On Mar. 6, Netflix released the four-part documentary "The Dinosaurs." It drew attention because Steven Spielberg, who made the movie "Jurassic Park," joined as an executive producer, but the scientific community focused more on the sound. That's because the insect sounds from the dinosaur-inhabited forest were reconstructed based on scientific research findings.
A research team led by Fernando Montealegre-Zapata of Lincoln University in the United States said it "reconstructed the sounds produced by Kiturami and katydids 165 million years ago in the Middle Jurassic of the Mesozoic by rubbing their wings together," in the Proceedings of the National Academy of Sciences (PNAS) on Aug. 25 local time. Spielberg inserted this sound into the documentary.
◇Compared with modern insects, AI reproduces sounds
From summer to fall, Kiturami or katydids in the forest make sounds to find mates by rubbing their wings together. On one forewing is a wing vein called the file, with serrated, knobby protrusions like a saw. When these protrusions strike the scraper at the edge of the opposite wing, the wing vibrates and makes sound.
Montealegre-Zapata, together with Dong Ren of Capital Normal University in China, analyzed 20 wing fossils of insects corresponding to nine species of the family Gryllidae and the family Tettigoniidae that lived in Inner Mongolia in the Middle Jurassic. They focused particularly on the file with protrusions and the overall wing shape. That's because the sound made when a bush-cricket rubs its wings is determined by the spacing of the protrusions on the file and the wing area.
To reconstruct the sounds of Jurassic insects, the researchers analyzed their descendants today. They confirmed the structures of the wing's file and scraper, and fired lasers at the wings to confirm vibration modes. With this information, they built a computer model of insect sounds and identified the frequency and basic structure of the sounds produced by fossil wings. They then used artificial intelligence (AI) to estimate the rate at which the basic sound was repeated and reproduced the bush-cricket sounds of a Jurassic forest.
Many of the reproduced sounds had a very narrow frequency band. They were the simplest pure tones, with only a single frequency. The researchers suggested that in forests noisy at night with many animal calls, bush-crickets produced pure tones to conceal their location while effectively transmitting their own signals. In other words, each insect effectively had its own musical note.
◇Insects that produced ultrasound also identified
Jurassic insects were estimated to have produced vibrations at a relatively low frequency band around 5 kHz, similar to today's Kiturami. But some insects had higher frequency bands. Based on its wing structure, Sigmaboilus peregrinus was estimated to have produced sound in ultrasound above 20 kHz, beyond the range of human hearing.
Until now, scientists thought insects came to communicate with ultrasound because of bats. Bats emit ultrasound into their surroundings and detect reflections off objects to determine their locations. If insects emit ultrasound, they can jam bats or provide false information.
The findings show insects produced ultrasound 100 million years before bats appeared. The researchers interpreted this as the result of an "acoustic arms race" in Jurassic forests. As early mammals became better at locating sound-producing insects, the insects in turn evolved higher-pitched sounds. Montealegre-Zapata said, "Bats may not have introduced ultrasound into a quiet environment for the first time; they may have entered a soundscape already filled with ultrasonic signals."
However, the study has a decisive limitation. From the wing structures preserved in fossils, the researchers identified the pitch and basic structure of the insects' sounds, but they cannot know the rhythm and tempo of the songs. Those are controlled by the insect's nervous system and wing movements, neither of which are preserved in fossils. To depict the age of dinosaurs, imagination from someone like Spielberg is still needed.
References
PNAS (2026), DOI: https://doi.org/10.1073/pnas.2615107123