Holotype
Encyclopedia
A holotype is a single physical example (or illustration) of an organism
, known to have been used when the species
(or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several such, but explicitly designated as the holotype. Under the ICZN
, a holotype is one of several kinds of name-bearing type
s.
For example, the holotype for the butterfly
Lycaeides idas longinus is a preserved specimen of that species, held by the Museum of Comparative Zoology
at Harvard University
.
A holotype is not necessarily 'typical' of that taxon, although ideally it should be. Sometimes just a fragment of an organism is the holotype, for example in the case of a fossil
. The holotype of Pelorosaurus humerocristatus, a large herbivore
dinosaur
from the early Jurassic
period, is a fossil leg bone stored at the Natural History Museum
in London
. Even if a better specimen is subsequently found, the holotype is not superseded.
In the absence of a holotype (e.g. it was lost) another type may be selected, out of a range of different kinds of type, depending on the case. Note that in the ICBN and ICZN the definitions of types are similar in intent but not identical in terminology or underlying concept.
For example in both the ICBN and the ICZN a "neotype" is a type that was later appointed in the absence of the original holotype. Additionally, under the ICZN the Commission is empowered to replace a holotype with a "neotype", when the holotype turns out to lack important diagnostic features needed to distinguish the species from its close relatives. For example, the crocodile-like archosaur
ian reptile Parasuchus hislopi Lydekker
, 1885 was described based on a premaxilla
ry rostrum
(part of the snout), but this is no longer sufficient to distinguish Parasuchus from its close relatives. This made the name Parasuchus hislopi a nomen dubium
. Texan paleontologist Sankar Chatterjee
proposed that a new type specimen, a complete skeleton, be designated. The International Commission on Zoological Nomenclature
considered the case and agreed to replace the original type specimen with the proposed neotype.
The procedures for the designation of a new type specimen when the original is lost come into play for some recent, high-profile species description
s in which the specimen designated as the holotype was a living individual that was allowed to remain in the wild (e.g.,). In such a case, there is no actual type specimen available for study, and the possibility exists that - should there be any perceived ambiguity in the identity of the species - subsequent authors can invoke various clauses in the ICZN Code
that allow for the designation of a neotype. Remarkably, the Code explicitly states that the designation of a neotype must be based upon an actual physical specimen that is "the property of a recognized scientific or educational institution", but there is no such requirement for a holotype.
Under the ICBN, an additional and clarifying type could be designated, an epitype under §9.7 of the Vienna Code, where the original material is demonstrably ambiguous or insufficient. Great care must be used in speaking of types, as definitions are very precise: a conserved type would be used to clarify a nomen ambiguum or "fix" a name which has come to apply to material that disagrees with its holotype (that is, where the holotype clearly belongs to another taxa under current usage).
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...
, known to have been used when the species
Species
In 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...
(or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several such, but explicitly designated as the holotype. Under the ICZN
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...
, a holotype is one of several kinds of 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...
s.
For example, the holotype for the butterfly
Butterfly
A butterfly is a mainly day-flying insect of the order Lepidoptera, which includes the butterflies and moths. Like other holometabolous insects, the butterfly's life cycle consists of four parts: egg, larva, pupa and adult. Most species are diurnal. Butterflies have large, often brightly coloured...
Lycaeides idas longinus is a preserved specimen of that species, held by the Museum of Comparative Zoology
Museum of Comparative Zoology
The Museum of Comparative Zoology, full name "The Louis Agassiz Museum of Comparative Zoology", often abbreviated simply to "MCZ", is a zoology museum located on the grounds of Harvard University in Cambridge, Massachusetts. It is one of three museums which collectively comprise the Harvard Museum...
at Harvard University
Harvard University
Harvard University is a private Ivy League university located in Cambridge, Massachusetts, United States, established in 1636 by the Massachusetts legislature. Harvard is the oldest institution of higher learning in the United States and the first corporation chartered in the country...
.
A holotype is not necessarily 'typical' of that taxon, although ideally it should be. Sometimes just a fragment of an organism is the holotype, for example in the case of a fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
. The holotype of Pelorosaurus humerocristatus, a large herbivore
Herbivore
Herbivores are organisms that are anatomically and physiologically adapted to eat plant-based foods. Herbivory is a form of consumption in which an organism principally eats autotrophs such as plants, algae and photosynthesizing bacteria. More generally, organisms that feed on autotrophs in...
dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
from the early Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
period, is a fossil leg bone stored at 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
London
London is the capital city of :England and the :United Kingdom, the largest metropolitan area in the United Kingdom, and the largest urban zone in the European Union by most measures. Located on the River Thames, London has been a major settlement for two millennia, its history going back to its...
. Even if a better specimen is subsequently found, the holotype is not superseded.
In the absence of a holotype (e.g. it was lost) another type may be selected, out of a range of different kinds of type, depending on the case. Note that in the ICBN and ICZN the definitions of types are similar in intent but not identical in terminology or underlying concept.
For example in both the ICBN and the ICZN a "neotype" is a type that was later appointed in the absence of the original holotype. Additionally, under the ICZN the Commission is empowered to replace a holotype with a "neotype", when the holotype turns out to lack important diagnostic features needed to distinguish the species from its close relatives. For example, the crocodile-like archosaur
Archosaur
Archosaurs are a group of diapsid amniotes whose living representatives consist of modern birds and crocodilians. This group also includes all extinct non-avian dinosaurs, many extinct crocodilian relatives, and pterosaurs. Archosauria, the archosaur clade, is a crown group that includes the most...
ian reptile Parasuchus hislopi Lydekker
Richard Lydekker
Richard Lydekker was an English naturalist, geologist and writer of numerous books on natural history.-Biography:...
, 1885 was described based on a premaxilla
Premaxilla
The incisive bone is the portion of the maxilla adjacent to the incisors. It is a pair of small cranial bones at the very tip of the jaws of many animals, usually bearing teeth, but not always. They are connected to the maxilla and the nasals....
ry rostrum
Rostrum (anatomy)
The term rostrum is used for a number of unrelated structures in different groups of animals:*In crustaceans, the rostrum is the forward extension of the carapace in front of the eyes....
(part of the snout), but this is no longer sufficient to distinguish Parasuchus from its close relatives. This made the name Parasuchus hislopi a nomen dubium
Nomen dubium
In zoological nomenclature, a nomen dubium is a scientific name that is of unknown or doubtful application...
. Texan paleontologist Sankar Chatterjee
Sankar Chatterjee
Sankar Chatterjee is a paleontologist, and is the Paul W. Horn Professor of Geosciences at Texas Tech University and Curator of Paleontology at the Museum of Texas Tech University. He earned his Ph. D. from the University of Calcutta in 1970 and was a Post-doctoral Fellow at the Smithsonian...
proposed that a new type specimen, a complete skeleton, be designated. 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...
considered the case and agreed to replace the original type specimen with the proposed neotype.
The procedures for the designation of a new type specimen when the original is lost come into play for some recent, high-profile 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...
s in which the specimen designated as the holotype was a living individual that was allowed to remain in the wild (e.g.,). In such a case, there is no actual type specimen available for study, and the possibility exists that - should there be any perceived ambiguity in the identity of the species - subsequent authors can invoke various clauses in the ICZN 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...
that allow for the designation of a neotype. Remarkably, the Code explicitly states that the designation of a neotype must be based upon an actual physical specimen that is "the property of a recognized scientific or educational institution", but there is no such requirement for a holotype.
Under the ICBN, an additional and clarifying type could be designated, an epitype under §9.7 of the Vienna Code, where the original material is demonstrably ambiguous or insufficient. Great care must be used in speaking of types, as definitions are very precise: a conserved type would be used to clarify a nomen ambiguum or "fix" a name which has come to apply to material that disagrees with its holotype (that is, where the holotype clearly belongs to another taxa under current usage).
External Links
- BOA Photographs of type specimens of Neotropical Rhopalocera.