Taxonomy and Nomenclature
Taxonomy is the scientific study of naming, defining (circumscribing) and classifying groups of biological organisms based on shared characteristics. Organisms are grouped into taxa (singular: taxon) and these groups are given a taxonomic rank; groups of a given rank can be aggregated to form a more inclusive group of higher rank, thus creating a taxonomic hierarchy. The Kingdoms or largest grouping of specimens are subdivided into Phyla (singular: Phylum) which are further subdivided into Classes, Orders, Families, Genera (singular: Genus), and species. There may also be super- and sub-divisions as well.
The system of nomenclature used today was introduced in the 1700’s by the Swedish naturalist Carolus Linnaeus (1701-1778). In biology, it uses two names (binomial), the first, capitalized, the generic name (genus) and the second in lower case, the specific name (species).
In the case of living species, the species unit (fundamental unit) is usually defined as the interfertility of its individual members. In paleontological classification, a species is defined by its statistical measurement of variation of its members. When there are not enough individual specimens, emphasis is placed on the corresponding characteristics that may indicate that certain individuals belong to the same species. The name is given by the discoverer of the species which is then Latinized.
Paleontologists may also use qualifying terms such as “cf” or “aff” (Homotherium cf. crenatidens – saber tooth cat) indicating a similarity or affinity to another species at the same time, admitting that the organism in question does not possess characteristics that match exactly with those of the species they have been associated.
The application of binomial nomenclature is governed by various internationally agreed codes of rules, of which are the International Code of Zoological Nomenclature (ICZN) for animals and the International Code of Nomenclature for algae, fungi, and plants (ICNafp), and the International Code of Nomenclature of Prokaryotes (ICNP). These codes also govern how Paleontologists name new fossil taxa.
The objects of the Codes are to promote stability and universality in the scientific names of animals, et. al. and to ensure that the name of each taxon is unique and distinct.
For more information on the Nomenclature Codes, visit their websites.
Types
In biology, a type is a 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.
According to a precise set of rules laid down in the ICZN, ICNafp, and the ICNP, 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 museum or herbarium research collection, but failing that, an image of an individual of that taxon has sometimes been designated as a type. 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 also 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. 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 type locality.
Type Specimens
(Taken from the Nomenclature Codes: ICZN, ICNafp, ICNP)
Holotype
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 scientists.
Paratype
When the original description designated a holotype, there may be additional specimens that the author designates as additional representatives of the same species, termed paratypes. These are not name-bearing types.
Allotype
An allotype is a specimen of the opposite sex to the holotype, designated from among paratypes. The word was also formerly used for a specimen that shows features not seen in the holotype of a fossil. The term is not regulated by the ICZN.
Neotype
A neotype is 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
A syntype is any one of two or more specimens that is listed in a species description where no holotype was designated; historically, syntypes were often explicitly designated as such, and under the present ICZN 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 that still exist are still considered name-bearing types.
Lectotype
A lectotype is a specimen later selected to serve as the single type specimen for species originally described from a set of syntypes. In zoology, 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. Having a single name-bearing type reduces the potential for confusion, especially considering that it is not uncommon for a series of syntypes to contain specimens of more than one species.
Paralectotype
A paralectotype is 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.
Iconotype
An illustration on which a new species or subspecies was based. For instance, the Burmese python, Python bivittatus, is one of many species that are based on illustrations by Albertus Seba (1734).
Ergatotype
An ergatotype is a specimen selected to represent a worker member in hymenopterans (wasps, bees, ants, et. al.) which have polymorphic castes.