Ancient fish used lungs to hear underwater, fossils reveal

Scientists have uncovered a remarkable sensory adaptation in ancient fish. A study published in Communications Biology reveals that some prehistoric species used their lungs to hear underwater. The discovery sheds new light on how early vertebrates processed sound in their environment.

The research focused on 240-million-year-old coelacanth fossils from the Triassic period. These findings highlight an unusual anatomical feature not seen in modern fish. The team examined fossils of two coelacanth species from what is now China. Using high-resolution computed tomography (HRCT), they reconstructed the cranial anatomy in detail. Their analysis showed a unique passage connecting the lung to the inner ear.

Sound waves absorbed by the lung organ travelled through this channel, allowing the fish to detect vibrations. This sensory system gave the creatures an advantage in murky or deep waters where visibility was poor. The same study also identified the oldest known bony fish fossils, Eosteus chongqingensis, in Early Silurian deposits near Xiushan, Chongqing.

Modern coelacanths, the living descendants of these prehistoric fish, still thrive in deep-sea habitats. Unlike their ancestors, today's species rely entirely on gills for breathing and lack the lung-based hearing system. The research confirms that some ancient fish developed specialised adaptations for underwater hearing. By repurposing their lungs, these Triassic coelacanths could sense sound in ways unseen in later species. The findings provide concrete evidence of how early vertebrates interacted with their acoustic surroundings.