|Most insect fossils look like this. This is an impression of an ancient dragonfly from the Jurassic.|
Crickets, katydids and grasshoppers are well-known, of course, for their mating calls. Like most frogs and birds, these insects make noise to attract the opposite sex. A male cricket chirps to signal to nearby females that he’s ready for mating. Mating calls are handy, since a loud sound can reach potential mates a long distance off, and since a lady cricket may be able to follow a sound more easily than a scent when trying to find Mr. Cricket hidden in the grass, particularly since crickets and their kin hop around a lot, possibly leaving a fragmented scent trail. You may have heard that some crickets’ chirping can even be used as a thermometer! Fossil evidence indicates that these noisy insects have been singing to each other since before the time of the dinosaurs.
The new fossil katydid was described by Jun-Jie Gu and colleagues from Beijing, working alongside other scientists from Bristol, UK and Kansas, USA. This fossil bug, named Archaboilus musicus, comes from Inner Mongolia, China and lived 165 million years ago, in the middle of the Jurassic Period. (The scientific publication is available here, if you’re interested.) The fossil itself is an impression of the large wings of the insect, and it is so exceptionally preserved that even the fine details of the wings can be examined. And that is where the story gets really interesting, for it is the anatomy of the cricket wing that holds the secret to its song.
|Left: Photos of the fossil itself. Close-ups of the left and right wing impressions.|
Right: Line drawings of the wings, to give a clearer view of the structure.
From Gu et al. 2012.
Crickets and katydids make noise by a process called stridulation, the rubbing together of certain body parts, in this case, the wings. One wing has a file, a series of ridges, while the other wing has a scraper, or plectrum. When the wings are slid past each other, the scraper is dragged across the file and it produces a sound (grasshoppers are a little different, their scraper is on their hind leg, which they drag across the file on their wing). What kind of sound is produced is dependent upon the anatomy of the file. If you have enough information about the structure of the file, you can make a number of inferences about the kind of sound the bug makes. And as it happens, the remarkable preservation of the fossil of A. musicus gives us tons of information.
A. musicus had symmetrical wings – a file and a scraper on each wing – and the structure of these files is preserved beautifully in the fossil. According to the researchers who did the study, the fossil’s file is ideal for producing low-frequency, pure-tone sounds. Comparing the fossil’s anatomy with living katydids and crickets, the authors could even estimate the frequency of the ancient bug’s chirps (6.4 kHz, if you’re wondering). Modern-day katydids who produce similar style sounds are all nocturnal, chirping at night while lying low during the day, and it’s probable that Archaboilus lived a similar lifestyle. In addition, the authors state that low-frequency chirps are better for communicating on the ground than for calling from the trees, implying that our fossil katydid lived on the ground while it called out for mates.
|Left: Microscope image of the file of a modern-day katydid (Cyphoderris).|
Right: Close-up of the file of the fossil Archaboilus. The two are very similar.
From Gu et al. 2012.
How about that? We’ve put together a detailed idea of the lifestyle of this 165 million-year-old insect, just by knowing what kind of sound it made, which we can figure out just by looking at the structure of part of its wing. That’s paleontology at its best.
But there’s more!
As stated, A. musicus only chirped at one frequency, which implies that other frequencies in the night sky may have already been occupied by the mating calls of other animals. Night time in the Jurassic forest may have featured a whole orchestra of sounds from all different sorts of insects and amphibians. Isn’t it fun to imagine what it would have sounded like listening to a chorus of ancient animals singing to each other in the Jurassic night?
Well get this. These scientists were able to learn so much from this fossil, and get such a complete understanding of how this insect produced its sound, that they were able to recreate it. By taking the information the fossil offered and comparing it to modern-day chirping insects, these paleontologists produced this soundtrack: the chirp of Archaboilus musicus.
For a more technical take on this study, check out the post about it over on my buddy Steve's blog, Ninjemys!