Holotype
From Free net encyclopedia
A holotype is one of several possible types. A holotype is the single physical example (or illustration) of an organism, known to be used when the taxon was formally described.
For example, the holotype for the butterfly Lycaeides idas longinus is held by the Museum of Comparative Zoology at Harvard University, and the holotype for the extinct mammal Cimolodon is at the University of Alberta.
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 rare fossil. The holotype of Pelorosausus 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 Even if a better specimen is subsequently found, the holotype is not superseded.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. A type is what fixes a name to a taxon. Note that in the ICBN and ICZN the definitions of types are similar but not identical. For example in both the ICBN and the ICZN a "neotype" is a type that was later appointed in the absence of original material. 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.Template:Ref The International Commission on Zoological Nomenclature considered the case and agreed to replace the original type specimen with the proposed neotype.Template:Ref.
Under the ICBN, also, a replacement type could be appointed by such a procedure, but this would be called a "conserved type". However a conserved type would not be appointed in the case of a type that is insufficiently clear: in that case an additional and clarifying type could be designated, a so-called "epitype". Great care must be used in speaking of types, as definitions are very precise.