Also called the giant sloth, Megatherium was a close cousin of modern tree sloths, but this prehistoric beast was as big as an elephant and lived on the ground. Fossilized dung shows it was a herbivore that ate dozens of different kinds of plant.
It normally walked on all fours but could also rear up on its hindlimbs to reach high branches, which it pulled down with its claws. Megatherium vanished soon after humans first reached the Americas, perhaps hunted to extinction.
■ When: 5 million–10,000 years ago (Late Neogene)
■ Fossil location: S. America
■ Habitat: Woodlands
■ Length: 20 ft (6 m)
■ Diet: Plants
When Megatherium walked upright it was almost twice the height of an elephant. It was covered with thick, shaggy hair, under which were bony plates that formed a kind of armor. The teeth were blunt for mashing leaves, but some experts think Megatherium may have also used its claws to scavenge on dead meat or even kill for food.
Megatherium had enormous, curved claws that it used to grasp branches and fight predators. It could not place its feet flat on the ground—instead, it walked on the sides of its feet, with the claws turned inward.
hip bones were especially strong. They supported the weight of the huge body when the animal stood upright. The stout tail also helped, acting as a prop.
Modern sloths appear to be the laziest animals on Earth, sleeping up to 18 hours a day and moving with amazing slowness when awake. Unlike Megatherium, today’s sloths spend their lives hanging upside down from trees. They cling to branches with long arms and hooked claws, even sleeping and eating upside down.