Today’s sperm whale has no functional teeth in its upper jaw and only small ones in its lower jaw (which are mostly used in fights). It feeds through suction, relying on a rush of water to carry its prey into its open mouth. But Leviathan’s mouth was full of huge teeth, the largest of which were a foot long and around 4 inches wide. This was no suction feeder! Leviathan clearly grabbed its prey with a powerful bite, inflicting deep wounds and tearing off flesh as killer whales do, but with a skull three times bigger.
Leviathan was at the very top of the food chain and it must have needed a lot of food. While modern sperm whales mainly eat squid, Lambert thinks that Leviathan used its fearsome teeth to kill its own kind – the giant baleen whales. At the same point in prehistory, baleen whales started becoming much bigger and they were certainly the most common large animals in the area that Leviathan lived in. Lambert thinks that the giant predator evolved to take advantage of this rich source of energy. He says, “We think that medium-size baleen whales, rich in fat, would have been very convenient prey for Leviathan.”
This whale swam off the coast of Peru 12 million years ago. There's lots more about Leviathan melvillei at Not Exactly Rocket Science. Link