Chirps, trills and clicks — these are the sounds of Earth’s forest 165 million years ago:
This buzzy chorus contains the calls of nine species of prehistoric insects that an international team of scientists spent more than a decade reconstructing.
The insects, which are the relatives of modern-day crickets and grasshopper-like insects known as katydids, created sound by rubbing their wings together. By studying the fossilized wings of these ancient insects, as well as the bioacoustics of their living relatives, the researchers were able to use computer modeling and machine learning to replicate their calls.
They say this cacophony is the best evidence-based approximation of a Jurassic soundscape ever created. They published their work, and audio samples, in the journal Proceedings of the National Academy of Sciences.
Although this soundscape accounts for only a small fraction of the sounds that echoed through the forests of the Jurassic, it’s as close as scientists have gotten so far.
For decades, paleontologists have tried to figure out what dinosaurs sounded like. But the soft tissues responsible for producing and shaping the sounds they made, like their lungs, throats and mouths, rarely fossilize. (And despite what you may have seen in “Jurassic Park III,” one cannot simply blow air through a model of a dinosaur’s vocal organ to see what it sounded like.)
The insects living alongside these dinosaurs, however, present a better acoustic chance: Scientists have unearthed dozens of fossilized insects from the Jurassic whose sound-producing wings were perfectly preserved.
Over a decade ago, Jun-Jie Gu, a professor of entomology at Sichuan Agricultural University, and his colleagues got their hands on 20 such specimens. Their bumper crop of fossils, which were found in Inner Mongolia, China, contained nine species of cricket and katydid ancestors, all of which had unique structures on their front wings.
Although these bygone insects are millions of years diverged from their modern relatives, they share many characteristics, including size and shape. Like their cricket and katydid relatives, they had comb-like ridges on one wing and a scraping structure on the other. When rubbed together, the scraping structure catches the ridges, creating a series of rapid clicks that blend together to form a continuous chirp. The resonance and pitch of their chirps depend largely on the spacing of their ridges and the surface area and speed of their wings.
To reconstruct the calls of these long-extinct insects, the researchers started by mapping how their living relatives make sound. They used high-speed cameras and a technique known as laser Doppler vibrometry to measure the precise movements and vibrations of the insects’ wings. The researchers used this data to create and test a computer model that could predict how a wing’s structure influences the sounds it makes.
Finally, the researchers plugged 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 they had already 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 known as Sigmaboilus peregrinus went beyond what humans can hear, producing a high-frequency ultrasonic call.
“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 make their debut on Earth until roughly 100 million years after the end of the Jurassic.
In their study, Dr. Gu and his colleagues challenge the long-held view that bats were the primary drivers of ultrasonic communication in insects, arguing that insects in the Jurassic had ample reasons to evolve the ability. One reason, Dr. Gu proposed, is that these insects wanted to “have their own channels.”
If every insect in the forest sang their songs at the same frequency, he said, all their messages would have gotten 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 said.
Another explanation the researchers provided 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 with the new study, called the work “a beautiful validation of our ability to use the traits of modern-day species to look into the past.”
Dr. Gu hopes that his work will help people rely less on Hollywood when trying to imagine what life was like 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 said.
Still, Dr. Gu’s team hasn’t completely rejected Hollywood: The researchers spent years helping the creators of the new Netflix documentary mini-series “The Dinosaurs” create an accurate soundscape for their Jurassic scenes.
Having the calls of these extinct insects allowed producers on the show 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 said of adding in a layer of insect sounds, “but we did it because every choice like that makes the whole much more realistic.”
