One has to wonder: if there were ever any other intelligent species (that we couldn't breed with) on this planet alongside us, then we probably wiped them out..
Why would we necessarily be what wiped them out? Intelligent dinosaurs may have been wiped out by an asteroid/volcanic activity/climate disruption (or whatever the most current theory is).
While they werent dumb lizards, i havent heard anyone claim dinos were dolphin or ape-smart. The brains were small and structured very differently than animals we today consider smart.