29 May 2009

One Name, One Taxon

One of the primary goals of a nomenclatural code should be to make sure that names refer to one taxon and one taxon only. This principle is mentioned in the ICZN's preamble (emphasis added):
The objects of the Code are to promote stability and universality in the scientific names of animals and to ensure that the name of each taxon is unique and distinct. All its provisions and recommendations are subservient to those ends and none restricts the freedom of taxonomic thought or actions.
This point is reiterated in Article 52:
52.1. Statement of the Principle of Homonymy. When two or more taxa are distinguished from each other they must not be denoted by the same name.
Yet there are numerous cases in zoological nomenclature where this rule is flagrantly ignored. A few:
  • "Echinoidea" is the name of a superfamily containing Echinus (a sea urchin genus), but also the name of a class containing that superfamily.
  • "Ophiuroidea" is the name of a superfamily containing Ophiura (a brittle star genus), but also the name of a class containing that superfamily.
  • "Chelonia" is a genus of turtle, but also used as the name of the order containing all turtles.
  • "Pterodactyloidea" is the name of taxon given various ranks (usually suborder) including most short-tailed pterosaurs, but also the name of a superfamily within that taxon.
This is getting to be an actual problem for me, because parts of Names on Nodes rely on the principle that a name only has one meaning under a given authority. When I create a database entry for urn:isbn:0853010064::Pterodactyloidea, is it for a suborder or a superfamily? ICZN rules actually dictate that the superfamily has precedence, since Family Pterodactylidae Meyer 1830 has precedence over Suborder Pterodactyloidea Plieninger 1901. (The ICZN considers the naming of any taxon whose rank is in the family group as implicitly naming taxa for all ranks of the family group; thus, naming Family Pterodactylidae implicitly names Superfamily Pterodactyloidea, Subfamily Pterodactylinae, Tribe Pterodactylini, and Subtribe Pterodactylina.) People who use "Pterodactyloidea" for a suborder, beware! You are violating the rules of the ICZN! (WhooOOOOoo!!)

The situation with "Echinoidea" is even worse. As near as I can tell, Family Echinidae was named by Gray in 1825 (thus implicitly naming Superfamily Echinoidea), but Class Echinoidea was already named by Leske in 1778. And the ICZN mandates that the superfamily including Echinus must be named "Echinoidea" if the family is named "Echinidae". I'm not sure how this is supposed to play out ... does Echinus simply not get a name for its superfamily? Those poor wee urchins....

(And people wonder why I support an alternative nomenclatural code without mandated suffixes for ranks!)

In the case of Chelonia, people are generally using another name ("Testudines") for the order nowadays, but in other cases I've got a real problem, especially if I hope to automatically pull a lot of this data from other databases.

11 comments:

  1. When I create a database entry for urn:isbn:0853010064::Pterodactyloidea, is it for a suborder or a superfamily? ICZN rules actually dictate that the superfamily has precedence, since Family Pterodactylidae Meyer 1830 has precedence over Suborder Pterodactyloidea Plieninger 1901.No, Mike, you're wrong. The ICZN does not regulate names above family group except for in very limited ways, and not as regards homonymy (Art. 1.2.2), so Pterydactyloidea can be both a superfamily and a suborder, and Gnathostomata can be both a group of vertebrates and a group of echinoids. Also, names that are in different group levels do not compete for homonymy, so the isopod superfamily Oniscoidea is not a homonym of the isopod genus Oniscoidea.

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  2. Huh... so would the superfamily containing genus _Oniscoidea_ be Superfamily Oniscoidoidea?

    And yeah, as far as the ICZN is concerned, Pterodactyloidea is a superfamily, as is Spinosauroidea (which was named as a clade, IIRC). Ranks above superfamily don't compete for priority since they are not governed by anything. Does this mean the use of Azhdarchoidea within Pterodactyloidea is incorrect under the ICZN? I'm guessing yeah.

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  3. Well, if it doesn't follow its own preamble, what good is it? I mean, seriously, this would make it basically useless as a nomenclatural authority. (Names of higher taxa are also not tied to ranks, nor are they in any way actually defined by the code, so the Gnathostomata example need not be devastating. The Pterodactyloidea example, however, is, because the code explicitly defines the name as referring to a superfamily.)

    Also, names that are in different group levels do not compete for homonymyIs there a specific rule that addresses this? Because Art. 52.1 seems pretty clear on the point otherwise.

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  4. I've never seen Pterodactyloidea used as a "superfamily" within Pterodactyloidea. I certainly can't think of any one paper that reuses the name for two clades (but I'm not an expert on the pterosaur literature).

    This: "naming Family Pterodactylidae implicitly names Superfamily Pterodactyloidea, Subfamily Pterodactylinae, Tribe Pterodactylini, and Subtribe Pterodactylina" looks like a useless rule that no good will ever come of. Why does this rule exist?

    At this point I don't even think of the "-idae" clades as being "families," because there's no such thing. I don't care if one ends up inside another. I guess the new trend in dinosaur nomenclature of using "-ia" instead of "-idae" is good if it allows more freedom from silly ICZN rules.

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  5. Brad, the Principle of Co-ordination (the rule that naming a family automatically implies the superfamily, etc.) rule is there primarily to simplify priorities, so that, for instance, Pterodactyloidea has the same priority relative to Azhdarchoidea as Pterodactylidae has to Azhdarchidae. It looks like a bit of a silly rule on paper, but it turns out to be very convenient in real life (especially as family-group names in zoology took a long time to settle into any sort of system, and working out priorities for them can be nightmarish enough as it is).

    Regarding names ending in "-oidea", the Code says (Art. 29.2) that "The suffix -OIDEA is used for a superfamily name", not "names ending in -oidea are superfamilies", so names like Pterodactyloidea and Echinoidea are not necessarily superfamilies. It is true that the superfamily including Pterodactylus (if used as such) should be called Pterodactyloidea, but as Brad pointed out, all pterosaur workers have developed convenient blind spots to allow them to ignore this little detail (a similar situation existed until recently with the name Elephantoidea).

    Article 29.2.1, coming straight after the bit about rank-endings for family-group names, states that "Names in the genus and species groups which have endings identical with those of the suffixes of family-group names are not affected by this Article", and gives examples such as the frog genus Ranoidea, and the bird species Collocalia terraereginae. And yes, if there was a superfamily based on Oniscoidea, it would be called Oniscoideoidea.

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  6. (Incidentally, note that the other rank-based codes [botanical code, etc.] do not consider all homotypic taxa of the same rank group to necessarily have the same citation. This is a peculiarity of the zoological code, which has larger regulated rank groups.)

    Christopher, I still don't see how this affects priority and homonymy. All that rule says is that Article 29 does not apply to "Ranoidea" since that name was first used for a genus. The article primarily concerns orthography, not priority. By Art. 52.1, Ranoidea the genus still has precedence over Ranoidea the superfamily.

    In fact, look at the last rule of the article, the only one to mention homonymy (italics added):

    29.6. Avoidance of homonymy in family-group names. An author wishing to establish a new family-group name must avoid its homonymy with any known previously established names by forming an appropriate stem from the name of the type genus. (See Article 55.3.1 for the elimination of homonymy between existing family-group names).

    What this says to me is that if Rana has a superfamily but Genus Ranoidea has precedence, then the superfamily should be named "Ranaoidea".

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  7. I think generic names have no need to be distiguished from supra-generic names. Dove genus Columbina is homonym of a subtribe Columbina (from Columba).

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  8. Two commenters so far have asserted that the ICZN allows homonyms between rank groups, but nobody has shown where this is stated in the code. I am unable to find any such rule. In the absence of such a rule, Article 52.1 seems quite clear: there are to be no homonyms, period.

    I'm not sure when Genus Columbina and the Columba-typified family group were named. If the genus was named first, then the subtribe, if named, must have a different name, such as "Columbaina". If the family group was named first, then it seems pretty clear to me that the genus would have to be renamed.

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  9. Columbina dates from 1825; Columbina (if Bock [1994] is correct, which is always a bit of an iffy if) dates from 1820.

    Mike, I totally disagree with your interpretation that 29.2.1 concerns orthography only, not homonymy, I would say that the "not affected" refers to the point in the previous article that publishing a family-group name in one form automatically excludes publication in another form for another taxon (so, for instance, Leptosomidae and Leptosominae are homonyms).

    The other point concerns Art. 11.7.1.1. "[A family-group name must] be a noun in the nominative plural" vs. Art. 11.8. "A genus-group name (see also Article 10.3) must be a word of two or more letters and must be, or be treated as, a noun in the nominative singular". Family-group names therefore cannot be homonyms of genus-group names because the former are plurals, while the latter are singulars.

    There is also the principle expressed in Articles 18 and 23.3.7, that names are not to be deemed invalid on the grounds of tautonymy (a bit of a long shot, yes, but it establishes the principle that genus-group and species-group names, at least, are separate categories).

    Beyond that, I simply have to resort to hand-waving, and the point that, to the best of my knowledge, no-one has ever interpreted the Code to mean that genus-group and species-group names can be homonyms, because family-group and genus-group names have always been treated as separate, non-overlapping entities. I do agree that it is a grievious oversight that something that would require only a single line - "Art. Z. Family-group, genus-group and species-group names are fundamentally separate categories and do not compete for homonymy" is not stated outright and is left to the field of allusion and assumption. Part of the problem is that family-group names were not covered by the old Règles, and the family-group rules have been tacked on over the years. I'm sure that if you looked you'd find even more significant contradictions than this one.

    There's quite a few of these trans-group "homonyms" about, so it could potentially be a fairly notable issue.

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  10. Mike, I totally disagree with your interpretation that 29.2.1 concerns orthography only, not homonymy, I would say that the "not affected" refers to the point in the previous article that publishing a family-group name in one form automatically excludes publication in another form for another taxon (so, for instance, Leptosomidae and Leptosominae are homonyms).


    The previous article is about the case of initial letters in names. At any rate, Art. 29.2.1 says, "not affected by this Article" (emphasis added), i.e., by Article 29. Unless you can find something in that article, not a previous one, I fail to see the relevance.

    Your point about plural vs. singular won't help, either. Consider that one and only one of the following possibilities is true, if "Columbina" is a noun:
    1. "Columbina" is a plural word, not singular.
    2. "Columbina" is a singular word, not plural.
    3. "Columbina" may be plural or singular.
    4. "Columbina" is neither plural nor singular.

    #4 is nonsensical under the rules of Latin grammar. If #1 is true, then it should never have been used for a genus. If #2 is true, then all subtribe names are invalid(!) Clearly, #3 is true, and therefore plurals and singulars can be homonyms. (This is even true in English: look at the singular "sheep" and its plural, "sheep".)

    (a bit of a long shot, yes, but it establishes the principle that genus-group and species-group names, at least, are separate categories)


    That was never in doubt, though. Species-group names consist of two or more words, while other names do not, so it's impossible for them to be homonyms, anyway. I suppose there's the exception of subgenus names, e.g. Subgenus Gorilla (Gorilla) vs. Species Gorilla gorilla, but I'd say those aren't homonyms, either, because they are differentiated by the presence or absence of parentheses (which are a necessary component of the subgenus name). (They are also distinguished by case, but that's a shakier argument. Fortunately, I don't think I need it.)

    So, in the end, you're taking a contextualist position (what did the authors mean to say, even if they never said it?), while I'm taking a textualist position (what did the authors say and what did they mean when they said it?). I think the contextualist approach opens the door to all kinds of confusion (and don't we have enough already?). You're arguing that something that was not written should have precedence over something that was written, and was written twice (point #5 in the Introduction, Art. 52.1). Is that any kind of way for a code to operate? What's the point of even having a code, then, if you already know what they meant to say, and know that when they said the direct opposite (twice!) they didn't really mean it?

    I'm surprised you haven't mentioned Article 53 yet (defining homonymy within rank groups), because that does indicate a sentiment that agrees with your interpretation. However, it fails to explicitly say that names in different groups are not considered homonyms. Either here or Art. 52.1 (or both) would be the place for the authors to speak up, if that's what they intended. (I'm no mind-reader.)

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  11. The stem of a genus ending in -oidea is -oide so it will translate into a family-group name as -oideidae e.g. Cerithidea is in the subfamily Cerithideinae, so homonymy is avoided. Where a family-group name is the same as a genus-group name and this is likely to cause confusion, an application can be made to the ICZN to change one or the other. Such cases are presumably not so frequent that they require an additional Article written into the Code. Anybody is free to propose new names for divisions above family-group level (e.g. Class Echinoida to replace Echinoidea, although preferably avoiding names that have already been used). It is then up to zoologists whether they accept the new divisions or not. Such names that are widely accepted and used can be considered valid.

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