<<Maybe they didn't fit on the ark? >>
I think some dinosaurs went in the ark. Some large mammals went into the ark, why not some large birds and reptiles? I think reptiles had a harder time adjusting with the new world climate than most mammals. So I think many animal kinds went extinct after the flood including surviving dinosaurs.
I'm reminded of the tales of dragons and great serpent-like beasts in Chinese and European folklore. The Aztecs had that folklore too. I'm pretty sure all that folklore has its basis in fact. So some dinosaurs survived but eventually died off. In Europe, they were slain to extinction by brave knights undergoing a required rite of passage if they had any hope of marrying a fair maiden.