Trophic convergence drives morphological convergence in marine tetrapods

Abstract

Marine tetrapod clades (e.g. seals, whales) independently adapted to marine life through the Mesozoic and Caenozoic, and provide iconic examples of convergent evolution. Apparent morphological convergence is often explained as the result of adaptation to similar ecological niches. However, quantitative tests of this hypothesis are uncommon. We use dietary data to classify the feeding ecology of extant marine tetrapods and identify patterns in skull and tooth morphology that discriminate trophic groups across clades. Mapping these patterns onto phylogeny reveals coordinated evolutionary shifts in diet and morphology in different marine tetrapod lineages. Similarities in morphology between species with similar diets-even across large phylogenetic distances-are consistent with previous hypotheses that shared functional constraints drive convergent evolution in marine tetrapods.

Keywords: convergent evolution; feeding adaptation; functional morphology; marine mammal; marine reptile.

Figure 1.

(a) Cluster analysis of dietary data for marine tetrapods. Red numbers show bootstrap confidence intervals. (b) Summarized phylogenetic distribution of trophic guilds across all species in this analysis (see the electronic supplementary material for detailed phylogeny and sources). Silhouettes in (b) by Chris Huh, Vince Smith, Steven Traver from phylopic.org and the authors.

Figure 2.

Phylomorphospace using the first two LD axes of three LDAs incorporating (a) skull measurements only, (b) tooth measurements only, (c) both skull and tooth measurements. Colours denote trophic groups (see key); dashed lines indicate divergence prior to marine invasion.