MORPHOLOGY OF THE CORNUAL SINUSES IN CHASMOSAURINE HORNED DINOSAURS (ORNITHISCHIA: CERATOPSIDAE)

The ceratopsids, or horned dinosaurs, are well-known for their bizarre cranial ornamentation consisting of horns, frills, and knobs of bone. While the external features of the ceratopsid skull are well-described, many aspects of their internal cranial anatomy are poorly known. Hollow cavities called cornual sinuses occupy the basal portion of the postorbital, or brow, horns in many members of the subfamily Chasmosaurinae. The sinuses are absent in Chasmosaurus, relatively small in Anchiceratops, and variably developed in Triceratops, Pentaceratops, and Torosaurus. Their presence or absence is not known in Arrhinoceratops. The cornual sinus cavities of most chasmosaurines have not been examined, so they were described as a first step towards understanding their function and evolution. The cornual sinuses are relatively simple structures in chasmosaurines, consisting of an ovate cavity that extends into the postorbital horncore. These sinuses are domed distally, and small folds of bone may be present on the sinus cavity walls. The bone enclosing the cornual sinus cavity is extensively vascularized in some specimens. The function of the sinuses is problematic, but it is possible that they eliminated structurally unnecessary bone from the horncore, thereby reducing skull mass.