We tend to associate dinosaurs with thunderous roars, but new research indicates that this is likely incorrect.
You’d feel it rather than hear it – a deep, visceral throb rising from somewhere beyond the dense foliage. It would rumble in your ribcage and bristle the hairs on your neck like a foghorn. It would have been terrifying in the Cretaceous period’s dense forests.
We have few clues for what noises dinosaurs might have made while they ruled the Earth before being killed off 66 million years ago. The remarkable stony remains discovered by palaeontologists provide evidence of these creatures’ physical prowess but not much about how they interacted and communicated. Of course, sound does not become fossilised.
However, based on what we know about animal behaviour, dinosaurs were almost certainly not silent.
Scientists are now piecing together some of the clues about how dinosaurs might have sounded, thanks to new, rare fossils and advanced analysis techniques.
This puzzle has no single solution. Dinosaurs dominated the planet for around 179 million years and during that time, evolved into an enormous array of different shapes and sizes. Some were extremely small, such as the Albinykus, which weighed less than a kilogramme (2.2lbs) and was probably less than 2ft (60cm) long. Others, such as the titanosaur Patagotitan mayorum, which may have weighed up to 72 tonnes, were among the largest animals to have ever lived on land. They could run on two legs or plod on four. They would have made a wide range of noises in addition to their diverse body shapes.
Some dinosaurs had extremely long necks, up to 16m (52ft) in the largest sauropods, which would have altered the sounds they made (think about what happens when a trombone is extended). Others had strange skull structures that, like wind instruments, could have amplified and changed the tone of the animals. A herbivorous hadrosaur named Parasaurolophus tubicen, for example, would have been responsible for the terrifying calls described at the beginning of this article.
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P. tubicen had a massive crest protruding from the back of its head that was nearly 1m (3.2ft) long. Inside, there were three pairs of hollow tubes running from the nose to the top of the crest, where two of the pairs made a U-bend to wind back down towards the animal’s airways and the base of the skull. The other pair expanded to form a large chamber near the crest’s peak. They came together to form a 2.9m (9.5ft) long resonating chamber.
Palaeontologists at the New Mexico Museum of Natural History and Science discovered a nearly complete skull of this strange-looking Parasaurolophus in 1995. They were able to take 350 images of the crest using a computerised tomography (CT) scanner, allowing them to see inside in unprecedented detail. The organ was then digitally reconstructed and simulated how it would behave if air was blown through it in collaboration with computer scientists.
“I would describe the sound as otherworldly,” says Tom Williamson, who worked on the dig and is now the museum’s curator of palaeontology. “It sent chills through my spine, I remember.”
The vibrating grunts of the southern cassowary, which lives in Australia, are the closest analogues he can find in living animals today. This flightless bird makes a series of deep bellows and growls that reverberate through the dense jungle in which it lives.
“I can easily picture a misty Late Cretaceous rainforest setting with those eerie sounds thundering in the background,” Williamson says. “The sounds are low in frequency, which is exactly what is required to penetrate the dense undergrowth.”
Fossilised remains of these animals have even inspired some to create musical instruments based on hadrosaur skulls
Williamson and colleagues simulated the sound P. tubicen might have made with and without various vocal organs, such as the larynx found in mammals and modern reptiles. They discovered that even without a larynx or equivalent voice box, the dinosaur may have made a noise due to how air would have resonated inside the crest when the animal blew air through it, similar to blowing over the opening of a jug.
“We didn’t have preserved soft tissues, so we don’t know if these dinosaurs had sound-producing organs like mammals and birds,” Williamson says. “Because the crest is such a long structure, it became clear that a sound-producing organ was not required to get it to resonate.”
Other hadrosaurs had similar, if not so dramatic, musical crests on their skulls that are thought to have doubled as a visual display and an aid to vocalisation. The majority of these animals would have made low-frequency sounds, and the fossilised remains of these animals have even inspired some to create musical instruments based on hadrosaur skulls.
Not all dinosaurs had what amounted to a trumpet on top of their heads. Furthermore, there is no fossil evidence of dinosaur voice boxes, leading some to speculate that the animals were mute.
“We do have fossil clues that can tell us about different parameters of the airways like diameter and length,” says Julia Clarke, a palaeontologist at the University of Texas at Austin. “We can compare those geometries to see how they relate to today’s dinosaurs – birds.”
Clarke, on the other hand, has another clue that has added another piece to the puzzle. In the mid-2000s, she and her colleagues examined the preserved skeleton of an early type of bird discovered on Vega Island, a tiny spit of land at the tip of the Antarctic Peninsula, by Argentinian researchers over a decade earlier. The fossil itself is still partially embedded in a rock. Clarke and her team were able to detect bits of the fossil that were hidden from view by using advanced CT scanning techniques. They then used the scans to digitally reconstruct the fossil.
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