Palpebral (bone)

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. It is also known as the adlacrimal^[1] or supraorbital, although the latter term may not be confused with the supraorbital in osteichthyan fishes.^[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.^[7]

Palpebral bone (highlighted) of Heterodontosaurus

Palpebral bone (highlighted) of Pliosaurus