New Evidence of the Feeding Behaviors of Coronodon and the Origin of Filter Feeding in Mysticetes (Mammalia: Cetacea) Revisited

Coronodon includes species of basal toothed mysticetes that were initially interpreted as engaging in raptorial feeding and dental filtration. Here, the feeding of this extinct genus is revisited based on recently described specimens and species. Associations between tooth position and types of dental wear were tested, and evidence for feeding behaviors was tabulated using scores from 14 craniodental characters, each mapped onto five alternate phylogenetic hypotheses. Individual character states were interpreted as being supportive, neutral, or contradictory evidence to raptorial feeding, suction feeding, baleen filtration, or dental filtration. Wear in Coronodon was found to be significantly more concentrated on mesial teeth, mesial cusps, higher cusps, and upper teeth. Upper teeth also had mesial cusps more worn than distal cusps, inconsistent with predictions of the dental filtration hypothesis. Wear in notches was correlated with wear on neighboring cusps, and side wear was concentrated on occlusal sides, suggesting both were caused by raptorial feeding. These observations raise the possibility that raptorial feeding was the primary, and maybe even the only, mode of feeding for Coronodon. The feeding scores of reconstructed ancestors leading to crown mysticetes typically display a stepwise decrease in raptorial feeding, a stepwise increase in baleen filtration, and, occasionally, an intermediate but weakly supported stage of dental filtration. For most toothed mysticetes, there is little evidence for or against suction feeding. The method we have developed for studying the origin of baleen can be expanded and allows for multiple hypotheses to be tested without undue emphasis on any particular taxon or set of characters.