A Winning Design The Life of Mammals

This is one of the coldest places on Earth - the high Arctic.

Here, the temperature drops to 50 degrees below freezing.

If I didn't have all this specialist clothing on, the cold would kill me in minutes

and yet there are animals that live here all the time.

And one of the most remarkable is hunting just over there.

An arctic fox.

The only reason that it and I don't freeze solid is that we're both mammals,

and have the mammal's ability to use our food to heat our bodies. We're warm-blooded.

The reason that it is more at home up here than I am

is it has more of another mammalian characteristic, hair, than I have.

Its body is insulated with fur.

Warm-bloodedness is one of the key factors that have enabled mammals to conquer the Earth,

and to develop the most complex bodies in the whole animal kingdom.

In this series, we will travel the world to discover just how varied and how astonishing mammals are.

We go to Africa - where the mammals are at their most spectacular.

Here the plains are thronged

with specialist grass eaters.

And there are other mammals here too, with different tastes.

Some hunting mammals have become the fastest creatures on Earth...

..and those they hunt have had to respond or die.

Some mammals have become fearsomely strong and aggressive.

They fight for mates.

They fight for food.

Some even have to fight for a place to live.

Wherever you go, you find a bewildering variety of mammals.

Some are miniatures -

a few inches long.

Others are massive.

And the biggest of those on land are dwarfed by those in the sea.

I can see its tail -

just under my boat here. And it's coming up.

There! The blue whale!

It's the biggest creature that has EVER existed on the planet.

Mammals are as at home in the water

as they are on land.

Some lounge around on the surface...

..others prefer to do so on the beach.

We will go underground to track them,

and up into the tops of the tallest trees.

Mammals have even taken to the air and challenged the birds.

In some places, they congregate in astronomical numbers. They thrive almost everywhere.

And how they do so depends, as does so much in the life of mammals, on what they eat.

Between them, they tackle everything that's edible.

Some are very particular about their food.

Others will simply take the best of whatever's around at the time.

On top of the menu, right now, is salmon.

We will look at the lives of our closest relatives...

LAUGHS

..and they will lead us to ourselves...

..perhaps, the most successful variation

of the mammal's winning design.

To catch a glimpse of the very beginnings of the mammalian dynasty, we must travel to Australia.

I'm looking for one of the most ancient of all mammals.

It's so ancient, it shares at least one characteristic with reptiles.

It's a very elusive creature, but here, in South Australia,

there's a population that have been fitted with radio transmitters, and I can track them with this aerial.

And I've got a very strong signal.

At first glance, you might think that this mammal is some sort of hedgehog

or perhaps a porcupine,

but actually it's weirdly different

from a hedgehog, a porcupine or almost any other kind of mammal.

It's an echidna.

And you can tell that it's a mammal because it's got hair.

And only mammals have hair.

Indeed, some of its hairs have been enlarged and strengthened

and then turned into big spines,

which give it such an effective armour.

This hair helps to keep the echidna warm,

making sure that it doesn't lose valuable body heat to the cold air.

The fuel with which the echidna and every other mammal generates that heat is, of course, food.

On a cold winter's day like this, the echidna spends most of its time searching for its next meal.

Although echidnas have good eyesight and excellent hearing,

it's their sense of smell which guides them to food.

They sniff out insects and grubs,

and get at them by ripping open the nests and tunnels with their claws.

That beak-like snout pokes into holes, and then out comes a long sticky tongue

that flicks into cracks and crevices to lick up whatever's worth eating.

Echidnas are particularly fond of ants and termites,

and will even climb trees to find them.

This particular female has an unusually healthy appetite because she's about to breed.

And the way she does so is the reason why the echidna is such a truly weird mammal.

The echidna doesn't give birth to live babies. She lays an egg.

It's hidden in her fur in a shallow depression on her underside.

It's no bigger than a marble.

Inside it, a young echidna is slowly developing.

After her baby hatches, she carries it around on her underside for about 50 days,

until it begins to develop spines. She then deposits it in a burrow,

where it stays and grows for nearly seven months.

But how does she feed it during this long time?

To answer that question, we need to find the only other egg-laying mammal in the world today.

And it too lives here in Australia.

Just surfacing beside me here

is one of the most extraordinary animals.

So bizarre that, when specimens of it were first sent from Australia to Europe,

people thought it must be a fake.

But it's not.

It's real... It's alive...

It's a platypus.

That bill looks as though it should belong to a duck,

but it's not hard like a bird's beak - it's rubbery.

Like the echidna, the platypus feeds on small invertebrates,

but it looks for them underwater.

Once it's collected a mouthful, it takes them up to the surface and grinds them to a pulp.

It doesn't have teeth, but horny plates inside the bill do the job.

But how does it find that food?

Underwater, it closes its white eyelids tight, so it can't see anything.

But it has a remote-sensing device - its bill.

As it sweeps it from side to side like a metal detector,

sensors in it pick up the infinitesimal electric currents

that are given off by ALL living things.

There were very few other mammals on Earth 100 million years ago when the first platypus appeared,

but there was another animal hunting in rivers.

Birds.

As the platypus grubs around on the riverbed, it attracts fish, which the cormorant then snaps up.

Water birds are among the most ancient bird families,

so this could be a scene just after the death of the dinosaurs,

when a new kind of animal had appeared on Earth - one with warm blood and fur.

The platypus has had enough.

She's heading back home for her breeding burrow.

For there, at the end of a tunnel that may be 20 yards long,

safe in a leaf-lined nesting chamber, she's laid an egg.

Exactly what goes on inside her nest no-one really knew.

No-one had even succeeded in breeding platypus in captivity until very recently,

and, certainly, no-one at all had ever seen inside an occupied platypus's nest...until now.

We have bored, very carefully, a hole into the nest that lies below here and inserted this tube.

This is an optical probe with a little light on the end, and I can manipulate it like this...

..so that I can scan it.

If I then insert that inside this tube, I'll be able to see something

that no-one has ever seen before.

Aha. That's her in close-up.

There's her eye, her ear. It looks as though she's seen us.

Yeah, she's... She's nibbling it.

Oh, not worth eating.

She doesn't seem particularly disturbed by it.

But has her egg hatched?

I think that quivering may have something to do with feeding.

I'll move the camera and see what's going on.

Yes. And there it is - its milk.

Milk is the perfect food. It provides the growing youngster with everything it wants,

and only mammals produce milk. In most mammals, of course, it comes from a nipple,

but in this very primitive mammal, it simply oozes through the skin.

She's leaving.

Off she goes.

The end of her furry tail.

But what's that among the leaves?

And there it is. Yes. That's her baby.

I'll zoom in on it.

Now, you can see it. A tiny little grub-like creature. It's naked and blind.

On its bill is a tiny spike. That's an egg tooth that it used to cut its way out of its shell,

in just the same way as reptiles and birds do.

It can only be a few days old.

The platypus and echidna are the only mammals alive that lay eggs -

living links with the egg-laying reptiles from which mammals are descended.

They're both so well-adapted to their ways of life

that they're still very successful and are widespread in Australia.

That's an achievement - for they've been around for 100 million years,

as the fossil evidence makes clear.

Most of that evidence is just tiny fragments,

but at Riversleigh, in Northern Australia, it's a different story.

50 million years ago, Australia was much wetter than it is today, and just here was then a swampy area.

The bones of animals that died in or around those swamps

became buried in limey mud at the bottom of the pools and are now preserved in limestone.

This rock is full of bone. Here's the rectangular boney plate from the back of a crocodile.

The rest of it looks as though it's bird bone.

But the limestone in which these bones are embedded is so hard,

that the only way to get them out is to put the whole block in a bath of acid for a few weeks.

The limestone then dissolves away, and what is left is sometimes the most extraordinary bones -

beautifully preserved.

This is the skull

of an extinct platypus - about 15 million years old.

It's been called Obdurodon, which means enduring tooth,

because unlike today's platypus, which has no teeth,

this one still has them. They're the empty sockets of the molars. They're two little premolars.

But what was this place like 15 million years ago, when Obdurodon was alive?

The night sky would have been full of the calls of animals

in the surrounding lush tropical forests.

Obdurodon would have spent much of its time swimming in pools.

But in the trees there were other mammals of a rather different kind.

Marsupials.

There were many different kinds of possums - very similar to those alive today.

Down on the ground, though, there were less familiar creatures - like this large marsupial leaf eater.

Nothing like it is alive today.

There were great numbers of small mouse-sized animals which, judging from their teeth, ate insects.

Others had a taste for flesh.

Preying on these small animals -

-a marsupial lion...

-LION GROWLS

..which was certainly big enough to make a meal of an unwary Obdurodon.

As the millions of years passed, Australia began to dry out.

The rainforests retreated and were replaced by grassy plains.

And as the landscape changed, so did the marsupial mammals.

They thrived and diversified into many different species,

and are still abundant today.

They differ from the platypus and echidna in the way they reproduce.

Instead of laying eggs, they produce young

without protective shells. And this grey kangaroo is about to do so.

Out comes not a shelled egg, but a tiny underdeveloped little worm.

It weighs less than a lump of sugar,

it has no back legs, but it has forelegs,

and they are just strong enough to pull it through its mother's fur.

It's started on an extraordinary journey.

To survive, it must get to a pouch higher up on its mother's belly.

Instinctively, this tiny living particle climbs upwards

against the pull of gravity and towards the smell of the pouch.

After about three minutes, it reaches the lip of the pouch and clambers down to safety inside.

There, it clamps its tiny mouth on its mother's nipple

and takes its first meal of milk.

As it grows, the ingredients of the milk coming from the nipple change

to ensure that the infant gets exactly the nutrients it needs

for each stage of its development.

By the time it's nine months old, it's getting a bit cramped - it's time to enter the outside world.

It's almost like a second birth.

He's a little unsteady at first, but Mum offers a helping hand.

Now, he's known as a joey.

It's all a bit much for one day, and he heads back to mother's pouch.

It will be another year before he's fully independent.

Other marsupials have taken to the trees - koalas.

They too have pouches.

Indeed, it's the Latin word marsupial, meaning pouch or purse, that gives the whole group its name.

When a koala joey emerges,

it clings tight to Mother for several days

before it risks going solo.

Koalas feed on gum tree leaves - eucalyptus.

But they're hardly an ideal food. They're tough, indigestible

and full of unpleasant chemicals.

The youngster learns from Mother how to pick the palatable leaves.

But even these contain little nourishment, so koalas eat a lot

and spend almost all their waking hours doing so.

And when they're not feeding, they conserve energy - they go to sleep.

Only koalas can live on a diet of these particular gum leaves.

Australia seems to be full of difficult diets in awkward places,

but there are marsupials that can deal with almost every one of them.

The vast continent of Australia stretches from the temperate and sometimes chilly south,

right up into the tropics.

In the centre there are dry sun-baked deserts,

where it's only too easy to die from thirst.

There are mountain ranges, which in winter are crested with snow.

But the mammalian characteristics of warm blood and insulating fur

enables marsupials to cope with almost anything.

The wombat has fur so thick that it can remain active throughout winter,

even in the coldest parts of Australia.

It feeds on grass and other plants,

and the strong front limbs, with which it digs itself burrows,

are equally good at clearing away snow to find food.

Its pouch opens backwards, so that the youngster doesn't get a face full of snow, as Mum digs.

Numbats live in woodland.

But, even there, it can get quite cold at nights,

and this family are warming themselves in the early morning sun.

Fur needs to be kept in prime condition,

if it's to function as an insulator,

so grooming is essential.

These dry eucalyptus forests may look unpromising as a source of food,

but there are plenty of termites.

Numbats have just the right equipment to collect them.

That spectacular tongue has to be kept well-anointed with sticky saliva,

and numbats spend some time making quite sure that it is.

With gear like that, a numbat can collect 20,000 termites in a day.

This creature's ancestors might also have used their tongues to collect insects,

but the mammal tongue is a highly-adaptable instrument.

and now, the honey possum uses it to gather pollen and nectar.

It's one of the most specialised feeders of all mammals.

Its tongue has a brush on its tip,

which soaks up nectar from even the deepest flowers.

These boulders are home to a less-fussy marsupial, which will collect whatever food is around.

At the moment, there's an unusual delicacy -

these moths sheltering from the summer sun.

The mountain pygmy possum might be small, but it has a huge appetite.

Moths provide a fast-food snack, high in energy-rich fat,

and the pygmy possum will eat as much as it can, and put on fat to see it through leaner times.

Only the indigestible wings are discarded.

At other times, the pygmy possum lives on berries and seeds -

picking them off with its nimble fingers.

The striped possum has a particular taste for grubs.

It lives in the few fragments of rainforest

that survive in North-Eastern Australia.

It's got all that's necessary to collect them -

an excellent sense of smell, strong teeth to chew away the bark and a long sticky tongue.

But perhaps the most challenging of all Australian environments

is the arid hot desert at the continent's heart.

There is little to eat, little to drink and few places to hide...

..but marsupials have colonised this country, too.

Everybody would recognise those as kangaroos...

..but the kangaroos belong to a very big family - there are kangaroos, wallaroos and wallabies,

big ones and small ones. These are red kangaroos -

the biggest of the family. They're particularly at home in this dry country.

This can be one of the hottest places on earth,

so red kangaroos don't have to worry about keeping warm.

Their problem is overheating. All mammals can sweat to lose heat,

but water is in short supply here,

and red kangaroos only do so when they are on the move.

Instead, during the hottest part of the day, they make use of whatever shade they can find.

Wiping saliva on their forearms

helps to lose unwanted heat.

Blood vessels are close to the surface of the skin - and as the saliva evaporates, the blood cools.

They only feed in the morning and evening, when it's cooler.

When they do, it's hard not to notice the extraordinary way by which they get about.

The tail acts rather like a fifth leg,

propping up the kangaroo as it swings forwards its huge hind limbs.

It looks ungainly when they're moving slowly, but when a kangaroo senses danger,

the advantage of these unusual proportions becomes very obvious.

Hopping at full speed

a kangaroo can outpace a racehorse.

They're the only large mammals in the world that have developed this way of getting about,

but it's a very efficient way of doing so.

Tendons in the back legs act like giant springs - storing energy as the kangaroo lands

and then releasing it to propel the animal forward.

By recycling energy like this,

kangaroos can quickly cover vast distances to escape predators or to search for food and water.

It's not just out on the flat that hopping works well - some marsupials hop around on cliffs.

The rock wallaby's key to success lies in its feet.

The soles have thick corrugated skin - pads which give them a grip on every kind of surface.

The wallaby can bounce about this difficult terrain with confidence.

There's little to drink here,

and though adults get the fluid they need from their diet, growing youngsters may find that difficult.

This youngster is after an extra drink. Rock wallabies are able to bring up fluid from the stomach

to ensure that their young don't go thirsty. It's a special adaptation to this arid environment.

Grey kangaroos live out on the relatively well-watered grassy plains.

They are among the most sociable of all Australian marsupials,

but living in groups can lead to problems in getting on together.

Last season's joeys are fast approaching independence,

which means that their mothers will soon be ready to mate again.

Males use their sense of smell to find out if a female is sexually available,

and will court her for several days.

Having found one who seems to be promising,

a male stays close to her side to try and ensure that HE, and no other male, mates with her.

The most dominant male

is likely to be the one to father most of the next generation,

and that is worth fighting for.

Joeys also fight, but it's just play boxing -

a way of learning skills that will be important in later life.

But it's not always a fair fight.

Fortunately, this little one still has Mother to see off the neighbourhood bully.

Marsupials first appeared about 100 million years ago,

towards the end of the age of the dinosaurs.

Then, Australia was part of a great supercontinent,

but as the millions of years rolled by, that continent began to split apart. One fragment drifted south -

Antarctica. As it got closer to the South Pole, so it got colder, became covered with snow and ice

and its animal inhabitants died out.

A second part was Australia.

It drifted north and got warmer.

And here marsupials flourished.

But there was a third part. It too drifted north.

It too had a population of marsupials. And they're still there.

That was South America.

It may well have been in this region of the supercontinent

that the marsupial mammals first appeared. Many died out, but there are STILL a lot of survivors.

This is one of the most elusive of them.

It lives in the streams of the Amazon forest

and operates only at night -

getting around in the blackness by feeling its way with its front paws and luxuriant whiskers.

It's the yapok or water opossum.

These pictures,

taken with infra-red cameras, may well be the first time it's been filmed in its natural environment.

It's hunting for fish and crustaceans.

Its fur is so thick that its skin doesn't get wet.

It has webbed feet to propel it through the water.

It's too dark for even the sharpest eyes

to see very much.

The yapok relies on its acute sense of smell and hearing to locate its food.

It swims with its arms apart, groping for its prey with its highly-sensitive fingers.

It usually takes its catch

to the shelter of nearby vegetation to devour it.

But it doesn't only feed in the shallows.

The yapok has a large territory,

and there are many deeper pools in which to swim.

Underwater, it swims with its eyes shut, like the platypus,

and hunts entirely by feel.

The female yapok can also shut her pouch, and does so with such muscular strength

that water doesn't get in and drown her babies, though, no doubt, they must be close to suffocation

after a few minutes of fishing.

It's been a good night's hunting,

and the yapok retreats to its burrow as day breaks.

The yapok is the only aquatic marsupial in the world.

Most of the marsupials in Central and South America live high in the canopy of the rainforest.

Just how many there are up there no-one really suspected,

until scientists started using cranes, like this one.

Apparatus like this gives such easy access to this high canopy

that it's now possible to get an accurate idea

of just how rich wildlife is up here.

While we might think of Australia as the land of the marsupials, in places, this rainforest

may have more of them than any other kind of mammal.

Most of them are strictly nocturnal.

And though they are abundant, they, like everything else in these forests, can be difficult to spot.

Many are similar to this woolly opossum -

tree dwellers with few specialisations and a broad diet,

which can include flowers, fruit and insects.

These marsupial mammals, of course,

reproduce in just the same way as their Australian relatives.

They give birth to babies at a very early stage in their development.

Their pouch isn't as well formed

as that of a kangaroo or a koala,

but their young survive, clinging to their mother's underside.

Marsupial mammals dominate Australia,

and flourish in the forests of Central and South America,

but, alongside them, are living a different kind of mammal - a kind to which we ourselves belong.

And it's only that kind that you find everywhere else in the world.

The plains of Africa, for example, have an abundance of mammals,

but not one of them is a marsupial.

They all reproduce in a fundamentally different way.

This wildebeest has nourished her baby within her

by means of a remarkable organ on the wall of her womb - a placenta.

It's a circular pad, rich in blood vessels, that is connected to her baby by the umbilical chord,

through which she has fed her growing youngster.

Blood vessels from the baby run up through the chords of the placenta,

and pass so close to those of its mother,

that they're able to absorb nutrient from her blood and carry it back to the unborn infant.

But all this is about to change.

Giving birth to such a large highly-developed baby places great strains on the mother.

It's pretty traumatic for the baby, too.

There's a great advantage in being born this way.

There are plenty of animals around for whom a new-born calf

would make a welcome meal.

But this mammal baby, reared with the help of a placenta, is able to get to its feet

within minutes of its birth.

And while it's finding its balance, its mother is there to defend it.

Now, the baby can be fed,

in the same way as all mammal babies, with its mother's milk.

Placental babies may still have months, even years to go,

before they are fully independent.

Those early months, when they were protected in their mother's body,

have given these babies an invaluable start in life.

So whether mammals lay eggs or give birth to live young,

whether their babies develop in a womb or in a pouch,

they've managed to live almost everywhere.

The warm-blooded, furry, milk-producing, mammalian body, in all its multitudinous variations,

really is a winning design.

The duck-billed platypus seems to me

just about the most extraordinary animal alive in the world today.

I first tried to film it some 25 years ago for Life On Earth.

We offered a generous grant to any scientist who could work out

how we could peek inside the breeding burrow of a platypus.

There were no takers. Everyone said it was quite impossible.

This time, with new technology, we've managed to do just that.

Europeans first encountered the extraordinary platypus in 1798.

200 years later, we barely understand even the simplest aspects of its life.

Piecing the evidence together has proved a fascinating detective story.

Helping us unravel the mystery is platypus scientist Tanya Rankin.

When the first platypus skin was sent to England, scientists thought it was a hoax.

And they poked and prodded and jabbed at this thing

thinking that it was a bill attached to a skin, but it was a real animal.

Some scientists took it personally that there was this mammal that did not fit their classification.

They had this rigorous idea of what a mammal, a reptile and a bird was,

and the platypus was a bit of each.

It took at least 100 years before it was confirmed that they laid eggs.

Egg-layers like the platypus or echidna, and the possums, both have a quite extraordinary birth process.

25 years ago, when filming Life On Earth, we may have failed to film the platypus birth,

but we did make progress. For the first time ever, we filmed this -

new-born opossums moving from the birth canal to the mother's pouch.

But the birth itself happens so quickly, and the babies are so small, we thought we'd missed it.

Only when we looked at the film frame by frame did we see the moment of birth in this Australian possum.

But this is a scientific image, not a natural one. That was the challenge this time around.

We've been getting pictures of what goes on in a breeding burrow or nest hole for some time.

The standard way is to set up a breeding colony, and then provide them with an artificial nest hole

in which you have preformed holes in which you can put your camera.

But that wouldn't work with duck-billed platypus. Platypus had never been bred in captivity.

It would have to be in the wild. One of the first people to do such a thing was Simon King,

who worked with another creature that lives beside rivers and burrows holes in the bank.

Not a mammal, but a bird - the kingfisher.

How do the two compare? Kingfishers are brightly-coloured spectacular birds -

not common, but very conspicuous. Not so, the platypus.

Platypuses are really difficult to see in the wild. They're brown, they come out at dusk -

very low profile in the water. So you could be walking past one and you wouldn't even know it.

They live in similar places. This a typical platypus river,

while Simon found his kingfishers in a Somerset peat cutting.

When an adult bird flies into a hole carrying a fish, you know she's got young inside,

but that's not possible with a platypus. Because a female feeds her young with milk,

you can't tell whether one is a mother or not. Tanya needed technology to locate a nest burrow.

I work with radio tracking - looking at their movements

and what sort of habitat use they have of the river.

I track them to their burrows during the day and find out where the nesting chambers are.

Once Tanya had located a burrow,

Mark Lamble handled the camera work.

Birds are a joy. Once they have chicks, their bond is very strong

and they'll return to the nest.

With patience and care, you can use large-scale methods to look inside that nest.

The platypus would be far more sensitive to disturbance.

This meant that it was one turn at a time for Mark.

It took 10 hours in the sun before they could insert the probe.

The first burrow wasn't used as a nest.

It's painstaking work. The final stages are similar for both teams.

Finally, Simon filmed the behaviour he was looking for.

And after three nests,

I saw inside a burrow for the first time

thanks to Mark and Tanya.

It was an incredible experience,

because it was something that had never been done before - to actually look inside a living, active burrow.

It's so hard to describe. It was just incredible.

And, finally, I saw the image I had waited 25 years to see.

Ah!

That little baby platypus, that we caught on camera,

could not have been more than 3cm long - shorter than my thumb.

The colour of it just amazed me.

It never occurred to me that you'd get a magenta platypus. It was astounding.

I learnt a lot about the workings inside a burrow.

Even the structure of the nest, with the way the leaves lie, what they're made of,

gave me a better understanding of the ingenuity of these animals.

Although we've discovered a great deal about the platypus in recent years,

we still don't fully understand the function of that extraordinary feature, its bill.

It's rubbery, covered in skin with a good blood supply and a lavish network of nerves.

The platypus brain has a larger area receiving nerves from the bill than either its eyes or ears.

So what is the bill detecting?

An early naturalist, Harry Burrell, always thought that platypuses had to use some sort of a sixth sense,

because they close their eyes, ears and nostrils underwater,

yet they can capture tiny prey, such as insects and shrimp.

It wasn't until 1986 that scientists ran experiments with platypuses

just using a nine-volt battery, to see if platypuses could sense that.

They were astonished at the results. This sensory system has not been found in any other mammal.

It's called electroreception -

and the detectors are tiny pits on the bill.

Magnified 1,000 times, this is what they look like.

They're incredibly sensitive -

detecting electrical currents that are given off by muscle activity

and that carry very well in water.

The tail flick of a shrimp can be picked up by the platypus.

They use electroreception for hunting prey, but also for navigation underwater.

They do this triangulation thing with the electrical sense

and then this delayed physical movement of the water, and they pick that up with these bills

and they manage to collect up enormous amounts of food.

They can eat up to 25-30% of their body weight every night. It's tiny insects that they are picking up.

The platypus can read a riverbed in a very different way to us.

Even trying to visualise how the system works is a challenge.

It shows that, far from a joke, the platypus is a unique animal

that's developed some very special and very successful features

at the dawn of the life of mammals.

In the next programme of The Life Of Mammals, we meet insect hunters.

These mammals race to conquer the planet,

and they now include the most bizarre mammals ever to walk the Earth or to take to the sky.