Integration of multi-level dental diversity links macro-evolutionary patterns to ecological strategies across sharks.

Abstract

The exceptional dental diversity in sharks is frequently used as a proxy for ecological function. However, functional inferences from morphology need to consider morphological features across different organizational scales and spatial resolutions. Here, we compare morphological features ranging from sub-dental patterns to whole dentitions within a large ensemble of species encompassing all extant shark orders. Although taxa scoring high for different heterodonty measures are distributed throughout the phylogeny, the two shark superorders show a different degree of modularity between mono- and dignathic heterodonty as well as substantial differences in ecological niches. Intriguingly, we observe two alternative ways of increasing dental complexity: either at the tooth- or dentition-level. Correlating heterodonty and single-tooth complexity with ecological and life-history traits, we find that pelagic and demersal species evolve dental complexity in different ways. We track trait variability as a function of genetic distance, thus quantifying dental trait adaptability at different resolutions. Overall, intermediate resolution levels, namely the degree of monognathic heterodonty, predict ecological traits best but carry a relatively low phylogenetic signal, suggesting a more dynamic adaptability on shorter evolutionary timescales. This raises macro-evolutionary interpretations about the evolvability of nested modular phenotypic structures, with important implications for paleo-ecological inferences from sequentially homologous traits.