Egg tooth 2574635 219491733 2008-06-15T14:08:43Z Shinnin 2147459 +fi [[Image:Egg tooth 21l07.JPG|right|thumb|A [[Senegal Parrot]] chick at about 2 wks from hatching. The egg tooth is near to the tip of its beak on the upper mandible.]] In some [[egg (biology)|egg]]-laying [[animal]]s, 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 [[bird]]s and [[reptile]]s, and similar structures exist in [[monotreme]]s, [[Eleutherodactylus|Eleutherodactyl]] [[frog]]s, and [[spider]]s. Some [[lizard]]s and [[snake]]s 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'''.<ref>{{cite web|url=http://www.merriam-webster.com/dictionary/Pipping|title=Definition and etymology of "pipping"|publisher=[[Webster's Dictionary]]|accessdate=2008-04-03}}</ref> ==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. [[Kiwi]]s lack an egg tooth, instead using their legs and beak to break through a relatively thin eggshell. The [[superprecocial]] [[megapode]]s possess an egg tooth in their early embryonic development, but instead use their claws during hatching. ==Reptiles== [[Image:Egg_tooth.jpg|200px|thumb|Borneo Short-tailed Python, ''Python breitensteini'' hatching, egg tooth visible]] [[Image:Egg-tooth2.jpg‎|frame|Picture of a [[red-eared slider]] hatchling with an egg tooth.]] 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. ==Development of the egg tooth== A 121 million year old fossilized egg, complete with well-developed embryo, was discovered in northeastern [[China]] in 2004. The bird has no egg tooth, indicating that they are a more recent innovation. Prior to the development of the egg tooth, baby birds likely used sharp claws to break through their shells. <ref>[http://www.abc.net.au/science/news/stories/s1128684.htm News in Science - Pterosaur egg about to hatch - 10/06/2004<!-- Bot generated title -->]</ref> ==References== <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] [[Category:Teeth]] [[de:Eizahn]] [[fr:Diamant (télolécithe)]] [[fi:Munahammas]] [[sv:Äggtand]]