The 84th Annual Meeting of the American Association of Physical Anthropologists (2015)


Smaller posterior semicircular canals are associated with leaping in Colobus

TODD C. RAE1, PAUL M. JOHNSON1, WATARU YANO2 and EISHI HIRASAKI3.

1Centre for Research in Evolutionary and Environmental Anthropology, University of Roehampton, 2Dept of Oral Anatomy, Asahi University School of Dentistry, 3Primate Research Institute, Kyoto University

March 27, 2015 9:00, Grand Ballroom A/B Add to calendar

The semicircular canals of the inner ear are the organ of balance, tracking head rotation during movement and facilitating reflexive stabilisation of vision. Morphological characteristics of the canals have been correlated with agility scores based on multiple measures of behaviour. To date, however, the relationship between semicircular canal morphology and specific locomotor behaviours, such as leaping, is unknown. Knowledge of such a relationship could strengthen the inferences of locomotion of extinct taxa beyond agility, as the semicircular canals are preserved in fossils.

To test this, the crania of closely related primate species (Colobus guereza and C. polykomos) differing in the percentage of leaping in their locomotor repertoire were examined using microscopic computed tomography (μCT). Three-dimensional virtual models were derived using the software package AVIZO, and two measurements (mean canal radius of curvature and enclosed planar area) of each of the three canals were measured relative to two cranial size proxies.

While ‘agile’ species have larger anterior canals, there was no corresponding significant difference between Colobus spp. Instead, the ‘leaping’ form (C. guereza) possesses significantly smaller posterior canals. This may be related to the need for leapers to recover balance quickly upon landing. While this difference suggests a method by which specific locomotor behaviours can be inferred for extinct primates, what remains unclear at present is whether this phenomenon is applicable outside the genus examined. The authors are currently extending the study to other pairs of taxa that also differ in the amount of leaping in their locomotor repertoire.

Financial support provided by a Japan Society for the Promotion of Science Fellowship awarded to TCR and a Primate Society of Great Britain grant awarded to PMJ.