The mosasaur, a long snake-like sea serpent measuring nearly 65 feet long, ruled the seas in the late Cretaceous Period (70 million years ago). Consider it “Dino-Jaws:” ruthless in its pursuit of prey in fresh or salt water. This creature is based on a real group of animals that evolved from the first lizards and took to the sea during the time of dinosaurs. The killer whales of their age, they fed off anything—including other mosasaurs.