Jurassic katydids sang in a deeper register than their modern-day kin, a new study suggests. Katydids, crickets, and a number of other creatures make their musical chirps by scraping one rough body part against another—a process known as stridulation. Previously, scientists hadn't discovered fossils that preserved the music-making structures, so they couldn't determine whether the ancient insects chirped at a single frequency, as some living species do, or across a variety of frequencies. Now, an analysis of katydid wing fragments (second and fourth images from left) from 165-million-year-old rocks in northern China that include well-preserved versions of the music-making structures (depicted at left and third from left) reveals that the ancient katydids sang at a single frequency of about 6.4 kilohertz, or about 6400 cycles per second. That tone is about half the frequency created by today's katydids but within the range of tones generated by living species of crickets, the researchers report online today in the Proceedings of the National Academy of Sciences. The single-frequency chirps, each of which lasted about 16 milliseconds (as heard in the video), would have helped the katydids distinguish the calls of their species amid the cacophony of a forest filled with other insects. Because all modern-day katydids that use single-tone chirps are active at night, the team suggests that the newly described Jurassic species also was nocturnal—a lifestyle that would have diminished predation by small dinosaurs that foraged in the daytime.
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