RE: Coelurosaur ischium unique?

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

> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> Ken Kinman
>
>     Does the coelurosaur ischium always possess at least two of the
> following three features?   Each of these features is
> occasionally lacking
> in a few coelurosaurs, but I believe that all coelurosaurs have
> at least two
> of the three (and most would have all three):
>      Ischium (1) reduced to less than 2/3 length of the pubis;
> (2) lacking
> an ischial foot; and (3) possessing a prominent, triangular obturator
> process (placed more than 25% down the ischial shaft).

Many coelurosaurs have ischia which are longer than 2/3 pubis length:
tyrannosauroids, ornithomimosaurs, some alvarezsaurids, some
therizinosauroids.  Indeed, this feature had "traditionally" been considered
a maniraptoran rather than a coelurosaurian feature.

Ornithomimosaurs, compsognathids, and a few other non-tyrannosauroid,
non-maniraptoran forms retain an ischial foot.

The "triangular obturator process" of..., well..., me is been very cogently
shown (by Rauhut, in press) to be the result of two separate, independant
derived character states rather than a single transformation from a
trapezoidal form.  Paper is in press, so it isn't up to me to elaborate.
What I can say, though, is that some very derived maniraptorans lack a
triangular obturatur process altogether, while others have more proximally
placed (but quite large) processes.

>      And the flipside (converse?) of this question is---Are there any
> non-coelurosaurs which also display at least two of those three ischial
> characteristics?

Not as such.  The most "coelurosaur"-like ischium among non-coelurosaurs are
those of _Allosaurus_, which doesn't look quite like it is normally prepared
(or preserved).  See the recent paper on the Portuguese _Allo._ for a
preview.

                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
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