Reconstruction of an extinct soundscape reveals ultrasonic communication in the Jurassic

A salient feature of biodiverse habitats is the acoustic landscape, which reveals key animal interactions and their ecologies. 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 fossils1. Unlike tetrapod vocal cords, the sound-producing organs present in the sclerotised cuticle of some arthropods do fossilise well2-4. For example, the stridulatory structures (file, plectrum) can be observed and measured in the fossilised forewings of male katydids and allies. These fossils incorporate a fingerprint of the acoustic signals they generated4-7, offering a unique window into the soundscapes of the past. Call frequencies can be inferred from fossilised wings using phylogenetically informed predictions8, yet the reconstruction of wing vibrations and the songs’ temporal patterns from fossil material remains elusive. Integrating phylogenetics, biomechanics, numerical simulations, and an AI-based approach, 20 ensiferan fossils (representing nine species) from a single location (Jiulongshan Formation, Inner Mongolia, China) were studied to recreate the acoustic landscape of the Middle Jurassic. These early singing insects produced pure-tone calls, an adaptation to avoid localization by eavesdropping predators. These species also exhibited rich diversity in their calling song frequencies and call repertoires, facilitated by specialised file morphologies and variation in wing size. While most species communicated using low frequencies, one species likely broadcast ultrasounds (>20 kHz). These findings support the hypothesis that ultrasonic communication in insects was established long before the emergence of bats, which appeared as fossil records in the Eocene. Analysis of mammalian hearing thresholds through time unveils potential undocumented coevolutionary pressures and constraints exerted by eavesdropping predators, prior to the evolution of echolocating bats. The arms race between ensiferan singing and auditory capabilities of early mammals likely constituted one of the key selective pressures driving Jurassic insect song diversity and the evolution of both mammalian and insect hearing systems.