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Re: pelicanomimus



> From: tholtz@geochange.er.usgs.gov
> > >
> > >Ah, this is important.  Assuming for now that this is a valid
> > >synapomorphy, not a convergence, it forbids placing Pelecanimimus
> > >is a stem group ("Coelurosauria") AND Harpymimus in Ornithomimosauria.
> > >[That would make either the "stem" group or the ornithomimosaurs
> > >polyphyletic, which no biologist will accept].
> > 
> > What the hell are you talking about?  It does nothing of the sort.  A whole
> > range of synapomorphies place ornithomimosaurs in Coelurosauria (see
> > Gauthier) and additional characters show that Ornithomimosauria is a member
> > of the coelurosaurian subgroup Maniraptora (the aforementioned ref. 23). 
>
>The difference here is the difference between the stict cladistic
>approach to taxonomy and the non-cladistic approach.  I treat
>Maniraptorea as a taxon that may, or may not, include all of the
>descendents of the latest common ancestor of its members.

Again, I have exactly the same complaint as you're usage of Ornithodira. 
Maniraptora was specifically a cladistic taxon named by one of the most
rabid cladists you're likely to find.  If you want a "parataxon" (in the
sense of Olshevsky) for the group you want to describe, come up with a new
one (or maybe use Deinonychosauria).


>What I was trying to get at was that if Pelecanimimus is closer
>to Ornithomimidae than Harpymimus is, then there are three valid
>alternatives, unless one is a cladist:
>       1) place both Harpymimus and Pelecanimimus in
>          Ornithomimosauria

Actually, this is a perfectly good cladistic option, and the one I take.

>       2) place both in the paraphyletic stem group, whatever
>          one wishes to call it.
>       3) place Pelecanimimus all by itself in a more derived
>          group than Ornithomimosauria; which seems like excessive
>          splitting to me.

I agree.  However, you do exactly that with your

>At the time I wrote the above, I was using "Coelurosauria"
>as the name of the stem group for the entire nexus under
>consideration.  However, as it really only includes Compsognathidae,
>that is probably a poor choice of name.

Agreed.  Compsognathidae would be a better term for what you are
describing, and one which would be less likely to get my dander up. ;-)

>
>After evaluating the new evidence, I am considering a classification
>something like the following:
>
>       Taxon A (?Coelurosauria)
>           Stem taxon (?what to name it?)
>               Compsognathidae
>           Maniraptorea
>               Dromaeosauidae
>               Oviraptoridae
>               Avimimidae
>               Caenagnathidae (= Elmisauridae)
>               Troodontidae
>           Ornithomimosauria
>               Harpymimidae
>               Pelecanimimidae
>               Ornithomimidae
>           Segnosauria
>               Alxasauridae
>               Therizinosauridae (= Segnosauridae)

In my present classification, Compsognathus is the sister taxon to
Maniraptora.  Within Maniraptora are the monophyletic groups Ornitholestes,
Therizinosauroidea (=Alxasaurus + Therizinosauridae), Oviraptorosauria
(=Oviraptoridae + Caenagnathidae), the Dromaeosauridae-bird clade, and
Arctometatarsalia (=Avimimidae + Elmisauridae + Tyrannosauridae +
Bullatosauria (=Troodontidae + Ornithomimosauria)).  The whole group
Composgnathus + Maniraptora would be Coelurosauria.

>
>But, I am having a hard time coming up with good names for
>some of these groups.

Then don't.  Phylogenetic taxonomy frees oneself from the need to name many
"ranks" for a monotypic taxon (such as Saururae, Archaeopterygiformes, and
Archaeopterygidae for the single genus Archaeopteryx).

>Given the way the names are used now,
>I suppose Coelurosauria is a usabel name for the largest group,
>but I do not really like using it for a group that includes the
>dromaeosaurs as the most "typical" members.  And the name
>Dromaeosauria doesn't seem right for a group containing the
>Oviraptorids and Avimimids.

Currie, Novas, Ostrom, Gauthier, Dodson, Weishampel, Osmo'lska, and myself
(among many others) are perfectly willing to use that name for the group. 
You can call it what you wish, but part of taxonomy works by agreement
about definitions.

>> Thus, Pel. & Harpy. are ornithomimosaurs AND maniraptorans AND
> > coelurosaurs. 
>
>Only if you use a strict cladistic classification, *or*
>you decide the groups should be defined that inclusively.
>
> >  The hand of ornithomimosaurs are thus transformed from the
> > basal maniraptoran condition.  Given the structure of the hand of
> > Harpymimus (which retains a primitively short mc I), it would appear that
> > the hand of Pelecanimimus is either convergent with Ornithomimidae, or that
> > Harpymimus represents an outgroup to the Ornithomimidae-Pelecanimimus
> > clade.
>
>Quite.  If it is convergent, then inclusion of Pelecanimimus
>in Ornithomimosauria is not necessary, as it is an "outgroup"
>under that situation.

But if, for other reasons, it is found to be closer to Ornithomimidae than
either is to Harpymimus, it would still be considered an
ornithomimosaurian.

>
>In fact, of the four major subgroups of Theropoda, I am
>satisfied with the names of only two (Herrerasauria and
>Ceratosauria).  I think both of the names "Carnosauria"
>and "Coelurosauria" should be retired as formal names.

You may do as you wish.  I agree with you on Carnosauria, since
carnosaurian monophyly has yet to be well established.  However, everyone
else but yourself seems to agree that Coelurosauria is an appropriate name
for the bird-like theropods.
                                     

                                
Thomas R. Holtz, Jr.
Vertebrate Paleontologist in Exile
U.S. Geological Survey
Branch of Paleontology & Stratigraphy
MS 970 National Center
Reston, VA  22092

email:  tholtz@geochange.er.usgs.gov 
Phone:  703-648-5280
FAX:            703-648-5420