A 250-million-year-old fossil reveals the origins of mammal hearing

Sensitive hearing may have evolved in mammal ancestors far earlier than scientists once believed. By modeling how sound moved through the skull of Thrinaxodon, a 250-million-year-old mammal predecessor, researchers found it likely used an early eardrum to hear airborne sounds. This challenges the long-held idea that these animals mainly “listened” through their jaws or bones. The results reveal that a key feature of modern mammal hearing was already taking shape deep in prehistory.