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Re: Ceratopsine phylogeny questions



 While browsing the SVP meeting abstracts yesterday, This was, IMHO,
 one of the more interesting ones:

Quite so!!!

Scannella briefly compared that situation to the synonymy of *Nanotyrannus* and *Tyrannosaurus*, and *Dracorex*, *Stygimoloch* and *Pachycephalosaurus*.

The obvious question -- whether Scannella had looked at postcranial histology, too -- was immediately asked, and immediately answered by "as soon as I get back to the US", which means he started last week. :-)

 As the abstract notes, _Triceratops_ was named before _Torosaurus_,
 so it would seem _Torosaurus_ would be sunk into _Triceratops_.

Correct.

 However, since the type specimen of _Triceratops_ does not exhibit
 the adult frill morphology of the genus, how, if at all, would this
 affect the nomenclature?

Not at all. As long as the type specimen can be shown to the new & improved *Triceratops*, there's no problem.

 In addition, it would seem possible that _Arrhinoceratops_ from the
 older Horseshoe Canyon Fm. might represent the adult morph (and
 senior synonym) of the recently named _Eotriceratops_.  If the latter
 turns out to be the case, are there any real diagnostic differences
 between the adult morph of _Triceratops_ and _Arrhinoceratops_ that
 would justify separating these taxa at the generic level?

What do you mean by "generic level"? There is no such thing as a "generic level". .-)

As long as they can be reliably told apart, which appears to be the case (correct me if I'm wrong), they should be considered different species; whether you want to consider them different genera in addition is entirely left to your (yes, your) taste.

 To potentially muddy the waters further, where does this place the
 taxonomic status of _Torosaurus utahensis_?

Good question. Wasn't mentioned in the talk or the question session. I guess it could be a near-adult ontogenetic stage or a separate southern species of *Triceratops*.