Endocranial anatomy of the ceratopsid dinosaur and interpretations of sensory and motor function.

is one of the well-known Cretaceous ceratopsian dinosaurs. The ecology of has been controversial because of its unique morphological features. However, arguments based on brain and inner ear structures have been scarce. In this study, two braincases (FPDM-V-9677 and FPDM-V-9775) were analyzed with computed tomography to generate three-dimensional virtual renderings of the endocasts of the cranial cavities and bony labyrinths. Quantitative analysis, including comparison of linear measurements of the degree of development of the olfactory bulb and inner ear, was performed on these virtual endocasts to acquire detailed neuroanatomical information. When compared with other dinosaurs, the olfactory bulb of is relatively small, indicating that had a reduced acuity in sense of smell. The lateral semicircular canal reveals that the basicranial axis of is approximately 45° to the ground, which is an effective angle to display their horns as well as frill, and to graze. The semicircular canals of are relatively smaller than those of primitive ceratopsians, such as and , suggesting that sensory input for the reflexive stabilization of gaze and posture of was less developed than that of primitive ceratopsians. The cochlear length of is relatively short when compared with other dinosaurs. Because cochlear length correlates with hearing frequency, was likely adapted to hearing low frequencies.