Among odontocetes, members of the family Kogiidae (pygmy and dwarf spermwhales) are known as small-sized and in many respects enigmatic relatives of the greatsperm whale Physeter macrocephalus. Most of the still scanty fossilrecord of Kogiidae is represented by isolated skulls and ear bones fromNeogene deposits of the Northern Hemisphere, with the significant exceptionof Scaphokogia, a highly autapomorphic genus from late Miocenedeposits of the Pisco Formation exposed along the southern coast of Peru. Here we report on anew fossil kogiid from Aguada de Lomas, a site where the late Miocene beds ofthe Pisco Formation are exposed. This specimen consists of an almost completecranium representing a new taxon of Kogiidae: Koristocetus pesceigen. et sp. nov. Koristocetus mainly differs from extantKogia spp. by displaying a larger temporal fossa andwell-individualized dental alveoli on the upper jaws. Coupled with arelatively elongated rostrum, these characters suggest thatKoristocetus retained some degree of raptorial feeding abilities,contrasting with the strong suction feeding specialization seen in Recentkogiids. Our phylogenetic analysis recognizes Koristocetus as theearliest branching member of the subfamily Kogiinae. Interestingly,Koristocetus shared the southern coast of present-day Peru withmembers of the genus Scaphokogia, whose unique convex rostrum andunusual neurocranial morphology seemingly indicate a peculiar foragingspecialization that has still to be understood. In conclusion,Koristocetus evokes a long history of high diversity, morphologicaldisparity, and sympatric habits in fossil kogiids, thus suggesting that ourcomprehension of the evolutionary history of pygmy and dwarf sperm whales isstill far from being exhaustive.