At the 19:30 mark the Godzilla roar track can be heard from the red Tyrannosuarus Rex.
The idea that there exists a prehistoric world beneath the earth's surface dates back to Jules Verne's 1864 novel "Journey to the Center of the Earth," which was adapted into the film Journey to the Center of the Earth (1959). Many similar prehistoric worlds exist in popular culture, from the Pellucidar novels of Edgar Rice Burroughs to Ka-Zar's Hidden Land in Marvel Comics.
Annie is inexplicably nicknamed "Mint" throughout this story, possibly as a result of her hoping to receive peppermint candies when they visited Lunk's friend's hometown in Paper Hero (1985).