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Theropod forelimb design and it's implications...

     When asked why skeletal restorations accompanying his papers always showed 
     theropod hands and forearms in a neutral ("shaking hands") position (as 
     opposed to G.S. Paul's restorations where they are always shown pronated), 
     Paul Sereno once indicated (personal communication) that theropods could 
     not pronate/supinate their hands because of the anatomy of their wrist, 
     that pronating hands were a feature of primates and not dinosaurs.
     Is this a commonly agreed upon theory?  (Is there such a thing as a 
     commonly agreed upon theory?)
     My inexperienced eye cannot find any feature of theropod anatomy which 
     prohibits pronation/supination.  Dr. Sereno may have been referring to the 
     lunate metacarpal, but I don't see how this would restrict flexibility in 
     what is basically a forearm rotation.
     I have trouble with this theory for three reasons:
     1)  Ancestral reptiles could rotate their forearms as part of quadropedal 
     2)  I am under the impression that earlier quadropedal archosaurs held 
     their forelimb pronate while walking.  For that matter, all quadropedal 
     dinosaurs did.
     3)  What is the utility of a grasping manus which would be most useful 
     (correct?) if moved in the sagittal plane, but can only grasp in a 
     swatting motion?
     Does anyone have any insight?
     Jonathan R. Wagner