Intraspecific variation of Megalonychid sloths from Hispaniola and the taxonomic implications

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.

KEYWORDS:

• Sexual dimorphism
• geographic variation
• late Pleistocene
• Parocnus
• Acratocnus
• Neocnus

Acknowledgments

Thanks and appreciation to the following institutions and individuals for access to collections making this study possible: American Museum of Natural History: R. MacPhee, J. Galkin; University of Florida: R. Hulburt Jr; Museo del Hombre Dominicano: C. Martinez, R. Rimoli; Museo Nacional de Historia Natural – Santo Domingo: J. Almonte; Museum of Comparative Zoology, Harvard: S. Pierce, J. Cundiff; National Museum of Natural History: A. Millhouse. Extra thanks to the following for additional support and assistance: S. Cooke, P. Lehman, A. Rosenberger, A. Mychajliw, A. Farke, R. Haupt, J. Brito, L. Koper, V. Naples, J. Olsson and A. Roth. Special gratitude is given to the Dominican Republic Speleological Society for the work in recovering many of the new specimens, and to the Guerrero Herrera family for locality access. This manuscript was improved by the suggestions and critiques of A. Boscani, M. Macias, and an anonymous reviewer. We are indebted to funding assistance from internal grants from Ohio Northern University and Philadelphia College of Osteopathic Medicine, as well as from a 2015 Ernst Mayr Travel Grant that provided initial access to the Dominican Republic specimens.

Disclosure statement

No potential conflict of interest was reported by the authors.