A new kogiid from the late Miocene of Peru: insights into sympatry, disparity, and niche partitioning in fossil pygmy sperm whales

Among odontocetes, members of the currently monotypic family Kogiidae are known as small-sized and largely enigmatic relatives of the great sperm whale Physeter macrocephalus. Most of the still scanty fossil record of Kogiidae is represented by isolated skulls and ear bones from Neogene deposits of the Northern Hemisphere, with the significant exception of Scaphokogia, a highly autapomorphic genus from the late Miocene deposits of the Pisco Formation, southern coast of Peru. Here we report on a new fossil kogiid specimen from Aguada de Lomas, a site where the upper Miocene beds of the Pisco Formation are exposed. This specimen (MUSM 888) consists of an almost complete Kogia-like cranium, which represents a new taxon of Kogiidae sharing many similarities with the recently described Nanokogia isthmia, from the late Miocene of Panama. MUSM 888 mainly differs from the latter taxon and from extant Kogia spp. by displaying a larger, anterolaterally elongated temporal fossa and well-defined dental alveoli on the upper jaws. Coupled with a relatively elongated rostrum, these characters suggest that MUSM 888 retained some degree of raptorial feeding abilities, contrasting with the strong suction feeding specialization seen in Kogia spp. Interestingly, MUSM 888 shared the southern coast of present day Peru with members of the subfamily Scaphokogiinae, whose unique convex rostrum and unusual neurocranial morphology seemingly indicate a peculiar foraging specialization that has still to be understood. In conclusion, the finding of MUSM 888 supports a long history of high diversity, morphological disparity, and sympatric habits in fossil kogiids, thus suggesting that our comprehension of the evolutionary path of pygmy sperm whales is still far from being exhaustive