Scientists Recreate Jurassic Forest Sounds from Fossilized Insects

Researchers have recreated the sounds of a Jurassic Period forest in Mongolia, focusing on the calls of katydids, an insect species known for its sound-making abilities. The study, based on fossil evidence, provides insight into the acoustic environment of 165 million years ago.

Paleontologists examined the delicate file and plectrum structure of katydid fossils to reconstruct their melodies. The file, a serrated hard strip on the underside of the left forewing, is scraped by a plectrum on the edge of the right forewing. This process creates vibrations that are resonated and amplified by a drum-like cell. The spacing of teeth on the plectra determines the frequency of the sound, with closely spaced teeth producing high frequencies and wider spacing yielding lower frequencies. The amplitude of the sound can be varied by the amount of pressure exerted from the file on the plectrum.

In the Jurassic forest, katydids had no competition for airspace from bats, as bats did not evolve for another million years. However, katydids had specialized ears to detect each other's calls, located on their front legs just below the knees. These ears have a three-part structure similar to that of mammals, with sound traveling into the outer ears, through the middle ears, and to the inner ears where a tiny sensory organ detects the sound vibrations.

The study authors hypothesize that the ability to produce sound by wing stridulation could have appeared before hearing as a defensive tool to deter terrestrial predators. In the Jurassic forests of China, there were plenty of insectivorous mammals and reptiles, such as tree-climbing theropods and flying pterosaurs, which might have been repelled by the katydids' squeaky calls.

Lead researcher Fernando Montealegre-Zapata, a biologist at the University of Lincoln in the UK, stated that the study provides a unique insight into the acoustic communication of ancient insects. "This is the first time we have been able to reconstruct the sounds of a Jurassic forest," he said. "It's a fascinating glimpse into the past."

The study, published in the journal PNAS, was conducted by an international team of researchers from the University of Lincoln, Capital Normal University in Beijing, and the Field Museum in Chicago. The team's findings contribute to our understanding of the evolution of acoustic communication in insects and the acoustic environment of the Jurassic Period.