[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Oviraptorosauria (and Abelisauroidea)



John R. Hutchinson wrote:
>Sues never explicitly defined it although his use of the term implied a
>node-based definition
        Although he did give a definition of _Caenagnathidae_ (inae?)
including a very large number of anchor taxa (one of which was simply a
specimen).

>You're right that it doesn't matter much; _Abelisaurus_ and _Carnotaurus_
>are clearly close relatives.
        True, but should we not separate phylogenetic taxonomy as much as
possible from our preconcieved notions of phylogeny? _Saurolophus_ and
_Parasaurolophus_ may be "clearly" good hadrosaurines and lambeosaurines
respectively, but if Horner's phylogeny is correct, Sereno has defined
_Hadrosaurus_ out of the Hadrosauroidea. Suuure, sooner or later we have to
make a cut, but as Mike points out, the "Ornithosuchia problem" shows the
potential to rear its ugly head time and again. Just look at many of
Sereno's proposed definitions.
        
        As an aside, someone involved with said paper said a while back that
they thought giving definitions in the form "CARNOSAURS sharing a more
recent common ancestor with X than with Y" was a good idea and did something
worthwhile. Anyone care to elaborate? Sounds like an idea which is very much
*against* the principles of PT (i.e. recognizing real groups, no matter
where they may be in the phylogeny). Anyone care to comment.
        
        On a related subject (of course, all subjects are related... :),
someone also mentioned that they didn't like multiple anchor taxa, as these
did not promote stability. I tend to feel the opposite is true, and I'd be
interested in hearing why people think this. Probably off-list would be
appropriate, since this is a dinosaur forum.

        (BTW: I haven't read the paper yet, because my membership
application appears to be holed up somewhere in the SVP in-basket.)

>Just like it's a bit safer and more operational
>to define archosauromorph subclades by reference to living/well known
>archosauromorphs rather than to _Archosaurus_.  Again, no rules yet.
        This is, I must admit, a situation where the "rules" may need to be
relaxed. In this case, it has to do with the taxonomic history of the
Archosauria, which does seem to be rather independant of _Archosaurus_. A
simlar argument might even be made for some more exclusive taxa, such as
Ceratopsia. However, in the realm of the "family-rank taxon", these taxa
have traditionally been associated with a type genus. Obviously, such
traditions are meangingless in PT. However, in the change to a phylogenetic
system, we must try to respect the original intent of these taxa as much as
possible.

T. Mike Keesey wrote (quoting JRH):
>> You're right that it doesn't matter much; _Abelisaurus_ and _Carnotaurus_
>> are clearly close relatives.  In this case we made an exception and used
>> the better known specimen (_Carnotaurus_ has a good skeleton; _Abelisaurus_
>> is much more fragmentary).
>
>But if
>A) They are *clearly* close relatives, where's the danger in using
>_Abelisaurus_ as the anchor?
        None whatsoever, except:
1) Abelisaurus is less likely to show up on a cladogram (I don't think it
was on the Majungatholusgram, come to think of it), which may lead people to
wonder how anyone feels justified in applying the definition. IMHO, this is
an understandable concern, but not worth risking #2 below.

2) There always exists the possibility that _Abelisaurus_ is not so closely
related to _Carnotaurus_.
        This, of course, would distress everyone involved. No matter how
hard we try to accept PT, we are used to thinking in typological terms. We
all *know* what an "abelisaur" is, and we don't want to think about it being
something different. Oddly, this is an instance where Linnean taxonomy may
have a slight advantage. In Linnean taxonomy (according to my
understanding), you can't define a family with a non-eponymous type genus.
The Linnean taxonomist is perfectly happy to accept that the Abelisauridae
might include very few of the taxa he thought it did at one time.
        For some reason there seems to be resistance to accepting that
phylogenetic taxa *must* be allowed to be fluid as well. If we start trying
to "stabilize" p-taxa to conform to our expectations we abandon the
philosophical basis (indeed, the philosophical superiority) of PT and PT
becomes nothing more than another clever way to define typological (although
monophyletic) taxa.
        I am ranting like a good purist, and I don't really expect anyone to
be enthusiastic about this perspective. I have noticed that the
philosophy-driven approach is frequently dismissed in favor of more
"workable" or "practical" ideas. However, I must reiterate that failure to
adopt PT in the form it was originally described (i.e. recognizing natural
groups in the phylogenetic record regardless of preconcieved notions) will
result in a system which is only slightly better than more traditional
phylogenetic (cladistic) schemes. IMHO, that wouldn't be worth the effort.

>B) There is any doubt due to _Abelisaurus_' fragmentary nature,
>wouldn't it be safer to anchor with _Abelisaurus_ anyway?
        Or, the other alternative is to name Carnotauridae. An unpleasant
prospect, but possible. A third alternative is to name the more inclusive
groups something other than "Abel-jank", such as Gondwanaeatumupus [long u,
George, plural of... is it fourth of fifth declension?) or whatever. Again,
of course, for access to the literature, adopting a traditionally accepted
term is better.        
        I love being a purist. All the "jocks" get to make fun of you
because you are "causing trouble" and making things "too complicated" for no
good reason, aall the "wannabes" get to poo-poo you because you're not doing
things the right (i.e. traditional) way, and all the progressives wish you'd
shut up so they can effect at least some change. And then there's all the
other purists who don't have it quite right, do they...? :)

        Later y'all,
        
        Wagner
--------------------------------------------------------------------------------
     Jonathan R. Wagner, Dept. of Geosciences, TTU, Lubbock, TX 79409-1053
 "Only those whose life is short can truly believe that love is forever"-Lorien