Ears once breathed, Swedish fossil research shows

A Swedish study of 370-million-year-old fossil fish has shown that ears probably first developed as respiratory organs, one of the researchers on the project said.

The fossils "show how the ear developed in detail as a complex process of steps ... and that the (first development) had to do with breathing," Per Ahlberg of Uppsala University, north of Stockholm, told AFP.

Intrigued by how ears in the first land crawlers developed, Ahlberg and colleague Martin Brazeau have studied ear-like features in fossils of pre-historic fish called Panderichthys.

"The Panderichthys is the closest relation to early land crawlers of all the fish fossils we know," Ahlberg said.

While land crawlers have a middle ear, which is needed to amplify the relatively weak sound waves that travel through the air to the eardrum, sea creatures have no eardrums and only need an inner ear to hear the much stronger sound waves that travel through water.

Where land animals have a middle ear, ancient fish had spiracle cavities resembling the blowholes in modern-day sharks and stingrays.

In the Panderichthys, the bony structure around this cavity was wider than in previous species and closely resembled a middle ear cavity. However, it clearly had nothing to do with hearing, Ahlberg said.

"It is clear that this transformation had nothing to do with hearing since there is still no connection to the inner ear. So there must have been another reason why this transformation took place. A natural explanation is that this had to do with breathing," he said.

While previous research had indicated that the middle ear developed rapidly in land crawlers, Ahlberg and Brazeau's study, which was published in the science journal Nature this week, shows a more gradual evolution of hearing.

"Interestingly, if you look at the earliest land crawlers, their middle ear appears to have the same shape as in the Panderichthys, and since they don't appear to have had eardrums, it's probable that they too still breathed through their ears," Ahlberg said.

"I would guess that in the earliest land animals, the breathing function is still there, but a hearing function also gradually begins to develop."

The Swedish researchers findings run counter to claims by proponents of creationism that sensory organs are so complex that they must have been designed by a higher power.

"All research revealing evolution is a slap in the face of creationism, but our results are especially interesting since evolution first is drawn in one direction ... and then in another. It's hard to believe that if God wanted to design an ear, this is the way He'd go about it," Ahlberg said.