Megatheria were a group of elephant-size giant sloths that lived from 2 million to 8,000 years ago. Their smaller giant sloth cousins were the Mylodon. Unlike its living relatives, the tree sloths, Megatherium must have been one of the most impressive animals to walk the Earth. Weighing almost as much as an elephant, it had huge claws on its feet. These claws meant that it could not put its feet flat on the ground and so, like a modern anteater, it had to walk on the sides of its feet. Amazingly, its footprints show that it walked mainly on just its hind legs.

Some cryptozoologists have investigated reports of megatheria surviving in South America. In the 1890s an Argentinean explorer, geographer and adventurer, Ramon Lista, was hunting in a portion of his country, known as Patagonia, when a large, unknown creature covered with long hair trotted past his party. To Lista, the creature looked like a gigantic armadillo. The party shot at the beast, but the bullets seemed to have no effect.

Professor Florentino Ameghino, a paleontologist in Argentina, heard the Lista story and began to wonder if the strange beast was a giant sloth that had somehow survived till the present day. He might not have put much stock in the Lista story if it had not been for the legends he had collected from natives in the Patagonia region about hunting such a large creature in ancient times.

The animal in the stories was nocturnal, and slept during the day in burrows it dug with its large claws. The natives also found it difficult to get their arrows to penetrate the animal's skin.

Ameghino, furthermore, had a piece of physical evidence: A small section of apparently fresh hide found by a rancher named Eberhardt on his property in a cave in 1895. The hide was studded with small, hard, calcium nodules and would have been impervious to the teeth of many predators. It seemed likely that it would have also resisted native arrows, along with Lista's bullets.

So sure was Ameghino this was the creature Lista had seen, he decided to name it after him: Neomylodon listai, or "Lista's new Mylodon."

Expeditions to Eberhardt's cave and other caves soon recovered additional pieces of hide. With the development of the debated Carbon-14 dating method in the twentieth century, the age of the Mylodon remains in the Eberhardt's cave was apparantly settled. In short, the skin was estimated to be roughly 11,000 to 5,000 years old. Conditions in the caves may have preserved the skin, making it look fresh to the eye and fooling Ameghino.

No additional evidence has turned up that the giant sloth survives today.