Inside Nature's Giants (2009) s01e03 Episode Script
The Crocodile
"This programme contains scenes some viewers may find upsetting.
" Hidden inside every giant that walks the Earth is a remarkable story of survival.
If you've ever wondered why an elephant or whale is so large, a giraffe's neck so long, or a crocodile's bite so strong, the answer lies in their gross anatomy.
Traditional wildlife films tell us how animals behave.
But to truly understand how theirbodies evolved, you need to go under their skin.
Just as you might lift the bonnet of a car to find out how it works, we'll look inside an animal to reveal its incredible inner workings.
Tonight, in front of an invited audience, we will open up the ultimate predator, the crocodile.
Welcome to the Royal Veterinary College where we are about to begin an investigation into the life and death of this 280kg Nile Crocodile.
Sadly, the animal died unexpectedly at a crocodile conservation and breeding centre in the south of France.
But as well as investigating the death of this animal tonight, we're also going to be celebrating a life that has changed little since the time of the dinosaurs.
When other animals died out, crocodiles survived.
The secret of their success lies in ancient anatomy that allows them to submerge like a submarine, launch from the water at speed and lock on to prey with the most powerful bite in the animal kingdom.
It can digest a meal of meat, bone and hooves with ease.
From the solar panels in its skin to the most sophisticated heart on the planet, every part of its anatomy has evolved to solve a problem.
And we will uncover evolution solutions one by one, to find out why this primeval looking beast has survived for long.
Richard Dawkins will be telling us exactly how ancient this animal is.
And biologist, Simon Watt, will come face to face with the crocodile's bite.
And here, our dissection will be lead by international crocodile expert, Dr Greg Erickson.
Greg, we're uncovering the animal for the first time.
You haven't seen it before but tell us what we've got.
Wow, it's impressive.
Huge, isn't it? A big male Nile Crocodile, it's like maybe four metres.
Greg, what's the first thing you want to do and why? Well, to understand how these animals tick, we need to figure out how they generate their bite forces.
We're going to flip it over to do that.
Wow! That's an impressive animal, huh? How we doing down there? Yeah.
Someone on this leg here.
There we go.
As we progress, we'll be looking for clues that may solve the mystery of this animal's sudden death.
Samuel Martin is a leading crocodile expert and the director of the breeding centre where the animal died.
He noticed this crocodile had been swimming strangely but was shocked to find his animal dead just a few days later.
It was 17, normally crocodiles can live as long as we do.
The death is a complete mystery.
The first area we're going to uncover is the crocodile's jaw.
You can see at the moment, what they're trying to do is just to dissect away and peel back the skin under the throat, this bit here.
We're starting to see underneath the base of the tongue.
It's very, very thick skin, as you'd imagine.
This is a gladiator of an animal and its protection in its skin is absolutely vital.
While the team is working let's look at how the crocodile uses its devastating bite to ambush in the wild.
Even a huge 20ft croc can lie hidden in shallow water and then launch itself in a fraction of a second.
A crocodile bite is far stronger than a lion or a great white shark.
And once it's locked on, it won't let go.
Perhaps the most telling demonstration of the unforgiving strength of the crocodile's bite, was caught on home video in Florida.
Alligator wrestler, Kenny Cypress, is lucky to get out of this encounter with his head intact.
(GASPING) But just look at how many people it takes to prise those jaws apart.
The dissection team is exposing the underside of the jaw and we're starting to see the base of the tongue.
Jaw anatomy is Greg's specialty.
He's leading authority on the bites of everything from dinosaurs through to modern day crocs.
Collecting bite force measurements requires courage.
So our intrepid biologist, Simon Watt, travelled to Florida to see what it takes.
This is where Greg conducts his research.
I'd like to give it a go.
This is the equipment he shoves into the alligators' mouths.
I'm going to try it first, if I may? You may, let me reset it.
You're good to go.
How was that? 78 and half pounds.
Is that even good for a human? It little low! Not bad.
We'll try it on the alligators, see if they can do any better.
He's a big one! ALLIGATOR HISSES In the wild, crocodiles and alligators like this one have to take advantage of every single opportunity for a meal.
So they've evolved incredible bite forces allowing them to take down some of the biggest creatures.
In Africa, crocodiles take down things like zebra and wildebeest.
Alligators here take down deer and humans are not exempt from the menu.
Wow! Nice teeth! OK, everybody set? ALLIGATOR HISSES Hold that head straight, if you can.
Here we go! Great bite.
Lets have a look.
So that's 1,413 pounds.
That's about 600 and something kilograms, would that be right? Somewhere in there.
Incredible.
That's what? 20 times stronger than my bite! When I move this meter, this animal is going to reassert itself and the force will be about 90% of the initial force.
Here we go, watch this.
Look at that.
That's it right there! If you could bench press a Mini Cooper then you get out of there.
It's coming.
It'snot coming! it's pretty amazing, actually, that we are able to keep it closed using only tape, but now we can't even get this thing yanked out of it.
It's unbelievable.
These are the massive muscles responsible for that bite.
These muscles are very pale.
They're not oxidated muscles.
There's not a lot of blood flow to them.
Because of the properties of these muscles, these animals can generate really explosive bite forces but they can't sustain it.
So can I get a hand flipping this big boy? What we want to do now is to compare these huge jaw closer muscles with the muscles on the other side of the head, the jaw openers.
For some reason these muscles are so weak that a few loops of tape can hold the jaw shut.
These are the muscles that this animal uses to lift its skull up.
That's this one here, right? Notice how dark it is.
It can hold its mouth open for a long time because it's continually getting oxygen and energy, unlike the pterygoid muscles that we just looked at which are muscles for really rapid forces but not sustained.
The dissection team has revealed the hidden secrets of the crocodile's jaw.
Two rather small, weak muscles open the jaw.
It is the huge jaw closers that make the crocodile's bite so strong.
Anchored beneath the skull, these muscles pull the upper jaw down with tremendous force.
Most other big biters have muscles high on their heads, but the crocodile's low slung jaw muscles enable it to have a stealthy low profile in the water.
Go ahead and put a rope under there.
Oh, yeah.
Here is comes.
Getting a grip.
One, two Hold it! That's about it.
Cool.
Well that's great.
This provides a great demonstration of how this muscle comes off the back of the skull here and comes down around the jaw and comes up through here and basically pulls down on this part of the skull.
Pretty impressive! But not all crocodiles have such big bites.
Some have adapted to evolve different jaws to suit different environments.
These are two members of the crocodile family.
This is a Gharial from India and this is a Saltwater Crocodile from Australia.
One of the things we see when we look at these skulls is that they're related animals and every bit of the skull matches.
They are adapted to catch different prey.
This one is adapted to catch fish, this one is adapted to catch large animals that are on land.
What this one needs is rapid movement of the jaw snapping them shut with immense speed, with very little water resistance.
What this one has is the ability not to shut the jaws particularly fast, but great force for hanging on and then crushing bones once it's got it.
You cannot have both.
Evolution is filled with compromises.
You can't have both high speed and great force.
There are many other such compromises.
Everything about this Gharial skull can be interpreted as going for high speed of snapping shut, everything about this Salt Water crocodile can be interpreted as great force of jaw rather than great speed.
So, that's the bite, but in the anatomy of a kill, it's just the beginning.
So far, we've seen how a crocodile bites by exposing its mighty jaw muscles.
But what happens next? If you think about the way a crocodile kills, it doesn't kill by actually killing with its teeth.
It simply uses its jaws as big pincers to be able to grab hold of its prey and then drag it into the water to drown it.
This hunting technique is simple, but frighteningly effective.
The teeth of this animal's jaws are very simplistic, they're just cones and they're not particularly sharp.
What they're designed to do is sustain stresses from any direction.
When they get a hold of prey item and its struggling, it's not likely to break their teeth no matter which way they bend.
Also these animals, once they get hold of prey item, go into death rolls, they spin, and the teeth can sustain that.
Without sharp teeth for slicing through meat, crocodiles use the death roll to tear off chunks of food.
But this technique causes a problem.
A mystery of the death roll is how crocodiles manage to keep their mouth open underwater without drowning.
Here to show us how they do it is comparative anatomist Joy Reidenberg.
Joy has looked down the throats of hundreds of animals and is a world expert on vocal and breathing anatomy.
We're looking at the tip of the snout of the crocodile.
Right here are the nostrils and these have little valves that can flop open to allow air in and then close up like little plugs.
Then we've got a passageway that runs from the tip of the rostrum all the way inside the skull, and then dives down into the larynx, which is below this.
If we open up the mouth - Alun, if you could just lift that up for me - we see inside, the complicated arrangement of the inside of this mouth has a valve that keeps water from going into the larynx or voice box.
So this ridge over here overlaps with the soft palate and that keeps water from getting into the larynx.
When we look inside - if you can lift that higher - we can see inside there is a voice box right here.
This is the larynx and there's the opening into the larynx and we're looking down a pipe that goes into the trachea and all the way to the lungs.
This is where air would pass and when this animal elevates its larynx up like that, it seals this opening, and it's connecting the opening of the larynx into the nasal passageway which is back here.
This animal has a built-in snorkel to allow it to breath from the nose all the way down to the lungs and not let water that's in its mouth get into here and drown the animal.
If the animal wants to grab a fish, this is also a wonderful trap for catching a fish.
If it's lying on the bottom of a river bed with its mouth open waiting for a fish to swim across, it needs to make a current to draw the fish into the mouth so the fish doesn't keep swimming right by.
It does that by using the tongue as a piston.
This big broad flat tongue just drops down like that and now the fish is drawn in with the current and then it can snap the jaws shut, trapping the fish.
As we've seen, the head of this animal is equipped with the jaws and teeth it needs to trap and kill its prey.
But first it has to catch that prey, and to do that, it uses a huge piece of anatomy that represents almost half of a crocodile's body - its tail.
What I'm doing here is exposing the tail muscles of this crocodile.
I want to show you that this is almost all muscle in the tail.
There's very little bone and if you pull this back, that whole thickness, almost as deep as my hand can go there, is solid muscle.
That's on one side the same is on the other side.
So almost all of this bulk is just muscle.
Let's flop this over.
There's the propeller.
These fins right here are made out of keratin, they're really stiff, like what your fingernails are made out of.
What these animals do is they thrust their tail back and forth like this and because it has an S-shape motion to it, it causes thrust to be generated backwards and allows these animals to move forwards.
They can swim 20mph.
It's really amazing.
Crocodiles have evolved as masters of the water's edge.
They move with ease in the water, but they can also slide up onto dry land on their bellies.
If they want to go further, they'll lift up into a high walk.
And if smaller crocs really need to move fast, they can bound like a rabbit.
It's thought this running ability may date back to the time of the dinosaurs when small crocodile ancestors lived on land and ran down their prey.
We can trace the crocodile's entire history through its fossilized remains.
The evolutionary story of the crocodiles begins some 320 million years ago.
Amphibians had pioneered their way from the sea to the land.
But early reptiles had a trick up their sleeves, their eggs.
Amphibians need to stay close to water to keep their eggs moist.
But the covering of a reptile egg keeps vital fluids inside.
Away from water, reptiles thrived.
Over the next 100 million years, there was an explosion of different reptile body forms.
The age of the reptiles had arrived.
250 million years ago, acatastrophic event occurred.
No-one knows for sure what happened, but virtually all life on Earth was wiped out.
The reptiles were among the few groups to survive.
This opened the door for them to fill the gaps left by the extinct animals.
The archosaurs, literally the ruling lizards, took centre stage.
One evolutionary line led to the birds and dinosaurs and the other to the crocodilians.
The earliest crocodilians lived on land, like the long-legged Terrestrisuchus, a fast runner not much bigger than a rabbit.
Later, some crocodiles took to the water.
Their eyes and nostrils moved to the top of their heads allowing them to keep a low profile in the water.
And supported by the water, their bodies surged in size.
110 million years ago, enormous "mega-crocs", like Sarcosuchus, grew up to 12 metres long.
The length of a bus! Whilst these super-crocs died out, their smaller cousins flourished and started to resemble more modern crocodiles.
Remarkably, over the last 100 million years, they've hardly changed at all.
Do you want to go ahead and give us a mid line? So what is it about this prehistoric internal anatomy that's worked so well for so long? We're about to investigate the crocodile's stomach to find out how it digests the huge chunks of meat it swallows before they start rotting inside.
I don't know when this animal last fed.
About a week before it died.
Might be fish or pork, we don't know.
Probably highly digested already.
The guys are just reflecting the skin off the ventral surface of the crocodile to give us access to its organs.
We hope this will also reveal clues about why this particular animal died.
The diaphragm will have a lot of fat, so we need to be careful when you get down into there.
It's very difficult doing this dissection because the underlying structures are so close to the muscular wall.
We have gone into something, maybe the bladder or stomach.
The way the digestive system is laid out, it's nothing like I have seen before.
It's amazing.
Yeah, this is the duodenum.
Yeah.
And the stomach must be somewhere here.
No, this is the stomach here.
We're trying to get oriented here.
Samuel Martin thinks his crocodile may have eaten something that led to its premature death.
When it comes to solving mysterious animal deaths, Professor Alun Williams is the Hercule Poirot of veterinary pathology.
He is eager to investigate the stomach contents.
OK, we're coming down your end, Alun.
So So So this end belongs Yeah, let's lay it out as it was.
Bring it back this way.
For me, the most impressive thing about this digestive system is that for such a massive animal, how small it is.
What goes on in here in terms of the breakdown of huge chunks of animal into tiny little pieces, is just extraordinary.
And think about the shapes of things that are coming down here.
These animals are swallowing limbs of ungulates, big sections of bone, etc.
big sections of bone, etc.
So hoof and the whole lot.
Yeah, I've found fishing lures, shotgun wads, coins, house cats, you name it! So this has to distend in all kinds of directions to allow them to feed at all.
These animals cannot use their teeth to orally process their food, they're just ripping off chunks and swallowing them fairly whole.
Greg, if you could hold the jar for us, please.
We'll just try and lift this up.
These are the stomach contents.
These are the stomach contents.
Mm.
OK, here we go, I got something here.
Samuel, this is a very dark green colour.
Very strange.
This white material, if I just lift some of this out That's it.
What do you make of this? It's weird.
What does it feel like? Like cheese.
The green colour probably means, maybe after the meal he may have eaten something he should not have.
Maybe some leaves or something.
Do you see pica in crocodiles, so if they are unwell they might have a deranged appetite and start eating things they wouldn't normally eat? Yeah, it does happen from time to time.
They're also very curious, they come to any new thing and might swallow it just by mistake.
But here it's quite strange.
I've opened lots of alligator stomachs from the wild and I've never seen anything like this.
This is completely foreign to me.
Have we got a possibility here that this could be a toxic reaction? It could well be.
Is that a leaf?! Yeah.
We got a leaf.
And that looks almost like a wheel from a toy car, so heaven only knows what this crocodile has been eating! It cannot be the reason.
That could have been in there for years.
This stuff is really an alien brew.
We know it's abnormal and more tests need to be done to find out what's in it, but the unique thing about the crocodile is, to help digest these huge quantities of protein that it ingests when it kills and consumes a third of a wildebeest, it produces ten times more acid than we do.
How they do that? You won't believe this, but you have to dig deeper into the crocodile.
Shall we choose our weapons? Great, thank you.
Let's take the trachea down to about here.
'The dissection team's delving deeper into the crocodile.
'We hope to find out what caused this animal's mysterious death.
'And we want to uncover more 'of the prehistoric parts hidden deep inside.
' In some ways, the chest cavity's very familiar.
It's got the same components we've got - two lungs and a heart.
But in some ways it's incredibly different.
Guys, you're still dissecting.
Can we just have quick look at the big picture anatomy here? OK, so this is the trachea, or windpipe, of the animal.
This part goes forward towards the larynx or voice box and this part continues down towards the lungs.
Here we have complete rings which reinforce the trachea and keep it from collapsing as this animal is swallowing massive prey through this really large oesophagus that can really stretch to encompass very large bits of food because these animals can't process it down with the teeth they have, which are just grabbing teeth - not mashing teeth like you have in other animals.
So this oesophagus is going to stretch out and take over this whole area, which means the trachea gets pushed off to the side, which is unusual because, in other animals, it comes down the midline.
'To find out just how big a breath our croc can take, 'we want to try to inflate the lungs with compressed air.
' Okey-dokey.
Perfect fit.
Look at that! Shall we give it a whirl? Go for it! Wow! That's impressive.
That is impressive.
A huge amount of air.
Yeah.
They can take in about four times the amount of air that we can.
And this is essentially the Scuba tank for these animals.
A big animal like this can stay under water for as long as a half hour, which is a long time.
The way they inspire or bring in this air is using the muscles on their ribs and that expands the chest, just like it does in us.
But they also have another secret, they have the diaphragmatic muscles which are right here.
These attach back on to the pubis and when they pull backwards, they pull back on the liver and expand the pleural cavities here so even more air can get sucked in.
It's like a piston.
It's like a piston.
Yeah, it's like a piston - exactly.
This unique muscle helps crocodiles breathe.
But monitoring its activity underwater shows it is active even after breathing has stopped.
It seems crocodiles and alligators like this one use this muscle to move the air-filled lungs inside their body and shift their centre of buoyancy.
They can adjust their position in the water like a submarine.
A crocodile sinking silently from the surface is an iconic image of a predator at work.
Never make a ripple, never make a splash.
It's an excellent adaptation.
We're about to venture into the very heart of the crocodile.
Surprisingly, it has some of the most sophisticated plumbing found in any animal.
This is all fat.
Yeah.
Very delicately go down through there.
There's a lot more tubes than you see in a human heart, so it's a little bit tricky.
'The artery that takes blood from the heart to the rest of the body, 'is called the aortic arch.
'But bizarrely, unlike most animals, crocodiles have more than one.
' We're trying to find the other aortic arch.
In humans, you have just a left aortic arch.
In birds, we have a right aortic arch.
And if you look at amphibians, you actually have both.
Embryologically you start with both, and lose one or the other depending which way you go on that evolutionary tree.
Crocodiles have kept the right aortic arch like birds do but, interestingly, this animal, the crocodile, may also have some remnant of the left aortic arch.
So we're looking to trace that and see if we can see that here.
Just like us, the crocodile has an artery to take blood from the heart to the lungs and an aorta to take blood to the rest of the body.
But the crocodile's mysterious extra aorta has puzzled biologists for decades.
In many ways, this is quite a familiar heart.
But it's when you get to the pipe work it all starts to get pretty complex.
That's something absolutely unique to a crocodile.
'This aortic anomaly is the focus of research for Colleen Farmer.
'In her rooftop lab in Utah, she's had a remarkable breakthrough 'that might explain the need for this extra blood vessel.
'Her feisty subjects are a group of American alligators.
'She wants to see if there is a link between the extra aorta 'and why crocodiles don't suffer excruciating indigestion.
' So, Colleen, what are you hoping to see by feeding these huge bits of meat and bone? I want to understand how fast they digest their food.
And one way to do that is to actually image the bones that they swallow.
So they don't chew their food, they just swallow big pieces whole so the bone will end up in the stomach of the animal intact.
And then we're going to catch one of them and take it up to the X-ray machine to take our first measurement of the bone.
This alligator is different from the others.
Its extra aorta is blocked and Colleen hopes to see if it affects its digestion.
So co-operative.
Each day, she X-rays her alligators to check how quickly they are digesting food.
In those with blocked aortas, she finds digestion has almost ground to a halt.
The extra aorta clearly plays a crucial role.
And the secret lies inside the heart.
Blood that has been round the body is rich in carbon dioxide - a vital ingredient in the production of stomach acid.
When needed, a tiny valve in the heart diverts this acidic blood to the stomach and this generates extra stomach acid.
This is the adaptation that allows crocodiles to digest the massive prey that they hunt.
We know that our crocodile wasn't digesting food properly.
And, before it died, Samuel had noticed it was behaving strangely, lingering in the water longer than usual.
Crocodiles and alligators normally spend most of their day lying out in the sun, warming their cold-blooded bodies.
They compete for the best basking sites and call to each other to mark territory or attract a mate.
Joy wants to test just what sort of noise this animal is capable of making and find out whether Samuel recognises the sound of his crocodile.
If this animal were to exhale and send a lot of air through its throat, we should get some sound from the voice box, the larynx which is located right in here.
I might need you to lift the mouth for me so we can get the air to come out.
Let's see what happens.
(ROARING) Oh, yeah, that's exactly it! It sounds really like this.
And when it comes from way through the lungs, it's even more strong and more impressive.
(ROARING) That's it.
That's it.
Do they do it with the mouth right open or? Oh yeah.
Very often the peak of roaring is during the mating season.
It goes a lot showing how impressive I am and how strong I can yell and telling other males, "OK, I want to keep my piece of water for me.
" How do we know this one's a male apart from just it's big, but is that enough? Actually it is.
With crocodiles, the males are much larger than the females.
These animals, the males, can get up to 5.
5m and a really big female is like 3m long.
And this is certainly a male - it's 4m.
OK.
In terms of sexual organs then, they're completely hidden in the cloaca.
The testes and the ovaries in the females are found in behind the guts when the animal's on its back.
So, they're dorsally positioned on these animals and, in this case, going along the epididymis here where the sperm's stored, it's going to be conducted out to the penis here.
These fingers will sort of come together to help channel the sperm into the female.
Sorry to interrupt, you know when you were blowing up the lungs, inflating the lungs, and you said the right side was not inflating as much, if you look in there, we have a most horrible mess.
We've got really strong adhesions between the lung and the chest wall.
So it had a respiratory problem.
So it had a respiratory problem.
It certainly has a respiratory problem.
So we think the digestive system problems that we saw, whatever that was, that green alien soup that came out of its stomach, probably secondary to the fact that it was very ill.
Yep.
Another important fact is that the testes at this time of the year should have been much bigger.
If it would have been sexually active, it would have been that size about.
So it probably meant that this animal was completely dominated by other males, so had no real sexual activity.
Probably could not access to the best basking site and could not thermoregulate properly.
This animal would have been under a lot of stress then, is that what you're saying? And that's a vicious cycle presumably.
Once you become ill, you can't get then to your basking site.
You can't get to food quicker and it's just a downward spiral.
That's probably why it did eat some leaves, some vegetation material, instead of proper meat.
So, kind of out of desperation.
So it looks as if we're getting some real clues here.
And we're starting to get a picture of what may have caused this animal's death, but we're not there yet.
When you're dissecting the individual components of a large adult crocodile, it's difficult to get your head round the sense of scale and how all the bits fit together.
The team also wants to look at a small crocodile that died in Samuel's park.
It has been frozen and cut down the midline, to act as a kind of map of where everything fits.
Lets start at the head.
If we clear some of the ice out of this area here - we're just showing the oral cavity - so this is all ice that was in the mouth.
And now we can see the tongue.
Here's the tongue.
This structure right here is tongue, and right behind the tongue is the overlap of the larynx with the soft palate right over here.
There's that palatal valve.
If we follow down here we also have an oesophagus that runs parallel to the trachea.
Right below it is the heart, and below the heart is the liver.
It's interesting how, if you look at the whole animal, what a small proportion of its body actually has its vital organs in it.
Most of this animal is just muscle.
It's all this stuff.
These are the muscles that allow it to be able to do the death roll, these are the muscles that allow it to twist, turn and swim.
Then all the way down to its tail, massive muscles that control its powerhouse, its propulsion, its tail.
At the end of the day, a crocodile uses the minimum amount of space for all its vital organs.
What it is, is one big muscle.
One huge muscular killing machine.
GROWLING Perhaps the ultimate test of a crocodile's powerful body is in a head to head battle with another crocodile.
SNARLING And in the competition for food, other predators are always a threat.
GROWLING AND SNARLING Our gladiator's defence lies hidden inside its skin.
This is the skin from the bottom of the head under the jaw, continuing through the belly region all the way down to where the tail would begin.
And we're looking at the belly surface of this animal and it's relatively smooth even though its armour plated.
That allows this animal to easily slide along the mud flats if it's on the bank of the river and wants to slide back into the river.
But if you look at the other side, the back is not smooth anymore like it is on the belly.
It's actually got a lot of bumps on it that are raised up in the back here as you get towards the tail.
Looks like those spines you imagine on a dragon going down its back.
This makes for wonderful armour so if this animal was in a fight with another big male crocodile, this would keep the animal protected.
So it's a wonderful bit of armour plating.
In fact, even the ancient Egyptians and the Romans used this as armour.
They would dry off an alligator skin, prepare it and wear it as armour.
So, if we look at this armour more closely, we're going to try and understand the structure.
Let's take a look at one of these scutes.
So if we pull one off by dissecting it off here - it's quite hard to cut through the skin.
If this were easy to cut through, it wouldn't be good armour, would it? We see a lot of thick skin here, a lot of connective tissue.
Let's take a look what's inside one of these.
We have a whole bunch of bones here that have been cleaned off so you don't see the skin any more, and they actually overlap one over the next just like this.
Leaving them overlapped like that, allows no chinks in the armour.
So these animals are quite well protected when these armour plates overlap.
So these scutes offer all kinds of advantages to a crocodile.
Camouflage first off, obviously protection, but also they may help the crocodilecontrol its body temperature, which, for a so called cold-blooded animal, is key to its survival.
So how does an animal with such hard armour plating on it be able to manage its temperature? You'd think this would prevent it from being able to get its blood to the surface.
Let's look at one that's been cut so you can see the inside of it.
You can see very fine little channels running up and down here.
These fine little channels are actually for blood vessels that run up and down through the plate all the way to the surface.
And then those blood vessels are going to run underneath the skin.
So this animal is going to be able to absorb a lot of energy from the sun, which is going to heat up the blood vessels and then be able to carry the heat back into the animal.
Kind of like a big solar panel.
So that is going to allow a lot of heat exchange to occur all along the back of the animal.
From its bone-crushing bite to its armour-plated solar panels, we see how effective the crocodile's prehistoric adaptations have been.
But this animal has something else that may hold the key to its survival.
It was thought that poachers had killed off the crocodile in the Ankarana region of Madagascar, but locals recently pointed scientists to a group of crocodiles living deep inside these caves.
The investigating team was amazed to find crocodiles surviving in such cool conditions.
These animals could be living proof that, because crocodiles are cold blooded and can slow down their metabolism, they can survive harsh times on a bare minimum of food and warmth.
As tough as these animals are, something unusual happened to our crocodile for it to die so young.
Having examined this entire animal, pathologist, Alun Williams can deliver his final verdict.
If you remember what we found in the stomach was a lot of this soapy-like material and it's got a single small stone, which crocodiles are known to swallow to aid their digestion process, but, apart from this and a bit of mucus, the stomach was empty as indeed was the whole of the rest of the digestive system, which suggests to me that this crocodile hadn't eaten for quite some time.
The big problem that this crocodile had though, was in its lungs.
If you remember when we were inflating the lungs, one of them didn't inflate particularly well.
Well there were also lots of abscesses present in this lung as well, so one here for example.
Some smaller ones here.
Another one just here.
And if we just cut into this larger abscess, it's very firm material, suggesting it's been there for some time.
And we've got this lovely abscess with a thick capsule around it.
That has taken weeks or longer to develop and probably enough to stop the crocodile eating.
And this infection has now spread round the body.
And the crocodile has been unable to cope with this particularly well because if you look in this little jar here, the liver is floating.
And it shouldn't do that.
And what it's suggesting to me is that there's a lot of fat in the liver.
So the crocodile hasn't been eating because it's been unwell.
The animal has been mobilising its fat reserves, sending it to the liver to be processed, and it's been doing it so quickly that the liver gets overloaded and the cells swell up with all this fat, and the cells stop working.
So you're really into this vicious cycle and that's what drags the animal down at the end of the day.
Our dissection has revealed that our crocodile died of a severe lung infection and the complications that followed.
But, as well as solving the mystery of our animal's death, we explored ancient anatomy dating back to the time of the dinosaurs.
When one says that crocodiles have been around for a very long time, what one means is they haven't changed very much for a very long time.
Presumably what it means is that they've found a very satisfactory way of life and there's no particular reason to change it.
From the outside, crocodiles may look prehistoric.
But, as our autopsy has shown, under the skin they're anything but primitive.
In fact, their bodies are brilliantly adapted to the way they live.
And surely that's why they've survived unchanged for so long.
Next week, we'll be looking inside the giraffe.
We'll find out how it controls its massive blood pressure, and we'll investigate new theories that explain the mystery of this animal's extraordinary neck.
It's a beautiful example of historical legacy.
Red Bee Media Ltd
" Hidden inside every giant that walks the Earth is a remarkable story of survival.
If you've ever wondered why an elephant or whale is so large, a giraffe's neck so long, or a crocodile's bite so strong, the answer lies in their gross anatomy.
Traditional wildlife films tell us how animals behave.
But to truly understand how theirbodies evolved, you need to go under their skin.
Just as you might lift the bonnet of a car to find out how it works, we'll look inside an animal to reveal its incredible inner workings.
Tonight, in front of an invited audience, we will open up the ultimate predator, the crocodile.
Welcome to the Royal Veterinary College where we are about to begin an investigation into the life and death of this 280kg Nile Crocodile.
Sadly, the animal died unexpectedly at a crocodile conservation and breeding centre in the south of France.
But as well as investigating the death of this animal tonight, we're also going to be celebrating a life that has changed little since the time of the dinosaurs.
When other animals died out, crocodiles survived.
The secret of their success lies in ancient anatomy that allows them to submerge like a submarine, launch from the water at speed and lock on to prey with the most powerful bite in the animal kingdom.
It can digest a meal of meat, bone and hooves with ease.
From the solar panels in its skin to the most sophisticated heart on the planet, every part of its anatomy has evolved to solve a problem.
And we will uncover evolution solutions one by one, to find out why this primeval looking beast has survived for long.
Richard Dawkins will be telling us exactly how ancient this animal is.
And biologist, Simon Watt, will come face to face with the crocodile's bite.
And here, our dissection will be lead by international crocodile expert, Dr Greg Erickson.
Greg, we're uncovering the animal for the first time.
You haven't seen it before but tell us what we've got.
Wow, it's impressive.
Huge, isn't it? A big male Nile Crocodile, it's like maybe four metres.
Greg, what's the first thing you want to do and why? Well, to understand how these animals tick, we need to figure out how they generate their bite forces.
We're going to flip it over to do that.
Wow! That's an impressive animal, huh? How we doing down there? Yeah.
Someone on this leg here.
There we go.
As we progress, we'll be looking for clues that may solve the mystery of this animal's sudden death.
Samuel Martin is a leading crocodile expert and the director of the breeding centre where the animal died.
He noticed this crocodile had been swimming strangely but was shocked to find his animal dead just a few days later.
It was 17, normally crocodiles can live as long as we do.
The death is a complete mystery.
The first area we're going to uncover is the crocodile's jaw.
You can see at the moment, what they're trying to do is just to dissect away and peel back the skin under the throat, this bit here.
We're starting to see underneath the base of the tongue.
It's very, very thick skin, as you'd imagine.
This is a gladiator of an animal and its protection in its skin is absolutely vital.
While the team is working let's look at how the crocodile uses its devastating bite to ambush in the wild.
Even a huge 20ft croc can lie hidden in shallow water and then launch itself in a fraction of a second.
A crocodile bite is far stronger than a lion or a great white shark.
And once it's locked on, it won't let go.
Perhaps the most telling demonstration of the unforgiving strength of the crocodile's bite, was caught on home video in Florida.
Alligator wrestler, Kenny Cypress, is lucky to get out of this encounter with his head intact.
(GASPING) But just look at how many people it takes to prise those jaws apart.
The dissection team is exposing the underside of the jaw and we're starting to see the base of the tongue.
Jaw anatomy is Greg's specialty.
He's leading authority on the bites of everything from dinosaurs through to modern day crocs.
Collecting bite force measurements requires courage.
So our intrepid biologist, Simon Watt, travelled to Florida to see what it takes.
This is where Greg conducts his research.
I'd like to give it a go.
This is the equipment he shoves into the alligators' mouths.
I'm going to try it first, if I may? You may, let me reset it.
You're good to go.
How was that? 78 and half pounds.
Is that even good for a human? It little low! Not bad.
We'll try it on the alligators, see if they can do any better.
He's a big one! ALLIGATOR HISSES In the wild, crocodiles and alligators like this one have to take advantage of every single opportunity for a meal.
So they've evolved incredible bite forces allowing them to take down some of the biggest creatures.
In Africa, crocodiles take down things like zebra and wildebeest.
Alligators here take down deer and humans are not exempt from the menu.
Wow! Nice teeth! OK, everybody set? ALLIGATOR HISSES Hold that head straight, if you can.
Here we go! Great bite.
Lets have a look.
So that's 1,413 pounds.
That's about 600 and something kilograms, would that be right? Somewhere in there.
Incredible.
That's what? 20 times stronger than my bite! When I move this meter, this animal is going to reassert itself and the force will be about 90% of the initial force.
Here we go, watch this.
Look at that.
That's it right there! If you could bench press a Mini Cooper then you get out of there.
It's coming.
It'snot coming! it's pretty amazing, actually, that we are able to keep it closed using only tape, but now we can't even get this thing yanked out of it.
It's unbelievable.
These are the massive muscles responsible for that bite.
These muscles are very pale.
They're not oxidated muscles.
There's not a lot of blood flow to them.
Because of the properties of these muscles, these animals can generate really explosive bite forces but they can't sustain it.
So can I get a hand flipping this big boy? What we want to do now is to compare these huge jaw closer muscles with the muscles on the other side of the head, the jaw openers.
For some reason these muscles are so weak that a few loops of tape can hold the jaw shut.
These are the muscles that this animal uses to lift its skull up.
That's this one here, right? Notice how dark it is.
It can hold its mouth open for a long time because it's continually getting oxygen and energy, unlike the pterygoid muscles that we just looked at which are muscles for really rapid forces but not sustained.
The dissection team has revealed the hidden secrets of the crocodile's jaw.
Two rather small, weak muscles open the jaw.
It is the huge jaw closers that make the crocodile's bite so strong.
Anchored beneath the skull, these muscles pull the upper jaw down with tremendous force.
Most other big biters have muscles high on their heads, but the crocodile's low slung jaw muscles enable it to have a stealthy low profile in the water.
Go ahead and put a rope under there.
Oh, yeah.
Here is comes.
Getting a grip.
One, two Hold it! That's about it.
Cool.
Well that's great.
This provides a great demonstration of how this muscle comes off the back of the skull here and comes down around the jaw and comes up through here and basically pulls down on this part of the skull.
Pretty impressive! But not all crocodiles have such big bites.
Some have adapted to evolve different jaws to suit different environments.
These are two members of the crocodile family.
This is a Gharial from India and this is a Saltwater Crocodile from Australia.
One of the things we see when we look at these skulls is that they're related animals and every bit of the skull matches.
They are adapted to catch different prey.
This one is adapted to catch fish, this one is adapted to catch large animals that are on land.
What this one needs is rapid movement of the jaw snapping them shut with immense speed, with very little water resistance.
What this one has is the ability not to shut the jaws particularly fast, but great force for hanging on and then crushing bones once it's got it.
You cannot have both.
Evolution is filled with compromises.
You can't have both high speed and great force.
There are many other such compromises.
Everything about this Gharial skull can be interpreted as going for high speed of snapping shut, everything about this Salt Water crocodile can be interpreted as great force of jaw rather than great speed.
So, that's the bite, but in the anatomy of a kill, it's just the beginning.
So far, we've seen how a crocodile bites by exposing its mighty jaw muscles.
But what happens next? If you think about the way a crocodile kills, it doesn't kill by actually killing with its teeth.
It simply uses its jaws as big pincers to be able to grab hold of its prey and then drag it into the water to drown it.
This hunting technique is simple, but frighteningly effective.
The teeth of this animal's jaws are very simplistic, they're just cones and they're not particularly sharp.
What they're designed to do is sustain stresses from any direction.
When they get a hold of prey item and its struggling, it's not likely to break their teeth no matter which way they bend.
Also these animals, once they get hold of prey item, go into death rolls, they spin, and the teeth can sustain that.
Without sharp teeth for slicing through meat, crocodiles use the death roll to tear off chunks of food.
But this technique causes a problem.
A mystery of the death roll is how crocodiles manage to keep their mouth open underwater without drowning.
Here to show us how they do it is comparative anatomist Joy Reidenberg.
Joy has looked down the throats of hundreds of animals and is a world expert on vocal and breathing anatomy.
We're looking at the tip of the snout of the crocodile.
Right here are the nostrils and these have little valves that can flop open to allow air in and then close up like little plugs.
Then we've got a passageway that runs from the tip of the rostrum all the way inside the skull, and then dives down into the larynx, which is below this.
If we open up the mouth - Alun, if you could just lift that up for me - we see inside, the complicated arrangement of the inside of this mouth has a valve that keeps water from going into the larynx or voice box.
So this ridge over here overlaps with the soft palate and that keeps water from getting into the larynx.
When we look inside - if you can lift that higher - we can see inside there is a voice box right here.
This is the larynx and there's the opening into the larynx and we're looking down a pipe that goes into the trachea and all the way to the lungs.
This is where air would pass and when this animal elevates its larynx up like that, it seals this opening, and it's connecting the opening of the larynx into the nasal passageway which is back here.
This animal has a built-in snorkel to allow it to breath from the nose all the way down to the lungs and not let water that's in its mouth get into here and drown the animal.
If the animal wants to grab a fish, this is also a wonderful trap for catching a fish.
If it's lying on the bottom of a river bed with its mouth open waiting for a fish to swim across, it needs to make a current to draw the fish into the mouth so the fish doesn't keep swimming right by.
It does that by using the tongue as a piston.
This big broad flat tongue just drops down like that and now the fish is drawn in with the current and then it can snap the jaws shut, trapping the fish.
As we've seen, the head of this animal is equipped with the jaws and teeth it needs to trap and kill its prey.
But first it has to catch that prey, and to do that, it uses a huge piece of anatomy that represents almost half of a crocodile's body - its tail.
What I'm doing here is exposing the tail muscles of this crocodile.
I want to show you that this is almost all muscle in the tail.
There's very little bone and if you pull this back, that whole thickness, almost as deep as my hand can go there, is solid muscle.
That's on one side the same is on the other side.
So almost all of this bulk is just muscle.
Let's flop this over.
There's the propeller.
These fins right here are made out of keratin, they're really stiff, like what your fingernails are made out of.
What these animals do is they thrust their tail back and forth like this and because it has an S-shape motion to it, it causes thrust to be generated backwards and allows these animals to move forwards.
They can swim 20mph.
It's really amazing.
Crocodiles have evolved as masters of the water's edge.
They move with ease in the water, but they can also slide up onto dry land on their bellies.
If they want to go further, they'll lift up into a high walk.
And if smaller crocs really need to move fast, they can bound like a rabbit.
It's thought this running ability may date back to the time of the dinosaurs when small crocodile ancestors lived on land and ran down their prey.
We can trace the crocodile's entire history through its fossilized remains.
The evolutionary story of the crocodiles begins some 320 million years ago.
Amphibians had pioneered their way from the sea to the land.
But early reptiles had a trick up their sleeves, their eggs.
Amphibians need to stay close to water to keep their eggs moist.
But the covering of a reptile egg keeps vital fluids inside.
Away from water, reptiles thrived.
Over the next 100 million years, there was an explosion of different reptile body forms.
The age of the reptiles had arrived.
250 million years ago, acatastrophic event occurred.
No-one knows for sure what happened, but virtually all life on Earth was wiped out.
The reptiles were among the few groups to survive.
This opened the door for them to fill the gaps left by the extinct animals.
The archosaurs, literally the ruling lizards, took centre stage.
One evolutionary line led to the birds and dinosaurs and the other to the crocodilians.
The earliest crocodilians lived on land, like the long-legged Terrestrisuchus, a fast runner not much bigger than a rabbit.
Later, some crocodiles took to the water.
Their eyes and nostrils moved to the top of their heads allowing them to keep a low profile in the water.
And supported by the water, their bodies surged in size.
110 million years ago, enormous "mega-crocs", like Sarcosuchus, grew up to 12 metres long.
The length of a bus! Whilst these super-crocs died out, their smaller cousins flourished and started to resemble more modern crocodiles.
Remarkably, over the last 100 million years, they've hardly changed at all.
Do you want to go ahead and give us a mid line? So what is it about this prehistoric internal anatomy that's worked so well for so long? We're about to investigate the crocodile's stomach to find out how it digests the huge chunks of meat it swallows before they start rotting inside.
I don't know when this animal last fed.
About a week before it died.
Might be fish or pork, we don't know.
Probably highly digested already.
The guys are just reflecting the skin off the ventral surface of the crocodile to give us access to its organs.
We hope this will also reveal clues about why this particular animal died.
The diaphragm will have a lot of fat, so we need to be careful when you get down into there.
It's very difficult doing this dissection because the underlying structures are so close to the muscular wall.
We have gone into something, maybe the bladder or stomach.
The way the digestive system is laid out, it's nothing like I have seen before.
It's amazing.
Yeah, this is the duodenum.
Yeah.
And the stomach must be somewhere here.
No, this is the stomach here.
We're trying to get oriented here.
Samuel Martin thinks his crocodile may have eaten something that led to its premature death.
When it comes to solving mysterious animal deaths, Professor Alun Williams is the Hercule Poirot of veterinary pathology.
He is eager to investigate the stomach contents.
OK, we're coming down your end, Alun.
So So So this end belongs Yeah, let's lay it out as it was.
Bring it back this way.
For me, the most impressive thing about this digestive system is that for such a massive animal, how small it is.
What goes on in here in terms of the breakdown of huge chunks of animal into tiny little pieces, is just extraordinary.
And think about the shapes of things that are coming down here.
These animals are swallowing limbs of ungulates, big sections of bone, etc.
big sections of bone, etc.
So hoof and the whole lot.
Yeah, I've found fishing lures, shotgun wads, coins, house cats, you name it! So this has to distend in all kinds of directions to allow them to feed at all.
These animals cannot use their teeth to orally process their food, they're just ripping off chunks and swallowing them fairly whole.
Greg, if you could hold the jar for us, please.
We'll just try and lift this up.
These are the stomach contents.
These are the stomach contents.
Mm.
OK, here we go, I got something here.
Samuel, this is a very dark green colour.
Very strange.
This white material, if I just lift some of this out That's it.
What do you make of this? It's weird.
What does it feel like? Like cheese.
The green colour probably means, maybe after the meal he may have eaten something he should not have.
Maybe some leaves or something.
Do you see pica in crocodiles, so if they are unwell they might have a deranged appetite and start eating things they wouldn't normally eat? Yeah, it does happen from time to time.
They're also very curious, they come to any new thing and might swallow it just by mistake.
But here it's quite strange.
I've opened lots of alligator stomachs from the wild and I've never seen anything like this.
This is completely foreign to me.
Have we got a possibility here that this could be a toxic reaction? It could well be.
Is that a leaf?! Yeah.
We got a leaf.
And that looks almost like a wheel from a toy car, so heaven only knows what this crocodile has been eating! It cannot be the reason.
That could have been in there for years.
This stuff is really an alien brew.
We know it's abnormal and more tests need to be done to find out what's in it, but the unique thing about the crocodile is, to help digest these huge quantities of protein that it ingests when it kills and consumes a third of a wildebeest, it produces ten times more acid than we do.
How they do that? You won't believe this, but you have to dig deeper into the crocodile.
Shall we choose our weapons? Great, thank you.
Let's take the trachea down to about here.
'The dissection team's delving deeper into the crocodile.
'We hope to find out what caused this animal's mysterious death.
'And we want to uncover more 'of the prehistoric parts hidden deep inside.
' In some ways, the chest cavity's very familiar.
It's got the same components we've got - two lungs and a heart.
But in some ways it's incredibly different.
Guys, you're still dissecting.
Can we just have quick look at the big picture anatomy here? OK, so this is the trachea, or windpipe, of the animal.
This part goes forward towards the larynx or voice box and this part continues down towards the lungs.
Here we have complete rings which reinforce the trachea and keep it from collapsing as this animal is swallowing massive prey through this really large oesophagus that can really stretch to encompass very large bits of food because these animals can't process it down with the teeth they have, which are just grabbing teeth - not mashing teeth like you have in other animals.
So this oesophagus is going to stretch out and take over this whole area, which means the trachea gets pushed off to the side, which is unusual because, in other animals, it comes down the midline.
'To find out just how big a breath our croc can take, 'we want to try to inflate the lungs with compressed air.
' Okey-dokey.
Perfect fit.
Look at that! Shall we give it a whirl? Go for it! Wow! That's impressive.
That is impressive.
A huge amount of air.
Yeah.
They can take in about four times the amount of air that we can.
And this is essentially the Scuba tank for these animals.
A big animal like this can stay under water for as long as a half hour, which is a long time.
The way they inspire or bring in this air is using the muscles on their ribs and that expands the chest, just like it does in us.
But they also have another secret, they have the diaphragmatic muscles which are right here.
These attach back on to the pubis and when they pull backwards, they pull back on the liver and expand the pleural cavities here so even more air can get sucked in.
It's like a piston.
It's like a piston.
Yeah, it's like a piston - exactly.
This unique muscle helps crocodiles breathe.
But monitoring its activity underwater shows it is active even after breathing has stopped.
It seems crocodiles and alligators like this one use this muscle to move the air-filled lungs inside their body and shift their centre of buoyancy.
They can adjust their position in the water like a submarine.
A crocodile sinking silently from the surface is an iconic image of a predator at work.
Never make a ripple, never make a splash.
It's an excellent adaptation.
We're about to venture into the very heart of the crocodile.
Surprisingly, it has some of the most sophisticated plumbing found in any animal.
This is all fat.
Yeah.
Very delicately go down through there.
There's a lot more tubes than you see in a human heart, so it's a little bit tricky.
'The artery that takes blood from the heart to the rest of the body, 'is called the aortic arch.
'But bizarrely, unlike most animals, crocodiles have more than one.
' We're trying to find the other aortic arch.
In humans, you have just a left aortic arch.
In birds, we have a right aortic arch.
And if you look at amphibians, you actually have both.
Embryologically you start with both, and lose one or the other depending which way you go on that evolutionary tree.
Crocodiles have kept the right aortic arch like birds do but, interestingly, this animal, the crocodile, may also have some remnant of the left aortic arch.
So we're looking to trace that and see if we can see that here.
Just like us, the crocodile has an artery to take blood from the heart to the lungs and an aorta to take blood to the rest of the body.
But the crocodile's mysterious extra aorta has puzzled biologists for decades.
In many ways, this is quite a familiar heart.
But it's when you get to the pipe work it all starts to get pretty complex.
That's something absolutely unique to a crocodile.
'This aortic anomaly is the focus of research for Colleen Farmer.
'In her rooftop lab in Utah, she's had a remarkable breakthrough 'that might explain the need for this extra blood vessel.
'Her feisty subjects are a group of American alligators.
'She wants to see if there is a link between the extra aorta 'and why crocodiles don't suffer excruciating indigestion.
' So, Colleen, what are you hoping to see by feeding these huge bits of meat and bone? I want to understand how fast they digest their food.
And one way to do that is to actually image the bones that they swallow.
So they don't chew their food, they just swallow big pieces whole so the bone will end up in the stomach of the animal intact.
And then we're going to catch one of them and take it up to the X-ray machine to take our first measurement of the bone.
This alligator is different from the others.
Its extra aorta is blocked and Colleen hopes to see if it affects its digestion.
So co-operative.
Each day, she X-rays her alligators to check how quickly they are digesting food.
In those with blocked aortas, she finds digestion has almost ground to a halt.
The extra aorta clearly plays a crucial role.
And the secret lies inside the heart.
Blood that has been round the body is rich in carbon dioxide - a vital ingredient in the production of stomach acid.
When needed, a tiny valve in the heart diverts this acidic blood to the stomach and this generates extra stomach acid.
This is the adaptation that allows crocodiles to digest the massive prey that they hunt.
We know that our crocodile wasn't digesting food properly.
And, before it died, Samuel had noticed it was behaving strangely, lingering in the water longer than usual.
Crocodiles and alligators normally spend most of their day lying out in the sun, warming their cold-blooded bodies.
They compete for the best basking sites and call to each other to mark territory or attract a mate.
Joy wants to test just what sort of noise this animal is capable of making and find out whether Samuel recognises the sound of his crocodile.
If this animal were to exhale and send a lot of air through its throat, we should get some sound from the voice box, the larynx which is located right in here.
I might need you to lift the mouth for me so we can get the air to come out.
Let's see what happens.
(ROARING) Oh, yeah, that's exactly it! It sounds really like this.
And when it comes from way through the lungs, it's even more strong and more impressive.
(ROARING) That's it.
That's it.
Do they do it with the mouth right open or? Oh yeah.
Very often the peak of roaring is during the mating season.
It goes a lot showing how impressive I am and how strong I can yell and telling other males, "OK, I want to keep my piece of water for me.
" How do we know this one's a male apart from just it's big, but is that enough? Actually it is.
With crocodiles, the males are much larger than the females.
These animals, the males, can get up to 5.
5m and a really big female is like 3m long.
And this is certainly a male - it's 4m.
OK.
In terms of sexual organs then, they're completely hidden in the cloaca.
The testes and the ovaries in the females are found in behind the guts when the animal's on its back.
So, they're dorsally positioned on these animals and, in this case, going along the epididymis here where the sperm's stored, it's going to be conducted out to the penis here.
These fingers will sort of come together to help channel the sperm into the female.
Sorry to interrupt, you know when you were blowing up the lungs, inflating the lungs, and you said the right side was not inflating as much, if you look in there, we have a most horrible mess.
We've got really strong adhesions between the lung and the chest wall.
So it had a respiratory problem.
So it had a respiratory problem.
It certainly has a respiratory problem.
So we think the digestive system problems that we saw, whatever that was, that green alien soup that came out of its stomach, probably secondary to the fact that it was very ill.
Yep.
Another important fact is that the testes at this time of the year should have been much bigger.
If it would have been sexually active, it would have been that size about.
So it probably meant that this animal was completely dominated by other males, so had no real sexual activity.
Probably could not access to the best basking site and could not thermoregulate properly.
This animal would have been under a lot of stress then, is that what you're saying? And that's a vicious cycle presumably.
Once you become ill, you can't get then to your basking site.
You can't get to food quicker and it's just a downward spiral.
That's probably why it did eat some leaves, some vegetation material, instead of proper meat.
So, kind of out of desperation.
So it looks as if we're getting some real clues here.
And we're starting to get a picture of what may have caused this animal's death, but we're not there yet.
When you're dissecting the individual components of a large adult crocodile, it's difficult to get your head round the sense of scale and how all the bits fit together.
The team also wants to look at a small crocodile that died in Samuel's park.
It has been frozen and cut down the midline, to act as a kind of map of where everything fits.
Lets start at the head.
If we clear some of the ice out of this area here - we're just showing the oral cavity - so this is all ice that was in the mouth.
And now we can see the tongue.
Here's the tongue.
This structure right here is tongue, and right behind the tongue is the overlap of the larynx with the soft palate right over here.
There's that palatal valve.
If we follow down here we also have an oesophagus that runs parallel to the trachea.
Right below it is the heart, and below the heart is the liver.
It's interesting how, if you look at the whole animal, what a small proportion of its body actually has its vital organs in it.
Most of this animal is just muscle.
It's all this stuff.
These are the muscles that allow it to be able to do the death roll, these are the muscles that allow it to twist, turn and swim.
Then all the way down to its tail, massive muscles that control its powerhouse, its propulsion, its tail.
At the end of the day, a crocodile uses the minimum amount of space for all its vital organs.
What it is, is one big muscle.
One huge muscular killing machine.
GROWLING Perhaps the ultimate test of a crocodile's powerful body is in a head to head battle with another crocodile.
SNARLING And in the competition for food, other predators are always a threat.
GROWLING AND SNARLING Our gladiator's defence lies hidden inside its skin.
This is the skin from the bottom of the head under the jaw, continuing through the belly region all the way down to where the tail would begin.
And we're looking at the belly surface of this animal and it's relatively smooth even though its armour plated.
That allows this animal to easily slide along the mud flats if it's on the bank of the river and wants to slide back into the river.
But if you look at the other side, the back is not smooth anymore like it is on the belly.
It's actually got a lot of bumps on it that are raised up in the back here as you get towards the tail.
Looks like those spines you imagine on a dragon going down its back.
This makes for wonderful armour so if this animal was in a fight with another big male crocodile, this would keep the animal protected.
So it's a wonderful bit of armour plating.
In fact, even the ancient Egyptians and the Romans used this as armour.
They would dry off an alligator skin, prepare it and wear it as armour.
So, if we look at this armour more closely, we're going to try and understand the structure.
Let's take a look at one of these scutes.
So if we pull one off by dissecting it off here - it's quite hard to cut through the skin.
If this were easy to cut through, it wouldn't be good armour, would it? We see a lot of thick skin here, a lot of connective tissue.
Let's take a look what's inside one of these.
We have a whole bunch of bones here that have been cleaned off so you don't see the skin any more, and they actually overlap one over the next just like this.
Leaving them overlapped like that, allows no chinks in the armour.
So these animals are quite well protected when these armour plates overlap.
So these scutes offer all kinds of advantages to a crocodile.
Camouflage first off, obviously protection, but also they may help the crocodilecontrol its body temperature, which, for a so called cold-blooded animal, is key to its survival.
So how does an animal with such hard armour plating on it be able to manage its temperature? You'd think this would prevent it from being able to get its blood to the surface.
Let's look at one that's been cut so you can see the inside of it.
You can see very fine little channels running up and down here.
These fine little channels are actually for blood vessels that run up and down through the plate all the way to the surface.
And then those blood vessels are going to run underneath the skin.
So this animal is going to be able to absorb a lot of energy from the sun, which is going to heat up the blood vessels and then be able to carry the heat back into the animal.
Kind of like a big solar panel.
So that is going to allow a lot of heat exchange to occur all along the back of the animal.
From its bone-crushing bite to its armour-plated solar panels, we see how effective the crocodile's prehistoric adaptations have been.
But this animal has something else that may hold the key to its survival.
It was thought that poachers had killed off the crocodile in the Ankarana region of Madagascar, but locals recently pointed scientists to a group of crocodiles living deep inside these caves.
The investigating team was amazed to find crocodiles surviving in such cool conditions.
These animals could be living proof that, because crocodiles are cold blooded and can slow down their metabolism, they can survive harsh times on a bare minimum of food and warmth.
As tough as these animals are, something unusual happened to our crocodile for it to die so young.
Having examined this entire animal, pathologist, Alun Williams can deliver his final verdict.
If you remember what we found in the stomach was a lot of this soapy-like material and it's got a single small stone, which crocodiles are known to swallow to aid their digestion process, but, apart from this and a bit of mucus, the stomach was empty as indeed was the whole of the rest of the digestive system, which suggests to me that this crocodile hadn't eaten for quite some time.
The big problem that this crocodile had though, was in its lungs.
If you remember when we were inflating the lungs, one of them didn't inflate particularly well.
Well there were also lots of abscesses present in this lung as well, so one here for example.
Some smaller ones here.
Another one just here.
And if we just cut into this larger abscess, it's very firm material, suggesting it's been there for some time.
And we've got this lovely abscess with a thick capsule around it.
That has taken weeks or longer to develop and probably enough to stop the crocodile eating.
And this infection has now spread round the body.
And the crocodile has been unable to cope with this particularly well because if you look in this little jar here, the liver is floating.
And it shouldn't do that.
And what it's suggesting to me is that there's a lot of fat in the liver.
So the crocodile hasn't been eating because it's been unwell.
The animal has been mobilising its fat reserves, sending it to the liver to be processed, and it's been doing it so quickly that the liver gets overloaded and the cells swell up with all this fat, and the cells stop working.
So you're really into this vicious cycle and that's what drags the animal down at the end of the day.
Our dissection has revealed that our crocodile died of a severe lung infection and the complications that followed.
But, as well as solving the mystery of our animal's death, we explored ancient anatomy dating back to the time of the dinosaurs.
When one says that crocodiles have been around for a very long time, what one means is they haven't changed very much for a very long time.
Presumably what it means is that they've found a very satisfactory way of life and there's no particular reason to change it.
From the outside, crocodiles may look prehistoric.
But, as our autopsy has shown, under the skin they're anything but primitive.
In fact, their bodies are brilliantly adapted to the way they live.
And surely that's why they've survived unchanged for so long.
Next week, we'll be looking inside the giraffe.
We'll find out how it controls its massive blood pressure, and we'll investigate new theories that explain the mystery of this animal's extraordinary neck.
It's a beautiful example of historical legacy.
Red Bee Media Ltd