Palpebral (bone)
The palpebral bone is a term applied to a number of small dermal bones found in the region of the eye socket in a variety of animals. The names "palpebral" and "supraorbital" have been applied to number of bones dorsal to the eye in a wide variety of taxa; many of these are known or believed to not have a homologous origin. [1]
These bones are also known as the adlacrimal[2], supraciliary[1], parafrontal[3], or supraorbital, although the latter term may not be confused with the supraorbital in osteichthyan fishes.[4] The supraorbital in osteichthyan fishes is not considered homologous with the palpebral of any tetrapods, as it arises from a cartilaginous precursor.[1]
Evolution
[edit]In early tetrapods
[edit]The non-amniote tetrapod genera Seymouria and Discosauriscus possess an element referred to as the palpebral.[5]
In ornithischians
[edit]
In ornithischian dinosaurs, the palpebral ancestrally forms a prong that projects from the front upper corner of the orbit. The rough texture of the palpebral and of the skull bones dorsal to it (the frontal and postorbital) suggest that they functioned to support a membrane of soft tissue that made up the roof of the orbit. Ossification of this membrane led to the evolution of the middle and posterior supraorbitals and incorporated the palpebral into the skull roof as the anterior supraorbital.[6] Because the so-called palpebral of ornithischians is not homologous with the palpebral of crocodilians, a 2012 paper by Sterling Nesbitt and colleagues recommended that the element be referred to by another name.[1] Nevertheless, other authors have continued to refer to the element as the palpebral.[7][8]
It is large in heterodontosaurids,[9] basal ornithopods such as Thescelosaurus (as Bugenasaura) and Dryosaurus,[9][10] and basal ceratopsians such as Archaeoceratops;[11] 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".[12] In such cases, the expanded palpebral may have functioned to shade the eye.[13]
In pachycephalosaurs, hadrosaurs, ceratopsids, and later thyreophorans, the palpebral is incorporated into the skull roof.
The ossified eyelid of the ankylosaur Euoplocephalus was historically thought to be homologous to the "palpebral" of other ornithischians, but is now thought to be an osteoderm.[6][4]
In other sauropsids
[edit]The palpebral bones of crocodilians develop from the upper eyelid in a process identical to that of the post-cranial osteoderms, suggesting that it is an osteoderm itself. In some crocodilians, including Osteolaemus and Paleosuchus, multiple palpebrals may be present. In some fossil pseudosuchians, the palpebral is fully integrated into the skull roof.[1]
Aetosaurs possess palpebrals, but it is unclear if they are homologous to those of modern crocodilians.[1]
Palpebrals are present in various groups of lizards: lacertids, some scincoids, and anguimorphs except possibly Heloderma.[14][15] A 2010 paper recommended restricting the use of the term "palpebral" to the element present in the clade autarchoglossa, and recommended the term supraorbital for the element in Loxocemus and pythons, and the term "parafrontal" for the element(s) in some geckos.[3] The parafrontals of geckos form a number of small ossifications that differ strongly from osteoderms, develop deep to the dermis and do not correspond to the overlying scales; in some geckos which lack the parafrontals, a continuous sheet of mesenchyme is present in the same position.[3] The palpebrals of autarchoglossans develop deep to the osteoderms when both are present.[15]
An element informally referred to as the "palpebral" has been described among some pliosaurids.[16] However, the identity (and indeed the presence) of this element is in question.[17]
Elements referred to as palpebrals are also present in pterosaurs and some birds.[1]
References
[edit]
- 1 2 3 4 5 6 7 Nesbitt, Sterling J.; Turner, Alan H.; Weinbaum, Jonathan C. (September 2012). "A survey of skeletal elements in the orbit of Pseudosuchia and the origin of the crocodylian palpebral". Earth and Environmental Science Transactions of the Royal Society of Edinburgh. 103 (3–4): 365–381. Bibcode:2012EESTR.103..365N. doi:10.1017/S1755691013000224. ISSN 1755-6910.
- ↑ Hyman, Libbie Henrietta (1942). Comparative Vertebrate Anatomy (2nd ed.). Chicago, Illinois, US: The University of Chicago Press. p. 177.
- 1 2 3 Daza, Juan Diego; Bauer, Aaron Matthew (2010). "The Circumorbital Bones of the Gekkota (Reptilia: Squamata)". The Anatomical Record. 293 (3): 402–413. doi:10.1002/ar.21039. ISSN 1932-8494. PMID 19937637.
- 1 2 Coombs, Walter P. (1972). "The bony eyelid of Euoplocephalus (Reptilia, Ornithischia)". Journal of Paleontology. 46 (5): 637–650. ISSN 0022-3360. JSTOR 1303019.
- ↑ Bratislava, Jozef Klembara (1995-03-01). "The external gills and ornamentation of skull roof bones of the Lower Permian tetrapodDiscosauriscus (Kuhn 1933) with remarks to its ontogeny". Paläontologische Zeitschrift. 69 (1): 265–281. Bibcode:1995PalZ...69..265B. doi:10.1007/BF02985990. ISSN 1236-9874.
{{cite journal}}: Check|issn=value (help) - 1 2 Maidment, Susannah C. R.; Porro, Laura B. (March 2010). "Homology of the palpebral and origin of supraorbital ossifications in ornithischian dinosaurs". Lethaia. 43 (1): 95–111. Bibcode:2010Letha..43...95M. doi:10.1111/j.1502-3931.2009.00172.x. ISSN 0024-1164.
- ↑ Norman, David B, FLS; Baron, Matthew G; Garcia, Mauricio S; Müller, Rodrigo Temp (2022-12-01). "Taxonomic, palaeobiological and evolutionary implications of a phylogenetic hypothesis for Ornithischia (Archosauria: Dinosauria)". Zoological Journal of the Linnean Society. 196 (4): 1273–1309. doi:10.1093/zoolinnean/zlac062. ISSN 0024-4082.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ↑ Wang, Yan-Chao; Zhang, Qian-Nan; You, Hai-Lu (2026-08-03). "Cranial osteology of Archaeoceratops oshimai (Ornithischia: Ceratopsia) and phylogenetic evaluation of basal Ceratopsia". Historical Biology. 38 (8): 2820–2837. doi:10.1080/08912963.2025.2568096. ISSN 0891-2963.
- 1 2 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.
- ↑ 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.
- ↑ 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.
- ↑ 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.
- ↑ 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.
- ↑ Estes, Richard; de Queiroz, Kevin; Gauthier, Jacques (1988). "Phylogenetic relationships within Squamata". In Estes, Richard; Pregill, Gregory (eds.). Phylogenetic relationships of the lizard families: Essays commemorating Charles L. Camp. Stanford, California: Stanford University Press. pp. 119–281. ISBN 0-8047-1435-5.
- 1 2 Maisano, Jessica Anderson; Bell, Christopher J.; Gauthier, Jacques A.; Rowe, Timothy (2002). "The osteoderms and palpebral in Lanthanotus borneensis (Squamata: Anguimorpha)". Journal of Herpetology. 36 (4): 678–682. Bibcode:2002JHerp..36..678M. doi:10.2307/1565940. JSTOR 1565940.
- ↑ Ketchum, Hilary F.; Benson, Roger B. J. (2011). "The cranial anatomy and taxonomy of Peloneustes philarchus (Sauropterygia, Pliosauridae) from the Peterborough Member (Callovian, Middle Jurassic) of the United Kingdom". Palaeontology. 54 (3): 639–665. Bibcode:2011Palgy..54..639K. doi:10.1111/j.1475-4983.2011.01050.x. ISSN 1475-4983.
- ↑ Fischer, Valentin; Benson, Roger B J; Zverkov, Nikolay G; Arkhangelsky, Maxim S; Stenshin, Ilya M; Uspensky, Gleb N; Prilepskaya, Natalya E (2023-05-01). "Anatomy and relationships of the bizarre Early Cretaceous pliosaurid Luskhan itilensis". Zoological Journal of the Linnean Society. 198 (1): 220–256. doi:10.1093/zoolinnean/zlac108. ISSN 0024-4082.
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