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."

1 Definitions
2 Type species
3 Type genus
4 See also
- 4.1 External links and references

[edit] Definitions

A type specimen is a vernacular term (not a formally defined term) typically used for an individual or fossil that is any of the various name-bearing types for 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. Historically, there may be more than one type specimen, but this practice has been largely discontinued.
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.
The type series are all those specimens included by the author in a taxon's formal description, unless the author explicitly or implicitly excludes them as part of the series.

Although in reality biologists may examine many specimens (if available) of a new taxon in coming up with a written species description, under the formal rules for naming species (the International Code of Zoological Nomenclature), a single type should be designated. When a single specimen is designated in the original description as the type for a species it is called a holotype. The holotype is typically stored in a museum or other collection to be available for later examination by other biologists as needed. Included in the type description should be a discussion of similarities to and differences from closely related species and where a type specimen or specimens are deposited for examination. The geographical location where a type specimen originated is known as its type locality or type location.

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, the following of which are formally defined:

Paratype – Any additional specimen listed in the type series, where the original description designated a holotype. These are not name-bearing types.
Neotype – A specimen later selected to serve as the single type specimen when an original holotype has been lost or destroyed, or where the original author never cited a specimen.
Syntype – Any of two or more specimens listed in a species description where a holotype was not designated; historically, syntypes were often explicitly designated as such, and under the present Code this is a requirement, but modern attempts to publish species description based on syntypes are generally frowned upon by practicing taxonomists, and most are gradually being replaced by lectotypes. Those which still exist are still considered name-bearing types.
Lectotype – A specimen later selected to serve as the single type specimen for species originally described from a set of syntypes.
Paralectotype – Any additional specimen from among a set of syntypes, after a lectotype has been designated from among them. These are not name-bearing types.
Hapantotype – A special case in Protistans where the type consists of two or more specimens of "directly related individuals representing distinct stages in the life cycle"; these are collectively treated as a single entity, and lectotypes cannot be designated from among them.

The various types listed above are needed because many species descriptions go back one or two centuries and holotype 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, if the type cannot be found, or one has never existed, upon the clarity of the description. The ICZN has not always existed (the first edition of the Code was only in 1961), nor always required a type specimen, and many "type-less" species exist, perhaps the most notable being Homo sapiens. This example is instructive: the current edition of the Code, Article 75.3, prohibits the designation of a neotype unless there is "an exceptional need" for "clarifying the taxonomic status" of a species; as the status and identity of H. sapiens is not questioned, there is no exceptional need for clarification, and "any such neotype designation is invalid" (Article 75.2). Recently some species have been described where the type specimen was released alive back into the wild, such as the Bulo Burti Bush-shrike (Laniarius liberatus), in which the species description included DNA sequences from blood and feather samples. Assuming there is no future question as to the status of such a species, the absence of the type specimen does not invalidate the name, but it may be necessary in the future to designate a neotype for such a taxon, should any questions arise.

There are many other permutations and variations on terms using the suffix "-type" (e.g., allotype, cotype, topotype, generitype, isoneotype, etc.) but these are not formally regulated by the Code, and a great many are obsolete and/or idiosyncratic.

The term fixation is used by the Code for the declaration of a name-bearing type, whether by original or subsequent designation.

[edit] Type species

Each genus must have a designated type species (the term "genotype" was once used for this but has been abandoned because the word has been co-opted for use in genetics, and is much better known in that context). The description of a genus is usually based primarily on its type species, modified and expanded by the features of other included species. The generic name is permanently associated with the name-bearing type of its type species.

Ideally, a type species best exemplifies the essential characteristics of the genus to which it belongs, but this is subjective and, ultimately, technically irrelevant, as it is not a requirement of the Code. If the type species proves, upon closer examination, to belong to a pre-existing genus (a common occurrence), then all of the constituent species must be either moved into the pre-existing genus, or disassociated from the original type species and given a new generic name; the old generic name passes into synonymy, and is abandoned, unless there is a pressing need to make an exception (decided case-by-case, via petition to the International Commission on Zoological Nomenclature).

[edit] Type genus

A type genus is 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. It is not uncommon for the name of a family to be based upon the name of a type genus which has passed into synonymy; the family name does not need to be changed in such a situation.