Katydids had the first known insect ears 160 million years ago
More than 100 million years ago, chirping insects known as katydids dominated the sounds of Earth’s nights. Now fossils reveal what the ears of katydids that heard these sounds looked like.
Twenty-four katydid fossils about 160 million years old discovered in China represent the first known insect earsresearchers report on December 12 at Proceedings of the National Academy of Sciences.
These ancient sound sensors – identical to those found on today’s katydids – may have 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 earth to send sound waves through the air, allowing creatures to communicate over longer distances than sight often permits (SN: 07/15/21). While some insects use their antennae to detect vibrations in the air, katydids have mammalian 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. .
Analyzes of Chinese fossils push the known record for the ability of male and female katydid ears to listen for potential mates or male competitors to the mid-Jurassic, between 157 million and 166 million years ago. Former record holders for oldest insect ears, grasshoppers and crickets found in coloradoare about 50 million years old.
Additionally, sound-producing structures on 87 fossilized wings of male katydids from China, South Africa, and Kyrgyzstan—which date to around 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 about 20 hertz to 20 kilohertz.)
High-frequency chirps do not travel far, which would have allowed katydids to communicate over short distances. Such a trait may have been useful because mammalian hearing was improving around the same time, Xu says. Limiting the range of certain calls could have helped grasshoppers hide from prying predators looking for a feast of insects.