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Re: Taxonomy Question



Saint Abyssal a écrit :

> Is there a term that refers categorically to junior synonyms, nomena dubia, lapsus calami, and all the other situations that cause scientists to disregard genera and species? I've always called them "invalid taxa" but technically that only applies to nomena nuda. I've considered referring to them as "rejected" but that sounds like I mean a nomen rejectum. Is there an actual term that I can use for non-accepted genera and species?

A good question indeed, since the same terminology is often used to designate the status of both taxa and nomina. We should first distinguish "invalid nomina" and "invalid taxa". The status of a nomen involves the International Code of Zoological Nomenclature (for an animal): "invalid" refers here to the nomenclatural status of the nomen and is objective. The status of a taxon, however, is independent from that of the nomen. Its status is given by taxonomists who judge if this taxon (i.e. the holotype/type species/type genus and hypodigm) is diagnosable.

In short:

Nomen: object => Nomenclatural status (objective).
Taxon: concept => Taxonomic status (subjective).

Therefore:

Synonymy => Taxonomy - except in the case of objective synonymy (same holotype/type species/type genus) where it involves nomenclature.
Nomina dubia => Taxonomy.
Nomina nuda => Nomenclature.
Lapsus calami => Nomenclature.
Homonymy => Nomenclature.

In most papers, however, scientists say "taxon" when they mean "nomen"... The difference is significant, though: an invalid taxon MAY have a valid nomen, but a valid taxon MUST have a valid nomen. Also, taxa invalidated by taxonomists should be distinguished from those bearing an invalid name. Practically, we could call these cases: nomenclatural/taxonomic validity, or subjective/objective validity.

A nomenclaturally invalid taxon would thus bear a nomen nudum, but a taxonomically invalid taxon could bear a nomen nudum or a nomen dubium, or any nomen following the rules of the ICZN.

Let's take for example:

> The Spanish sauropod taxon Galveosaurus:

Its holotype was described independently by Sánchez-Hernández and Barco et al. in 2005, as respectively Galveosaurus herreroi and Galvesaurus herreroi. Both nomina follow the rules of the ICZN, and are thus nomenclaturally valid. As they are based on the same holotype, they are objective synonyms and only the senior synonym, Galveosaurus, is valid regarding the ICZN.

> The English sauropod Cetiosaurus:

The holotype of its type species, Cetiosaurus brevis, is undiagnostic according to Upchurch and Martin (2003). Although Cetiosaurus and Cetiosaurus brevis are valid regarding nomenclature, they are invalid regarding taxonomy (nomina dubia). Cetiosaurus includes also C. oxoniensis, which is based on diagnosable material. If the ICZN accepts to suppress C. brevis as proposed by Upchurch et al. and chooses instead C. oxoniensis as type specie, then Cetiosaurus would be valid nomenclaturally AND taxonomically.

> The Nigerien iguanodont Gravisaurus tenerensis:

This nomen was erected in the PhD dissertation of Chabli in 1988, but it is not published sensu the ICZN. Even if the specimen described represent indeed a new taxon according to taxonomists, this taxon was invalid taxonomically until it was given a proper name - Lurdusaurus tenerensis - in 1999 by Taquet and Russell.

Cheers,
Jocelyn Falconnet


PS: I just had an idea; what do you think of: "approved"/"reprouved" for taxonomy and "valid"/"invalid" for nomenclature ?