The extinct odontocete Prosqualodon australis Lydekker1894 (early Miocene, Gaiman Formation, Chubut Province, Argentina) is for the first time described in-depth based on the holotype (MLP 5-8, a partial skull) and a referred specimen (MLP 5-9, an almost complete skull; Cabrera, 1926).Besides, the first phylogenetic analysis including this species as an operational taxonomic unit itself is presented, considering a comprehensive morphological matrix of odontocetes. The peculiar morphology of the anterior projection of the antorbital process along with plesiomorphic dental features(such as well-marked heterodont, large lateromedially compressed teeth withlong crowns, reticulated enamel, and birradiculated teeth in the maxillae) are proposed to diagnose the species. Also, the body length of P. australis is inferred to vary at least between 2 and 3 m between the juvenile and the adult stages. Comparative anatomical studies showontogenetic and intraspecific differences between the specimens analyzed. Thephylogenetic analyses show P. australisas a stem-Odontoceti and Prosqualodonas a paraphyletic genus. The relative basal position of P. australis in the optimal treesrecovered may respond to plesiomorphic skull characteristics. Also due to thelack of preserved earbones in P.australis, the future description of tympano-periotic bones might led tonew phylogenetic results.Fil: Gaetán, Carlos Maximiliano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; ArgentinaFil: Buono, Mónica Romina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto Patagónico de Geología y Paleontología; ArgentinaFil: Gaetano, Leandro Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; ArgentinaXXXII Jornadas Argentinas de Paleontología Vertebrados y VII Jornadas Técnicas Paleontología VertebradosCorrientesArgentinaAsociación Paleontológica Argentin
