Gasosaurus (was Re: MJ coelurosaurians)

["Thomas R. Holtz, Jr." <th81@umail.umd.edu>]

At 04:23 PM 2/10/99 -0800, Nick Pharris wrote:

>_Gasosaurus_ is no coelurosaurian.  If the illustration of the pelvis in
>_The Dinosauria_ can be trusted, it appears to be a basal carnosaur of
>some kind.

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.), although some (the obturator foramen) are lost in
allosaurid carnosaurs, and independantly in advanced coelurosaurs.

_Gasosaurus_ has a few features of the femur it shares with coelurosaurs,
particularly the size and shape of the anterior trochanter and the femoral
head.  So it is weakly supported as a basal coelurosaur.

Even the skulls and the metatarsi of basal coelurosaurs and carnosaurs are
very similar: my new analysis shows that some of the features that Greg Paul
used to unite allosaurs, _Ornitholestes_, _Proceratosaurus_, and
tyrannosaurs are actually avetheropod characters (or slightly more
inclusive) which were lost independantly in certain other carnosaur and
coelurosaur groups.

>Greg Paul suggested that _Proceratosaurus_ was related to _Ornitholestes_
>(and hence, in today's parlance, a basal coelurosaur).  I know too little
>about this animal to be able to comment intelligently.
>
It has additional features not used by Greg Paul which do securely place it
within Coelurosauria, making it the oldest secure coelurosaurian at present
(pending confirmation of the identity of the Yunnan "therizinosauroid").

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:tholtz@geol.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661