Cephalopod beak

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] Composed primarily of chitin and cross-linked proteins,[3][4][5][6] beaks are more-or-less indigestible and 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 the mantle length and total body weight of the original animal as well as the total ingested biomass of the species.[8][9][10][11][12][13][14] Cephalopod beaks gradually become less stiff as one moves from the tip to the base, a gradient that results from differing chemical composition. In hydrated beaks of the Humboldt squid (Dosidicus gigas) this stiffness gradient spans two orders of magnitude.[15]

Fossilised remains of beaks are known from a number of cephalopod groups, both extant and extinct, including squids, octopuses, belemnites, and vampyromorphs.[16][17][18][19][20][21][22] Aptychi – paired plate-like structures found in ammonites – may also have been jaw elements.[23][24][25][26]

The beak may also be referred to as the mandibles or jaws.[19]

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] 


Giant squid beak and associated muscles with hand for scale

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 
Upper rostral length 


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  1. 1 2 3 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). "The jaw apparatus of Recent Nautilus and its palaeontological implications." (PDF). 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). "Jumbo squid beaks: Inspiration for design of robust organic composites." (PDF). 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. 1 2 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). "A beak key for eight eastern tropical Pacific cephalopod species with relationships between their beak dimensions and size." (PDF). Fishery Bulletin 80(2): 357–370.
  10. Wolff, G.A. (1984). "Identification and estimation of size from the beaks of 18 species of cephalopods from the Pacific Ocean." (PDF). NOAA Technical Report NMFS 17, NOAA/National Marine Fisheries Service.
  11. Jackson, G.D. (1995). The use of beaks as tools for biomass estimation in the deepwater squid Moroteuthis ingens (Cephalopoda: Onychoteuthidae) in New Zealand waters. Polar Biology 15(1): 9–14. doi:10.1007/BF00236118
  12. Jackson, G.D. & J.F. McKinnon (1996). Beak length analysis of arrow squid Nototodarus sloanii (Cephalopoda: Ommastrephidae) in southern New Zealand waters. Polar Biology 16(3): 227–230. doi:10.1007/BF02329211
  13. Jackson, G.D., N.G. Buxton & M.J.A. George (1997). Beak length analysis of Moroteuthis ingens (Cephalopoda: Onychoteuthidae) from the Falkland Islands region of the Patagonian Shelf. Journal of the Marine Biological Association of the United Kingdom 77(4): 1235–1238. doi:10.1017/S0025315400038765
  14. Gröger, J., U. Piatkowski & H. Heinemann (2000). "Beak length analysis of the Southern Ocean squid Psychroteuthis glacialis (Cephalopoda: Psychroteuthidae) and its use for size and biomass estimation." (PDF). Polar Biology 23(1): 70–74. doi:10.1007/s003000050009
  15. Miserez, A., T. Schneberk, C. Sun, F.W. Zok & J.H. Waite (2008). The transition from stiff to compliant materials in squid beaks. Science 319(5871): 1816–1819. doi:10.1126/science.1154117
  16. 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
  17. 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.
  18. Tanabe, K. & N.H. Landman (2002). Morphological diversity of the jaws of Cretaceous Ammonoidea. Abhandlungen der Geologischen Bundesanstalt, Wien 57: 157–165.
  19. 1 2 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:TCJFTU]2.0.CO;2
  20. 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
  21. 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
  22. 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
  23. Morton, N. (1981). Aptychi: the myth of the ammonite operculum. Lethaia 14(1): 57–61. doi:10.1111/j.1502-3931.1981.tb01074.x
  24. 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
  25. 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
  26. 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

Further reading

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