Intraspecific variation of Megalonychid sloths from Hispaniola and the taxonomic implications

Abstract

ABSTRACT Megalonychid sloth fossils have been found on numerous islands across the Antilles, with most associated with the Greater Antilles. New specimens from the Dominican Republic permit exploration of intraspecific variation ranges the recognised taxa (Acratocnus, Parocnus, Megalocnus, Neocnus) of Hispaniola. Using length of upper limb bones as a proxy for body mass, sexual dimorphism and geographic variation were explored, along with additional assessments about changes to the known taxonomy resulting from intraspecific variations. Sexual dimorphism is considered to occur, at differing levels, for all Hispaniola sloths, supported by the presence of large and short morphs within individual localities. Geographically, Acratocnus exhibits differences between northern and southern paleo-island sites, suggesting the existence of two subspecies or an unrecognised new, northern paleo-island species. Megalocnus zile is considered a junior synonym of Parocnus serus, as it falls within morphological variation ranges for that taxon. Parocnus specimens from Parque Nacional del Este are ~15% smaller than all other sites, regardless of paleo-island association, and may represent a new species. Results for Neocnus demonstrate the necessity for a reassessment of the current taxonomy and recognised characters. Radiometric dates are needed for more localities in order to rule out patterns resulting from temporal variation.