Fossils Reveal the Songs of Jurassic-Era Insects

Researchers have reconstructed the songs of ancient relatives of today's katydids, insects related to crickets, using fossils from Daohugou, a rural site in China. The fossils belong to ensiferans, a group that also includes crickets and grigs, and date to the Jurassic Period, 200 million to 145 million years ago, when the area was a hot, humid forest with giant ferns and conifers. The team, including Jun-Jie Gu, an evolutionary biologist at Sichuan Agricultural University in Chengdu, China, published its findings August 25 in the Proceedings of the National Academy of Sciences (PNAS), a peer-reviewed journal.

The fossils preserve wing structures these insects used to make mating calls by strumming their wings, which biophysicist Fernando Montealegre-Zapata of the University of Lincoln in England calls "nature's violin." One wing carries a row of microscopic teeth; as the wings close, a scraper on the other wing strikes the teeth, producing vibrations the wing amplifies into a "syllable," the basic unit of sound. A song emerges as the insect opens and closes its wings.

For 20 fossils representing nine extinct species, the researchers simulated wing acoustics from tooth spacing, wing size and vibrating area, then used an evolutionary family tree to estimate call pitch. They checked the method against living katydids, crickets and grigs, using only wing photos. Fossils do not preserve syllable repetition, so the team trained a machine-learning model on living ensiferans, whose repetition patterns relate to body size and temperature, to simulate calls at Jurassic temperatures.

Roy Plotnick, a paleobiologist at the University of Illinois Chicago who was not involved in the study, said the work shows each species had a distinctive call, which could help mate recognition. Scans of the fossils' ears, on their forelegs, support this. One species called in ultrasound, above human hearing, nearly 100 million years before bats evolved it. Gu said the fossils show "we can actually hear what 165-million-year-old animals were saying."