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RE: Ceratops (was RE: Glishades ericksoni, ...)
Tim Williams 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
> 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.
I agree in that case it would be useless as a specifier for that clade. My
point is that we need to determine if it is a member of that clade, and if it
is, then I would advocate using it as an internal specifier.
> 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.
That's too fatalistic for me, considering the small amount of study that's been
devoted to Ceratops. Remember what I wrote to Jaime regarding tyrannosaurid
pes, which have always been considered undiagnostic between genera. Yet Carr
(2005) studied them for his Alectrosaurus redescription and found hundreds of
variable characters. Maybe ceratopsid postorbital horn cores and occipital
condyles are similar in that regard, and maybe they're not.
>> 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."
That one sentence isn't enough for me. Is "pronounced lateral inflection" as
pronounced as in Ceratops? It's evidently not as pronounced as in
Albertaceratops, for instance. Which individuals of which taxa are we talking
about? How are they different from other individuals of the same age or
different age? My point is that far too often, taxa are relegated to nomen
dubium status based on broad statements like these that are more assertion than
demonstration. I'd like some detailed study of ceratopsian postorbital regions
and occipital condyles, with figures and measurement tables, which concludes
explicitly that "variables x, y and z of Ceratops can be seen to overlap both
taxa A and B within the range of individual variation demonstrated here for
ceratopsid taxa." THEN I'll be satisfied a taxon is a nomen dubium. High
standards, sure. But we're relegating someone's taxon to the trash heap. It's
the least we can do.
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