We haven't found all the dinosaurs ever to exist. An intelligent species would have a good chance of doing something significant with their corpses, probably reducing the already small chances of fossilization. They were around for a hell of a long time, plenty of time to evolve the necessary intelligence.
You say it's unlikely they got to the level of great apes, but just what the hell are you basing that on? They had the geological time, a major component, and actually, they may well have had the brains.
As for brain size and birds, ever heard of the grey parrot Alex? Word vocabulary of 150 or so, and used in context. There's a grey parrot out there with a vocab of around 950 words.
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Some of the theropods, mainly the two legged, carnivorous ones, had fairly large brain size, especially compared to body size. There's been 65000000 years since the dinos left this earth, you think anything mankind has made could last that long? I sure as hell don't. There'd be no evidence if they'd made it to a tribal level, and there's no reason why they couldn't.
Brain size does not automatically equate to intelligence, not by a long way. And there's been plenty of things around on this earth, for much longer than the mammals. Intelligence is almost a guaranteed outcome of evolution in my mind, just how much intelligence is another question, but with all these species around with us capable of so much, it's not too hard to believe it could arise.
EDIT You think you could kill a bear with a spear/club/sword? Personally I think it would kill you, and that a bear would kill most people, regardless of their basic armament. Yes you can kill a bear armed only with a spear, but it's not easy, and it's not guarenteed. And you're still sort of missing my point that we're not dealing with humans here, but creatures that could already have their own decent defense.