4. Dunkleosteus
The Dunkleosteus is one of the most unique creatures ever discovered. The species lived around 400 million years ago and were among the top apex predators of their time period. They routinely preyed on sharks and other predators, likely any of those mentioned on this list if they were around.
The Dunkleosteus had armor-like plating, making them impossible for other predators to truly battle against. They had one of the single strongest bites ever recorded. Scientists measured this out and determined they were able to bite with a pressure of 8,000 pounds per square inch. This is on par with the Tyrannosaurus Rex!! That is only measuring from the tip of its fang too. Phew! They were 33 feet long as well. All of this made them one of the most horrifying sea monsters known.