A reevaluation of the hyoid bones of protoceratops andrewsi granger and gregory, 1923 (ornithischia: Ceratopsia) and a review of hyoid elements in ornithischian dinosaurs

We present a reinterpretation of the bones previously identified as ossified hyoid elements in the Asian Late Cretaceous ceratopsian dinosaur Protoceratops andrewsi Granger and Gregory, 1923. Comparisons with other ceratopsian skeletons indicate that the tetraradiate bone tentatively regarded as a first ceratobranchial is actually an incomplete middle cervical rib, and the larger, flattened elements identified as second ceratobranchials are partial sternal plates. As in nearly all other ornithischian dinosaurs for which this area of the skeleton is known, the ossified hyoid apparatus of P. andrewsi probably consisted of a pair of rod-like first ceratobranchials; two additional, splint-like or sheet-like bones that are most frequently interpreted as ceratohyals may also have been present