Think of the chattiest creatures in the animal kingdom and songbirds, dolphins, and—yes—humans probably come to mind. Turtles probably don’t register. But these charismatic reptiles also communicate using a large repertoire of clicks, snorts, and chortles. Now, by recording the “voices” of turtles and other supposedly quiet animals, scientists have concluded that all land vertebrate vocalizations—from the canary’s song to the lion’s roar—have a common root that dates back more than 400 million years.
The findings imply animals began to vocalize very early in their evolutionary history—even before they possessed well-developed ears, says W. Tecumseh Fitch, a bioacoustician at the University of Vienna who was not involved with the work. “It suggests our ears evolved to hear these vocalizations.”
Several years ago, University of Arizona evolutionary ecologist John Wiens and his graduate student Zhuo Chen started looking into the evolutionary roots of acoustic communication—basically defined as the sounds animals make with their mouths using their lungs. Combing the scientific literature, the duo compiled a family tree of all the acoustic animals known at the time, eventually concluding such soundmaking abilities arose multiple times in vertebrates between 100 million and 200 million years ago.
But Gabriel Jorgewich-Cohen, an evolutionary biologist at the University of Zürich, noticed an oversight: turtles. Though Wiens and Chen had found that only two of 14 families of turtles made sounds, he was finding a lot more. He spent 2 years recording 50 turtle species in the act of “speaking.”
Microphones in hand, Jorgewich-Cohen and his colleagues had also discovered acoustic vocalizations in three other creatures not known to do so: a legless amphibian called a caecilian; a lizardlike New Zealand reptile called a tuatara; and lungfish, a freshwater, air-breathing fish that is considered to be the closest living relative of land animals.
“They really were able to get some very unusual recordings from some very unusual species,” says Fitch, who studies the evolution of speech.
Of the 53 species Jorgewich-Cohen’s team recorded, the star was the South American wood turtle (Rhinoclemmys punctularia), a fist-size species sometimes sold as a pet. It made more than 30 vocalizations, including a creaking door utterance used exclusively by males courting females and a squeaking, crying sound produced only by young turtles. In general, some sounds were associated with aggression such as biting, whereas others seemed to be a way to greet new individuals and were often accompanied by head bobbing.
By adding this previously unknown chatter to the existing data on acoustic communication, Jorgewich-Cohen and colleagues built a new, more comprehensive evolutionary tree consisting of some 1800 species. Every branch of this tree contained animals that made these sounds, they report today in Nature Communications, suggesting acoustic communication evolved just once in a common ancestor of land animals and lungfish approximately 407 million years ago.
“That’s amazing!” says Elizabeth Derryberry, a behavioral ecologist at the University of Tennessee, Knoxville, who was not involved with the work. “It suggests that acoustic communication evolved in concert with lungs.”
The work could help scientists trace the evolution of communication in our own species, adds Anthony Russell, an emeritus evolutionary biologist at the University of Calgary. But he expects the new findings to draw controversy. The researchers assume other animals are listening and responding to the vocalizations they recorded in many of the quieter species, “but such an assumption is, at best, very bold,” he says. It could be that no one pays any attention to these noises.
Jorgewich-Cohen is already working on that problem. He is presently documenting how turtles and other quieter species use these sounds. He also wants to compare the sounds of land vertebrate and lungfish with those of other fish to see whether the acoustic evolutionary tree extends even further back in time. “Do we share the ability of sound production with some groups of fish?” he asks. “If yes, the origins of acoustic communication must be much older than what we hypothesize.”