Using lasers, computer models and AI, researchers reconstructed the calls of 165-million-year-old relatives of modern crickets and katydids from fossilized wing fragments found in China; one of these fossil insects called at frequencies beyond human hearing, challenging the long-held assumption that bat predation was what pushed insects into the ultrasonic realm.
“Very little is known about the acoustic landscape of long-gone environments, such as the Jurassic forests,” Dr. Jun-Jie Gu of Sichuan Agricultural University and colleagues wrote in their paper.
“The sounds made by dinosaurs and other charismatic vertebrates are not definitively known because their vocal organs rarely preserve well in fossils.”
“Unlike tetrapod vocal cords, the sound-producing organs present in the sclerotized cuticle of some arthropods do fossilize well.”
“For example, the stridulatory structures (file, plectrum) can be observed and measured in the fossilized forewings of male crickets and allies.”
“These fossils incorporate a fingerprint of the acoustic signals they generated, offering a unique window into the soundscapes of the past.”
In their research, the authors analyzed 20 fossilized ensiferan insects — seven species within the Prophalangopsidae and two within Haglidae, an extinct family that existed from the Triassic to Cretaceous — unearthed from the Jiulongshan Formation in Inner Mongolia, China.
Dated to the Middle Jurassic, roughly 165 million years ago, the fossils preserved the delicate wing structures these insects used to ‘sing’ by rubbing one wing against the other — a process called stridulation.
To decode these ancient songs, the researchers combined several techniques: phylogenetic analysis comparing the fossils to nearly 100 living insect species, laser vibrometry measurements of modern insect wings, computer simulations of how the fossilized wings would have vibrated, and machine-learning models trained to predict call patterns from wing shape.
Their results show a surprisingly diverse soundscape: most of the nine species produced low, pure-tone calls around 5 kHz (kilohertz), similar to those of some living crickets.
But one species, Sigmaboilus peregrinus, appears to have called at frequencies above 20 kHz, in the ultrasonic range, beyond what humans can hear.
The finding is significant because it predates the emergence of bats, which appeared roughly 55 million years later and are typically credited with driving the evolution of ultrasonic communication and hearing in insects, as a way to evade echolocating predators.
The new evidence suggests ultrasonic signaling in insects was already established long before bats existed.
This means bats were not the sole force behind the evolution of high-frequency insect calls.
Instead, the scientists propose that early mammals and other predators could have pressured insects to develop quieter, harder-to-localize pure-tone signals.
