Its name was Leviathan melvillei (yes, named for Herman Melville). It was the size of its modern relative, the sperm whale, but had a full set of enormous (36cm) teeth and a habit of dining on other whales. You could say it incorporated the deadliest features of the modern sperm and orca, except the teeth were bigger than on any other marine animal, living or extinct. Thirteen million years ago, this was the unchallenged apex predator of the oceans.
COMMENT: This fascinating creature is a good reminder that prehistory still holds many surprises. While Alan Grant in Jurassic Park may have lamented the impending death of his profession, the truth is we still need paleontologists, and will for many generations to come. There are whole worlds yet to be understood.