A colossal mammal that roamed South America some 10,000 years ago may have transformed the landscape in ways few imagined—by digging massive underground tunnels. Dubbed "palaeoburrows," these mysterious caves were discovered in Brazil by Professor Heinrich Frank from the Federal University of Rio Grande do Sul. Frank was puzzled by their size and structure when he first crawled through one found during a construction project in Novo Hamburgo. His inspection revealed unmistakable clues: claw marks embedded in the walls and ceilings.
What could have left those giant claw marks? Image credit: Heinrich Frank
Frank concluded these tunnels couldn’t have been created by geological processes. "There’s no natural formation capable of producing such long, branching tunnels with elliptical cross-sections and claw marks on every surface," he told Discover.His findings suggested the tunnels were carved by an extinct creature with tremendous digging ability—most likely the giant ground sloth, known scientifically as Megatherium americanum. Though some scientists initially speculated that giant armadillos might have been responsible, the scale of the burrows and the deep claw marks pointed to Megatherium, one of the largest land mammals of the Pleistocene epoch.Thousands of Prehistoric Burrows Across Brazil
Frank discovered his first palaeoburrow in the early 2000s and quickly realized it was part of a much larger phenomenon. He found more than 1,500 similar tunnels across Rio Grande do Sul, with hundreds more stretching through the neighboring state of Santa Catarina. Some of these tunnels extend hundreds of feet, branching off like a maze. The largest recorded tunnel spans 2,000 feet in length, measures six feet tall, and five feet wide."When you explore these burrows, it feels like something ancient could still be lurking around the corner," Frank wrote, describing the eerie sensation of being inside what once housed a massive animal.These giant sloths, second only to mammoths in size, stood up to 15 feet tall and weighed approximately 2,590 kilograms (5,709 pounds). They were herbivores, despite their enormous claws, which were likely used for digging rather than defense or tree-climbing. However, the purpose of the tunnels remains a mystery. A smaller den could have served to avoid predators or harsh weather, so researchers speculate that multiple sloths might have inherited and expanded the burrows over generations.
Image credit: Rodolfo Nogueira / SourceA Legacy of Prehistoric Giants
The first Megatherium fossils were unearthed in 1787 by Manuel Torres in Argentina. These remains were later shipped to Spain, where the original skeleton is still displayed at the Museo Nacional de Ciencias in Madrid. In 1796, the renowned French anatomist Georges Cuvier classified the creature as a sloth and initially believed it used its claws for climbing. However, Cuvier eventually proposed a digging lifestyle for the animal, which aligns with the palaeoburrows' discovery centuries later.Though these sloths were plant-eaters, they weren’t immune to danger. Fossil evidence suggests they coexisted with early humans, who may have hunted them for food. Some Megatherium bones display cut marks, hinting that human activity might have contributed to the animal's extinction.
Charles also collected Megatherium fossils during his voyage on the Beagle in 1832. The pieces were used complete the Megatherium skeleton still on display today at the Natural History Museum in London. Photo: BallistaTo date, however, no fossils or organic remains have been found inside the palaeoburrows, leaving their exact age and origin open to further investigation. Heinrich Frank and his team continue to explore these ancient tunnels, hoping future discoveries will shed more light on these architectural marvels and the creatures that built them.
Model of a Megatherium at Crystal Palace, London. Image credits: Jim Linwood / failing_angel
What could have left those giant claw marks? Image credit: Heinrich Frank
Frank concluded these tunnels couldn’t have been created by geological processes. "There’s no natural formation capable of producing such long, branching tunnels with elliptical cross-sections and claw marks on every surface," he told Discover.His findings suggested the tunnels were carved by an extinct creature with tremendous digging ability—most likely the giant ground sloth, known scientifically as Megatherium americanum. Though some scientists initially speculated that giant armadillos might have been responsible, the scale of the burrows and the deep claw marks pointed to Megatherium, one of the largest land mammals of the Pleistocene epoch.Thousands of Prehistoric Burrows Across Brazil
Frank discovered his first palaeoburrow in the early 2000s and quickly realized it was part of a much larger phenomenon. He found more than 1,500 similar tunnels across Rio Grande do Sul, with hundreds more stretching through the neighboring state of Santa Catarina. Some of these tunnels extend hundreds of feet, branching off like a maze. The largest recorded tunnel spans 2,000 feet in length, measures six feet tall, and five feet wide."When you explore these burrows, it feels like something ancient could still be lurking around the corner," Frank wrote, describing the eerie sensation of being inside what once housed a massive animal.These giant sloths, second only to mammoths in size, stood up to 15 feet tall and weighed approximately 2,590 kilograms (5,709 pounds). They were herbivores, despite their enormous claws, which were likely used for digging rather than defense or tree-climbing. However, the purpose of the tunnels remains a mystery. A smaller den could have served to avoid predators or harsh weather, so researchers speculate that multiple sloths might have inherited and expanded the burrows over generations.
Image credit: Rodolfo Nogueira / SourceA Legacy of Prehistoric Giants
The first Megatherium fossils were unearthed in 1787 by Manuel Torres in Argentina. These remains were later shipped to Spain, where the original skeleton is still displayed at the Museo Nacional de Ciencias in Madrid. In 1796, the renowned French anatomist Georges Cuvier classified the creature as a sloth and initially believed it used its claws for climbing. However, Cuvier eventually proposed a digging lifestyle for the animal, which aligns with the palaeoburrows' discovery centuries later.Though these sloths were plant-eaters, they weren’t immune to danger. Fossil evidence suggests they coexisted with early humans, who may have hunted them for food. Some Megatherium bones display cut marks, hinting that human activity might have contributed to the animal's extinction.
Charles also collected Megatherium fossils during his voyage on the Beagle in 1832. The pieces were used complete the Megatherium skeleton still on display today at the Natural History Museum in London. Photo: BallistaTo date, however, no fossils or organic remains have been found inside the palaeoburrows, leaving their exact age and origin open to further investigation. Heinrich Frank and his team continue to explore these ancient tunnels, hoping future discoveries will shed more light on these architectural marvels and the creatures that built them.
Model of a Megatherium at Crystal Palace, London. Image credits: Jim Linwood / failing_angel