Thursday, February 09, 2012

Ancient Forest Music

Millions of years ago, forests were buzzing with noise from a variety of organisms. In a sea of sound, it's hard to make yourself heard to friends or potential mates. You need a strategy, and scientists have reconstructed fossilized insect wings to discover the best approach: communicate loudly at a continuous frequency.

To recreate the sounds of the ancient jungle, scientists examined a well-preserved fossil of an ancient cricket found in northern China. Aptly named A. Musicus, the katydid — a type of cricket — moved its wings in a scissoring motion to create music 165 million years ago.

Researchers noticed that A. Musicus had a special file on its wings that made pure sounds audible from long distances. Using over 100 teeth on its file, the cricket could create low-frequency tones to attract females by rubbing its symmetric wings together. You can hear the cricket's song in the video below.

Video Courtesy PNAS/Gu et al.

The research team compared the fossil to the structures of present day crickets to help reconstruct the sounds it used to make. Based on the structure of the wing files, the research team could determine the frequency of the crickets' mating call. They found that the A. Musicus likely produced tones aroung 6 KHz, a relatively low frequency compared to some modern day crickets.

And maintaining a steady frequency was very important for A. Musicus. Having a pure sound at a steady frequency allows for the sound to travel better at low frequency ranges in the lower part of a forest.

Over time, A. Musicus developed wing files that were spaced farther and farther apart towards the end. Because the files accelerate as the cricket rubs them together, this increasing spacing ensures that the frequency of sounds stays the same. As the spacing increases, so does the speed of the moving files, so the time between teeth hitting each other stays constant. One pulse from the cricket, or the time it takes for one wing to rub across the entire length of the other, lasts for about 16 milliseconds.

Also, being able to produce a very specific frequency may have enabled the cricket to talk to only to other crickets without attracting attention from predators. Certainly, that would have been a useful skill in the dangerous environment of the Jurassic forest.

You can find the research paper published in the Proceedings of the National Academy of Sciences here.

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