Jurassic Insects Sang 165 Million Years Before Bats

A team of scientists measured structures on 20 fossilized insect wings roughly 165 million years old and used them to calculate what those insects sounded like while they were alive. The insects belong to the order Orthoptera, relatives of today’s crickets and grasshoppers, and their fossils were found in the Jiulongshan Formation in Inner Mongolia, China. The study appears in Proceedings of the National Academy of Sciences, volume 123, issue 36, article e2615107123, DOI 10.1073/pnas.2615107123, with Jun-Jie Gu of Sichuan Agricultural University as lead author. The result is the first reconstruction of a soundscape from a Jurassic forest, and it shows that ultrasonic calling in insects existed well before bats appeared on Earth.

Until now the prevailing view held that bats, with their echolocation, forced insects to shift to ultrasonic frequencies beyond that predator’s hearing range. Gu and colleagues, in the paper published in Proceedings of the National Academy of Sciences, write that “very little is known about the soundscape of long vanished environments, such as Jurassic forests,” so they set out to fill that gap with fossil evidence rather than assumption.

How sound is read out of stone

Insects in this group produce sound by rubbing one wing against the other, a process called stridulation. Tiny, tooth-like ridges on the wing, which are well preserved in fossils, reveal the spacing between the edges that generated the sound, and that spacing, combined with the size of the vibrating wing, determines the frequency of the call. The authors analyzed nine species, seven from the family Prophalangopsidae and two from the family Haglidae, combining phylogenetic analysis, laser Doppler vibrometry, numerical simulations of wing vibration, and a machine learning based model to estimate the likely calling frequencies. From that data they assembled a hypothetical soundscape of a Jurassic forest.

Did bats really trigger the rise of ultrasound?

The results show a diversity that was not expected. Most of the nine species called with a pure tone around five kilohertz, within the range of human hearing, similar to some crickets alive today. One species, Sigmaboilus peregrinus, produced calls above 20 kilohertz, in the ultrasonic range, beyond what a human ear can detect. “We reconstructed their acoustic landscape and revealed pure tone, diverse, and in some cases ultrasonic calls,” the research team writes in the paper.

That finding is exactly what undercuts the long standing assumption. For decades, bats have been cited in the scientific literature as the main driver behind the evolution of ultrasonic hearing and calling in insects, since they are nocturnal hunters that rely on echolocation. If insects were already using ultrasound before bats even existed, that mechanism cannot be the sole explanation. “This refutes the hypothesis that bats were the sole driver of ultrasound evolution in these insects,” the authors write.

Sources differ on the exact size of the time gap. The site Sci.News reports that bats appeared roughly 55 million years after these insects, while a direct quote from the paper itself, carried by the same site, puts the gap at nearly 100 million years. Phys.org does not give a specific figure, stating only that the insects used ultrasound long before bats appeared. Either way, both sources agree on the sequence: ultrasonic calling predates bats.

So who was listening to insects before bats existed

According to the authors, the diversity of calls, from pure tones to ultrasound, may have served a defensive purpose. Early mammals and similar predators with sensitive hearing were likely already listening for insect calls, pushing insects to develop new ways of calling out to avoid detection. A shift to higher frequencies could have let males attract females while making it harder for predators to pinpoint their location, while at the same time differences in frequency may have kept the calls of different species in the same forest from overlapping and drowning each other out.

These are conclusions the authors themselves frame as a plausible explanation, not a proven mechanism. The study is a reconstruction based on the morphology of fossilized wings, phylogenetic comparison with nearly a hundred living species, and a machine learning model, not a recording of actual sound or a direct observation of Jurassic predator behavior. It can reveal the frequency and likely structure of the calls, but not whether predators of that era actually responded to these sounds, nor that predator pressure is the only reason behind the diversity found. The link between the presence of early predators and the evolution of quieter, harder to locate calls remains a connection the authors propose, not a causal relationship this study has proven.