Feb. 6, 2012 at 3:19 PM ET
Researchers have re-created the love song of a katydid from 165 million years ago, based on an analysis of fossilized wings found in northwest China. They say the chirp adds an aural dimension to our picture of the forests of the Jurassic Era.
"The Jurassic forest was already packed with many animals singing at night," Fernando Montealegre-Zapata, a University of Bristol biologist who specializes in insect sounds, told me today. "I'm not just talking about the crickets but the frogs. That would create a noisy environment, and in a noisy environment the best way to communicate is with a single frequency, and loudly."
That assumption fits with the analysis conducted by Montealegre-Zapata and his colleagues, which appears in this week's Proceedings of the National Academy of Sciences. They started with a well-preserved Middle Jurassic fossil, one of several found by Chinese paleontologists at Inner Mongolia's Jiulongshan Formation. This particular fossil revealed the wing structure for a long-extinct species of katydid, also known as a bushcricket, which has been dubbed Archabolilus musicus.
In life, the bug would have had relatively large wings, measuring more than 2.8 inches (7 centimeters) in length, with broad stripes of color. Its closest living relatives include katydids (Tettigonidae) and grigs (Prophalangopsidae).
The researchers made detailed measurements of the fossil wing's parts, including the organs that katydids use to produce their mating calls. Scientists believe that ancient katydid, like their modern-day descendants, strummed their songs by rubbing the tiny teeth of one wing against a plectrum on the other wing.
For comparison's sake, Montealegre-Zapata and a colleague of his at the University of Bristol, Daniel Robert, analyzed the wing structures of 59 modern-day katydid species. They fed all those readings and the characteristics of the insects' songs into a mathematical model. Then they looked at where A. musicus would fit in that model.
Their conclusion, based on the size of the wing and the precise spacing of the teeth, was that the Jurassic katydid would emit a steady tone at a frequency of 6.4 kHz for 16 milliseconds. That was enough information to reconstruct the sound, which you can hear by clicking on the video button above.
The researchers' reconstruction has the calls coming less than a second apart, because that would be the typical frequency for species of katydids that are not threatened by bats. Paleontologists say bats were not a threat to Jurassic bugs because they didn't exist during that period.
The single-tone call would have come through loud and clear to other katydids, Montealegre-Zapata said in a news release.
"For Archaboilus, as for living bushcricket species, singing constitutes a key component of mate attraction," he said. "Singing loud and clear advertises the presence, location and quality of the singer, a message that females choose to respond to — or not. Using a single tone, the male's call carries further and better, and therefore is likely to serenade more females. However, it also makes the male more conspicuous to predators if they have also evolved ears to eavesdrop on these mating calls."
His guess is that the Jurassic katydid was a nocturnal creature, since all present-day katydids that use musical calls are nocturnal. That would have kept the crickets from being picked off by daytime predators such as the feathered, flying Archaeopteryx. But Montealegre-Zapata said they may have made tasty morsels for bug-eating Jurassic mammals such as Morganucodon and Dryolestes (which could conceivably hear the cricket calls).
The findings strongly suggest that katydids were well-adapted for music-making during the Middle Jurassic, 165 million years ago. That led the researchers to speculate that the katydid's distant ancestors might have begun chirping more than 50 million years earlier, during the Triassic Period, thanks to "the formation of random teeth across several veins on the forewings, and the associated production of noisy sounds."
Reconstructing the ancient song of a katydid could also help answer questions about modern-day insect communications, Montealegre-Zapata said. There's quite a bit of variation to the chirps of katydids and crickets, as you'll find out if you listen to the audio clips on this webpage. Over time, musical bugs may well change their tune to suit their biggest fans and frustrate their worst foes.
Montealegre-Zapata said the reconstruction of the Jurassic katydid's love song "suggests the evolutionary mechanisms that drove modern bushcrickets to develop ultrasonic signals for sexual pairing and for avoiding an increasingly relevant echolocating predator — but that only happened 100 million years later, possibly with the appearance of bats."
More about prehistoric sounds:
In addition to Montealegre-Zapata and Robert, authors of the PNAS study, "Wing Stridulation in a Jurassic Katydid (Insect, Orthoptera) Produced Low-Pitched Musical Calls to Attract Females," include Jun-Jie Gu, Michael S. Engel, Ge-Xia Qiao and Dong Ren.
Alan Boyle is msnbc.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.