The Evolution of Feeding Motor Patterns in Lizards: Modulatory Complexity and Possible Constraints

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Abstract
Previous research indicated that the evolution of feeding motor patterns across major taxonomic groups might have occurred without large modifications of the control of the jaw and hyolingual muscles. However, the proposal of this evolutionary scheme was hampered by the lack of data for some key taxa such as lizards. Recent data on jaw and hyolingual feeding motor patterns of a number of lizard families suggest extensive variability within and among species. Although most lizards respond to changes in the structural properties of food items by modulating the activation of the jaw and hyolingual muscles, some food specialists might have lost this ability. Whereas the overall similarity in motor patterns across different lineages of lizards is large for the hyolingual muscles, jaw muscle activation patterns seem to be more flexible. Nevertheless, all data suggest that both the jaw and hyolingual system are complexly integrated. The elimination of feedback pathways from the hyolingual system through nerve transection experiments clearly shows that feeding cycles are largely shaped by feedback interactions. Yet, novel motor patterns including unilateral control seem to have emerged in the evolution from lizards to snakes.