According to Buchmann, while most smaller caves are around 50 meters long, the Pará state caves have combined internal galleries that add up to over 1,500 meters long. If confirmed, it would represent the largest ichnofossil ever described.
Several Alternate Theories Behind Mysterious Ancient Amazon Caves
Several alternative theories have been proposed to explain the mysterious nature of the mysterious ancient Amazon caves. For example, Vizcaino believes they may have been burrowed gradually, with several generations adding to the caves’ overall size.
“Palaeoburrows must be transgenerational,” he explained, “as the energy cost decreases when the work is done by many individuals.”
Néstor Toledo, a comparative anatomist at the La Plata Museum, says that giant sloths aren’t the only animals from the last ice age that could have made the caves. Instead, he suggests that giant prehistoric armadillos might have carved many smaller burrows, ranging from 0.6–1.5 meters wide by 0.5–0.9 meters high, to hide from predators. For the larger caves, Toledo suggests that giant sloths “could have started digging to protect themselves from a colder and drier climate.” They may have also used the caves to hide offspring.
One researcher skeptical of this explanation is Cástor Cartelle, a paleontologist and curator of the archaeology collection at the PUC Minas Museum of Natural Sciences in Belo Horizonte, Brazil. According to Cartelle, animals of this enormous size wouldn’t need to seek shelter from predators.
“Why would an animal this size need refuge?” he asks.
Still, Cartelle acknowledges that the scratches that match the giant sloth claw patterns suggest that the ancient beasts could have used naturally existing caves to sharpen their claws.
“The markings on the walls match the number of fingers and the anatomy of these animals, but it really makes no sense to me in saying they have carved these burrows,” he says.
More Scientists Needed to Find and Study the Caves
In the article’s conclusion, several local researchers highlight the urgent need for more international scientists to study and categorize the hundreds of known paleo burrows and search for undiscovered ones. Arthur Philippe Bechtel, a geographer at the Federal University of Santa Catarina in Florianópolis, Brazil, says that researchers “don’t have many measurements” of the various rock types and environments in which the caves are found. He also notes that there is a lack of standardization in the research, which makes analysis difficult.
João Henrique Ricetti, a paleontologist at Contestado University in Mafra, Brazil, says that attracting people to this field of research is difficult since the work is unlikely to produce “mind-boggling studies in the short term.” Still, Luis Buatois, an ichnologist at the University of Saskatchewan in Saskatoon, Canada, says that these mysterious ancient Amazon caves “are spectacular enough to gain attention from scientists in other parts of the world,” and he encourages researchers to come and study these unusual structures.
“This is an archaeological and palaeontological marvel,” says Juliano Campos, an archaeologist at the University of the Extreme South of Santa Catarina (UNESC) in Criciúma, Brazil.
“The more diverse people come to study the place, the more knowledge we’ll have about it,” says Alano, whose scientific guests still mostly originate from the local region. “Who knows what they’ll find in the future?”
Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.