Meeting Abstract
90.1 Thursday, Jan. 7 Jaw kinematics in lepidosaurs and mammals and the evolution of amniote chewing. ROSS, C.F.*; HERREL, A.; METZGER, K.A.; REED, D.A.; SCHAERLAEKEN, V.; GEORGI, J.; BADEN, A.L.; WOLFF, M.S.; University of Chicago, IL; Museum National d’Histoire Naturelle, France; Hofstra University, NJ; University of Chicago, IL; University of Antwerp, Belgium; Midwestern University, AZ; Stony Brook University, NY; New York University, NY rossc@uchicago.edu
Mammals chew more rhythmically than lepidosaurs and show less variance in chew cycle durations. The research presented here evaluated possible reasons for this difference in relationship to variation in sensorimotor systems. Variance in the absolute and relative durations of the phases of the gape cycle was calculated from kinematic data gathered from a range of lepidosaurs and mammals. Bone strain data from the mandibular corpus were used to evaluate how lepidosaurs modulate bite force during chewing. Mammals exhibit less variance in overall gape cycle duration than in the durations of its constituent phases, suggesting trade-offs in variance among the phases of the gape cycle. Similar effects are much less pronounced in lepidosaurs. In addition, mammals show isometric changes in gape cycle temporal shape: the relative durations of the phases of the gape cycle change little with increasing cycle time. In contrast, in lepidosaurs the variance in total gape cycle duration is associated with increases in the proportion of the cycle made up by the slow open phase. Tupinambis resembles mammals in rate-modulating bite force. We hypothesize that in mammals the central nervous system includes a representation of the optimal chew cycle duration maintained using afferent feedback on the ongoing state of the chew cycle. The differences between lepidosaurs and mammals may not lie in the nature of the sensory information collected and its feedback to the feeding system during slow open, but rather the processing of that information by the CNS and its use for modulating other gape cycle phases.
