Meeting Abstract

P3.170  Sunday, Jan. 6  Global Sensitivity of the Mammalian Head to Rotation: Importance of Semicircular Canal Orientation for Locomotor Agility in Therian Mammals BERLIN, J/C*; KIRK, E/C; RODGERS, M/C; ROWE, T/B; HULLAR, T/E; University of Texas, Austin; University of Texas, Austin; University of Texas, Austin; University of Texas, Austin; Washington University in St. Louis School of Medicine JeriCR55@aol.com

Determining locomotor abilities of extinct mammals is difficult in the absence of postcranial fossil elements. Previous methods compared the radius of curvature (R) of semicircular canals with qualitative assessments of locomotor agility in extant taxa. This approach ignores the effects of canal orientation on vestibular sensitivity, and how deviations of canal orientations from orthogonality influence the location of global maximum rotational sensitivity. We present a program that estimates vestibular sensitivity in 3 dimensions using measurements of the orientation and the R for all six semicircular canals. This represents a significant advance over prior methods that focus on canal radius of curvature only. We quantified semicircular canal size and orientation in a comparative sample of 40 therian mammals. Phylogenetically-informed statistical comparisons of this sample reveal that gliding and saltatory species have relatively high global maximum sensitivity to angular head accelerations. By contrast, fossorial species have relatively low global maximum sensitivity to angular head accelerations. These analyses indicate that locomotor mode in mammals is correlated with vestibular sensitivity, suggesting that CT data on semicircular canals may be used to test locomotor hypotheses for fossil species.