title: Inner ear development in cetaceans.
abstract: Cetaceans face the challenge of maintaining equilibrium underwater and obtaining sensory input within a dense, low-visibility medium. The cetacean ear represents a key innovation that marked their evolution from terrestrial artiodactyls to among the most fully aquatic mammals in existence. Using micro-CT and histological data, we document shape and size changes in the cetacean inner ear during ontogeny, and demonstrate that, as a proportion of gestation time, the cetacean inner ear is precocial in its growth compared with that of suid artiodactyls. Cetacean inner ears begin ossifying and reach near-adult shape as early as at 32% of the gestation period, and near-adult dimensions as early as at 27% newborn total length. Our earliest embryos with measurable inner ears (13% newborn length) exhibit a flattened cochlea (i.e. smaller distance from cochlear apex to round window) compared with later and adult stages. Inner ears of Sus scrofa have neither begun ossifying nor reached near-adult dimensions at 55% of the gestation period, but have an adult-like ratio of cochlear diameters to each other, suggesting an adult-like shape. The precocial development of the cetacean inner ear complements previous work demonstrating precocial development of other cetacean anatomical features such as the locomotor muscles to facilitate swimming at the moment of birth.
authors.affiliation: Department of Zoology, University of Cambridge, Cambridge, UK.
authors.forename: Tara
authors.initials: T
authors.lastname: Thean
authors.affiliation: Helmholtz-Zentrum Berlin, Berlin, Germany.
authors.forename: Nikolay
authors.initials: N
authors.lastname: Kardjilov
authors.affiliation: Department of Zoology, University of Cambridge, Cambridge, UK.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Asher
mesh_terms: D000818:Animals; D050616:Balaenoptera / Q000033:anatomy & histology / Q000254:growth & development*; D002591:Cetacea / Q000033:anatomy & histology / Q000254:growth & development; D003051:Cochlea / Q000033:anatomy & histology / Q000254:growth & development; D050696:Common Dolphins / Q000033:anatomy & histology / Q000254:growth & development*; D007758:Ear, Inner / Q000033:anatomy & histology / Q000254:growth & development*; D050640:Humpback Whale / Q000033:anatomy & histology / Q000254:growth & development*; D012665:Semicircular Canals / Q000033:anatomy & histology / Q000254:growth & development; D013045:Species Specificity; D034421:Sus scrofa
keywords: artiodactyl; cetacean; cochlea; inner ear; ontogeny; ossification; semicircular canals; suiform