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The system of naming animals that was adopted by zoologists and detailed in the International Code of Zoological Nomenclature, which applies to both living and extinct animals. The present system is founded on the 10th edition of C. Linnaeus's Systema Naturae (1758) and has evolved through international agreements culminating in the Code adopted in 1985. The primary objective of the Code is to promote the stability of the names of taxa (groups of organisms) by providing rules concerning name usage and the activity of naming new taxa. The rules are binding for taxa ranked at certain levels and nonbinding on taxa ranked at other levels. See Animal systematics
Zoological nomenclature is built around four basic features. (1) The correct names of certain taxa are either unique or unique combinations. (2) These names are formed and treated as Latin names and are universally applicable, regardless of the native language of the zoologist. (3) The Code for animals is separate and independent from similar codes for plants and bacteria. (4) No provisions of the Code are meant to restrict the intellectual freedom of individual scientists to pursue their own research.
There are four common reasons why nomenclature may change. (1) New species are found that were once considered parts of other species. (2) Taxonomic revisions may uncover older names or mistakes in identification of types. (3) Taxa may be combined, creating homonyms that require replacement. (4) Concepts of the relationships of animals change. Stability is subservient to progress in understanding animal diversity.
The articles in the Code are directed toward the names of taxa at three levels. The family group includes taxa ranked as at the family and tribe levels (including super- and subfamilies). The genus group includes taxa below subtribe and above species. The species group includes taxa ranked as species or subspecies. Taxa above the family group level are not specifically treated, and their formation and use are not strictly regulated. For each group, provisions are made that are either binding or recommended.
The basis for naming animals is binominal nomenclature, that is, a system of two-part names. The first name of each species is formed from the generic name, and the second is a trivial name, or species epithet. The two names agree in gender unless the specific epithet is a patronym (named for a person). The combination must be unique; no other animal can have the same binominal. The formal name of a species also includes the author, so the formal name for humans is Homo sapiens Linnaeus. The genus, as a higher taxon, may have one or many species, each with a different epithet. Homo includes H. sapiens, H. erectus, H. habilis, and so forth. One feature of the Linnaean binominal system is that species epithets can be used over and over again, so long as they are used in different genera. Tyrannosaurus rex is a large dinosaur, and Percina rex is a small fresh-water fish. The epithet rex is not the species name of Percina rex because all species names are binominal in form. It is recommended that names of genera and species be set in a different typeface from normal text; italics is conventional. Different names for the same species are termed synonyms, and the senior synonym is usually correct (principle of priority). Modern species descriptions are accompanied by a description that attempts to show how the species is different from others, and the designation of one or more type specimens.
All higher taxonomic names have one part (uninominal) and are plural. Names of taxa of the family and genus groups must be unique. The names of genera are in Latin or latinized, are displayed in italics, and may be used alone. The names of the family group are formed by a root and an ending specific to a particular hierarchical level: family Hominidae (root + idae), subfamily Homininae (root + inae). The endings of superfamilies (root + oidea) and tribes (root + ini) are recommended but not mandated. The endings of taxa higher than the family group vary. For example, orders of fishes are formed by adding -iformes to the root (Salmoniformes), while in insects the ending is usually -ptera (Coleoptera). See Classification, biological, Taxonomic categories