Two fossil crania referable to the siluriform fish family Ariidae are described. The specimens come from the Early Late Miocene-Lower Middle Miocene Saladar Member of the Gran Bajo del Gualicho Formation, located at Salinas del Gualicho, Río Negro province, Argentina. The materials are referred to a new species of the recent genus Genidens. The new taxon is distinguished from remaining living species in having a very short, broadened and rounded supraoccipital process, subrounded extrascapular and wide mesethmoid with a median notch, flat frontals, and straight lateral margins of the sphenotics. Genidens ancestralis sp. nov. represents the oldest (and only known) fossil record for the genus, and constitutes a relatively small-sized species, very similar in general traits to living forms of Genidens.
Siluriformes; Ariidae; Genidens; Gran Bajo del Gualicho Formation; Patagonia