Hi!

As far as I know, the "page precedence" does not matter. Although it is used by some taxonomists, it is not written anywhere in the ICZN. As you said and according to the article 24 of the ICZN, if two taxa were published in the same publication, you should follow the authority of the first reviser of the group. In your case, that may be Carvalho et al. 2003 or some older publication yet to be identified.

Antoine is right, there is no such thing as “page priority”, so if you can clearly identify the first reviser/revisers, you must follow his/her/their recommendations. “Position precedence” only affects type species (see: http://iczn.org/content/there-such-thing-%E2%80%9Cpage-priority%E2%80%9D).

I agree with Antoine and Balazs. Page precedence is not a rule. Anyway the Eshmeyer catalogue already lists Potamotrygon dumerilii  as a synonym of  Potamotrygon orbigny

Thank you Antoine, Balázs and Edoardo! Like Antoine said some taxonomist friends suggested that the page could have precedence, although it is not written in the ICZN. I'll try to figure out if there is an older publication that already lists P. dumerilii as a junior synonym of P. orbignyi, but I don't think so.  

Thank you very much!

Page priority is not relevant. The first reviser is difficult to ascertain in this case; Carvalho et al. in Reis et al. (2003: 25) chose P. orbignyi as the valid name.

There is no real need to find the formal first reviser and stick to his decision. As the preamble of the Code points out:

“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.”

I would therefore suggest to follow the recently accepted name Potamotrygon orbignyi (Castelnau 1855) with Trygon dumerilii Castelnau 1855 as a junior synonym, as to promote stability of nomenclature in this group.

As a further comment, there is a discrepancy of spelling of the species name; Castelnau (1855) alternatively used ‘d’orbignyi’ (in the text) and ‘orbignyi’ (in the figure caption). However, the majority of subsequent authors has used the spelling Potamotrygon orbignyi; this spelling should be conserved, again to promote stability.

I agree with the statements above.

There is no such thing as 'page priority' and thus it seems wise to promote stability by sticking to the 'First Reviser's' decision of synonymity:

“24.2. Determination by the First Reviser.

24.2.1. Statement of the Principle of the First Reviser. When the precedence between names or nomenclatural acts cannot be objectively determined, the precedence is fixed by the action of the first author citing in a published work those names or acts and selecting from them; this author is termed the "First Reviser".

24.2.2. Determination of precedence of names or acts by the First Reviser. If two or more names, different or identical, and based on the same or different types, or two or more nomenclatural acts, are published on the same date in the same or different works, the precedence of the names or acts is fixed by the First Reviser unless Article 24.1 applies.“

However, as a general guideline (but not as a rule!) it might be a good idea to use a 'page priority' in cases where there is no previous nomenclatural action of the taxa involved, or in other words: if one is the 'First Reviser'. (which is not the case in the given problem of sting rays).

I also give similar advise about different spellings of species names (for first revisers): if the original description of a species contains different spellings of the same name I would give the spelling used in the text precedence over the spelling used in captions.

Generally the 'First Reviser' chooses the correct spelling of a name with multiple spellings in the original publication: “24.2.3. Selection of correct original spellings. If a name is spelled in more than one way in the original work, the first author to have cited them together and to have selected one spelling as correct is the First Reviser. The selected spelling (if not incorrect under Articles 32.4. or 32.5) is thereby fixed as the correct original spelling; any other spelling is incorrect (and therefore unavailable [Art. 32.4]). “

The ICZN code contains an option to determine the correct spelling by usage of one particular spelling in favour of another in subsequent publications of the original author: “24.2.4. Original authors may be deemed to be First Revisers of spellings. When the author, or one of joint authors, of two different original spellings of the same name subsequently uses one of them as valid in a work (including the author's or publisher's corrigenda), and neither had previously been selected as the correct spelling by a First Reviser, the author is deemed to be the First Reviser, whether or not the author cites both spellings together (that used as valid becomes the correct original spelling). “

So in your case, João Paulo Capretz Batista Da Silva, the principle of 'first reviser' is not only used to determine the correct spelling (‘d’orbignyi’ (in the text) vs. ‘orbignyi’ (in the figure caption)) but also to determine precedence of names (as both homonyms are from the same original publication).

I agree with both you Ronald Frickle and Jens Carl Dieter Kosh. Thank you for your helpful comments. I'm following the principle of 'First Reviser' as indicated by you. The correct spelling was determined by Duméril (1865) and followed by most of subsequent authors (Gunther, 1870; Ribeiro, 1907; Garman, 1877, 1913; Rosa, 1985; and many others). 

However, as indicated by the code only the apostrophe should have been removed and the correct spelling would be dorbignyi.

"32.5.2. A name published with a diacritic or other mark, ligature, apostrophe, or hyphen, or a species-group name published as separate words of which any is an abbreviation, is to be corrected."

"32.5.2.3. In a compound species-group name published as words united by an apostrophe or a hyphen, the words are to be united by removing the mark concerned (but see Article 32.5.2.4.3)."

Nevertheless, as pointed out by Ronald Frickle, the spelling orbignyi was used by most of subsequent authors and should be maintained in order to promote stability.

Thank you very much for this clarifying discussion!

Jens, in his last comment, suggested that it would be a good idea to follow the "page priority" when no "First reviser" is known.

After giving it some thought, I think that would be a better idea to give priority to the species that is best defined, that is the species with the most complete type material, and the most detailed diagnosis (if any).

For example, giving the priority to a species name defined based on a complete cranium compared to a species name defined on a single tooth (not as uncommon as it could seem) would greatly simplify the work of subsequent taxonomists working on the same group and prevent the creation of even more nomenclatural puzzles.

Not sure if that's clear, but in some cases similar to the example I gave, that seems to be a better idea than just following the "page priority".

Best,

Antoine

I agree with with Antoine Souron's statement about type specimen completeness.

In cases where one homonym species is described under different names in the same original  publication and one of these proposed species is based on more complete material, it makes sense to favour the species name based on the more complete dataset. I would use 'page priority' only as a guideline when both species are based on type material that is of similar completness.

Thanks for clarifying that, Antoine. It seemed obvious to me, but it's good to phrase it in a more precise way.

The holotypes of both species are greatly distorted, fluid-preserved specimens, neither of which appears superior to the other. Have a look at the photos available online:

http://science.mnhn.fr/institution/mnhn/collection/ic/item/0000-2333

http://science.mnhn.fr/institution/mnhn/collection/ic/item/0000-2367

Physical classification is highly essential.

Dear Joåo,

In the 2013 "Rayas de agua dulce de Suramérica" (Lasso, Rosa, Sanchez-Duarte, Morales-Betancourt & Agudelo-Cordoba Eds), both combinations of names appear as valid species (with the correction spelling dumeril to dumerilii), and also you are co-author of P. orbignyi. I understand that you will proposed that they were synonyms. I am right? Please, could you clarify this point? Thanks a lot!

Dear Gustavo Chiaramonte,

The spelling dumerilii has been used correctly since the original description of the species by Castelnau (1855). So, the spelling was not corrected in "Rayas de agua dulce de Suramérica". During my masters I proposed that P. dumerilii fell within the range of intraspecific variation presented by P. orbignyi (based on several morphological characters, including external morphology and internal anatomy). Consequently, I considered it as a junior synonym of P. orbignyi. However, in "Rayas de agua dulce de Suramérica", I did not coauthor the chapter of P. dumerilii since I had uncovered a series of morphological evidence not to consider it as a valid species. Currently there is a disagreement in considering P. dumerilii as valid or not, and some researchers still consider this species as valid (based exclusively on dorsal disc coloration). That is why I only coauthored the chapter of P. orbignyi, which is the only valid species in my opinion. I pretend to publish the results of my masters until the end of this semester showing all the morphological characters that led me to this conclusion. However, nomenclatural acts are only valid in published works, which is not the case of my master’s dissertation. In the meantime and even in the future, I cannot prevent other researchers to consider P. dumerilii as a valid species, but only present in a published work as much morphological evidence as possible in order to substantiate my hypothesis.

I hope I have clarified this topic for you.

Best,

João

Dear João, I understand you perfectly, and hope you can publish the results of your master successfully. I'll be waiting for them. Meanwhile, I'll take your opinion into account in any future work that may involve this / these species. Thank you very much. Regards

Gustavo