Chirps, trills, and clicks—these are the sounds that once filled Earth’s forests 165 million years ago.
This remarkable auditory reconstruction features the calls of nine prehistoric insect species, the result of more than a decade of meticulous work by an international scientific team.
These ancient insects, relatives of modern crickets and grasshopper-like katydids, produced sound by rubbing their wings together. By examining the fossilized wings of these prehistoric creatures alongside the bioacoustics of their living descendants, researchers employed computer modeling and machine learning techniques to replicate their calls.
According to the team, this reconstructed soundscape represents the most evidence-based approximation of a Jurassic auditory environment ever achieved. Their findings, along with audio samples, were published in the journal Proceedings of the National Academy of Sciences.
While this soundscape captures only a fraction of the sounds that would have echoed through Jurassic forests, it represents the closest scientists have come to understanding the acoustic world of that era.
For decades, paleontologists have sought to determine what sounds dinosaurs made. However, the soft tissues responsible for producing and modulating sound—such as lungs, throats, and mouths—rarely fossilize. (Despite what viewers may have seen in “Jurassic Park III,” one cannot simply blow air through a model of a dinosaur’s vocal organ to determine its sound.)
Insects living alongside these dinosaurs offer a more promising avenue for acoustic reconstruction: scientists have discovered numerous fossilized insects from the Jurassic period whose sound-producing wings remained perfectly preserved.
More than a decade ago, Jun-Jie Gu, a professor of entomology at Sichuan Agricultural University, and collaborators obtained 20 such specimens. These exceptional fossils, discovered in Inner Mongolia, China, included nine species of cricket and katydid ancestors, each possessing unique structures on their front wings.
Although these extinct insects diverged from their modern relatives millions of years ago, they share many characteristics, including size and shape. Like contemporary crickets and katydids, they featured comb-like ridges on one wing and a scraping structure on the other. When rubbed together, the scraping structure caught the ridges, producing a series of rapid clicks that blended into continuous chirps. The resonance and pitch of these chirps depended largely on ridge spacing, wing surface area, and wing movement speed.
To reconstruct the calls of these extinct insects, researchers began by mapping how their living relatives produce sound. They utilized high-speed cameras and laser Doppler vibrometry to measure the precise movements and vibrations of insect wings. This data enabled them to develop and validate a computer model capable of predicting how wing structure influences sound production.
Finally, the researchers input 2D models of the insect wings into their computer model, along with information about each species’ relationship to the living insects whose movements and songs had already been studied. The result was a collection of nine distinct calls that straddles the line between familiar and otherworldly.
The insect chirps spanned the frequency spectrum, but one species—Sigmaboilus peregrinus—produced sounds beyond human hearing, generating high-frequency ultrasonic calls.
“The first time we reconstructed the song and saw it was over 20 kilohertz, we were so excited,” said Dr. Gu. Scientists have long theorized that insects developed ultrasonic communication to evade their newly evolved adversaries: bats. However, bats did not appear on Earth until roughly 100 million years after the Jurassic period ended.
In their study, Dr. Gu and colleagues challenge the conventional view that bats were the primary drivers of ultrasonic communication in insects, arguing that Jurassic insects had ample reasons to evolve this ability. One possibility, Dr. Gu suggests, is that these insects wanted to “have their own channels.”
If every forest insect sang at the same frequency, he explained, all their messages would have become muffled.
“One hundred sixty-five million years ago, the insect community may have already had sophisticated acoustic niches—multiple species occupying different frequency bands from low to high,” Dr. Gu observed.
Another explanation the researchers propose is that these insects evolved ultrasonic calls to avoid detection by early mammals and other predators.
“It’s a very plausible hypothesis,” said Rex Cocroft, a professor of biological sciences at the University of Missouri. “Predation is a major force in the evolution of communication.”
Dr. Cocroft, who studies insect communication and was not involved in the new study, described the work as “a beautiful validation of our ability to use the traits of modern-day species to look into the past.”
Dr. Gu hopes his work will encourage people to rely less on Hollywood when imagining life during the Jurassic.
“Before, all the sounds of the Jurassic came from films like ‘Jurassic Park,’ but those sounds are not real. They come from artists. This is the first reconstruction of the acoustic landscape of insects in ancient forests based on scientific methods and real fossil materials,” he stated.
Nevertheless, Dr. Gu’s team has not completely rejected Hollywood: the researchers spent years assisting the creators of the new Netflix documentary mini-series “The Dinosaurs” in developing an accurate soundscape for their Jurassic scenes.
Having the calls of these extinct insects allowed producers to “weave a much deeper, more accurate fabric of Jurassic audio reality, more so than has ever been done before onscreen,” said Thomas Land, a zoologist who worked as a researcher on the show. “It’s such a small detail,” Mr. Land noted of adding insect sounds, “but we did it because every choice like that makes the whole much more realistic.”
