A supposed heterodontosaurid tooth from the Rhaetian of Switzerland and a reassessment of the European Late Triassic record of Ornithischia (Dinosauria)

Verifiable remains of ornithischian dinosaurs are scarce in Upper Triassic sediments. An isolated tooth from the Rhaetic bone bed of Hallau, Switzerland, has previously been referred to the ornithischian clade Heterodontosauridae. We redescribe this tooth, demonstrating that it cannot be assigned to Ornithischia but does resemble enigmatic teeth from the Owl Rock Formation of North America and may represent a new taxon or clade of archosauriform reptiles. The identification of all other Late Triassic teeth from Europe previously assigned to Ornithischia is problematic, and we here regard these specimens as pertaining to Archosauriformes indet. Bone fragments from the Westbury Formation of England have been assigned to the ornithischian clade Stegosauria, but cannot be referred with certainty to any reptilian clade. There is no persuasive body fossil evidence for ornithischian dinosaurs in the Late Triassic of Europe; ornithischians may have been limited in diversity, abundance and geographical distribution during this time period, radiating only after the end of the Triassic.