Ground sloths are large land mammals that lived from the early Oligocene (about 35 million years ago) to as recently as 1550 CE on the Caribbean islands of Hispanola and Cuba. The largest, Megatherium, whose name means "great beast," weighed up to five tons, the weight of an African Bull Elephant, and was too large to have any predators. Standing upright, it would have been 20 ft (6 m) tall, making it the largest mammal ever known to walk the Earth. Ground sloths lived in both North and South America.
Ground sloths were herbivores, like their modern relatives, the tree sloths, which they resemble more in genetic relationship than external appearance. Unlike most herbivores, they had large, spiky claws which could have been used to strip the leaves from trees and dispatch any would-be predators. Their claws were so huge that they had to walk on them sideways. In another adaptation to protect them from predators, ground sloths had very thick skin and fur. This would have also helped them during the last Ice Age, and unlike some other large mammals, they did survive the Ice Age and went extinct only afterward.
Like many extinct animals, ground sloths are often the subject of works on cryptozoology, which assert that the animal has been sighted in historical times in Argentina or elsewhere. This myth may derive partially from the fact that ground sloths went extinct so recently that their subfossilized dung can be found in caves, and in some rare instances, well-preserved subfossil remains of the animal itself. It seems likely that enough DNA would be intact in these specimens that ground sloth DNA will eventually be sequenced and studied in its entirety.
Ground sloths were likely hunted to extinction by humans on the mainland around the end of the last Ice Age, just like so many other large animals worldwide. Before their historic expedition, explorers Lewis and Clark were instructed by President Jefferson to be on the lookout for ground sloths in the Western United States, but they were never located.