New imaging and computational methods let paleontologists test a long-standing idea about the origin of sensitive mammal hearing. The team at the University of Chicago scanned a well-known Thrinaxodon liorhinus specimen from the Museum of Paleontology at the University of California, Berkeley in UChicago’s PaleoCT Laboratory, then built a precise 3D model of its skull and jaw. They ran finite element analysis with Strand7 software, assigning material properties from living animals — for example bone thickness, density and flexibility — and simulated a range of sound pressures and frequencies.
The simulations show that a thin membrane tucked into a crook of the jaw would have produced the right vibrations to move the small ear bones and stimulate auditory nerves. The models indicate that eardrum-based hearing would have been more effective than hearing only by bone conduction or by so-called “jaw listening,” although some jaw conduction likely remained in use.
Because of these results, an eardrum-based mode of hearing now appears nearly 50 million years earlier than previously thought. Sensitive hearing would have helped mostly nocturnal mammal ancestors survive alongside dinosaurs. The study appears in PNAS and received support from UChicago, the National Institutes of Health and the National Science Foundation; the idea was first proposed by Edgar Allin about fifty years ago but could only be tested with modern methods.
Difficult words
- paleontologist — scientist who studies ancient life and fossilspaleontologists
- specimen — single example of a plant or animal
- finite element analysis — computer method to test physical stresses
- membrane — thin flexible layer that covers or separates
- eardrum-based — hearing that uses a thin vibrating membrane in ear
- bone conduction — hearing when vibrations pass through skull bones
- frequency — number of sound or vibration cycles per secondfrequencies
- auditory — relating to hearing or the sense of hearing
- nocturnal — active during the night rather than daytime
- simulate — to make a model or imitation of somethingsimulations, simulated
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Discussion questions
- How might sensitive hearing have helped mostly nocturnal ancestors survive alongside dinosaurs? Give reasons from the article.
- What advantages do modern imaging and computational methods give paleontologists when testing old ideas?
- The article says some jaw conduction likely remained in use. Do you think multiple hearing methods could be useful together? Why or why not?
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