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

References
  1. Hyman, Libbie Henrietta (1942). Comparative Vertebrate Anatomy (2nd ed.). Chicago, Illinois, US: The University of Chicago Press. p. 177.
  2. Coombs, Walter P. (1972). "The bony eyelid of Euoplocephalus (Reptilia, Ornithischia)". Journal of Paleontology. 46 (5): 637–650. ISSN 0022-3360. JSTOR 1303019.
  3. Norman, David B.; Sues, Hans-Dieter; Witmer, Larry M.; Coria, Rodolfo A. (2004). "Basal Ornithopoda". In Weishampel, David B.; Dodson, Peter; Osmólska, Halszka (eds.). The Dinosauria (2nd ed.). Berkeley: University of California Press. pp. 393–412. ISBN 978-0-520-24209-8.
  4. Sues, Hans-Dieter; Norman, David B. (1990). "Hypsilophodontidae, Tenontosaurus, Dryosauridae". In Weishampel, David B.; Osmólska, Halszka; Dodson, Peter (eds.). The Dinosauria (1st ed.). Berkeley: University of California Press. pp. 498–509. ISBN 978-0-520-06727-1.
  5. You Hailu and Dodson, Peter. (2004). Basal Ceratopsia. In: Weishampel, David B.; Dodson, Peter; and Osmolska, Halszka (eds.) The Dinosauria (2nd Edition). Berkeley: University of California Press. p. 478–493.
  6. Paul, Gregory S. (2000). "Restoring the Life Appearances of Dinosaurs". In Paul, Gregory S. (ed.). The Scientific American Book of Dinosaurs. New York: St. Martin's Press. p. 102. ISBN 978-0-312-26226-6.
  7. Naish, Darren; David M. Martill (2001). "Ornithopod dinosaurs". Dinosaurs of the Isle of Wight. London: The Palaeontological Association. p. 79. ISBN 978-0-901702-72-2.
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