In the minds of many, the clearest pictures of dinosaurs probably come from a certain movie, but scientists are constantly revising our understanding of their appearance, their size and, with a new study, their vocalizations. A team from the University of Texas at Austin has identified the oldest-known fossil of a bird's vocal organ, which helps paint a picture about how dinosaurs transitioned from making closed-mouth coos and booms, towards the diverse birdsong their descendants sing today.

Modern birds make their lovely chirrups and whistles with the help of an organ known as the syrinx, which sits at the fork of the trachea, just above the lungs, and vibrates to create sound. The soft tissues at work there are supported by rings of cartilage, which tend not to fossilize as well as bone, but examples of the organ have been found in the past.

This particular discovery was made in a Vegavis iaai fossil, an early species of bird that lived around 66 million years ago, during the time of the dinosaurs. That makes it the oldest known fossilized syrinx, and interestingly, dates it to a time when many other animals, lacking a syrinx, were likely making ostrich-like closed-mouth vocalizations. After the discovery, the team spent two years scouring other dinosaur fossils for signs of the organ, with no luck, which led them to the conclusion that the syrinx may have been a relative late-comer in the avian evolutionary tree.

The syrinx (top), sits at the fork of the trachea in birds and allows them to produce diverse songs and calls, very differently to the larynx-based vocal organ of crocodiles and other species(Credit: J. Clarke/UT Austin)

"This finding helps explain why no such organ has been preserved in a nonbird dinosaur or crocodile relative," says Julia Clarke, who led the study and originally discovered the syrinx in an existing fossil. "This is another important step to figuring out what dinosaurs sounded like as well as giving us insight into the evolution of birds."

The fossil was discovered in Antarctica in 1992, but its syrinx wasn't found until 2013. Looking at the asymmetrical shape of it, the team was able to better infer how the animal might have sounded, letting it honk like its modern relatives, ducks and geese.

Comparing it to other modern and fossilized syrinxes, the team hopes to learn more about how this and other early birds vocalized, and other anatomical changes over time that may be linked, such as brain size.

"Here, we begin to outline how fossilizable characteristics of the syrinx may inform us about sound features, but we need a lot more data on living birds," says Franz Goller, co-author of the study. "Remarkably, prior to this work, there is almost no discussion of these important questions."

The research was published in the journal Nature, and the team describes the study in the video below.

Source: UT Austin

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