If you dig through your nearest toy box, you’ll
find some pretty familiar forms of ancient life.You got your Triceratops, your Tyrannosaur, and one of my personal favorites, the Pachycephalosaurus But you know one animal in here that doesn’t
quite belong? The one that’s doing its own thing? The stegosaurus. If you take it as a given that extinct dinosaurs
were all weird and wonderful, then you gotta at least consider that Stegosaurus was one
of the weirdest and wonderfulest. Stegosaurus is the most recognizable genus
of the stegosaurids, four-legged herbivores that sported bony plates and spiky spines
on their backs, earning them the name that means “roofed lizard.” But unlike the other dinosaurs you find in
the toy box which lived in Cretaceous Period, stegosaurids hit their prime much
earlier, in the Jurassic. This is when some of the largest herbivores, like Diplodocus,
roamed the Earth, while carnivores, like Allosaurus, had just come on the scene. It was in this environment that Stegosaurus
thrived, with the help of some awesome adaptations. But in some ways, despite all that armor,
it might have been under-equipped. Because its brain was almost impossibly small. Stegosaurus had the one of the lowest brain-to-body
ratios of any known dinosaur. The animal itself could grow up to 9 meters long -- about the
size of a small bus -- but its brain was only about 60 square centimeters, the size of a
puppy’s. And when I say that this was almost “impossibly
small,” what I mean is, for a century or so, some paleontologists actually thought
that stegosaurus must’ve had a second brain … ...iiiin its butt. In the 1880s, Yale paleontologist O. C. Marsh
found that some specimens of Stegosaurus had a big cavity in it sacrum, where the spinal
column meets the pelvis. And he figured, since the brain in the head
probably wasn’t doing very much, maybe Stegosaurus was getting some help from its -- for lack
of a better word -- butt-brain. This led to a pernicious myth that Stegosaurus
had, if not an actual second brain, at least a separate bundle of nervous tissue that helped
control its tail and legs. We know now, of course, that Stegosaurus didn’t
have two brains. And some experts think that cavity in its sacrum was actually used
to store glycogen, the starchy compound that animals -- including you and me -- use to
store energy. And just because its brain was small, that
doesn’t mean Stegosaurus was stupid. In fact, you didn't want to tangle with this
thing. Because: It had a secret weapon: the thagomizer. That’s the unofficial name for the dinosaur’s
spiky tail. Not all stegosaurids had thagomizers, but
for those that did, like Stegosaurus and Kentrosaurus, fossil evidence suggests they were verrry
effective weapons. In 2014, the study of an Allosaurus fossil
from Wyoming showed that its pubic bone had a puncture wound that matched the spikes on
a stegosaur’s tail. Researchers concluded that the Allosaurus
had attacked a Stegosaurus, which landed a blow right in the predator’s groin. The
wound became so badly infected that it killed the Allosaurus, and the fossil record preserved
what’s probably the most gruesome groin shot ever documented. Now, I’m sure you’re wondering about the
thagomizer’s name. Well, in 1982, Gary Larson's comic strip The Far Side depicted a group of cavemen getting
a lesson in dinosaur anatomy. And it shows the weaponized tail of the stegosaurus, labelled
as a “thagomizer,” quote, “after the late Thag Simmons.” Ok I know what you're going to say, cavemen and dinosaurs did not live at
the same time, but the point is, the name stuck. By the 1990s, paleontologists actually started referring
to this tail feature as a thagomizer. And when I interviewed Dr. Robert Bakker,
the researcher who studied the Wyoming Allosaurus, he assured me that thagomizer is an accepted
term for a stegosaurid’s spiky tail. Now, by far the most recognizable parts of
a stegosaurid are the bony plates along its back, often called scutes. Not "scutes" by the way, I looked it up...scutes And if you want to start a real,
brawl among a bunch of paleontologists, just ask them what those scutes were for. Because, they are still some of the most hotly
debated features in dinosaur physiology. For a long time, it was argued that the scutes
were there for thermoregulation. In the 1970s, researchers found tubes running
through some fossilized scutes, and thought that they may have circulated blood through
the plates to radiate heat. But not everyone agrees with this. Some experts
have pointed out that not all stegosaurids have a full array of scutes, so if they did give them some advantage, they would be more common. Others have noted that the tubes don’t actually
run all the way through the plates, which they would do, if their job was to circulate
blood. Now you might also think that the scutes were
defensive. But if that were the case, some experts have asked why they only
appear along the back, and not on the sides or the skull? The most recent theory is that stegosaurs
had scutes because … they just looked awesome. After all, modern-day birds have made a very
good living by having lots of features that are just for display. So why couldn’t the
same have been true for extinct dinosaurs? In 2005, a paper from Berkeley suggested that
the plates helped the dinosaurs tell one species from another. Ten years later, another study from Princeton
proposed that the plates were even sex-specific, with females having tall, skinny plates, while
males sported bigger, broader ones. But, again, not everyone agrees. What I think everyone can agree on is that
stegosaurids are famous for good reason. They might not have had the biggest brains,
but they cut a distinctive figure back in the Jurassic, with their scutes
and their spiky tails, which they knew how to use. What do you want to know about the story of
life on Earth? Let us know in the comments below. And don’t forget to go to youtube.com/eons
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