Giant ground sloths emerged about 10 million years ago on the South American continent. Around 5 million years ago, they expanded their range through Central America into North America. These giant ground sloths are distant relatives of today’s sloths, which mostly live in trees and are significantly smaller. There were many different species of ground sloths, but all of them are extinct. Some of these sloths could grow as large as a small elephant!

One of these large ground sloth species from the Pleistocene, or Ice Age, is the so-called Jefferson’s ground sloth, Megalonyx jeffersonii, named after the third U.S. President, Thomas Jefferson (1743–1826). In 1797, while still Vice President, Jefferson published a description of skeletal parts in the transactions of the Philosophical Society in Philadelphia, including the terminal phalanges (toe bones) of an unknown animal. These toe bones, to which claws were attached, were exceptionally large (15 to 20 cm long!) and resembled the claws of a lion. Jefferson attributed the bones to a “Great Claw Animal” (Megalonyx) and speculated that the species might still be alive somewhere. It was later discovered that this was not the case. To honor Jefferson, the genus name Megalonyx was retained, and the species name jeffersonii was introduced in 1822 by the French paleontologist Anselme Gaëtan Desmarest (1784–1838).

Jefferson’s ground sloth was a large, slow-moving mammal, significantly bigger than a cow and up to three meters long. It was part of the megafauna of the late Pleistocene. This ground sloth was a herbivore. With its enormous claws and long nails, it could easily pull branches and twigs from trees and shrubs toward itself to strip the leaves using its specialized teeth.

Megalonyx jeffersonii was found exclusively in North America, as far north as Alaska (USA) and the Yukon (Canada), and must have been widespread in prairie-like landscapes. Not only isolated skeletal parts but also numerous complete skeletons have been discovered. Around 11,000 years ago, Jefferson’s giant ground sloth became extinct. Since many bones of Jefferson’s ground sloths found in the United States show damage interpreted as evidence of human hunting, some researchers speculate that the species was overhunted to extinction.

In the cold, dry, and nearly treeless mammoth steppe of Eurasia, which extended across Beringia into North America, the woolly rhinoceros was a common animal, especially in the very arid regions. While the woolly mammoth managed to cross from Eurasia into North America via the Bering Land Bridge and was not deterred by the wet, swampy terrain, the woolly rhinoceros avoided such areas and never reached North America. The same applies to Jefferson’s ground sloth in North America. It is believed that this animal also avoided the swampy habitats of Beringia and therefore never appeared in Eurasia.