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saurischian grasping hands

I have been musing over some illustrations in The Dinosauria and 
elsewhere of theropod and prosauropod "hands."  My understanding has been 
that primitively, saurischian hands have grasping capability.  I would 
surmise that theropod and prosauropod hands worked in the same way to 
grasp something.  That was certainly Bakker's & Galton's position several 
years ago in discussing the connection between theropods and 
sauropodomorphs.  Yet for theropods the thumb is often shown "facing" the 
other fingers, or laterally (numerous illustrations, although it's not 
this way in The Dinosauria for Harpymimus--p. 234, elmisaurids--p. 246, 
or Deinonychus--p. 274), while for prosauropods the thumb seems always to 
be shown facing outward, or medially (e.g., The Dinosauria, p. 329), away 
from the rest of the fingers.  Why are these different?  

Heterodontosaurus and Psittacosaurus also had somewhat opposable thumbs, 
but I believe the operation was not the same as in saurischians.  Are 
there other grasping ornithischians, especially among less derived forms, 
wherein the thumb is offset laterally (across the "palm") during flexure?

Wish I had some working models.

Illustrations of dinosaurs show them involved in various activities, but 
those with grasping hand are rarely shown carrying things.  Humans are 
almost always depicted using their hands, each hand grasping something.  
Wouldn't dinosaurs with grasping hands also have found them of use for 
holding things--one item in one hand, and another item in the other 
(i.e., not just gathering up a double arm-load of something)?  

How do we know that Heterodontosaurus didn't throw rocks?  OK, that's a 
joke, but otherwise I'm serious!

Norman R. King                                       tel:  (812) 464-1794
Department of Geosciences                            fax:  (812) 464-1960
University of Southern Indiana
8600 University Blvd.
Evansville, IN 47712                      e-mail:  nking.ucs@smtp.usi.edu