Megalocnidae is an extinct family of sloths, known from the Greater Antilles from the Early Miocene to the Mid-Holocene. They are known from Cuba, Hispaniola and Puerto Rico, but are absent from Jamaica. While they were formerly placed in the Megalonychidae alongside two-toed sloths and ground sloths like Megalonyx, recent mitochondrial DNA and collagen sequencing studies place them as basal to all other sloths. They displayed significant diversity in body size and lifestyle, with Megalocnus being terrestrial and probably weighing several hundred kilograms, while Neocnus was likely arboreal and similar in weight to extant tree sloths, at less than 10 kilograms.
Origin
It is thought that sloths arrived in the Caribbean from South America around the Eocene-Oligocene boundary about 33 Ma ago, when there was a significant sea level drop caused by a glaciation episode. This has been associated with the GAARlandia hypothesis, where the Aves Ridge formed a land bridge during the interval, allowing overland migration into the Greater Antilles. The existence of such a land bridge has been questioned because of the lack of geological evidence for the Aves Ridge having been subaerially exposed as well as the fact that many other South American animals are absent from the Greater Antilles, making a complete land bridge unlikely. The earliest evidence suggesting the presence of sloths in the Caribbean is a partial femur from the Early Oligocene of Puerto Rico. More definitive remains are known for Imagocnus from Early Miocene Cuba.
Taxonomy
The taxonomy of Caribbean sloths is in flux, with the number of species present among the Pleistocene-Holocene taxa in question; some species are likely junior synonyms, while the diversity of some genera is probably understated. The mitochondrial DNA study suggests that Acratocnusye and Parocnus serus are deeply divergent from each other, having split during the Oligocene, suggesting an early radiation within the group; they proposed the families Acratocnidae and Parocnidae within a new superfamily, Megalocnoidea. Based on White and MacPhee :
* †Parocnus browni Pleistocene to Holocene of Cuba
* †Parocnus serus Pleistocene to Holocene of Hispaniola
Neocnus
*†N. gliriformis Pleistocene to Holocene of Cuba
*†N. major Pleistocene to Holocene of Cuba
* †N. comes Pleistocene to Holocene of Hispaniola
* †N. dousman Pleistocene to Holocene of Hispaniola
* †N. toupiti Pleistocene to Holocene of Hispaniola
Imagocnus
*I. zazae Early Miocene of Cuba
Paulocnus from Pliocene - Early Pleistocene deposits in Curaçao has been suggested to be part of Megalonychidae while Megalocnidae was considered part of the group, its location close to mainland South America and considerable displacement from the Greater Antilles make referral to Megalocnidae questionable. For other sloth taxa of the Caribbean, see Pilosans of the Caribbean.
Sloths in the Caribbean survived about 5000 years longer than ground sloths on the mainland. On Cuba the latest date for Megalocnus is calibrated 4700 BP. while dates for Parocnus browni are around 6250 BP. On Hispaniola the dates for some indeterminate sloth specimens are around 5000 BP; these dates roughly coincide with the first settlement of the Caribbean, which suggests that humans were the cause of the extinction.
