A Functional Perspective on the Evolution of the Cochlea.

Area of Science:

• Paleontology
• Evolutionary Biology
• Mammalian Auditory System

Background:

• The cochlea is a critical auditory organ in mammals, responsible for converting sound vibrations into neural signals.
• Understanding its evolutionary history provides insights into mammalian diversification and sensory adaptation.

Purpose of the Study:

• To review paleontological and molecular data on mammalian cochlear evolution.
• To reconstruct the evolutionary timeline of key cochlear features and auditory sensitivity.

Main Methods:

• Comparative analysis of paleontological data.
• Review of studies on the morphology and molecular evolution of the cochlea in monotremes, marsupials, and placentals.

Main Results:

• The organ of Corti with hair cells and electromotility likely evolved early in mammalian history.
• Cochlear coiling, loss of the lagenar macula, and bony laminae developed after monotreme divergence but before marsupial/placental split.
• Ultrasonic hearing range extension and prestin optimization in outer hair cells occurred later, primarily in placentals.

Conclusions:

• Mammalian cochlear evolution involved a stepwise acquisition of unique features.
• Significant auditory adaptations, including ultrasonic hearing, were refined later in specific mammalian lineages.