A new genus of megalonychid sloth (Mammalia, Xenarthra) from the late Pleistocene (Lujanian) of Sierra de Perija, Zulia State, Venezuela

ABSTRACT

A skull and a partial skeleton of a large late Pleistocene megalonychid sloth recovered from a cave on Cerro Pintado, Sierra de Perijá Mountain Range, a branch of the northern Andes, in Zulia State, Venezuela, is described as a new genus and species, Megistonyx oreobios. A cladistic analysis of the new taxon based on cranial characters indicates that it is closely related to Ahytherium, another late Pleistocene megalonychid from South America known from cranial remains, and suggests that there may have been at least two distinct clades within the family since the late Miocene. Megistonyx oreobios is one of a number of extinct sloth taxa found at high elevations in South America and suggests that many extinct sloth taxa were not as thermally sensitive as their modern relatives and were capable of living under colder climatic conditions.

ACKNOWLEDGMENTS

We thank the Evolving Earth Foundation for providing funding for the radiocarbon dating of Megistonyx. Preparation of the sample for radiocarbon analysis was done by T. Stafford. T. Rowe, M. Colbert, and staff of the High resolution X-ray Computed Tomography Facility, Department of Geosciences, University of Texas, Austin, made the CAT scan of the skull of Megistonyx possible. We thank D. Orchard, the manager of the Foundation for Quaternary Paleontology of Venezuela, for his help in the study of the material; and C. Bell, F. Urbani, L. Lanier, T. Barros, A. Viloria, and A. Fariñas, for their assistance and camaraderie during laboratory and field activities. We are especially thankful to J. M. Moody for his contributions to the 1997 Cerro Pintado expedition, and the recovery of all the Megistonyx material. For access to specimens used in the phylogenetic analysis, we thank J. Bloch and R. Hulbert of the Florida Museum of Natural History, University of Florida, Gainesville, Florida; C. Norris and D. Brinkman of the Peabody Museum, Yale University, New Haven, Connecticut; and J. C. Fernicola and A. Kramarz of the Museo Argentino de Ciencias Naturales ‘Bernardino Rivadavia,’ Buenos Aires, Argentina. Finally, we thank François Pujos, Juan Carlos Fernicola, and several anonymous reviewers whose insightful comments greatly improved the manuscript.

Handling editor: Guillermo Rougier