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Like many animals, humans rely primarily on eyesight to find their way around. But eyes aren't much use in the dark, so some creatures, including many bats, 'hear' their way instead. Using echolocation, a sophisticated system of orientation involving echoes, they can build up an acoustic picture of their surroundings, detect obstacles and find prey. Some echolocating bats use tongue clicks, but most use signals produced in the larynx. Until now, no morphological feature had been linked to the capacity for laryngeal echolocation. This meant that we did not know whether a crucial fossil species, Onychonycteris finneyi, which lived up to about 55 million years ago, could echolocate. Now, Brock Fenton at the University of Western Ontario in London, Canada, and his team have learned more (see page 939). Fenton tells Nature about the implications of their discovery.

How did the study come about?

Coauthor Nina Veselka chose bats for a scholar's electives programme that the University of Western Ontario offers to undergraduates. She began examining bat skulls to determine the arrangement and functional significance of little-studied bones. We borrowed 35 specimens from the Royal Ontario Museum in Toronto and performed micro-computed tomography on them. This imaging technique allowed us to see the fine details of the bats' ear and throat regions: the larynges, stylohyals and tympanic bones. Previous work had relied on dissecting these bones, a challenge in animals as small as bats.

What did you discover?

We found that the fusion or connection of two bone structures — the stylohyal bone in a bat's throat and the tympanic bone in the ear region of its skull — was a feature of all laryngeally echolocating bat species we studied. This distinguished these bats from all others in our sample, including one that echolocates with tongue clicks. We examined a skull from an O. finneyi specimen and found this same fusion feature, although it's possible the contact between the two bones is an artefact of preservation. So although we believe O. finneyi had the capacity for laryngeal echolocation, we aren't certain. We hope to obtain better-preserved fossils that will allow us to obtain a better picture of when laryngeal echolocation appeared.

How does the fusion point to laryngeal echolocation?

Echolocation works because bats can compare the calls they make with what they hear. The connection allows the bat to register in its brain the outgoing signal for comparison with returning echoes without the original signal's deafening the bat.