Over 100 million years ago, chirping insects known as katydids dominated Earth’s night sounds. Now, the fossils reveal what the ears of the katydid that heard those sounds were like.
Twenty-four fossils of nearly 160-million-year-old katydids unearthed in China represent the first known insect ears, researchers report Dec. 12 in Journal of the Academy of Sciences.
These ancient sound sensors — the same as those found in modern katydids — picked up the first short-range, high-frequency calls of any kind, helping insects hide from predators.
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Insects were the first inhabitants of the earth to send sound waves through the air to communicate with creatures over greater 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 eardrums to hear (SN: 11/15/12). However, because well-preserved insect eardrums are rare in the fossil record, it is unclear how katydid ears evolved, say paleontologist Chunpeng Xu of the Nanjing Institute of Geology and Paleontology in China and colleagues.
Analyzes of Chinese fossils date back to the mid-Jurassic period, between 157 million and 166 million years ago. The previous record holders of the oldest eared insects, the katydids and cicadas found in Colorado, are about 50 million years old.
What’s more, the sound structures in 87 fossil 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 of up to 16 kilohertz. . (Humans, by comparison, can hear frequencies from roughly 20 hertz up to 20 kilohertz).
The high frequency of pipits is not far away, which would allow the katydids to communicate over a short distance. Such a feature may have been useful because the hearing mammal around the same time Xu says better. Restricting certain calls could help katydids hide from curious predators on the hunt for the insect feast.
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