Is there any scientific evidence that specifically rules out mythical creatures existing presently or in the past?

Answer 1

It depends on what mythical creature you are talking about. Dragons could have existed, but they would not have been able to fly (it is aerodynamically impossible), and they would not have been able to breathe fire. Animals similar to dragons but without those two characteristics did exist in the past.

Animals similar to the Loch Ness Monster definitely existed (have a look at Liopleurodon and Plesiosaurus). We are pretty sure that none of these creatures are alive today.

Answer 2

There is no scientific evidence that definitively rules out the existence of mythical creatures in the past, as absence of evidence is not evidence of absence. However, the lack of physical evidence, such as fossils or remains, for creatures like unicorns or dragons suggests that they are more likely fictional rather than real beings.