A team at the University of Chicago used detailed CT scans and engineering simulations to test hearing in early mammal predecessors. They studied Thrinaxodon liorhinus, a 250-million-year-old cynodont, by scanning a well-known specimen from the Museum of Paleontology at the University of California, Berkeley in UChicago’s PaleoCT Laboratory. The scans produced a precise 3D model of the skull and jaw bones.
Researchers ran finite element analysis with Strand7 software. They gave the model material properties from living animals, such as bone thickness, density and flexibility, and simulated different sound pressures and frequencies. The results show a membrane tucked into a jaw crook could vibrate like an eardrum and move the ear bones to stimulate auditory nerves.
The models suggest this eardrum-based hearing was more effective than hearing by bone conduction or only “jaw listening,” though some jaw listening likely remained. The finding pushes the origin of modern middle-ear hearing earlier in the evolutionary timeline.
Difficult words
- specimen — an animal or object used for scientific study
- finite element analysis — a computer method to test physical structures
- simulate — to copy or show how something behavessimulated
- membrane — a thin flexible layer of tissue or material
- cynodont — an early mammal-like reptile in the fossil record
- bone conduction — sound transmission through bones to the inner ear
- eardrum — a thin membrane that vibrates with sound
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Discussion questions
- Why did the researchers use material properties from living animals in their simulations?
- How does the finding that eardrum-based hearing appeared earlier change our view of mammal evolution?
- Do you think some form of "jaw listening" could still help animals today? Why or why not?
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