[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
RE: Ceratops (was RE: Glishades ericksoni, ...)
Michael Mortimer <firstname.lastname@example.org> 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.
> 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 with _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
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
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.
> 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."