Re: Obturator processes

["Mickey Mortimer" <mickey_mortimer@email.msn.com>]

Nick Pharris wrote-

>Well..._Yangchuanosaurus_ has been *restored* with an ischial foramen, but
>the restored pelvic area looks quite different from photos I've seen of the
>type of _Y. shangyouensis_.  And if you compare the structures at the base
>of the ischium in _Yangchuanosaurus_ and _Sinraptor_, they don't match up.
>Where _S. dongi_ shows a beautiful obturator flange, the restored _Y.
>shangyouensis_ shows only a smooth, curving ventral margin on the ischium.
>Also, the restoration of the _Yangchuanosaurus_ ischium indicates that the
>bone bridge across the ischiadic "foramen" in _Y._ is incomplete--thus,
>particularly after comparison with the very closely related _Sinraptor_, it
>may be that the bridge was not there at all.

This could very well be true, especially taking into acount the immature
nature of the specimen and the poorly restored ilium (with it's
coelurosaur-like caudoventral slope and pointed preacetabular process).

>This may also apply to the bone bridge shown as closing off the pubic
>foramen.  _Sinraptor_ shows an incomplete bridge, and the bridge looks
>incomplete in photos of _Y._ as well.


This is less probable, as I can easily picture the bridge in Sinraptor dongi
being complete with just a little bone added.  Also, the pubic foramen in
Sinraptor hepingensis is completely closed.
All of this has very little phylogenetic significance because the only
difference between a pubic foramen and a pubic notch is less completely
ossified bone, the two are easily evolved from one another.  The obturator
flange/absence//process/foramen transformation would seem to be more
complex.

Mickey Mortimer