It’s a staple of every children’s book and natural history museum exhibition-not to mention every single incarnation of Jurassic Park: dinosaurs unleashed fearsome roars. But, according to one new study, they may actually have been far more softly spoken, and communicated through closed lip ‘coos’.

Yes, coos.

In a study published in the journal Evolution a team of researchers examined the sounds made by 52 bird species that use “closed-mouth” vocalizations. To imagine what such vocalizations sound like, do away with the chirpiness of songbirds, and think of the low, murmuring tones of a pigeon or a dove.

That’s what the study suggests dinosaurs might have sounded like when defending territory or attempting to track a mate. And as mind-boggling as that might be, consider the fact that birds are basically today’s living dinosaurs.

Colors show probability of each branch being an open-mouth vocalizer (blue) or a closed-mouth vocalizer (red). Pies show the probabilities that the ancestors of birds and crocodiles, palaeognath birds, and neognath birds used closed-mouth vocalization. Credit: Tobias Riede

As Chad Eliason, a postdoctoral researcher at The University of Texas Jackson School of Geosciences and the study’s co-author said in a statement:

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.

And so,

Looking at the distribution of closed-mouth vocalization in birds that are alive today could tell us how dinosaurs vocalized.

X-ray image of a ring dove (Streptopelia risoria) producing cooing sounds with a closed mouth.

But given that fossils don’t come with audio recorders, it’s pretty difficult to be certain as to whether or not this repeatedly evolving trait applied to the ancestors of modern day archosaurs. But, the very fact that not only birds, but also crocodiles use closed-mouth vocalizations shows us that the trait can emerge in a diverse range of archosaurs, and emerge fairly easily given the right environmental and behavioral conditions.

Julia Clarke, a professor at the Jackson School of Geosciences and co-author, elaborated:

To make any kind of sense of what nonavian dinosaurs sounded like, we need to understand how living birds vocalize… 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.

So, not a roar, but at least the coos may have been “booming.”

Lead image by PePeEfe (Own work) [CC BY-SA 4.0 (http://creativecommons.org/licenses/by-sa/4.0)], via Wikimedia Commons