The ground sloths of the extinct genus Megalocnus ("Great Sloth") were among the largest of the Caribbean ground sloths, with individuals estimated to have weighed up to 90 kg (200 lb) when alive. Two species are known, M. rodens of Cuba, and M. zile of Hispaniola. Subfossils of M. rodens indicate survival well into the Holocene, prompting speculation that they may have survived in the montane forests of the Cuban highlands until the 15th or 16th century. However, the most recent AMS radiocarbon date reported is 4190 BP, calibrated to c. 4700 BP. This is similar to the most recent date reported for a Hispaniolan sloth, 4391 BP, calibrated to c. 5000 BP, for the small and probably arboreal Neocnus comes, and some 1200 years after the earliest known date for human occupation of Cuba, 5140 BP, calibrated to c. 5900 BP.

Their relatives include other Caribbean ground sloths, such as Acratocnus, Mesocnus, Miocnus, Neocnus, Parocnus, and Paulocnus.