Listen up – ears are older than we thought

A new finding suggests that the modern ear may have developed much sooner that scientists had previously thought.

 
The 260 million-year-old fossil of the small reptile Bashkyroleter mesensis, from central Russia, owner of the first known ‘modern’ ear. Reconstruction (in pink, below) of the extremely large eardrum structure. Entire skull approximately 6.5 cm in length. Credit: Linda Tsuji and Johannes Müller

Paleobiologists from Germany hope that the discovery of the first anatomically modern ear in a group of 260 million-year-old fossil reptiles significantly pushes back the date of the origin of an advanced sense of hearing.

Until now the ability of modern animals to hear a wide range of frequencies – highly important for prey capture, escape, and communication – was long assumed to have only evolved shortly before the origin of dinosaurs, not much longer than 200 million years ago.

But these fossils demonstrate that this advanced ear was in existence much earlier than previously suggested. In these small reptiles the outside of the cheek was covered with a large eardrum, and a bone comparable to our own hearing ossicles connected this structure with the inner ear and the brain. Johannes Müller and Linda Tsuji, paleobiologists at the Natural History Museum of the Humboldt University in Berlin, also examined the functional performance of this unique auditory arrangement, and discovered that these little reptiles were able to hear at least as well as a modern lizard.

The researchers are not entirely sure why the animals would have developed such an advanced ear. 

“Of course this question cannot be answered with certainty”, said Müller, “but when we compared these fossils with modern land vertebrates, we recognized that animals with an excellent sense of hearing such as cats, owls, or geckos, are all active at night or under low-light conditions. And maybe this is what these Permian reptiles did too.”

As the fossils from the Mezen River also possess comparatively large eyes, another typical feature of vertebrates living in the dark, these reptiles indeed might have been among the first land vertebrates to pursue a specifically nocturnal lifestyle.


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