Prehistoric Voice Box Reveals Dinosaur-Era Sounds

Sixty-eight million years ago when dinosaurs roamed the Earth and Antarctica was warm and pleasant, a bird that looked like a cross between a duck and a goose filled the Antarctic skies with a deafening, honking call. Scientists know this through analysis of the oldest fossilized syrinx - a bird's equivalent of a voice box.

The organ, nicknamed the "squawk box," was a syrinx of Vegavis iaai, a Cretaceous-age bird found on Antarctica's Vega Island 66-69 million years ago. The discovery, outlined in the journal Nature, offers key, tangible evidence not only for what some prehistoric birds sounded like, but also birds' oversized relatives - dinosaurs.

Since birds evolved from dinosaurs, they may have developed the syrinx later - and dinosaurs likely never developed it. This means dinosaurs might not have been able to make noises similar to bird calls. In fact, it's also likely dinosaurs did not roar.

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"Roaring is biologically implausible for dinosaurs," said Julia Clarke, a paleontologist at The University of Texas at Austin Jackson School of Geosciences, who discovered the squawk box. "We need to kill the dinosaur roar."

Clarke and her colleagues propose that most dinosaurs may have lacked a syrinx.

"This does not mean that they were silent," she said. "Crocodiles produce load low frequency sounds with a closed mouth. Most dinosaurs could have used the crocodile approach with a larynx (voice box) and made these kinds of sounds."

To determine what sounds V. iaai made, Clarke and her team used a high resolution X-ray imaging technique called microcomputed tomography to construct a three-dimensional computerized model of the syrinx. They also looked at how 12 groups of present-day birds vocalize, noting the related "hardware" of these birds that is made up bones and soft tissues. The researchers then compared that data on modern birds with their V. iaai squawk box model.

"Evidence from both other skeletal material as well as the syrinx indicates Vegavis iaai is closely related to living ducks and geese," Clarke said. "The shape of the asymmetrical syrinx (left vs right sides) is most similar to living female ducks. In males the syrinx is even more asymmetrical - with a giant protrusion on one side. Both male and female ducks create loud honks with an open mouth."

This means the dinosaur-era bird likely honked like a duck or a goose.

Intriguingly, the squawk box of this bird was more complex than that of even some birds today. Since these birds evolved from relatives that lived before V. iaai, an even simpler sound-producing organ must have emerged before V. iaii's lifetime. When that precisely happened, for now, remains a mystery.

The discovery, however, does suggest that "the sound landscape would be much more diverse" for birds during the dino age than that for dinosaurs, which weren't birds. (All birds are now considered to be dinosaurs, though.) Clarke added that the sounds would have included, not just honks, but also higher pitched calls and rooster-like crows. Neither the prehistoric birds nor the dinosaurs could roar, based on the fossil evidence.

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Patrick O'Connor is in the Department of Biomedical Sciences at the Heritage College of Osteopathic Medicine and the Ohio Center for Ecology and Evolutionary Studies. He too is interested in how dinosaurs and ancient birds vocalized and commented that this study "documents, for the first time, the syrinx in a Mesozoic bird. It is only one of a very few examples in the entire fossil record of birds for this part of the body, and it is a part of a bird that we know is extremely important in birds alive today with their vast array of vocalizations and social interactions that are an essential part of their biology."

As for what the dinosaurs may have sounded like, O'Connor believes they made an array of "standard reptile sounds such as hisses, squeaks and barks."

To better determine what sounds birds living in the Dino Age made, part of Clarke's team is working with engineers to reconstruct how the ancient birds communicated. Birds are not proverbial "bird brains," as they are actually among the animal kingdom's smartest creatures.

As a result, the researchers think that one reason birds evolved such big brains was so they could process sounds and other forms of communication. Previously it was thought that most of their development was geared toward wings and flight, but mating, conflicts and other more social matters were clearly also important to the ancient birds.

Top image: Dinosaurs and recreations of the bird Vegavis iaai based on a new specimen recovered in Antarctica. Credit: Gabriel L. Lio -for the Museo de Ciencias Naturales, Bernardino Rivadavia, Argentina