Megatheriidae

Megatheriidae is a family of extinct ground sloths that lived from approximately 23 mya—11,000 years ago, existing for approximately 22.89 million years.

Megatheriids appeared later in the Oligocene, some 30 million years ago, also in South America. The group includes the heavily built Megatherium (given its name 'great beast' by Georges Cuvier) and Eremotherium. An early megatheriid, the more slightly built Hapalops, reached a length of about 1.2 meters. The nothrotheres have recently been placed in their own family, Nothrotheriidae.

The skeletal structure of these ground sloths indicates that the animals were massive. Their thick bones and even thicker joints (especially those on the hind legs) gave their appendages tremendous power that, combined with their size and fearsome claws, provided a formidable defense against predators.

The earliest megatheriid in North America was Eremotherium eomigrans which arrived 2.2 million years ago, after crossing the recently formed Panamanian land bridge. At more than five tons in weight, 6 meters in length, and able to reach as high as 17 feet (5.2 m), it was taller than an African bush elephant bull. Unlike relatives, this species retained a plesiomorphic extra claw. While other species of Eremotherium had four fingers with only two or three claws, E. eomigrans had five fingers, four of them with claws up to nearly a foot long.