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. Families Superfamily Hesperioidea: Hesperiidae Superfamily Papilionoidea: Papilionidae Pieridae Nymphalidae Lycaenidae Riodinidae A butterfly is a flying insect of the order Lepidoptera belonging to one of the superfamilies Hesperioidea (the skippers) and Papilionoidea (all other butterflies). ... Harvard University is a private university in Cambridge, Massachusetts, USA, and a member of the Ivy League. ... Orders Subclass Embrithopoda (extinct) Subclass Creodonta (extinct) Hyaenodontidae Oxyaenidae Subclass Multituberculata (extinct) Plagiaulacida Cimolodonta Subclass Palaeoryctoides (extinct) Subclass Triconodonta (extinct) Subclass Placentalia Afrosoricida Artiodactyla Carnivora Cetacea Chiroptera Dermoptera Desmostylia (extinct) Hyracoidea Insectivora Lagomorpha Macroscelidea Perissodactyla Pholidota Primates Proboscidea Rodentia Scandentia Sirenia Tubulidentata Xenarthra Subclass Marsupialia Dasyuromorphia Didelphimorphia Diprotodontia Microbiotheria Notoryctemorphia... Species             Ref. ... University of Alberta on the south side of Edmonton The University of Alberta is situated along the south bank of the North Saskatchewan River in the heart of the city of Edmonton, Alberta, Canada. ...

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 Even if a better specimen is subsequently found, the holotype is not superseded. A fossil Ammonite Fossils are the mineralized remains of animals or plants or other traces such as footprints. ... In zoology, an herbivore is an animal that is adapted to eat primarily plant matter (rather than meat). ... Orders Saurischia    Sauropodomorpha    Theropoda Ornithischia Dinosaurs are animals that dominated the terrestrial ecosystem for over 100 million years. ... The Jurassic period is a major unit of the geologic timescale that extends from about 200 million years BP at the end of the Triassic to 146 million years BP at the beginning of the Cretaceous. ... The Natural History Museum in South Kensington, London, has an ornate terracotta facade typical of high Victorian architecture. ... The clock tower of the Palace of Westminster, which contains Big Ben London is the capital city of the United Kingdom and of England. ...

In the absense 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 absense 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.^[1] The International Commission on Zoological Nomenclature considered the case and agreed to replace the original type specimen with the proposed neotype.^[2]. Groups Crurotarsi     Crocodilia (crocodiles) Ornithodira     Pterosauria     Dinosauria        Aves (birds) Archosaurs (Greek for ruling reptiles) are a group of diapsid reptiles that first evolved from Archosauriform ancestors during the Olenekian (Lower Triassic). ... Richard Lydekker (1849 - April 16, 1915) was an English naturalist, geologist and writer of numerous books on natural history. ... The maxillae are the largest bones of the face, except for the mandible, and form, by their union, the whole of the upper jaw. ... A rostrum (Latin beak) is an anatomical structure resembling a birds beak, such as part of the carapace of a crustacean. ... Professor 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. ... The International Code of Zoological Nomenclature is a set of rules in zoology that have one fundamental aim: to provide the maximum universality and continuity in classifying all animals according to taxonomic judgment. ...

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.

References

1. ^  Case 3165, Bulletin of Zoological Nomenclature 58:1, 30 March 2001.
2. ^  Opinion 2045, Bulletin of Zoological Nomenclature 60:2, 30 June 2003.