An egg tooth is a temporary, sharp projection present on the bill or snout of an oviparous animal at hatching. It allows the hatchling to penetrate the eggshell from inside and break free. Birds, reptiles, and monotremes possess egg teeth as hatchlings. [1] Similar structures exist in eleutherodactyl frogs, and spiders. [2]
When it is close to hatching, a chick uses its egg tooth to pierce the air sac between the membrane and the eggshell. This sac provides a few hours' worth of air, during which time the chick hatches. When a chick is ready to hatch from its egg, it begins the process of "pipping"; forcing the egg tooth through the shell repeatedly as the embryo rotates, eventually cutting away a section at the blunt end of the egg, leaving a hole through which the bird may emerge. [3] Some species, including woodpeckers, have two egg teeth; one on both the upper and lower bill. [4] After time the egg tooth falls off or is absorbed into the growing chick's bill. [5]
Some precocial species such as the kiwi, and superprecocial species including megapodes, do not require an egg tooth to assist them in hatching. They are strong enough at the time of hatching to use their legs and feet to crack open the egg. Megapode embryos develop and shed their egg tooth before hatching. [6]
Most squamates (lizards and snakes) also lay eggs, and similarly need an egg tooth. Unlike in other amniotes, the egg tooth of squamates is an actual tooth which develops from the premaxilla. [1]
A baby crocodile has an egg tooth on the end of its snout. It is a tough piece of skin which is resorbed 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 helps free it. [7]
Crocodiles or true crocodiles are large semiaquatic reptiles that live throughout the tropics in Africa, Asia, the Americas and Australia. The term crocodile is sometimes used even more loosely to include all extant members of the order Crocodilia, which includes the alligators and caimans, the gharial and false gharial among other extinct taxa.
The megapodes, also known as incubator birds or mound-builders, are stocky, medium-large, chicken-like birds with small heads and large feet in the family Megapodiidae. Their name literally means "large foot" and is a reference to the heavy legs and feet typical of these terrestrial birds. All are browsers, and all except the malleefowl occupy wooded habitats. Most are brown or black in color. Megapodes are superprecocial, hatching from their eggs in the most mature condition of any bird. They hatch with open eyes, bodily coordination and strength, full wing feathers, and downy body feathers, and are able to run, pursue prey and, in some species, fly on the day they hatch.
In animals, viviparity is development of the embryo inside the body of the mother, with the maternal circulation providing for the metabolic needs of the embryo's development, until the mother gives birth to a fully or partially developed juvenile that is at least metabolically independent. This is opposed to oviparity, where the embryos develop independently outside the mother in eggs until they are developed enough to break out as hatchlings; and ovoviviparity, where the embryos are developed in eggs that remain carried inside the mother's body until the hatchlings emerge from the mother as juveniles, similar to a live birth.
Ovoviviparity, ovovivipary, ovivipary, or aplacental viviparity is a term used as a "bridging" form of reproduction between egg-laying oviparous and live-bearing viviparous reproduction. Ovoviviparous animals possess embryos that develop inside eggs that remain in the mother's body until they are ready to hatch.
Among animals which produce eggs, the yolk is the nutrient-bearing portion of the egg whose primary function is to supply food for the development of the embryo. Some types of egg contain no yolk, for example because they are laid in situations where the food supply is sufficient or because the embryo develops in the parent's body, which supplies the food, usually through a placenta. Reproductive systems in which the mother's body supplies the embryo directly are said to be matrotrophic; those in which the embryo is supplied by yolk are said to be lecithotrophic. In many species, such as all birds, and most reptiles and insects, the yolk takes the form of a special storage organ constructed in the reproductive tract of the mother. In many other animals, especially very small species such as some fish and invertebrates, the yolk material is not in a special organ, but inside the egg cell.
An egg is an organic vessel grown by an animal to carry a possibly fertilized egg cell and to incubate from it an embryo within the egg until the embryo has become an animal fetus that can survive on its own, at which point the animal hatches.
Egg incubation is the process by which an egg, of oviparous (egg-laying) animals, develops an embryo within the egg, after the egg's formation and ovipositional release. Egg incubation is done under favorable environmental conditions, possibly by brooding and hatching the egg.
Stenonychosaurus is a genus of troodontid dinosaur from the Late Cretaceous Dinosaur Park Formation of Alberta, Canada, as well as possibly the Two Medicine Formation. The type and only species, S. inequalis, was named by Charles Mortram Sternberg in 1932, based on a foot, fragments of a hand, and some caudal vertebrae from the Late Cretaceous of Alberta. S. inequalis was reassigned in 1987 by Phil Currie to the genus Troodon, which was reverted by the recognition of Stenonychosaurus as a separate genus from the possibly dubious Troodon in 2017 by Evans et al. and also later in the same year by Van der Reest and Currie.
A hatchery is a facility where eggs are hatched under artificial conditions, especially those of fish, poultry or even turtles. It may be used for ex situ conservation purposes, i.e. to breed rare or endangered species under controlled conditions; alternatively, it may be for economic reasons.
In oviparous biology, a hatchling is a newly hatched fish, amphibian, reptile, or bird. A group of mammals called monotremes lay eggs, and their young are hatchlings as well.
An eggshell is the outer covering of a hard-shelled egg and of some forms of eggs with soft outer coats.
Byronosaurus is a genus of troodontid dinosaur from the Late Cretaceous Period of Mongolia.
The Nicobar megapode or Nicobar scrubfowl is a megapode found in some of the Nicobar Islands (India). Like other megapode relatives, it builds a large mound nest with soil and vegetation, with the eggs hatched by the heat produced by decomposition. Newly hatched chicks climb out of the loose soil of the mound and being fully feathered are capable of flight. The Nicobar Islands are on the edge of the distribution of megapodes, well separated from the nearest ranges of other megapode species. Being restricted to small islands and threatened by hunting, the species is vulnerable to extinction. The 2004 tsunami is believed to have wiped out populations on some islands and reduced populations on several others.
Mecistops is a genus of crocodiles, the slender-snouted crocodiles, native to sub-Saharan Africa.
Bird eggs are laid by the females and range in quantity from one to up to seventeen. Clutch size may vary latitudinally within a species. Some birds lay eggs even when the eggs have not been fertilized; it is not uncommon for pet owners to find their lone bird nesting on a clutch of infertile eggs, which are sometimes called wind-eggs.
Dinosaur eggs are the organic vessels in which a dinosaur embryo develops. When the first scientifically documented remains of non-avian dinosaurs were being described in England during the 1820s, it was presumed that dinosaurs had laid eggs because they were reptiles. In 1859, the first scientifically documented dinosaur egg fossils were discovered in France by Jean-Jacques Poech, although they were mistaken for giant bird eggs.
Ningchengopterus is a genus of pterodactyloid pterosaur from the Early Cretaceous period. Its fossil remains were found in the Yixian Formation of what is now China.
Gobioolithus is an oogenus of fossil bird egg native to Mongolia. They are small, smooth-shelled, and elongated eggs that were first discovered in the 1960s and early 70s during a series of fossil-hunting expeditions in the Gobi desert. Two oospecies have been described: Gobioolithus minor and G. major. The eggs were probably laid in colonial nesting sites on the banks of rivers and lakes.
Egg repair is the process of repairing the eggshell of a live egg, particularly for live birds as eggs may be damaged by parent birds with sharp claws that can punch holes in a fertilized egg. Eggs are repaired by gluing a piece of another egg of the same shape over the top. Cracked eggs can be repaired by applying white glue. Broken or cracked eggs are likely to be infected by bacteria, followed by death of the embryo. Antiseptic can be used to kill surface bacteria prior to repair.
Precocial species in birds and mammals are those in which the young are relatively mature and mobile from the moment of birth or hatching. They are normally nidifugous, meaning that they leave the nest shortly after birth or hatching. Altricial species are those in which the young are underdeveloped at the time of birth, but with the aid of their parents mature after birth. These categories form a continuum, without distinct gaps between them.
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