It is likely that some dinosaurs mumbled or cooed with closed mouths, according to a study.
According to the study published in the journal Evolution, researchers highlighted how dinosaurs made sound and also examined the evolution of a specialized way birds emit sound -- closed-mouth vocalization.
As birds descended from dinosaurs, the study endeavors to understand the origin and evolution of the unique vocal organ of birds and the large array of sounds it can produce.
Closed-mouth vocalization is the sound that is emitted through the skin in the neck area while the beak is kept closed. To make it, birds typically push air that drives sound production into an esophageal pouch rather than exhaling through the open beak.
To understand when and how closed-mouth vocalization evolved, researchers used a statistical approach to analyze 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 vocalization.
"Looking at the distribution of closed-mouth vocalization in birds that are alive today could tell us how dinosaurs vocalized," said Chad Eliason, Researcher, University of Texas.
Interestingly, only animals with a relatively large body size (about the size of a dove or larger) use closed-mouth vocalization behavior.
As dinosaurs are members of the archosaur group and many had large body sizes, it is likely that some dinosaurs made closed-mouthed vocalizations in a manner similar to birds today, perhaps during mating displays.
"Our results show that closed-mouth vocalization has evolved at least 16 times in archosaurs, a group that includes birds, dinosaurs and crocodiles,” added Eliason.
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Researchers, however, are still not certain about how the ancestors of modern archosaurs vocalized. But the occurrence of closed-mouth vocalization across birds and crocodiles -- the two surviving groups of archosaurs -- indicates that closed-mouth vocalization can emerge in diverse archosaur species depending on behavioral or environmental circumstances.