Reptilicus (1961)

"Invincible...Indestructible! What was this awesome BEAST born 50 million years out of time?"

A portion of the tail of a prehistoric reptile is discovered in Denmark. It regenerates into the entire reptile, which proceeds to destroy buildings and property and generally make a nuisance of itself. It can fly, swim, and walk, and has impenetrable scales, which makes it difficult to kill.