All extant taxon have a two-part beak, or rostrum, situated in the buccal mass and surrounded by the muscular Cephalopod limb. The dorsal (upper) mandible fits into the ventral (lower) mandible and together they function in a scissor-like fashion.[Young, R.E., M. Vecchione & K.M. Mangold (1999). Cephalopoda Glossary. Tree of Life Web Project.][Young, R.E., M. Vecchione & K.M. Mangold (2000). Cephalopod Beak Terminology. Tree of Life Web Project.] The beak may also be referred to as the mandibles or jaws.[Tanabe, K., Y. Hikida & Y. Iba (2006). Two coleoid jaws from the Upper Cretaceous of Hokkaido, Japan. Journal of Paleontology 80(1): 138–145. ] These beaks are different from Beak because they crush bone while most bird beaks do not.
Fossilized remains of beaks are known from a number of cephalopod-groups, both extant and extinct, including , octopus, , and .[Zakharov, Y.D. & T.A. Lominadze (1983). New data on the jaw apparatus of fossil cephalopods. Lethaia 16(1): 67–78. ][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.][Tanabe, K. & N.H. Landman (2002). Morphological diversity of the jaws of Cretaceous Ammonoidea. Abhandlungen der Geologischen Bundesanstalt, Wien 57: 157–165.][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. ][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. ][Tanabe, K. (2012). Comparative morphology of modern and fossil coleoid jaw apparatuses. Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen 266(1): 9–18. ] Aptychus - paired plate-like structures found in - may also have been jaw elements.[Morton, N. (1981). Aptychi: the myth of the ammonite operculum. Lethaia 14(1): 57–61. ][Morton, N. & M. Nixon (1987). Size and function of ammonite aptychi in comparison with buccal masses of modem cephalopods. Lethaia 20(3): 231–238. ][Lehmann, U. & C. Kulicki (1990). Double function of aptychi (Ammonoidea) as jaw elements and opercula. Lethaia 23: 325–331. ][Seilacher, A. (1993). Ammonite aptychi; how to transform a jaw into an operculum? American Journal of Science 293: 20–32. ]
Composition
Composed primarily of
chitin and cross-linked
,
[Saunders, W.B., C. Spinosa, C. Teichert & R.C. Banks (1978). Palaeontology 21(1): 129–141.][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. ][Miserez, A., Y. Li, J.H. Waite & F. Zok (2007). Acta Biomaterialia 3(1): 139–149. ][ Organic composite is exceptionally robust: jumbo squid . Ask Nature.] beaks are more or less indigestible and are often the only identifiable cephalopod remains found in the stomachs of predatory species such as
.
[Clarke, M.R. (1986). A Handbook for the Identification of Cephalopod Beaks. Oxford University Press, Oxford.] 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.
[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. ]
Measurements
The abbreviations
LRL and
URL are commonly used in
teuthology to refer to
lower rostral length and
upper rostral length, respectively. These are the standard measures of beak-size in
Decapodiformes;
hood length is preferred for
Octopodiformes.
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.
[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.][Wolff, G.A. (1981). Fishery Bulletin 80(2): 357–370.][Wolff, G.A. (1984). NOAA Technical Report NMFS 17, NOAA/National Marine Fisheries Service.][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. ][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. ][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. ][Gröger, J., U. Piatkowski & H. Heinemann (2000). Polar Biology 23(1): 70–74. ]
Further reading
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Aldridge, A.E. (2009). Can beak shape help to research the life history of squid? New Zealand Journal of Marine and Freshwater Research 43(5): 1061–1067.
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Bolstad, K.S. (2006). Sexual dimorphism in the beaks of Moroteuthis ingens Smith, 1881 (Cephalopoda: Oegopsida: Onychoteuthidae). New Zealand Journal of Zoology 33(4): 317–327.
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Chen, X., H. Lu, B. Liu, Y. Chen, S. Li & M. Jin (2012). Species identification of Ommastrephes bartramii, Dosidicus gigas, Sthenoteuthis oualaniensis and Illex argentinus (Ommastrephidae) using beak morphological variables. Scientia Marina 76(3): 473–481.
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Cherel, Y. & K.A. Hobson (2005). Stable isotopes, beaks and predators: a new tool to study the trophic ecology of cephalopods, including giant and colossal squids. Proceedings of the Royal Society B: Biological Sciences 272(1572): 1601–1607.
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Clarke, M.R. & N. MacLeod (1974). Cephalopod remains from a sperm whale caught off Vigo, Spain. Journal of the Marine Biological Association of the United Kingdom 54(4): 959–968.
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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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Clarke, M.R. & R.E. Young (1998). Description and analysis of cephalopod beaks from stomachs of six species of odontocete cetaceans stranded on Hawaiian shores. Journal of the Marine Biological Association of the United Kingdom 78(2): 623–641.
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Hernańdez-García, V., U. Piatkowski & M.R. Clarke (1998). Development of the darkening of Todarodes sagittatus beaks and its relation to growth and reproduction. South African Journal of Marine Science 20(1): 363–373.
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Hernández-López, J.L. & J.J. Castro-Hernández (2001). Fishery Bulletin 99(4): 679–684.
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Hobson, K.A. & Y. Cherel (2006). Isotopic reconstruction of marine food webs using cephalopod beaks: new insight from captively raised Sepia officinalis. Canadian Journal of Zoology 84(5): 766–770.
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Hsu, C.-C. (2002). Geomorphometric study of Octopus and Cistopus (Cephalopoda: Octopodidae) based on landmarks of beaks. Master's thesis, National Sun Yat-sen University, Kaohsiung, Taiwan.
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Ivanovic, M.L. & N.E. Brunetti (1997). Description of Illex argentinus beaks and rostral length relationships with size and weight of squids. Revista de Investigación y Desarrollo Pesquero 11: 135–144.
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Lalas, C. (2009). Estimates of size for the large octopus Macroctopus maorum from measures of beaks in prey remains. New Zealand Journal of Marine and Freshwater Research 43(2): 635–642.
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Lefkaditou E. & P. Bekas (2004). Analysis of beak morphometry of the horned octopus Eledone cirrhosa (Cephalopoda: Octopoda) in the Thracian Sea (NE Mediterranean). Mediterranean Marine Science 5(1): 143–149.
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Lu, C.C. & R. Ickeringill (2002). Museum Victoria Science Reports 6: 1–65.
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Martínez, P., A. Sanjuan & Á. Guerra (2002). Identification of Illex coindetii, I. illecebrosus and I. argentinus (Cephalopoda: Ommastrephidae) throughout the Atlantic Ocean; by body and beak characters. Marine Biology 141(1): 131–143.
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Ogden, R.S., A.L. Allcock, P.C. Watts & J.P. Thorpe (1998). The role of beak shape in octopodid taxonomy. South African Journal of Marine Science 20(1): 29–36.
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Roeleveld, M.A.C. (2000). Giant squid beaks: implications for systematics. Journal of the Marine Biological Association of the UK 80(1): 185–187.
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Uchikawa, K., M. Sakai, T. Wakabayashi & T. Ichii (2009). The relationship between paralarval feeding and morphological changes in the proboscis and beaks of the neon flying squid Ommastrephes bartramii. Fisheries Science 75(2): 317–323.
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Xavier, J.C., M.R. Clarke, M.C. Magalhães, G. Stowasser, C. Blanco & Y. Cherel (2007). Arquipélago: Life and Marine Sciences 24: 41–48.
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Xavier, J.C. & Y. Cherel (2009). British Antarctic Survey, Cambridge. 129 pp.
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Xavier, J.C., R.A. Phillips & Y. Cherel (2011). Cephalopods in marine predator diet assessments: why identifying upper and lower beaks is important. ICES Journal of Marine Science 68(9): 1857–1864.
