Gorgo

Greedy sailors capture a giant lizard off the coast of Ireland and sell it to a London circus. Then its mother shows up.

Gorgo is a 1961 British-American science fiction monster film directed by Eugène Lourié. The film focuses on Gorgo, an ancient large sea monster brought back to London for exploitation, and Ogra, his even larger mother, who rampages across London to search for him. The film was featured in an episode of the cult movie-mocking television show Mystery Science Theater 3000.