Le Méga Shark revient mais il va devoir faire face à un crocodile géant : le Crocosaurus. Attaquant beaucoup d'humains, les deux monstres se battent en duel. L'amiral Calvin et l'agent Hutchinson décident alors d'envoyer le lieutenant Terry McKormick et le chasseur Nigel Putman mettre un terme aux attaques des deux monstres.
Four astronauts in 1960 travel to a planet called Nova that has just entered Earth's solar system. The crew begins studying the planet to see if it's suitable for a possible Earth colony. After first discovering normal Earth animals such as a kinkajou and an alligator, they soon encounter and battle giant insects, an enormous snake, prehistoric mammals, dinosaurs, and - on an island - the titular character, King Dinosaur, a putative Tyrannosaurus Rex. Eventually, the scientists blow up the island with an atomic bomb, killing all of its inhabitants.
The film takes place in Tokyo in 2003, where two reporters, Hana Izumi and Hyuga Kanata, have arrived to document unusual seismic disturbances that have been picked up around Tokyo. The disturbances are originally thought to be aftershocks left over from a supposed massive earthquake on the Kanto Fault that occurred two years previously, causing hundreds of thousands of casualties and several hundred billion dollars in damage(possibly referencing the real-life Fukuoka earthquake or the Miyagi earthquake), although careful analysis of the evidence suggests otherwise.
A newlywed deputy, Martin Gordon (Vic Savage), encounters an alien spacecraft that has crash landed in fictional Angel County in California. A large, hairy, slug-like, omnivorous monster emerges from the side of an impacted spaceship. A second one, still tethered inside, kills a forest ranger and the sheriff (Byrd Holland) when they independently enter the craft to investigate.
A megalodon (prehistoric shark) is accidentally awakened by an oil company's explorations, trapping a group of art thieves and a group of young female college students on an abandoned island in the middle of a lake. The two groups band together to fight off the monster's attacks and fall victim to the shark one by one until only two of the girls are left, who manage to defeat the shark. However, another shark is revealed to be alive as it kills two fisherman who are nearby.