Septomaxilla

The septomaxilla is a skull bone found in tetrapods. A generally small bone, it is associated with the nasal opening of the skull, either within or adjacent to it, and with the nasolacrimal duct.[1] The homology of the septomaxilla of tetrapods to bones present in fish is disputed; it has been variously suggested to be homologous to the anterior tectal or lateral rostral.[2][3]

It is particularly well developed within many non-mammalian synapsids, where it forms a floor to the nasal opening.[1] It is present as a distinct bone above the premaxilla in monotreme mammals.[4] In most therian mammals, it is generally suggested to have been lost (though it has been proposed to be present in xenarthrans[5]),[1] but it has recently been argued by some authors that in fact the "premaxilla" of therian mammals is actually developmentally homologous to the septomaxilla, which they suggest had become enlarged and tooth-bearing, with the true premaxilla being entirely lost.[6]

The septomaxilla is retained by some living amphibians (lissamphibians) including frogs, salamanders[1] and caecilians,[7] as well as lepidosaurian reptiles including snakes, some lizards[8] and the tuatara.[9] It has been lost in turtles.[1]

The septomaxilla is rarely found in archosauromorphs, but has been identified in Tanystropheus, Trilophosaurus,[10] the rhynchosaurs Hyperodapedon and Teyumbaita,[11] Prolacerta, and the basal archosauriform Proterosuchus.[10] There is no evidence for a septomaxilla in archosauriforms (including living crocodilians and birds) other than Proterosuchus.[12] An element found in phytosaurs sometimes called the "septomaxilla" is not homologous to the septomaxilla of other tetrapods.[13]

References

  1. ^ a b c d e Hillenius, Willem J. (2000-06-14). "Septomaxilla of nonmammalian synapsids: Soft-tissue correlates and a new functional interpretation". Journal of Morphology. 245 (1): 29–50. doi:10.1002/1097-4687(200007)245:1<29::AID-JMOR3>3.0.CO;2-B. ISSN 0362-2525. PMID 10861830.
  2. ^ Clack, J. A. (1994-04-19). "Acanthostega gunnari, a Devonian tetrapod from Greenland; the snout, palate and ventral parts of the braincase, with a discussion of their significance". Meddelelser om Grønland. Geoscience. 31. doi:10.7146/moggeosci.v31i.140691. ISSN 0106-1046.
  3. ^ Clack, J. A. (2001). "Eucritta melanolimnetes from the Early Carboniferous of Scotland, a stem tetrapod showing a mosaic of characteristics". Earth and Environmental Science Transactions of the Royal Society of Edinburgh. 92 (1): 75–95. doi:10.1017/S0263593300000055. ISSN 0263-5933.
  4. ^ Higashiyama, Hiroki; Koyabu, Daisuke; Hirasawa, Tatsuya; Werneburg, Ingmar; Kuratani, Shigeru; Kurihara, Hiroki (2021-11-02). "Mammalian face as an evolutionary novelty". Proceedings of the National Academy of Sciences. 118 (44) e2111876118. Bibcode:2021PNAS..11811876H. doi:10.1073/pnas.2111876118. ISSN 0027-8424. PMC 8673075. PMID 34716275.
  5. ^ Zeller, U.; Wible, J. R.; Elsner, M. (March 1993). "New ontogenetic evidence on the septomaxilla ofTamandua andCholoepus (Mammalia, Xenarthra), with a reevaluation of the homology of the mammalian septomaxilla". Journal of Mammalian Evolution. 1 (1): 31–46. doi:10.1007/BF01027598. ISSN 1064-7554.
  6. ^ Higashiyama, Hiroki; Koyabu, Daisuke; Kurihara, Hiroki (2022-08-26). "Evolution of the therian face through complete loss of the premaxilla". Evolution & Development. 25 (1): 103–118. doi:10.1111/ede.12417. ISSN 1520-541X. PMID 36017615.
  7. ^ Bardua, Carla; Wilkinson, Mark; Gower, David J.; Sherratt, Emma; Goswami, Anjali (December 2019). "Morphological evolution and modularity of the caecilian skull". BMC Evolutionary Biology. 19 (1) 30. Bibcode:2019BMCEE..19...30B. doi:10.1186/s12862-018-1342-7. ISSN 1471-2148. PMC 6343317. PMID 30669965.
  8. ^ Richman, Joy M.; Buchtová, Marcela; Boughner, Julia C. (May 2006). "Comparative ontogeny and phylogeny of the upper jaw skeleton in amniotes". Developmental Dynamics. 235 (5): 1230–1243. doi:10.1002/dvdy.20716. ISSN 1058-8388. PMID 16496291.
  9. ^ Diaz, Raul E.; Trainor, Paul A. (2019), Ziermann, Janine M.; Diaz Jr, Raul E.; Diogo, Rui (eds.), "An Integrative View of Lepidosaur Cranial Anatomy, Development, and Diversification", Heads, Jaws, and Muscles, Cham: Springer International Publishing, pp. 207–227, doi:10.1007/978-3-319-93560-7_9, ISBN 978-3-319-93559-1, retrieved 2026-05-11{{citation}}: CS1 maint: work parameter with ISBN (link)
  10. ^ a b Spiekman, Stephan N. F. (2018-12-20). "A new specimen of Prolacerta broomi from the lower Fremouw Formation (Early Triassic) of Antarctica, its biogeographical implications and a taxonomic revision". Scientific Reports. 8 (1) 17996. Bibcode:2018NatSR...817996S. doi:10.1038/s41598-018-36499-6. ISSN 2045-2322. PMC 6301955. PMID 30573764.
  11. ^ Gentil, Adriel R.; Ezcurra, Martín D. (2021-09-08). "Skull osteology of the holotype of the rhynchosaur Hyperodapedon sanjuanensis (Sill, 1970) from the Upper Triassic Ischigualasto Formation of Argentina". The Anatomical Record. 305 (5): 1168–1200. doi:10.1002/ar.24771. ISSN 1932-8494. PMID 34496139.
  12. ^ Ezcurra, Martín D. (2016-04-28). "The phylogenetic relationships of basal archosauromorphs, with an emphasis on the systematics of proterosuchian archosauriforms". PeerJ. 4 1778. doi:10.7717/peerj.1778. ISSN 2167-8359. PMC 4860341. PMID 27162705.
  13. ^ Nesbitt, Sterling J. (2011-04-29). "The early evolution of archosaurs: relationships and the origin of major clades". Bulletin of the American Museum of Natural History. 352: 1–292. doi:10.1206/352.1. ISSN 0003-0090.
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