1. Early humans would have seen fossils and surmised the existence of such creatures.
2. I am open to the possibility of the survival up until quite recently of some sort of very large dinosaur-like lizards or snakes, that humans may have seen.
3. However, anyone who thinks that humans were alive at the same time as Dinosaurs in the common term of the word i.e. T Rex, Brontosaurus, Stegasaurus, etc, is someone who is either a total moron or is an otherwise smart person who has abandoned all capacity for reason when dealing with religious issues.
And the scientific basis of your assertion is...?