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The Collaborative International Dictionary

Taxon \Tax"on\ (t[a^]ks"[o^]n), n.; pl. taxa or taxons. a taxonomic group, or the name of a taxonomic grouping.

Douglas Harper's Etymology Dictionary

1929, from German (1926), shortened from taxonomie (see taxonomy).


n. (context taxonomy English) Any of the taxonomic categories, such as phylum or subspecies.

  1. n. animal or plant group having natural relations [syn: taxonomic group, taxonomic category]

  2. [also: taxa (pl)]


In biology, a taxon (plural taxa; back-formation from taxonomy) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular name and given a particular ranking, especially if and when it is accepted or becomes established. It is not uncommon, however, for taxonomists to remain at odds over what belongs to a taxon and the criteria used for inclusion. If a taxon is given a formal scientific name, its use is then governed by one of the nomenclature codes specifying which scientific name is correct for a particular grouping.

Although preceded by Linnaeus's system in Systema Naturae (10th edition, 1758) and unpublished work by Bernard and Antoine Laurent de Jussieu, the notion of a unit-based "natural system" of biological classification was first made widely available in 1805 through the publication, as the introduction to the third edition of Jean-Baptiste Lamarck's Flore françoise, of Augustin Pyramus de Candolle's Principes élémentaires de botanique, an exposition of a system for the "natural classification" of plants. Since then, systematists have striven to construct an accurate classification encompassing the diversity of life; today, a "good" or "useful" taxon is commonly taken to be one that reflects evolutionary relationships.

Many modern systematists, such as advocates of phylogenetic nomenclature, use cladistic methods that require taxa to be monophyletic (all descendants of some ancestor). Their basic unit, therefore, is the clade rather than the taxon. Similarly, among those contemporary taxonomists working with the traditional Linnean (binomial) nomenclature, few propose taxa they know to be paraphyletic. An example of a well-established taxon that is not also a clade is the classReptilia, the reptiles.

Usage examples of "taxon".

Since for primitive mammals sleepless nights would have been more dangerous for the survival of the taxon than sexless nights, sleep should be a more powerful drive than sex-which, at least in most of us, it seems to be.

Named after Phil Hoffmann because it was one of his students who identified it as a basal spinosaur, maybe even the node taxon for the clade.

Lazarus taxon was one that disappeared from the fossil record, as if extinct, only to reappear later, as if rising from the dead.

Many more taxa exist, of course, than are shown by the few points in the figure.

But the curve is representative of the much denser array of points that would be necessary to characterize the tens of millions of separate taxa which have emerged during the history of life on our planet.

The major taxa, which have evolved most recently, are by and large the most complicated.

The genetic instructions of all the other taxa on Earth are written in the same language, with the same code book.

Since animal taxa such as mammals, reptiles or amphibians contain members with very different brain sizes, we cannot give a reliable estimate of the number of neurons in the brain of a typical representative of each taxon.

The cognitive abilities of chimpanzees force us, I think, to raise searching questions about the boundaries of the community of beings to which special ethical considerations are due, and can, I hope, help to extend our ethical perspectives downward through the taxa on Earth and upwards to extraterrestrial organisms, if they exist.

Although the relationship between these two taxa is not completely explained at the moment, such a division is presently accepted.

Due to the incompleteness of remains, exact relations among particular taxa included here are still difficult to determine.