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PISANOSAURUS



George Olshevsky wrote (quoting me):
<< PB:  Are you sure?  It is quite clear then, that if the pubes are
homologous
to those in ornithischians, then Therizinosaurs are ornithischains, and not
only that, ornithischains more derived than _Pisanosaurus_ which has a
*propubic* pelvis.  Is that what you're saying George?  If it isn't, then the
retroverted pubes are just as likely to be derived for theropod pubes
convergent to ornithischians.>>

REPLY: The pelvis of _Pisanosaurus_ is known only from a matrix impression,
so we have little idea what it was really like. But what looks like an
impresion of a propubic pelvis is much more likely to be that of a pelvis in
which there is a fairly well developed prepubic process. This is how
Bonaparte interpreted it in his original description. Everything else known
about _Pisanosaurus_ suggests this.>>

I find this extremely unlikely.  Even though it is simply a matrix
impresison, it clearly shows the pubis going straight away from the
acetabulum at about 20 degrees forward of the verticle axis of the pelvis.
 _Pisanosaurus_ was propubic as much as _Allosaurus_ or _Plateosaurus_ are --
unless of course the pubic shaft took an increadible U-turn somewhere
mid-shaft where we can't see it....

Check out Figure 14-A on page 191 of:

Sereno, P C.  1991.  _Lesothosaurus_, "fabrosaurids," and the early evolution
of the Ornithischia.  JVP 11(2):168-197.

There is no indication of any retroverted pubic shaft or a prepubic process,
just a normal propubic pelvis.

Peter Buchholz
Tetanurae@aol.com

"Am I not getting through to him!?"