What makes a whale a whale?

Flippers, the need to breath air, the ability to give milk, and a streamlined shape. There are plenty of signs that let us immediately distinguish whales from fish and the other creatures of the sea. Yet, alone or in combination, the traits I just mentioned aren’t unique to whales. Seals and sea lions, for example, are also flippered, air-breathing, milk-giving, streamlined mammals. If you truly wish to draw out leviathan, you have to look beyond the blubber to a clue made of bone.

The secret is in the skull. Being mammals, whales have domes of bone on their skulls that enclose the middle ear. These are called tympanic bullae. But whales have a peculiar modification to