A new basal delphinidan species (genus Kentriodon) from the Lower Miocene of Peru

Nowadays, the cetacean infraorder Delphinida consists of the oceanic dolphins and porpoises plus a handful of riverine and (sub-)Arctic forms. Overall, delphinidans account for more than half of the living cetacean species, thus comprising the core of the present-day marine mammal diversity. As for several other modern cetacean groups (i.e. sperm whales), the Early Miocene (ca 23.0–16.0 million years ago) represents a key interval for the evolutionary history of Delphinida, as it is during this time span that delphinidans became broadly distributed worldwide, first and foremost with the geographically widespread genus Kentriodon and closely related forms (Kentriodontidae s.s.). Here, we report on a collection of ten specimens of a small delphinidan with kentriodontid characters from Burdigalian (ca 19–18 million years ago) strata of the Chilcatay Formation exposed at the highly fossiliferous localities of Ullujaya and Zamaca (East Pisco Basin, southern Peru). Consisting of diagnostic, fairly complete and well-preserved cranial remains (close in size to Kentriodon diusinus and Brevirostrodelphis dividum), these new specimens display a unique combination of morphological characters, including a crescent-shaped exposure of the maxilla medial to the premaxilla anterior to the bony nares, a furrow-like internasal fossa, pterygoid sinuses that do not extend onto the rostrum base, and a sharp, medially bent ventromedial keel of the tympanic bulla. The above features diagnose a new species within the genus Kentriodon. Our maximum parsimony phylogenetic analyses recover this new species as closely related to Kentriodon pernix and Kentriodon nakajimai (respectively from the Burdigalian of Maryland and Serravallian to Tortonian of Japan). Overall, our new results contribute to expanding the outstanding cetacean palaeodiversity of the Neogene strata of the East Pisco Basin and of basal delphinidans during the Early Miocene.