beak
In zoology, the beak ( lat. Rostrum ), the jaw covered with horn sheaths, is the pointed mouth part of birds , turtles , platypus , beaked whales and cephalopods . In the vertebrates among the beak-bearing species, the beak serves as a replacement for teeth that no longer exist in evolutionary terms .
Birds
In birds, the beak is rarely used for chewing, except for parrots , for example , but mainly as a gripping tool for picking up, tearing off or cutting off food, especially in birds of prey. It also fulfills various technical functions, for example as a “chisel” when building a nest, as a “strainer” when digging, it is used to peel seeds when eating, or as a climbing aid. The shape of the beak, which is very different in the bird world, is closely related to function, especially to the type of food and the method of obtaining food. For example, there are crooked and pointed beaks, crossbills, and scabbles.
In birds, the beak is divided into the upper and lower beak. The bony basis is the upper and lower jaw , which are covered with horny substance . At the upper beak, the horn sheath ( Rhamphotheca ) forms a convex back or ridge ( Culmen ), the edge of the beak is called the tomium , and the curved front part is called the beak dome ( dertrum ). The nostril is mostly at the base of the upper beak, only at the tip of the beak in the kiwi . At the lower beak , the tip is known as the dill ( Myxa ) and the edge of the beak as the dill edge ( Gonys ). At the base of the beak, the skin of many birds is modified to become wax skin .
The horny substance has a different surface profile. In some species, for example in the genus of the sawmill , it forms a tooth-like bar, in others, such as the swimming ducks, lamellae, which are used to filter food.
If the beaks are misaligned or if they are not worn out as a result of inappropriate housing and feeding, the horny substance is no longer sufficiently rubbed off and lengthening and / or curvature occurs which, in extreme form, completely prevents food intake. For pet birds, shortening or even surgical beak correction is necessary. In factory farming of hybrid chickens and turkeys , the beaks are shortened to prevent cannibalism.
Turtles
In the order of the turtles (Testudinata), the teeth are completely regressed in all recent forms , they are toothless ( edentat ). They use a horny beak to bite , anatomically referred to as rhamphotheca (more rarely, like other beaks, also called rostrum). The beak is the jawbone (maxilla, premaxilla and maxilla and mandible, mandible on). It has a cutting edge ( tomium ) which, depending on the diet and type, can be smooth or tooth-like jagged. The shape of the beak is determined by the shape of the underlying jawbone; the horny beak rarely has small ribs or tubercles that are not pre-formed in the jawbone. The jaw with the beak can, depending on the diet, widen like a plate or be sculpted by ribs or ridges. When the mouth is closed, the slightly wider upper beak usually grips the lower beak, so that the jaws functionally usually do not work directly against each other, but cut off food material like scissors. The tip of the upper bill often forms a stepped, hook-like extension, such a hooked bill is particularly prominent, for example, in the alligator turtles , in the snapping turtle the lower bill is also serrated like a hook. The upper beak can also have a serrated, serrated appearance through several juxtaposed tips ( tomiodont ), whereby there are shapes with two or three such teeth. This perforation is visible when the mouth is closed through the overlapping upper beak. Often these are larger in males than in females ( sexual dimorphism ).
Cephalopods
In cephalopods, especially cuttlefish , the beak (also called horned jaw, anatomically also called rostrum) sits at the mouth opening, which is located in the middle between the tentacles. It is used by the predatory animals to shred their prey. In many species, the poison formed in the posterior salivary glands, which act as poison glands, is also applied through the bite, thereby paralyzing the prey. The beak sits inside an almost spherical, muscular pharynx. In the living animal, it is also covered by flexible lips and is usually not freely visible. The beak is made up of two jaws that work against each other, also called mandibles, the rear edges of which are usually widened like wings to enlarge the attachment surface of the muscles. At the front it ends in points, the shape of which is often compared to a parrot's beak. The upper jaw is usually more pointed than the lower jaw. A tongue-like ridge, the odontophore, sits in the head of the pharynx between the two jaws of the beak. This carries the radula sitting in a pouch , which in cephalopods only has a gripping function and is used together with the beak to treat the prey. The cuttlefish beak is a non-bio-mineralized structure made up entirely of chitin and proteins, yet it is hard enough to allow some species to crack clamshells. On the other hand, in the pearl boats and the (extinct) other nautiloids , the beak is mineralized by calcium deposits. The beak is secreted by special glandular cells called Beccublasts.
Since the beaks of the squid are almost the only hard parts of the soft-skinned and rapidly decomposing individual, they are used to determine the species, particularly from the stomach contents of squid-eating ( teutophage ) predators. For some species, the size of the squid captured can be deduced from the size of the beak.
fishes
In swordfish , sailfish and some other species, the shape of the head to a sword-like point (the rostrum) is also called the beak.
Individual evidence
- ^ Richard Nickel, August Schummer, Eugen Seiferle: Textbook of the anatomy of domestic animals. Volume 5. Anatomy of Birds. Verlag Parey im MVS, 3rd edition 2004, ISBN 978-3-8304-4153-3 , p. 176.
- ↑ Mark Beaman and Steven Madge: Handbook of Bird Identification, Europe and Western Palearctic. Verlag Eugen Ulmer, 2nd, corrected edition 2007, ISBN 978-3-8001-5494-4 , p. 17 ff.
- ^ Albert Schweitzer Foundation: Critical report on the subject of shortening the beak
- ↑ Patrick D. Moldowan, Ronald J. Brooks, Jacqueline D. Litzgus: Turtles with `` teeth '': beak morphology of Testudines with a focus on the tomiodonts of Painted Turtles (Chrysemys spp.). In: Zoomorphology , Volume 135, 2015, Issue 1, pp. 121-135. doi: 10.1007 / s00435-015-0288-1
- ^ A b Eve Boucaut-Camou & Renata Boucher-Rodoni: Feeding and digestion in Cephalopods. Chapter 3 in ASM Saleuddin, Karl M. Wilbur (editors): The Mollusca. Volume 5: Physiology, Part 2. Academic Press, New York, etc. 1983. ISBN 978-0-12-751405-5 .
- ↑ Volker Storch, Ulrich Welsch: Mollusca, molluscs. Cephalopoda, cephalopod. In: Kükenthal's zoological internship. 27th edition, Springer Spectrum Berlin / Heidelberg 2014. ISBN 978-3-642-41936-2
- ^ Ali Miserez, Youli Li, J. Herbert Waite, Frank Zok (2007): Jumbo squid beaks: Inspiration for design of robust organic composites. Acta Biomaterialia 3: 139-149. doi: 10.1016 / j.actbio.2006.09.004
- ^ W. Bruce Saunders, Claude Spinosa, Curt Teichert, RC Banks (1978): The jaw apparatus of Recent Nautilus and its palaeontological implications. Palaeontology 21 (1): 129-141.
- ↑ cf. for example Jose Xavier and Yves Cherel: Cephalopod beak guide for the Southern Ocean. British Antarctic Survey, Cambridge, UK, 2009, 129 pages
