Monster from a Prehistoric Planet

An expedition in the South Pacific lands on a tropical island where the natives worship the mysterious deity Gappa. An earthquake opens up an underground cavern and a baby reptile is discovered inside. The natives warn the foreigners to leave the hatching alone, but they don't listen and take it back to a zoo in Japan. Soon after, moma and papa Gappa start smashing Tokyo looking for their kidnapped child.

Gappa: The Triphibian Monster (Daikyojū Gappa) is a 1967 kaiju film directed by Haruyasu Noguchi. The film is about a group of Japanese reporters who discover an infant monster called a Gappa on Obelisk Island. The reporters cage the creature and take it to Japan where it becomes a media attraction. This angers the natives of the island and Gappa's full-grown parents, who head toward Japan to find their child. Its plot virtually duplicates that of the 1961 kaiju film Gorgo.