Re: Platecarpus tympaniticus - how to analyze a nomen dubium

[Tim Williams <tijawi@yahoo.com>]

On Mon, 20/9/10, Michael Mortimer <mickey_mortimer111@msn.com> wrote:


> Tim Williams and I have been having quite a discussion on
> the DML this year about nomina dubia and how they should be
> treated.  In the most recent JVP, Konishi et al. (2010)
> present an excellent example of my philosophy in this
> matter.  Platecarpus tympaniticus is the type species of
> this well known genus of mosasaurs.  It's based on
> fragments described by Leidy back in 1865 and ignored
> (Williston, 1898) or declared a nomen dubium (Russell, 1967)
> since.  


Yes, it's a great study.  Over 500 mosasaur specimens were surveyed.  Not a bad 
day's work.


But I think I know where you're headed here.  I'm willing to give taxa based on 
fragmentary material a fair go.  But... IMHO for the sake of taxonomic 
stability, such taxa should not give their names to higher-level taxonomy.  
This is because phylogenetic definitions of family-level clades include the 
name-giving taxon as a specifier (which makes sense), so we should choose 
name-giving taxa with care.


I notice _Platecarpus_ hasn't given its name to any superfamilies, families, 
subfamilies, or tribes.  So unlike _Stegosaurus_ or _Ceratops_, its status has 
no knock-on effects for higher-level taxonomy.


> Incidentally, note that despite the fact Russell
> thought it was indeterminate within the genus Platecarpus,
> he retained it as the type species and kept other diagnostic
> species in the genus (like I'm recommending for
> Stegosaurus).


This sounds like a very bad idea.  Note that a fossil species is supposed to 
represent a distinct biological entity: a species.  Maintaining a 
non-diagnostic type species solely for bookkeeping reasons strikes me as going 
against the entire purpose of biological taxonomy.  


Taxonomy is not just about compiling lists.  It's a way of classifying real 
species.  If we cannot demonstrate that _S. armatus_ was a separate species 
(because the type material cannot be distinguished from diagnostic 
_Stegosaurus_ species) then the taxon is toast.  P
here's no good evidence that this ever represented a real species, then let it 
go.  There's no point converting it into an OTU, and running a phylogenetic 
analysis with it - all for the sake of keeping Ceratopsidae afloat.  Sure, 
_Ceratops montanus_ might be a real taxon; but we're probably going to need 
more material to confirm this.  Until this day comes (and it may never come), 
then let's stop playing silly-buggers and pretending that it's fine to have 
_Ceratops_ as an appropriate name-giving genus for an important family of 
dinosaurs.



Cheers

Tim