Petrosal (periotic) and inner ear of a Pliocene kogiine whale (Kogiinae, Odontoceti): implications on relationships and hearing evolution of toothed whales

Abstract

ABSTRACT This study describes the petrosal (periotic) bone and the inner ear of a fossil pygmy sperm whale (Kogiinae, Physeteridae, Cetacea) from the Yorktown Formation (Pliocene) of the Lee Creek Mines of North Carolina. A cladistic analysis of 36 petrosal characters among 18 cetacean taxa shows that extant and fossil kogiines are diagnosed by a plate-like and posteriorly oriented posterior process of the petrosal. The Physeteridae is diagnosed by two petrosal apomorphies: presence of an incudal process for the articulation of the incus, and an enlarged accessory ossicle. Petrosal apomorphies suggest that physeterids and ziphiids are sister groups among the odontocetes, and that the Mysticeti and Odontoceti are both monophyletic. The cochlear spiral of the Pliocene kogiine petrosal has two full turns and a cochlear basal/height ratio of 0.6. Within the cochlear canal, the secondary bony lamina for the basilar membrane is present in one and one-quarter turns of the cochlea. The width of the basilar membra...