Jurassic cricket's song recreated

08.02.2012 14:07

BBC: Night-time in the Jurassic forest was punctuated by the unmistakable sound of chirping bush crickets.

This is according to scientists who have reconstructed the song of a cricket that chirped 165 million years ago.

A remarkably complete fossil of the prehistoric insect enabled the team to see the structures in its wings that rubbed together to make the sound.

The international team report their findings in the journal PNAS.

Scientists from the US and China discovered the tiny fossil and named their newly discovered species Archaboilus musicus , because the music-making structures in its body were so clearly visible.

When insect expert Dr Fernando Montealegre Zapata, from the University of Bristol, found out that his colleagues had such a remarkable fossil, he was keen to see it.

"I was very surprised," he told BBC Nature, "because those [structures] are very very small - at the microscopic level."

Dr Zapata studies sound production and communication in living insects, working out how the musical instruments contained in many insects' bodies produce a particular sound, and exactly how that sound is made.

He immediately asked the question: "Could we reproduce the sounds [this insect made] from that fossil?"

Ancient music
Just like modern bush crickets - also known as katydids - the Jurassic insects produced music with their wings. A "plectrum" on one wing was dragged along a microscopic comb-like structure on the other.

This produces a continuous "chirp" as the male insects rub, or "stridulate" their wings in a scissor-like motion. Dr Zapata described this stridulation as similar to playing a tiny violin.

By looking at the wing structures, he explained, "I could estimate that the animal made pure, musical tones".

Such a single-note tone would have transmitted efficiently - a regular wave of sound penetrating a noisy environment cluttered with vegetation. This would have allowed a female cricket to detect a male's song from tens of metres away.

Dr Zapata then set out to calculate the frequency of the tone, which denotes how high- or low-pitched it sounded. To to this, he simply compared the size and shape of its music-making or "stridulatory" instruments to those of living cricket species.
"I produced a graph of [living] species, plotting the measurements of their sound-making structures against the frequency of the sound they made," he explained.

"Using the measurements, I could plot this extinct species onto that graph."

He discovered that A. musicus used a relatively low-pitched song, compared with modern bush crickets.

This suggested that the Jurassic forest was a cluttered and "noisy environment - especially at night", he said.

"There were probably frogs, other [insects] and sounds from the water," he said.

Being nocturnal, A. musicus would not have had to hide its musical call from predators that were active during the day, including the famous Jurassic bird, Archaeopteryx.

The crickets may have been hunted by early mammals. But bats - many of which feast on nocturnal insects - did not appear until about 100 million years later.

"That's when the modern katydids became ultrasonic," said Dr Zapata.

The researcher emphasised how lucky he and his team were to find this extraordinary fossil.

"This animal allows us to build a picture of the ecology of the Jurassic forest," he said, "and will give hints as to how other animals were singing at the time."

Prof Mike Ritchie from the University of St Andrews said it was surprising that "way back in early cricket time, they were already producing these very musical calls".

"People thought singing in crickets probably evolved later from a startle reflex," he told BBC Nature.

"But this suggests that [very early on] they were already... producing these lovely, pure tones to compete for a mate.

"If you think of Jurassic Park, we now know what it would have sounded like and it's different from what we expected; it's much more like today."
By Victoria Gill
Science reporter, BBC Nature