A new species of <i>Kentriodon</i> (Cetacea, Odontoceti, Kentriodontidae) from the Miocene of Japan

Kentriodontids are small- to medium-sized odontocetes with a wide geographic range that flourished during the Miocene. They are closely related to crown Delphinida. Seven fossil kentriodontid specimens have been recovered from the Haraichi Formation, Annaka Group (latest middle/earliest late Miocene, Serravallian/Tortonian), Gunma Prefecture, Japan. We describe and diagnose a new species of the genus <i>Kentriodon</i>. <i>Kentriodon nakajimai</i>, sp. nov., has a larger fossa for the hamular and preorbital lobes of the pterygoid sinuses, which suggests that the species was more highly adapted for diving than other <i>Kentriodon</i> species. Asymmetric development of left and right maxillary crests indicates asymmetric development of the facial muscles attached to the melon. If this is the case, it suggests that <i>K. nakajimai</i> possessed a more sophisticated echolocation system than other kentriodontids. Phylogenetic analysis suggests that <i>K. nakajimai</i> is most closely related to <i>K. obscurus</i> and the genus <i>Kentriodon</i> may have originated in the Pacific and then dispersed into the Atlantic several times.