What is a type specimen?
A type specimen is the original specimen used to name a new species. It is the name-bearing specimen, against which any new discoveries must be compared. Ideally, the type specimen preserves some feature that distinguishes the new species from all previously known ones.

Are there different kinds of type specimens?
In fact, yes. In principle, scientists choose a holotype specimen as the one and only type. This holotype (meaning “whole type”) should be relatively well preserved and as complete as possible. For dinosaurs, the majority of species are based on only a single specimen, which is the holotype.

Some animals may more commonly be found in groups, especially colonial organisms. In these instances, scientists would sometimes choose several animals from a single population to represent the type. This allows a greater range of variation to be accommodated in the description of the species. Such a group is called a syntype series (“together type”, although these are not usually used today.

Sometimes the original holotype is very incomplete or poorly preserved, and does not allow scientists to compare the species with other forms. This is more commonly the case with species that were named in the early days of paleontology. When fewer dinosaurs were known, it was easier to distinguish new finds from old ones even when just a few bones had been found. Now these older finds are often not identifiable as distinct species. If new, better materials have been found since the originals, scientists can designate a neotype (“new type”) that is more informative. At other times the species may be determined to be a nomen dubium (“doubtful name”).

How are type specimens determined?
An experienced scientist must compare any new find with the most similar preexisting species. If the new material is different, the scientist may name a new species and designate a type. This must be done in print, and accompanied by a description of what features of the new find make it distinct. These are called the diagnostic characters of the new species. In addition, the type must be reposited in a museum or other permanent institution, which allows other scientists to study it. The naming of new species is governed by a set of rules called the International Code of Zoological Nomenclature.

Who determines which specimen is the type?
Usually the scientist who discovers the first specimen of a new species also describes it in the scientific literature, and therefore is also the person who determines the type. Sometimes, however, a new species may be identified from a specimen that had been discovered years previously. In this case the scientist who describes the species and determines the type may be different from the one who first discovered the specimen.

What happens if the type specimen is lost, damaged, or destroyed?
Unfortunately, these accidents do happen to type specimens, despite the safeguards that museums employ to protect them. Some types may be damaged through use (study) or the effects of exposure and time, but others have been lost to building damage and the destruction caused by war.

In these instances, scientists can designate another specimen (the neotype, see above) to serve as the new holotype. However, many times there are no other specimens available—the holotypes of the theropod dinosaurs Spinosaurus aegyptiacus and Bahariasaurus ingens are good examples, having been destroyed in an Allied bombing attack on Munich in World War II. The only option is to rely on the descriptions, photographs, and drawings of these specimens (which ideally formed the original description) as proxies for the types. Surviving casts may also be used.