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

Michael Mortimer <mickey_mortimer111@msn.com> wrote:

> The phylogenetic analysis would still allow us to establish
> the relationships of Ceratops- it just might indicate a
> range of relationships are possible.  But this is
> useful information to have if we're trying to determine if
> Ceratops is a member of the Chasmosaurus+Centrosaurus
> clade.

Hmmm... you know, I would have said the exact opposite.  If a range of 
relationships is possible for _Ceratops_, including both *inside* and *outside* 
the Chasmosaurus+Centrosaurus clade being equally parsimonious, then it would 
seem to me that _Ceratops_ is utterly useless as a specifier.  

> When people say that non-chasmosaurine+centrosaurine taxa
> may have Ceratops-like brow horns, I recall it basically
> referring to their large size.  But other variables
> like curvature, orientation, etc. may apply as well.

In the case of _Ceratops_, these variables do indeed apply.

> Since as I noted, we can include any taxon in a
> phylogenetic analysis, I suppose your criterion would be a
> family eponym has to have an exact placement when included
> in an analysis?  But this doesn't work either. 

No, I'm not saying that either.  _Ceratops_ is a nomen dubium, which adds an 
extra complication.  Read on... 

> Think of Troodontidae (or Saurornithoididae if you think
> Troodon's type is problematic).  Last time I heard, we
> don't know where Saurornithoides or Troodon go in comparison
> to other derived troodontids like Zanabazar, Borogovia,
> Tochisaurus, etc..  How is that different than not
> knowing where Ceratops goes relative to Albertoceratops,
> Anchiceratops, Arrhinoceratops, Pentaceratops, Agujaceratops
> and Triceratops?

It is different because _Ceratops montanus_ is a nomen dubium, so the name is 
limited to the type specimen *only*.  As a nomen dubium, no further material 
can be referred to _C. montanus_, and the type specimen for _C. montanus_ 
cannot be referred to another genus or species.  This is the unhappy fate of a 
nomen dubium.

Unless something changes - such as designating a new type specimen (neotype) 
for _Ceratops_ - it will always be a nomen dubium.  So the name _Ceratops_ will 
always be limited to those two horn cores + occipital condyle.  

_Saurornithoides_ and _Troodon_ are a different matter altogether.  There is an 
excellent chance that further troodontid specimens will help resolve the 
positions of these taxa within troodontid phylogeny.  But _Ceratops_ is a lost 

> Lots of valid taxa are based on single elements- Kemkemia,
> Ozraptor, Becklespinax, Iliosuchus, Kakuru, Rapator,
> Unquillosaurus, Caenagnathasia, Pneumatoraptor,
> Richardoestesia, Itemirus, Urbacodon, the famous
> Xenoposeidon...

True.  But these specimens have automorphies, or at least novel character 
combinations.  Neither applies to _Ceratops_.  

Look, I know the term 'nomen dubium' is subjective.  I'm certainly not 
advocating regarding all taxa described from a single element as a nomen 
dubium.  But in many cases it is quite obvious that a name is a nomen dubium.  
One example is the original type specimen for _Iguanodon_.  That's why a 
neotype needed to be designated for _Iguanodon_ (including a new type species). 

If the original _C. montanus_ locality is re-discovered, and comparable 
diagnostic material is found that matches the type specimen (i.e., specimens 
that have very long and strongly laterally oriented postorbital horn cores), 
then a case could be made to switch the type specimen to a specimen that is 
diagnostic.  But this hasn't happened.

> Or
> is horn core orientation variable enough between individuals
> and throughout ontogeny that this isn't actually a useful
> feature after all?  

That is my impression.  Ryan (2007) actually addresses this point: 

    "All Chasmosaurinae, with the exception of Chasmosaurus belli, C.
    irvinensis, and C. russelli, have robust orbital horncores, and 
    individuals of some taxa can show a pronounced lateral inflection of 
    the horns. Given that the holotype material of Ceratops montanus lacks 
    diagnostic features it must remain a nomen dubium."