Seals’ Dual-World Ears: How Amphibious Hearing Evolved
3D ear scans reveal that seals have cavernous, blood-filled ear tissue that expands during dives to conduct underwater sound into the middle ear, enabling true amphibious hearing (air and water). Fossil and comparative data show freshwater ancestors like Puijila heard only in air, while early marine seals such as Enaliarctos developed underwater hearing about 26 million years ago; later true seals refined middle-ear structures for acute underwater hearing. Seals also sing underwater and excel at rhythm, but rising ocean noise threatens their communication, underscoring the need to reduce acoustic pollution in marine environments.