The fearsome roar of Tyrannosaurus Rex as portrayed in film has left many a cinema-goer quaking in their seat. But new research suggests the king of the dinosaurs made a far more sinister sound. For a new BBC documentary, naturalist Chris Packham visited Julia Clarke, professor of Vertebrate Palaeontology at the University of Texas, to test out a the theory that dinosaurs actually sounded more like birds and reptiles, than today’s predatory mammals. “The most chilling noises in the natural world today come from predators, the howl of the wolf, the roar of the tiger, but experts now doubt that T-Rex sounded anything like them,” said Packham. Dinosaurs are the ancestors of birds and are closely related to alligators and crocodiles, so Prof Clarke used the sound of the Eurasian bittern, which makes an unearthly booming call, and the vocalisations of Chinese crocodiles to estimate the noise T-Rex would have made. Chris Packham with Tristan the Tyrannosaurus Rex in Berlin at the Naturkundemuseum in Berlin Credit: Gordon Welters When Professor Clarke scaled up the sound to match the size of the huge dinosaur the call became an ominous low rumble, subtle, yet scary enough to make the hairs on the back of your neck stand up. In fact, the noise is akin to the rhythmic low thud of T-Rex footsteps in Jurassic Park or the sinister base notes which announced the arrival of the great white in Jaws. Prof Clarke said that our aversion to such sounds today, which are often present in horror film soundtracks, may stem from an innate memory of the long-forgotten noises of dangerous predators. “I feel like this sound just induces fear,” she said. “People think you need a roar to be really scary, but that is scariest sound you’ll have ever heard. I don’t know if we have some deep seated adaptive response to low frequency sounds but I would not be surprised. Chris Packham and Professor Julia Clark hear the sound of T-Rex for the first time Credit: BBC “Across animals deeper sounds are a pretty true signal of larger body sizes so the kinds of sounds we were listening would correlate with a really big animal. Natural selection to fear these kinds of sounds seems really plausible. “If we look at any of the classic dinosaur movies T-Rex is roaring. The reason we probably thought of this as appropriate is that large carnivores, most of them are mammals and those are sounds that they produce. “But when we think about T-Rex, he is an animal that is most closely related to birds and alligators and crocodiles and those animals make very different kinds of sounds.” Chris Packham goes in search of the real T.Rex in a new documentary for the BBC which airs in January Credit: Gordon Welters T-Rex probably did not need to even open its mouth to make the terrifying noise. Among birds and reptilians, closed mouth vocalisation is common. And the rumble may have reached such a deep frequency that it may have been ‘felt’ rather than heard. The researchers were able to estimate just how deep T-Rex vocalisations got by analysing what the huge dinosaur could hear. Dr Larry Witmer, at Ohio University, took scans of a braincase of a T-Rex fossil, which still contained the outlines of the hearing organs. “We can get information from looking at the structure of the inner ear,” he said. “What that suggests is T-Rex actually had a very sensitive hearing organ which was especially sensitive to low frequencies, potentially frequencies that are even lower than what most of us can hear.” T-Rex probably did not roar like today's carnivores but made a sinister, closed-mouth rumble Credit: Jurassic Park Such low rumbles would have been able to travel vast distances. Today large mammals such as elephants can ‘talk’ over miles, while whale song has been picked thousands of miles from its source. “It’s such a low frequency that you wouldn’t have just heard it, you would have felt it too,” added Packham. “There is a sort of primal fear that is associated with sounds like that. “And when you think about it, T-Rex didn’t need to roar, it needed to be able to communicate over huge areas. They probably travelled huge distances with migrating animals which they hunted. “This could be the first time for 66 million years that this sound has been heard on Earth. It’s a shot in the dark, but we are using the evidence we’ve got. I think it is the scariest sound I have ever felt.” The Real T.rex with Chris Packham will be broadcast at 9pm on January 2 on BBC Two. read more Disclaimer: Chances are that this post was requested by an advertiser.