Derived faunivores are the forerunners of major synapsid radiations

Abstract Evolutionary radiations generate most of Earth’s biodiversity, but are there common ecomorphological traits among the progenitors of radiations? In Synapsida (mammalian total group), ‘small-bodied faunivore’ has been hypothesized as the ancestral state of most major radiating clades, but this has not been quantitatively assessed across multiple radiations. To examine macroevolutionary patterns in a phylogenetic context, we generated a time-calibrated meta-phylogeny (‘metatree’) comprising 2,128 synapsid species from the Carboniferous through the Eocene (305–34 Ma), based on 270 published character matrices. We used comparative methods to investigate body size and dietary evolution during successive synapsid radiations. Faunivory is the ancestral diet of each major synapsid radiation, but small body size is only established as the common ancestral state of radiations near the origin of Mammaliaformes in the Late Triassic. The faunivorous ancestors of synapsid radiations typically have numerous novel characters compared to their contemporaries, and these derived traits may have helped them to survive faunal turnover events and subsequently radiate.