Dinosaurs may have cooed with closed mouths

Dinosaurs are often depicted as roaring ferociously, but it is likely that some of these prehistoric creatures may have mumbled or cooed with closed mouths, according to a new study.
The researcher from The University of Texas at Austin, Midwestern University in Arizona examined the evolution of a specialised way birds emit sound - closed-mouth vocalisation.
The study helps understand the origin and evolution of the unique vocal organ of birds and the large array of sounds it can produce. Since birds descended from dinosaurs, the research may also shed light on how dinosaurs made sound.
Closed-mouth vocalisations are sounds that are emitted through the skin in the neck area while the beak is kept closed.

To make them, birds typically push air that drives sound production into an esophageal pouch rather than exhale through the open beak. The coos of doves are an example of this behaviour.
Compared with sounds emitted through an open beak, closed-mouth vocalisations are often much quieter and lower in pitch.

Birds making closed-mouth vocalisations usually do so only to attract mates or defend their territory. At other times, they emit sounds through an open mouth.
To understand when and how closed-mouth vocalisation evolved, researchers including those from Memorial University of Newfoundland and the University of Utah used a statistical approach to analyse the distribution of this vocal ability among birds and other reptilian groups.

In total, the researchers identified 52 out of 208 investigated bird species that use closed-mouth vocalisation.
"Looking at the distribution of closed-mouth vocalisation in birds that are alive today could tell us how dinosaurs vocalised," said Chad Eliason, a postdoctoral researcher at The University of Texas.
"Our results show that closed-mouth vocalisation has evolved at least 16 times in archosaurs, a group that includes birds, dinosaurs and crocodiles. Interestingly, only animals with a relatively large body size (about the size of a dove or larger) use closed-mouth vocalisation behaviour," Eliason said.
Researchers still are not certain about how the ancestors of modern archosaurs vocalised. However, the occurrence of closed-mouth vocalisation across birds and crocodiles - the two surviving groups of archosaurs - indicates that closed-mouth vocalisation can emerge in diverse archosaur species depending on behavioural or environmental circumstances, said Tobias Riede, from Midwestern University.

Since dinosaurs are members of the archosaur group, and many had large body sizes, it is likely that some dinosaurs made closed-mouthed vocalisations in a manner similar to birds today, perhaps during mating displays.
However, at this point in time, no direct fossil evidence exists to reveal what dinosaurs sounded like.
The study was published in the journal Evolution.