Over 100 million years ago, the chirps of insects known as katydids dominated the sounds of Earth’s nights. Now, fossils reveal what the katydid ears that heard those sounds looked like.
Twenty-four fossils of roughly 160 million-year-old katydids unearthed in China represent the earliest known insect ears, researchers report December 12 in Proceedings of the National Academy of Sciences.
These ancient sensors of sound — identical to the ones found on today’s katydids — may have picked up the first short-range, high-frequency calls of any kind, helping the insects hide from predators.
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Insects were the first land dwellers to send sound waves through the air, allowing the creatures to communicate over longer distances than sight often allows (SN: 7/15/21). While some insects use their antennae to detect vibrations in the air, katydids have mammal-like ears that use an eardrum to hear (SN: 11/15/12). Yet because well-preserved insect eardrums are rare in the fossil record, it’s unclear how katydid ears evolved, say paleontologist Chunpeng Xu of the Nanjing Institute of Geology and Paleontology in China and colleagues.
Analyses of the Chinese fossils push the known record of male and female katydid ears’ ability to listen for potential mates or male competitors to the mid-Jurassic, between 157 million and 166 million years ago. The previous record holders for oldest insect ears, katydids and crickets found in Colorado, are around 50 million years old.
What’s more, sound-producing structures on 87 fossilized male katydid wings from China, South Africa and Kyrgyzstan — which date from about 157 million to 242 million years ago — may have generated a variety of chirps, including high-frequency calls up to 16 kilohertz. (Humans, by comparison, can hear frequencies from roughly 20 hertz to 20 kilohertz.)
High-frequency chirps don’t travel far, which would have allowed katydids to communicate over short distances. Such a trait may have been useful because mammal hearing was improving around the same time, Xu says. Limiting the range of some calls could have helped katydids hide from predatory eavesdroppers on the hunt for an insect feast.