First place: black dragon lived at the end of Cretaceous, at the same time as the famous Tyrannosaurus rex. When Tyrannosaurus Rex dominated the land, black dragon also dominated the ocean. There are many kinds of black dragon, the largest of which is 18 meters long. It is fierce and gregarious. They feed on sharks, swordfish, ancient turtles and even other black dragon. If there is anything more dangerous than meeting a black dragon in the ocean at the end of Cretaceous, it is meeting their families. Second place: the smooth-faced odontosaurus lived in the ocean of Jurassic (65.438+55 billion years ago-65.438+45 billion years ago), and it was the largest and most dangerous beast that ever existed on the earth. It can grow up to 25 meters at most, and any other kind of life in the ocean may become its food. Because the swimming speed of Pterodactylon is not as fast as that of black dragon, the relative risk is reduced. Tooth dragons with smooth sides like sharks. Third place: Megalodon knew from its name that this creature had huge teeth. Megalodon lived in the warm ocean 4 million years ago, when human ancestors just learned to walk upright. Megalodon sharks are 15 meters long and feed on large whales. When the ice age came, whales migrated to polar waters. Megalodon, which lost its food, became extinct. Fourth place: The mechanical toothed whale (Wang Long whale) lived in the Sahara desert 36 million years ago, but it was still a warm ocean at that time. The mechanical toothed whale is 18 meters long, feeds on other whales and large sharks, and even dives into swamps at high tide to feed on archaeopteryx. The El Ni? o phenomenon intensified, and after the glaciers appeared in the Antarctic continent, the mechanical toothed whales that lost their food gradually became extinct. Fifth place: Dungeon Fish, an armored metamorphosis fish, lived in Devonian 360 million years ago and ruled the ocean for about 50 million years. Dungeon fish is about 9 meters long and weighs 4 to 5 tons, weighing two or three elephants. The headgear of the dungeon is about 5 cm thick. Dungeon fish feed on other kinds of soft-shelled turtles. Sixth place: ichthyosaurs lived in the Triassic period 230 million years ago, when the first dinosaur, coelomosaurus, just appeared. It is 8 meters long. Seventh place: Nautilus Nautilus lived in the Ordovician 450 million years ago and was ten meters long.