As has been pointed out, alligators are an example of modern dinosaurs. So clearly all dinosaur species did not die. Speaking in terms as wide as "dinosaur" is almost meaningless, for this reason.

Also, in all cultures around the world, there is the "dragon". Though there are different species of dragon (like dinosaurs), one might wonder how people who were not in communication with each other could independently invent the same "fictional" animals.

Also, new species of creatures are still being discovered and catalogued today. This shows that just because we don't see a species doesn't mean it isn't there, and we still don't know everything.

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Every generation needs a new revolution. -Thomas Jefferson