Biological type
Encyclopedia
In biology, a type is one particular specimen (or in some cases a group of specimens) of an organism
to which the scientific name of that organism is formally attached. In other words, a type is an example that serves to anchor or centralize the defining features of that particular taxon
.
A taxon is a scientifically named grouping of organisms with other like organisms, a set that includes some organisms and excludes others, based on a detailed published description (for example a species description
) and on the provision of type material, which is usually available to scientists for examination in a major museum research collection, or similar institution.
and the ICBN, the scientific name of every taxon is almost always based on one particular specimen, or in some cases specimens. Types are of great significance to biologists, especially to taxonomists. Types are usually physical specimens that are kept in a specially designated type collection in a museum
research collection, or are a particular plant sample in a herbarium
. Usually types are a physical example of the taxon, but failing that, an image of an individual of that taxon can be used. This material is the "type" or "types" of that taxon. Describing species and appointing type specimens is part of scientific nomenclature and alpha taxonomy
.
When identifying material, a scientist attempts to apply a taxon name to a specimen or group of specimens based on his or her understanding of the relevant taxa, based on (at least) having read the type description(s), preferably based on an examination of all the type material of all of the relevant taxa. If there is more than one named type that all appear to be the same taxon, then the oldest name takes precedence, and is considered to be the correct name of the material in hand. If on the other hand the taxon appears never to have been named at all, then the scientist or another qualified expert picks a type specimen and publishes a new name and an official description.
This process is crucial to the science of biological taxonomy
. People's ideas of how living things should be grouped changes and shifts over time. How do we know that that that we call "Canis lupus" is the same thing, or approximately the same thing, as what they will be calling "Canis lupus" in 200 years time? It is possible to check this because there is a particular wolf specimen preserved in a museum somewhere, and everyone who uses that name – no matter what else they may mean by it – will mean that particular specimen.
Depending on the nomenclature code
applied to the organism in question, a type can be a specimen, a culture, an illustration, a description, or a taxon.
For example, in the research collection of the Natural History Museum
in London, there is a bird specimen numbered 1886.6.24.20. This is a specimen of a kind of bird commonly known as the Spotted Harrier
, which currently bears the scientific name Circus assimilis. This particular specimen is the holotype
for that species; the name Circus assimilis refers, by definition, to the species of that particular specimen. That species was named and described by Jardine and Selby in 1828, and the holotype was placed in the museum collection so that other scientists might refer to it as necessary.
Note that at least for type specimens there is no requirement for a "typical" individual to be used. Genera
and families
, particularly those established by early taxonomists, tend to be named after species that are more "typical" for them, but here too this is not always the case and due to changes in systematics
cannot be. Hence, the term name-bearing type
or onomatophore is sometimes used, to denote the fact that biological types do not define "typical" individuals or taxa, but rather fix a scientific name to a specific operational taxonomic unit. Type specimens are theoretically even allowed to be aberrant or deformed individuals or color variations, though this is rarely chosen to be the case, as it makes it hard to determine to which population the individual belonged.
The usage of the term type is somewhat complicated by slightly different uses in botany
and zoology
. In the PhyloCode
, type-based definitions are replaced by phylogenetic definitions
.
, a type (typus, nomenclatural type), "is that element to which the name of a taxon is permanently attached." In botany a type is either a specimen or an illustration. A specimen is a real plant (or one or more parts of a plant or a lot of small plants), dead and kept safe, "curated", in a herbarium (or the equivalent for fungi). Examples of where an illustration may serve as a type are (this is not an exclusive listing):
Note that a type fixes only a name to a single representative of the taxon. A type does not determine the circumscription (therefore a taxon is independent of its type species or specimen) of the taxon. For example, the common dandelion is a controversial taxon: some botanists consider it to consist of over a hundred species, although most botanists regard it to be a single species. The type of the name Taraxacum officinale is the same whether the circumscription of the species includes all those small species (Taraxacum officinale is a 'big' species) or whether the circumscription is limited to only one small species among the other hundred (Taraxacum officinale is a 'small' species). In this case the name Taraxacum officinale is the same and the type of the name is the same, but the extent of what the name actually applies to varies strongly. Setting the circumscription of a taxon is done by a taxonomist in a publication.
Miscellaneous notes:
In zoological nomenclature
, the type of a species (or subspecies) is a specimen (or series of specimens), the type of a genus (or subgenus) is a species, and the type of a suprageneric taxon (e.g., family, etc.) is a genus. Names higher than superfamily rank do not have types. A "name-bearing type
" "provides the objective standard of reference whereby the application of the name of a nominal taxon can be determined."
), a single type must be designated, as part of the published description.
When a single specimen is clearly designated in the original description, this specimen is known as the holotype
of that species. The holotype is typically placed in a major museum, or similar well-known public collection, so that it is freely available for later examination by other biologists. Type illustrations have also been used by zoologists, as in the case of the Réunion Parakeet, which is known only from historical illustrations and descriptions.
A type description must include a diagnosis (typically, a discussion of similarities to and differences from closely related species), and an indication of where the type specimen or specimens are deposited for examination. The geographical location where a type specimen was originally found is known as its . In the case of parasites, the term type host (or symbiotype) is used to indicate the host organism from which the type specimen was obtained.
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:
The various types listed above are necessary because many species were described one or two centuries ago, when a single type specimen, a holotype, was often not designated. Also, types were not always carefully preserved, and intervening events such as wars and fires have resulted in destruction of original type material. The validity of a species name often rests 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 existed only since 1961, when the first edition of the Code
was published. The ICZN does not always demand a type specimen for the historical validity of a species, and many "type-less" species do 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 Boubou
(a bushshrike
), described as 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 a 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. However, in the case of the bushshrike, ornithologists have argued that the specimen was a rare and hitherto unknown color morph of a long-known species, using only the available blood and feather samples. While there is still some debate on the need to deposit actual killed individuals as type specimens, it can be observed that given proper vouchering and storage, tissue samples can be just as valuable even in case disputes about the validity of a species arise.
There are many other permutations and variations on terms using the suffix "-type" (e.g., allotype
, cotype, topotype, generitype, isotype
, isoneotype, etc.) but these are not formally regulated by the Code, and a great many are obsolete and/or idiosyncratic. However, some of these categories can potentially apply to genuine type specimens, such as a neotype; e.g., isotypic/topotypic specimens are preferred to other specimens, when they are available at the time a neotype is chosen (because they are from the same time and/or place as the original type).
The term fixation is used by the Code for the declaration of a name-bearing type, whether by original or subsequent designation.
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
).
Organism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...
to which the scientific name of that organism is formally attached. In other words, a type is an example that serves to anchor or centralize the defining features of that particular taxon
Taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...
.
A taxon is a scientifically named grouping of organisms with other like organisms, a set that includes some organisms and excludes others, based on a detailed published description (for example a species description
Species description
A species description or type description is a formal description of a newly discovered species, usually in the form of a scientific paper. Its purpose is to give a clear description of a new species of organism and explain how it differs from species which have been described previously, or are...
) and on the provision of type material, which is usually available to scientists for examination in a major museum research collection, or similar institution.
Type specimen
According to a precise set of rules laid down by the ICZNInternational Commission on Zoological Nomenclature
The International Commission on Zoological Nomenclature is an organization dedicated to "achieving stability and sense in the scientific naming of animals". Founded in 1895, it currently comprises 28 members from 20 countries, mainly practicing zoological taxonomists...
and the ICBN, the scientific name of every taxon is almost always based on one particular specimen, or in some cases specimens. Types are of great significance to biologists, especially to taxonomists. Types are usually physical specimens that are kept in a specially designated type collection in a museum
Museum
A museum is an institution that cares for a collection of artifacts and other objects of scientific, artistic, cultural, or historical importance and makes them available for public viewing through exhibits that may be permanent or temporary. Most large museums are located in major cities...
research collection, or are a particular plant sample in a herbarium
Herbarium
In botany, a herbarium – sometimes known by the Anglicized term herbar – is a collection of preserved plant specimens. These specimens may be whole plants or plant parts: these will usually be in a dried form, mounted on a sheet, but depending upon the material may also be kept in...
. Usually types are a physical example of the taxon, but failing that, an image of an individual of that taxon can be used. This material is the "type" or "types" of that taxon. Describing species and appointing type specimens is part of scientific nomenclature and alpha taxonomy
Alpha taxonomy
Alpha taxonomy is the discipline concerned with finding, describing and naming species of living or fossil organisms. This field is supported by institutions holding collections of these organisms, with relevant data, carefully curated: such institutes include natural history museums, herbaria and...
.
When identifying material, a scientist attempts to apply a taxon name to a specimen or group of specimens based on his or her understanding of the relevant taxa, based on (at least) having read the type description(s), preferably based on an examination of all the type material of all of the relevant taxa. If there is more than one named type that all appear to be the same taxon, then the oldest name takes precedence, and is considered to be the correct name of the material in hand. If on the other hand the taxon appears never to have been named at all, then the scientist or another qualified expert picks a type specimen and publishes a new name and an official description.
This process is crucial to the science of biological taxonomy
Taxonomy
Taxonomy is the science of identifying and naming species, and arranging them into a classification. The field of taxonomy, sometimes referred to as "biological taxonomy", revolves around the description and use of taxonomic units, known as taxa...
. People's ideas of how living things should be grouped changes and shifts over time. How do we know that that that we call "Canis lupus" is the same thing, or approximately the same thing, as what they will be calling "Canis lupus" in 200 years time? It is possible to check this because there is a particular wolf specimen preserved in a museum somewhere, and everyone who uses that name – no matter what else they may mean by it – will mean that particular specimen.
Depending on the nomenclature code
Nomenclature Codes
Nomenclature codes or codes of nomenclature are the various rulebooks that govern biological taxonomic nomenclature, each in their own broad field of organisms...
applied to the organism in question, a type can be a specimen, a culture, an illustration, a description, or a taxon.
For example, in the research collection of the Natural History Museum
Natural History Museum
The Natural History Museum is one of three large museums on Exhibition Road, South Kensington, London, England . Its main frontage is on Cromwell Road...
in London, there is a bird specimen numbered 1886.6.24.20. This is a specimen of a kind of bird commonly known as the Spotted Harrier
Spotted Harrier
The Spotted Harrier, Circus assimilis, also known as the Smoke Hawk, is a large Australasian bird of prey in the family Accipitridae.-Description:It is similar to the Swamp Harrier, distinguished by grey upperparts, chestnut facial disc and dark rump...
, which currently bears the scientific name Circus assimilis. This particular specimen is the holotype
Holotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
for that species; the name Circus assimilis refers, by definition, to the species of that particular specimen. That species was named and described by Jardine and Selby in 1828, and the holotype was placed in the museum collection so that other scientists might refer to it as necessary.
Note that at least for type specimens there is no requirement for a "typical" individual to be used. Genera
Genera
Genera is a commercial operating system and development environment for Lisp machines developed by Symbolics. It is essentially a fork of an earlier operating system originating on the MIT AI Lab's Lisp machines which Symbolics had used in common with LMI and Texas Instruments...
and families
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
, particularly those established by early taxonomists, tend to be named after species that are more "typical" for them, but here too this is not always the case and due to changes in systematics
Systematics
Biological systematics is the study of the diversification of terrestrial life, both past and present, and the relationships among living things through time. Relationships are visualized as evolutionary trees...
cannot be. Hence, the term name-bearing type
Name-bearing type
Under the International Code of Zoological Nomenclature , the name-bearing type is the biological type that determines the application of a name. Each taxon regulated by the Code at least potentially has a name-bearing type. The name-bearing type can be either a type genus , type species , or type...
or onomatophore is sometimes used, to denote the fact that biological types do not define "typical" individuals or taxa, but rather fix a scientific name to a specific operational taxonomic unit. Type specimens are theoretically even allowed to be aberrant or deformed individuals or color variations, though this is rarely chosen to be the case, as it makes it hard to determine to which population the individual belonged.
The usage of the term type is somewhat complicated by slightly different uses in botany
Botany
Botany, plant science, or plant biology is a branch of biology that involves the scientific study of plant life. Traditionally, botany also included the study of fungi, algae and viruses...
and zoology
Zoology
Zoology |zoölogy]]), is the branch of biology that relates to the animal kingdom, including the structure, embryology, evolution, classification, habits, and distribution of all animals, both living and extinct...
. In the PhyloCode
PhyloCode
The International Code of Phylogenetic Nomenclature, known as the PhyloCode for short, is a developing draft for a formal set of rules governing phylogenetic nomenclature...
, type-based definitions are replaced by phylogenetic definitions
Phylogenetic nomenclature
Phylogenetic nomenclature or phylogenetic taxonomy is an alternative to rank-based nomenclature, applying definitions from cladistics . Its two defining features are the use of phylogenetic definitions of biological taxon names, and the lack of obligatory ranks...
.
Types in botany
In botanical nomenclatureBotanical nomenclature
Botanical nomenclature is the formal, scientific naming of plants. It is related to, but distinct from taxonomy. Plant taxonomy is concerned with grouping and classifying plants; botanical nomenclature then provides names for the results of this process. The starting point for modern botanical...
, a type (typus, nomenclatural type), "is that element to which the name of a taxon is permanently attached." In botany a type is either a specimen or an illustration. A specimen is a real plant (or one or more parts of a plant or a lot of small plants), dead and kept safe, "curated", in a herbarium (or the equivalent for fungi). Examples of where an illustration may serve as a type are (this is not an exclusive listing):
- A detailed drawing, painting, etc., depicting the plant, from the early days of plant taxonomy. A dried plant was difficult to transport and hard to keep safe for the future; many specimens from the early days of botany have since been lost or damaged. Highly skilled botanical artists were sometimes employed by a botanist to make a faithful and detailed illustration. Some such illustrations have become the best record and have been chosen to serve as the type of a taxon.
- A detailed picture of something that can be seen only through a microscope. A tiny 'plant' on a microscope slideMicroscope slideA microscope slide is a thin flat piece of glass, typically 75 by 25 mm and about 1 mm thick, used to hold objects for examination under a microscope. Typically the object is placed or secured on the slide, and then both are inserted together in the microscope for viewing...
makes for a poor type: the microscope slide may be lost or damaged, or it may be very difficult to find the 'plant' in question among whatever else is on the microscope slide. An illustration makes for a much more reliable type (Art 37.5 of the Vienna Code, 2006).
Note that a type fixes only a name to a single representative of the taxon. A type does not determine the circumscription (therefore a taxon is independent of its type species or specimen) of the taxon. For example, the common dandelion is a controversial taxon: some botanists consider it to consist of over a hundred species, although most botanists regard it to be a single species. The type of the name Taraxacum officinale is the same whether the circumscription of the species includes all those small species (Taraxacum officinale is a 'big' species) or whether the circumscription is limited to only one small species among the other hundred (Taraxacum officinale is a 'small' species). In this case the name Taraxacum officinale is the same and the type of the name is the same, but the extent of what the name actually applies to varies strongly. Setting the circumscription of a taxon is done by a taxonomist in a publication.
Miscellaneous notes:
- Only a species or an infraspecific taxon can have a type of its own. For most new taxa (published on or after 1 January 2007, article 37) at these ranks a type should not be an illustration.
- A genus has the same type as that of one of its species (article 10).
- A family has the same type as that of one of its genera (article 10).
- The ICBN provides a listing of the various kinds of type (article 9), the most important of which is the holotypeHolotypeA holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
. Note that the word "type" appears in botanical literature as a part of several terms that have no status under the ICBN: for example a clonotype, an herbariumHerbariumIn botany, a herbarium – sometimes known by the Anglicized term herbar – is a collection of preserved plant specimens. These specimens may be whole plants or plant parts: these will usually be in a dried form, mounted on a sheet, but depending upon the material may also be kept in...
specimen vegetatively propagated from (and thus a cloneCloningCloning in biology is the process of producing similar populations of genetically identical individuals that occurs in nature when organisms such as bacteria, insects or plants reproduce asexually. Cloning in biotechnology refers to processes used to create copies of DNA fragments , cells , or...
of) the same plant from which a type specimen was made that is used for documenting the type collection.
Types in zoology
International Code of Zoological Nomenclature
The International Code of Zoological Nomenclature is a widely accepted convention in zoology that rules the formal scientific naming of organisms treated as animals...
, the type of a species (or subspecies) is a specimen (or series of specimens), the type of a genus (or subgenus) is a species, and the type of a suprageneric taxon (e.g., family, etc.) is a genus. Names higher than superfamily rank do not have types. A "name-bearing type
Name-bearing type
Under the International Code of Zoological Nomenclature , the name-bearing type is the biological type that determines the application of a name. Each taxon regulated by the Code at least potentially has a name-bearing type. The name-bearing type can be either a type genus , type species , or type...
" "provides the objective standard of reference whereby the application of the name of a nominal taxon can be determined."
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 speciesSpeciesIn biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
. 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 skullcapSkullcapSkullcap or skull cap may refer to:* Calvaria , in anatomy, the top part of the skull* Headgear:** A Kippah or yarmulke, a small cloth skullcap worn by Orthodox Jewish men and some Jewish women...
, thigh bones, part of a pelvis, some ribs, and some arm and shoulder bones. There may be more than one type specimen, but there is (at least in modern times) only one holotypeHolotypeA holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
. - A type speciesType speciesIn biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
is the nominal species that is the name-bearing type of a nominal genusGenusIn biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
or subgenusSubgenusIn biology, a subgenus is a taxonomic rank directly below genus.In zoology, a subgeneric name can be used independently or included in a species name, in parentheses, placed between the generic name and the specific epithet: e.g. the Tiger Cowry of the Indo-Pacific, Cypraea tigris Linnaeus, which...
. - A type genusType genusIn biological classification, a type genus is a representative genus, as with regard to a biological family. The term and concept is used much more often and much more formally in zoology than it is in botany, and the definition is dependent on the nomenclatural Code that applies:* In zoological...
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.
Use of types
Although in reality biologists may examine many specimens (when available) of a new taxon before writing an official published species description, nonetheless, under the formal rules for naming species (the International Code of Zoological NomenclatureInternational Code of Zoological Nomenclature
The International Code of Zoological Nomenclature is a widely accepted convention in zoology that rules the formal scientific naming of organisms treated as animals...
), a single type must be designated, as part of the published description.
When a single specimen is clearly designated in the original description, this specimen is known as the holotype
Holotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
of that species. The holotype is typically placed in a major museum, or similar well-known public collection, so that it is freely available for later examination by other biologists. Type illustrations have also been used by zoologists, as in the case of the Réunion Parakeet, which is known only from historical illustrations and descriptions.
A type description must include a diagnosis (typically, a discussion of similarities to and differences from closely related species), and an indication of where the type specimen or specimens are deposited for examination. The geographical location where a type specimen was originally found is known as its . In the case of parasites, the term type host (or symbiotype) is used to indicate the host organism from which the type specimen was obtained.
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:
- ParatypeParatypeParatype is a technical term used in the scientific naming of species and other taxa of organisms. The exact meaning of the term paratype when it is used in zoology is not the same as the meaning when it is used in botany...
– Any additional specimen other than the holotype, 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.
- SyntypeSyntypeIn biological nomenclature, a syntype is a term used to indicate a specimen with a special status.In zoological nomenclature, a syntype is defined as "Each specimen of a type series from which neither a holotype nor a lectotype has been designated [Arts. 72.1.2, 73.2, 74]. The syntypes...
– 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 CodeInternational Code of Zoological NomenclatureThe International Code of Zoological Nomenclature is a widely accepted convention in zoology that rules the formal scientific naming of organisms treated as animals...
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 lectotypeLectotypeIn botanical nomenclature and zoological nomenclature, a lectotype is a kind of name-bearing type. When a species was originally described on the basis of a name-bearing type consisting of multiple specimens, one of those may be designated as the lectotype...
s. Those that still exist are still considered name-bearing types. - LectotypeLectotypeIn botanical nomenclature and zoological nomenclature, a lectotype is a kind of name-bearing type. When a species was originally described on the basis of a name-bearing type consisting of multiple specimens, one of those may be designated as the 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 lectotypeLectotypeIn botanical nomenclature and zoological nomenclature, a lectotype is a kind of name-bearing type. When a species was originally described on the basis of a name-bearing type consisting of multiple specimens, one of those may be designated as the lectotype...
s cannot be designated from among them.
The various types listed above are necessary because many species were described one or two centuries ago, when a single type specimen, a holotype, was often not designated. Also, types were not always carefully preserved, and intervening events such as wars and fires have resulted in destruction of original type material. The validity of a species name often rests 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
International Commission on Zoological Nomenclature
The International Commission on Zoological Nomenclature is an organization dedicated to "achieving stability and sense in the scientific naming of animals". Founded in 1895, it currently comprises 28 members from 20 countries, mainly practicing zoological taxonomists...
has existed only since 1961, when the first edition of the Code
International Code of Zoological Nomenclature
The International Code of Zoological Nomenclature is a widely accepted convention in zoology that rules the formal scientific naming of organisms treated as animals...
was published. The ICZN does not always demand a type specimen for the historical validity of a species, and many "type-less" species do exist, perhaps the most notable being Homo sapiens. This example is instructive: the current edition of the Code
International Code of Zoological Nomenclature
The International Code of Zoological Nomenclature is a widely accepted convention in zoology that rules the formal scientific naming of organisms treated as animals...
, 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 Boubou
Bulo Burti Boubou
The Somali Boubou is a medium-size bushshrike. It was split from the Tropical Boubou as a result of DNA sequence analysis, and this change in status was recognized by the International Ornithological Committee in 2008...
(a bushshrike
Bushshrike
The bushshrikes are smallish passerine bird species. They were formerly classed with the true shrikes in the family Laniidae, but are now considered sufficiently distinctive to be separated from that group as the family Malaconotidae....
), described as 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 a 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. However, in the case of the bushshrike, ornithologists have argued that the specimen was a rare and hitherto unknown color morph of a long-known species, using only the available blood and feather samples. While there is still some debate on the need to deposit actual killed individuals as type specimens, it can be observed that given proper vouchering and storage, tissue samples can be just as valuable even in case disputes about the validity of a species arise.
There are many other permutations and variations on terms using the suffix "-type" (e.g., allotype
Allotype
Allotype can refer to:* In zoological nomenclature, an allotype is a specimen of the opposite sex to the holotype, designated from among paratypes * In immunology, an immunoglobulin allotype...
, cotype, topotype, generitype, isotype
Isotype
Isotype can refer to:* In crystallography, an "isotype" is a synonym for isomorph* In biology, per the International Code of Botanical Nomenclature, the "isotype" is a duplicate of the holotype....
, isoneotype, etc.) but these are not formally regulated by the Code, and a great many are obsolete and/or idiosyncratic. However, some of these categories can potentially apply to genuine type specimens, such as a neotype; e.g., isotypic/topotypic specimens are preferred to other specimens, when they are available at the time a neotype is chosen (because they are from the same time and/or place as the original type).
The term fixation is used by the Code for the declaration of a name-bearing type, whether by original or subsequent designation.
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 geneticsGenetics
Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....
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
International Commission on Zoological Nomenclature
The International Commission on Zoological Nomenclature is an organization dedicated to "achieving stability and sense in the scientific naming of animals". Founded in 1895, it currently comprises 28 members from 20 countries, mainly practicing zoological taxonomists...
).
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 that has passed into synonymy; the family name does not need to be changed in such a situation.External links
- ICZN Code: International Code of Zoological Nomenclature, the official website
- Fishbase Glossary section.
- A compendium of terms