A new physeteroid from the late Miocene of Peru expands the diversity of extinct dwarf and pygmy sperm whales (Cetacea: Odontoceti: Kogiidae)

Abstract

Nowadays, the odontocete family Kogiidae is monotypic and only includes two species of diminutive relatives of the great sperm whale Physeter Linnaeus, 1758. Conversely, a growing body of extinct species indicates that kogiids were diverse and disparate during the late Neogene. The fossil record of Kogiidae is, to date, represented by several cranial specimens from Mio-Pliocene localities of the Northern Hemisphere, with the significant Southern Hemisphere exception of the Pisco Formation of Peru, from which two genera were known so far, including Scaphokogia Muizon, 1988, a highly idiosyncratic form characterised by a distinctly spoon-shaped dorsal surface of the neurocranium and a downturned semicylindrical rostrum, which is even placed in its own subfamily Scaphokogiinae. Here, we report on two skulls of Kogiidae from the Messinian (upper Miocene) portion of the Pisco Formation exposed in the East Pisco Basin. These two skulls are referred to the new taxon Platyscaphokogia landinii n. gen., n. sp., which our phylogenetic analysis recovers as sister group of Scaphokogia, within the subfamily Scaphokogiinae. Although Platyscaphokogia n. gen. shares with Scaphokogia a remarkably spoon-like dorsal aspect of the neurocranium, it retains a non-pachyostotic, dorsoventrally thin rostrum that distinctly points anteriorly; as such, Platyscaphokogia n. gen. might be regarded as testifying an early stage in the evolution of the scaphokogiine cranial anatomy. Morphofunctional and palaeoecological considerations allow for hypothesising that Platyscaphokogia n. gen. was a raptorial physeteroid that foraged along the water column in relatively open-sea palaeoenvironments. In conclusion, our finds expand the palaeodiversity of Kogiidae, as well as our knowledge on the late Miocene sperm whales of the southeastern Pacific, and further suggest that the fossil content of the East Pisco Basin is crucial for reconstructing the Neogene evolutionary history of physeteroids.