RE: Coelurosaur phylogeny

["Thomas R. Holtz, Jr." <tholtz@geol.umd.edu>]

> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> Ivan Kwan
>
> OK, so while everyone here is arguing whether to use Segnosauria or
> Theriznosauria, my questions are still unanswered. Basically,
>
> 1) Are _Compsognathus_, _Sinosauropteryx_, _Proceratosaurus_ &
> _Ornitholestes_ considered basal maniraptors, basal maniraptoriformes or
> basal coelurosaurs? And what is their phylogenetic placing relative to
> tyrannosaurs & ornithomimosaurs?

Yes.  Okay, to be a little clearer, there are several different recently (or
just about to be) published analyses on theropod phylogenetics.  In all, the
four you mention are basal to the "classic" maniraptorans (oviraptorosaurs,
deinonychosaurs, birds).  In some, compsognathids and/or _Ornitholestes_ are
basal maniraptorans; in others, they are basal coelurosaurs.

> 2) Are tyrannosaurs considered outside maniraptoriformes & thus
> classified
> as basal coelurosaurs?

In most recent analyses, yes.  But, for example, in Holtz (2000) they were
maniraptoriforms, and in Sereno (1999) they were honest-to-goodness
maniraptorans.

> 3) Are ornithomimosaurs a part of maniraptoriformes or also basal
> coelurosaurs?

Ornithomimosaurs are, BY DEFINITION, maniraptoriforms!!  Maniraptoriformes =
the most recent common ancestor of _Passer domesticus_ & _Ornithomimus
velox_, and all of its descendants.

> I've come up with 3 arrangements here:
>
> 1) Coelurosauria includes tyrannosaurs & maniraptoriformes.
> Maniraptoriformes includes (in order) ornitholestids, compsognathids,
> ornithomimosaurs & maniraptors.
>
> 2) Coelurosauria are ornitholestids, compsognathids & maniraptoriformes,
> which is made up of tyrannosaurs, ornithomimosaurs & maniraptors.
>
> 3) Coelurosauria is same as (2), except that compsognathids &
> ornitholestids
> are basal maniraptors.
>
> which one is closest?

All three topologies you have suggested have been results of various
analyses.

Part of the problem here is that you are looking for a definite answer.
That isn't how science works.  Instead, what you want is the best answer
given the data at hand.  However, the data at hand have not been 100%
decisive in this case.

Hope this helps.

(For what its worth, my recent in-press analyses put all the taxa you list
as basal coelurosaurs, basal even to tyrannosauroids).

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796