It wasn’t just the roars of the dinosaurs that made up the soundscape of the animal world during the Jurassic period.
Crickets and grasshoppers communicated through a variety of songs and high-pitched sounds, some of which you can now listen to thanks to Thorin Jonsson from the Institute of Biology at the University of Graz.
Together with his colleagues from the universities of Lincoln, Bristol (UK), Beijing (China), and Tempe (USA) their findings on what are so far the oldest traces of sound on Earth have just been published in the journal PNAS.
Insects from the order Orthoptera, such as crickets and grasshoppers, rub wing structures against one another or against their legs to produce sounds called “stridulations.” Pitch and rhythm depend on the number and spacing of the teeth on the wing’s ridge, as well as the shape and movement of the wings.
Though vocal cords and other biological acoustic organs can’t be fossilized along with the sounds they made, the imprints left by these wings confer very precise information on the animal’s stridulations.
Jonsson’s Chinese research partners have discovered extremely well-preserved fossils of 9 different grasshopper species that lived at the same time in the same region, namely during the Middle Jurassic period in what is now Inner Mongolia.
The sound-producing structures are so clearly visible on these fossils that the biologists were able to reconstruct the pitches and musical units of the mating calls through various analyses, simulations, and AI-assisted evaluations that even produced the specific number of hertz each insect would sound off at.
“Our findings reveal a wide variety of call frequencies. Several species produced pure, low-pitched sounds like modern crickets, whilst others produced higher frequencies, similar to our native leafhoppers,” reports Jonsson.
The study isn’t just the first to do this with insects. It’s the oldest evidence of sound ever reproduced by anyone. Think of it like the famous Epitaph of Seikilos. This Greek funerary song was inscribed on a gravestone, and is able to be read by musicians several thousand years after it was last played.
Similarly, the physical features on the grasshoppers’ wings act like musical notation, and though scientists can’t reproduce them on a lyre like the Epitaph of Seikilos, AI can simulate them on a computer sound board.
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One species among the 9 surprised the researchers. A relative of the katydid called Sigmaboilus peregrinus communicated in the ultrasonic range between 20 and 22 kilohertz—a frequency that’s just above the human range of hearing.
For all the delicious proof of concept novelty the study provided, this discovery carries implications for the evolutionary biology of Orthoptera.
It was previously theorized that stridulatory insects whose stridulations reach into ultrasonic frequencies were pressured to do so by the incredibly precise hearing of bats. However, S. peregrinus lived millions of years before the first known bat existed.
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The team took the liberty afforded by their discovery to hypothesize other reasons why an animal would have to vocalize at such high frequencies. While not a bat, it could have been an example of the insect attempting to avoid detection by other predators. Alternatively, it could be a mating strategy by males to allow their calls to rise above the din of the Jurassic jungle night.
“This allowed us to demonstrate that the world during the Jurassic Period was acoustically far richer and more diverse than previously thought,” the biologist summarizes.
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