Egg tooth

Egg tooth

In some egg-laying animals, the egg tooth is a small, sharp, cranial protuberance used by offspring to break or tear through the egg's surface during hatching. It is present in most birds and reptiles, and similar structures exist in monotremes, Eleutherodactyl frogs, and spiders.

Some lizards and snakes develop a true tooth that is shed after use; other reptiles and birds generally develop an analogous epidermal horn that is reabsorbed or falls off.

In birds, the process of breaking open the eggshell is commonly referred to as pipping. [cite web|url=http://www.merriam-webster.com/dictionary/Pipping|title=Definition and etymology of "pipping"|publisher=Webster's Dictionary|accessdate=2008-04-03]

Birds

Baby birds have a pipping muscle on the back of their necks. It is this muscle which gives them the strength to force the egg tooth through the inner membrane of the eggshell.

When a baby bird becomes too large to absorb oxygen through the pores of its eggshell, it uses its egg tooth to peck a hole in the air sac located at the flat end of the egg. This sac provides a few hours worth of air, during which the baby bird breaks through the eggshell to the outside. The egg tooth falls off several weeks after hatching.

Kiwis lack an egg tooth, instead using their legs and beak to break through a relatively thin eggshell. The superprecocial megapodes possess an egg tooth in their early embryonic development, but instead use their claws during hatching.

Reptiles

Baby snakes generally hatch from eggs with tough, leathery shells. A baby snake's egg tooth tears a hole directly through the shell, and falls off the first time the snake sheds its skin. Lizards have similarly leathery eggshells.

A baby crocodile has an egg tooth on the end of its snout. It is a tough piece of skin which is totally reabsorbed less than two months after hatching. Crocodile eggs are similar to those of birds in that they have an inner membrane and an outer one. The egg tooth is used to tear open the inner membrane; the baby crocodile can then push its way through the outer shell. If conditions are particularly dry that year, the inner membrane may be too tough for the crocodile to break through, and without assistance it will simply die inside the egg. Generally, however, the mother crocodile is there to help free it.

References

* [http://www.flmnh.ufl.edu/natsci/herpetology/brittoncrocs/cbd-mor1.htm Crocodile Biology Database]
* [http://news.nationalgeographic.com/news/2004/10/1021_041021_bird_embryo_2.html National Geographic]


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Look at other dictionaries:

  • egg tooth — n. a tooth like structure on the nose or beak of young reptiles and birds used to break the egg membrane or shell at the time of hatching …   English World dictionary

  • egg tooth — egg′ tooth n. zool. a calcareous prominence at the tip of the beak or upper jaw of an embryonic bird or reptile, used to break through the eggshell at hatching • Etymology: 1890–95 …   From formal English to slang

  • egg tooth — a calcareous prominence at the tip of the beak or upper jaw of an embryonic bird or reptile, used to break through the eggshell at hatching. [1890 95] * * * ▪ anatomy       tooth or toothlike structure used by the young of many egg laying species …   Universalium

  • egg tooth — noun : a hard sharp prominence on the tip of the beak or nose of embryo birds and oviparous reptiles with which they break through the eggshell; also : an analogous chitinous prominence on the head of an insect * * * a calcareous prominence at… …   Useful english dictionary

  • egg-tooth — see egg burster …   Dictionary of invertebrate zoology

  • egg tooth — noun Date: 1893 a hard sharp prominence on the beak of an unhatched bird or the nose of an unhatched reptile that is used to break through the eggshell …   New Collegiate Dictionary

  • egg tooth — noun A small, sharp, cranial protuberance used by offspring to break or tear through the eggs surface during hatching …   Wiktionary

  • egg tooth — noun a hard white protuberance on the beak or jaw of an embryo bird or reptile, used for breaking out of the shell …   English new terms dictionary

  • egg tooth — /ˈɛg tuθ/ (say eg toohth) noun a calcareous point on the tip of the beak or upper jaw, by which an unhatched bird or reptile breaks through the eggshell on hatching …  

  • Egg (biology) — Bird eggs and others (click on image for key) …   Wikipedia

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