38.5  Monday, Jan. 5  Semicircular Canal Morphology as Evidence of Sensory Adaptation to Locomotor Environment in Amniotes GEORGI, Justin A; Midwestern University, Glendale, AZ jgeorg@midwestern.edu

The vestibular system is a critical component of the neural control of locomotion in vertebrates. Integrated in the cerebellum with visual and proprioceptive inputs, the signals from the semicircular ducts provide vital information about rotational movement relative to the environment, and drive stabilization reflexes.

The semicircular ducts leave distinct canals through the bones of the posterior braincase which preserve some of the morphologies that determine the system’s functional parameters. Therefore, because the semicircular ducts have morphologies that determine the functional response of the system, and because some of these morphologies can be determined via the semicircular canals, it has been previously hypothesized that semicircular canal morphology can be used to link an organisms locomotion with semicircular duct biomechanics.

To test the underlying assumption of this hypothesis, adaptive change in biophysical parameters, the semicircular canals of a broad array of amniotes were examined. Within the semicircular canals of carnivoran mammals, turtles, varanids, and crocodilians there is, despite marked phylogenetic differences in shape, a consistent pattern of shape change that correlates with terrestrial, semi-aquatic, or aquatic locomotor behavior. This pattern is strongest in the anterior semicircular canal where the common crus and the peak of the canal adjacent to the common crus become shorter the more aquatic the animals behavior. This change in anterior semicircular canal shape is strongly tied to factors of limb morphology that correlate with locomotion and not with factors of skull morphology, supporting the hypothesis that this is adaptive change of the biomechanics of the semicircular canal system.