Jurassic tune made audible: the love song of an extinct cricket
The love song of an extinct cricket that lived 165 million years ago has been brought back to life in an interdisciplinary research project involving experts in biomechanics, bioacoustics and palaeontologists. The song – possibly the most ancient known musical song documented to date – was reconstructed from microscopic wing features on a fossil discovered in North East China. It allows us to listen to a musical song that would have been heard by dinosaurs and early mammals roaming Jurassic forests at night, and to conjecture on the auditory capabilities of these animals at the time.
HFSP Cross-Disciplinary Fellow Fernando Montealegre-Z and colleagues
Some 165 million years ago, the world was host to a diversity of sounds. Primitive bushcrickets and croaking amphibians were among the first animals to produce loud sounds by stridulation (rubbing certain body parts together). Modern-day bushcrickets – also known as katydids – produce mating calls by rubbing a row of teeth on one wing against a plectrum on the other wing. But how their primitive ancestors produced sound and what their songs actually sounded like was unknown – until now.
This research project was the product of an interdisciplinary international collaboration between bioacousticians and palaeontologists. On discovering several insect fossils, a group of Chinese palaeontologists from the Capital Normal in Beijing and from the University of Kansas contacted Dr Fernando Montealegre-Z, an HFSP Long-Term Fellow, expert in the biomechanics of hearing and singing in insects at Bristol’s School of Biological Sciences, UK. The Chinese researchers provided an exceptionally detailed bushcricket fossil from the Mid Jurassic period. The specimen had such well-preserved wing features that the details of its stridulating organs were clearly visible under an optical microscope. Such information has never been obtained before from insect fossils.
Dr Montealegre-Z examined the anatomical construction of the fossil’s song apparatus, and compared it to 59 living bushcricket species for which the biomechanics of sound production was known. He concluded that this animal must have produced a single pure tone frequency (a musical song). Therefore the fossil was named as Archaboilus musicus. Amazingly, based on the detailed morphology of fossil wings, Dr Montealegre-Z could reconstruct the songs emitted by these ancient insects. Following biomechanical principles that he discovered some years ago, he established that this extinct insect sang a tone pitched at 6.4kHz and that every bout of singing lasted 16 milliseconds (See figure). This turned out to be enough information to acoustically reconstruct a complete sequence of the song itself, possibly the most ancient known musical song documented to date.
This finding indicates that pure tone communication was already exploited by animals in the middle Jurassic, some 165 million years ago. For this extinct insect, as for living bushcricket species, singing constitutes a key component of mate attraction. Singing loud and clear advertises the presence, location and quality of the singer, a message that females choose to respond to – or not. Using a single tone, the male’s call carries further and better in noisy environments, and therefore is likely to serenade more females, but females should be tuned to the male's frequency. This also implies that the acoustic environment was already quite noisy 165 million years ago with many animals (such as amphibians and other arthropods) singing at the same time, possibly chorusing, within the additional background noise produced by waterfalls, streams and wind. Today, all species of katydids that use musical calls are nocturnal so musical calls in the Jurassic were also most likely an adaptation to nocturnal life. Being nocturnal, Archaboilus musicus probably escaped from diurnal predators like the bird ancestorArchaeopterix, but probably faced nocturnal Jurassic insectivorous mammals like Morganucodon, which were able to listen to sounds of low frequencies such as that of A. musicus.
This Jurassic bushcricket thus sheds light on the potential auditory capacity of these insects to detect such conspecific notes, as well as that of other animals to predate on them. It also suggests the evolutionary mechanisms that drove modern bushcrickets to develop ultrasonic communication for sexual pairing and for listening and avoiding an increasingly relevant echolocating predator, but that only happened 100 million years later, possibly with the appearance of bats.
Reference
Wing stridulation in a jurassic katydid (insecta, orthoptera) produced low-pitched musical calls to attract females. Gu*, J. J., Montealegre-Z*, F., Robert, D., Engel, M. S., Qiao, G. X. & Ren, D. 2012. Proc. Natl. Acad. Sci. USA, DOI:10.1073/pnas.111837210 (*) joint first authors
