Synonymy

The existence of more than one name (synonym) for a taxon is not uncommon and can arise for a number of reasons:

Due to the re-combination of a name, which we examine in How to record a Parenthetic Author.
Due to the recognition that two previously published species are actually the same, or that two names actually refer to the same species.

It is this latter case that we deal with here.

The two broad categories of synonymy are Homotypic or Objective and Heterotypic or Subjective:

Synonymy	Description
Homotypic / Objective	Two or more synonyms are derived from the same Type specimenIn Taxonomy Type specimens are specimens selected to typify the described species. They are made available (often in museums) for study by Taxonomists. The Type Series is all specimens on which the description of a new species or genus is based. The Holotype is the single specimen published as "the Type" by the Name Author. An Isotype is a duplicate specimen of the Holotype collected at the same place and time as the Holotype. The Syntype is one of two or more specimens cited by the author when no Holotype was designated or it is any one of two or more specimens originally designated as Types. The Neotype specimen is selected as the Type where the original Types are known to be destroyed. Paratypes are the non-Holotype Syntypes. (the same holotype). Also known as objective or nomenclatural synonyms as the basis for recognizing synonymy is empirical (the same type specimen was used to define the species). Example In 1910 Wood described a new zoological species Gus hus Wood, 1910 and in 1950 Brown described Jus kus Brown, 1950. In 2004 another scientist realized that Brown had used the same HolotypeIn Taxonomy the definitive Type specimen on which a scientific name of a species is based. as Wood and that the two names refer to the same species. In this case: The currently accepted name is Gus hus Wood, 1910 as it has priority (it was published first). The scientific name Jus kus Brown, 1950 would remain exactly as it is as no re-combination has taken place, but it would be considered a homotypic synonym of Gus hus Wood, 1910 and would not be a currently accepted name.
Heterotypic / Subjective	Two or more synonyms are derived from different type specimens. Also known as subjective or taxonomic synonyms as the basis for recognizing synonymy is a matter of opinion. Example In 2002 Wood described a new zoological species Cus dus Wood, 2002 and in 2003 Brown described Vus wus Brown, 2003 (using different type specimens). In 2004 another scientist decided that these two names actually refer to the same species. In this case: The currently accepted name would be Cus dus Wood, 2002 as it has PriorityIn Taxonomy, where two or more scientific names are synonyms, the Name that was published before the others is said to have Priority and is the Currently Accepted Name for a species.. Vus wus Brown, 2003 would remain exactly as it is as no re-combination has taken place, but it would be considered a heterotypic synonym of Cus dus Wood, 2002 and would not be a currently accepted name.

Synonymy

Description

Homotypic / Objective

Two or more synonyms are derived from the same Type specimenIn Taxonomy Type specimens are specimens selected to typify the described species. They are made available (often in museums) for study by Taxonomists. The Type Series is all specimens on which the description of a new species or genus is based. The Holotype is the single specimen published as "the Type" by the Name Author. An Isotype is a duplicate specimen of the Holotype collected at the same place and time as the Holotype. The Syntype is one of two or more specimens cited by the author when no Holotype was designated or it is any one of two or more specimens originally designated as Types. The Neotype specimen is selected as the Type where the original Types are known to be destroyed. Paratypes are the non-Holotype Syntypes. (the same holotype).

Also known as objective or nomenclatural synonyms as the basis for recognizing synonymy is empirical (the same type specimen was used to define the species).

Example

In 1910 Wood described a new zoological species Gus hus Wood, 1910 and in 1950 Brown described Jus kus Brown, 1950. In 2004 another scientist realized that Brown had used the same HolotypeIn Taxonomy the definitive Type specimen on which a scientific name of a species is based. as Wood and that the two names refer to the same species. In this case:

The currently accepted name is Gus hus Wood, 1910 as it has priority (it was published first).
The scientific name Jus kus Brown, 1950 would remain exactly as it is as no re-combination has taken place, but it would be considered a homotypic synonym of Gus hus Wood, 1910 and would not be a currently accepted name.

Heterotypic / Subjective

Two or more synonyms are derived from different type specimens.

Also known as subjective or taxonomic synonyms as the basis for recognizing synonymy is a matter of opinion.

Example

In 2002 Wood described a new zoological species Cus dus Wood, 2002 and in 2003 Brown described Vus wus Brown, 2003 (using different type specimens). In 2004 another scientist decided that these two names actually refer to the same species. In this case:

The currently accepted name would be Cus dus Wood, 2002 as it has PriorityIn Taxonomy, where two or more scientific names are synonyms, the Name that was published before the others is said to have Priority and is the Currently Accepted Name for a species..
Vus wus Brown, 2003 would remain exactly as it is as no re-combination has taken place, but it would be considered a heterotypic synonym of Cus dus Wood, 2002 and would not be a currently accepted name.

Note: Where names are synonymous (and by definition interchangeable), only one of the names is identified as the currently accepted name.

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