Megatherium was a sloth, but nothing like the slow, small animals that hang from trees in the rainforests today. It lived on the ground, on the open plains of the Pampas in what are now Argentina and Uruguay, and it weighed about as much as an Asian elephant. Its name means “great beast”. It vanished about 12 000 years ago, along with most of South America’s other giants.
A giant browser
The skeleton is about 6 m long, with a huge body, massive hind legs and a thick tail. Volume-based estimates put its weight at about 3.7 to 4 tonnes. Its fingers ended in long claws on the three middle digits, and its hind feet were turned inwards, so that it walked on their outer edges and heels.
Its narrow snout is thought to have carried a thick, grasping upper lip, much like a black rhinoceros has, used to strip leaves and twigs from branches. Chemical analysis of its bones supports a diet of plants. An older suggestion that it also ate meat has little support.
To reach higher branches, Megatherium is widely thought to have reared up on its hind legs, propped on its tail like a tripod. Some fossils have injuries to the collarbone, which a 2022 study read as signs that it leaned against tree trunks with its forelimbs while doing so.
Furry after all
Some older reconstructions showed Megatherium almost hairless, like an elephant. A study published in 2025 tested this with a model of its body temperature, combined with chemical measurements from a fossil tooth that point to a body temperature of about 31 °C. Assuming a metabolism like that of living sloths and armadillos, the answer was that, in the cool, dry climate of the Pampas, it needed a dense coat about 3 cm deep all year round. Thinner fur would have left it cold; much thicker fur would have overheated it. Whether its metabolism really was that slow is still uncertain.
No skin or hair of Megatherium has survived, so this coat is calculated rather than seen. Well-preserved fur is known only from smaller ground sloths, such as Mylodon.
Found on a riverbank
The first skeleton was dug from the bank of the Luján River in Argentina in 1787 and shipped to Madrid. In 1796 the French anatomist Cuvier named it from drawings of the skeleton, which he never saw in person.
What killed the giant sloths
Megatherium disappeared about 12 000 years ago, in the same wave of extinctions that took more than 80 per cent of South America’s large mammals. A large study published in Science in 2025, based on more than 400 fossils and ancient DNA, found that ground sloths had grown to their greatest sizes during the ice ages and then declined rapidly from about 15 000 years ago. The authors concluded that changes in climate do not explain that collapse and that it points to people, although the cause of the South American extinctions as a whole is still debated, with hunting and climate change both proposed.
There is direct evidence that humans hunted it. At Campo Laborde, in the Argentine Pampas, archaeologists found the butchered bones of a Megatherium about 12 600 years old, the only confirmed kill site of a giant ground sloth in the Americas.
