How did mammals develop hearing?

Published 13 January 2016

The presence of hair might be the most obvious feature of humans and other mammals from reptilian ancestors, however, a less obvious, but arguably the more important difference is the presence of our complex, highly sensitive ears.

Fig 1 rept-mamml copyPublished in the Proceedings of the Royal Society of London a new international study by researchers from the University of New England (UNE) and University of Queensland challenges long-held ideas about just how mammals developed super-sensitive hearing.

“What is clear is that over tens of millions of years – bones that once formed part of the reptilian jaw were greatly downsized, repositioned and repurposed to help conduct sound more effectively to the inner ear in mammals,” co-author and director of UNE’s Function, Evolution and Anatomy Research (FEAR) lab, Associate Professor Stephen Wroe.

“One explanation has been that these bones were pushed away as the mammalian brain expanded. It has also been widely thought that the evolutionary process, which is now well-documented in the fossil record, is quite tightly recapitulated during the development of living mammals.”

“In some mammals, the process whereby bones in the embryo’s jaw shrink and move to become part of the ear is relatively easy to track. This makes them a great test case for examining theories on the jaw transition.”

Using high resolution CAT scan data of Australian marsupial embryos the research team showed that there was no support for the notion that the process was driven by an expanding brain. It was also clear that the process documented in the fossil record is perhaps not so perfectly recreated in the development of living animals.


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For further information, contact A/Prof Stephen Wroe on +61 2 6773 3261 or



Caption for mammal image: A study used marsupials, such as this rat kangaroo, to challenge current ideas about how mammals evolved stronger hearing than reptiles. Credit: Stephanie Hing.