Miniaturization coincides with anatomical novelties during lissamphibian origins

Abstract Evolutionary miniaturization is often accompanied by phenotypic rearrangement, and may play an important role in occupying new adaptive zones. This process has hypothesised relevance to the origin of lissamphibians, which include the smallest living tetrapods. We test this by quantifying patterns of evolution of body size and other traits, using a dataset of 577 fossil and extant members of the lissamphibian total-group. We find that initial body size reduction occurred on the direct stem lineage leading to Lissamphibia and further miniaturization occurred in the crown group, giving rise to the down-shifted size distribution of living species. This coincides with rearrangements of skull morphology and the diversification of body shapes, indicating invasion of a fundamentally distinct adaptive zone. Our finding provides a compelling case of the potential contribution of miniaturization to ecological innovation at a macroevolutionary scale, facilitating the diversification and persistence of lissamphibians through ∼300 million years of evolutionary time.