Song of the Jurassic

          A walk in the broadleaf forest can be a cacaphonous concert of creatures of all kinds trilling from all sides – no matter what time of day. Dawn brings out the birds, dusk the frogs, high noon the cicadas, night the crickets – some of them overlap the light and the darkness. We imagine this symphony stands out in contrast to the silence of the ancient primeval forests. There was a time long ago when the first trees stood alone, before of animals arose to animate the soundscape. Gradually, the forests came alive. But how could we really know those prehistoric voices?
          Well, through a technical exercise in microanatomy and acoustic ecology, a single well preserved imprint in stone has revealed to us the sound of one such long lost forest. The call of an extinct katydid has been resurrected – a resonant chirp that echoed below the coniferous canopy above northeastern China during the age of the dinosaurs. Using a knowledge of modern biomechanics, the pitch and duration of this call was predicted from the geometry of the comb and plecturm structures visible on the wings of a fossilized insect that lived 165 million years ago. (Plecturm has the meaning “to pluck” as with a guitar pick.)
          The reconstructed sound is a musical note at a frequency just above the highest key on the piano. Through that, members of the reconstruction team were able to infer how this katydid lived, and what the Jurassic forest around him was like.
          The fossil record shows that the frogs and toads, the cicadas, and the singing reptiles (with and without feathers) had not appeared yet at the time of this katydid. Nevertheless, his call was a pure tone. This suggests that the insect was reserving one particular channel of bandwidth in a woods that was already host to a crowded chorus – of wind and water sounds, and the calls of other creatures now long gone.
          The katydid call was not hypersonic – like that of many modern katydids – but produced a lower (6.4 kHz) note that would carry for a greater distance. Such a chirp would have been well suited to hail from a perch close to the ground among the trunks of the tree ferns that grew in the open understory.
          The insect was big  – three inches long with resonant sounding-board wings that would have amplified his song. (Potentially even larger and louder katydids – predators with wingspans approaching that of a kestrel – are known from the fossil record of the preceding Triassic period.)  Predation was part of the Jurassic picture painted by this reconstruction. The stridulation of the Jurassic katydid would have been audible to the mammalian insectivores of those forests – small creatures that hunted by sound at night, then hid from the dominant diurnal reptilians.
          This reconstruction work is published in the Proceedings of the U. S. National Academy of Sciences by Gu et al (Wing stridulation in a Jurassic katydid produced low-pitched musical calls to attract females: PNAS vol 109, p 3868).  You can listen to the insect calling @
http://planetearth.nerc.ac.uk/news/story.aspx?id=1149.   Start the digital record playing and let your mind wander back in time.

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