The first vertebrate superpredator lived 360 – 415 million years ago, in the late Devonian period, when life was just beginning to colonize the land. It was a gigantic, 10 meter (33 ft) carnivorous armored fish, Dunkleosteus telleri. This fish would have been comparable to the size of a school bus. It weighed around 4 tons, and had not only the strongest bite of anything alive at the time, but probably the strongest bite in the history of all life up to today. Computer extrapolations of its likely muscles suggest that it bit with 8,000 pounds per square inch of force at the tip of its fangs. It was also the first predator to evolve the flesh-tearing feature of bladed jaws.
Dunkleosteus ate anything that moved. Sharks, fish, invertebrates, and other Dunkleosteus. Its fossils are associated with the half-digested debris of fish corpses. Once it started eating, Dunkleosteus probably didn't know when to stop. It was easier to have it be evolutionarily programmed to eat as much as it could at all times, to keep it prepared for possible dry spells. Dunkleosteus would be an apex predator in the aquatic ecosystems of the Devonian, meaning it ate practically everything and was preyed upon by nothing.
Paleontologists who have studied Dunkleosteus argue that it would probably win in a fight with a Great White Shark if it had survived until today. This monster was able to open its huge mouth in a fiftieth of a second, creating a suction effect which would draw small fish into its mouth. It likely could have swallowed a human whole. Because it was heavily armored on the front, this fish would have been very difficult to face head-on. Some of its choice prey, primitive sharks, had not yet evolved bladed jaws, putting it at a terrible disadvantage with this superpredator.
Dunkleosteus is probably not the greatest marine predator of all time - plesiosaurs could have killed it with ease, and many modern whales are simply too big for anything but a school of Dunkleosteus to have an effect. (And there is little evidence Dunkleosteus traveled in schools.) Of course, these animals never lived at the same time, so there's no way we could determine the winner of such a competition. But it sure is fascinating to think about.