Think of a Tyrannosaurus rex. What sound comes to mind? Likely a fearsome, ground-shaking roar, etched into our collective imagination by movies like Jurassic Park. But paleontologists now reveal that this iconic sound is probably far from the truth. The actual soundscape of the dinosaur age was likely much more varied, and perhaps, even stranger, dominated by deep rumbles, resonant booms, and bird-like chirps.
The biggest challenge in discovering dinosaur sounds is that, unlike bones and teeth, the soft tissues responsible for producing sound – like larynxes or syrinxes – rarely fossilize. Sound itself, of course, leaves no trace in the rock record that spans the dinosaurs’ incredible 179-million-year reign. For decades, this lack of direct evidence left their voices largely to the realm of speculation and Hollywood sound design.
Unlocking Secrets from Bone
Despite the challenges, scientists are using ingenious methods and rare fossil finds to piece together clues about dinosaur vocalizations. One approach involves studying specific anatomical features preserved in bone that might have influenced sound production or transmission.
Take, for example, the remarkable crest of the herbivorous hadrosaur, Parasaurolophus tubicen. This creature sported an elongated, hollow crest on its head, almost a meter long. Advanced CT scanning of fossil skulls revealed the internal structure: a network of looping, hollow tubes and chambers running from the nose into the crest and back down to the airways. Scientists realized this elaborate structure acted as a powerful resonating chamber, much like a wind instrument or a trombone.
By digitally reconstructing the internal airways and simulating air passing through them, researchers were able to estimate the sounds Parasaurolophus might have produced. The result was a deep, low-frequency boom or rumble. These low-pitched sounds were particularly effective in penetrating the dense, humid forests of the Late Cretaceous period, suggesting they might have been used for long-distance communication or locating herd members. Crucially, the research showed that the crest itself could resonate air, meaning a complex voice box wasn’t even strictly necessary to create this sound.
Clues from Living Relatives
Since direct fossil evidence is scarce, scientists rely on a method called “phylogenetic bracketing.” This involves looking at modern-day animals that are the closest living relatives of dinosaurs – birds and crocodiles. By identifying vocal traits shared by both groups, researchers can infer characteristics likely present in their ancient dinosaur cousins.
Crocodilians, which split from a common ancestor with dinosaurs around 240 million years ago, offer one set of clues. Unlike the open-mouthed roars of movie monsters, crocodiles often produce deep, low-frequency rumbles using a closed mouth. These sounds can be so powerful they create visible vibrations in the water around them. Given the enormous size of many dinosaurs, scientists propose that giant species may have produced extremely low-pitched, closed-mouth rumbles, possibly even in the infrasound range – frequencies too low for human ears to easily perceive, but which might be felt as powerful vibrations. The common depiction of a predatory dinosaur roaring with its mouth wide open before an attack is also behaviorally questionable; predators typically prefer stealth over announcing their presence.
Birds, the direct descendants of dinosaurs, provide another vital perspective. Most vertebrates use a larynx for sound, but birds possess a unique vocal organ called a syrinx, located deep in the chest. A syrinx can allow for much more complex sounds, sometimes enabling birds to produce multiple pitches simultaneously. If non-avian dinosaurs had similar structures, their sounds could have been incredibly varied. Modern examples like the southern cassowary, known for its vibrating, booming bellows that travel through jungle undergrowth, offer a possible parallel for larger dinosaurs. Smaller, more bird-like dinosaurs might have produced squawks, whistles, or clicks.
Synthesizing these observations, scientists believe that dinosaur sounds were likely a diverse mix, incorporating elements of both avian complexity and crocodilian low-frequency power. Closed-mouth vocalization, similar to the cooing of doves or the booming of ostriches, is considered a strong possibility for many species, potentially used in social contexts like mating displays.
Echoes in Ancient Ears
Further insights come from studying fossilized dinosaur ears. Paleontologists can reconstruct the inner ear structure and delicate bones (stapes) preserved within skulls. Unlike mammals, which have three middle ear bones, dinosaurs possessed only a single stapes. This bone is key to transmitting sound vibrations to the inner ear.
The structure and size of the stapes suggest that many dinosaurs were particularly well-tuned to hear low-frequency sounds. In large species like T. rex, the stapes could be quite large, reinforcing this ability. However, the length of the cochlea, another inner ear structure, also provides clues about hearing range. A longer cochlea generally indicates the ability to hear a wider range of frequencies. Intriguingly, research on a mid-Cretaceous tyrannosaur ancestor, Timurlengia euotica, revealed unusually long cochlear ducts, suggesting it could perceive a broader spectrum of sounds than many other dinosaurs.
This capacity for hearing higher frequencies led some paleontologists to propose a fascinating hypothesis related to parental care. The elongation of the cochlea appears relatively early in the evolutionary lineage that includes dinosaurs, birds, and crocodiles (Archosauria). Since both modern bird chicks and young crocodiles use high-pitched “location calls” or chirps to communicate with parents, the ability to hear these frequencies might have evolved to support parental care behaviors in dinosaurs, suggesting baby dinosaurs also chirped and relied on their parents listening.
A Symphony of the Cretaceous
Piecing together these clues from anatomy, living relatives, and hearing capabilities paints a picture of a prehistoric soundscape far richer and more complex than simple roars.
Large dinosaurs, governed by the physical scaling relationship between body size and frequency, likely produced sounds far below or at the very low end of human hearing – deep rumbles, powerful booms, and vibrations felt through the ground. These infrasound calls could have traveled long distances, serving for communication within herds or territories. Some giant sauropods, like Diplodocus, might have even relied on tactile communication, using their incredibly long tails to stay in contact with companions while moving.
Smaller dinosaurs would have likely produced higher-pitched sounds, such as squawks, chirps, or screeches. And as the ear evidence suggests, the air might have been filled with the sounds of baby dinosaurs chirping for attention from their parents.
While we may never know exactly what every dinosaur sounded like, the scientific journey using fossils, comparative anatomy, and advanced imaging reveals a world of sound far more diverse and scientifically plausible than the roaring giants of fiction. The next time you imagine walking with dinosaurs, picture not just the thunder of their footsteps, but a resonant landscape vibrating with deep rumbles, booming calls from crested heads, the potential chatter of varied vocalizations, and perhaps, the faint chirps of young echoing through the ancient forests.
References
- https://www.bbc.com/future/article/20221212-the-mysterious-song-of-the-dinosaurs
- https://www.vox.com/unexplainable/2022/8/24/23318134/dinosaur-roar-science-birds-crocodiles-paleontology
- https://podcasts.apple.com/mt/podcast/what-did-dinosaurs-sound-like/id703720228?i=1000512300117
- https://www.sciencenorway.no/dinosaurs-palaeontology/what-did-dinosaurs-actually-sound-like/2307958
