Carboniferous recumbirostran elucidates the origins of terrestrial herbivory

The evolution of herbivory is one of the most important ecological events in the evolution of terrestrial vertebrates and impacted the ecosystems they inhabited. Herbivory independently developed in a number of tetrapod clades during the Late Carboniferous and Permian, eventually leading to the establishment of the basic structure of modern terrestrial ecosystems. Here we describe a Late Carboniferous pantylid ‘microsaur’, Tyrannoroter heberti gen. et sp. nov., with expansive occluding palatal and coronoid dental batteries. The shape of the teeth, as revealed by high-resolution micro-computed tomography data, indicates wear from both shearing and grinding motions consistent with herbivory. New data from historical pantylid fossils show that similar adaptations can be traced back as far as the Bashkirian (~318 million years ago), indicating that terrestrial herbivory was already widespread within this group, and originated rapidly following the terrestrialization of tetrapods. The placement of recumbirostran ‘microsaurs’ on the amniote stem suggests that terrestrial herbivory is not an amniote innovation, although the phylogenetic position of ‘microsaurian’ tetrapods remains uncertain. Under any phylogenetic scenario, the data presented here reveal that pantylids acquired adaptations to herbivory independently, probably via durophagous omnivory, feeding on insects, shelled animals and tough plant material. A new species of pantylid microsaur from the Late Carboniferous of Cape Breton Island, Nova Scotia, has teeth with dental occlusion consistent with herbivory, indicating an early transition to this condition among terrestrial tetrapods.