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RE: Ceratops (was RE: Glishades ericksoni, ...)



Michael Mortimer <mickey_mortimer111@msn.com> wrote:


> Er... there's nothing stopping someone from including
> nomina dubia in phylogenetic analyses.  


Of course there's nothing stopping someone from including _Ceratops montanus_ 
in a phylogenetic analysis.  But this is not the same as saying that there is a 
*good* reason for including _Ceratops montanus_ in a phylogenetic analysis.    


Your suggestion is just special pleading.  _Ceratops_ is the name-bearing genus 
for the Ceratopsidae, and therefore you are pretending it's a useful OTU for a 
phylogenetic analysis.  But it isn't.  The type material of _Ceratops montanus_ 
could belong to any number of derived, brow-horned ceratopsians - including (as 
noted by Ryan, 2007) _Albertaceratops_.  In fact, decent cranial material that 
was thought by Trexler and Sweeney (1995) to belong to _Ceratops montanus_ was 
later assigned to _Albertaceratops_.  


Including a deliberately phoney OTU like _Ceratops_ in a phylogenetic analysis 
alongside valid OTUs (like _Albertaceratops_) defeats the entire purpose of a 
phylogenetic analysis, which is to establish relationships among taxa.  


> It will just
> make a polytomy in the range of all the taxa it cannot be
> distinguished from.  And if that polytomy is within the
> Chasmosaurinae+Centrosaurinae clade, then using Ceratopsidae
> for that clade is just fine.


Does that mean we should include every other crappy ceratopsian fossil in a 
phylogenetic analysis, simply because it has a name?  All those awful 
_Dysganus_ species, for example?  Of course not.  There's no reason why we 
should be treating _Ceratops_ any differently to other ceratopsian nomina 
dubia.  


> My preference would be to only abandon names if the
> eponymous taxon isn't necessarily located within that
> clade.  


Yes, I agree.  But as pointed out by myself and others, there is no good 
evidence that _Ceratops_ actually belongs in the Ceratopsidae, because 
non-chasmosaurine and non-centrosaurine ceratopsids may indeed have 
_Ceratops_like orbital horns.  


However, you are advocating defining Ceratopsidae such that it *must* include 
_Ceratops_, which from where I'm sitting is putting the cart before the horse.  
If a genus does not qualify as a valid OTU, it shouldn't be put into a 
phylogenetic analysis.  And if the genus can't be put into a phylogenetic 
analysis, then we shouldn't be using it to name family-level taxa after.


> "Dubious" is just too subjective a notion.  


Not in the case of _Ceratops montanus_.  I mean, come on!  Two horn cores and 
an occipital condyle??!!  


> Of course this requires actual hard work and
> exhaustive comparison instead of just saying "Taxon X is
> only based on one bone whose original diagnosis is no longer
> valid- it's undiagnostic."  Has anyone actually tried
> to compare Ceratops to other related taxa?  


Yep.  The hard work has been done, by the likes of Penkalski and Dodson (1999) 
and Ryan (2007).  Based on comparisons with other ceratopsian taxa, both 
studies concluded that _Ceratops_ was a nomen dubium.  (There might be other 
studies too - these are just the ones that come to mind.)  



Cheers

Tim