Why Did The T. Rex Have Tiny Little Arms?

Tyrannosaurus rex was a giant predator that roamed the earth, so why did it have such tiny arms?

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Episode Transcript

Speaker 1 (00:02):
Welcome to brain stuff. From how stuff works. A brain
stuff is Christian saga with a name that literally means
tyrant lizard king. You'd assume that Tyrannosaurus rex would get
a bit more respect, But the giant predators disproportionately small
arms have been the subject of ridicule for decades. They

(00:22):
are also a scientific puzzle. More than one hundred years
after discovery of this species, experts still don't know why
a huge animal, one that could reach links of forty
feet or twelve meters or more, had four limbs that
weren't much longer than an adult humans. If the arms
were limp muscle free pegs, it'd be easy to assume

(00:45):
that they serve no purpose. However, the evidence hints at
a more complicated story. A few studies have argued that,
judging by the muscle scars left behind on t rex
limb bones, a full grown dinosaur could curl or than
two hundred and twenty pounds or one hundred kilograms with
each one of their biceps. Then again, this isn't as

(01:07):
impressive as it sounds. Thomas ore Holtz, a vertebrate paleontologist
at the University of Maryland, tells us that some people
like to overrate Tarrannosaurus is upper body strength. That figure
from before only translates to about one point to five
per cent of the dinosaurs total body weight, which may

(01:28):
have been in the ballpark of around eight tons or
eight thousand kilograms. Holtz says that's like a two hundred
pound or man being proud of the ability to curl
two point five pounds or one kilogram. On these grounds,
a few experts have concluded that Tarrannosaurus's arms were either

(01:50):
functionless or seldom used, but not all paleontologists by this idea.
For his money, Kenneth Carpenter of Utah State University thinks
the little limbs made great hunting tools. In two thousand eight,
he and fellow paleontologist Christine Lipkin compared the five Tyrannosaurus

(02:10):
rex wishbones or ferculars that were known to science at
the time. Shaped like a giant boomerang, the fercular sits
between the shoulder blades. Three of the five wishbones that
Carpenter and Lipkin studied show telltale signs of injury. Among
these were stress fractures, which must have re healed in life.

(02:32):
So what does this mean, while, according to Carpenter, the
four limbs were subjected to a great deal of repetitive stress,
which was not uniform or steady. Instead, there were moments
of extraordinarily great force applied to the arms. The most
likely explanation is that t Rex used its four limbs

(02:52):
to grab hold of large struggling prey. A plus sized
thrashing victim could ease silly fracture the carnivores wishbone or
at least tear a few arm muscles loose. Other ideas
about the purpose of t rex arms have nothing to
do with subduing victims. One school of thought involves naptime.

(03:14):
Perhaps after a good night's sleep, Torannosaurus used those arms
to push itself up off the ground, or maybe they
had a sexier function. Henry Fairfield Osborne, the paleontologists who
named this species back in nineteen o five, believed that
males used their four limbs to grab hold of their mates.

(03:34):
As Holts and others have admitted, there simply isn't enough
evidence at this time to conclusively refute or verify any
of these notions. Such is often the nature of paleontology.
Today's episode was written by Mark Mancini, produced by Dylan Fagin,

(03:57):
and for more on this and other topics, please visit
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