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Re: pelicanomimus



From: tholtz@geochange.er.usgs.gov
 > I wrote:
 > >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 your 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).

It is rather excessive to be denied the use of any and all taxonomic
names established by cladists!  The long standing tradition in
taxonomy is to use the existing name for a revised group if the
contents revised group are "substantially the same" as the prior
contents.  You, yourself, have done this in using the names
Coelurosauria and Carnosauria for cladistically defined taxa.

In traditional taxonomic usage a taxon is "substantially the same"
is the differences amount to only a few additions and/or deletions,
compared to the totality of the group.

By this criterion, a Maniraptorea that excludes a few small derived
groups is still "substantially the same".

This is not true with regard to the "ultra-restricted" usage
of Coelurosauria I was considering.  In that case, the "revised"
group excluded almost the entire prior content.  (Even the
cladistic version of Coelurosauria stretches things, as all of
the Triassic members of the group - almost half of the well-
known genera, have been removed to Ceratosauria).

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

That is a family name - the stem taxon of Coelurosauria/Maniraptora
has to be the same rank as the other subtaxa.  So, unless no
intervening taxonomic levels are used, a higher level name is
needed.

If I am retain the split of the group into infraorders or suborders,
thent he stem taxon must be of that rank.  [I am currently
reconsidering that for reasons I will discuss below].
 > 
 > >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. 

Which means it must be in a taxon of the same rank.

However, I am slightly reconsidering the classification I presented
above, due to the significance of Pelecanimimus.  When added to
Ornithomimosauria, it changes the most likely reconstruction of
the most recent common ancestor of that group.  The new probable
form of the first ornithomimosaur comes out rather similar to
Ornitholestes, which is only barely distinguishable from the common
ancestor of the Maniraptora!

This means that, given the most useful span of the stem group(s),
the revised Maniraptora as I define it above is polyphyletic
(assuming your placement of Ornithomimosauria in the cladogram).

Taking this into account, the revised classification comes out
more like the following:

        Coelurosauria/Maniraptora
            Stem group
                Compsognathidae
                Ornitholestidae
            Segnosaurs/Therizinosaurs
                Alxasauridae
                Therizinosauridae
            Dromaeosaurs
                Dromaeosauridae
            Oviraptosaurs
                Oviraptosauridae
                Caenagnathidae
            Avimimoids
                Avimimidae
                ?Tyrannosauridae
                ?Elmisauridae
            Troodontoids
                Troodontidae
            Ornithimimosaurs
                Harpymimidae
                Pelecanimimidae
                Ornithomimidae

With this style of grouping, the subgroups look more like
superfamilies than ordinal level groups.

Also, given this grouping, I would prefer to call the whole
thing Maniraptora, and thus avoid the name Coelurosauria.

 > 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.
 > 

I have one question here.  Based on my research so far, I have
synonymized Elmisaurus with some other genus (I cannot remember
which, as the records are at home - but it is one of Caenagnathus,
Chirostenotes, or Microvenator).  Your seperation of Elmisauridae
from Caenagnathidae now has me wondering if I missed some article
on these organisms.  Or is Elmisauridae close to the base of the
arctometatarsalian clade, and thus seperated from Caenagnathidae by
relatively few intervening synapomorphies?
 > >
 > >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. 

Even if it is monophyletic, it is too far revised from the older
concept.  Too many of the former members are now in Ceratosauria.

Of course, under the circumstances, I am currently pretty much
stuck with the name.

swf@elsegundoca.ncr.com         sarima@netcom.com

The peace of God be with you.