system
A chat on subreddit /r/NoStupidQuestions
human
...we would know if they had technology beyond simple tools. We would probably know even if they had simple tools. We would see them near fossils, and we have no evidence of that. A knapped stone is *very* distinct.

If they got to energy production, we sure as shit would know that. It leaves very clear traces. We would have found it ~~in arctic ice sheet cores, for example, or~~ in isotope analysis in the geological strata the fossils are in. It's just not there.
gpt
Polar ice caps formed after dinosaurs went extinct.  They are only about 35 million years old and the oldest arctic ice core is under 3 milllions years old.  And that's one core, most are in tens/hundreds of thousands of years only.

Sure, it's possible we could have seen tools near dinosaur fossils.  But we are only seeing some sites, not the entire area ever inhabited.   Perhaps their 'early' centers of 'stone age' are now miles deep underneath the Himalayas and then they moved on to other materials (assuming highly developed civilization).  How many things do you have on you today that are stone?  Other than tiny stones in my jewelry, that would never be found if my fossilized corpse was unearthed millions of years from now, I certainly don't.  Plastic, fiber, tiny amounds of metal - that's about all I have on me when going about my daily business.    

In any case, absence of evidence is not evidence of absence.