Megalonyx jeffersonii, or Jefferson’s ground sloth, is an extinct species of giant ground sloth that lived from the Illinoian Stage during the Middle Pleistocene (150,000 years BP) through to the Rancholabrean of the Late Pleistocene (10,000 BCE). Its closest living relatives are the two-toed tree sloths of the genus Choloepus.
This species ranged widely in North America. It belongs to the genus Megalonyx, a name proposed by Thomas Jefferson, future president of the United States, in 1797. (Jefferson’s surname was appended to the animal as the specific epithet in 1822 by the French zoologist Anselme Gaëtan Desmarest.)
Did you guys know Jefferson thought the bones he was sent were from a lion? You can read some more information on Wikipedia for a quick summary.