extinction, in biology, disappearance of species of living organisms. Extinction occurs as a result of changed conditions to which the species is not suited. If no member of the affected species survives and reproduces, the entire line dies out, leaving no descendants. This was the case with the saber-toothed tiger (Smilodon) of North America, which is not ancestral to any living species. However, a species may also become extinct through its gradual evolution evolution, concept that embodies the belief that existing animals and plants developed by a process of gradual, continuous change from previously existing forms. This theory, also known as descent with modification, constitutes organic evolution.
..... Click the link for more information. into a new species, as a result of natural selection for characteristics suited for new conditions. An example of the latter situation is the evolution of horses horse, hoofed, herbivorous mammal now represented by a single extant genus, Equus. The term horse commonly refers only to the domestic Equus caballus and to the wild Przewalski's horse .
..... Click the link for more information. from the eophippus (Hyracotherium) to Miohippus to Merychippus to the present-day Equus. There has been an unbroken line of descent, yet horses of the earlier types no longer exist. Human activities, such as overhunting a species or destroying its habitat, have caused the extinction of some species, such as the passenger pigeon pigeon, common name for members of the large family Columbidae, land birds, cosmopolitan in temperate and tropical regions, characterized by stout bodies, short necks, small heads, and thick, heavy plumage.
..... Click the link for more information. and dodo dodo, a flightless forest-dwelling bird of Mauritius, extinct since the late 17th cent. The dodo was closely related to the two species of solitaire bird, extinct flightless giants found on the other islands in the Mascarene Islands.
..... Click the link for more information. , and threatened many others (see endangered species endangered species, any plant or animal species whose ability to survive and reproduce has been jeopardized by human activities. In 1999 the U.S. government, in accordance with the U.S.
..... Click the link for more information. ). See also mass extinction mass extinction, the extinction of a large percentage of the earth's species, opening ecological niches for other species to fill. There have been at least ten such events.
..... Click the link for more information. .

extinction (of species)

Dying out or termination of a species. It occurs when a species can no longer reproduce at replacement levels. Most past extinctions are thought to have resulted from environmental changes that the doomed species was either unable to adapt to or that caused it to adapt so thoroughly that it became a distinctly new species. The effect of humans on the environment, through hunting, collecting, and habitat destruction, has become the principal factor in plant and animal extinctions.

Extinction

bald eagle

once on verge of extinction, this bird is now protected; still an endangered species. [Ecology: Hammond, 290]

dinosaur

dinosaurs died out, unable to adapt to environmental change. [Ecology: Hammond, 290]

dodo

large, flightless bird exterminated on Mauritius. [Ecology: Wallechinsky, 131]

great auk

hunters killed such large numbers, these birds became extinct in 1840s. [Ecology: Hammond, 290]

heath hen

human settlement of U.S. Atlantic Coast contributed to the extinction of these birds. [Ecology: Hammond, 290]

Last of the Mohicans, The

novel foreseeing the extinction of various Indian tribes. [Am. Lit.: The Last of the Mohicans]

mastodon

similar to the elephant, the mastodon is now extinct. [Ecology: Hammond, 290]

moa

large ostrichlike bird, hunted chiefly for its food; it died out in 1914. [Ecology: Hammond, 290]

passenger pigeon

hunted to extinction by 1914; vast numbers once darkened American skies during migratory flights. [Ecology: EB, VII: 786]

saber-toothed tiger

wild cat that died out about 12,000 years ago. [Ecology: Hammond, 290]

Last of the Barons, The

portrays England’s brilliant aristocracy as dying breed (1470s). [Br. Lit.: The Last of the Barons, Magill I, 492–494]

whale

many species in danger of extinction, owing to massive hunting. [Ecology: Hammond, 290]

Extinction (redirected from Extict)

extinction (of species)

Extinction
(redirected from Extict)