Using lasers, computer models, and machine learning, researchers have reconstructed the 165-million-year-old calls of Jurassic insects from fossilized wing fragments unearthed in China, according to a study published in the Proceedings of the National Academy of Sciences. The findings reveal that an extinct bush-cricket species called at frequencies beyond human hearing, proving that ultrasonic communication existed long before bats evolved.
Decoding the Soundscapes of the Middle Jurassic
Very little is known about the acoustic landscape of long-gone environments, such as the Jurassic forests, according to Dr. Jun-Jie Gu of Sichuan Agricultural University and his colleagues. Because vertebrate vocal organs rarely preserve well in the fossil record, researchers turned to the sclerotized cuticle of arthropods. Stridulatory structures like files and plectrums preserve exceptionally well on fossilized forewings.
The research team analyzed 20 fossilized ensiferan insects unearthed from the Jiulongshan Formation in Inner Mongolia, China. Dated to the Middle Jurassic, these fossils preserve delicate wing structures used to sing by rubbing one wing against another. To decode the ancient songs, researchers combined phylogenetic analysis comparing the fossils to nearly 100 living insect species, laser vibrometry measurements of modern insect wings, computer simulations of wing vibrations, and machine-learning models trained to predict call patterns from wing shape.
Did you know?
Insects were the first land animals to communicate by sending sound waves through the air, utilizing stridulation long before vertebrate vocal cords evolved into complex speech or calls.
Challenging the Bat Predation Hypothesis
Most of the nine analyzed species produced low, pure-tone calls around 5 kHz, similar to living crickets. However, according to the study, one species called Sigmaboilus peregrinus produced frequencies above 20 kHz in the ultrasonic range, beyond what humans can hear.
This discovery challenges the long-held assumption that bat predation drove the evolution of ultrasonic communication in insects. Bats appeared roughly 55 million years later, meaning ultrasonic signaling was already established in insects long before echolocating predators took to the skies. Instead of bats, the authors suggest early mammals and non-mammalian ancestors pressured insects to develop quieter, harder-to-localize pure-tone signals.
| Species / Group | Time Period | Acoustic Frequency |
|---|---|---|
| Jurassic Ensiferans (Majority) | Middle Jurassic (165 Million Years Ago) | Low audio (~5 kHz pure-tone) |
| Sigmaboilus peregrinus | Middle Jurassic (165 Million Years Ago) | Ultrasonic (Above 20 kHz) |
Ecological Drivers and Early Mammalian Hearing
Competition for acoustic space among crowded calling species also drove the diversification of these ancient signaling strategies. According to co-author Professor Edmund Jarzembowski, the bones of early mammals show improved hearing by the Jurassic, a development likely driven by predatory eavesdropping on these singing insects. Xu Chunpeng of the Nanjing Institute of Geology and Palaeontology explained that katydids had the upper hand in ancient nights, using sound to navigate and attract mates.
Researchers also analyzed rare living links like Prophalangopsis obscura. By using micro-scanning laser-doppler vibrometry on a 150-year-old museum specimen, scientists reconstructed its low-pitch song at approximately 5 kHz, confirming traits consistent with ancient prophalangopsids.
Frequently Asked Questions
How did researchers reconstruct 165-million-year-old insect calls?
Researchers combined phylogenetic analysis, laser vibrometry on modern insect wings, computer simulations of fossilized wing vibrations, and machine-learning models trained on wing morphology.
Did bats drive the evolution of high-frequency insect calls?
What pressures caused insects to develop ultrasonic signals?
Scientists propose that early mammals, non-mammalian ancestors, and acoustic niche partitioning among crowded calling species drove the evolution of high-frequency and pure-tone signals.
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