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Reptiles and amphibians are sometimes thought of as primitive, dull and dim-witted.

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In fact, of course, they can be lethally fast,

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spectacularly beautiful,

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surprisingly affectionate and very sophisticated.

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They have remarkably varied ways of catching their prey...

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and of defending themselves.

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They can produce a great turn of speed

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and fight with impressive zest.

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Some have spectacular colours and show off to one another.

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They communicate with calls.

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CROAKING

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And with gestures.

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And there! That's it!

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The full works!

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Reptiles have scaly skins

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and amphibians, soft moist ones.

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None of them live at a uniform pace,

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but switch from the fast to the slow lane within a year or an hour.

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Unlike us, they get their energy directly from the sun.

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And although being called "cold-blooded"

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might suggest they are unemotional,

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they can be touchingly warm-hearted as mates...

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..and as parents.

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And that's just the beginning.

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There are a whole lot of other warm-hearted truths to be discovered

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to give the phrase "Life in Cold Blood" a completely new meaning.

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The Galapagos Islands.

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Some of the reptiles that live here are particularly skilful

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at solving the problems of getting their energy directly from sunshine.

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Marine iguanas face a major thermal challenge

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every morning of their lives.

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During the night, their bodies cool.

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And now they must warm up quickly

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in order that they can become active and start feeding.

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Their bodies and skins are black,

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which is very efficient at absorbing heat

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and they bask with their black flanks broadside to the sun.

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The rate at which they absorb warmth is invisible to the naked eye,

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but very clear indeed to a thermal camera.

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First thing, they're cold and purplish blue.

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But slowly, as they warm up,

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a golden glow spreads through their bodies.

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And eventually, after half an hour or so,

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they become as hot as the rocks beneath them.

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Once they are thoroughly warmed up,

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marine iguanas can maintain their body temperature

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just about as constantly as I can, and what's more,

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at about the same level or indeed slightly higher,

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around 37 degrees Centigrade.

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Now they need to feed.

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There's nothing to eat on or around these barren rocks except seaweed,

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and to get that, they'll have to swim.

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But the sea around here is surprisingly cold,

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around 15 to 16 degrees C entigrade,

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and only the bigger iguanas can absorb enough heat

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to power the dives to enable them to go to the seaweed at any depth.

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However, their bodies are now thorough warmed up.

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The thermal camera shows them as golden yellow

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as they clamber down

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over the cold blue rocks and dive into the sea.

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Although their islands lie almost exactly on the equator,

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the sea here is permanently chilled

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by a cold current that sweeps up from the depths of the ocean.

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So they won't be able to stay in the water for very long.

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They have no time to waste.

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In the shallows close to the shore,

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the seaweed has been heavily cropped.

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To get a good meal,

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they may have to dive to at least 15 feet - five metres.

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They're able to reduce the chilling effect of the cold water by closing

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down the blood supply to their limbs and the outer part of their bodies.

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But even so, their body temperature may drop by ten degrees or so.

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A cooling like that would kill a human diver.

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After five to ten minutes on the sea floor, most iguanas have had enough

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and they return to the surface

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and the life-saving warmth of the rocky shore.

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A recently emerged iguana is black - it's chilled to the bone.

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Now they need heat in order to be able to digest that meal of seaweed

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and they get that by spread-eagling themselves

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on these black, hot, sun-baked rocks.

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Their image warms from black...

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to purple...

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and then from red to orange.

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In the evening, the temperature falls,

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and they huddle together to retain their warmth as long as possible.

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They will have to wait until the following morning

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before they can re-warm themselves sufficiently to feed again.

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Most kinds of lizards have this daily schedule.

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Side-blotched lizards in California certainly do.

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You can see from the colour of my face that my body is warm.

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That's because I've got a central heating system

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which I have fuelled with my breakfast.

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In fact about 80% of what I eat

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is used in keeping my body temperature high and steady.

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These lizards, however, squander very little of the energy

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of the energy they get from their food on warming themselves.

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They, like the marine iguanas,

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get nearly all they need for that by basking on the warm rocks.

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And so important is the need for warmth,

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that the females actually choose their males

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on the basis of which has the best underfloor heating.

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Each male sits on his pile of boulders doing press-ups

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to signal his ownership and to warn off other males.

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Intruders are confronted immediately and, if necessary, attacked.

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And the victor returns to sit on his wonderfully warm throne.

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Look at his rocky kingdom with a thermal camera

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and it's immediately clear why it's so precious.

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The rocks are very much hotter than the surrounding grassland

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and big, tall ones catch the sun earlier and retain its heat longer.

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So not only does the sun warm him from above,

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his rocks do from beneath.

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The most powerful dominant male has, naturally, the best pile of rocks.

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And, not surprisingly, almost all the females.

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But is it the males themselves

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or their assets that the females are interested in?

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To find out, let's move their hot rocks

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and give them to a subordinate male.

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The females quickly recognise that a more desirable residence

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has appeared in the neighbourhood, and start to move across.

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And the sex-starved wimp suddenly finds himself amazingly popular!

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So, the females do indeed go for the males with the hottest rocks.

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These lizards on a small islet

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off the shores of Menorca in the Mediterranean

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get their heat from another, and very unusual, source.

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Ow!

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Sorry!

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They're very curious. I'm the new boy on the block.

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The new object in their environment.

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And that one just gave me a little nip.

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They investigate the world around them by tasting it,

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and they are still trying to work out what I am.

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Their island is rocky and not particularly rich in food.

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The lizards are primarily insect-eaters,

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but during the flowering season, they also take nectar.

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They collect it from plants, like spurge, which is very common.

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And they have a very special relationship with this flower.

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It's called the dead horse arum.

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It certainly looks like carrion.

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And...

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Ooh, dear me, it smells very strongly of carrion.

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As a consequence of both its looks and its smell,

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it attracts carrion flies.

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Of course, it's the flies that the lizards are after.

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But as well as providing food for the lizards,

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this extraordinary flower helps them in another way.

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This central part, which is called a spadix,

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is slightly warm, as you can see from a thermal camera.

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The chemical process that produces the disgusting smell

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also creates heat and raises the temperature of the flower

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by up to five degrees above the surroundings,

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sufficiently high for a lizard to warm itself on it on a cold morning.

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And in case you find that hard to believe,

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here is confirmation from the thermal camera.

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The purplish-blue lizard quickly takes on

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the same temperature and colour as the arum.

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And sitting on arums brings another benefit...

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Breakfast.

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A fly, lured by the smell, crawls inside.

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The lizard hears the fly buzzing within.

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The fly, of course,

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can't find anything it wants, but now it can't get out.

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The entrance to the flower is blocked by the lizard.

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And the lizard gets an easy meal.

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Two months later,

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the arum flowers have shrivelled and produced their fruits.

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Until 20 years ago, the lizards ignored these withered bundles.

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After all, they hardly look like food.

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But then a particularly inquisitive individual

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sampled a fruit and found the soft flesh around the seed rather good.

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The habit spread and now the whole lizard population,

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uniquely in the Mediterranean, have become arum fruit-eaters.

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They do take a bit of swallowing,

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but seeds passing through a lizard's gut not only survive

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but germinate even more easily.

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As a result, the arums, which were rather scarce here 20 years ago,

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have suddenly become abundant all over the island.

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A cold, windswept island off the coast of South Africa

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is not the first place you would go to if you were looking for reptiles.

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But here on Dassen Island, among penguins and seagulls,

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there's one of the greatest concentration of tortoises

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to be found anywhere on Earth.

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There are about 5,000 of them on this one tiny island.

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The penguins and other birds, thanks to their warm blood,

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are active, no matter how cold it is,

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but the tortoises have to wait for the day to warm up

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before they can get about their business.

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They bask in the sunshine, powering up their bodies

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to the optimum working temperature of 33 degrees Centigrade,

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and then they go off to feed.

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As the day progresses, the temperature rises quickly

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and even before noon it's too hot for comfort.

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The tortoises have to head for shade.

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In the late afternoon, it gets cooler

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and the tortoises venture out again.

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For them, this is the best time.

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They're thoroughly warmed up,

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they've digested their morning meal and they've got energy to spare.

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The males begin to fight,

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jousting like medieval knights,

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using a projection on the front of the shell like a lance.

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The technique is to get the spike under your opponent

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and then flick him over on to his back.

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Contests can last for half an hour.

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The loser tries to right himself,

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but the winner keeps biting his legs.

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At last, the victor loses interest and goes off to find the female

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who caused the argument in the first place.

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As for the loser, if he doesn't manage to right himself soon,

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he may cook in the sun.

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Tortoises are able to sunbathe out in the open,

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because their strong bony shell

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gives them almost complete protection from predators.

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Less well-armoured reptiles like lizards are vulnerable, of course,

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to hawks and coyotes and foxes and cats.

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And in the morning, when those warm-blooded animals

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are already active,

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the lizards are cold and can't move fast. So they have a problem.

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But they also have a solution...secret sunbathing.

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You really can't see them until you are right on top of them.

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And there's one there.

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I'm in Arizona,

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and that at my feet is a lizard buried in the sand up to its neck.

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Even while it's buried, it can use the sunshine to warm its whole body.

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It can control the supply of blood to its head

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so that it pools in a cavity behind the eye.

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Soon, the blood there is as much as five degrees

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above the temperature of the rest of its body.

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Then the animal opens the major blood vessels in its neck

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and the hot blood circulates

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so that its whole body is thoroughly warmed,

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even though it's still mostly below ground.

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This...

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is a horned lizard...

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and very beautiful, too.

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This particular species is called the regal horned lizard

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because it has this splendid crown of spikes at the back of his neck.

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When he's hidden, they break up the outline of his head

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and so you hardly see him at all.

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And now in the warmth of my hand and in the sunshine,

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I guess he has warmed up quite a lot and if I put him down,

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he now at last may be able to run for it.

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And indeed he does.

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South African armadillo lizards, which live on these rocky outcrops,

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have a different solution to the problem of safe sunbathing.

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They've turned it into a social activity.

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Whole families of them live together in the crevices among the rocks

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and in the morning, they all emerge to warm up in the sun.

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Of course, there is safety in numbers.

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There are lots of eyes to spot danger if it appears.

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And when one sunbather takes fright, they all dive for safety.

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If a predator is quick, it IS possible to grab one.

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But even then, an armadillo lizard is not going to be an easy meal.

253
00:22:02,120 --> 00:22:03,240
Ow!

254
00:22:04,960 --> 00:22:08,440
They have an additional form of defence.

255
00:22:08,440 --> 00:22:11,160
They bite their tails.

256
00:22:11,160 --> 00:22:14,920
The reason they do that is that it covers up

257
00:22:14,920 --> 00:22:18,720
their vulnerable underside

258
00:22:18,720 --> 00:22:23,240
and exposes only these very sharp spiny scales,

259
00:22:23,240 --> 00:22:25,400
which is a very good protection

260
00:22:25,400 --> 00:22:29,000
against predators like snakes or mongooses.

261
00:22:30,520 --> 00:22:33,400
They stay like this for quite a long time

262
00:22:33,400 --> 00:22:36,280
before they are confident enough to uncurl.

263
00:22:36,280 --> 00:22:39,720
I'll put him down and see how he does.

264
00:22:52,880 --> 00:22:58,880
Sunset, necessarily, brings an end to activity for most reptiles.

265
00:23:00,640 --> 00:23:03,240
But not for all.

266
00:23:04,120 --> 00:23:05,160
A leopard gecko.

267
00:23:05,160 --> 00:23:07,280
It, like most geckos, is nocturnal

268
00:23:07,280 --> 00:23:10,160
and it manages to get all the heat it needs from the rocks

269
00:23:10,160 --> 00:23:12,360
which retain something of their warmth

270
00:23:12,360 --> 00:23:15,640
for several hours after the sun has set.

271
00:23:17,200 --> 00:23:20,520
This male is in search of a mate.

272
00:23:20,520 --> 00:23:23,440
She is less brightly coloured.

273
00:23:26,760 --> 00:23:30,120
They inspect one another.

274
00:23:33,480 --> 00:23:36,240
He collects her scent with his tongue

275
00:23:36,240 --> 00:23:40,800
and discovers that not only is she female but she's sexually available.

276
00:23:47,720 --> 00:23:50,240
He's interested.

277
00:23:54,080 --> 00:23:56,960
He nibbles her neck and strokes her flanks,

278
00:23:56,960 --> 00:23:59,840
all part of his elaborate courtship routine.

279
00:24:07,400 --> 00:24:10,240
Copulation begins.

280
00:24:12,640 --> 00:24:15,720
This is the time in mammals and birds

281
00:24:15,720 --> 00:24:17,720
when the sex of the young is determined.

282
00:24:17,720 --> 00:24:21,480
But not in a number of reptiles, including geckos.

283
00:24:21,480 --> 00:24:26,360
Once again, it's temperature that profoundly influences their lives.

284
00:24:28,560 --> 00:24:32,160
The female goes away to lay her eggs.

285
00:24:33,680 --> 00:24:37,760
She has chosen a place where the temperature is about 31 degrees.

286
00:24:37,760 --> 00:24:41,160
As her body is the same temperature as her environment,

287
00:24:41,160 --> 00:24:45,520
she can't heat her eggs by sitting on them as warm-blooded birds do,

288
00:24:45,520 --> 00:24:49,840
so they're exactly the same temperature as the rocks beneath.

289
00:24:52,200 --> 00:24:55,080
After a couple of months, both eggs begin to hatch.

290
00:24:59,840 --> 00:25:02,520
The first to emerge is a male.

291
00:25:10,600 --> 00:25:13,480
And the second will be too.

292
00:25:13,480 --> 00:25:16,360
It's the temperature which has determined that.

293
00:25:16,360 --> 00:25:18,720
If it had been a few degrees lower,

294
00:25:18,720 --> 00:25:22,080
both eggs would have developed into females.

295
00:25:30,920 --> 00:25:35,880
Crocodiles have their sex determined by temperature in a similar way.

296
00:25:35,880 --> 00:25:41,560
This clutch belongs to the Indian fish-eating crocodile, the gharial.

297
00:25:48,920 --> 00:25:53,360
LOW SQUEAKING

298
00:25:53,360 --> 00:25:56,160
The female has heard the calls from below ground

299
00:25:56,160 --> 00:25:59,120
made by her hatching young

300
00:25:59,120 --> 00:26:02,040
and is helping them to dig their way out of the sand.

301
00:26:12,240 --> 00:26:15,200
They immediately make their way down to the water.

302
00:26:17,720 --> 00:26:19,680
And mother goes too.

303
00:26:34,560 --> 00:26:38,520
Here, of course, they are nice and warm.

304
00:26:38,520 --> 00:26:42,840
Water retains its daytime heat better and longer than rock,

305
00:26:42,840 --> 00:26:46,680
so unlike many other reptiles, gharials and other crocodilians

306
00:26:46,680 --> 00:26:49,600
have enough energy to feed actively all night.

307
00:27:18,720 --> 00:27:23,200
While being nocturnal is unusual among reptiles,

308
00:27:23,200 --> 00:27:26,320
it's the norm for amphibians.

309
00:27:26,320 --> 00:27:29,640
Their skin is not scaly and watertight like a reptile's.

310
00:27:29,640 --> 00:27:31,800
It's soft, moist and permeable.

311
00:27:31,800 --> 00:27:36,200
If they exposed themselves to sunlight for any length of time,

312
00:27:36,200 --> 00:27:38,640
they would dry out and die.

313
00:27:38,640 --> 00:27:42,120
So most frogs only leave their shelters at night.

314
00:27:46,040 --> 00:27:49,040
Since they can't absorb sunshine directly,

315
00:27:49,040 --> 00:27:52,120
they either get heat from their surroundings

316
00:27:52,120 --> 00:27:54,960
or draw their energy from the fat reserves

317
00:27:54,960 --> 00:27:57,720
that they built up when the feeding was good.

318
00:27:57,720 --> 00:28:01,920
But even so, they seldom hop unless they have very good reason to do so.

319
00:28:04,040 --> 00:28:09,040
This frog, however, the South American waxy monkey frog,

320
00:28:09,040 --> 00:28:10,640
is exceptional.

321
00:28:10,640 --> 00:28:13,400
It's one of the few that can tolerate

322
00:28:13,400 --> 00:28:15,840
direct sunshine for any length of time.

323
00:28:17,800 --> 00:28:23,280
And that is because it secretes a wax from glands on its neck.

324
00:28:36,480 --> 00:28:40,280
No human sunbather goes to more trouble than they do

325
00:28:40,280 --> 00:28:45,240
to make quite sure that every part of their skin is properly anointed.

326
00:29:10,480 --> 00:29:14,280
The sunshine may also bring them an extra benefit.

327
00:29:14,280 --> 00:29:17,800
It probably protects them from the fungal infections

328
00:29:17,800 --> 00:29:21,080
to which many moist-skinned amphibians are prone.

329
00:29:28,160 --> 00:29:31,080
In the rainforests of Central America,

330
00:29:31,080 --> 00:29:33,440
the air is heavy with moisture.

331
00:29:33,440 --> 00:29:35,720
So the poison arrow frogs

332
00:29:35,720 --> 00:29:38,400
can risk basking in the little patches of sunshine

333
00:29:38,400 --> 00:29:41,640
that dapple the forest floor and if they begin to dry out,

334
00:29:41,640 --> 00:29:44,440
they can retreat into the leaf-litter.

335
00:29:45,720 --> 00:29:47,680
RAPID CHIRRUPING

336
00:29:47,680 --> 00:29:51,560
The sunshine gives them sufficient energy to permit the extravagance of

337
00:29:51,560 --> 00:29:57,040
calling almost continuously in defence of their territories.

338
00:30:00,440 --> 00:30:02,960
They even have enough spare energy

339
00:30:02,960 --> 00:30:06,080
to indulge in long battles with their neighbours.

340
00:30:52,400 --> 00:30:56,840
These fights can go on for well over half an hour at a time

341
00:30:56,840 --> 00:31:00,400
until both contestants are completely exhausted.

342
00:31:07,880 --> 00:31:12,720
So a moist skin limits not only where amphibians can live,

343
00:31:12,720 --> 00:31:15,280
but how energetic they can be.

344
00:31:15,280 --> 00:31:21,480
Out in the sunshine, dry-skinned reptiles have more options.

345
00:31:21,480 --> 00:31:25,280
By collecting solar power so efficiently,

346
00:31:25,280 --> 00:31:30,040
reptiles need to use very little of the energy they generate themselves

347
00:31:30,040 --> 00:31:31,560
to warm their bodies.

348
00:31:31,560 --> 00:31:33,760
In fact, they use around a tenth

349
00:31:33,760 --> 00:31:36,800
compared with a mammal of a similar size.

350
00:31:36,800 --> 00:31:40,680
That means they don't have to eat very often.

351
00:31:40,960 --> 00:31:42,960
A puff adder like this one

352
00:31:42,960 --> 00:31:46,880
can wait almost indefinitely for its next meal.

353
00:31:46,880 --> 00:31:51,360
Amongst predators, patience really is a virtue.

354
00:31:55,480 --> 00:31:59,640
Whilst waiting for a meal to wander within striking distance,

355
00:31:59,640 --> 00:32:03,080
a snake shuts down its body processes

356
00:32:03,080 --> 00:32:06,120
so that it uses the minimum amount of energy.

357
00:32:06,120 --> 00:32:09,880
Only the equivalent of a pilot light is left on.

358
00:32:09,880 --> 00:32:12,800
And it can remain like this for weeks.

359
00:32:15,480 --> 00:32:19,560
All around it, mammals are expending their energy in a way that,

360
00:32:19,560 --> 00:32:23,640
compared with the snake, seems extraordinarily extravagant.

361
00:32:37,320 --> 00:32:42,120
But when a snake needs to move fast, it can do so with lightning speed.

362
00:32:52,040 --> 00:32:57,320
Once its prey is secured, a snake can take its time over its meal.

363
00:32:57,320 --> 00:33:03,440
This gigantic python is feeding on a deer.

364
00:33:03,440 --> 00:33:07,800
A python kills its prey by wrapping its coils around it and squeezing

365
00:33:07,800 --> 00:33:13,000
its victim so tightly and for long that it can no longer breathe.

366
00:33:13,000 --> 00:33:16,960
But swallowing its meal takes time.

367
00:33:16,960 --> 00:33:20,160
The deer will go down head first.

368
00:33:20,160 --> 00:33:22,000
It's much easier that way.

369
00:33:31,600 --> 00:33:35,880
The ligaments connecting the snake's upper and lower jaw are elastic

370
00:33:35,880 --> 00:33:38,880
so that it can engulf the deer's head,

371
00:33:38,880 --> 00:33:42,160
even though it is much bigger than its own.

372
00:33:42,160 --> 00:33:45,680
With its mouth stretched tightly around its meal,

373
00:33:45,680 --> 00:33:48,520
the snake can't breathe in a normal way.

374
00:33:48,520 --> 00:33:52,640
But it's able to push the top of its windpipe right out of its mouth

375
00:33:52,640 --> 00:33:55,720
and so continue to take in air.

376
00:34:15,640 --> 00:34:21,400
After some hours, all that can be seen of the deer are its hind legs.

377
00:34:32,320 --> 00:34:35,240
Once the meal has been completely swallowed,

378
00:34:35,240 --> 00:34:38,760
the inner workings of the snake's body change greatly.

379
00:34:40,280 --> 00:34:44,240
Its digestive processes switch to full power

380
00:34:44,240 --> 00:34:47,600
and increase their activity 40 times.

381
00:34:47,600 --> 00:34:51,880
There is an explosion of biochemical activity.

382
00:34:51,880 --> 00:34:55,240
The liver, the secretions of which power digestion,

383
00:34:55,240 --> 00:34:57,360
doubles in size within two days.

384
00:34:59,160 --> 00:35:02,720
The heart grows by some 40%.

385
00:35:05,800 --> 00:35:11,680
It will take the python at least a week to completely digest this enormous meal.

386
00:35:11,680 --> 00:35:16,280
But then it will not need to feed again for months, or even a year.

387
00:35:19,360 --> 00:35:21,240
This ability to switch off

388
00:35:21,240 --> 00:35:24,600
helps reptiles and amphibians in another way.

389
00:35:26,720 --> 00:35:30,480
A baby North American painted turtle.

390
00:35:30,480 --> 00:35:34,400
It and the rest of its clutch have only just hatched.

391
00:35:34,400 --> 00:35:39,400
But it's late in the year, and the chill of winter has already begun.

392
00:35:40,160 --> 00:35:43,240
If the hatchlings clambered out of their hole now,

393
00:35:43,240 --> 00:35:46,800
they would find nothing to eat, so they stay where they are.

394
00:35:53,120 --> 00:35:57,200
The temperature will fall to -10 degrees.

395
00:35:59,360 --> 00:36:04,760
Ice crystals grow around the babies and even inside their bodies.

396
00:36:04,760 --> 00:36:08,680
But their tissues are protected by a kind of antifreeze.

397
00:36:12,000 --> 00:36:14,520
This would kill any mammal or bird.

398
00:36:18,040 --> 00:36:22,840
They remain in this deep freeze for up to six months.

399
00:36:28,800 --> 00:36:32,720
But spring comes at last.

400
00:36:37,880 --> 00:36:42,280
The ice melts around them and eventually within them.

401
00:36:50,960 --> 00:36:54,520
Slowly they begin to come to life.

402
00:37:11,520 --> 00:37:15,480
It takes quite a time for them to become fully functional,

403
00:37:15,480 --> 00:37:18,840
but eventually they are ready to face the outside world.

404
00:37:31,960 --> 00:37:37,640
So by allowing their bodies to cool, they have avoided the hard times.

405
00:37:48,440 --> 00:37:50,320
With the arrival of spring,

406
00:37:50,320 --> 00:37:53,760
their parents are now preparing to breed again.

407
00:38:01,320 --> 00:38:03,280
The male courts the female

408
00:38:03,280 --> 00:38:07,400
by gently strumming her cheeks with his long claws.

409
00:38:11,160 --> 00:38:13,560
And she responds.

410
00:38:19,200 --> 00:38:23,080
Cold blood is clearly no barrier to affection.

411
00:38:23,080 --> 00:38:25,560
In fact, reptiles can conduct

412
00:38:25,560 --> 00:38:29,280
as complex and as sensitive a courtship as many a mammal.

413
00:38:37,240 --> 00:38:41,800
This is the biggest of all living reptiles and one of the most feared.

414
00:38:41,800 --> 00:38:46,360
If one creature were to be labelled a cold-blooded killer,

415
00:38:46,360 --> 00:38:47,680
it would be this.

416
00:38:47,680 --> 00:38:49,600
A saltwater crocodile,

417
00:38:49,600 --> 00:38:54,000
a monster that can grow to a length of 20 feet - 6 metres -

418
00:38:54,000 --> 00:38:56,360
and weigh a tonne.

419
00:39:03,000 --> 00:39:06,200
But male and female, when they court,

420
00:39:06,200 --> 00:39:08,200
blow bubbles at one another.

421
00:39:15,560 --> 00:39:19,840
He is three times her size and could easily crush her,

422
00:39:19,840 --> 00:39:23,200
yet he treats her with great gentleness.

423
00:39:28,040 --> 00:39:29,800
He strokes her back.

424
00:39:42,000 --> 00:39:46,680
Slowly, he aligns his body with hers.

425
00:40:13,360 --> 00:40:16,120
So union is achieved.

426
00:40:26,360 --> 00:40:30,760
Crocodiles are among the most ancient of reptiles.

427
00:40:30,760 --> 00:40:35,400
Their ancestors appeared at about the same time as the dinosaurs.

428
00:40:35,400 --> 00:40:40,800
But what about them? Were dinosaurs similarly cold-blooded?

429
00:40:42,320 --> 00:40:44,680
The rocks of the North American West

430
00:40:44,680 --> 00:40:47,640
are particularly rich in dinosaur fossils.

431
00:40:49,280 --> 00:40:51,800
A hundred million years ago

432
00:40:51,800 --> 00:40:56,840
this was a horizontal mud-flat at the edge of the sea.

433
00:40:56,840 --> 00:40:59,800
And across it came an adult dinosaur

434
00:40:59,800 --> 00:41:03,840
with a smaller, younger one trotting alongside,

435
00:41:03,840 --> 00:41:08,160
leaving their footprints behind to be fossilised.

436
00:41:09,680 --> 00:41:13,400
They were iguanadons, a herd of them,

437
00:41:13,400 --> 00:41:17,160
together with some bird-footed dinosaurs.

438
00:41:17,160 --> 00:41:19,680
Were these all solar-powered?

439
00:41:21,640 --> 00:41:25,880
Some of the ancient reptiles had specific adaptations

440
00:41:25,880 --> 00:41:27,960
to help them collect heat.

441
00:41:27,960 --> 00:41:34,200
This is a plate from the back of a stegosaurus,

442
00:41:34,200 --> 00:41:38,160
and you can still see the lines where the blood vessels ran

443
00:41:38,160 --> 00:41:42,520
which collected the heat and carried it to the rest of the body.

444
00:41:42,520 --> 00:41:46,840
So, for the stegosaurus at least, the need to collect heat

445
00:41:46,840 --> 00:41:49,480
seems to have been just as important

446
00:41:49,480 --> 00:41:52,360
as it is for its relatives alive today.

447
00:41:52,360 --> 00:41:58,040
But there are clues that suggest that ancient reptiles were better at

448
00:41:58,040 --> 00:42:02,200
maintaining their temperature than their modern counterparts.

449
00:42:02,200 --> 00:42:07,920
This is the jaw-bone of a very large and very famous dinosaur.

450
00:42:10,720 --> 00:42:16,920
In life, its head would have been 18 feet - six metres - above ground.

451
00:42:19,560 --> 00:42:23,240
This is the jaw of Tyrannosaurus rex.

452
00:42:31,520 --> 00:42:34,760
An animal as big as this has a very large body mass

453
00:42:34,760 --> 00:42:37,080
which retains heat very well,

454
00:42:37,080 --> 00:42:42,040
so perhaps these huge dinosaurs were, in fact, warm all the time,

455
00:42:42,040 --> 00:42:45,880
simply because they were too big to lose all their heat overnight,

456
00:42:45,880 --> 00:42:47,560
as a smaller reptile would.

457
00:42:50,520 --> 00:42:52,800
But what about when they were small?

458
00:42:52,800 --> 00:42:57,200
Were adolescent tyrannosaurs able to maintain a steady body temperature?

459
00:42:57,200 --> 00:43:00,640
Were they, in short, warm-blooded?

460
00:43:00,640 --> 00:43:02,640
Evidence on that can be found

461
00:43:02,640 --> 00:43:05,760
in the microscopic structure of their bones.

462
00:43:12,640 --> 00:43:14,160
This...

463
00:43:16,160 --> 00:43:19,520
is the leg bone of a young Tyrannosaurus,

464
00:43:19,520 --> 00:43:22,520
and it has bands in it.

465
00:43:22,520 --> 00:43:26,000
The inner section, formed when the animal was young,

466
00:43:26,000 --> 00:43:27,480
has an open structure,

467
00:43:27,480 --> 00:43:30,960
like the bone of a fast-growing warm-blooded mammal.

468
00:43:32,480 --> 00:43:37,200
The outer part is more dense, more like that of today's reptiles.

469
00:43:37,200 --> 00:43:42,360
But whether the dinosaurs were really truly warm-blooded,

470
00:43:42,360 --> 00:43:44,000
we may never know.

471
00:43:44,000 --> 00:43:48,920
What we do know, however, is that dinosaurs were extraordinarily

472
00:43:48,920 --> 00:43:53,720
successful and dominated the earth for 150 million years.

473
00:43:55,520 --> 00:43:59,760
But there are some reptiles today that can keep their body temperature

474
00:43:59,760 --> 00:44:02,640
well above that of their surroundings.

475
00:44:02,640 --> 00:44:07,240
And these are the tracks of one of them.

476
00:44:07,240 --> 00:44:12,960
These giants haul themselves up out of the sea along beaches like this

477
00:44:12,960 --> 00:44:15,320
in many parts of the tropics.

478
00:44:15,320 --> 00:44:17,240
But in order not to disturb them,

479
00:44:17,240 --> 00:44:21,560
I'll turn this light out and we'll look for them with infrared cameras.

480
00:44:28,000 --> 00:44:30,240
Leatherback turtles.

481
00:44:30,240 --> 00:44:33,960
Like crocodiles, turtles are very ancient creatures,

482
00:44:33,960 --> 00:44:38,600
having first appeared at about the same time as the early dinosaurs.

483
00:44:38,600 --> 00:44:42,320
Today leatherbacks are the biggest of all reptiles

484
00:44:42,320 --> 00:44:44,800
and the most widely distributed,

485
00:44:44,800 --> 00:44:48,280
for they are found all the way from these warm tropical waters

486
00:44:48,280 --> 00:44:50,280
to the freezing seas of the Arctic.

487
00:44:57,680 --> 00:45:00,440
These have come ashore on a beach in Trinidad,

488
00:45:00,440 --> 00:45:03,040
where almost certainly they were hatched.

489
00:45:03,040 --> 00:45:06,760
Now they, in their turn, are laying their eggs here.

490
00:45:13,640 --> 00:45:19,720
Leatherbacks, we know, can generate heat internally,

491
00:45:19,720 --> 00:45:23,440
and there is proof of that if you have a look at her eggs

492
00:45:23,440 --> 00:45:28,520
that she is laying right now on that thermal camera.

493
00:45:28,520 --> 00:45:31,400
They are emerging from her body

494
00:45:31,400 --> 00:45:37,400
and lo and behold, they are bright yellow, verging on white,

495
00:45:37,400 --> 00:45:41,160
proving that they are warmer than their surroundings.

496
00:45:42,840 --> 00:45:48,680
She generates that heat within her body from special deposits of fat

497
00:45:48,680 --> 00:45:52,640
so that she can maintain her internal body temperature

498
00:45:52,640 --> 00:45:56,720
up to 8C above that of the water through which she swims.

499
00:45:59,080 --> 00:46:01,520
As she sweeps away the surface sand,

500
00:46:01,520 --> 00:46:05,680
you can see that the sand too is yellower, warmer, than the outside

501
00:46:05,680 --> 00:46:09,680
of her shell, for it still retains the heat it acquired during the day.

502
00:46:16,920 --> 00:46:19,640
So how do leatherbacks retain

503
00:46:19,640 --> 00:46:24,680
that precious and expensive internally generated heat?

504
00:46:24,680 --> 00:46:29,520
Well, to start with, they have their huge size to help them.

505
00:46:29,520 --> 00:46:32,040
They really are massive animals.

506
00:46:32,040 --> 00:46:35,680
This one is getting on for two metres - six feet long,

507
00:46:35,680 --> 00:46:38,760
and they can grow to weigh a tonne and a half.

508
00:46:38,760 --> 00:46:42,280
And, of course, big objects retain their heat

509
00:46:42,280 --> 00:46:45,520
very much more readily than small ones do.

510
00:46:45,520 --> 00:46:47,680
And there's another reason.

511
00:46:47,680 --> 00:46:52,600
Now, I am bright yellow going into white,

512
00:46:52,600 --> 00:46:56,000
which shows that I'm losing a great deal of my heat.

513
00:46:56,000 --> 00:47:00,360
But she, on the other hand, is very much darker,

514
00:47:00,360 --> 00:47:05,120
and that is because she has an internal layer of fat,

515
00:47:05,120 --> 00:47:10,240
an insulating layer just beneath the shell, which wraps round her body.

516
00:47:12,400 --> 00:47:16,560
The leatherbacks are the only reptiles in the world

517
00:47:16,560 --> 00:47:19,240
to have this kind of insulation.

518
00:47:28,320 --> 00:47:33,280
Her eggs laid, she fills in the hole with sand.

519
00:47:35,080 --> 00:47:38,320
And now she's on her way back to the sea.

520
00:47:40,000 --> 00:47:43,360
Life in cold blood has been a great success.

521
00:47:43,360 --> 00:47:48,480
It has, after all, endured for some 350 million years.

522
00:47:50,000 --> 00:47:51,840
But how did it all begin?

523
00:47:51,840 --> 00:47:55,320
To find the answer to that, we have to go back in time

524
00:47:55,320 --> 00:47:56,880
and back to the water,

525
00:47:56,880 --> 00:48:02,400
to the age when strange fish were hauling themselves up onto the land,

526
00:48:02,400 --> 00:48:05,920
fish that were the ancestors of the amphibians.

527
00:48:19,720 --> 00:48:24,800
Amphibians and reptiles are not easy creatures to film.

528
00:48:24,800 --> 00:48:27,880
They certainly do interesting things,

529
00:48:27,880 --> 00:48:32,360
but they also spend a great deal of time doing nothing much.

530
00:48:33,960 --> 00:48:39,760
We needed the help of scientists who really understood these creatures.

531
00:48:39,760 --> 00:48:44,520
Some workers have spent over 20 years studying their animals

532
00:48:44,520 --> 00:48:47,000
both in the lab and in the field.

533
00:48:47,000 --> 00:48:49,960
They investigate the lives of their chosen species

534
00:48:49,960 --> 00:48:54,920
using all kinds of gear, some sophisticated,

535
00:48:54,920 --> 00:48:57,760
some perhaps less so.

536
00:49:06,360 --> 00:49:08,920
With their help we had a rare chance

537
00:49:08,920 --> 00:49:12,360
to get under the skin of some of our subjects.

538
00:49:20,120 --> 00:49:26,200
Madagascar was going to be a very important location for us.

539
00:49:26,200 --> 00:49:28,800
It's a huge island, 1,000 miles long,

540
00:49:28,800 --> 00:49:31,120
with a great variety of habitats,

541
00:49:31,120 --> 00:49:33,600
and it's extraordinarily rich in reptiles.

542
00:49:38,800 --> 00:49:42,440
I first went to Madagascar back in 1960

543
00:49:42,440 --> 00:49:46,000
filming for a series called Zoo Quest.

544
00:49:48,920 --> 00:49:51,920
Back then I was trying to film all kinds of creatures,

545
00:49:51,920 --> 00:49:56,600
including the monkey-like lemurs and many rare birds.

546
00:49:56,600 --> 00:50:00,800
But I was particularly fascinated by the island's chameleons.

547
00:50:03,800 --> 00:50:07,920
There are, in fact, more species of chameleons in Madagascar

548
00:50:07,920 --> 00:50:11,040
than in all the rest of the world put together.

549
00:50:14,200 --> 00:50:17,520
There is one, the pygmy leaf chameleon,

550
00:50:17,520 --> 00:50:20,600
which was said to be only an inch or so long.

551
00:50:20,600 --> 00:50:23,320
I yearned to see it, but I never found it.

552
00:50:26,000 --> 00:50:32,200
Now I was back, and this time reptiles were our sole subject.

553
00:50:34,680 --> 00:50:37,480
Although Madagascar is only separated

554
00:50:37,480 --> 00:50:40,840
from the east coast of Africa by 300 miles of sea,

555
00:50:40,840 --> 00:50:43,360
its people, and particularly its animals,

556
00:50:43,360 --> 00:50:46,520
are very different indeed from those on the continent,

557
00:50:46,520 --> 00:50:50,240
with hundred of species that are found nowhere else in the world.

558
00:50:51,800 --> 00:50:54,880
Once again, I was in search of chameleons.

559
00:50:57,120 --> 00:51:00,720
Then, all television was black and white,

560
00:51:00,720 --> 00:51:04,760
but now I could film and record chameleons in colour,

561
00:51:04,760 --> 00:51:06,880
and what colours they have!

562
00:51:24,800 --> 00:51:27,960
We had come in the rainy season,

563
00:51:27,960 --> 00:51:30,880
when most creatures, including reptiles, tend to breed

564
00:51:30,880 --> 00:51:34,960
and are therefore particularly active and interesting.

565
00:51:35,960 --> 00:51:39,240
And this time I had the help of Bertrand Razafimahatratra,

566
00:51:39,240 --> 00:51:44,200
a Malagasy naturalist who's made a particular study of chameleons.

567
00:51:44,200 --> 00:51:46,600
He's worked on them for over ten years

568
00:51:46,600 --> 00:51:48,640
and knows most kinds very well.

569
00:51:48,640 --> 00:51:53,960
I asked him about the pygmy species that had fascinated me for so long.

570
00:51:53,960 --> 00:51:56,120
So, that really is full grown?

571
00:51:56,120 --> 00:51:58,200
Yes, full grown.

572
00:51:58,200 --> 00:52:00,280
But it's only that big.

573
00:52:00,280 --> 00:52:02,640
Yes, it's very small.

574
00:52:04,920 --> 00:52:07,840
He suggested that although chameleons

575
00:52:07,840 --> 00:52:11,880
are mostly active during the day, we should look for them at night,

576
00:52:11,880 --> 00:52:14,320
because most of them turn pale in the dark

577
00:52:14,320 --> 00:52:18,080
and are therefore easily picked out in the light of our torches.

578
00:52:23,000 --> 00:52:24,520
Ah!

579
00:52:28,000 --> 00:52:30,040
What is that?

580
00:52:30,040 --> 00:52:32,120
What species?

581
00:52:32,120 --> 00:52:33,800
This is oustelets.

582
00:52:33,800 --> 00:52:35,560
Oustelets...

583
00:52:35,560 --> 00:52:38,400
And male or female?

584
00:52:38,400 --> 00:52:40,040
- Female.
- How do you know?

585
00:52:40,040 --> 00:52:42,040
The colour.

586
00:52:42,040 --> 00:52:45,200
Oh, there's another!

587
00:52:45,200 --> 00:52:48,800
This one was far from upset at being woken up.

588
00:52:50,320 --> 00:52:51,840
Ah!

589
00:52:53,680 --> 00:52:56,240
It fed!

590
00:52:56,240 --> 00:52:58,800
That's absolutely extraordinary.

591
00:52:58,800 --> 00:53:01,320
It can't possibly feed normally in the darkness.

592
00:53:02,920 --> 00:53:07,520
It just takes advantage of our light and finds an insect. Bravo.

593
00:53:07,520 --> 00:53:10,160
Let's go and see if we can find more.

594
00:53:12,480 --> 00:53:15,280
Bertrand explained that there was another reason

595
00:53:15,280 --> 00:53:18,040
why night was the best time to look for chameleons.

596
00:53:18,040 --> 00:53:22,360
When they go to sleep, they climb to the very far end of branches,

597
00:53:22,360 --> 00:53:26,240
where they're out of the way of predators such as snakes.

598
00:53:26,240 --> 00:53:31,480
And of course that was where we found them, just as he said.

599
00:53:43,520 --> 00:53:45,520
Oh, that's a big one.

600
00:53:47,040 --> 00:53:48,560
Beautiful.

601
00:53:55,640 --> 00:53:58,440
This one is just a baby.

602
00:53:58,440 --> 00:54:00,800
And how old do you think that is?

603
00:54:00,800 --> 00:54:02,920
I think just a few days.

604
00:54:02,920 --> 00:54:05,080
A few days?

605
00:54:06,600 --> 00:54:08,960
So even when it's newly hatched,

606
00:54:08,960 --> 00:54:12,040
it knows to come to the end of the branch?

607
00:54:12,040 --> 00:54:14,040
Yes, yeah.

608
00:54:14,040 --> 00:54:18,360
Look, they chew the tip of the branch.

609
00:54:18,360 --> 00:54:21,200
Yes... They're very difficult to get.

610
00:54:21,200 --> 00:54:25,600
Of course, if it was in the day, a bird could get it, but at night...

611
00:54:25,600 --> 00:54:27,240
At night, safe.

612
00:54:28,320 --> 00:54:35,280
Back in 1960, my chameleon-hunting techniques weren't quite so expert.

613
00:54:43,640 --> 00:54:48,840
However, I did discover that if you put a stick in front of a chameleon,

614
00:54:48,840 --> 00:54:51,920
it will usually obligingly walk onto it.

615
00:55:00,880 --> 00:55:02,920
But now, with Bertrand as my guide,

616
00:55:02,920 --> 00:55:07,160
we could search for the wonderful species I'd failed to find before.

617
00:55:07,160 --> 00:55:08,760
Would they be down here?

618
00:55:11,200 --> 00:55:16,880
'It lives on the ground, almost invisible among the leaf-litter.'

619
00:55:16,880 --> 00:55:19,320
That?

620
00:55:19,320 --> 00:55:21,640
'But Bertrand spotted it.'

621
00:55:28,080 --> 00:55:30,600
How extraordinary!

622
00:55:32,120 --> 00:55:37,040
This is the pygmy leaf chameleon,

623
00:55:37,720 --> 00:55:41,480
the smallest chameleon in the world.

624
00:55:41,480 --> 00:55:45,960
- In the world!
- And probably the smallest reptiles in the world.

625
00:55:45,960 --> 00:55:47,240
Of any kind.

626
00:55:49,000 --> 00:55:53,280
You know...I'd heard about these,

627
00:55:53,280 --> 00:55:57,040
and I was here in Madagascar

628
00:55:57,040 --> 00:56:00,680
47 years ago,

629
00:56:00,680 --> 00:56:06,280
and I read about these, and I never saw one,

630
00:56:06,280 --> 00:56:10,240
and I think it was because...

631
00:56:10,240 --> 00:56:12,800
I never knew they were as small as this.

632
00:56:14,680 --> 00:56:18,600
That is absolutely extraordinary.

633
00:56:18,600 --> 00:56:22,080
It's about the size of a bluebottle,

634
00:56:22,080 --> 00:56:24,520
a blow-fly.

635
00:56:24,520 --> 00:56:27,320
And what does it feed on?

636
00:56:27,320 --> 00:56:30,200
- Small fly.
- Small flies?

637
00:56:31,720 --> 00:56:34,000
How absolutely wonderful!

638
00:56:37,040 --> 00:56:39,880
I am astonished.

639
00:56:40,160 --> 00:56:44,360
That is the most marvellous thing I have seen

640
00:56:44,360 --> 00:56:47,400
for a very, very long time.

641
00:56:47,680 --> 00:56:51,520
Finding the pygmy chameleon would not have been possible

642
00:56:51,520 --> 00:56:54,640
without Bertrand's expertise and sharp eyes.

643
00:56:54,640 --> 00:56:57,440
He's just one of the scientists who has helped reveal to us

644
00:56:57,440 --> 00:57:01,720
the secret lives of reptiles and amphibians.

645
00:57:09,480 --> 00:57:12,640
To find out more about Open University programmes,

646
00:57:12,640 --> 00:57:16,760
call 0870 787 4455

647
00:57:16,760 --> 00:57:21,600
or go to bbc.co.uk/nature.

648
00:57:26,360 --> 00:57:30,680
Next week, join me for the story of the amorous amphibians,

649
00:57:30,680 --> 00:57:32,520
the land invaders.

650
00:57:59,480 --> 00:58:02,640
Subtitles by Red Bee Media Ltd

651
00:58:03,200 --> 00:58:05,960
E-mail subtitling@bbc.co.uk