53 species previously thought to be silent have vocal communication

It turns out that birds, amphibians, and mammals aren’t the only animals to communicate through sound. Scientists have discovered dozens of animal species that were once thought to be silent, but are actually voice communicators, including singing sea turtles and living fossils that produce acoustics.

Tuatara, considered living fossils, also use voice communication. / Credit: Gabriel Jorgewich-Cohen

An international research team has found evidence that 53 species of four major groups of vertebrate organisms – turtles, tuatara, limbless amphibians and lungfish – all thought to be silent creatures, actually intentionally create sounds to communicate. Their findings were published Tuesday in Nature Communications.

Gabriel Jorgewich-Cohen, a Ph. student at the University of Zurich’s Paleontological Institute and Museum and lead author of the study, said their results provide evidence of “acoustic ability in several groups previously considered non-vocal”.

He specifically pointed to turtles, which his team found exhibit “large and complex acoustic repertoires.” Turtles will make sounds to indicate when they are ready to mate, she said, but they also communicate with each other much earlier, before they even hatch.

“The sea turtles will sing from inside their egg to synchronize hatching,” he said in an interview with BBC News. “If they call from within, they all go out together and hopefully avoid being eaten.”

One type of sea turtle, Natator depressus, otherwise known as the flat-backed turtle, was recorded making sounds that resemble croaking, scratching, and chirping. And the South American river turtle makes sounds as it cares for its young, Jorgewich-Cohen said.

Acoustic sounds produced by tuatara – lizard-like creatures whose closest relatives are now extinct reptiles that once roamed dinosaurs – were also detected – as well as a species of caecilian and the South American lungfish, which reside in the water but have lungs that require air to survive. Jorgewich-Cohen told CBS News that males of most species make sounds during courtship and that some make sounds when fighting members of their own species.

The researchers did not include defensive sounds in their research, such as the hissing and sniffing of lizards.

With these findings, the Jorgewich-Cohen team was also able to trace the evolution of vertebrate vocalization and map vocal communication in the vertebrate tree of life. That mapping showed that this style of communication is an ancient technique that did not evolve between various groups, but from a common origin.

That origin, the researchers said, existed about 407 million years ago during the Devonian period, a time when the supercontinent Gondwana was still intact and the “Age of Pisces” began.

Despite this ancient origin, it took scientists years to make these discoveries about vertebrate communication. Jorgewich-Cohen told CBS News there are “many reasons” for such a delay.

“Science is influenced by humans and we tend to focus on things we can easily perceive. The fact that frogs, birds and mammals make frequent audible sounds makes them good models for studying,” he said, adding that many of the species studied by his teams were not studied because they were not so obviously vocal.

“The fact that sounds are refracted by water also makes it harder for us to hear,” he added. “Also, some of these species don’t vocalize as often as birds do. Some don’t vocalize very loudly and some are so rare that most people never see them.”

For Jorgewich-Cohen, these findings are just the beginning of his research. She told the American Association for the Advancement of Science that she is carrying out her studies to compare the sounds made by terrestrial vertebrates and lungfish with those made by other fish to create a more accurate and detailed evolutionary tree.

“Do we share the sound production capability with any group of fish?” she asked during the interview. “If so, the origins of acoustic communication must be much older than we assume.”

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