Fossilized wings have made it possible to hear the sounds of insects that disappeared around 165 million years ago.
Researchers studied 20 wings belonging to nine species discovered in Inner Mongolia, China. These Middle Jurassic insects were related to modern grasshoppers and crickets. In these animals, the male can produce a call by rubbing part of one wing against the other. The fossil wings preserved traces of this sound-producing mechanism.
Reconstruction of a Jurassic mammal and insect.
Credit: Chuang Zhao
To understand how a fossil can reveal a sound, the wings must be examined very closely. A row of small teeth rubs against another part of the wing. Their spacing, along with the size of the vibrating area, directly influences the frequency produced. These structures are sufficiently well preserved on some fossils to be measured.
The team compared these measurements with those of living insects and with the relationships between the species. Computer models were then used to estimate the frequency and general form of the calls. A machine-learning method complemented the work by estimating their likely rhythm.
Several species may have emitted sounds around 5,000 Hz, a frequency comparable to that of some modern crickets. But one species, Sigmaboilus peregrinus, stands out. Its call may have exceeded 20,000 Hz, entering the ultrasonic range.
Why emit such high-pitched sounds? The authors suggest several possibilities. High-pitched calls may have allowed males to communicate with nearby females while being harder for certain predators to detect. Different frequencies could also have helped several species living in the same place avoid masking one another’s calls.
The researchers specifically mention early mammals and other small predators capable of hearing these insects. Pressure from these animals may have encouraged the diversification of the signals.
The method now opens up the possibility of reconstructing other vanished soundscapes when the sound-producing organs are sufficiently well fossilized. New specimens could reveal which frequencies dominated in different environments and how animal communication changed over the course of evolution.