The present study entails a description of several well-preserved skulls from the diminutive, extinct West Indian megalonychid sloth genus Neocnus Arredondo, 1961, recovered from Holocene cave deposits in Haiti and housed in the collections of the Florida Museum of Natural History. Detailed descriptions and illustrations are provided of the external anatomy of the bones in the auditory region and orbital wall, and their suturai connections. The foramina in these regions are also described and illustrated in detail, and their contents reconstructed. The orbitotemporal osteology of Neocnus is compared to its purported closest relatives in the subfamily Choloepodinae, the somewhat larger extinct Antillean sloth genus Acratocnus Anthony, 1961, and the extant two-toed sloth Choloepus Linnaeus, 1758. Contrary to recent phylogenetic hypotheses, which link either Choloepus and Acratocnus or Choloepus and Neocnus as sister taxa, Neocnus and Acratocnus exhibit more similarities to one another in the anatomy of their orbitotemporal bones than either does to Choloepus. This may be explained in part by the highly autapomorphous anatomy of Choloepus. The study highlights the need for further anatomical investigations of Antillean sloths, and for further, more comprehensive phylogenetic investigations of the sloth family Megalonychidae.
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Vol. 80 • No. 1