A new kentriodontid dolphin (Cetacea, Odontoceti, Delphinida) from the Middle Miocene of the southeastern Pacific

The origin of most modern families of dolphins and porpoises has to be found during the Early to Middle Miocene, presumably among the stock of early delphinidan forms generally attributed to the family Kentriodontidae Slijper, 1936. The East Pisco Basin (Peru) is a major source of Miocene odontocetes (echolocating toothed cetaceans), but up to now a majority of the finds originate from the Lower Miocene Chilcatay Formation and the Upper Miocene deposits of the Pisco Formation. Apart from the poorly known early delphinidan Incacetus broggii Colbert, 1944, very little is known for the Middle Miocene layers of the Pisco Formation. Based on a sample of three skulls collected from the Langhian to Serravallian (14.7-12.6 Ma) P0 allomember of the Pisco Formation in two localities (Santa Rosa and Mal Paso) of the East Pisco Basin, we describe a new genus and species of early delphinidan, Mesokentriodon protohumboldti n. gen., n. sp. Characterized by a moderately elongated rostrum and 40 teeth per upper row, this medium-sized dolphin shares many cranial similarities with, among others, the smaller Kentriodon pernix Kellogg, 1927, the type species of the type genus of the family Kentriodontidae. As our phylogenetic analyses consistently recover the new taxon in a clade that also includes K. pernix, we confidently identify it as a kentriodontid, though the content of this family varies considerably across the various analyses using different implied weighting protocols. Our favoured hypothesis is that kentriodontids are stem-group delphinidans whose chronostratigraphic distribution fills a major Early to Middle Miocene time interval before the appearance of the earliest members of the extant delphinidan lineages (Lipotidae Zhou, Qian & Li, 1978, Inioidea Muizon, 1988, and Delphinoidea Gray, 1821). This new species improves the relatively poor Middle Miocene fossil record of cetaceans in the East Pisco Basin and highlights the potential of the lower portion of the Pisco Formation for enhancing our understanding of the emergence of the modern delphinidan clades.