Animal
Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and independently. All animals are also heterotrophs, meaning they must ingest other organisms or their products for sustenance.
Most known animal phyla appeared in the fossil record as marine species during the Cambrian explosion, about 542 million years ago.
Read more about Animal: Etymology, Characteristics, Origin and Fossil Record, Model Organisms, History of Classification, Ethics
Famous quotes containing the word animal:
“Power is, in nature, the essential measure of right. Nature suffers nothing to remain in her kingdoms which cannot help itself. The genesis and maturation of a planet, its poise and orbit, the bended tree recovering itself from the strong wind, the vital resources of every animal and vegetable, are demonstrations of the self-sufficing and therefore self-relying soul.”
—Ralph Waldo Emerson (1803–1882)
“The hounding of a dog pursuing a fox or other animal in the horizon may have first suggested the notes of the hunting-horn to alternate with and relieve the lungs of the dog. This natural bugle long resounded in the woods of the ancient world before the horn was invented.”
—Henry David Thoreau (1817–1862)
“In the animal kingdom, the rule is, eat or be eaten; in the human kingdom, define or be defined.”
—Thomas Szasz (b. 1920)