The bigger problem is that a civilization requires more than sentience and intelligence. Things like hands, fingers, ability to vocalize, body posture, environment, incentives such as physical disadvantages against predators, curiosity and so on. Great apes are the only ones who seems to possess all that right now, and we were the ones to make a civilization, everyone else with some kind of disadvantage didn't. Maybe other species had a tendency to evolve a greater intelligence, but without all the rest, had not enough use for it and didn't.
Even if there's a very intelligent group of dolphins somewhere to speak a complex language worthy of a prehistoric human tribe, they are unlikely to develop a writing system, to use anything beyond the simplest tools, or to ever process materials and objects in any significant way. Anything short of an interaction with humans would leave them primitive in the short term (millions of years). Same thing for, say, the cleverest of dogs. Elephants seem to have some remarkable skills for manipulating things with their trunks, so they could be onto something one day. Bears as dog's cousins are not exactly the stupidest of creatures, and also seem to be in the middle of discovering how to use their evolving front paws to grab things. Too bad squirrels are not good in the brain department – those creatures are dexterous. And worse, none of those creatures come close to apes and dolphins (or do they? selective breeding done by humans might come to the rescue)
Speaking of dinosaurs, they didn't do bad either. Parrots and crows are little geniuses. Although they are handicapped physically and aren't going anywhere, they seem to be an indication that the civilization could have sprung from the dinosaur lineage, not our own. Distant Origin is not that crazy. We just got lucky. But assuming a tendency of growing complexity and intelligence, it is unlikely (but not impossible) for there to have been dinosaur Einsteins, even the wisest birds of today aren't wiser than many mammals, I am assuming their ancestors were only dumber.
But as unlikely as it is, thinking of an undiscovered dinosaur species that used and built tools, built houses, cooked food, etc., is truly fascinating and gets me dreamy. Not knowing how easy intelligence evolves makes it worth pondering at least. I adore the image of velociraptors opening doors.