Speaker 1: Welcome to brain stuff. From how stuff works. A brain
Speaker 1: stuff is Christian saga with a name that literally means
Speaker 1: tyrant lizard king. You'd assume that Tyrannosaurus rex would get
Speaker 1: a bit more respect, But the giant predators disproportionately small
Speaker 1: arms have been the subject of ridicule for decades. They
Speaker 1: are also a scientific puzzle. More than one hundred years
Speaker 1: after discovery of this species, experts still don't know why
Speaker 1: a huge animal, one that could reach links of forty
Speaker 1: feet or twelve meters or more, had four limbs that
Speaker 1: weren't much longer than an adult humans. If the arms
Speaker 1: were limp muscle free pegs, it'd be easy to assume
Speaker 1: that they serve no purpose. However, the evidence hints at
Speaker 1: a more complicated story. A few studies have argued that,
Speaker 1: judging by the muscle scars left behind on t rex
Speaker 1: limb bones, a full grown dinosaur could curl or than
Speaker 1: two hundred and twenty pounds or one hundred kilograms with
Speaker 1: each one of their biceps. Then again, this isn't as
Speaker 1: impressive as it sounds. Thomas ore Holtz, a vertebrate paleontologist
Speaker 1: at the University of Maryland, tells us that some people
Speaker 1: like to overrate Tarrannosaurus is upper body strength. That figure
Speaker 1: from before only translates to about one point to five
Speaker 1: per cent of the dinosaurs total body weight, which may
Speaker 1: have been in the ballpark of around eight tons or
Speaker 1: eight thousand kilograms. Holtz says that's like a two hundred
Speaker 1: pound or man being proud of the ability to curl
Speaker 1: two point five pounds or one kilogram. On these grounds,
Speaker 1: a few experts have concluded that Tarrannosaurus's arms were either
Speaker 1: functionless or seldom used, but not all paleontologists by this idea.
Speaker 1: For his money, Kenneth Carpenter of Utah State University thinks
Speaker 1: the little limbs made great hunting tools. In two thousand eight,
Speaker 1: he and fellow paleontologist Christine Lipkin compared the five Tyrannosaurus
Speaker 1: rex wishbones or ferculars that were known to science at
Speaker 1: the time. Shaped like a giant boomerang, the fercular sits
Speaker 1: between the shoulder blades. Three of the five wishbones that
Speaker 1: Carpenter and Lipkin studied show telltale signs of injury. Among
Speaker 1: these were stress fractures, which must have re healed in life.
Speaker 1: So what does this mean, while, according to Carpenter, the
Speaker 1: four limbs were subjected to a great deal of repetitive stress,
Speaker 1: which was not uniform or steady. Instead, there were moments
Speaker 1: of extraordinarily great force applied to the arms. The most
Speaker 1: likely explanation is that t Rex used its four limbs
Speaker 1: to grab hold of large struggling prey. A plus sized
Speaker 1: thrashing victim could ease silly fracture the carnivores wishbone or
Speaker 1: at least tear a few arm muscles loose. Other ideas
Speaker 1: about the purpose of t rex arms have nothing to
Speaker 1: do with subduing victims. One school of thought involves naptime.
Speaker 1: Perhaps after a good night's sleep, Torannosaurus used those arms
Speaker 1: to push itself up off the ground, or maybe they
Speaker 1: had a sexier function. Henry Fairfield Osborne, the paleontologists who
Speaker 1: named this species back in nineteen o five, believed that
Speaker 1: males used their four limbs to grab hold of their mates.
Speaker 1: As Holts and others have admitted, there simply isn't enough
Speaker 1: evidence at this time to conclusively refute or verify any
Speaker 1: of these notions. Such is often the nature of paleontology.
Speaker 1: Today's episode was written by Mark Mancini, produced by Dylan Fagin,
Speaker 1: and for more on this and other topics, please visit
Speaker 1: at how Stuff Work dot momm