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Re: Gasosaurus (was Re: MJ coelurosaurians)

On Thu, 11 Feb 1999, Thomas R. Holtz, Jr. wrote:

> The illo isn't bad.  However, the supposed "carnosaurian" or "megalosaurian"
> features (trapezoidal ischial obturator process, retention of the obturator
> foramen, retention of the ischial foot) are primitive features for
> Avetheropoda and its immediate outgroups (_Afrovenator_, etc.).  These
> features are also found in basal carnosaurs (_Monolophosaurus_,
> _Yangchaunosaurus_, etc.), 

_Monolophosaurus_ does not have an obturator flange of any kind, if the
original description is accurate.  It retains a full ischiadic plate,
pierced by a foramen.  IMHO, that makes it a basal tetanuran or an
avetheropod more basal than _Afrovenator_ or spinosaurs.

As discussed before, published illustrations of the pelvis of
_Yangchuanosaurus_ are a mess.  I tend to rely more on the pelvis of
_Sinraptor_ to illustrate sinraptorid characters.

All right.  I'll give you that the quadrangular obturator flange seen in
carnosaurs may be a basal avetheropod feature, further "whittled down" in
coelurosaurs into a triangular obturator process.  But that means that
spinosaurs are most likely basal avetheropods as well (or carnosaurs),
rather than megalosaur relatives.

> although some (the obturator foramen) are lost in
> allosaurid carnosaurs, 

and carcharodontosaurids; sinraptorids show an intermediate stage, with
the obturator foramen largely surrounded by a bony hook.

> and independently in advanced coelurosaurs.


Nick Pharris
Pacific Lutheran University
Tacoma, WA 98447