Reconstruction of an extinct soundscape reveals ultrasonic communication in the Jurassic.

Very little is known about the acoustic landscape of long-gone environments, such as the Jurassic forests. The sounds made by dinosaurs and other charismatic vertebrates are not definitively known because their vocal organs rarely preserve well in fossils. Unlike tetrapod vocal cords, the sound-producing organs present in the sclerotized cuticle of some arthropods do fossilize well. For example, the stridulatory structures (file, plectrum) can be observed and measured in the fossilized forewings of male crickets and allies. These fossils incorporate a fingerprint of the acoustic signals they generated, offering a unique window into the soundscapes of the past. While call frequencies can be inferred from fossilized wings using phylogenetically informed predictions, the reconstruction of wing vibrations and the songs' temporal patterns from fossil material remains elusive. Integrating phylogenetics, laser Doppler-vibrometry, numerical simulations, and an AI-based approach, 20 ensiferan fossils (nine species) from a single location (Jiulongshan Formation, Inner Mongolia, China) were studied to recreate the acoustic landscape of the Middle Jurassic. These insects produced pure-tone calls, an adaptation to avoid localization by eavesdropping predators. They also exhibited rich diversity in their calling song frequencies and repertoires, facilitated by specialized file morphologies and wing-size variation. One species called above 20 kHz, suggesting that ultrasonic communication in insects was established long before the emergence of bats in the Eocene. Evolving mammalian hearing thresholds suggest early predators imposed acoustic pressures before bats. This arms race with singing ensiferans likely drove Jurassic insect song diversity and the evolution of mammalian and insect auditory systems.