CONVERGENT EVOLUTION IN TOOTH MORPHOLOGY OF FILTER FEEDING LAMNIFORM SHARKS

The basking shark (Cetorhinus maximus) and megamouth shark (Megachasma pelagios) are two species of filter feeding sharks, both belonging to the order Lamniformes. There are two conflicting hypotheses regarding the origins of filter feeding in lamniform sharks; that there is a single origin of filter feeding within Lamniformes, or conversely, the filter feeding adaptations have been developed independently due to different ancestral conditions. Evidence obtained from several morphological and molecular studies strongly supports the latter hypothesis. Because evidence suggests that C. maximus and M. pelagios have developed their filter feeding adaptations independently, we expect to see convergent evolution in tooth morphology within these two lineages. Geometric morphometric Procrustes and relative warp analyses were performed on fossil and Recent teeth of megamouth and basking sharks to determine if there is commonality among tooth shape. Resulting relative warp axes were interpreted using percent variation explained and compared by species. A series of multivariate analyses of variance (MANOVA) was used to test for significant differences in heterodonty and a series of one-way analyses of variance (ANOVA) with corresponding Tukey intervals (95% CI) was used to test for morphological differences in overall mean tooth shapes between fossil and Recent megamouth and basking shark teeth for each significant relative warp axis. The results of the MANOVAs showed significant differences in heterodonty and support independently derived filter feeding adaptations and the results of the ANOVAs and corresponding Tukey intervals support convergent evolution in tooth morphology within these two species of filter feeding lamniform sharks.