Pop culture would have us believe that fearsome dinosaurs growled before chomping down their prey, but a new study in Texas suggests that some dinosaurs more likely cooed like doves instead of roaring like lions.

Ferocious Dinosaurs?

Millions of years ago, the Tyrannosaurus rex gobbled up other large dinosaurs in a single bite and ran rampantly in the forested river valleys of North America.

In pop culture, the T-rex is depicted as a ferocious and ruthless dinosaur, with its big head, razor-sharp teeth and enormous whip tail, which may have helped it hunt for food. For instance, this prominent dinosaur has been featured in movies such as Jurassic Park, where it was portrayed as a frightening and vicious animal.

Now, a team of researchers from the University of Texas at Austin, Memorial University of Newfoundland, Midwestern University in Arizona and the University of Utah found a clue that may change our perceptions and turn these beasts into less scary creatures.

The Link Between Birds And Dinosaurs

Modern birds make low-pitched sounds called closed-mouth vocalizations by pushing air that powers the production of sound into a pouch in the esophagus.

Birds do this instead of exhaling the air out of their beaks, so the sound is generated through the skin in the neck area. They often emit sounds while defending their own territory or while trying to attract mates. Examples include the cooing of doves, ostriches or pigeons.

According to scientists, there is no direct fossil evidence yet to tell us how or what dinosaurs sounded like when they were alive. But the new report, which focuses on the evolution of vocalizations of birds, may provide us fresh insight because modern birds descended from dinosaurs.

Evolution Of Vocalization

In order to understand how closed-mouth vocalization progressed over time, the researchers used a statistical approach to examine its distribution among birds and reptiles. Out of 208 bird species, the team identified 52 that use closed-mouth vocalization.

Chad Eliason, study co-author and a postdoctoral researcher, says their findings show that the vocal ability evolved at least 16 times among archosaurs — a group of birds, dinosaurs and crocodiles.

He says animals with a relatively big body size, particularly those about the size of a dove or bigger, found it easier to perform closed-mouth vocalizations.

Physiology professor Tobias Riede, the first author of the study, says the connection with larger bodies is "a matter of physics."

Riede says the rise and fall of the elastic cavity could become a challenge depending on the size of the animal. He says the lung pressure needed to inflate a cavity all depends on the tension in the cavity's wall. This tension increases for smaller bodies.

Scientists say that the occurrence of closed-mouth vocalizations across crocodiles and birds — the only surviving archosaurs — suggests that the ability can come from a wide range of archosaur species depending on circumstances, be it environmental or behavioral.

Bird-Like Cooing And Mumbling

Most dinosaurs such as the T-rex had relatively large bodies. Researchers say it is likely that some dinosaur groups used closed-mouth vocalizations, cooing and mumbling like the birds of today.

Scientists still have no fossil evidence to support this theory, but Julia Clarke, co-author of the report, says the findings offer clues.

Clarke says to understand what nonavian dinosaurs sounded like, it is important to understand how modern birds vocalize.

She says this would change our image of the Jurassic world: dinosaurs were not only feathered, but they may have made closed-mouth sounds and had protruding necks.

Details of the study are published in the journal Evolution.

Photo: Greg Clarke | Flickr

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