In films such as Jurassic World, predatory dinosaurs are typically shown giving off a fearsome roar before unleashing carnage on their unsuspecting victims, but a new study published online in the journal Evolution indicates that they may have actually sounded quite different.

According to researchers from Midwestern University in Arizona, the University of Texas at Austin, some dinosaurs would have mumbled or cooed with closed mouths, similar to how many modern-day bird species can emit sounds with their beaks shut tightly.

“Looking at the distribution of closed-mouth vocalization in birds that are alive today could tell us how dinosaurs vocalized,” Chad Eliason, a postdoctoral researcher at the UT Austin Jackson School of Geosciences and co-author of the study, explained in a statement Monday.

“Our results show that closed-mouth vocalization 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 vocalization behavior,” he added.

Here is an example of what this sounds like in an ostrich:

Examining modern birds for more insight

Eliason, lead author Tobias Riede, a physiology professor at Midwestern University, and their colleagues examined the evolution of closed-mouth vocalizations in birds in order to learn more about how they developed their unique vocal organ. Since birds descended from dinosaurs, they believe that their work could also reveal how those ancient lizards produced sound.

Closed-mouth vocalizations, the study authors explained, are typically emitted through the skin in the neck region while the beak remains closed. Birds produce these noises by pushing the air which precipitates sound production into an esophageal pouch instead of through an open beak, producing a call that tends to be quieter and lower in pitch than open-mouth vocalizations.

To better understand how these calls, which are only used by birds when they want to attract a mate or need to defend their territory, evolved, the research team developed a statistical method which they used to analyze the distribution of these calls among bird and reptilian groups. They analyzed 208 bird species and found that 52 utilize closed-mouth vocalizations.

The reason for this, Riede explained, is due to simple physics: “The inflation of an elastic cavity could present a size-dependent challenge. The lung pressure required to inflate a cavity depends on the tension in the wall of the cavity, and this tension increases for smaller body sizes.” While the study makes a compelling argument, the researchers admit that there is no direct evidence in the fossil record that indicates just what dinosaur might have actually sounded like.

“To make any kind of sense of what nonavian dinosaurs sounded like, we need to understand how living birds vocalize,” said study co-author Julia Clarke, a professor at the Jackson School of Geosciences. “This makes for a very different Jurassic world. Not only were dinosaurs feathered, but they may have had bulging necks and made booming, closed-mouth sounds.”

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Image credit: Thinkstock

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