0:00:03 > 0:00:05The natural world is full of extraordinary animals
0:00:05 > 0:00:08with amazing life histories.
0:00:09 > 0:00:12Yet certain stories are more intriguing than most.
0:00:15 > 0:00:18The mysteries of a butterfly's lifecycle
0:00:18 > 0:00:21or the strange biology of the emperor penguin.
0:00:22 > 0:00:25Some of these creatures were surrounded by myth
0:00:25 > 0:00:28and misunderstandings for a very long time.
0:00:29 > 0:00:33And some have only recently revealed their secrets.
0:00:34 > 0:00:37These are the animals that stand out from the crowd,
0:00:37 > 0:00:42the curiosities I find particularly fascinating.
0:00:51 > 0:00:56The bodies of some animals stretch and shrink in extraordinary ways.
0:00:57 > 0:01:01Constrictor snakes can swallow prey twice their own size.
0:01:03 > 0:01:06While the camel's hump can almost double in weight,
0:01:06 > 0:01:10giving it the energy to travel huge distances across deserts.
0:01:11 > 0:01:15What is the secret behind such expandable bodies?
0:01:26 > 0:01:29We've long been fascinated by the camel's ability
0:01:29 > 0:01:32to live in the harshest of deserts.
0:01:32 > 0:01:34Places where, during summer,
0:01:34 > 0:01:38temperatures can soar up to 50-degrees Celsius.
0:01:38 > 0:01:42While, in winter, they can drop to 30-degrees below freezing.
0:01:46 > 0:01:48With little in the way of food or water,
0:01:48 > 0:01:52camels can sometimes go without eating or drinking for over a week.
0:01:54 > 0:01:57Most other animals couldn't survive conditions like this.
0:01:57 > 0:02:00How does the camel do it?
0:02:03 > 0:02:07The camel's secret was thought to lie in its hump.
0:02:07 > 0:02:11In a healthy camel, it can be big and firm like this one
0:02:11 > 0:02:13and can weigh as much as 30 kilos,
0:02:13 > 0:02:16which is the weight of a ten-year-old child.
0:02:16 > 0:02:20But if the camel goes without food and particularly water
0:02:20 > 0:02:24for any length of time, then the hump can get floppy
0:02:24 > 0:02:28and even droop over on one side, as that one has done.
0:02:28 > 0:02:34So people used to think that the camel stored water in its hump.
0:02:38 > 0:02:42In fact, there are two different kinds of camel.
0:02:42 > 0:02:47The one-humped or dromedary and the two-humped or Bactrian.
0:02:48 > 0:02:50Nearly all camels alive today
0:02:50 > 0:02:53are the domesticated descendants of one or the other.
0:02:56 > 0:03:01The wild dromedary almost certainly doesn't exist.
0:03:01 > 0:03:05And only a few Bactrian camels remain roaming the deserts
0:03:05 > 0:03:07of central Asia.
0:03:07 > 0:03:09The camel is a very tough animal
0:03:09 > 0:03:15but, in the wild today, it's rarer than the giant panda.
0:03:17 > 0:03:20It's hard to say where the idea of a water-storing hump came from.
0:03:20 > 0:03:24The Ancient Romans were the first to suggest
0:03:24 > 0:03:27that the camel may have a built-in water reservoir.
0:03:29 > 0:03:32And then, later on, people got the idea that it had two stomachs,
0:03:32 > 0:03:35one for food and one for water.
0:03:36 > 0:03:40In the 18th century, an eminent anatomist, John Hunter,
0:03:40 > 0:03:44decided to investigate the truth behind these assertions
0:03:44 > 0:03:46and he dissected a camel.
0:03:46 > 0:03:51He found that the stomach consisted of three or four compartments,
0:03:51 > 0:03:53similar to those of a cow or a sheep.
0:03:53 > 0:03:56But inside one of those compartments,
0:03:56 > 0:03:59he discovered these pocket-like structures,
0:03:59 > 0:04:03which are not found in any other large mammal.
0:04:03 > 0:04:05Hunter didn't know what the pockets were for.
0:04:05 > 0:04:08But others after him proposed
0:04:08 > 0:04:12that they were special water-storage cells.
0:04:12 > 0:04:16And then, despite any kind of evidence to prove that this was true,
0:04:16 > 0:04:20for another 250 years, books on natural history,
0:04:20 > 0:04:22like this one, featured illustrations
0:04:22 > 0:04:26of water-storage cells in the camel's stomach.
0:04:28 > 0:04:30We now know that that's not true,
0:04:30 > 0:04:34even though we don't know exactly what the strange pockets are for.
0:04:35 > 0:04:38But the camel's hump is certainly not filled with water.
0:04:38 > 0:04:41It's made entirely of fatty tissue.
0:04:41 > 0:04:46It is, in fact, an energy reserve for times when food is scarce.
0:04:46 > 0:04:49And it can expand to such a degree
0:04:49 > 0:04:52that it makes up 80% of the camel's body fat.
0:04:54 > 0:04:59This enables a camel to go for two weeks without feeding, if necessary.
0:05:00 > 0:05:03But there's a twist to the story.
0:05:05 > 0:05:07When fat is broken down in the body,
0:05:07 > 0:05:11it produces not just energy but also water.
0:05:11 > 0:05:15In fact, each gram of fat broken down during metabolism
0:05:15 > 0:05:17produces one gram of water.
0:05:17 > 0:05:23So could the camel's hump provide it with extra water after all?
0:05:25 > 0:05:28A fatty hump that contains both food and water
0:05:28 > 0:05:31would seem to be just what a desert animal needs.
0:05:31 > 0:05:34But it's not as simple as that.
0:05:34 > 0:05:38To consume its fat, an animal needs more oxygen,
0:05:38 > 0:05:40so it has to breathe more.
0:05:40 > 0:05:43So when living on the fat in its hump, the camel
0:05:43 > 0:05:48actually loses more water through its airways than it gains.
0:05:49 > 0:05:53So the camel doesn't have a secret store of water.
0:05:53 > 0:05:57How then can it survive in a waterless desert?
0:05:58 > 0:06:01Camels can go without drinking for more than a week because
0:06:01 > 0:06:06they have an extraordinary ability to retain their body moisture.
0:06:06 > 0:06:11We ourselves lose over a litre of water a day
0:06:11 > 0:06:13through our moisture-laden breath.
0:06:13 > 0:06:16But the camel has nostrils which it can shut tight
0:06:16 > 0:06:19and that not only keeps out the sand
0:06:19 > 0:06:24but retains the breath within the nose and there the moisture
0:06:24 > 0:06:28can be reabsorbed by the linings of the nostrils.
0:06:32 > 0:06:34Most mammals also lose a lot of water
0:06:34 > 0:06:37when they cool their bodies by sweating.
0:06:39 > 0:06:42But camels can endure a rise in body temperature
0:06:42 > 0:06:47that would kill most other mammals without sweating.
0:06:50 > 0:06:54If our temperature goes up by as little as one degree,
0:06:54 > 0:06:56it's a sign of illness.
0:06:56 > 0:07:01While three degrees causes vital organ damage and eventually death.
0:07:03 > 0:07:09The camel can cope with as much as a six-degrees rise with no ill-effect.
0:07:10 > 0:07:13This means that camels don't have to sweat
0:07:13 > 0:07:18until conditions get very hot indeed and, if necessary,
0:07:18 > 0:07:23they tolerate losing more of their body water than other mammals.
0:07:25 > 0:07:29When animals become dehydrated, their blood becomes thicker
0:07:29 > 0:07:31and more difficult to pump through the body.
0:07:31 > 0:07:36If we lose 10% of our body water, we start to go dizzy and blind
0:07:36 > 0:07:40and at 15% our internal organs start to fail.
0:07:41 > 0:07:45Camels, however, can lose a third of their body water with no ill-effect,
0:07:45 > 0:07:49something that would kill most other animals.
0:07:49 > 0:07:51How do they do it?
0:07:51 > 0:07:55Well, some of the answers may lie in the shape of their blood cells.
0:07:55 > 0:08:00These are the red blood cells from a human being,
0:08:00 > 0:08:03which are disc-shaped like that of most mammals.
0:08:03 > 0:08:07These, on the other hand, are from a camel
0:08:07 > 0:08:11and are slimmer and more oval in shape.
0:08:11 > 0:08:15It may be that the oval streamlined shape
0:08:15 > 0:08:19makes it easier for the blood to flow when the animal is dehydrated.
0:08:21 > 0:08:25Certainly, a camel's blood is less thick and sticky than ours.
0:08:25 > 0:08:29The cells also have particularly strong walls.
0:08:29 > 0:08:32This prevents them from rupturing
0:08:32 > 0:08:35when the animal suddenly drinks large amounts of water.
0:08:35 > 0:08:37And when they do find water,
0:08:37 > 0:08:41camels have the ability to drink it very quickly.
0:08:42 > 0:08:46A single camel can take the contents of all these bottles,
0:08:46 > 0:08:49that's 100 litres, in a mere ten minutes.
0:08:49 > 0:08:53For any other animal to do that, it would be extremely dangerous.
0:08:53 > 0:08:57But the camel has the ability to hold the water in the stomach
0:08:57 > 0:09:00and only release it into the bloodstream very slowly
0:09:00 > 0:09:03in a way that does no damage.
0:09:06 > 0:09:10We now understand how camels can survive harsh desert conditions
0:09:10 > 0:09:14and yet, surprisingly, new research suggests
0:09:14 > 0:09:18that they may first have evolved to live in the cold Arctic.
0:09:20 > 0:09:23Scientists have recently discovered the fossil bones
0:09:23 > 0:09:28of giant shaggy camels that roamed the forests of the Canadian Arctic
0:09:28 > 0:09:31some three-and-a-half million years ago.
0:09:33 > 0:09:37The Arctic camel was a third larger than the modern Bactrian.
0:09:37 > 0:09:42But, otherwise, looked very similar and that may be no coincidence.
0:09:43 > 0:09:48The wide flat feet that stop the camel from sinking into desert sand
0:09:48 > 0:09:52could also have helped its ancestors walk in deep snow.
0:09:52 > 0:09:55And a fatty hump provided the food reserve
0:09:55 > 0:09:59a camel would need to survive long cold winters.
0:10:01 > 0:10:05We may never fully understand the mysteries of the camel's hump,
0:10:05 > 0:10:10whether it evolved first as a way of keeping warm or staying cool.
0:10:10 > 0:10:15But we have unravelled many other mysteries of the animal's body
0:10:15 > 0:10:17that enable it to endure conditions
0:10:17 > 0:10:21that few other animals would be able to withstand.
0:10:23 > 0:10:28The camel's expandable hump was a mystery to us for centuries.
0:10:28 > 0:10:33Our second curiosity can stretch its body in even more extraordinary ways
0:10:33 > 0:10:37and devour prey many times its own size.
0:10:38 > 0:10:43This is a green anaconda, one of the largest snakes in the world.
0:10:43 > 0:10:47It's about four-metres long and weighs 70 kilos
0:10:47 > 0:10:49and it's only a half grown.
0:10:49 > 0:10:51They can grow to a length of six metres
0:10:51 > 0:10:54and weigh twice as much as this one.
0:10:54 > 0:10:59But it's their ability to be able to swallow enormous prey
0:10:59 > 0:11:02that's really grabbed our imagination.
0:11:02 > 0:11:05Could one of these really bite a man
0:11:05 > 0:11:09and swallow him whole and alive?
0:11:09 > 0:11:13In the 16th century, European explorers
0:11:13 > 0:11:15venturing into the Amazon jungle
0:11:15 > 0:11:20were fascinated by tales of a huge river monster.
0:11:20 > 0:11:23It was said to devour cattle and deer
0:11:23 > 0:11:26and to spit out water like shot from a cannon,
0:11:26 > 0:11:29knocking animals out of trees.
0:11:29 > 0:11:33These fantastic stories led people to go in search
0:11:33 > 0:11:36of this marvellous beast.
0:11:37 > 0:11:42In 1907, a British explorer, Colonel Percy Fawcett,
0:11:42 > 0:11:47claimed to have encountered an enormous snake on the Amazon River.
0:11:47 > 0:11:52"A huge head," he said, "rose up from the water
0:11:52 > 0:11:57"dangerously close to his canoe and a colossal anaconda emerged."
0:11:57 > 0:12:01Greatly alarmed, he shot the snake dead.
0:12:02 > 0:12:07He claimed that, when measured, it proved to be nearly 19 metres,
0:12:07 > 0:12:09over 60-feet long.
0:12:09 > 0:12:13But Fawcett's account was met with disbelief
0:12:13 > 0:12:17and he never provided convincing proof because, soon after that,
0:12:17 > 0:12:22he vanished into the Brazilian jungle and was never seen again.
0:12:24 > 0:12:26The creature that Fawcett encountered
0:12:26 > 0:12:29was almost certainly a green anaconda.
0:12:29 > 0:12:34Despite their massive proportions, these huge snakes are seldom seen
0:12:34 > 0:12:37because they spend most of their time in water
0:12:37 > 0:12:40waiting in ambush for their prey.
0:12:43 > 0:12:47In this murky world, they're certainly well camouflaged
0:12:47 > 0:12:50and so some people believed that somewhere
0:12:50 > 0:12:54another real monster might still be lurking unseen.
0:12:57 > 0:13:02In the 1960s, a snake was brought to the Museum of Zoology
0:13:02 > 0:13:07at the University College London. This is it.
0:13:07 > 0:13:10It had lived in London Zoo for some years before it died
0:13:10 > 0:13:12and it was five-metres long.
0:13:12 > 0:13:15A lot of work went into preparing the skeleton,
0:13:15 > 0:13:18it had to be carried out onto the flat roof of the museum.
0:13:18 > 0:13:23And it was finally displayed in this rather unusual way,
0:13:23 > 0:13:25wrapped around the branch of a tree.
0:13:29 > 0:13:33For years, the museum displayed it as an anaconda.
0:13:33 > 0:13:38But, in 2012, a member of the public saw an old photo of the snake
0:13:38 > 0:13:42on the museum's website and pointed out that it looked like
0:13:42 > 0:13:45an African rock python and not an anaconda.
0:13:45 > 0:13:49It's unclear how the mistake came about.
0:13:49 > 0:13:52The markings on the two snakes are quite different.
0:13:52 > 0:13:56But both are giants. And there is much controversy
0:13:56 > 0:14:00as to which species is the largest snake of all.
0:14:00 > 0:14:05Anacondas, pythons and boas, like this one, don't kill with venom,
0:14:05 > 0:14:10they're constrictors, they squeeze their prey to death.
0:14:10 > 0:14:14And their coils can exert a very strong pressure indeed,
0:14:14 > 0:14:17as I can feel with this one on my arm.
0:14:18 > 0:14:23But a big anaconda can squeeze with a force of around 4,000 kilos,
0:14:23 > 0:14:28that's like having a bus on your chest and that can certainly
0:14:28 > 0:14:32crush the spine of a deer or a capybara.
0:14:33 > 0:14:38And yet, constrictor snakes don't usually crush their prey.
0:14:38 > 0:14:41In most cases, they simply squeeze it so hard
0:14:41 > 0:14:44that the animal can't breathe.
0:14:44 > 0:14:47Every time its prey tries to inhale,
0:14:47 > 0:14:51the snake's powerful muscles squeeze harder.
0:14:52 > 0:14:55The unfortunate victim then either dies because
0:14:55 > 0:14:58its blood can no longer circulate or suffocates.
0:15:08 > 0:15:13An anaconda or a python can kill prey that is not only twice
0:15:13 > 0:15:18its own body size but many times bigger than its head.
0:15:18 > 0:15:21So how does it manage to swallow its victim whole?
0:15:25 > 0:15:30Popular folklore has it that anacondas and pythons unhinge
0:15:30 > 0:15:34or dislocate their jaws to swallow large prey.
0:15:34 > 0:15:38That is not true. They do, however,
0:15:38 > 0:15:42have the ability to open their mouths wider than most animals.
0:15:42 > 0:15:46Pythons and anacondas have this additional
0:15:46 > 0:15:49bone attached to the back of their jaws.
0:15:49 > 0:15:54This provides a double hinge at the joint and allows them
0:15:54 > 0:15:59to open their jaws extremely wide both downwards and sideways.
0:15:59 > 0:16:05In addition, the two sides of the lower jaw are not fused
0:16:05 > 0:16:09together but joined by an elastic ligament.
0:16:09 > 0:16:12This gives the jaws a lot of stretch
0:16:12 > 0:16:16and they can even move apart when the snake is swallowing large prey.
0:16:16 > 0:16:23It also allows each side of the jaw to move independently of the other.
0:16:23 > 0:16:27When eating a meal, particularly one that is much larger than itself,
0:16:27 > 0:16:33the snake can alternately move its jaws on either side of its head
0:16:33 > 0:16:38and "walk" its prey into its mouth, even while its victim is still alive.
0:16:40 > 0:16:46As the jaws open wide, the snake's elastic skin stretches.
0:16:46 > 0:16:50But the mobility of the skull comes with a price.
0:16:50 > 0:16:54Many of the joints that in other snakes are solid
0:16:54 > 0:16:58have been replaced by mobile ones.
0:16:58 > 0:17:02So the skull has less crushing power. As a consequence,
0:17:02 > 0:17:08the snake has to use its entire body to overpower its prey.
0:17:12 > 0:17:16Getting large prey into the mouth is one problem but how does the snake
0:17:16 > 0:17:20push it all the way down the length of its body into its stomach?
0:17:23 > 0:17:28This is a Burmese python and it hasn't fed for a long time.
0:17:28 > 0:17:33So I'm hoping to give it a little breakfast with a dead rat.
0:17:35 > 0:17:37What about that?
0:17:48 > 0:17:52Saliva from the salivary glands in the mouth has moistened the prey
0:17:52 > 0:17:55so it's easier to swallow.
0:17:55 > 0:18:01And now it's moving its jaws, drawing the rat farther down its throat,
0:18:01 > 0:18:04until, eventually, the muscles of the flanks take over,
0:18:04 > 0:18:08squeezing the prey and pushing against the ribs,
0:18:08 > 0:18:11so that it looks as though the snake is, as it were,
0:18:11 > 0:18:14crawling around the rat.
0:18:17 > 0:18:22And that will continue for some time as the prey is worked down
0:18:22 > 0:18:27into the snake's body, until, eventually, it reaches the stomach,
0:18:27 > 0:18:29which is around the middle here.
0:18:35 > 0:18:39Equally remarkable is what happens inside the snake.
0:18:42 > 0:18:47After months of fasting, it has to restart its digestive system quickly.
0:18:49 > 0:18:54Within a day, some of the internal organs double in size.
0:18:54 > 0:18:58The heart expands, pumping greater volumes of blood around the body.
0:18:58 > 0:19:04And special cells in the lining of the stomach produce powerful enzymes
0:19:04 > 0:19:06that break down flesh and bones.
0:19:10 > 0:19:12And when the prey is entirely digested,
0:19:12 > 0:19:16the python's organs return to normal again.
0:19:19 > 0:19:23Anacondas and pythons are able to take in
0:19:23 > 0:19:26enormous meals in a single mouthful.
0:19:28 > 0:19:31But how do they then survive fasting for months on end?
0:19:35 > 0:19:39Like all cold-blooded animals, snakes get much of their heat from the sun,
0:19:39 > 0:19:43so they need less food to fuel their bodies
0:19:43 > 0:19:47and most of what they eat is converted directly into body mass.
0:19:49 > 0:19:52Snakes continue to grow throughout their lives
0:19:52 > 0:19:55and anacondas get bigger than any other species
0:19:55 > 0:19:58because they live mostly in water.
0:19:58 > 0:20:02Their massive bodies supported by its buoyancy.
0:20:05 > 0:20:08So it's certainly possible that an anaconda
0:20:08 > 0:20:11could grow to an enormous size.
0:20:12 > 0:20:15But how large can a snake really get?
0:20:20 > 0:20:23In 2009, further light was shed on this question
0:20:23 > 0:20:27with the discovery of the fossils of a super-snake.
0:20:27 > 0:20:30It was given the name Titanoboa
0:20:30 > 0:20:34and it suggests that snakes can get very large indeed.
0:20:34 > 0:20:38Titanoboa was nearly 13-metres long,
0:20:38 > 0:20:41the length of a bus, and must have weighed over a tonne.
0:20:41 > 0:20:44It lived around 60-million years ago,
0:20:44 > 0:20:47shortly after the extinction of the dinosaurs.
0:20:47 > 0:20:51We don't know for sure but it may be that the warmer climate of the earth
0:20:51 > 0:20:56at the time allowed cold-blooded snakes to grow much larger in size.
0:20:56 > 0:21:00What is certain is that, for at least ten-million years,
0:21:00 > 0:21:05Titanoboa was the largest predator on the planet.
0:21:08 > 0:21:14Both the camel and the anaconda can withstand extreme periods of fasting.
0:21:15 > 0:21:18But it's only by looking inside the camel's hump
0:21:18 > 0:21:22and the anaconda's stomach that we've discovered the truth
0:21:22 > 0:21:25behind their amazing expandable bodies.