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Re: CARNOTAURUS ARMS



At 01:52 PM 1/14/98 GMT, Darren Naish wrote:

>Another problem I have with _Carnotaurus_ - though actually with 
>abelisaurids in general - is the maxillary fenestra. In 
>_Carnotaurus_, there is at least one (actually two) depressions 
>rostral to the ant. fenestra, and within the ant. fossa (sensu 
>Witmer). 

For a probable resolution to the situation of fenestration in theropod
maxillae, see:

Witmer, L.M.  1997.  The evolution of the antorbital cavity of archosaurs: a
study in soft-tissue reconstruction in the fossil record with an analysis of
function of pneumaticity.  Society of Vertebrate Paleontology Memoir 3: 1-73.

Larry argues (pretty convincingly) that the opening at the end of the
antorbital fossa of abelisaurs, Dilophosaurus, Ceratosaurus, etc. is
homologous to the promaxillary foramen (once thought be certain authors who
shall be me to be a coelurosaur, or at best avetheropod, character).
Similarly, the larger opening in the front of the snout of Sinraptor,
labelled the maxillary fenestra by Currie & Zhao, is ALSO the promaxillary
foramen.  This structure turns out to be basal to neotheropods (ceratosaurs
+ tetanurines), and its absence in coelophysids (but not coelophysoids in
general), Torvosaurus, therizinosaurs, and advanced birds is derived rather
than primitive.

So, in terms of a series of transformations, the condition in the maxillae
of theropods goes from:
antorbital fenestra only (basal archosaur condition) -> antorbital fenestra
+ promaxillary foramen -> antorbital fenestra + maxillary fenestra +
promaxillary foramen.  The latter condition seems to be a tetanurine feature.

>If this isn't worthy of a response from Tom Holtz I don't know what 
>is;)

Damn you, I'm trying to write here!! :-)

You owe me an immediate fax of the Nature Sinosauropteryx paper for this!! :-)

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:th81@umail.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661