If you close your eyes and picture a dinosaur,
I mean just the archetypal textbook dinosaur,
there are really only, what, three contenders.
You've got the T -Rex, the Triceratops, and then
you have the one we are diving into today. The
one with the plates. The one with the kite -shaped
plates along its back and the spikes on the tail.
The Stegosaurus. It is an absolute icon of the
Jurassic. It really is. It's one of those animals
that's so visually distinct that even if you
aren't a paleontology buff, you know exactly
what it is. The Mohawk dinosaur. Exactly. Right.
But here's the thing that really struck me while
I was going through the research for this deep
dive. Yeah. For an animal that is so instantly
recognizable to us now, we spent arguably the
first hundred years of our relationship with
it getting almost every single detail wrong.
That is a perfect way to frame it. It feels like
the history of the Stegosaurus is basically a
history of paleontologists just scratching their
heads and saying, wait, that can't be right.
It's a complete paradox. It's a pop culture celebrity.
But scientifically, it has been a century long
puzzle. We've had to assemble it, dismantle it,
and then reassemble it multiple times. And it
all starts with a name, right? You know what
Stegosaurus actually translates to? Roof lizard.
Roof lizard. Which... When you look at a modern
reconstruction with those vertical plates, it
makes zero sense. None at all. A roof is flat.
It covers you. And these are standing straight
up. Exactly. And that name is basically a fossil
of a mistake. It goes back to 1877 and Othniel
Charles Marsh. O .C. Marsh. When he found the
first fossils in Colorado, nothing was articulated.
The bones were a jumbled mess. He found these
large, flat, bony slabs, the plates, and he just...
He didn't have a reference point. So his best
guess was that they lay flat against the animal's
back. Like shingles on a house. Overlapping,
just like shingles on a roof, yeah. So the name
roof lizard is literally a description of construction
error. He thought he was looking at some kind
of giant armored turtle thing. He did. Marsha's
early notes actually speculate that it might
have been an aquatic animal, something like a
turtle. Wow. It just shows you how difficult
it is to reconstruct an animal when you're working
with a jigsaw puzzle that's missing half the
pieces, has no box, cover. And the pieces are
150 million years old. And we have to add the
context of the Bone Wars here. Oh, absolutely.
Marsh wasn't just working in a vacuum. He was
working in a, well, a war zone. This was the
late 19th century. And he was locked in this
bitter rivalry with Edward Drinker Cope. That
context is crucial. The bone wars drove discovery,
but they also drove haste. Marsh and Cope were
racing to name species, trying to outpublish
each other. They were sabotaging each other's
dig sites, right? Oh, yeah. Sabotaging sites,
bribing porters, shipping crates of bones back
east before they were even fully prepped. So
in that kind of environment, you don't really
take the time to ponder the details. You just
name it, claim it, and move on. Exactly. And
that rush led to some wild theories. After the
turtle phase, Marsh realized it was a dinosaur,
but because the front legs were so much shorter
than the back legs, he thought it was bipedal,
walked on two legs. He briefly proposed it was
bipedal. I mean, can you imagine a five -ton
Stegosaurus trying to walk like a person? The
physics just don't work. It would just face plant.
It would be terrifying, but yeah, physically
impossible. And it took decades to correct these
assumptions. Even when the first skeleton of
Stegosaurus undulatus was mounted in 1910. Way
after Marsh described it. They set the plates
in pairs, side by side. Like butterfly wings.
Precisely. It wasn't until the 1960s, so nearly
a century after the discovery, that the alternating
row arrangement became the standard. The staggered
pattern we see today. Right, that chiral pattern
from Stegosaurus stenops, which is the species
most of us know. So now that we've cleared up
the shingle confusion, let's look at the actual
animal. Because the anatomy is incredibly weird,
even when you get it right. It's a lowrider.
That is the best description for it. It's a quadruped,
but the build is totally unique. The forelimbs
are short and stocky, while the hind limbs are
long and columnar. And that forces the whole
body into this permanent downward slope. It does.
It puts the head very close to the ground, about
a meter high, and the tail way up in the air.
But what about the movement? I was reading about
the stride length, and it seems like that mismatch
in leg size put a hard speed limit on the animal.
It absolutely did. It's a biomechanical bottleneck.
If you have long back legs and short front legs,
you just can't gallop. The back legs would overtake
the front legs. And the animal would, as you
said, faceplant. It's the classic flat tire effect.
Exactly. The estimated maximum speed is roughly,
what, 15 to 17 kilometers per hour? So about
9 to 11 miles per hour. A reasonably fit human
could outrun a stegosaurus. Yeah. It wasn't built
for speed. It was built for stability and for
browsing on low vegetation. A tank, basically.
But a tank with a famously small driver. Yeah.
We have to talk about the brain. It is the most
legendary insult in paleontology. The walnut
comparison. The dumb dinosaur stereotype. It
is legendary. And, well, unfortunately for the
stegosaurus, it is factually accurate. How accurate?
For an animal weighing around 4 .5 metric tons,
that's bigger than an elephant, the brain weighed
only about 80 grams. Which is roughly the size
of a dog's brain. Yes. A walnut. But this is
where the myth making comes in again. Because
the brain was so comically small, early scientists,
Marsh again, he couldn't believe it could run
the whole body. Right. So he proposed the sacral
brain. I remember learning this in school. The
idea that it had a second brain in its butt to
control the tail. That was a very popular theory
for a very long time. Marsh found this huge canal
in the hip vertebrae, the neural canal. It was
massive, wasn't it? Almost 20 times larger. than
the brain case in the skull. So the logic was
the head is empty, so the hips must be doing
the thinking. At least handling the reflexes.
But modern science has debunked that. It wasn't
a brain. Not nervous tissue. No. We can look
at modern birds, which are living dinosaurs,
for the answer. They have a similar structure
called a glycogen body. Okay, what's that? It's
a specialized organ for storing energy glycogen,
and it possibly helps with balance. So not a
second brain. It was a battery pack. A very well
-stocked pantry for the nervous system. That's
a good way to put it. So the stegosaurus really
was operating on just that 80 -gram brain. It
was. But... We need to be careful with our mammalian
bias here. We tend to equate intelligence with
evolutionary success. Sure. Sagasaurus didn't
need to solve puzzles or hunt in packs. It needed
to eat ferns, thermoregulate, and not get eaten
by Allosaurus. And considering the genus lasted
for millions of years... That walnut brain was
perfectly adequate for the job. Absolutely. Speaking
of not getting eaten, let's move to the defining
feature, the plates. The Great Plate Debate.
Right. We're talking about 17 to 22 of these
structures. And anatomically, these are osteoderms,
right? They aren't part of the skeleton proper.
That's a key distinction. If you look at a skeleton
in a museum, the plates are wired onto the vertebrae.
But in life, they weren't attached to the bone.
They were sort of floating in the skin. Bone
skin. That's what osteoderm means. Crocodiles
have them. Armadillos have them. But in those
animals, osteoderms are clearly armor. They lay
flat. They're a shield. And for a long time,
that was the theory for Stegosaurus, too. That
they were armor plates to stop a bite. Yeah,
but that falls apart pretty quick when you look
at the placement. It really does. If you were
designing a tank, you wouldn't put a row of billboards
on the roof and leave the sides completely exposed.
Exactly. The flanks, the belly, the most vulnerable
parts are wide open. Plus, the internal structure
of the plates is surprisingly porous. they aren't
dense solid bone like a turtle shell and allosaurus
bites into one it would probably shatter okay
so if it's not armor we move to theory number
two which i find fascinating the radiator theory
the thermoregulation hypothesis because the bone
is so porous it suggests it was heavily vascularized
filled with blood vessels so the idea is the
animal could turn its broadside to the morning
sun to warm up or face into the wind to cool
down. Pretty much. It's like the ears of an African
elephant. Exactly like that. And this led to
that vivid imagery of the blushing Stegosaurus.
The idea that they could pump blood into the
plates to turn them bright red. Yeah, to scare
off predators or maybe signal to mates. It's
such a cool image. But my reading suggests this
theory is kind of losing steam. It is, primarily
because of its cousins. If you look at related
stegosaurs, like Kentrosaurus, they don't have
these big broad plates. They have spikes. And
spikes are terrible radiators. Horrible. They
don't have the surface area. So if thermoregulation
was the main reason they evolved, why didn't
all stegosaurs have flat plates? It suggests
the cooling effect might have been a secondary
benefit, not the main purpose. That's the thinking.
Which brings us to the explanation that usually
wins out in biology when nothing else makes sense.
Sex. Sex. Display and dominance. It's almost
always the answer when you see an extravagant,
energy -expensive structure that doesn't seem
to help with survival. It's the peacock's tail
argument. You grow these massive things to say,
look at me, I'm so healthy I can afford to grow
these. giant billboards on my back. Precisely.
And we have some fossil evidence for this. In
Hesperosaurus, a very close relative, we see
sexual dimorphism. Meaning males and females
look different. Right. One morph has wide oval
plates and the other has taller, pointier ones.
That strongly suggests a male -female distinction.
And there's a detail about their appearance that
I think changes how we visualize them. The fossils
are just the bone core, right? That's right.
The bone is just the scaffold. In life, they
would have been covered in a keratin sheath,
same material as a bird's beak or your fingernails.
So the plates would have been way bigger than
the fossils suggest. Significantly larger and
likely much sharper at the edges. And keratin
holds pigment really well. So we should be picturing
these things with bright, vibrant colors. Maybe
patterns. A seven -ton animal with a neon billboard
on its back. It changes the whole vibe of the
Jurassic. Okay, so the plates are for show. But
the tail? The tail means business. We have to
talk about the Thagomizer. And I love that we
can use that word in a serious scientific context.
It is one of the rare times a cartoon changed
science. Gary Larson, the far side. He drew a
caveman pointing to the spikes and saying, now
this end is called the Thagomizer, after the
late Thag Simmons. And paleontologists thought
it was so perfect that they adopted it. It's
just perfect. Yeah. But the weapon itself is
terrifying. Four spikes, two pairs, and unlike
the vertical plates, these stuck out horizontally.
That orientation is critical. They are positioned
for a lateral swipe, and the engineering of the
tail is key. How so? Most dinosaurs have ossified
tendons, bony rods running down the tail to keep
it stiff for balance. Stegosaurus lacks those
in the tail section. Which means it wasn't a
stiff rudder, it was a whip. A highly flexible
muscular whip, and we have forensic evidence
that they used it. This isn't just speculation.
You mean the Allosaurus vertebra? That's the
one. The top predator of the Morrison Formation.
We found a tail vertebra with a puncture wound
in it. A hole that perfectly matches a stegosaur
spike. Perfectly. But here is the CSI part. The
bone shows signs of healing and infection. Which
means the Allosaurus didn't die immediately.
It survived the hit. It survived, but it spent
weeks or months in agony with a festering wound.
That tells us two things. Okay. First, that Stegosaurus
was actively fighting off apex predators. And
second, that the weapon was incredibly effective.
But they did break him sometimes, right? Oh,
yeah. We find about 10 % of Stegosaurus spikes
are trauma damage, like broken tips. So they
were using them in combat and using them often.
It completely reframes the animal. It's not a
passive grazer. It's a samurai. It's got a display
on its back and a sword in its, well, its tail.
A samurai that eats bushes. Let's talk about
that, the eating part. Because for a long time,
the diet was another area where we underestimated
this animal. Totally. The head is tiny. The teeth
are little pegs. It has a beak. The assumption
was it had an incredibly weak bite. That was
the consensus as recently as 2010. A study came
out suggesting the bite force was less than half
that of a Labrador retriever. So it could only
eat soft moss and cerns. Pretty much. But then
came Sophie. Sophie changed everything. This
is a specimen found in Wyoming in 2003, and it
is a marvel. 85 % intact, 360 bones. The most
well -preserved Stegosaurus ever found. And Sophie
proved the wimpy bite theory wrong. Completely.
When researchers modeled Sophie's skull in 2016,
they found the bite force was actually comparable
to a sheep or a cow. Now, a cow might not sound
terrifying, but they can grind through very tough,
fibrous material. Exactly. But Stegosaurus couldn't
grind side to side. It likely used a shearing
motion, like scissors, cropping and slicing.
So it wasn't just eating mush. No, it was likely
eating cycads, conifers, tougher woody plants.
They were the mowers of the Jurassic, clearing
out the underbrush. Sophie really was a revolution.
But we can't talk about modern stegosaurus discoveries
without talking about Apex. This is the dinosaur
in the room. We have to discuss Apex. This specimen
was discovered in 2022, and it's massive. But
the headline wasn't just the size, it was the
price tag. In July 2024, it sold at Sotheby's
for... $44 .6 million. It's a staggering number.
The most ever paid for a fossil. And this creates
a huge tension in the scientific community. It
creates a crisis, frankly. When a fossil of that
importance goes into a private collection, it
effectively disappears from science. Right. Even
if the owner says researchers can visit, there's
no guarantee of access forever. Science relies
on reproducibility. If I write a paper on Apex's
growth wings, and 50 years from now another scientist
wants to verify my work. But Apex is locked in
a vault or was sold to another anonymous buyer,
the science becomes unverifiable. It essentially
privatizes the data. It takes a piece of natural
history and turns it into an asset class. And
museums simply cannot compete. The Natural History
Museum can't drop $45 million on one specimen.
So we're seeing this trend where the best fossils
are moving out of the public trust. It's a complicated
legacy for such a magnificent find. And it really
highlights how active this field still is. Stegosaurus
isn't a solved dinosaur. Not at all. From the
bone wars to the biomechanics of Sophie and now
the ethics of the Apex auction, it's still generating
debate. And it has stayed in the public eye the
whole time, from the 1933 King Kong to becoming
the state fossil of Colorado. I love that story.
That was a fourth grade class, right? It was.
A teacher and her students campaigned for two
years to get the bill passed. It just shows you
that this animal captures the imagination of
children and adults in a way few others do. It's
the combination of the weirdness and the coolness.
So if we pull all of this together, we've come
a very long way from O .C. Marsh's shingleback
turtle. We have. We've moved from a clumsy, bipedal
aquatic mistake to a sophisticated, well -adapted
animal. We know it lived in her. protecting its
young. We know it was a lowrider specialist clearing
the forest floor. And we know it had a deadly
whip -like tail that could fend off the top predators
of its time. And we know that despite that tiny
brain, it was an evolutionary success story.
It didn't need to do calculus. It just needed
to survive. Evolution doesn't optimize for IQ
points. It optimizes for passing on genes. And
the Stegosaurus design just worked. So as we
wrap up this redemption arc, What is the one
thing that still sticks with you? What's the
lingering mystery? For me, it's still the plates.
We have decent theories display, maybe some thermoregulation.
But we don't know. Were they different colors
in different seasons? Did they pump blood to
flash warnings? We're looking at rocks and trying
to reconstruct behavior. Exactly. It reminds
us that even with an animal as famous as this,
we are essentially looking at shadows on a wall.
We are piecing together a life from fragments
of bone. And maybe, just maybe, somewhere in
the Morrison Formation, there's another Sophie
waiting to be found that will finally tell us
exactly why the roof lizard decided to wear a
mohawk. I certainly hope so. Thanks for diving
deep with us. Keep questioning what you think
you know, and we'll catch you on the next one.