“We estimate that the species would have been capable of honk-like sounds,” said first author Julia Clarke of the University of Texas at Austin. “Honk-like and quack-like.”
Vegavis iaai isn't a newly discovered species. The fossil was discovered on Vega Island in the Arctic Peninsula over two decades ago. It took awhile for the fossil to be properly prepared — the soft, delicate bird bones were locked up tight in a hard “cantaloupe of rock” called a concretion — but Clarke helped identify it as a novel species in a paper published in 2005.
While analyzing the remains in high resolution, Clarke found something special, hidden in a spot where rock hadn't quite been removed from the specimen: signs of a syrinx, an organ found in modern birds. It sits near the heart, composed of rings of thick cartilage and soft tissues, and allows birds to make their unique vocalizations.
Based on the shape of the syrinx, the researchers believe the bird would have made honks like a modern duck. That's a pretty satisfying find, given the fact that Vegavis iaai was already thought to be most closely related to ducks and geese.
Clarke feels it was a lucky find: The soft tissue of the syrinx is often absent in fossils, so the fact that the structure was preserved at all is no small feat. If the specimen hadn't been exquisitely prepared, with most of the rock around it removed, Clarke wouldn't have been looking at it in such high resolution. But if the rock matrix had been cleared away from the spot she stumbled upon, it might have brought the delicate vocal organ with it. All the stars aligned, and Clarke was fortunate enough to have bird squawks on the brain at the time.
“I honestly don’t know if I’d have seen or recognized these structures if I hadn’t already started a project trying to fugue out how we’d approach the question of studying avian dinosaur vocalization,” she said.
Clarke and her colleagues went back to study other recently found fossils, looking for more signs of syrinxes. They've found at least one other squawk box: one in a 50-million-year-old bird that had been reported, but never studied. (Clarke and her team fixed that problem, and are talking with engineers about using the shape of the organ to reconstruct that slightly-less-ancient bird's sounds.) But in all their searching of non-avian dinosaurs, they didn't find any signs of similar structures in the literature. Since they now know that syrinxes from the age of the last non-avian dinosaurs can be preserved, they suspect that this conspicuous absence in the fossil record means that only would-be birds developed this particular structure.
“It's negative evidence,” Clarke said. “But it's still part of the story.”
So when did birds first make birdlike sounds? Scientists believe that birds began to break into the branches that would lead to extant species around 80 million year sago, Clarke explained, and it seems likely that this ancestral bird would have come with a syrinx already in tow.
“The big question is how much earlier it might go,” Clarke said. “Just look at feathers. We used to think they were unique to just this one group, and now we have them in a lot of non-flighted dinosaurs.”
But while scientists now believe that feathers first evolved for some other purpose — colorful mating displays or insulating layers to keep out the chill — and were then adapted as avian birds took flight, Clarke suspects that the syrinx came along later in the game, sometime during the Cretaceous period that began 145.5 million years ago. Flying may have led to honking (and chirping and tweeting, depending on the shape of the syrinx).
“We think it evolved after some of the respiratory innovations linked to the evolution of flight, sometime after that but before that bird ancestor,” Clarke said “But we can't be sure yet. What would be ideal is more data.”