Modern mammals have impressive hearing skills. We can detect a wide range of sounds thanks to our unique ear structures, like eardrums and tiny bones. A new study reveals that these features began to develop about 50 million years earlier than previously thought.
Researchers from the University of Chicago discovered this while studying a 250-million-year-old fossil of an ancient mammal ancestor called Thrinaxodon liorhinus. They used CT scans of the skull and jaw to create 3D models. This allowed them to simulate how the animal’s anatomy reacted to different sounds.
Thrinaxodon lived during the Early Triassic period, before dinosaurs roamed the Earth. It resembled a mix between a lizard and a fox. Notably, it had some genes that modern mammals still possess. This study suggests that its hearing structure shares similarities with ours.
In early cynodonts, the ear bones—malleus, incus, and stapes—were connected to the jaw. Over time, these bones detached, leading to the middle ear we recognize in mammals today.
For many years, scientists believed Thrinaxodon was a key piece in understanding how mammalian hearing evolved. In 1975, paleontologist Edgar Allin suggested it might have had an early eardrum. However, with the technology of that time, he couldn’t confirm his theory.
Fast forward to today, researchers used advanced engineering software to revisit this question. Alec Wilken, an evolutionary scientist, shared, “For almost a century, scientists have been trying to figure out how these animals could hear.” His team found new ways to explore this ancient question.
The new methods allowed them to examine the fossil in detail. By simulating how Thrinaxodon’s skull would respond to sound, they learned it could have heard through vibrations, even without fully developed ear bones.
This research indicates that Thrinaxodon had a hearing range from 38 to 1,243 hertz. For perspective, a healthy young person can usually hear between 20 and 20,000 hertz. Their peak sensitivity was around 1,000 hertz, similar to sounds you might hear in a quiet conversation.
This ability likely helped the ancient creature find food, avoid threats, and might have even been important for mating. The study was published in the Proceedings of the National Academy of Sciences.
As we look back, this study redefines our understanding of hearing evolution, showing how far our auditory systems have come since those early days. The evolution of hearing is a fascinating journey, connecting us across millions of years.
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