The Impact of Food Properties on Jaw Movements in Rodents: A Comparison Between Myomorphous and Hystricomorphous Species.

Rodents can be divided into three major morphological groups (myomorphy, sciuromorphy, and hystricomorphy; additionally, protogomorphy can be found in only one recent species) based on the configuration of the skull and jaw muscles. These three morphotypes have been suggested to be adapted to different food types and allow for different chewing movements. Previous authors have postulated that the masticatory grinding movements should occur mostly in the antero-posterior direction, but other studies have suggested that different degrees of antero-posterior movement may occur across the rodent tree of life and in response to differences in food properties. Here, we use 3D reconstructed movements from X-Ray videos to show that both morphology and food type influence masticatory movements in two myomorphous and two hystricomorphous rodents. Yet, while hystricomorphs do not change the frequency of their masticatory movements in response to different food items, myomorphs do so. Additionally, myomorphs and hystricomorphs that exhibit propalinal chewing movements tend to possess a relatively lower mandibular condyle. Overall, our data suggest that molar morphology, in connection with dietary habits, directly influences masticatory movements. These results show that relatively small differences in a relatively conserved bauplan can have a large impact on jaw movements.