In
zoological nomenclature, codified in the
International Code of Zoological Nomenclature, synonyms are different scientific names of the same
taxonomic rank that pertain to the same
taxon. For example, a particular species could, over time, have had two or more
species-rank names published for it, while the same is applicable at higher ranks such as genera, families, orders, etc. In each case, the earliest published name is called the
senior synonym, while the later name is the
junior synonym. In the case where two names for the same taxon have been published simultaneously, the valid name is selected according to the
principle of the first reviser such that, for example, of the names
Strix scandiaca and
Strix noctua (Aves), both published by
Linnaeus in the same work at the same date for the taxon now determined to be the
snowy owl, the epithet
scandiaca has been selected as the valid name, with
noctua becoming the junior synonym. (Incidentally, this species has since been reclassified and currently resides in the genus
Bubo, as
Bubo scandiacus.) One basic principle of zoological
nomenclature is that the earliest correctly published (and thus
available) name, the senior synonym, by default takes precedence in
naming rights, and therefore, unless other restrictions interfere, must be used for the taxon. However, junior synonyms are still important to document, because if the earliest name cannot be used (for example, because the same spelling had previously been used for a name established for another taxon), then the next available junior synonym must be used for the taxon. For other purposes, if a researcher is interested in consulting or compiling all currently known information regarding a taxon, some of this (including species descriptions, distribution, ecology and more) may well have been published under names now regarded as outdated (i.e., synonyms) and so it is again useful to know a list of historical synonyms that have been used for a given current (valid) taxon name.
Objective synonyms refer to taxa with the same
type and same rank (more or less the same taxon, although circumscription may vary, even widely). This may be species-group taxa of the same rank with the same
type specimen, genus-group taxa of the same rank with the same
type species or if their type species are themselves objective synonyms, of family-group taxa with the same type genus, etc. In the case of
subjective synonyms, there is no such shared type, so the synonymy is open to taxonomic judgement, meaning that there is room for debate: one researcher might consider the two (or more) types to refer to one and the same taxon, another might consider them to belong to different taxa. For example,
John Edward Gray published the name
Antilocapra anteflexa in 1855 for a species of
pronghorn, based on a pair of horns. However, it is now commonly accepted that his specimen was an unusual individual of the species
Antilocapra americana published by
George Ord in 1815. Ord's name thus takes precedence, with
Antilocapra anteflexa being a junior subjective synonym. Objective synonyms are common at the rank of genera, because for various reasons two genera may contain the same type species; these are objective synonyms. In many cases researchers established new generic names because they thought this was necessary or did not know that others had previously established another genus for the same group of species. An example is the genus
Pomatia Beck, 1837, which was established for a group of terrestrial snails containing as its type species the Burgundy or Roman snail
Helix pomatia—since
Helix pomatia was already the type species for the genus
Helix Linnaeus, 1758, the genus
Pomatia was an objective synonym (and useless). On the same occasion,
Helix is also a synonym of
Pomatia, but it is older and so it has precedence. At the species level, subjective synonyms are common because of an unexpectedly large range of variation in a species, or simple ignorance about an earlier description, may lead a biologist to describe a newly discovered specimen as a new species. A common reason for objective synonyms at this level is the creation of a replacement name. A junior synonym can be given precedence over a senior synonym, primarily when the senior name has not been used since 1899, and the junior name is in common use. The older name may be declared to be a
nomen oblitum, and the junior name declared a
nomen protectum. This rule exists primarily to prevent the confusion that would result if a well-known name, with a large accompanying body of literature, were to be replaced by a completely unfamiliar name. An example is the European land snail
Petasina edentula (
Draparnaud, 1805). In 2002, researchers found that an older name
Helix depilata Draparnaud, 1801 referred to the same species, but this name had never been used after 1899 and was fixed as a
nomen oblitum under this rule by Falkner
et al. 2002. Such a reversal of precedence is also possible if the senior synonym was established after 1900, but only if the
International Commission on Zoological Nomenclature (ICZN) approves an application. (Here the C in ICZN stands for Commission, not Code as it does at the beginning of
§ Zoology. The two are related, with only one word difference between their names.) For example, the scientific name of the
red imported fire ant,
Solenopsis invicta, was published by Buren in 1972, who did not know that this species was first named
Solenopsis saevissima wagneri by Santschi in 1916; as there were thousands of publications using the name
invicta before anyone discovered the synonymy, the ICZN, in 2001, ruled that
invicta would be given precedence over
wagneri. To qualify as a synonym in zoology, a name must be properly published in accordance with the rules. Manuscript names and names that were mentioned without any description (
nomina nuda) are not considered as synonyms in zoological nomenclature. ==Botany==