WEBVTT - Why Did The T. Rex Have Tiny Little Arms?

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<v Speaker 1>Welcome to brain stuff. From how stuff works. A brain

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<v Speaker 1>stuff is Christian saga with a name that literally means

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<v Speaker 1>tyrant lizard king. You'd assume that Tyrannosaurus rex would get

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<v Speaker 1>a bit more respect, But the giant predators disproportionately small

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<v Speaker 1>arms have been the subject of ridicule for decades. They

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<v Speaker 1>are also a scientific puzzle. More than one hundred years

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<v Speaker 1>after discovery of this species, experts still don't know why

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<v Speaker 1>a huge animal, one that could reach links of forty

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<v Speaker 1>feet or twelve meters or more, had four limbs that

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<v Speaker 1>weren't much longer than an adult humans. If the arms

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<v Speaker 1>were limp muscle free pegs, it'd be easy to assume

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<v Speaker 1>that they serve no purpose. However, the evidence hints at

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<v Speaker 1>a more complicated story. A few studies have argued that,

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<v Speaker 1>judging by the muscle scars left behind on t rex

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<v Speaker 1>limb bones, a full grown dinosaur could curl or than

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<v Speaker 1>two hundred and twenty pounds or one hundred kilograms with

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<v Speaker 1>each one of their biceps. Then again, this isn't as

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<v Speaker 1>impressive as it sounds. Thomas ore Holtz, a vertebrate paleontologist

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<v Speaker 1>at the University of Maryland, tells us that some people

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<v Speaker 1>like to overrate Tarrannosaurus is upper body strength. That figure

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<v Speaker 1>from before only translates to about one point to five

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<v Speaker 1>per cent of the dinosaurs total body weight, which may

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<v Speaker 1>have been in the ballpark of around eight tons or

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<v Speaker 1>eight thousand kilograms. Holtz says that's like a two hundred

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<v Speaker 1>pound or man being proud of the ability to curl

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<v Speaker 1>two point five pounds or one kilogram. On these grounds,

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<v Speaker 1>a few experts have concluded that Tarrannosaurus's arms were either

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<v Speaker 1>functionless or seldom used, but not all paleontologists by this idea.

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<v Speaker 1>For his money, Kenneth Carpenter of Utah State University thinks

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<v Speaker 1>the little limbs made great hunting tools. In two thousand eight,

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<v Speaker 1>he and fellow paleontologist Christine Lipkin compared the five Tyrannosaurus

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<v Speaker 1>rex wishbones or ferculars that were known to science at

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<v Speaker 1>the time. Shaped like a giant boomerang, the fercular sits

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<v Speaker 1>between the shoulder blades. Three of the five wishbones that

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<v Speaker 1>Carpenter and Lipkin studied show telltale signs of injury. Among

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<v Speaker 1>these were stress fractures, which must have re healed in life.

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<v Speaker 1>So what does this mean, while, according to Carpenter, the

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<v Speaker 1>four limbs were subjected to a great deal of repetitive stress,

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<v Speaker 1>which was not uniform or steady. Instead, there were moments

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<v Speaker 1>of extraordinarily great force applied to the arms. The most

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<v Speaker 1>likely explanation is that t Rex used its four limbs

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<v Speaker 1>to grab hold of large struggling prey. A plus sized

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<v Speaker 1>thrashing victim could ease silly fracture the carnivores wishbone or

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<v Speaker 1>at least tear a few arm muscles loose. Other ideas

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<v Speaker 1>about the purpose of t rex arms have nothing to

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<v Speaker 1>do with subduing victims. One school of thought involves naptime.

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<v Speaker 1>Perhaps after a good night's sleep, Torannosaurus used those arms

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<v Speaker 1>to push itself up off the ground, or maybe they

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<v Speaker 1>had a sexier function. Henry Fairfield Osborne, the paleontologists who

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<v Speaker 1>named this species back in nineteen o five, believed that

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<v Speaker 1>males used their four limbs to grab hold of their mates.

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<v Speaker 1>As Holts and others have admitted, there simply isn't enough

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<v Speaker 1>evidence at this time to conclusively refute or verify any

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<v Speaker 1>of these notions. Such is often the nature of paleontology.

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<v Speaker 1>Today's episode was written by Mark Mancini, produced by Dylan Fagin,

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<v Speaker 1>and for more on this and other topics, please visit

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<v Speaker 1>at how Stuff Work dot momm