Acratocnus is an extinct genus of ground sloth found in Cuba, Hispaniola and Puerto Rico.
Like all of the Antillean sloths, Acratocnus is a member of the family Megalonychidae, whose sole surviving genus is Choloepus, representing the two-toed tree sloths.
The species of Acratocnus were found on the islands of Puerto Rico, Cuba and Hispaniola, where they inhabited the montane forests of the highlands. The Puerto Rican ground sloth, Acratocnus odontrigonus is known from several poorly documented cave excavations in northwestern Puerto Rico. The various species are regarded as being semi-arboreal because of their (relatively speaking) small size and their large hooked claws.
The various species of Acratocnus ranged in weight from 50 to 150 lbs (22 to 68 kg), and were thus much larger than living tree sloths (genera Choloepus and Bradypus), which do not exceed 20 lbs (about 9 kg).
As with many sloth fossils, these species of sloth have not been radiometrically dated. It is suggested that the Puerto Rican and Hispaniolan Acratocnus species survived into the late Pleistocene but disappeared by the mid-Holocene. The related Cuban ground sloth, Megalocnus rodens, survived until at least c. 6600 BP, and the latest survival reported for any of the Antillean sloths is c. 5000 BP, for the Hispaniolan Neocnus comes, based on AMS radiocarbon dating. The cause(s) of their extinctions may have been climatic changes, or more likely, human hunting.