I don't mean to imply that I think there is any evidence for such a crazy thing as what I propose. It's more of a "what if", which is both the least scientific thing you can ask, and also the question that has led to so many breakthroughs I would think.
Personally I think that in order for a species as intelligent, and intelligent in the way that we are (whatever that means exactly ) would have ancestors much like the homo's before us (sniker if you want, I think that's a valid contraction).
After all, even if homosapien had completely died out I think there would have been some evidence left over from our close relatives. And they had quite impressive intelligences themselves - considering the tools and weapons neanderthan and erectis used.
It is interesting that erectis, or even australopithecus, are completely vanished. It is somewhat unfortunate, that the gap between human intelligence and that of our closest relative differ by such a seemingly large margin. Well, at least in such a seeminly large way - linguistically especially.
But still I wonder - if during the time of the dinosaurs there were some intelligent animal who surpassed all modern species in cleverness (perhaps with the exception of us, of course), but which vanished without, as they say, a trace.
certainly darwinian life is capable of our Intelligence, are we really the first example of it's pinnacle?