"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."