Whales show surprisingly vast differences in hearing ability. Baleen whales tune into infrasonic sounds to communicate over long distances. Toothed whales do just the opposite, relying on ultrasonic frequencies too high for humans to hear. Now researchers have fossil evidence from extinct early whale species to suggest that those differences in hearing arose only after whales evolved into the fully aquatic animals we know today.

Source: Extinct early whales listened like their relatives on land, fossil evidence shows