"There are still places on earth where we are not in charge..." "Where other life forms hold sway..." "Creatures with cold blood, and scaly skin..." "In this series we investigate the surprising abilities and bloodcurdling habits of these living cousins of the dinosaurs..." "So meet them if you dare... the awesome reptiles!" "Seventy million years ago, earth was a very different place  ruled by giant reptiles..." "Then, say scientists, a massive meteor crashed into Mexico and dinosaurs were done for..." "Warm-bIooded birds and mammals took over and multiplied and now they run the place but hold on... we're mammals ourselves, so are we biased?" "If a visitor from outer space happened to land in parts of Africa, tropical America, or certainly australia, they might think planet earth was dominated by fierce scaly creatures, with sharp teeth, extraordinary senses, and some very smart survival strategies." "In short, that it's the reptiles who still run the place..." "Four main reptile groups survive on earth today - ...cunning crocodiles" "...armoured tortoises and turtles ...fast-running Iizards" "...and slinky snakes" "There are more than 8000 reptile species... surprisingly that's way more than mammals and only just fewer than birds." "The main feature that sets them all apart from birds and mammals is their armoured, scaly skin." "And of course they're all cold" " blooded..." "Or are they?" "In this programme we'II track down the biggest, hottest, best armed, and most ferocious reptiles anywhere on Earth." "We'II discover who they are... what gives them their power..." "and which ones we most need to fear!" "ur mission begins in the waterways of tropical Africa." "No question who's the ruler here!" "... a giant that can grow nearly six metres long, and weighs close to a ton..." "the fearsome NiIe crocodile." "A hundred million years ago, crocodiles came up with a brilliantly simple way to make a living." "In the seasonal tropics, for several months each year, rivers and lakes are the only source of drinking water in a drought-parched landscape." "AII the croc needs to do is to stake out the local watering hole, and wait..." "Don't be fooled by the crocodile." "There's no more deadly and efficient predator on the planet." "But mammals aren't easy to catch." "The croc needs all its skill and cunning - and to stay out of sight until the Iast possible moment..." "That means staying underwater for long periods of time, but a crocodile breathes air, so how does it do that?" "The answer is in the way it rations the oxygen in its blood." "As a croc submerges, it slows down its heart from 40 beats a minute tojust three." "Inside the heart, unique valves lock together to seal off the arteries that supply muscles and lungs." "The oxygen-rich blood is then re-routed through a special hole between the heart chambers and pumped only to the brain and other vital organs." "Using this trick, the croc can stay submerged for up to 3 hours at a stretch." "meanwhile the unused oxygen still in its lungs acts as a kind of reserve 'scuba tank'..." "Once the croc is in ambush position, it can cash in its reserves of oxygen Ready for the final attack..." "In the water, the croc has a massive advantage over its prey... on land, it's a different story..." "unable to drown the buffalo, this croc's only chance is to hang on and tire its victim out." "But this warm-bIood has back-up, and the croc is smart enough to know when to cut and run..." "although they hunt in the water, crocs spend a Iot of their leisure time on land..." "They love the sun, and they'II grab any chance to bask." "Seen with a heat-sensitive thermal camera, a cool croc emerges from the water on to a warm sand bank." "Now watch this!" "..." "It has turned broadside-on to the rising sun... and within a few minutes, the sunny-side begins to glow." "It's a natural solar panel... blood circulates through the warm skin and carries heat back to the body core." "Within an hour or two, the whole croc is glowing with contentment." "And the best thing is:" "this heating system doesn't burn up any hard-won food as fuel," "Which makes the sun-worshipping croc more energy-efficient than any mammal..." "Yet we still have the cheek to call reptiles "primitive"!" "mammals like the zebra burn a Iot of fuel." "But they need to graze at Ieast six Hours a day, while a croc can make do with just one or two good meals a year." "So the soIar-powered reptile can afford to chill out..." "By the end of a hard day's sunbathing, the croc is a beacon against the cooling sand." "When it finally moves, it leaves a heat-print behind..." "Being coId-bIooded doesn't mean having cold blood." "reptiles simply let the outside heat them inside." "And if they get too hot, they gape to cool back down..." "But even the most energy-efficient croc needs fuel occasionally..." "Kenya's Mara River, something happens once a year to put a smile on every crocodile's face..." "The game herds gather for their annual migration..." "And with their solar batteries fully charged, the crocs are ready to gree them." "There's not much point in using ambush tactics in this situation... a bolder approach is required..." "The odds seem stacked against the prey." "But if any animals know how to cross a river full of crocs, it's wildebeest..." "They move as one - a huge, dense mob studded with horns and hooves." "There's a real risk of being trampled underfoot." "But the croc's built like a battIe-cruiser, its armoured back is designed to cope with anything warm-bIoods can throw at it." "And with so many thousands of potential meals passing by, it can afford to wait for the perfect opportunity..." "Most wiIdebeest and zebra make it safely to the other side... but more and more crocs are on their way..." "It's easy to see these ancient predators as mindless killing machines... but the truth is even scarier..." "Crocs are clever:" "of all reptiles, their brain is the most like ours." "When it suits them, they reveal an unexpected social side  they join forces and co-operate..." "If one croc's deadly, two are pretty much unstoppable..." "The first one buIIdozes the zebra into deeper water..." "Then a second grabs the head and drowns it..." "Co-ordinated hunting of this kind is common and continues even when other crocs close in for the feast..." "With no slicing teeth to butcher meat, crocs have developed a unique way of dividing a carcass...the famous death roll" "while one croc acts as an anchor, another takes a bite," "locks its neck muscles, and spins." "Something has to give..." "At the end of each spin, the croc is left with a mouthful of meat... and it is quite a mouthful - a Iarge croc's bite is five times bigger than a lion's." "Working together, the crocs gulp down every bit of their victim... bones, skin, hooves ... the lot." "They have an airtight flap at the back of their throat, so they can bite prey underwater without drowning." "But swallowing is always done on the surface." "The death roll isn't recommended by your dentist..." "Crocs lose a Iot of teeth." "But that's not a problem for this ruling reptile - it can regenerate up to three thousand lost or damaged teeth throughout its life..." "Sojust imagine having to live alongside such a scary monster..." "The Sepik River of Papua New Guinea is a stronghold of the estuarine, or saltwater, crocodile." "SaIties are even bigger than NiIe crocs - they grow to six metres long." "Anyone who travels through their territory ought to be very scared indeed..." "But for one small Sepik River tribe, sharing the bath-tub with man-eating crocs seems to be child's play." "These people believe they've reached a special understanding with their local ruling reptiles." "They call themselves "crocodile people"" "and brand almost everything they own to make sure that the crocs know who they are..." "A crocodiIe-headed canoe shows proper respect and is thought to be safe from attack." "But the villagers protect themselves in other ways too..." "At some point in their life, all members of the tribe must spend several weeks in the village spirit house, where they learn the traditional songs and wisdom of their crocodile culture." "At the end of this confinement they face a painful graduation ritual." "tribal elders cut their skin to form scars" "like the scales on a crocodile's back." "It's the ultimate mark of respect for the ultimate reptile predator." "So does it work?" "well, there's no evidence that these people are safer than the other Sepik tribes." "But that isn't the point." "Menaced every day of their lives by unseen, man-eating monsters, they need reassurance." "No one wants to live in constant dread, and in their unique system of beliefs, the crocodile people have found the perfect antidote to fear itself!" "So is it possible to be a ruling reptile without unleashing a reign of terror?" "This is the leatherback turtle - the gentle giant of the reptile world." "Leatherbacks grow as big as a double bed and can weigh more than a ton - that's heavier than even a crocodile." "This beach in Trinidad is a Mecca for atlantic Leatherbacks... they may journey thousands of miles to mate and lay their eggs here." "only the females come ashore, and only after dark..." "This giant surfer measures nearly three metres between her flipper tips... and that's a Iot of bulk to shift..." "it's hot, exhausting work..." "filmed with a thermal camera, we can see her body heat burning against the beach." "But it's night so her temperature is clearly not from basking in the sun... that glow comes from within..." "clearly some heat is generated simply by the effort of climbing ashore." "But what sets the leatherback apart from all the other reptiles is the way she controls her temperature." "A thick, bIubber-Iined shell acts as insulation, allowing her to maintain her core body temperature up to eighteen degrees above her surroundings..." "She is in effect a warm-bIood!" "over the two-month nesting season, up to ninety turtles per night visit this beach ... so there's something of a scramble for the best nest sites." "A female lays around fifty fertiIised eggs, plus a bunch of smaller sterile eggs designed to collapse to create extra manoeuvring room for the hatching babies." "No other turtle does this." "The whole nest-digging and egg-Iaying process takes up to three hours..." "and makes her overheat." "Through the thermal camera, the pectoral muscles that work her flippers glow like hot metal." "By dawn, only one or two stragglers remain on the beach." "The temperature will soon soar to dangerous levels it's time to get back to the sea..." "Nine weeks later, the eggs have hatched, and the babies have tunnelled up through the hard-packed sand to just below the surface." "Their digging is perfectly synchronised - and they all emerge at exactly the same moment." "Then they head straight for the sea..." "Like the wildebeest crossing the Mara river, making a quick dash together is the best hope of making it in one piece." "Entering the surf, the hatchlings instantly turn into perfect little aquanauts." "Over the next ten years they will criss-cross the oceans of the world in search of food, increasing in size more than ten thousand times." "Like a whale, an adult leatherback is provisioned with caIorie-rich bIubber, which combined with its warm blood means it can venture into Arctic waters far beyond the reach of any other reptile." "And its flexible shell can cope with astonishing pressures of more than a hundred atmospheres, so it can dive a thousand metres deep on a single breath..." "Leatherbacks feed on jellyfish..." "and to keep up their active lifestyle, they need to eat up to a ton of them each day." "unfortunately for the turtle, a floating plastic bag can look like ajeIIyfish." "But plastic won't digest - it just clogs up the turtle's insides..." "Add in the risk of drowning in fishing nets, and the future doesn't look bright... scientists predict Ieatherbacks may be headed for extinction within the next ten years." "But not all turtles live in the remote expanses of the ocean, and they aren't all as sweet-tempered as the leatherback..." "In the dark waters of a florida swamp Iurks a monster straight out of Jurassic Park..." "Though he may not suspect a thing, this fisherman is being watched..." "The alligator snapping turtle is an ambush specialist." "Its worm-Iike tongue is bait to lure fish into these deadly jaws." "It can hold its breath for long periods, patiently hiding in the mud until a likely meal passes its way..." "The cutting edges of the turtle's beak behave like scissor blades." "When they aren't snapping up fish, they hunt for carrion - slicing through muscle and bone with ease." "A big snapper will eat anything it can get its jaws around A dog is mere chicken feed." "It's not just size and appetite that puts the alligator snapper in the ruling reptile category Its body is built like a strong-box - virtually predator-proof." "surprisingly, turtles don't have an external shell like a clam." "Their armour is formed by the ribs, which fuse... into a rigid box protecting the organs inside." "The snapper's huge head won't fit in its shell..." "But less well defended land turtles can retract their head and legs right inside this portable fortress when they feel threatened..." "This is the giant galapagos tortoise." "It weighs as much as 4 grown men and lives well over a hundred years." "On this remote island chain, with no natural predators, this reptile is the undisputed king." "A person could fit inside this shell." "It's the elephant of the reptile world - its Latin name means "elephant footed"" " and when it comes to the mating season, there are other similarities too..." "Like elephants, but unlike other tortoises, the male is much bigger than the female." "He does all the chasing..." "in sIow-motion of course." "Most mating takes place towards the end of the warm wet season, between January and June, when the tortoises are weII-fed and able to nourish developing eggs." "The females may be fertile for more than a century, but only reproduce successfully about once every ten years" "As a result, some islands' races have been completely wipe out by fast breeding competotor, such as domestic goat" "Thanks to their veggie diet and slow pace of Iife, the giant tortoises of the galapagos have managed to survive this tough terrain..." "But to be a top predator a reptile needs a radically different design..." "This is a perentie - a kind of monitor lizard - and the closest thing australia has to a modern-day VeIociraptor." "A fuII-grown perentie has few natural enemies to worry about." "But in the australian bush, there isn't much prey either..." "Or at Ieast there wasn't..." "until the mid eighteen hundreds, when European settlers introduced rabbits to the outback." "They bred like...well...rabbits... and quickly became australia's most hated pest." "Enter the dragon, on pest patrol..." "Monitor Lizards have outsized lungs, a Iarge blood volume, and their muscles are exceptionally good at storing oxygen, making them the champion runners of the reptile world." "The best thing a bunny can do when it's caught on the hop is to go underground..." "But even there it isn't safe..." "The perentie's long, curved claws are perfect digging tools, and its stamina is exceptional." "Once it gets stuck in, there's no stopping it." "These exceptionally strong jaws and big teeth can crush a rabbit's skull in a single bite... killing it instantly." "Another triumph in the reptile's cold war with the warm-bIoods." "The perentie is a very effective predator, but far away to the East Iurks an even bigger dragon." "This is the largest lizard on the planet - the Komodo dragon." "A fuII-grown male can reach three metres long, and weigh more than a man." "Dragons live on just five small Indonesian islands, where they swagger about as if they own the place To all intents and purposes, they do!" "During the breeding season in particular, male dragons will do whatever it takes to defend their turf." "luckily, dragons have skin like chain-maiI." "Even a fuII-on fight seldom results in serious injury." "Like so many reptiles, the Komodo dragon is an ambush predator..." "It will stalk any passer-by - even a buffalo." "This is an ambitious target for a single Iizard... even top warm-bIooded predators like a lion or tiger would think twice." "But the Komodo dragon has a secret weapon..." "The dragon's teeth are a cross between a T-Rex and a great white shark - dagger- Iike cutting blades with serrated edges..." "But more than that they're coated in stinky slime seething with bacteria... and dragons don't floss!" "But in this case, bad breath is a good thing - for the dragon anyway." "These super-bugs are its partners in crime." "The buffalo was bitten on the leg..." "it's just a small wound, but already infected with festering bacteria - a time-bomb spreading poison throughout its bloodstream." "Having set the bugs to work, all the dragon has to do is track its victim over the next few days until it keels over and dies." "Tongue-fIicking is how a dragon collects the airborne smells that lead it to food." "And it can sniff a carcass from three miles away..." "But so can all its neighbours..." "communal feeding like this is good news for those nasty bacteria, which get to spread and prosper..." "On these barren islands one good meal may have to last for several months." "One dragon was recorded gorging close to its own body weight in a single sitting!" "This is ruling reptile power at its most gruesome." "Far away, in the Arizona deserts, a much smaller relative has hit upon a similar trick." "The GiIa monster is a sluggish ground-dweIIer..." "But isn't it asking for trouble, Iumbering around in full view?" "...there are always larger predators on the prowl like the coyote." "The giIa monster may not be the biggest or best armed, but it is well defended..." "Each bump on its skin is fortified internally with a bone, a style of armour-pIating not seen since the dinosaurs." "But the coyote has a powerful bite..." "could there be more to this lizard than meets the eye...?" "although the GiIa monster is a rare protected species, its placid nature and colourful skin attracts another kind of predator..." "unscrupulous reptile collectors..." "But messing with a gila monster can be a big mistake!" "When threatened, it shows lightning reactions." "steel trapjaws snap shut, and lock on tight." "As it chews, venom from modified salivary glands flows up grooves in its teeth and enters the wound." "A hefty dose can kill a man, or at Ieast cause agonising pain." "Scientists have recently discovered an extra and unique component to the giIa monster's bite which has the extraordinary effect of enhancing memory..." "So this is one bite you won't forget in a hurry!" "And that is good news for the giIa monster..." "Venom is the trademark of another group of ruling reptiles" " snakes." "The rattlesnake is loaded with the stuff." "But it's not keen to waste its precious venom on defence." "Instead it advertises it as a deterrent..." "That famous death rattle sends out a simple warning - that the snake is armed and ready to defend itself." "But if you're prey the buzz can actually be good news too - a rattlesnake in hunting mode keeps quiet..." "simply possessing venom can act as a powerful deterent to potential enemies, it allows snakes a degree of confidence which few other creatures of their size can match." "The African black mamba can kill ten people with the venom in a single bite." "It gets its name from the colour of its open mouth." "A large mamba can rear up two metres high... thanks to its unique skeleton." "It has around three hundred vertebrae and ribs, all linked by small but powerful muscles, giving it amazing flexibility and strength." "And here's another reason the black mamba's hair-raising to mammals - it's the fastest snake in the world." "This footage, from a mini camera on its back, is in real time..." "The secret of the mamba's locomotion is to throw its body into sideways sweeps, pushing off with the outside of its coils, Iike a tyre on a racetrack bend." "flat out, it can top thirteen miles an hour." "There's a good reason for this male mamba to get a wriggle on..." "It's that time of year again, and female scent is wafting on the breeze..." "But he's got a rival..." "so he'II have to fight." "At any moment, either rival could inflict a deadly knockout bite, but amazingly they never do." "This is a test of the fittest, not the deadliest." "The female watches from a ringside seat..." "Fight over;" "the winnerjoins her to Enjoy his prize - an afternoon of slinky passion in the tree-tops." "The loser, meanwhile, must restore his strength for the next time, by catching a meal..." "black mambas are the cheetahs of the reptile world, stalking their prey under cover... then relying on a burst of speed to clinch the deal." "And this sprinter is a Iong jumper too... it can launch itself four metres through the air..." "The mamba's fast and deadly... so does it deserve the ruling reptile crown?" "There's no doubt venom is the weapon that sets reptiles apart from the rest." "It gives some snakes a devastating power, way out of keeping with their size." "But most snakes aren't deadly." "The trouble is;" "it takes an expert to tell them apart, so how do we know which ones to be scared of?" "telling nice snakes from nasty ones is just as hard for other animals." "These bonnet macaque monkeys have a fixed response to any snake they see." "One raises the alarm;" "they all pull panic-stricken faces and rush to the highest branches, just in case..." "Monkeys, apes and humans are more likely to develop fear of snakes than any other phobia." "One in four people suffer from it." "Our brains are hard-wired to identify a serpent from the tiniest visual clue..." "What happens next is pure instinct, and takes less time than the blink of an eye." "The brain relays a message to its panic centre, the amigdaIa... adrenaline floods the body, blood rushes to the muscles, and endorphins are released to combat pain." "And amazingly, this entire emergency drill completely bypasses the conscious part of the brain." "So when it's over, the victim may remember nothing." "It's as if their brain had been hijacked by aliens..." "Which, in effect, it was..." "Severe snake phobia can make a monkey out of anyone!" "So does this natural defence mechanism still have a function?" "well that depends on where you live!" "The chilling fact is that in South Asia alone, an estimated twenty thousand people each year are still killed by venomous snakes..." "So, time to choose - which is the ultimate ruling reptile?" "Is it the snake." "The warm-bIooded Ieatherback - giant of them all?" "The crocodile, with its kiIIerjaws?" "Or the ferocious Komodo dragon?" "Whichever one we choose, it's worth remembering that most reptiles still alive today are predators... and doing very nicely too." "The dinosaurs may have gone, but their spirit lives on..." "ruling reptiles?" "...You'd better believe it!"