Giant ferocious dinosaurs may have cooed, not roared

A new study suggests that some dinosaurs may have used closed-mouth vocalizations in which sounds are projected through the thin skin of their necks(Credit: LadyofHats/Creative Commons)

The giant Tyrannosaurus Rex stomps through heavy foliage shaking the ground with every step. Its prey tries to outrun the mighty beast but it finds itself cornered in a cluster of trees. The king of the dinosaurs sees its dinner has nowhere to run, tilts back its giant head and bellows a mighty ... coo? That just might be the case based on new research.

A new study that will be published in next month's edition of the journal Evolution involving researchers from the University of Texas at Austin, Midwestern University in Glendale, Arizona, Memorial University of Newfoundland and the University of Utah suggests that some dinosaurs didn't scream through their giant mouths like tyrannical beasts. Instead, they may have emitted sounds such as coos and hoots much like some modern species of birds.

Researchers came to this conclusion by studying the evolutionary patterns of birds, one of the modern descendants of dinosaurs. Some species of birds like doves and owls use closed-mouth vocalization, a mechanism of speech where birds emit sounds through the skin in their necks by pushing air into an esophageal pouch in a move usually reserved for attracting mates or defending their territory.

Researchers ran through the evolutionary expansion of this form of speaking in 208 different species of birds. They identified 58 species that used closed-mouth vocalizations and charted their evolutionary history back to the age of dinosaurs. The results showed that closed-mouth vocalization evolved at least 16 times in the group known as the archosaurs, a group that holds birds and reptiles as well as all dinosaurs.

Bigger dinosaurs may have relied more on closed-mouth vocalization due to their massive size, says Tobias Riede, a physiology professor from Midwestern University who co-authored the study. It turns out that it takes a larger body to inflate the pouch for vocalization purposes.

"The inflation of an elastic cavity could present a size-dependent challenge," Riede says. "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." Therefore, smaller beasts would have had a harder time making closed-mouthed vocalizations.

This isn't the first time that scientists have suggested that dinosaurs spoke in ways other than the giant roars we've become accustomed to in stories and movies. Palentologist Phil Senter of Fayetteville State University in North Carolina published a paper in 2008, in the journal Historic Biology, suggesting that dinosaurs related to crocodiles and birds spoke in a similar fashion to closed-mouth vocalizations or didn't speak at all.

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