Rhynchosaurs were key herbivores over much of the world in the Middle and Late Triassic, often dominating their faunas ecologically. The anatomy of the Middle Triassic forms is debated in certain phylogenetically important details. Among several genera from the Anisian of England, Bentonyx sidensis is represented by a near-complete skull. New CT scanning of the holotype skull reveals previously concealed details of the palate and braincase in particular, and this allows comparison with other Middle Triassic rhynchosaurs and confirmation that Bentonyx is a distinct taxon from others of similar age including Fodonyx, Rhynchosaurus, Langeronyx, and Stenaulorhynchus. These are part of the first wave of rhynchosaur diversification in the Middle Triassic.

Key words: Reptilia, Rhynchosauria, Bentonyx , skull anatomy, Middle Triassic, Anisian, UK.

Thitiwoot Sethapanichsakul [sethapth@gmail.com; ORCID: https://orcid.org/0000-0001-5739-4774] and Michael J. Benton [mike.benton@bristol.ac.uk; ORCID: https://orcid.org/0000-0002-4323-1824], School of Earth Sciences, University of Bristol, Bristol, BS8 1RJ, UK. Robert Coram [rob@britishfossils.co.uk; ORCID: https://orcid.org/0000-0003-3048-6665], British Fossils, Unit 18-20 Bailie Gate Industrial Estate, Sturminster Marshall, Wimborne, Dorset BH21 4DB, UK; and School of Earth Sciences, University of Bristol, Bristol, BS8 1RJ, UK.