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.
Highlights
Terrestrial vertebrates have repeatedly readapted to marine life since their ancestors originally left the water over 300 Myr ago [1,2,3,4]
In roughly increasing trophic level, these are: (i) herbivores (H); (ii) benthic invertebrate specialists (B); (iii) zooplanktivores (Z); (iv and v) two distinct groups that feed primarily upon fish (FA and fish B (FB)), but differ in the relative proportion of types of fish consumed; (vi) a group that feeds on a roughly equal proportion of mesopelagic fish and cephalopods (FS); (vii) squid specialists (S) and (viii) apex predators (A), which consume a significant fraction of tetrapod prey in addition to fish and invertebrates
Previous studies of marine tetrapods have frequently suggested that trophic convergence is reflected in the evolution of marine tetrapod cranial and dental morphology [5,6,14]
Summary
Terrestrial vertebrates have repeatedly readapted to marine life since their ancestors originally left the water over 300 Myr ago [1,2,3,4]. These habitat shifts, and their attendant changes in diet and morphology, have resulted in increasing ecological and anatomical disparity within many secondarily marine tetrapod lineages. In contrast to this pattern of increasing disparity within lineages, distantly related marine tetrapod species have independently adapted towards similar lifestyles and morphologies [5,6], providing textbook illustrations of evolutionary convergence. We provide a quantitative approach for investigating ecomorphological convergence across living marine tetrapod clades
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