Meeting Abstract
Food processing, or cyclic application of dentition-clad surfaces to ingested food, is rhythmic among mammals (grand mean CV; Coefficient of Variation = 15%) and basal bony fishes (25%) and less so among lepidosaurs (lizards and their allies; 53%). This phylogenetic shift in rhythmicity from aquatic-feeding anamniotes to terrestrial amniotes is not readily explained by variation in the proprioceptive capabilities of the jaw closers. However, the shift might be influenced by changes in fluid properties (water to air) as vertebrates move from aquatic to terrestrial chewing. We examine variation in chewing rhythmicity across the fish-tetrapod transition using data from basal actinopterygians (Polypterus sp.), lungfishes (Neoceratodus fosterii; Protopterus annectens), and salamanders (Ambystoma mexicanum, Siren intermedia, Amphiuma means, Plethodon sp., Ichthyosaura alpestris, and Triturus carnifex). Among ancestral gnathostomes, processing rhythmicity rivals that of mammals (Polypterus, CV = 17%) and rhythmicity is generally high in aquatic-feeding sarcopterygians (Protopterus, 14%; Neoceratodus, 34%). The grand average CV for processing rhythmicity among lissamphibians (28%) is not statistically significantly different from that of other anamniote chewers. However, CV is consistently higher for terrestrialized than aquatic salamander morphs. These data suggest an ancestral state for gnathostomes of high processing rhythmicity, which is somewhat perturbed by transitions to terrestriality. However, to explain the uniquely arrhythmic chewing behavior of lepidosaurs we might need to invoke behavioral attributes, such as inertial food handling.
