Page "Cetacea" Paragraph 10

As with the eyes, cetacean ears are also small.

Life in the sea accounts for the cetacean's loss of its external ears, whose function is to collect and focus airborne sound waves.

However, water conducts sound better than air, so the external ear is unneeded: it is a tiny hole in the skin, just behind the eye.

The highly developed inner ear can detect sounds from dozens of miles away and discern from which direction the sound comes.