Type (zoology)
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In zoological nomenclature, a type is a specimen or a taxon. A "name-bearing type" "provides the objective standard of reference whereby the application of the name of a nominal taxon can be determined."
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Definitions
- A type specimen is a phrase that was used in previous editions of the Code for an individual or fossil that identifies a species. For example, the type specimen for the species Homo neanderthalensis was the specimen "Neanderthal-1" discovered by Johann Karl Fuhlrott in 1856 at Feldhofer in the Neander Valley in Germany, consisting of a skullcap, thigh bones, part of a pelvis, some ribs, and some arm and shoulder bones.
- A type species is the nominal species that is the name-bearing type of a nominal genus or subgenus.
- A type genus is the nominal genus that is the name-bearing type of a nominal family-group taxon.
Although in reality biologists may examine many specimens (if available) of the new species in coming up with a written species description, under the formal rules for naming species, a type should be designated. The single specimen designated as the type for a species is called a holotype. The holotype is stored (a process called curation) in a collection (a place where biological specimens are kept and maintained) to be available for later examination by other biologists as needed. Included in the type description would be a discussion of similarities to and differences from closely related species and where a type specimen or specimens were sent for curation. The location where a type specimen originated is known as its type location or type locality.
Zoological collections are maintained by universities and museums. Ensuring that types are kept in good condition and made available for examination by taxonomists are two important functions of such collections. And, while there is only one holotype designated, there can be other type specimens:
- Syntype – Any of two or more specimens listed in the species type description when a holotype was not designated.
- Lectotype – A specimen later selected.
- Neotype – A specimen later selected to serve as if it were a holotype when all specimens available and listed by the original species author have been lost or destroyed, or where the original author never cited a specimen. Isoneotypes are duplicate specimens of the neotype.
The various types described above are needed because many species descriptions go back one or two centuries and type designation was not always done, types were not always well kept or preserved, or intervening events have resulted in destruction of original type material. The validity of a species name can rest upon the availability of original type specimens; or as important, upon the clarity of the description attached to the type material.
Unlike the ICBN, the ICZN does not require a type specimen and one of the first species to be described without a type specimen was a rare Somalian bird, the Bulo Burti Bush-shrike (Laniarius liberatus). The species description was based on DNA from blood and feather samples.
Type species
By selecting a species within that genus a type species can be designated for the genus (The word genotype used to be used for this but it is now disrecommended because of the meaning use in genetics.) and the type specimen for that species becomes the generitype. The description of a genus is based primarily on its type species, modified and expanded by the features of other included species. The generic name is permanently associated with its type species.
Ideally, a type species best exemplifies the essential characteristics of the genus to which it belongs. However, this common definition is somewhat circular since once a species type specimen is designated as a generitype that species largely defines the "essential characteristics" of the genus. Whether or not the species is the "best" example considering all characteristics of all species assigned to a particular genus is not so important. Species that are "poor" examples relative to the type species with respect to enough characteristics (or a few "important" characteristics) are candidates for removal from the genus. If this process seems somewhat subjective: it is. Extensive rules keep zoological taxonomists reading from the same page.
The term fixation is used by the International Code of Zoological Nomenclature for the determination of a name-bearing type whether by original or subsequent designation.
Type genus
A type genus becomes that genus from which the name of a family or subfamily is formed. As with type species, the type genus is not necessarily the most representative, but is usually the earliest described, largest or best known genus.
See also
External links and references
- ICZN: International Code of Zoological Nomenclature, the official website
- Fishbase Glossary section.
