@futurebird I once ran a short-lived TTRPG campaign set in the Cretaceous, where the players were members of a sapient dinosaur species that had learned to make tools of wood, stone and obsidian - and bits of other dinosaurs. I based them on Troodon (because 1. those had unusually large brains for dinosaurs, and 2. they were omnivorous). Unfortunately, the setting was hard for me (at the time at least) to come up with good stories for.
I figured that an undiscovered dinosaur culture could make sense if they never made it to metalworking, and never reached a very large population.