Re: New papers in Geobios (and nomenclatoral gripe)

[Tim Williams <twilliams_alpha@hotmail.com>]

Mickey Mortimer wrote:

> To me, it seems a major problem in our disagreement is that you're giving 
> genera some special significance and tie with their type species

It is the ICZN that ties the genus to its type species.  It is quite 
explicit on this point...

Article 61. Principle of Typification.

61.1. Statement of the Principle of Typification. Each nominal taxon in the 
family, genus or species groups has actually or potentially a name-bearing 
type. The fixation of the name-bearing type of a nominal taxon provides the 
objective standard of reference for the application of the name it bears.

61.1.1. No matter how the boundaries of a taxonomic taxon may vary in the 
opinion of zoologists the valid name of such a taxon is determined [Art. 
23.3] from the name-bearing type(s) considered to belong within those 
boundaries.

61.1.2. Objectivity provided by typification is continuous through the 
hierarchy of names. It extends in ascending order from the species group to 
the family group. Thus the name-bearing type of a nominal species-group 
taxon is a specimen or a set of specimens (a holotype, lectotype, neotype or 
syntypes [Art. 72.1.2]), that of a nominal genus-group taxon is a nominal 
species defined objectively by its type; that of a nominal family-group 
taxon is the nominal genus on which its name is based.

61.1.3. Once fixed, name-bearing types are stable and provide objective 
continuity in the application of names. Thus the name-bearing type of any 
nominal taxon, once fixed in conformity with the provisions of the Code, is 
not subject to change except in the case of nominal genus-group taxa as 
provided in Article 70.3.2, of nominal species-group taxa as provided in 
Articles 74 and 75, and by use of the plenary power of the Commission [Art. 
81].

> And a species can be indeterminate within various levels of taxonomy, 
> including genus.

I follow the logic of your argument, but your argument is based on 
phylogenetic taxonomy, not nomenclature.   The ICZN deals purely in 
nomenclature, and the ICZN says it can't be done.

To examine your _Hadrosaurus_ analogy, you may indeed be able to demonstrate 
phylogenetically (such as based on shared derived characters) that 
_Hadrosaurus foulkii_ belongs in the Hadrosauridae; but the ICZN already 
treats this as a given.  Further, because the name-bearing type (_H. 
foulkii_) is indeterminate at the species level, both the genus- and 
family-level groups named after it are also invalid (61.1.2.).  It's a house 
of cards, I'm afraid.  Your phylogenetic rationale is spot-on, but the ICZN 
just isn't interested.

My analogy is the example of _Iguanodon anglicus_.  This was the original 
type species for _Iguanodon_, but it was based on type material that was 
specifically indeterminate.  The ICZN does not care how well known this 
genus is based on referred material, such as the excellent _I. 
bernissartensis_ specimens (61.1.1.).  You may say that _I. anglicus_ is 
different from _Hadrosaurus_, because it may have been difficult to 
demonstrate based on shared characters that _I. anglicus_ belongs in 
_Iguanodon_ given the inadequacy of the _I. anglicus_ type material.  But in 
the eyes of the ICZN, this doesn't matter.  The ICZN says that, as the type 
species, _I. anglicus_ MUST be in _Iguanodon_, and the validity of 
_Iguanodon_ is determined by the validity of _I. anglicus_ ("objective 
standard of reference"; 61.1.).

Rather than allow _Iguanodon_ to be sunk, in March 2000 the ICZN agreed to 
set aside _I. anglicus_ as the type species, and replace it with _I. 
bernissartensis_.  Thus, _Iguanodon_ was saved, because the ICZN determined 
that it was better for the purposes of nomenclatural stability to keep the 
genus alive.  Most genera with crappy type species aren't so lucky.  
_Mochlodon_ is one such example; nobody is going to petition the ICZN to 
ensure that the genus _Mochlodon_ is valid.  It doesn't quite have the same 
cachet as _Iguanodon_ or _Coelophysis_.  Poor _Mochlodon_.  :-(

> Now ranks don't really matter here.  Families and genera don't need to be 
> objctive entities for the examples to work, they just represent 
> phylogenetic levels where we have potentially competing names.

In a phylogenetic universe, this makes perfect sense.  But the ICZN has a 
narrower view of the world, and puts a lot of stock in the quality of the 
type.

> Another way of looking at it is that suessi is a nomen dubium because it 
> can't be distinguished from at least two valid entities (robustus and 
> shqiperorum).  But Mochlodon is synonymous with another taxon, because it 
> can't be distinguished from only one valid entity (Zalmoxes).  And because 
> Mochlodon has priority over Zalmoxes, it's a senior synonym.

Because the type of _Mochlodon suessi_ (originally _Iguanodon suessi_) 
cannot be distinguished from two other species (_Zalmoxes robustus_ and _Z. 
shqiperorum_), it is a nomen dubium.  (Unless _robustus_ and _shqiperorum_ 
are shown to be synonymous, then _M. suessi_ is valid and gets priority over 
both.)  As a nomen dubium, _Mochlodon_ must be removed from taxonomic usage, 
because the genus is tied to the type species.

Cheers

Tim