How marine mammal ears are different from ours

Anyone who has ever tried to hear underwater knows that a very different approach from hearing above water is necessary. Because water is five times more dense than air, there is a "acoustic impedance mismatch" between the two media, so an air-filled human ear is nearly useless underwater. To accomodate for this mismatch, baleen whales have a wax plug filling their external ears. This plug is thought to transmit sound to the inner ear from the water. Because the density of the plug is the same as the water, baleen whales are probably deaf in air. But the differences don't end there.

Marine mammals also need a streamlined head for fast and easy movement through water that external ears would impede. Instead, they have ear holes located right behind the eye. In bottlenosed dolphins, the ear hole is only 2-3 millimeters in diameter.

Some scientists believe that the toothed whales have ear channels that are open and filled with sea water. Others think that the ear channel is closed off, and both the channel and ear hole have become a vestigal organ--useless since they evolved (much like our appendix). Hearing in toothed whales, they suggest, occurs either by the bones of the skull transmitting sound to the inner ear--"bone conduction," or through "tissue conduction," where sound is conducted to the inner ear by deposits of fat that run up from the lower jaw.

Go to marine mammal acoustic article.