The loud, menacing roars attributed to dinosaurs in popular culture are largely works of fiction. Paleontologists cannot directly listen to the past because the soft tissues responsible for voice production rarely survive fossilization. Determining what dinosaurs actually sounded like relies on a complex process of inference and comparative anatomy. Scientists analyze the bony structures of extinct species alongside the vocal mechanisms of their living relatives. This approach suggests a world dominated by deep, resonant sounds, far different from the one commonly imagined.
The Anatomical Clues in Fossil Evidence
The primary challenge in reconstructing dinosaur sounds is the absence of preserved vocal organs, as the larynx and related soft tissues are cartilaginous and decay quickly. However, certain bony structures provide compelling indirect evidence regarding how air moved and resonated within the skull. For instance, the hyoid bones, which anchor the tongue, can sometimes be preserved. The nasal passages themselves are another source of information, especially in species with highly modified snouts. Hadrosaurs, or duck-billed dinosaurs, possessed complex cranial structures that acted as natural resonating chambers, such as the hollow, looping crest of Parasaurolophus.
CT scans and fluid dynamics modeling have allowed researchers to digitally recreate the internal pathways of these crests. These models suggest that air pushed through the long, coiled tubes would have produced deep, low-frequency sounds. While this confirms the potential for acoustic communication, it cannot definitively tell us the social context or the exact frequency of the resulting sound. The skull structure only provides the architectural blueprint for sound, not the final auditory output.
Insights from Modern Archosaur Vocalizations
To bridge the gap left by fossil limitations, paleontologists turn to the closest living relatives of dinosaurs: birds and crocodilians. These animals, collectively known as archosaurs, share a common ancestor with all dinosaurs and provide a biological framework for understanding ancient vocal mechanics. Examining the sounds they produce offers the most reliable window into the acoustic world of the Mesozoic Era.
Many modern archosaurs rely on low-frequency, closed-mouth vocalizations, which utilize internal resonance rather than an open-mouthed bellow or roar. Crocodiles, for example, produce deep rumbles and bellows with their mouths closed, often during courtship or territorial displays. Similarly, large birds like ostriches and the Eurasian bittern produce cooing or booming sounds by pushing air through their respiratory system while their beaks remain shut.
The vocal apparatus itself is a defining difference between the two archosaur groups, offering further clues about dinosaur sound. Birds possess a unique organ called the syrinx, located deep in the chest, which allows for complex, high-pitched songs and calls. The syrinx is a highly specialized structure that almost certainly evolved after the split between non-avian and avian dinosaurs. In contrast, crocodilians and most reptiles use a more primitive laryngeal structure. Because the syrinx is a relatively new avian adaptation, it is highly probable that non-avian dinosaurs used a simpler larynx more akin to that of a crocodile.
The Science of Reconstructing Dinosaur Sounds
Synthesizing the anatomical evidence with modern archosaur biology suggests that the Mesozoic soundscape was dominated by deep, low-frequency noises. Large-bodied dinosaurs, especially, would have been physiologically constrained to produce sounds below the human hearing threshold, known as infrasound. Sound waves at these low frequencies travel great distances through dense forest and across open plains, making them suitable for long-range communication.
The reconstructed acoustic model for Parasaurolophus provides a concrete example of this low-frequency communication. The air pushed through its meter-long crest would have exited as a powerful, resonating boom, perhaps similar to a foghorn or a trombone. This sound, used to identify species or signal during mating displays, would have traveled across several kilometers.
Applying these principles to large predatory dinosaurs like Tyrannosaurus rex leads to a surprising conclusion about their acoustic profile. The cinematic roar is energetically wasteful and biologically unlikely for a large terrestrial animal. Instead, a massive predator would likely have produced a sound that was felt more than heard. The immense size of T. rex suggests a deep, guttural, and resonant sound, similar to the low-frequency rumble of an alligator. This closed-mouth vocalization uses the chest and body cavity for resonance, allowing the predator to communicate territory without expending vast amounts of energy.