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 International Code of Zoological Nomenclature (ICZN), a holotype is one of several kinds of name-bearing types. In the International Code of Nomenclature for algae, fungi, and plants (ICN) and ICZN the definitions of types are similar in intent but not identical in terminology or underlying concept.
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. An isotype is a duplicate of the holotype and is often made for plants, where holotype and isotypes are often pieces from the same individual plant or samples from the same gathering.
A holotype is not necessarily "typical" of that taxon, although ideally it should be. Sometimes just a fragment of an organism is the holotype, particularly in the case of a fossil. For example, the holotype of Pelorosaurus (=Duriatitan) humerocristatus, a large herbivorous 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 Even if a better specimen is subsequently found, the holotype is not superseded.
Replacements for holotypes
Under the ICN, an additional and clarifying type could be designated, an epitype under Article 9.8, where the original material is demonstrably ambiguous or insufficient.
A conserved type (ICN article 14.3) is sometimes used to correct a problem with a name which has been misapplied; this specimen replaces the original holotype.
For example, in both the ICN 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 archosaurian reptile Parasuchus hislopi Lydekker, 1885 was described based on a premaxillary 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 descriptions in which the specimen designated as the holotype was a living individual that was allowed to remain in the wild (e.g. a new species of capuchin monkey, genus Cebus, Marleyimyia xylocopae, or the Arunachal macaque Macaca munzala). 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 ICZN 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.
Great care must be used in speaking of types, as definitions are very precise.
- Type (biology)
- Allotype (zoology)
- Type species
- Genetypes- genetic sequence data from type specimens.
- Case 3165, Bulletin of Zoological Nomenclature 58:1, 30 March 2001.
- Opinion 2045, Bulletin of Zoological Nomenclature 60:2, 30 June 2003.
- Mendes Pontes, A.R., Malta A. and Asfora, P.H. 2006. A new species of capuchin monkey, genus Cebus Erxleben (Cebidae, Primates): found at the very brink of extinction in the Pernambuco Endemism Centre. Zootaxa 1200: 1-12.
- Sinha, A.,Datta, A., Madhusudan, M. D. and Mishra, C. (2004). "The Arunachal macaque Macaca munzala: a new species from western Arunachal Pradesh, northeastern India". International Journal of Primatology volume: 26 issue: 977 pages: 989.
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- BOA Photographs of type specimens of Neotropical Rhopalocera.