I think of the word dinosaur as being in use since the creatures first walked the earth. But it's a relatively new term, only coined in the mid-1800's, and taken from the Greek word for a terrible lizard.
Since the Greeks did have a word for terrible lizard maybe they had an inkling that different beings once lived on the planet. Finding one fossil could have led to mythological tales.
I doubt I would have been able to survive long in such a fierce time. I just hope that some of the animals who went extinct were poisonous snakes. And I don't think I'll ever miss the T-Rex again.