dinosaur synapomorphies

["Ken Kinman" <kinman@hotmail.com>]

Hi all,
    I would like to see a discussion of some of the synapomorphies that 
unite dinosaurs, and would especially like to know which are regarded as the 
strongest synapomorphies (least likely to be convergent).
    To get the ball rolling, what about the "three or more sacral 
vertebrae" synapomorphy.  Could this not have easily occurred once in 
saurischians and once in ornithischians??
    Is it not true that Staurikosaurus has only 2 sacral vertebrae, and 
could this not be a primitive state rather than a reversal (3 sacrals back 
to 2)?  Are there other primitive dinosaurs that have only 2 sacral 
vertebrae??
                         Thanks, Ken Kinman
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