1. Duke University, Department of Biological Anthropology and Anatomy, Box 90383, Durham, North Carolina 27708-0383, USA
2. University of Toronto in Mississauga, Department of Zoology, 3359 Mississauga Road, Mississauga, Ontario L5L 1C6, Canada

Correspondence to: Robert R. Reisz² Correspondence and requests for materials should be addressed to R.R.R. (e-mail: Email: rreisz@credit.erin.utoronto.ca).

Abstract

Herbivores can increase their digestion rate by mechanically reducing particle size through oral trituration¹. Groups of terrestrial vertebrates with the greatest capacity to reduce tough plant foods orally are also the most abundant and diverse, as exemplified by ornithopod dinosaurs during the Mesozoic and extant artiodactyl and perissodactyl mammals². Thus, the effective oral processing of high-fibre plant material seems to represent an evolutionary innovation of both functional and macroevolutionary significance. However, evidence for oral processing is poorly documented in the fossil record, especially during the initial stages of terrestrial vertebrate diversification^{3, 4}. Here we report on the basal anomodont Suminia getmanovi, the only known Palaeozoic vertebrate in which unequivocal specializations in its cranium and teeth for high-fibre herbivory are well preserved. We propose that the capacity to comminute tough plant foods was critical to the diversification of anomodonts, the most diverse, widely dispersed and abundant group of Palaeozoic terrestrial vertebrates, and to the onset of modern terrestrial ecosystems.