I can't speak to dinosaur people, but the population genetics of our own DNA reveals that there were never many humans on the planet till recently, so that rules out any very large human civilization. (Unless they genetically altered themselves to hide the evidence! Ahaaa...)
I know, let’s modify our DNA so if we’re wiped out nobody will ever know we existed!
If whole populations were wiped out and the world was repopulated by a small remnant would that not account for it? Or if an extinct human species had an advanced civilisation?