New research on the evolution of bird vocalizations may help us understand how some dinosaurs vocalized. A study in the journal Evolution details how closed-mouth vocalizations evolved in birds and their ancestors.
Closed-mouth vocalizations are a unique type of vocalization found in birds and some of their relatives, including crocodiles. To make sounds without opening their beaks, birds push the air through the esophageal pouch. These sounds are generally quieter and lower frequency. The cooing noise of a pigeon is an example of a closed-mouth vocalization. These sounds are usually used for sexual displays while open mouth vocalizations can be used for general communication.
Using a grant from the Gordon and Betty Moore Foundation, researchers from several universities collaborated to analyze the vocalization types of over 200 bird species. They found that 52 species use closed-mouth vocalizations and that the trait has evolved separately at least 16 times in archosaurs. Archosauria is a clade representing birds, crocodiles, and dinosaurs. If closed-mouth vocalizations evolved in many archosaurs independently, at least some extinct dinosaurs would have used them. The researchers found that smaller birds only used open-mouth vocalizations; closed-mouth vocalizations were seen in larger animals. The lead author believes this is due to the amount of pressure needed to inflate the esophageal pouch. A small bird, such as a finch, wouldn’t have the necessary strength required.
Since dinosaurs are in the same clade as birds and tended to be large, it’s likely that many of them would have used closed-mouth vocalizations. Currently, scientists don’t entirely know how dinosaurs vocalized. This study suggests that at least some dinosaurs mumbled and made other low-frequency sounds. These low pitch noises may have been used for mating displays and could have been combined with open-mouthed vocalizations. We may not know exactly what dinosaurs sounded like but the coo of a pigeon may be more accurate than the loud roars seen in movies.
Tobias Riede et al. Coos, booms, and hoots: the evolution of closed-mouth vocal behavior in birds. Evolution (2016).