Monday, December 11, 2017

Sound Bites: Hearing a Tyrannosaurus rex

If you are a fan of dinosaurs, probably know what sound accompanies this image.

Watching Jurassic Park for the first time (and several times after that) introduced us to what Tyrannosaurus rex would be like, in their movements, behaviors, and sounds. This scene is never, ever going to get old. It was also perfect that my first viewing of Jurassic Park was at a drive-in during a rainstorm.

Hollywood is no stranger to using odd things to recreate visual and audio effects sounds with which we are familiar...or have no familiarity with at all because they haven't been invented yet (lightsaber swooshes), because we don't regularly stab people in the shower (chocolate syrup was used for blood in the original Psycho), or because the sound is so far in the past that no human has ever heard anything like it.

Elephant, tiger, and crocodile sounds were used to recreate the iconic Tyrannosaurus rex sounds. I am most interested in the use of the crocodile gurgling. In my opinion, especially as a person who has spent a lot of time in the wilderness and has heard countless mammal sounds, the crocodile gurgling of the Tyrannosaurus rex this is far more unsettling than the classic roar.

Hollywood gave us something terrible, awesome-sounding, and not-at-all-subtle for Tyrannosaurus rex because we, as human beings living in a time dominated by large fuzzy roaring mammals (lions and tigers and bears, oh my!), expect our large predators to roar, snarl, and bellow. Most of the animals used to create the classic sounds of the Jurassic Park Tyrannosaurus rex are large mammals.

Extant Phylogenetic Bracketing and the Sounds of Tyrannosaurus rex

Figuring out how an extinct mammoth sounds, or how an extinct species of large cat sounds, is not that difficult because we have large pachyderms and large felids around to use as examples. We use large mammals as a comparison against large dinosaurs because hey, that's what we have to work with. However, dinosaurs are not mammals. Dinosaurs belong to a group of animals called archosaurs. Archosaurs took a completely different evolutionary path from our group, the synapsids (mammals and mammal-like reptiles.) The archosaur group and the mammal-like reptile group have been doing their own things, evolutionary-speaking, for at least 250 million years.

Our present-day representatives of archosaurs are the crocodiles and the small theropods (a.k.a. birds). These animals are much closer to large non-avian dinosaurs in terms of evolutionary history, anatomy, and likely behavior, than are large mammals. Crocodiles evolved before large non-avian dinosaurs, and small present-day theropods (birds) became specialized after large non-avian theropods evolved. We have the beginning of the story (crocodiles) and the end of the story (present-day theropods), with large non-avian dinosaurs landing in the middle.

Using crocodiles and present-day birds to test hypotheses (questions) about extinct dinosaurs is called Extant Phylogenetic Bracketing. The present-day examples (crocodiles and birds) give us examples of what is possible for extinct animals (large theropods) that are also part of their group (archosaurs). A lot of the information we have on theropod dinosaur behavior comes from comparisons to the behavior of present-day birds, such as parental care and egg clutch sizes (Varricchio et al., 2008; Varricchio and Jackson, 2016) and potential courtship behaviors (Lockley et al., 2016).

Enter Dr. Julia Clarke, professor of vertebrate palaeontology at the University of Texas. She used extant phylogenetic bracketing to take two unsettling sounds (crocodile vocalizations and the booming call of the Eurasian Bittern), scaled them up to Tyrannosaurus rex-size, and....dang.

Here is the link to The Telegraph news article that contains a video playing the sound. I'll give you a minute or two to go and listen.

Was that not completely disconcerting? What if you were in the forest, and heard (or felt like the host mentioned) that sound behind you? I guarantee you'd have a case of the freakies: I know I would.

Humans have (when compared to the rest of the animal kingdom) a rather limited range of hearing. Humans, in general, can hear sounds between 20 Hz and 20 kHz. Sounds below 20 Hz are typically referred to as infrasound. Our species doesn't really hear infrasound all that well. Check out this link from the Cornell Lab's Elephant Listening Project. There are three sound clips at 10 Hz, 20 Hz, and 30 Hz. Can you hear the sound?

I could not hear any of the clips (I did feel pressure in my ears), but that's not surprising: I have not evolved to communicate using low-frequency sounds, unlike elephants and some birds (the link goes to a recording of a cassowary).

However, just because we (as a species) can't hear infrasound doesn't mean that some of us may not sense it in other ways. I felt a pressure in my ears when listening to the clips and afterward, I felt a low-grade headache. There have been studies done that suggest infrasound may induce feelings of unease in humans. One such study was the Purcell Room Concert of May 31, 2003. The audience listened to music, into which infrasound was inserted at specific times (the audience didn't know.) The audience was then asked to fill out a questionnaire detailing their experiences during the concert. To quote the webpage:

"During our concert, infrasound boosted the number of strange experiences reported among the audience, even among those who were unaware of its presence. Unusual reports included a sense of coldness, anxiety, and shivers down the spine. On average, infrasound boosted the number of strange experiences by around 22 percent. It also increased the intensity of any feelings reported."

Does this sound like any unexplained phenomena? Turn down the sound for this clip: it's a little loud.

There is a strong possibility that what people experience as a sign of a ghostly presence (coldness, anxiety, shivers, unease, etc.) could be their sensitivity to infrasound.

Here's a chilling thought: if Tyrannosaurus rex had part of its vocalizations in the low frequency or infrasound range, not only would we hear that menacing gurgle, but the vocalization would likely trigger an anxiety reaction during the encounter.

I'll leave you with this lovely clip of a vocalizing American Alligator. Have a Creepy Monday!

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