Monster from a Prehistoric Planet

Mr. Funazu wants to turn a tropical island called Obelisk island into a resort. Therefore, he leads an expedition from Tokyo to start develop the plan. Despite of the warnings of the native boy Saki two members of the expedition go into a forbidden area where they find a giant egg. The "bird-lizard", also referred to a "Gappa" is taken away by the scientists to a zoo in Japan. But the two parents of Gappa rise and destroy everything in their way in order to look for their baby -- even so far as Japan. Mr. Funazu is finally convinced to let go of the baby and return him to his parents to save Japan. But is this too late?