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Uploaded:2015-07-31
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Scientists dissect the human scream for the first time, and also re-think what was thought to be the biggest dinosaur in the world.

If you liked this video, check out more videos about natural history and paleontology on SciShow's sister channel, Eons: https://www.youtube.com/eons

Hosted by: Hank Green
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Sources:
http://www.nature.com/srep/2014/140904/srep06196/full/srep06196.html

http://www.cell.com/current-biology/fulltext/S0960-9822(15)00737-X

http://www.livescience.com/51158-dreadnoughtus-dinosaur-not-so-big.html

http://www.eurekalert.org/pub_releases/2015-06/uol-sdt_1060915.php

http://www.eurekalert.org/pub_releases/2015-07/cp-tes070915.php
(Intro)

Hank: Welcome back to SciShow News.  Now, you might be familiar with the phenomenon of human communication that we tend to engage in when we see things like a mouse in the bedroom or any combination of hockey masks and chainsaws or the latest Adam Sandler movie.  Scientists have a word for this sound, they call it "screaming", and recently, researchers at NYU realized that screaming is one kind of vocalization that's never been studied before.  So psychologists Luc Arnal and his colleagues set out to determine what actually characterizes a scream, like, what differentiates it from all the other sounds of distress that humans make, like shouting or crying, and why it evokes such a unique response in us.  

They created a sort of library of screams, compiled from things like YouTube videos of people being scared or surprised by stuff, and also from actors, either in horror movies or from so-called volunteer screamers who came into the lab to shriek in the interest of science.  The researchers then played their compendium of screams, along with more pleasant or neutral human sounds to 16 volunteers as they underwent brain scans.  What the psychologists found was that the screams didn't share a certain pitch of frequency, but they all had a quality known as "roughness", which measures how quickly the loudness of a sound changes.  While normal human speech varies in loudness between only 4 and 5 Hertz, or cycles per second, screams all changed in loudness rapidly, between about 30 and 150 Hertz.  

It turns out that the only other sounds that cover that same range of roughness are alarms.  Also, the brain scans of the test subjects showed that screams activate a different part of peoples' brains than other sounds.  While the more pleasant or neutral noises all triggered the primary auditory cortex, the region of the brain that logically enough, is right under your ears, the screams bypassed that area and fired up to the anterior amygdala, which the researchers described as the seat of your fear circuitry.  

So all this put together suggests that screaming occupies what the scientists called "a privileged niche" in the range of human communication.  In other words, we all definitely know a scream when we hear one, and now we know why.  

But here's something that we might not have totally understood the first time around, a dinosaur called "Dreadnoughtus".  Last year, around this time, we told you about the discovery of a fossil that was described as the largest dinosaur ever found.  Dreadnoughtus, as it was named, was uncovered in Argentina and based on the size of its skeleton, paleontologists from Philadelphia's Drexel University estimated it to have been as long as 26 meters and weigh more than 60 metric tons, which would have made it the most massive dinosaur in the books.  

But guess what?  A lot of science is about replicating results, and when another team of researchers remeasured the bones, they found that Dreadnoughtus was probably half as large as we thought.  The study, conducted by a group of British biologists, showed that the dinosaur, while still a new species to science, probably weighed no more than 30 to 40 tons, so y--not big at all, really.

So how could the original figure have been so far off?  Paleontologists usually estimate a dinosaur's mass based on its leg bones, particularly the humerus at the top of the front leg, or the femur or thigh bone in the back, because those are thought to be the animal's main load-bearing bones.  But the British researchers used a new computer model that took all of the bones that were recovered from Dreadnoughtus and then calculated how much tissue would correspond to that skeleton based on the ratios of bone, skin, muscle, fat, and other tissues from known land animals.  And their results showed that based on what we know about animal physiology, in their words, "The creature couldn't be as large as originally estimated."  For the record, though, the Drexel paleontologists who discovered Dreadnoughtus are sticking by their estimate.  The point out that the new measurements may change our understanding of the dinosaur's volume, but not its mass. 

As always, we're interested to hear what you think about this and any other news in the world of science.  Please, just remember to use your inside voices, and thank you for watching another episode of SciShow News, especially to our Patrons on Patreon, who make this channel possible for themselves and for everyone else.  If you want to know how you can help us keep making cool stuff like this, you can go to Patreon.com/SciShow, and if you wanna just keep getting smarter with us, you can go to YouTube.com/SciShow and subscribe.

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