Locomotor head movements and semicircular canal morphology in primates

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 109; no. 44; pp. 17914 - 17919
• Main Authors: Malinzak, Michael D, Kay, Richard F, Hullar, Timothy E
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 30-10-2012; National Acad Sciences
• Subjects: Agility; Angular velocity; Animal morphology; Animal physiology; Animals; Axes of rotation; Biological Sciences; Biomechanical Phenomena; Body mass index; Canals; Comparative analysis; Correlation analysis; ears; extinct species; Extinction; head; Head Movements; Locomotion; Phylogenetics; phylogeny; prediction; Primates; Primates - physiology; Semicircular canals; Semicircular Canals - anatomy & histology
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1206139109

Animal locomotion causes head rotations, which are detected by the semicircular canals of the inner ear. Morphologic features of the canals influence rotational sensitivity, and so it is hypothesized that locomotion and canal morphology are functionally related. Most prior research has compared subjective assessments of animal “agility” with a single determinant of rotational sensitivity: the mean canal radius of curvature (R). In fact, the paired variables of R and body mass are correlated with agility and have been used to infer locomotion in extinct species. To refine models of canal functional morphology and to improve locomotor inferences for extinct species, we compare 3D vector measurements of head rotation during locomotion with 3D vector measures of canal sensitivity. Contrary to the predictions of conventional models that are based upon R , we find that axes of rapid head rotation are not aligned with axes of either high or low sensitivity. Instead, animals with fast head rotations have similar sensitivities in all directions, which they achieve by orienting the three canals of each ear orthogonally (i.e., along planes at 90° angles to one another). The extent to which the canal configuration approaches orthogonality is correlated with rotational head speed independent of body mass and phylogeny, whereas R is not.