Measurements on the Turtle’s Shell that Help Illuminate How the Fishes Lateral Line Function Was Replaced by the Reptilian Hearing Organ

The acoustic sense of fish, embodied in the lateral line, no longer worked when amphibians ventured onto the land. The new acoustic environment where sound traveled in the thin medium of air rather than the relatively dense medium of water presented a major chal-lenge. The multiple sensors of the lateral line were replaced by one gross sensor, the tym-panic membrane or eardrum. We show acoustical measurements on the turtle shell that can suggest a possible explanation of how the turtle dealt with the issue of sensing the directionality of incoming sounds.