Livyatan

Most of you have probably heard of the Megalodon, which is basically a species of giant sharks. During parts of the period that the Megalodons roamed the ocean, there also existed another mighty beast of comparable size. A species of sperm whale, by the name of Livyatan, which also happened to be an apex predictor. Their prey even includes other whales.

(Their name was heavily inspired by the mythical Leviathans)

In the end, the Megalodons outlasted the Livyatans by a few million years.