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Re: Coelophysis/Rioarribasaurus



Norm King wrote:

<<Dinogeorge wrote (date/time?):

>Subsequently it has been suggested on the basis of obdurator
>foramen differences that there are probably 3 genera of small
>theropods at Ghost Ranch (Coelophysis, Rioarribasaurus and
>Syntarsus).>>

Sorry--I didn't write the above; Norm did. I just responded to it. (And I
probably wouldn't have misspelled "obturator," either.)

And Norm wrote:

<<Why should the obturator foramen be so important?  How variable is it in
large populations of coelophysids, especially in populations from
different locations?  On what basis SHOULD coelophysid genera be
distinguished, and why?  Why not establish three _species_ differentiated
on the basis of obturator foramen?:

                        _Coelophysis bauri_
                       "_Coelophysis euobturator_"
                       "_Coelophysis oddobturator_"

I'll bet that the mythical "Coelophysis obturator_" comes in three
variants of the fourth trochanter--acute, obtuse, and pendant.  Should we
therefore have two more species or two more genera?  How about just three
subspecies?>>

Sure. Why not?

In the final analysis, there is _no_ way to judge which features are
important in diagnosing a taxon; certainly not in advance of the study!
Cladists, for example, just accumulate characters, set up their  matrices,
and plug and chug the matrices through PAUP or HENNIG86, letting the computer
decide what's "important." But who's to say whether this method is any better
or more justifiable than any other? The type specimens of _Coelophysis bauri_
and _Rioarribasaurus colberti_ differ. Whether these differences are the
result of their belonging to different genera, different species, or merely
different individuals of the same species cannot be determined, because we
don't have living populations of these animals to examine and study.

But: _Coelophysis bauri_ and _Rioarribasaurus colberti_ occur in strata of
different ages, which makes it _more likely_ that they're at least in
different species, probably in different genera. Pending publication of
Sullivan et al.'s paper on the subject, that's all we can say.

And Norm wrote:

<<[Quoting me] >As far as I know, _Coelophysis_ itself has not been
identified >at Ghost Ranch (except by Colbert and those who agree with him,
of course).

Wait a minute!  Colbert identified it there FIRST, and that's what it was
called for decades!  "Except by...those who agree with him," you say.
But there were ONLY people who agreed with him for over 40 years!>>

Sorry, but that's not entirely correct. Kevin Padian's paper a decade ago on
_Coelophysis_ suggested there might well be differences between Cope's type
material and the Ghost Ranch theropods. One problem was that for 40 years _we
all had only Colbert's word_ on the identification, because not until 1989
did he publish his major study of _Coelophysis_, in which he actually tried
to compare Cope's types with the Ghost Ranch material. It was this
publication that inspired Hunt & Lucas's "rebuttal" paper. It is a testament
to Colbert's stature in vertebrate paleontology that his word was accepted
for so long _without_ a formal systematic study of the material.

And Norm wrote:

<<[Quoting me again:] >Bob Sullivan is working on a new diagnosis for
_Coelophysis_ >that distinguishes it from the Ghost Ranch theropods.

He could just as easily formulate a diagnosis to make all of the Ghost
Ranch theropods into _Coelophysis_.>>

Yes, by disregarding the differences between the type specimens. This is a
good thing? Why not return to the days of the 19th century, when all
pterosaurs were described as species of _Pterodactylus_, all theropods were
described as either _Megalosaurus_, _Deinodon_, or _Laelaps_, and all
duckbilled dinosaurs were described as _Trachodon_ or _Hadrosaurus_. The
point of creating a diagnosis is to _distinguish_ a taxon from its close
relatives of similar morphology.

And Norm wrote:

<<Quoting me: >Presently, we are free to use either _Coelophysis_ or
>_Rioarribasaurus_ for the Ghost Ranch theropods.

See?>>

See what? Now that the ICZN has become involved, it's a whole new ball game.
Now we have to await their ruling before we know which is the correct name
for the Ghost Ranch theropods, and also for Cope's original type material of
_Coelophysis_. And the ICZN knows NOTHING about dinosaurs, believe me.

And Norm wrote:

<<I admit that I am not an expert on coelophysids, so I won't continue on
this crusade, which I fear is lost, anyway.  My point is (and see my
previous posting in response to Bob Myers) that this situation is
unnecessarily complicated, and could have been handled better.  Why not
plan to handle similar situations in the future differently?  PLAN is the
operative word in that suggestion--remove the elements of chaos and
coersion.  Hunt and Lucas might have discussed their findings with
Colbert, and they could have issued a joint paper, or two papers
back-to-back, discussing the issue.  In absence of that, Hunt and Lucas
could have announced beforehand that they planned to establish a new
genus for the Ghost Ranch material, and their justification.  It might
have been good to get all the type material together and made available
for direct comparison by anyone interested--perhaps at a special session
at an SVP meeting.  With feedback from the paleontological community, the
perceived best course of action could have been taken that might have
avoided much or all of the confusion and other adverse effects caused by
decisions made by a relatively small group of people, announced as a
_fait accompli_.>>

Mein Gott!! This is FAR FAR FAR more complicated than simply publishing the
paper in which Hunt & Lucas presented the results of their work. That's all
any scientist is obliged to do. The type material for both _Coelophysis_ and
_Rioarribasaurus_ is at the American Museum of Natural History, available for
direct, practically side-by-side comparison by anyone who can get into the
collections. Hunt & Lucas aren't coercing anyone; they're simply saying, go
look at the material yourself, if you don't believe us.

In this situation, the "chaos" was caused entirely by those who
_unnecessarily_ petitioned the ICZN to remove the name _Coelophysis bauri_
from the specimen(s) to which Cope had attached it and to attach it to the
type specimen designated by Hunt & Lucas for _Rioarribasaurus_. This directly
infringed on the right of all scientists (not just Hunt & Lucas) to designate
as a holotype whatever specimen they feel like so designating. It also
violated the historical context of the taxon _Coelophysis bauri_.

Hunt & Lucas offered the name _Rioarribasaurus colberti_ for the Ghost Ranch
theropods. The vert-paleo community is free to reject their name simply by
NOT USING it and by continuing to use _Coelophysis bauri_ for those
theropods. In formal systematic studies of _Coelophysis bauri_, for example,
workers would just list _Rioarribasaurus colberti_ among the junior synonyms
of the species. This is the only proper response by those who disagree with
Hunt & Lucas's position. Eventually the proper name for the Ghost Ranch
theropods would float to the surface.