Meeting Abstract

S2.4  Tuesday, Jan. 4  Patterns of jaw-muscle recruitment evolution in mammals WILLIAMS, SH*; VINYARD, CJ; CROMPTON, AW; HYLANDER, WL; Ohio University, Athens; NEOUCOM, Rootstown; Harvard, Cambridge; Duke Univ., Durham willias7@ohio.edu

The evolution and subsequent diversification of mammals is characterized by marked changes in the morphology of the masticatory apparatus, and these marked changes are presumably linked to more efficient processing of foods. Much of our understanding of mammalian craniofacial function and evolution relies on physiological studies of jaw-muscle recruitment patterns during mastication. However, the most recent synthetic study of mammalian chewing motor patterns is a qualitative analysis of jaw-muscle motor patterns (Weijs, 1994). Since this study, a number of quantitative analyses of the electromyographic activity of the jaw-muscles in individual species have been conducted. Here, we provide a more comprehensive look at the evolution of jaw-muscle recruitment patterns across a broader range of taxa to understand how key physiological variables associated with feeding evolved across mammals. Major character state changes, such as relative muscle recruitment levels and timing of muscle recruitment, are assessed in a phylogenetic context using the most recent species-level phylogeny of mammals. Preliminary analyses of independent contrasts of motor pattern variables from four orders show significant correlations between the relative amount of superficial masseter and anterior and posterior temporalis peak activity but not between other jaw muscles. There is also a strong correlation between the peak timing of EMG activity in various parts of the working- and balancing-side temporalis muscle in contrast to the lack of correlation between different parts of the masseter muscle. Results from this work can be integrated with diet and morphology data to better understand the evolution of mammalian feeding. Supported by NSF.