Megalodon
These extinct animals roamed the planet up until their extinction 3.6 million years ago. They were the largest fish to ever exist, and grew up to 15 to 18 meters in length. This surpasses the largest recorded great white shark. Their teeth are probably the most terrifying aspect, which reached up to 18 centimeters long. Their name, megalodon, means “large tooth,” because they’re an extinct species of mackerel shark. Let’s just say that these aren’t the sort of animals you’d want to swim into while snorkeling in the ocean. It could easily fit several humans inside of its mouth. They’re also considered the largest marine predators to ever roam the seas (NHM).