ABSTRACT
— Megalonychid sloths are well known from the Quaternary of many West Indian islands, and some isolated remains date back as far as the early Oligocene. Phylogenetic relationships among these sloths have been unclear and controversial for numerous reasons, thus hindering biogeographical interpretations. As part of a complete systematic revision of West Indian megalonychids, we performed a cladistic analysis on 17 ingroup taxa using 69 osteological and dental characters. The analysis discovered three most-parsimonious trees that differ only in the placement of one incompletely known taxon. Two well-supported clades are identified, one of which includes the extant two-toed sloth Choloepus. Each major clade contains two or more genera, and within each genus, sister species are distributed across islands. Our results allow us to address two major biogeographical issues: the colonization of the Greater Antilles by megalonychid sloths, and the inter-island relationships of these sloths. An initial emplacement in the early Oligocene is consistent with overland dispersal across a short-lived land span connecting the developing Greater Antilles with northwestern South America. Our data suggest at least two separate invasions, and therefore a diphyletic origin of Antillean megalonychids. Inter-island distributions are explained most parsimoniously by island-island vicariance sometime before the end of the Miocene.
