Megalonyx (Greek for "great-claw") was a genus of ground sloths that lived in North America from the Pliocene through the Late Pleistocene. The most famous species, Megalonyx jeffersonii (Jefferson's ground sloth), grew to roughly ~3 m (10 ft) in length and reached very large body masses. These animals were powerful browsers with large, recurved claws used for grasping branches and defense.
First recognized from cave fossils in what is now West Virginia, the genus was named and described in the late 18th and early 19th centuries — Thomas Jefferson played a notable role in the early study and public awareness of these fossils. Megalonyx had a wide geographic range across much of North America and persisted until the end-Pleistocene extinction when ground sloths disappeared from the continent.