Megatherium americanum - The Giant Ground Sloth

The skeleton of Megatherium set up in the London Natural History Museum, and a depiction of a possibility of Megatherium behavior in life.

Though the population was already decreasing when the first humans arrived in South America, the disappearance of the Giant Sloth was helped along by the new immigrants. Using mammoth-hunting skills, this large and lumbering creature was an ideal kill for a human tribe. It was one of the many Pleistocene megafauna that went extinct during the Quaternary extinctions.

Extinct monsters. H. N. Hutchinson, 1896.

Art by ~IRIRIV  
Lived 1.9 million - 8,000 years ago

[Source for the following:  BBC Science and Nature]

Megatherium was a massive ground sloth, covered in long dark hair. It had huge claws, and weighed almost a much as an elephant. Fossilized footprints show that it often walked on its hind legs, although there is much debate as to what it looked like when it did.

Megatherium are herbivorous. They mainly browsed vegetation in woodlands and grasslands but possibly scavenged meat too.

The South American species is known from many skeletons, sets of fossilized footprints and even dung and hair. Finds have come from as far north as Texas and as far south as Argentina.

Ground sloths are members of the superorder Xenarthra [“strange joints”], a group of placental mammals which includes modern tree sloths, anteaters and armadillos as well as the extinct glyptodonts.

“Great Beast” (Megatherium) skeleton, from George Shaw’s Zoological Lectures delivered at the Royal Institution, 1800. 

Megatherium americana was one of the few species of South American megafauna to not die out soon after the Great American Interchange at the beginning of the Pliocine era, and there’s evidence that it was encountered and hunted by early humans, especially after it expanded northwards into southern North America.

The size of a bull elephant, Megatherium were largely quadrupeds, but could use their massive tail as a tripod-like base to allow themselves to stand on their hind legs and pull down the choicest branches of leaves. Their somewhat smaller (rhino-sized) ancestor Promegatherium is believed to be a direct ancestor of both Megatherium and modern-day sloths.