RE: Stokesosaurus

["Williams, Tim" <TiJaWi@agron.iastate.edu>]

Nick Longrich wrote:

> Additionally the assigned braincase has a groove running along the 
> ventral surface of the parasphenoid, this sulcus is typical of 
> primitive theropods like Coelophysis, Ceratosaurus, Sinraptor and 
> Allosaurus, [snip] so unless this groove is also present in 
> tyrannosaurids (I don't have any good  figures handy here) the presence 
> of this primitive feature in Stokesosaurus would argue against it 
> being a tyrannosaurid.


But the braincase is advanced in so many other features!  Look at how
anteroposteriorly compressed it is!  That's definitely a derived feature,
and sets it in sharp contrast to the long braincase of (say) _Marshosaurus_.


The derived nature of the braincase was noted by Chure and Madsen (1998),
who tentatively referred it to _Stokesosaurus_.  The braincase also shows
features in common with _Itemirus_ and Late Cretaceous tyrannosaurids.  

> Personally I'd like to see what the Liaoning beds present in the
> way of tyrannosaurids. 

Who wouldn't?  Considering that pre-Late Cretaceous tyrannosauroids were
fairly modestly proportioned, they might have been in the size range of the
described Liaoning theropods.  Then again, skeletal remains of pre-Late
Cretaceous tyrannosauroids are extremely rare... so far.



Tim


------------------------------------------------------------ 


Timothy J. Williams, Ph.D. 

USDA-ARS Researcher 
Agronomy Hall 
Iowa State University 
Ames IA 50014 

Phone: 515 294 9233 
Fax:   515 294 9359