Imagine, if you will, a creature that acts as
a mirror. Not a physical mirror, but a mirror
for our own intelligence, our own assumptions,
and really our understanding of the history of
life on Earth. That's a great way to put it.
And I'm not talking about some mythical shapeshifter.
I'm talking about a pile of old bones. It really
is the ultimate shapeshifter of the fossil record,
though. I mean, if you took a snapshot of how
scientists visualized this animal in, say, 1830.
Okay. Then you took another in 1850, then another
around 1900, and then you look at it today. You'd
think they were completely different animals.
You would swear you were looking at four, maybe
five completely different species. It's an incredible
transformation. We've had the giant sluggish
lizard model. We've had the horned. rhinoceros
-like elephant. The Crystal Palace version. Then
the Godzilla -style kangaroo tripod dragging
its tail. And now we have the modern version,
the all -terrain vehicle of the Cretaceous. The
ultimate herbivore. We are talking, of course,
about the Iguanodon. The one and only. And it's
so fascinating because Iguanodon isn't just another
dinosaur it is in many ways the dinosaur it's
the barometer for the entire field of paleontology
right because if you want to know what humans
thought about dinosaurs at any specific point
in the last 200 years you just have to look at
how they were drawing iguanodon exactly it tracks
the evolution of our science perfectly from the
early days of you know giant lizards. Which was
a total guess. A complete shot in the dark, really.
Then it moved to the slow, cold -blooded reptiles
of the mid -20th century. And finally, to the
active, dynamic, successful animals we know they
were today. And it's historically heavy, too.
I mean, this is foundational stuff. Along with
megalosaurus and hylasaurus, this was one of
the original three genera used to define the
very word dinosauria. That's right. Before Iguanodon
and the others, the word dinosaur literally didn't
exist. It is the foundation upon which the entire
house was built. So our mission for this deep
dive is pretty clear. We're going to unpack the
200 -year -old cold case of this animal. We're
going to look at the myths. Oh, there are so
many myths. Like that famous horn on the nose
that wasn't a horn at all. We're going to descend
into a Belgian coal mine to visit a dinosaur
graveyard. And we're going to figure out how
this so -called cow of the Cretaceous actually
lived. And I'll tell you, calling it a cow is
really selling it short. This thing was an evolutionary
masterpiece. So let's start at the beginning.
And in paleontology, the beginning is usually
just a scrap, a fragment. It almost always is.
In this case, it's a tooth. Take us back. We're
in Sussex, England, the 1820s. What does the
world look like scientifically? The 1820s. This
is a time when the concept of deep time is just
barely starting to form. People are finding fossils,
sure. They find big bones in quarries. But the
framework isn't there yet. So they don't know
what they're looking at. Not really. If you found
a massive thigh bone, you'd probably say it was
an elephant brought by the Romans or maybe. A
giant human. A giant human from the Bible, Goliath's
cousin or something. That was a very common explanation.
The idea of extinct worlds of giant reptiles
just wasn't in the public consciousness. And
into this world steps Gideon Mantell. Gideon
Mantell. He's a fascinating character. He's a
country doctor, a general practitioner in Lewis
Sussex. Not a formal academic. So his day job
is riding around on horseback visiting patients.
Exactly. Delivering babies, setting bones. But
his real passion, the thing that keeps him up
at night, is geology. He is obsessed with the
rocks of the Weald. He collects everything. And
there's a famous story about the discovery of
Iguanodon. I feel like I read this in every dinosaur
book I had as a kid. The legend of Marianne Mantel.
Ah, yes. The legend. It's a beautiful vignette,
isn't it? It's perfect. The story goes that in
the summer of 1822, Gideon is visiting a patient.
His wife, Marianne, accompanies him. While he
is inside the house tending to the sick, she's
wandering down the lane, kicking at a pile of
road metal. Just stones used to patch the road.
Right. And she spots something shiny, something
different. She sees a strange shape in the sandstone.
She picks it up, shows it to Gideon when he comes
out, and he realizes it's a fossil tooth unlike
anything he's ever seen. It's the perfect behind
-every -great -man story. It gives her the credit
for this world -changing discovery. But we have
to be the buzzkills today. Is it true? It's...
It's complicated. It's likely a myth or at least
a highly romanticized version of events. So he
made it up. Well, Mantel himself was very inconsistent
about it. In his early writings, say around 1827
and 1833, he stated that Marianne found them.
He gives her the credit. OK. But much later,
in 1851, shortly before he died, he explicitly
wrote in a book that he found them himself. The
classic retraction. Actually, it was me all along.
Right. And, you know, historians who have looked
into his medical practice know. that doctors
in the 1820s almost never took their wives on
patient calls. It just wasn't done. It would
have been unprofessional. Highly. So the whole
premise of the story is a bit shaky. So where
did the teeth actually come from? What's the
more likely scenario? It's quite possible Gideon
found them himself on one of his rides. Or, and
this is very common, he bought them from the
quarry men. The local workers knew the doctor
paid for curiosities, so they had saved the weird
rocks for him. That makes a lot of sense. But
regardless of who physically picked it up, whether
it was Marianne or Gideon, the teeth were the
spark. And what was so confusing about them?
He'd seen other fossils before. He had. He'd
even found large bones that he thought belonged
to a giant crocodile. But crocodiles are carnivores.
Their teeth are simple conical spikes for gripping
and tearing. But these were different. Completely
different. They were leaf -shaped. They had serrated
edges, like a steak knife. And most importantly,
they were worn flat on the top. Like a horse's
tooth. Or a cow's. Exactly. Or a cow's. They
were grinding teeth. And in 1822, that was a
paradox. Why? Because everyone knew that modern
reptiles, lizards, iguanas, crocodiles were meat
eaters or bug eaters. The idea of a reptile that
was an herbivore that didn't fit the accepted
model and the idea of a giant reptile that ate
plants, that was just impossible to them. So
he knows he has something revolutionary. He takes
these teeth to the experts. The Royal Society
in London. He does. He presents them in 1822.
And he gets absolutely stonewalled, just shut
down. Who were the gatekeepers at the time? Who
was he up against? The biggest names in the business.
First, William Buckland. He's an eccentric genius
at Oxford, a giant in the field. He looks at
the teeth and dismisses them. What does he say
they are? He says they are fish teeth. Fish teeth?
Really? To be fair, some fish do have grinding
teeth for crushing coral or shells, but it was
a very dismissive categorization. It was basically
saying, this isn't interesting. And then it gets
worse. It gets much worse. Charles Lyell, who
would go on to be the father of modern geology,
takes the teeth to Paris to show them to Georges
Cuvier. And for those who don't know, Cuvier
is basically the god of anatomy at this point.
He is the Napoleon of science. The man is a legend.
He can supposedly look at a single bone and reconstruct
an entire animal. He's never wrong. So what does
the great Cuvier say? Cuvier looks at these teeth
and says, these are the upper incisors of a rhinoceros.
A rhino. So he thinks Mantell has found a mammal.
A tertiary mammal, to be specific, something
relatively recent in geological terms. He assumes
the teeth must have been from a younger rock
layer and just got mixed into the older Cretaceous
stuff by accident. That must have been devastating
for Mantell. He's just a country doctor. And
the world's leading scientist is telling him,
stick to medicine, kid. You found a rhino tooth.
It was crushing. I mean, can you imagine? But
this is where Mantell's stubbornness or his genius
saves the day. He knew the geology. He knew those
teeth came from the Tillgate Forest sandstone.
which is ancient. It's from the age of reptiles.
No rhinos back then. Absolutely no mammals back
then, certainly not rhinos. So he refused to
accept Cuvier's verdict. He kept digging. And
eventually Cuvier comes around. He does. And
this is a mark of a true scientist. In 1824,
Mantel sends more specimens, better ones. Cuvier
takes a second look, sees the wear patterns,
realizes his mistake, and he writes a letter
to Mantel. What does it say? It says essentially,
you were right, I was wrong. He admits that these
are reptilian and that they must belong to a
previously unknown type of giant herbivore. That
letter must have been framed on Mantell's wall.
It was his ticket to legitimacy. It validated
everything. But he still had a problem. He knew
it was a giant herbivore reptile, but he didn't
know what it looked like. He had no model, no
blueprint. And this leads to that famous, the
aha moment at the Royal College of Surgeons.
The breakthrough. It's September 1824. Mantell
is in London, searching through the vast collections
of skeletons, trying to find a modern analog,
a match. He's looking at lizards, crocodiles,
turtles. Nothing matches. He's about to give
up. And then someone taps him on the shoulder.
Enter the unsung hero, Samuel Stutchbury. He's
a young assistant curator there. He walks by,
sees Mantell looking frustrated with these strange
fossil teeth, and says, wait a minute. Stutchbury
had just finished preparing a specimen of a modern
iguana. Which would have been a pretty exotic
animal in London at the time. Very. An iguana
from the Caribbean or South America. Stutchbury
goes to a jar or a cabinet, pulls out the iguana
skull, and shows Mantell the teeth. What's the
reaction? It was a perfect match. I mean, you
can imagine his eyes lighting up. The shape,
the serrations, the ridges, they were identical.
The only difference was the size. And how big
was the difference? It was massive. Mantell measured
them. The fossil teeth were 20 times larger than
the iguana teeth. So he does the math right there
on the spot. He does the scaling. It's simple
reasoning. If a modern iguana is, say, three
or four feet long, and this animal is 20 times
bigger. Then the animal must be 60 to 80 feet
long. That was the image. A colossal, 80 -foot
-long super iguana stalking the English countryside.
It's terrifying. And because of that incredible
resemblance, he needed a name. He toyed with
iguanasaurus, right? He did. Iguana lizard. Which,
if you translate iguana, which comes from the
Arawak word iwana for lizard, basically means
lizard lizard. A bit redundant. A little on the
nose. His friend William Coney Bear, who was
a clergyman and also a geologist, suggested something
more elegant. He proposed iguanoids, which means
iguana -like, or iguanodon. Iguana tooth. Iguana
tooth. And iguanodon just rolls off the tongue
better, doesn't it? It does. It has a ring to
it. It does. And on February 10, 1825, Mantell
formally published the paper. Iguanodon became
the second dinosaur ever named, just after Buckland's
megalosaurus. But again, to be clear, they aren't
calling them dinosaurs yet. No, not at all. To
them, they are just saurians, giant lizards.
The concept of dinosauria hasn't been invented.
So Mantell has his name. He has his teeth. He
has his 80 -foot lizard. But then he finds the
Maidstone specimen. And this is where the most
famous myth of Iguanodon is born. Ah, the Maidstone
slab. This is a game changer. It's found in 1834
in a quarry in Kent. The owner of the quarry
had it blown up with gunpowder, unfortunately.
When why? just to get at the rock. Fossils were
a nuisance, but Mantell managed to collect the
pieces. When he puzzled them back together, he
had the most complete skeleton of a large dinosaur
seen anywhere in the world up to that date. It
had limbs, ribs, vertebrae. Yeah. Real bones.
It had a lot of the puzzle pieces, and somewhere
in the middle of this jumbled block, there was
a spike. A single, conical, bony spike. Now Mantell
is still operating on the super iguana theory.
That's his only reference point. So he looks
at his modern iguana skull, specifically the
rhinoceros iguana, Cichlura cornuta. What does
it have on its nose? A little horn, a bump. A
small, bony tubercle, a bump. So for Mantel,
the logical deduction is simple. The big spike
goes on the nose of his big iguana. It makes
perfect sense if you assume the animal is just
a scaled -up lizard. It's a completely reasonable
conclusion. Completely. He placed that horn on
the snout, and for the next 50 years, every drawing,
every model, every scientific thought about Iguanodon
featured that unicorn horn. It's such a cool
image, though, the giant horned lizard. It is.
But the image was about to be completely demolished.
We leave the era of the lizard and enter the
era of the elephant. And this shift is driven
by one man, Sir Richard Owen. The villain of
the piece. Or is that unfair? Let's say. The
heavy handed architect. Owen was a genius, make
no mistake, a brilliant anatomist, but he was
also arrogant, politically savvy and deeply religious.
This is the 1840s. Darwin hasn't published on
the origin of species yet, but ideas of evolution,
what they call transmutation. The idea that simple
animals could turn into complex ones over time.
Exactly. Owen hated that idea. He believed in
a divinely created hierarchy of life. He wanted
to show that these ancient reptiles were not
primitive ancestors of modern lizards. He wanted
to show they were distinct, advanced, perfect
creations in their own right. So how does he
use iguanodon to do that? To fight this war against
transmutationism? He rebrands them. In 1842,
he coins the term dinosauria, terrible lizards
or fearfully great lizards, and he lumps iguanodon,
megalosaurus, and hyliosaurus into this new exclusive
group, but he changes their shape entirely. He
takes away the sprawling lizard look. Completely.
He argues that because they were so big and he
actually scaled them down for Mantell's 80 feet
to about 30 feet, but made them much, much bulkier,
they must have had a more advanced mammal -like
metabolism and posture. So he reconstructed them
as pachyderms. Pachyderms. Yeah. Like elephants
and rhinos. Yes. Heavy, four -legged, with pillar
-like legs held directly under the body. Thick
skin. Squat bodies. He basically... built a reptile
skin covering over a rhinoceros skeleton, and
of course he kept Mantell's nose horn. It fit
the rhino look perfectly. And this brings us
to the Crystal Palace. Because Owen didn't just
write papers, he built a theme park. The world's
first dinosaur park. It's an incredible story.
It's in Sydenham Hill, South London, starting
in 1852. After the Great Exhibition, the Crystal
Palace building was moved there, and the company
commissioned Benjamin Waterhouse Hawkins, a brilliant
sculptor, to build life -size models of these
antediluvian beasts. And Owen was the scientific
consultant. Owen directed every single detail.
They're still there. You can go see them today.
They are. A bit weathered. But they're there.
And you'll see the iguanodons. There are two
of them. One is standing. One is resting on its
belly. And they look like giant, scaly bulldogs.
They are massive, lumbering, rhino -like tanks.
And the confidence of these Victorian scientists,
they were so sure they were right that they held
a party inside one of the models. The dinner
in the Iguanodon, this is legendary stuff. It's
New Year's Eve, 1853. The mold for the standing
Iguanodon was finished, but they hadn't poured
the concrete yet, so it was a giant hollow shell.
So they just set up a table inside. Literally
inside the belly of the beast. Owen, the guest
of honor, sits at the head of the table. which
is physically located up inside the dinosaur's
head, and 20 other prominent men of science in
the press sit down the length of the body. Wait,
20 people? Was it that big? It was tight. Some
reports say 21 people. They had to sit very close.
But can you imagine the scene? It's dark. It's
illuminated by lanterns. They are in formal Victorian
evening wear tailcoats, cravats. And they're
eating a multi -course meal inside a dinosaur.
Raising a toast to the queen and to Professor
Owen, it was a PR masterstroke. It was a declaration
to the public. We have conquered the past. We
know exactly what these things were. Little did
they know they were eating dinner inside a magnificent
mistake. A truly magnificent mistake. Because
while Owen was dining in London, the real Iguanodon
was waiting to be found. And it wasn't in a forest
or a quarry. It was deep. deep underground. So
let's go to Belgium. The year is 1878. We're
in the village of Bernassart, right near the
French border. This is coal country. The Industrial
Revolution is hungry for fuel. We're at the Sambarb
Colliery. And how deep are we talking? We are
322 meters down. That's over a thousand feet.
So this is dark, damp, dangerous work. Extremely.
Two miners, Jules Créter and Alphonse Blanchard,
are following a coal seam called the Luron seam.
Suddenly, the coal just runs out. They hit a
pocket of clay. This is bad news for miners.
Clay is unstable. It can cause collapses. But
they see something in the clay. They see these
shiny black chunks, pyrite, fool's gold. At first,
they think, well, at least we found some gold.
But mixed in with the pyrite are these large,
hard, log -like things. They assume it's petrified
wood, old tree trunks. Which makes sense in a
coal mine. Coal is just old plants. Exactly.
So they take a pickaxe to one of the logs to
clear it out of the way. They chop through it
and bring the pieces up to the surface. The mine
managers look at it and realize, this isn't wood,
this is bone. So they call in the cavalry. They
contact the Royal Museum of Natural History in
Brussels, and what they find when they get there
is... It's just staggering. It wasn't just a
bone or two. It was a fissure, a sinkhole essentially,
that filled with clay millions of years ago.
And inside that clay were skeletons. Skeletons,
plural. Dozens. Over the next three years, Louis
Lepow and his team excavated at least 38 individuals.
Most of them were full -grown adults. And unlike
the Maidstone slab, these weren't jumbled. They
were articulated. Every bone in place. From the
tip of the nose to the end of the tail, perfect
three -dimensional skeletons. This transforms
the field overnight. You can't overstate the
importance of this. It's the difference between
having a few crumpled pages of a book and having
the entire encyclopedia suddenly appear. But
then tragedy strikes. Or, uh, chemistry strikes.
The pyrite disease. Yes, the curse of Berna Sartre.
You see, these bones have been sitting in red,
oxygen -free clay for 125 million years. The
groundwater there was rich in iron and sulfur.
Over eons, pyrite crystals, that's iron sulfide,
had formed inside the microscopic pores of the
bone. So the bones were literally infused with
fool's gold. Partially, yes. And underground,
that's fine. Pyrite is stable without oxygen.
But the moment they brought those bones up 322
meters into the fresh air... The oxygen hits
them. And the humidity changes. Pyrite reacts
with oxygen and water to form iron sulfate and
sulfuric acid. This chemical reaction causes
the crystals to expand dramatically. An expansion
inside a fossil bone sounds really bad. It's
catastrophic. The bones started to crack. Then
they started to swell and crumble. Then they
would literally turn to gray dust. The preparators
in Brussels would finish cleaning a beautiful
vertebra, go home for the night, and come back
the next morning to find a pile of powder on
the table. They were losing the greatest fossil
discovery in history as they were unearthing
it. It was a full -blown panic. Louis Dupas deserves
a medal for what he did. He turned the entire
lab into a scientific triage unit. He experimented
with everything. Finally, he developed a method.
What did he do? He submerged the bones in a boiling
vat of animal gelatin mixed with oil of cloves.
Oil of cloves? What was that for? It's a natural
fungicide and preservative. The hot gelatin would
seep into the pores and seal the pyrite off from
the air. Then he would wrap the bones in tinfoil
to seal them completely. It was messy, dangerous
work, but it arrested the decay for a few decades.
I read that in the 1930s, they tried to fix them
again with a new method. Yeah, and that was a
complete disaster. They tried to use alcohol
and shellac, but they didn't dry the bones enough
first. The shellac formed a hard, impermeable
seal on the outside, but it trapped moisture
inside. Oh no. So the disease flared up again
inside the shellac casing, destroying the bones
from the inside out. Oh, terrible mistake. It
wasn't until recently we actually figured it
out. Yeah, now we use things like polyethylene
glycol and keep the most fragile specimens in
climate -controlled glass cases with vacuum pumps
to remove all the oxygen. But the fact that we
have them at all is a miracle of 19th century
conservation. So, thanks to DePauw, we have the
bones. Now we need to put them together. And
to Louis Dullo. Louis Dullo. He is the man who
killed the rhino. He was put in charge of studying
and mounting these skeletons, and he looked at
these 38 skeletons and immediately saw that Richard
Owen was completely wrong. What was the dead
giveaway? The limbs. The front legs were significantly
shorter and more slender than the powerful hind
legs. A rhino has legs of roughly equal length
and strength. This animal had the build of...
Well, Dalla looked to Australia. It had the build
of a kangaroo. So we leave the elephant era and
enter the kangaroo era. The tripod era. Dallow
concluded that a guanodon was primarily a biped.
It walked on its hind legs. So he designed this
amazing mount, which you can still see in Brussels
today, where the animal stands bolt upright,
vertical spine, head 20 feet in there. And the
tail. What did he do with the tail? Dragging
on the ground, it forms the third leg of a tripod.
It's the classic Godzilla posture that dominated
monster movies for 50 years. And the horn. The
famous nose horn. The horn. This is the moment
of truth. With a complete articulated skeleton,
Dallow looked at the nose. There was no spike,
no bump, nothing. And he looked at the hand.
And there it was, on the thumb, digit one, a
massive conical spike sticking out of the wrist.
Mantell's nose horn was a thumb spike all along.
It's one of those truth is stranger than fiction
moments in science. It's just incredible. So
Dallow got the thumb right. He corrected the
biggest mistake. He got the bipedalism partially
right. But he got the tail wrong. He got the
tail very wrong. And this is the controversial
part. He probably knew it. What do you mean he
knew it? The fossils were preserved with something
called ossified tendons. These are ligaments
that have turned to bone. They ran along the
top of the spine and way down the tail. They
formed a stiff... bony lattice, like a trellis.
What does that do mechanically for the animal?
It turns the tail into a stiff rod. A plank.
You cannot bend a plank. But to make the Iguanodon
stand up like a kangaroo, with that S -curve
in its back, Dalo had to bend the tail. So what
did he do with the museum mount? In the mount,
he physically broke the connection between the
tail vertebrae to create that curve. He forced
the bones to fit his theory. He assumed it had
to be like a wallaby, so he made it a wallaby,
even if the bones themselves complained. That's
a huge cautionary tale for science right there.
It is. Don't force the data to fit the hypothesis.
But that image. The upright, tail -dragging Iguanodon
dominated the world for a century. It's the Iguanodon
in the original King Kong. It's the Iguanodon
in children's books until the 1980s. So when
did we finally fix the tail? That came with the
dinosaur renaissance, the late 60s, 70s, and
80s. Scientists like John Ostrom and Robert Baker
started arguing that dinosaurs were active and
dynamic, not sluggish lizards. And a paleontologist
named David Norman took a fresh look at the Bernassart
specimens. And Norman said, Unbreak the tail.
Essentially. He realized that the stiff tail
acted as a counterbalance. Think of it like a
seesaw. The hips are the fulcrum. The heavy tail
on one side balances the heavy chest and head
on the other. This means the animal held its
body horizontally. A flat back, parallel to the
ground. Right. No dragging the tail. That would
be physically impossible with those tendons locking
the vertebrae together. The tail was held straight
out behind it. And this must have completely
changed how we viewed its movement. Completely.
And Norman also did a really deep dive into the
hands. And this brings us to our modern view,
the Swiss army knife hand. I love this description
because the hand of a guanodon is just plain
weird. It's not like anything alive today. It's
a specialized multi -tool. It's fantastic. Let's
break it down digit by digit. Okay, digit one.
The thumb. The spike. Originally the nose horn.
We now know it sits on the wrist and it probably
pointed inward and sideways. What is it for?
Opening cans? The can opener theory was actually
proposed that it was for breaking open tough
seeds or fruit. But the biomechanics, the way
the muscles would have worked, strongly suggest
it was a weapon. A shiv. A stiletto. A close
quarters defensive weapon. If a predator, say
a neovanator or a baryonyx attacks, a granadon
can use that spike to inflict a devastating puncture
wound. Aim for the eyes, the neck, the soft belly.
It wasn't a slashing weapon. It was a stabbing
weapon. That is brutal. Okay, digits two, three,
and four. Middle fingers. These are the strangest
fingers in the dinosaur world. They are grouped
together, they are really robust, and the claws
aren't sharp hooks like you'd expect. They are
flattened and hoof -like. Hose on fingers, that's
bizarre. Exactly. And the wrist bones are all
interlocked so they can't rotate or flex much.
This means these three middle fingers were designed
for one thing, to bear weight. Iguanodon walked
on its hands. So it wasn't a biped after all.
It was what we call a facultative biped. This
is the alter... terrain vehicle concept. When
it was grazing or just moving slowly, it was
quadruped. It walked on all fours on those three
middle fingers. Okay. But because the front legs
were shorter than the back legs, if it needed
to run or if it needed to reach high leaves on
a tree, it could shift its weight back and stand
up running on its hind legs. That is incredibly
versatile. It's the best of both worlds. It has
the stability of a quadruped for low browsing
and the reach and potential speed of a biped
when it needed it. Okay. So that just leaves
digit five. The pinky? The pinky is the odd one
out. It hangs off to the side of the weight -bearing
hoof. It's long, it's slender, and it has extra
joints that make it very flexible. Prehensile.
Could it grab things? Effectively, yes. While
the thumb stabs and the middle fingers walk,
the pinky grabs. It could wrap around branches
and pull vegetation toward the mouth. Stab, walk,
grab. Three distinct functions in one hand. It's
evolutionary genius. It explains why Iguanodon
and its relatives were so incredibly successful
for so long. They could handle almost any situation.
Let's talk about the mouth. Because if you're
a giant herbivore, your main job is eating. And
Iguanodon had a very high -tech way of chewing.
It did. And this goes back to that old reptiles
don't chew bias. Mammals chew by moving their
jaw side to side like a cow or in a rotary motion.
Most reptile jaws just hinge open and shut. So
how do you grind tough plants with a simple hinge?
You invent something called pleurokinesis. Unpack
that word for us. Pleurokinesis. It means side
movement. The upper jaw bones of iguanodon, the
maxillae, weren't fused solid to the rest of
the skull. They had a mobile joint connecting
them. The upper jaw was mobile. It could flex.
When iguanodon bit down, the pressure of the
lower teeth hitting the upper teeth forced the
upper jaw bones to bow outwards. away from the
skull so its head got wider as it chewed the
cheeks pushed out just a little as the upper
teeth slid outward they would grind against the
inner surface of the lower teeth it created a
powerful shearing and grinding action without
the lower jaw needing to dislocate or move side
to side that is wild a flexing skull It was a
very efficient way to process very tough vegetation.
We're talking horsetails, cycads, conifers, things
that would be really hard to break down otherwise.
And this brings us to the Gardner theory of their
ecological role. I love this one. The idea that
Iguanodon changed the world just by eating. Think
about the early Cretaceous landscape. The world
is dominated by gymnosperms. These are slow -growing
plants like conifers, ferns, and cycads. Then,
iguanodon appears in huge numbers. It's a low
-browser. It's a super -efficient lawnmower.
It clears the brush. It devastates the slow -growing
plants at ground level. By constantly clearing
that understory, it creates a disturbance. And
who loves a disturbed environment? Weeds. Fast
-growing, opportunistic plants. Exactly. And
who are the new kids on the block in the Cretaceous,
botanically speaking? Angiosperms. Flowering
plants. They are the fast -growing weeds of the
dinosaur era. There is a very strong hypothesis
that the intense grazing pressure from huge herds
of Iguanodon and its relatives helped clear the
way for the evolutionary explosion of flowering
plants. So we might have roses and apple trees
today because Iguanodon ate all the ferns. It's
a distinct possibility. There are ecosystem engineers
on a massive scale. We've talked about the animal
itself. Let's talk about the family tree. Because
for a long time, it seems like if you found a
generic Big herbivore bone. You just slap the
label iguanodon on it. Ah, the wastebasket taxon.
A classic problem in paleontology. Explain that
term. It's exactly what it sounds like. In taxonomy,
sometimes you have a genus that becomes a dumping
ground for poorly understood fossils. For over
a century, if you found a big ornithopod, a bird
-hipped dinosaur, that wasn't clearly something
else. Scientists would just say, eh, looks kind
of like an iguanodon. Let's call it iguanodon.
So we ended up with iguanodon in England, iguanodon
in America, iguanodon in Mongolia. It was a mess.
It created this illusion of a single, globe -trotting
genus, but it obscured the real diversity. In
the early 2000s, researchers started the Great
Cleanup. They went back and looked at all these
supposed iguanodon species and realized most
of them were completely different animals. So
they broke them up into new genera? Yes. The
American one from South Dakota became dicotodon.
The lighter English one became mantellosaurus.
Others became beryllium or hypsilospinus. The
wastebasket was finally being sorted out. And
what happened to the original, the very first
tooth that Mantell found? This is the ultimate
irony. The tooth that started it all, the species
Iguanodon anglicus, is now considered a gnomon
dubium, a dubious name. Why? It was the first.
Because a single tooth isn't diagnostic enough.
You can't reliably distinguish it from the teeth
of Mantellosaurus or Beryllium. There are no
unique features. So technically, the original
Iguanodon isn't a valid species anymore. But
we still use the name Iguanodon, so how does
that work? We do. To save the famous name from
disappearing, the International Commission on
Zoological Nomenclature, the ICZN, made a special
ruling. They agreed to change the type species.
They swapped it. They swapped the original English
tooth for the beautiful Belgian skeletons. So
now, the official standard for what makes an
Iguanodon an Iguanodon is the animal from the
coal mine. Negronodon bernsartensis. And there
was some justice for Gideon Mantell in this big
taxonomic breakup, right? There was. A really
nice bit of poetic justice. Remember the maidstone
specimen? The one with the nose horn spike? The
one Mantell called his mantelpiece. That's the
one. The paleontologist Gregory Paul re -examined
it in the 2000s and realized it was much lighter
and more grassy than the big bulky Belgian beasts.
It was a different animal entirely. So he gave
it a new name. Mantellosaurus. That's a fantastic
tribute. It is. So now we know that the Iguanodons
of early Cretaceous Europe were actually a diverse
community of different related species, some
big and bulky like Iguanodon, some lighter and
faster like Mantellosaurus. Speaking of community,
let's talk behavior. Did they live in herds?
The Bernassart mine certainly suggests they did,
but with a major caveat. We used to think the
mine was a snapshot of a single herd that fell
into a ravine together. A Pompeii moment. A single
catastrophe. And now... More detailed geological
analysis suggests it might have been an accumulation
over a longer period of time. Maybe a few years,
maybe decades. It could have been a treacherous
marsh where animals got stuck periodically. Or
a river bend where carcasses washed up after
floods. So the mine itself doesn't prove they
walked together in life. But the footprints do.
The footprints are the smoking gun. We have trackway
sites, especially in Germany and England, where
you see the tracks of multiple animals of the
same species all walking side by side in the
same direction at the same speed. That is definitive
herding behavior. And those footprints connect
us all the way back to the start. The pre -dinosaur
era of discovery. The giant birds. Right. It
all comes full circle. In the early 1800s, before
Mantell even found his tooth, people were finding
these massive three -toed tracks in the sandstone
of the Weald. They look like giant turkey tracks,
but, you know, 20 inches wide. They thought they
were made by giant biblical ravens. Or other
monstrous birds sent by Noah during the flood.
It wasn't until we found a complete Iguanodon
foot skeleton that we realized. Iguanodon walked
on its toes, what we call digitigrade, just like
a bird. The three weight -bearing toes matched
the tracks perfectly. It's amazing how every
single piece of evidence, the teeth, the spike,
the tracks, the bones, was misunderstood at first
and then clarified later. That's the theme of
this whole story. It's a 200 -year -long process
of correction. So let's talk pop culture. Iguanodon
is everywhere, even if the people don't always
realize it. It's the everyman dinosaur. It's
not as flashy as a T -Rex or as weird as a Triceratops.
It's the solid, reliable citizen of the Mesozoic.
It inspired Godzilla. The original Japanese Godzilla
design from 1954 was a mashup. They took the
scales and plates of a Stegosaurus, the head
of a T -Rex, but the body and posture, that upright
tripod stance, the heavy thighs, the dragging
tail, that was pure Louis Dolo Granadon. And
Disney's dinosaur. The movie of the main character,
Aladar. A great depiction, actually, for its
time. Aladar. They gave him lips so he could
talk, which is scientifically debatable. A little
bit. But they captured the bulk. They captured
the use of the thumb spike for defense. And they
really captured the idea of them moving in large
social herds. And you can't forget Arthur Conan
Doyle. The Lost World. Absolutely not. You can't
have a Victorian dinosaur story without Iguanodon.
It represents that initial thrilling discovery
of a lost prehistoric world. So as we wrap up
this deep dive, what is the big takeaway? Why
does Iguanodon matter more than just being a
cool skeleton in a museum? I think Iguanodon
teaches us humility. It teaches us that science
is not a destination. It's a process. It's a
verb, not a noun. We're never done. We never
have the final answer. We're never done. Gideon
Mantell wasn't stupid for putting the horn on
the nose. He was using the best comparative anatomy
he had available to him. Richard Owen wasn't
stupid for making them elephants. He was correctly
interpreting the immense mass of the bones. Louis
Dallow wasn't stupid for creating the kangaroo
pose. He was reacting to the limb ratios. They
were all right, based on the evidence they had,
until they were wrong. Exactly. And today, with
our all -terrain vehicle, Swiss Army Hand Iguanodon,
we feel very confident. We think we've got it
figured out. But are we right? Maybe. Or maybe
in 50 years, a new scanner will reveal they had
feathers on their back. Or a colorful dewlap.
Or that the prehensile pinky finger was used
for something we haven't even guessed. And that's
the joy of it, the journey of the thumb spike.
From a nose horn on a concrete elephant to a
defensive weapon on a dynamic horizontal walker,
that journey is the perfect metaphor for human
curiosity. We guess, we test, we fail, and we
correct. And Iguanodon has been with us for every
single step of that 200 -year journey. from a
country doctor on horseback to the secretron
particle accelerators we use today. And it will
probably be with us for the next 200 teaching
us new things. Well, next time you see a picture
of an iguanodon, don't just see a dinosaur. See
a history lesson. See a detective story. And
definitely keep an eye on that thumb. And be
very glad you aren't a psyched plant in the early
Cretaceous. Exactly. Thanks for diving deep with
us today. Keep asking questions. Keep digging.
Stay curious.