Abstract

A new species of Hathliacynidae (Sparassodonta, Metatheria), Acyon myctoderos, from the middle Miocene of Quebrada Honda, Bolivia, is described. This new species is the largest known hathliacynid. Compared to the type species of the genus, A. tricuspidatus, Acyon myctoderos differs in having: (1) longer diastemata among premolars; (2) p2 comparatively more robust, with a better developed posterior cusp and with a sharp anterior crest; (3) lower molars with a more poorly developed anterobasal cingulum; (4) m1–m3 with hypoconulids less salient posteriorly and more vertically oriented; and (5) larger hypoconids at least on the m2. A phylogenetic analysis including nine taxa of Sparassodonta, with Mayulestes as the outgroup, showed that Acyon is more closely related to Cladosictis than to any other hathliacynid.