David Marjanovic 22.April 2002 wrote:
"Sauropsida retained 2 coronoids "up to" Dromeosauridae"
The presence of only one coronoid is one of the unambiguous synapomorphies of sauropsids (Reisz & Laurin 1997).
Some dinosaurs have a structure similar to a second coronoid (I raise this topic on this list one year ago), but probably, in my opinion, is a secondary developped one, not a true coronoid.
In any case it would be interesting to see the situation in archosauromorphs, in mesosuchus seems to be present only one coronoid (Dilkes 1997).