How do you imagine walking through a Jurassic forest? If you are lucky enough to find a fossil-rich region like the Junggar Basin in Northwest China, you could turn to the fossil record to get an idea of the sizes and shapes of the animals you might encounter (1). You could look to fossils of plants to reconstruct the canopy—especially since in this region, many stumps were found in growth position, and there are megaplant fossils as well as fossils of seeds and spores. You could look through databases of fossils and findings and create a detailed computer model of the plant and animal life that you might see or touch as you walk. You could look to geological records to understand what temperature and humidity might have felt like. But how do you imagine the sounds, particularly the animal calls and songs? What do you hear in a Jurassic forest?

Such a question is what Jun-Jie Gu and Fernando Montealegre-Z set out to answer, aided by a mid-Jurassic katydid fossil collected in the Juilongshan Formation in Inner Mongolia, China (2). The fossil, described as Archabolius musicus, a member of the extinct family Haglidae, had particularly well-preserved stridulatory structures according to the researchers. A. musicus finds its closest living relatives in the families Prophalangopsidae (includes hump-winged grigs) and Tettigoniidae (modern katydids).

Modern katydids “call” by rubbing a toothed vein on one wing against a plectrum on the other (stridulation). Their wings are asymmetric: the left wing has only a functional file, but the right wing has sound-radiating cells, a plectrum and only an atrophied or absent file. Modern katydids, therefore produce sound only by overlapping the left wing over the right wing. The A. musicus fossil, however, has symmetric wings more like the existing members of the Prophalangopsidae family.

Using songs and the biomechanics of wing stridulation in species that exist today as well as the few available wing fossils that have been found, the authors were able to reconstruct the main acoustical properties of the Jurassic katydid. In resonant (“musical”) species, the tooth spacing increases toward the basal end of the file. The tooth distribution and wing morphology of A. musicus, suggest that it produced resonant, pure-tone sounds. The authors fitted the length of the A. musicus file into phylogenetic regression models to predict the frequency of the sound: 6.4 kHz.

A clip of the call is available here.Movie from Gu, J-J. et al. (2012) PNAS 109, 3868–73 (suppl. info.)

This call is only an extrapolation of one of the many sounds you might have heard if you could have walked in a late Middle Jurassic Forest, but as more fossils are discovered and we learn more about how modern insects generate their calls, such extrapolations will become more accurate. Eventually perhaps, with the help of more math and biology, we will compose a Jurassic symphony from these bits of song.

References

1. Hinz, J.K. et al. (2010) A high-resolution three-dimensional reconstruction of a fossil forest (Upper Jurassic Shishugou Formation, Junggar Basin, China). Palaeobio Palaeoenv 90, 215–240. http://dx.doi.org/10.1007/s12549-010-0036-y
2. Gu, J-J. et al. (2012) Wing stridulation in a Jurassic katydid (Insecta, Orthoptera) produced low-pitched musical calls to attract females. http://pmid.us/22315416