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Cephalopod beak

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The beak of a giant squid, surrounded by the buccal mass and limbs

All extant cephalopods have a two-part beak, or rostrum, situated in the buccal mass and surrounded by the muscular head appendages. The dorsal (upper) mandible fits into the ventral (lower) mandible and together they function in a scissor-like fashion.[1][2] The beak is composed primarily of chitin and cross-linked proteins.[3][4][5][6] Because they are more-or-less indigestible, beaks are often the only identifiable cephalopod remains found in the stomachs of predatory species such as sperm whales.[7] They can be used to estimate mantle length and total body weight.[8][9]

Fossilised remains of beaks are known from a number of cephalopod groups, both extant and extinct, including squid, octopuses, belemnites, and vampyromorphs.[10][11][12][13][14][15][16] Aptychi – paired plate-like structures found in ammonites – may also have been jaw elements.[17][18][19][20]

The beak may also be referred to as the mandibles or jaws.[13]

  • Side view of the lower beak of Chiroteuthis picteti (3.6 mm LRL, 160 mm ML (estimate))[1] 3D red cyan glasses are recommended to view this image correctly.
    Side view of the lower beak of Chiroteuthis picteti (3.6 mm LRL, 160 mm ML (estimate))[1]
    3D red cyan glasses are recommended to view this image correctly.
  • Side view of the upper beak from the same specimen (2.7 mm URL)[1]
    Side view of the upper beak from the same specimen (2.7 mm URL)[1]

Measurements

The upper (left) and lower jaws of a giant squid following extraction

The abbreviations LRL and URL are commonly used in teuthology to refer to lower rostral length and upper rostral length, respectively. This is the standard measure of beak size in Decapodiformes; hood length is preferred for Octopodiformes.[7]

  • Lower rostral length
    Lower rostral length
  • Upper rostral length
    Upper rostral length

References

Wikimedia Commons has media related to Cephalopod beaks.
  1. ^ a b c Young, R.E., M. Vecchione & K.M. Mangold (1999). Cephalopoda Glossary. Tree of Life Web Project.
  2. ^ Young, R.E., M. Vecchione & K.M. Mangold (2000). Cephalopod Beak Terminology. Tree of Life Web Project.
  3. ^ Saunders, W.B., C. Spinosa, C. Teichert & R.C. Banks (1978). Template:PDFlink Palaeontology 21(1): 129–141.
  4. ^ Hunt, S. & M. Nixon (1981). A comparative study of protein composition in the chitin-protein complexes of the beak, pen, sucker disc, radula and oesophageal cuticle of cephalopods. Comparative Biochemistry and Physiology Part B: Comparative Biochemistry 68(4): 535–546. doi:10.1016/0305-0491(81)90071-7
  5. ^ Miserez, A., Y. Li, J.H. Waite & F. Zok (2007). Template:PDFlink Acta Biomaterialia 3(1): 139–149. doi:10.1016/j.actbio.2006.09.004
  6. ^ Organic composite is exceptionally robust: jumbo squid. Ask Nature.
  7. ^ a b Clarke, M.R. (1986). A Handbook for the Identification of Cephalopod Beaks. Oxford University Press, Oxford.
  8. ^ Clarke, M.R. (1962). The identification of cephalopod "beaks" and the relationship between beak size and total body weight. Bulletin of the British Museum (Natural History), Zoology 8(10): 419–480.
  9. ^ Wolff, G.A. (1981). Template:PDFlink Fishery Bulletin 80(2): 357–370.
  10. ^ Zakharov, Y.D. & T.A. Lominadze (1983). New data on the jaw apparatus of fossil cephalopods. Lethaia 16(1): 67–78. doi:10.1111/j.1502-3931.1983.tb02000.x
  11. ^ Kanie, Y. (1998). New vampyromorph (Coleoidea: Cephalopoda) jaw apparatuses from the Late Cretaceous of Japan. Bulletin of Gumma Museum of Natural History 2: 23–34.
  12. ^ Tanabe, K. & N.H. Landman (2002). Morphological diversity of the jaws of Cretaceous Ammonoidea. Abhandlungen der Geologischen Bundesanstalt, Wien 57: 157–165.
  13. ^ a b Tanabe, K., Y. Hikida & Y. Iba (2006). Two coleoid jaws from the Upper Cretaceous of Hokkaido, Japan. Journal of Paleontology 80(1): 138–145. doi:10.1666/0022-3360(2006)080[0138:TCJFTU2.0.CO;2]
  14. ^ Tanabe, K., P. Trask, R. Ross & Y. Hikida (2008). Late Cretaceous octobrachiate coleoid lower jaws from the north Pacific regions. Journal of Paleontology 82(2): 398–408. doi:10.1666/07-029.1
  15. ^ Klug, C., G. Schweigert, D. Fuchs & G. Dietl (2010). First record of a belemnite preserved with beaks, arms and ink sac from the Nusplingen Lithographic Limestone (Kimmeridgian, SW Germany). Lethaia 43(4): 445–456. doi:10.1111/j.1502-3931.2009.00203.x
  16. ^ Tanabe, K. (2012). Comparative morphology of modern and fossil coleoid jaw apparatuses. Neues Jahrbuch für Geologie und Paläontologie-Abhandlungen 266(1): 9–18. doi:10.1127/0077-7749/2012/0243
  17. ^ Morton, N. (1981). Aptychi: the myth of the ammonite operculum. Lethaia 14(1): 57–61. doi:10.1111/j.1502-3931.1981.tb01074.x
  18. ^ Morton, N. & M. Nixon (1987). Size and function of ammonite aptychi in comparison with buccal masses of modem cephalopods. Lethaia 20(3): 231–238. doi:10.1111/j.1502-3931.1987.tb02043.x
  19. ^ Lehmann, U. & C. Kulicki (1990). Double function of aptychi (Ammonoidea) as jaw elements and opercula. Lethaia 23: 325–331. doi:10.1111/j.1502-3931.1990.tb01365.x
  20. ^ Seilacher, A. (1993). Ammonite aptychi; how to transform a jaw into an operculum? American Journal of Science 293: 20–32. doi:10.2475/ajs.293.A.20
  • Clarke, M.R. & L. Maddock (1988). Beaks of living coleoid Cephalopoda. In: M.R. Clarke & E.R. Trueman (eds.) The Mollusca. Volume 12. Paleontology and Neontology of Cephalopods. Academic Press, San Diego. pp. 121–131.
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