Extinct early whales listened like their relatives on land, fossil evidence shows
(PHYSorg.com Archaeology & Fossils)

Whales rely on a keen sense of hearing for their underwater existence. But whales show surprisingly vast differences in hearing ability. Baleen whales tune into infrasonic sounds-at frequencies too low for humans to hear-to communicate over long distances. Toothed whales do just the opposite, relying on ultrasonic frequencies too high for humans to hear.