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00:00Hidden inside every giant that walks the earth is a remarkable story of survival.
00:16If you've ever wondered why an elephant or whale is so large, a giraffe's neck so long
00:23or a crocodile's bite so strong, the answer lies in their gross anatomy.
00:30Traditional wildlife films tell us how animals behave, but to truly understand how their
00:36bodies evolved, you need to go under their skin.
00:41Just as you might lift the bonnet of a car to find out how it works, we'll look inside
00:46an animal to reveal its incredible inner workings.
00:51Right in front of an invited audience, we're going to open up the ultimate predator, the crocodile.
00:58Welcome to the Royal Veterinary College, where we're about to begin an investigation into
01:22the life and death of this 280 kilo Nile crocodile.
01:27Sadly, the animal died unexpectedly at the Crocodile Conservation and Breeding Centre
01:32in the south of France, but as well as investigating the death of this animal tonight, we're also
01:37going to be celebrating a life that's changed little since the time of the dinosaurs.
01:44When other animals died out, crocodiles survived.
01:48The secret of their success lies in ancient anatomy that allows them to submerge like
01:54a submarine, launch from the water at speed, and lock onto prey with the most powerful
02:00bite in the animal kingdom.
02:04It can digest a meal of meat, bone, and hooves with ease.
02:09From the solar panels in its skin to the most sophisticated heart on the planet, every part
02:15of its anatomy has evolved to solve a problem.
02:19And we'll uncover evolution's solutions, one by one, to find out why this primeval-looking
02:25beast has survived for so long.
02:29Richard Dawkins will be telling us exactly how ancient this animal is, and biologist
02:34Simon Watt will come face to face with the crocodile's bite.
02:38And here, our dissection will be led by international crocodile expert, Dr. Greg Erickson.
02:44Greg, we're uncovering the animal for the first time.
02:46We haven't seen it before, but just tell us what we've got in front of us.
02:50Wow, it's impressive.
02:51It's huge, isn't it?
02:52Yeah.
02:53A big male Nile crocodile, looks like maybe four meters.
02:56So, Greg, what's the first thing you want to do and why?
02:59Well, to understand how these animals tick, we need to figure out how they generate their
03:03bite forces.
03:04We have to flip it over to do that.
03:05Wow.
03:06That's an impressive animal.
03:08How we doing down there?
03:09Good.
03:10Yeah.
03:11Someone on this leg.
03:12Here.
03:13There we go.
03:42As we progress, we'll be looking for clues that may solve the mystery of this animal's
03:46sudden death.
03:48Samuel Martin is a leading crocodile expert and the director of the breeding center where
03:52the animal died.
03:54He noticed this crocodile had been swimming strangely, but was shocked to find his animal
03:59dead just a few days later.
04:01It was 17, and normally crocodiles can live as long as we do.
04:05The death is a complete mystery.
04:08The first area we're going to uncover is the crocodile's jaw.
04:13You can see at the moment what they're trying to do is just to dissect away and peel back
04:18the skin under the throat.
04:20So this bit here, what you're starting to see underneath there is the base of the tongue.
04:24It's very, very thick skin, as you'd imagine.
04:27This is a gladiator of an animal, and its protection in its skin is absolutely vital.
04:32But while the team's working, let's look at how the crocodile uses its devastating bite
04:36to ambush in the wild.
04:49Even a huge 20-foot croc can lie hidden in shallow water and then launch itself in a
04:55fraction of a second.
05:03A crocodile bite is far stronger than a lion or a great white shark, and once it's locked
05:09on, it simply won't let go.
05:13But perhaps the most telling demonstration of the unforgiving strength of the crocodile's
05:17bite was caught on home video in Florida.
05:22Alligator wrestler Kenny Cypress is lucky to get out of this encounter with his head
05:26intact.
05:39But just look at how many people it takes to prise those jaws apart.
05:49The dissection team is exposing the underside of the jaw, and we're starting to see the
05:54base of the tongue.
05:56Jaw anatomy is Greg's speciality.
05:59He's a leading authority on the bites of everything from dinosaurs through to modern-day crocs.
06:05Collecting bite force measurements requires courage, so our intrepid biologist Simon Watt
06:11travelled to Florida to see what it takes.
06:15This is where Greg conducts most of his bite strength research, and I'd quite like to give
06:18it a go myself.
06:19So this is the equipment that he shoves into the alligator's mouths.
06:22I'm going to try it out first.
06:24You may.
06:25Hang on just a second.
06:26Let me reset it.
06:27Ready?
06:28All right.
06:29You're good to go.
06:30How's that?
06:3178 and a half pounds.
06:32Is that even good for a human?
06:33It's a little low.
06:34It's not bad.
06:35OK.
06:36Well, we'll try it out in the alligators now and see if they can do any better.
06:37OK.
06:39That's a big one.
06:40All right.
06:42OK.
06:45That's a big one.
07:08In the wild, crocodiles and alligators like this one have to take advantage of every single
07:12opportunity for a meal, and so they've involved these incredible bite forces, allowing them
07:16to take down some of the biggest creatures they can find.
07:19In Africa, crocodiles take down things like zebra and wildebeest.
07:23Alligators here take down deers, and humans are not exempt from the menu.
07:28Wow.
07:29Nice teeth.
07:30OK.
07:31Everybody set?
07:32Try to hold that head straight if you can.
07:41OK.
07:42Ready?
07:43Here we go.
07:44Everybody ready?
07:45Oh, my.
07:46Great bite.
07:48That was good.
07:49What was that?
07:51That's the reed, I can't see it.
07:55Let's have a look.
07:58So, that's 1,413 pounds.
08:01That's about 600 and something kilograms, would that be right?
08:04Yeah, somewhere in there.
08:05That's pretty incredible.
08:07That's what?
08:0820 times stronger than my bite.
08:10When I move this meter, this animal is going to reassert itself and the force will be about
08:1490% of the initial force.
08:16Here we go, watch this.
08:17Look at that.
08:18That's it right there.
08:19You know, if you could bench press like a mini Cooper or something, then you could get
08:26out of there.
08:27Come on, bud.
08:28That's it.
08:29It's coming, it's coming.
08:33It's not coming.
08:36It's pretty amazing, actually, that we were able to keep it closed using only tip.
08:41But now we can't even get this thing yanked out of it, it's unbelievable.
08:53These are the massive muscles responsible for that bite.
09:01These muscles are very pale, they're not oxidative muscles, there's not a lot of blood flow to
09:06them.
09:07And because of the properties of these muscles, these animals can generate really explosive
09:12bite forces, but they can't sustain it.
09:16So let me get a hand flipping this big boy.
09:22What we want to do now is to compare these huge jaw closer muscles with the muscles on
09:27the other side of the head, the jaw openers.
09:29For some reason, these muscles are so weak that a few loops of tape can hold the jaw
09:34shut.
09:35These are the muscles that this animal uses to lift its skull up.
09:39That's this one here, right?
09:40Yeah.
09:41And notice how dark it is.
09:44It can hold its mouth open for a long time, I mean, because it's continually getting oxygen
09:50and energy.
09:51It's like the pterygoid muscles that we just looked at, which are muscles for really, really
09:55rapid forces, but not sustained.
10:04The dissection team has revealed the hidden secrets of the crocodile's jaw.
10:10Two rather small, weak muscles open the jaw.
10:15It's the huge jaw closers that make the crocodile's bite so strong.
10:21Anchored beneath the skull, these muscles pull the upper jaw down with tremendous force.
10:27Most other big biters have muscles high on their heads, but the crocodile's low-slung
10:33jaw muscles enable it to have a stealthy low profile in the water.
10:43Go ahead and put a rope under there.
10:46Oh, yeah.
10:48There it goes.
10:55Get a good grip.
10:56One, two, three.
11:05Hold it.
11:06Too much more.
11:07That's about it.
11:08Yeah.
11:09Cool.
11:10Well, that's great.
11:11It's absolutely great.
11:15This provides a great demonstration of how this muscle comes off the back of the skull
11:19here and comes down around the jaw and then comes up through here and basically pulls
11:25down on this part of the skull, helping to bring these jaws together.
11:29Pretty impressive.
11:31But not all crocodiles have such big bites.
11:35Some have adapted to evolve different jaws to suit different environments.
11:41These are two members of the crocodile family.
11:44This is a gharial from India and this is a saltwater crocodile from Australia.
11:50One of the things we see as we look at these two skulls is that they're related animals
11:54and every bit of the skull matches.
11:57They are adapted to catch different kinds of prey.
12:01This one's adapted to catch fish.
12:03This one's adapted to catch large animals that are on land.
12:08What this one needs is rapid movement of the jaws,
12:12snapping them shut with immense speed with very little water resistance.
12:16What this one has is the ability not to shut the jaws particularly fast,
12:20but great force for hanging on and then crushing bones once it's got it.
12:26You cannot have both.
12:28Evolution is filled with compromises.
12:30You can't have both high speed and great force.
12:33There are many other such compromises.
12:36And everything about this gharial skull can be interpreted as going for high speed of snapping shut.
12:44Everything about this saltwater crocodile can be interpreted as great force of jaw rather than great speed.
12:51So that's the bite, but in the anatomy of a kill, it's just the beginning.
13:07So far we've seen how a crocodile bites by exposing its mighty jaw muscles.
13:13But what happens next?
13:15If you think about the way a crocodile kills, it doesn't kill by actually killing with its teeth.
13:20It just simply uses its jaws as big pincers to be able to grab hold of its prey
13:24and then drag it into the water to drown it.
13:28This hunting technique is simple, but frighteningly effective.
13:34The teeth of this animal's jaws are very simplistic.
13:37They're just cones and they're not particularly sharp.
13:40What they're designed to do is sustain stresses from any direction.
13:43So when they get a hold of a prey item and it's struggling,
13:45it's not likely to break their teeth no matter which way they bend.
13:48Also, these animals, once they get a hold of a prey item, will go into death rolls.
13:52They'll spin and the teeth can sustain that.
13:55Without sharp teeth for slicing through meat,
13:58crocodiles use the death roll to tear off chunks of food.
14:03But this technique causes a problem.
14:05One of the mysteries of the death roll is how crocodiles manage
14:08to keep their mouth open underwater without drowning.
14:14Here to show us how they do it is comparative anatomist Joy Ryden.
14:18Joy's looked down the throats of hundreds of animals
14:20and is a world expert on vocal and breathing anatomy.
14:27We're looking at the tip of the snout of the crocodile
14:29and right here are the nostrils.
14:31And these have little valves so they can flop open,
14:33allow air in, and then close up like little plugs.
14:36And then we have a passageway that runs from the tip of the rostrum
14:39all the way inside the skull to the top of the snout,
14:42which is where the mouth is.
14:44And then we have a passageway that runs from the tip of the rostrum
14:47all the way inside the skull and then dives down into the larynx,
14:50which is below this.
14:52And if we open up the mouth, Alan, if you could just lift that up for me,
14:55we see inside the complicated arrangement of the inside of this mouth
14:59has a valve that keeps water from going into the larynx or voice box.
15:03So this ridge over here overlaps with the soft palate
15:06and that keeps water from getting into the larynx.
15:08And when we open it up and look inside,
15:10you can lift that a little bit higher,
15:12we can see inside there is a voice box right here.
15:15This is the larynx, and there's the opening into the larynx.
15:19And we're looking down a pipe that goes down to the trachea
15:21and all the way down to the lungs.
15:23So this is where air would pass.
15:25And when this animal elevates its larynx up like that,
15:28it seals this opening, and it's connecting the opening of the larynx
15:31into the nasal passageway, which is back here.
15:34So this animal has a built-in snorkel to allow it to breathe
15:37from the nose all the way down to the lungs
15:39and not let water that's in its mouth get into here and drown the animal.
15:44If the animal wants to grab a fish,
15:46this is also a wonderful trap for catching a fish,
15:48but if it's lying on the bottom of a riverbank with its mouth open like this
15:51waiting for a fish to swim across,
15:53it needs to make a current to actually draw the fish into the mouth
15:56so the fish doesn't keep swimming right by.
15:58And it does that by using the tongue as a piston.
16:00So this big, broad, flat tongue just drops down like that,
16:04and now the fish is drawn in with the current,
16:06and then it can go ahead and snap those jaws shut,
16:08trapping the fish.
16:20As we've seen, the head of this animal is equipped
16:23with the jaws and teeth it needs to trap and kill its prey.
16:28But first it has to catch that prey,
16:30and to do that it uses a huge piece of anatomy
16:34that represents almost half of a crocodile's body.
16:37Its tail.
16:44What I'm doing here is I'm exposing the tail muscles of this crocodile,
16:48and what I want to show you here is that this is almost all muscle in the tail.
16:53There's very little bone here, and if you pull this back,
16:55that whole thickness, almost as deep as my hand can go there,
16:58is solid muscle.
17:00That's on one side. The same is on the other side.
17:02So almost all of this bulk is just muscle.
17:06Let's go ahead and flop this over.
17:09There's the propeller.
17:13These fins right here are made out of keratin.
17:15They're really stiff. It's like what your fingernails are made out of.
17:18What these animals do is they thrust their tail back and forth like this,
17:22and because it has an S-shaped motion to it,
17:25it causes thrust to be generated backwards
17:27and allows these animals to move forward.
17:29They can swim like 20 miles an hour.
17:31It's really amazing.
17:35Crocodiles have evolved as masters of the water's edge.
17:39They move with ease in the water,
17:41but they can also slide up onto dry land on their bellies.
17:46If they want to go further, they'll lift up into a high walk.
17:53And if smaller crocs really need to move fast, they can bound like a rabbit.
17:58It's thought this running ability may date back to the time of the dinosaurs,
18:02when small crocodile ancestors lived on land and ran down their prey.
18:14We can trace the crocodile's entire history through its fossilised remains.
18:21The evolutionary story of the crocodiles begins some 320 million years ago.
18:27Amphibians had pioneered their way from the sea to the land,
18:31but early reptiles had a trick up their sleeves, their eggs.
18:35Amphibians need to stay close to water to keep their eggs moist,
18:38but the covering of a reptile egg keeps vital fluids inside.
18:42Away from water, reptiles thrived,
18:45and over the next 100 million years,
18:47there was an explosion of different reptile body forms.
18:50The age of the reptiles had arrived.
18:54250 million years ago, a catastrophic event occurred.
18:58No one knows for sure what happened,
19:01but virtually all life on Earth was wiped out.
19:07The reptiles were among the few groups to survive.
19:10This opened the door for them to fill gaps left by the extinct animals.
19:15The archosaurs, literally the ruling lizards, took centre stage.
19:22One evolutionary line led to the birds and dinosaurs,
19:25the other to the crocodilians.
19:28The earliest crocodilians lived on land, like the long-legged Terrestrisuchus,
19:32a fast runner not much bigger than a rabbit.
19:35Later, some crocodiles took to the water.
19:38Their eyes and nostrils moved to the top of their heads,
19:41allowing them to keep a low profile in the water.
19:45And supported by the water, their bodies surged in size.
19:50110 million years ago, enormous megacrocs like Sarcosuchus
19:54grew up to 12 metres long, the length of a bus.
19:59Whilst these supercrocs died out, their smaller cousins flourished
20:03and started to resemble more modern crocodiles.
20:07Remarkably, over the last 100 million years,
20:11they've hardly changed at all.
20:14Want to go ahead and give us a midline?
20:19So what is it about this prehistoric internal anatomy
20:23that's worked so well for so long?
20:26We're about to investigate the crocodile's stomach
20:29to find out how it digests the huge chunks of meat it swallows
20:33before they start rotting inside.
20:39I don't know when this animal last saw me.
20:41I don't know when this animal last fed.
20:43About a week before it died.
20:45Might be fish or poultry, we don't know.
20:48And probably highly digested already.
20:56The guys are just reflecting the skin off the ventral surface
20:59of the crocodile to give us access to its organs.
21:02We hope this will also reveal clues about why this particular animal died.
21:07Now the diaphragmatic is going to have a lot of fat associated with it too,
21:11so we need to be careful when we get down into there.
21:21It's incredibly difficult doing this dissection
21:23because the underlying structures are so close to the muscular wall.
21:27And we have gone into something.
21:29Might be the gallbladder, might be the stomach.
21:31We just want to work it out at the moment.
21:33We just want to work it out at the moment.
21:34But actually the way that the digestive system is laid out
21:37is nothing like I've seen before.
21:38Absolutely amazing.
21:40Yeah, this is the duodenum.
21:46This is stomach here.
21:47Now we're trying to get oriented here.
21:53Samuel Martin thinks his crocodile may have eaten something
21:56that led to its premature death.
21:59And when it comes to solving mysterious animal deaths,
22:02Professor Alan Williams is the Hercule Poirot of veterinary pathology.
22:06He's eager to investigate the stomach contents.
22:17Wow.
22:19Are you OK?
22:20OK, so...
22:21That's a bit long on the same side.
22:22You all right?
22:25OK, we're coming down your end, Alan.
22:28So...
22:30Yeah, let's lay it out as it was.
22:33Bring it back this way.
22:34I mean, for me, the most impressive thing about this digestive system
22:37is for such a massive animal, how small it is.
22:40But essentially what goes on in here,
22:42in terms of the breakdown of huge chunks of animal
22:47into tiny little pieces, is just extraordinary.
22:50Yeah, and think about the shapes of the things that are coming down here.
22:53These animals are swallowing, you know, limbs of ungulates, you know.
22:58Big sections of bone...
23:00So you've got hoof and the whole lot.
23:02Yeah, and I've found fishing lures, shotgun wads, coins,
23:06house cats, you name it, in these animals.
23:09So this has to just stand in all kinds of directions
23:12to, you know, allow them to feed at all.
23:14These animals cannot use their teeth to orally process their food.
23:18They're just ripping off chunks and swallowing them fairly whole.
23:23Greg, if you could just hold the jar for us, please.
23:25We'll just try and lift this up.
23:27Right, these are the stomach contents.
23:29Wow.
23:35OK, if we can put them underneath.
23:37Yeah, squeeze it. There might be some larger...
23:39OK, here we go. I've got something here.
23:46That's it.
23:48So, Samuel, this is a very dark green colour.
23:51It's very strange, yeah.
23:53So this white material, if I just lift some of this out...
23:57That's it.
23:59What do you make of this?
24:01It's weird.
24:02What does it feel like?
24:03That's it.
24:04Like cheese.
24:05Like cheese, yeah.
24:07The green colour, it probably means that maybe after the meal
24:11he might have eaten something he should not have.
24:14Maybe some leaf or something.
24:17Do you see pica in crocodiles?
24:20So if they are unwell, they might have a deranged appetite
24:23and start eating things they wouldn't normally eat?
24:25Yeah, it does happen from time to time.
24:28They're also very curious, you know, and they come to any new thing
24:32and they might swallow it just by mistake.
24:36But here it's quite strange.
24:40I've opened lots of alligator stomachs from the wild.
24:43I've never seen anything like this.
24:45This is completely foreign to me.
24:47So this is very unusual.
24:49So we've got a possibility here this could be a toxic reaction.
24:52It could well be.
24:54Is that a leaf?
24:56Yeah.
24:57We've got a leaf.
25:00That looks almost like a wheel from a toy car.
25:02Yeah, yeah.
25:03So heaven only knows what this crocodile has been eating.
25:08It cannot be the reason.
25:10That could have been in there for years.
25:14This stuff is really an alien brew.
25:16We know it's very abnormal and there's a load more tests need to be done
25:19to try and find out what's in it.
25:21The unique thing about the crocodile, though,
25:23is to help digest these huge quantities of protein
25:26that it ingests when it kills and consumes something like a third of a wildebeest.
25:30It produces ten times more acid than we do.
25:34How they do that, you won't believe this,
25:36but you have to dig deeper into the crocodile.
25:46So we choose our weapons.
25:48Great, thank you.
25:50Yeah, let's take the trachea down to about here, I guess.
25:53The dissection team's delving deeper into the crocodile.
25:57We hope to find out what caused this animal's mysterious death.
26:02And we want to uncover more of the prehistoric parts hidden deep inside.
26:07In some ways, the chest cavity's very familiar.
26:09It's got all the same components we've got, two lungs and a heart.
26:12But in some ways, it's incredibly different.
26:14Guys, you're still dissecting it.
26:16Can we just have a quick look at the kind of big-picture anatomy here?
26:22OK, so this is the trachea, or the windpipe, of the animal.
26:25This part goes forward, this part goes back.
26:27And this is the trachea of the animal.
26:29And this is the trachea of the animal.
26:31And this is the trachea of the animal.
26:33OK, so this is the trachea, or the windpipe, of the animal.
26:36This part goes forward towards the larynx, or voice box.
26:39And this part continues down toward the lungs.
26:42And here we have complete rings, which reinforce the trachea and keep it from collapsing,
26:47as this animal is swallowing massive prey through this really large esophagus
26:52that can really stretch to encompass very large bits of food,
26:56because these animals can't process it down into little pieces with the teeth that they have,
27:00they're just grabbing teeth, they're not mashing teeth like you have in other animals.
27:03And so this esophagus is going to really stretch out and take over this whole area,
27:08which means the trachea gets pushed off to the side, which is very unusual,
27:11because in other animals the trachea comes down the midline.
27:19To find out just how big a breath our crop can take,
27:23we want to try to inflate the lungs with compressed air.
27:31Perfect fit, look at that.
27:34Should we give it a whirl?
27:35Go for it.
27:48That's impressive.
27:49That is an impressive volume of air.
27:51That's a huge amount of air.
27:53These animals can take in about four times the amount of air that we can,
27:56and this is essentially the scuba tank for these animals.
27:59A big animal like this can stay underwater for as long as a half hour, which is a long time.
28:05The way they inspire or bring in this air is using muscles on their ribs,
28:10and that expands the chest, just like it does in us.
28:13But they also have another secret, they have the diaphragmatic muscles,
28:16which are right here, and these attach back onto the pubis,
28:21and when they pull backwards, they pull back on the liver and help expand the pleural cavities here,
28:26so even more air can get sucked in.
28:29It's like a piston going up.
28:30Yeah, it's like a piston, exactly.
28:32This unique muscle helps crocodiles breathe,
28:35but monitoring its activity underwater shows it is active even after breathing is stopped.
28:43It seems crocodiles and alligators like this one use this muscle to move the air-filled lungs inside their body
28:50and shift their centre of buoyancy.
28:52They can adjust their position in the water like a submarine.
28:59A crocodile sinking silently from the surface is an iconic image of a predator at work.
29:04They never make a ripple, never make a splash.
29:07It's an excellent adaptation.
29:21We're about to venture into the very heart of the crocodile.
29:25Surprisingly, it has some of the most sophisticated plumbing found in any animal.
29:33This is all fat, huh?
29:34Yeah.
29:35We need to remove that.
29:36Very delicately going down through there.
29:40There's a lot more tubes than you see in a human heart, so it's a little bit tricky.
29:46The artery that takes blood from the heart to the rest of the body is called the aortic arch,
29:52and bizarrely, unlike most animals, crocodiles have more than one.
29:57We're trying to find the other aortic arch.
30:01In humans, you have just a left aortic arch.
30:04In birds, you have a right aortic arch.
30:06And if you look at amphibians, you actually have both.
30:10So embryologically, you start out with both and you lose one or the other
30:13depending on which way you go along that evolutionary tree.
30:15Crocodiles have kept the right aortic arch, like birds do.
30:19But interestingly, this animal, the crocodile, may also have some remnant of the left aortic arch.
30:25And so we're looking to trace that, see if we can find that here.
30:41Just like us, the crocodile has an artery to take blood from the heart to the lungs
30:46and an aorta to take blood to the rest of the body.
30:49But the crocodile's mysterious extra aorta has puzzled biologists for decades.
30:59In many ways, this is quite a familiar heart.
31:01But it's when you get to the pipework, it all starts to get pretty complex
31:05and that's something absolutely unique to a crocodile.
31:11This aortic anomaly is the focus of research for Colleen Farmer.
31:16In her rooftop lab in Utah, she's had a remarkable breakthrough
31:20that might explain the need for this extra blood vessel.
31:23Her feisty subjects are a group of American alligators.
31:27She wants to see if there is a link between the extra aorta
31:30and why crocodiles don't suffer excruciating indigestion.
31:35So Colleen, what are you hoping to see by feeding these huge bits of meat and bone?
31:39I want to understand how fast they digest their food.
31:42And one way to do that is to actually image the bones that they swallow.
31:46So they don't chew their food, they just swallow big pieces whole.
31:50So the bone will end up in the stomach of the animal intact.
31:54And then we're going to catch one of them and take it up to the x-ray machine
31:58to take our first measurement of the bone.
32:09This alligator is different from the others.
32:11Its extra aorta is blocked, and Colleen hopes to see if it affects its digestion.
32:26Each day she x-rays her alligators to check how quickly they are digesting food.
32:34In those with blocked aortas, she finds digestion has almost ground to a halt.
32:40The extra aorta clearly plays a crucial role.
32:45And the secret lies inside the heart.
32:49Blood that has been round the body is rich in carbon dioxide,
32:53a vital ingredient in the production of stomach acid.
32:57When needed, a tiny valve in the heart diverts this acidic blood to the stomach,
33:02and this generates extra stomach acid.
33:06This is the adaptation that allows crocodiles to digest the massive prey that they hunt.
33:18We know that our crocodile wasn't digesting food properly,
33:22and before it died, Samuel had noticed it was behaving strangely,
33:26lingering in the water longer than usual.
33:30Crocodiles and alligators normally spend most of their day lying out in the sun,
33:35warming their cold-blooded bodies.
33:38They compete for the best basking sites,
33:40and call to each other to mark territory or attract a mate.
33:48Joy wants to test just what sort of noise this animal is capable of making,
33:52and find out whether Samuel recognizes the sound of his crocodile.
33:56If this animal were to exhale and send a lot of air through its throat,
34:01we should get some sound from the voice box, the larynx, which is located right in here.
34:05I might need you to lift the mouth for me so that we can get the air to come out.
34:09OK, so about there?
34:11Yeah, let's see what happens.
34:14Oh yeah, this is exactly it.
34:17It sounds really like this, and when it comes from way through the lungs,
34:22it's even more strong and more impressive.
34:26That's it.
34:27Do they do it with the mouth right open, or...?
34:29Oh yeah, very often the peak of roaring is during the mating season.
34:34Yeah, it goes a lot, showing how impressive I am and how strong I can yell,
34:41and telling other males, OK, I want you to keep my piece of water for me.
34:56How do we know this one's a male, apart from just it's big, but is that enough?
35:01Well, actually it is. With crocodiles, the males are much larger than the females.
35:06These animals, the males can get up to 5.5 metres,
35:10and a really big female is only 3 metres long,
35:13and this is certainly a male, it's 4 metres.
35:16Right, OK, but in terms of sexual organs then, they're completely hidden in the cloaca.
35:21The testes and the ovaries in the females are found in behind the guts when the animal's on its back,
35:27so they're kind of dorsally positioned on these animals,
35:31and in this case, going along the epididymis here, where the sperm's stored,
35:37it's going to be conducted out to the penis here,
35:40and these fingers will sort of come together to help channel the sperm into the female.
35:47Sorry to interrupt, but you know when you were blowing up the lungs, inflating the lungs,
35:51and you said the right side was not inflating as much?
35:54If you look in there, we have the most horrible mess,
35:58and we've got really strong adhesions between the lung and the chest wall.
36:03So it had a respiratory problem?
36:05It certainly has a respiratory problem.
36:07OK, so we think the digestive system problems that we saw,
36:10whatever that was, that green alien soup that came out of its stomach,
36:14probably secondary to the fact that it was very ill?
36:17Indeed.
36:18OK.
36:19Another important fact is that the testes at this time of the year should have been much bigger.
36:24If it would have been sexually active, it would have been that size, about.
36:29So it probably meant that this animal was completely dominated by other males,
36:35so it had no real sexual activity,
36:38probably could not access to the best basking site and could not thermoregulate properly.
36:45This animal would have been under a lot of stress, that's what you're saying?
36:48Yeah.
36:49And that's a vicious cycle, presumably.
36:51Once you become ill, you can't get then to your basking sites,
36:55you can't get to food quicker, and it's just a downward spiral.
36:59Yeah, and it's probably why it ate some leaves and some vegetation material instead of proper meat.
37:06So kind of out of desperation?
37:08Yeah.
37:09So it looks as if we're getting some real clues here.
37:11And we're starting to get a picture of what may have caused this animal's death,
37:15but we're not there yet.
37:37When you're dissecting the individual components of a large adult crocodile,
37:42it's very difficult to get your head around the sense of scale and how all the bits fit together.
37:47The team also wants to look at a small crocodile that died in Samuels Park.
37:51It's been frozen and cut down the midline,
37:54to act as a kind of map for you of where everything fits.
37:58Let's start at the head.
38:00We clear some of the ice out of this area here.
38:03We're just showing you the oral cavity right over here.
38:05So this is all ice that was in the mouth.
38:07And now we can see the tongue.
38:09Here's the tongue.
38:10The structure right here is tongue.
38:12And right behind the tongue is the overlap of the larynx with the soft palate.
38:16Right over here, there's that palatal valve.
38:18If we follow down here, we also have an esophagus that runs parallel to the trachea.
38:22Right below it is the heart.
38:24And below the heart is the liver.
38:27It's interesting how, if you look at the whole animal,
38:30what a small proportion of its body actually has got its vital organs in it.
38:34Most of this animal is just muscles.
38:37It's all this stuff.
38:38These are the muscles that allow it to be able to do the death roll.
38:41These are the muscles that allow it to twist and turn and swim.
38:44And then all the way down to its tail,
38:47massive muscles that control its powerhouse, its propulsion, its tail.
38:52At the end of the day, a crocodile uses the minimum amount of space for all its vital organs.
38:58What it is is one big muscle, one huge muscular killing machine.
39:07Perhaps the ultimate test of a crocodile's powerful body
39:11is in a head-to-head battle with another crocodile.
39:17And in the competition for food, other predators are always a threat.
39:28Our gladiator's defence lies hidden inside its skin.
39:36This is the skin from the bottom of the head, under the jaw,
39:40continuing through the belly region all the way down to where the tail would begin.
39:44And we're looking at the belly surface of this animal,
39:47and you notice that it's relatively smooth, even though it's armour-plated.
39:50And that would allow this animal to easily slide along the mudflats
39:53if it's on the bank of the river and it wants to slide back into the river.
39:56But if we look at the other side of the animal,
39:58the back is not smooth anymore like it is on the belly.
40:01It's actually got a lot of bumps on it that are raised up quite a bit in the back here
40:05as you get towards the tail.
40:06It kind of looks like those spines you always imagine on a dragon going down its back.
40:10And this makes for wonderful armour.
40:12So if this animal was in a fight with another big male crocodile,
40:15this would keep the animal protected.
40:17So it's a wonderful bit of armour plating.
40:20In fact, even the ancient Egyptians and the Romans used this as armour.
40:24They would actually dry off an alligator's skin, prepare it, and wear it as armour.
40:28So if we look at this armour more closely,
40:31we're actually going to try and understand the structure of it.
40:34Let's take a look at one of these scutes.
40:36So if we pull one off by dissecting it off here,
40:38it's actually quite hard to cut through the skin here.
40:43If this were easy to cut through, it wouldn't be very good armour, would it?
40:47We see a lot of thick skin here, a lot of connective tissue.
40:52Let's take a look at what's inside one of these.
40:54We have a whole bunch of bones here that have been cleaned off,
40:57so you don't see the skin anymore.
40:59And they actually overlap one over the next, just like this.
41:03Leaving them overlapped like that allows no chinks in the armour.
41:07So these animals are quite well protected when these armour plates are overlapping.
41:11So these scutes offer all kinds of advantages to a crocodile.
41:16Camouflage, first off.
41:18Obviously, protection.
41:20But also, they may help the crocodile control its body temperature,
41:25which for a so-called cold-blooded animal is key to its survival.
41:31So how would an animal with such hard armour plating on it
41:34be able to manage its temperature?
41:36You'd think that this would prevent it from getting cold.
41:39You'd think that this would prevent it from being able to get its blood to the surface.
41:43Let's take a look at one of these that's been cut so we can see the inside of it.
41:48You can see very, very fine little channels running up and down here.
41:52These fine little channels are actually for blood vessels
41:55that are running up and down through the plate all the way to the surface.
42:00And then those blood vessels are going to run underneath the skin.
42:06So this animal is going to be able to absorb a lot of energy from the sun,
42:10which is going to heat up the blood vessels
42:12and then be able to carry the heat back into the animal,
42:15kind of like a big solar panel.
42:17So that is going to allow a lot of heat exchange to occur all along the back of the animal.
42:22From its bone-crushing bite to its armour-plated solar panels,
42:27we've seen how effective the crocodile's prehistoric adaptations have been.
42:33But this animal has something else that may hold the key to its survival.
42:46It was thought that poachers had killed off the crocodile in the Ankarana region of Madagascar,
42:52but locals recently pointed scientists to a group of crocodiles living deep inside these caves.
42:59The investigating team was amazed to find crocodiles surviving in such cool conditions.
43:07These animals could be living proof that because crocodiles are cold-blooded
43:12and can slow down their body's metabolism,
43:15they can survive harsh times on a bare minimum of food and warmth.
43:21As tough as these animals are, something unusual happened to our crocodile for it to die so young.
43:31Having examined this entire animal, pathologist Alan Williams can deliver his final verdict.
43:38If you remember, what we found in the stomach was a lot of this sort of soapy-like material,
43:45and it's got a single small stone which crocodiles are known to swallow to aid the digestion process.
43:51But apart from this and a bit of mucus, the stomach is empty,
43:55as indeed was the whole of the rest of the digestive system,
43:59which suggests to me that this crocodile hadn't been eating for quite some time.
44:03The big problem that this crocodile had, though, was in its lungs.
44:07And if you remember, when we were inflating the lungs, one of them didn't inflate.
44:12Well, there are also lots of abscesses present in this lung as well.
44:16So one here, for example, some smaller ones here, another one just here.
44:21And if we just cut into this larger abscess, it's very firm material,
44:25suggesting it's been there for some time.
44:28And we've got this lovely abscess with a thick capsule around it.
44:32That has taken weeks or longer to develop, probably enough to stop the crocodile eating.
44:38And this infection has now spread round the body.
44:41And the crocodile has been unable to cope with this particularly well,
44:46because if you look in this little jar here, the liver is floating, and they shouldn't do that.
44:51And what it's suggesting to me is that there's a lot of fat in the liver.
44:55So I think the crocodile hasn't been eating because it's been unwell.
44:59The animal has been mobilising its fat reserves, sending it to the liver to be processed,
45:05and it's basically done it so quickly, then the liver gets overloaded,
45:09and the cells swell up with all this fat, and the cells stop working.
45:13So you're really into this vicious cycle, and that's what drags the animal down at the end of the day.
45:19Our dissection has revealed that our crocodile died of a severe lung infection,
45:24and the complications that followed.
45:27But as well as solving the mystery of our animal's death,
45:30we've explored ancient anatomy that dates back to the time of the dinosaurs.
45:46When one says that crocodiles have been around for a very long time,
45:50what one means is they haven't changed very much for a very long time.
45:54Presumably, what it means is that they've found a very satisfactory way of life,
45:58and there's no particular reason to change it.
46:25From the outside, crocodiles may look prehistoric,
46:29but as our autopsies show, under the skin, they're anything but primitive.
46:35In fact, their bodies are brilliantly adapted to the way they live,
46:40and surely that's why they've survived unchanged for so long.
46:55Next week, we'll be looking inside the giraffe.
46:59We'll find out how it controls its massive blood pressure,
47:03and we'll investigate new theories that explain the mystery of this animal's extraordinary name.
47:10It's a beautiful example of historical legacy.
47:13It's a beautiful example of historical legacy.