Phylogenetic relationships of the European trilophosaurids <i>Tricuspisaurus thomasi</i> and <i>Variodens inopinatus</i>

Trilophosauridae are an extinct group of archosauromorphs from the Upper Triassic of western North America and Nova Scotia. Possible trilophosaurids <i>Tricuspisaurus thomasi</i> and <i>Variodens inopinatus</i> have also been reported from Upper Triassic fissure fills in the southwest of the United Kingdom, based on their multi-cuspid dentitions. Here, we provide an updated description of <i>V. inopinatus</i> and add to the description of <i>T. thomasi</i>, including re-examining CT scans of its holotype dentary. We confirm that the apparent gap on the dentary of <i>T. thomasi</i> is pathological, with the dentine of the teeth on either side of the gap asymmetrically thick, and that heavy vascularization of the anterior part of the dentary confirms it likely had a keratinous rhamphotheca. Our cladistic analyses, to which we add nine new characters, confirm that <i>T. thomasi</i> and <i>V. inopinatus</i> are closely related taxa and the youngest known trilophosaurids. Further, we support a previous suggestion that the relatively small size of these two European trilophosaurids results from insular dwarfism.