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Inner ear development in cetaceans

Accepted version
Peer-reviewed

Type

Article

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Authors

Thean, T 
Kardjilov, N 
Asher, RJ 

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.

Description

Keywords

artiodactyl, cetacean, cochlea, inner ear, ontogeny, ossification, semicircular canals, suiform

Journal Title

Journal of Anatomy

Conference Name

Journal ISSN

0021-8782
1469-7580

Volume Title

230

Publisher

Wiley
Sponsorship
The John Stanley Gardiner Studentship and Queens’ College provided financial support for this project. This research also received support from the SYNTHESYS Project (http://www.synthesys.info/), which is financed by European Community Research Infrastructure Action under the FP7 Integrating Activities Programme. The authors thank the editor and reviewers for their comments on the manuscript.