The palpebral bone is a small dermal bone found in the region of the eye socket in a variety of animals, including crocodilians and ornithischian dinosaurs.
[2] In ornithischians, the palpebral can form a prong that projects from the front upper corner of the orbit.
It is large in heterodontosaurids,[3] basal ornithopods such as Thescelosaurus (as Bugenasaura) and Dryosaurus,[3][4] and basal ceratopsians such as Archaeoceratops;[5] in these animals, the prong is elongate and would have stuck out and over the eye like a bony eyebrow.
As paleoartist Gregory S. Paul has noted, elongate palpebrals would have given their owners fierce-looking "eagle eyes".
[6] In such cases, the expanded palpebral may have functioned to shade the eye.