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00:00We human beings are very late comers to the skies, and although we might think that we're
00:21now pretty good at it, the natural world, with the help of several million years of evolution,
00:27has produced a dazzling range of aeronauts, whose talents are far beyond ours.
00:36The story of how animals managed to colonize the air is truly astonishing.
00:42First into the skies were insects. They initially had two pairs of wings, which in due course were
00:49modified in many different ways. But after having had the skies to themselves for about
00:57a hundred million years, a new group of animals took to the air, vertebrates, creatures with backbones.
01:09They faced a different challenge, for their bodies were much bigger and heavier.
01:15But eventually, they evolved several ways of solving that problem.
01:20We will travel the globe to trace the details of the extraordinary skills of the black-boned flies.
01:34Oh!
01:36This is Borneo.
01:50And here, there are still great tracts of pristine rainforest.
02:08Forest that is wonderfully rich in animals of all kinds.
02:12I am being winched up into one of the tallest trees here,
02:20in search of a creature that can give us a hint of how backbone animals first took to the air.
02:26And here, there are still great tracts of birds.
02:28And here, there are still great tracts of birds.
02:40Hidden among these leaves of this fern, high up here in the Canabry,
02:46there's a very remarkable little frog.
02:50It's a harlequin tree frog, and it's a very, very good climber.
02:58It spends most of its life up here, clambering around in the branches.
03:05Here, it's away from the numerous predators there are that might attack it down on the forest floor.
03:11But if, in fact, a predator were able to get up here to hunt it, a snake perhaps,
03:19well, the tree frog has a remarkable trick for defence.
03:36It glides.
03:37It has membranes between greatly elongated tones, so that each foot becomes a parachute,
03:45which slows the frog's descent, and so enables it to make a relatively safe landing.
03:58The vertebrates made their first forays into the air around 260 million years ago.
04:04And it's very likely that some of these pioneers use skinny membranes to control their falls,
04:10in much the same way as this little frog does.
04:13It has to be said that it's not a very good aerial navigator.
04:25It seems as though it just jumps and hopes for the best.
04:28But there are animals up here that glide around from tree to tree,
04:33which are very good navigators indeed, so good, in fact, that they can go from one tree to another,
04:40and never go down to the ground in their entire lives.
04:43One of them is a little lizard called Draco.
04:56Each male has his own little territory in the branches,
05:00and tries to attract females and worn-off rivals by flashing his dewlap.
05:13He also spreads colored flaps of skin from his flanks that, when fully extended,
05:20do more or less the same thing.
05:27But there are predators among the branches.
05:32Snakes also live up here, and they hunt lizards.
05:43But Draco's side flaps now serve another purpose.
06:13He uses them to glide by hitching forward his specially elongated ribs.
06:24And he is so skilled in the air that he can steer and land on the trunk of his choice.
06:29So, if you live up in the branches, it's less laborious and indeed safer to travel by air than to come down to the ground.
06:51But if you want to be a true flyer, you have to be able to fly not only downwards, but upwards.
06:58You have to have powered flight.
07:01This is another reptile, and one with even greater flying abilities than that little gliding lizard.
07:26You have to have powered.
07:31Today, sadly, it's extinct.
07:34This is dimorphodon.
07:52We can deduce from its fossils that it had the muscles needed to beat its wings.
07:57And computer imagery can show us what it must have looked like.
08:10Dimorphodon was one of the first large animals ever to travel by air 200 million years ago.
08:30It belonged to a group called the pterosaurs, the winged reptiles.
08:39It was probably a forest dweller and a descendant of a tree-living glider.
08:48This gliding ancestor might have had wings like those of Draco's that were made of skin
08:55and perhaps extended from its fingers down to its ankles.
09:00But pterosaurs had evolved larger wings with a hugely elongated fourth finger.
09:07The wing membrane was strengthened internally by thin rods of a stiffer tissue.
09:13There were muscle fibers, too, that enabled it to modify its contours as it flew.
09:18Looking at the wings in section reveals the secret of their efficiency.
09:25They have a rounded front edge and a sharp back edge, a shape known as an aerofoil.
09:34It works by forcing the air flowing above the wing to speed up.
09:39This faster air has a lower pressure, and the wing is sucked upwards.
09:45The larger the surface area of the wing, the greater lift it can produce.
09:54So it seems certain that pterosaurs were very competent flyers.
09:59And judging from their teeth, it seems likely that many fed on the great variety of insects
10:05that had preceded them into the air.
10:09Insects had had the skies to themselves for around 100 million years.
10:14Now, bigger creatures had arrived, reptiles.
10:24The pterosaur designed for flight proved hugely successful.
10:28And before long, they had spread out of the forests into new environments.
10:34And some became monsters.
10:44The first large animals to fly were winged reptiles, pterosaurs.
10:55They appeared in forests around 220 million years ago.
10:59As they became more successful, they ventured into more open country and spread around the world.
11:09A great number of them lived and fed near water.
11:12We know this because fossils of many species occur in rocks that were once mud at the bottom of lakes and shallow seas.
11:20And this one shows the skeleton of an animal that 150 million years ago fell to the bottom of a shallow lagoon.
11:31This is its head, here's its backbone, and tail, hind legs.
11:39And here, stretching from these long, extended finger bones, are its wings.
11:46And this fossil is particularly remarkable because it shows an impression of the membrane in extraordinary detail.
11:54You can see every little tiny fold.
11:57You can judge how an animal lived by its skull.
12:03And this one had these long jaws with forward-pointing teeth.
12:10And we think that that indicates that it lived by skimming across the surface of the lagoon
12:15and snatching up fish which impaled on those teeth.
12:19The pterosaurs diversified into a huge variety of forms.
12:32Many seem to have been particularly skilled at soaring and gliding over the oceans, looking for fish.
12:39Some developed huge head crests that were probably colored and used for display during courtship.
12:45And a few became very big indeed.
12:53This species had a wingspan of over 20 feet, seven meters.
13:03But not all pterosaurs lived in the forests or near water.
13:07An open, arid landscape like this one was the likely home of one of the most extraordinary.
13:13Around 70 million years ago, a pterosaur appeared that was of truly colossal proportions.
13:30That was one of the largest creatures that has ever flown.
13:52It was the size of a small aeroplane.
13:54And it was called Quetzalcoatlus.
14:06Its immense wingspan allowed it to ride on the currents of warm air that rise up from sun-heated land.
14:12It could then glide great distances, searching for food.
14:22Small creatures like lizards, or the dead bodies of much larger ones, dinosaurs.
14:28But the pterosaurs, with their wings of toughened skin, weren't the only group of reptiles to make it into those ancient skies.
14:52About 150 million years ago, another reptilian group appeared on the planet that also flew.
15:05Like most reptiles, including pterosaurs, these creatures began their lives inside an egg.
15:12But they had evolved a revolutionary new design for flight.
15:25One that would usher in a remarkable, fresh chapter in our story.
15:32And unlike the pterosaurs, they're still with us today.
15:36They are, of course, the birds.
16:00Some today can provide clues about how their ancestors managed to get into the air.
16:06This is the chick of a bird found in farmyards everywhere.
16:18A bantam hen.
16:19And at this very early stage in its life, it can show us something very interesting
16:39about the origin of that crucial piece of flying equipment, a feather.
16:47Its feathers are downy.
16:50That's to say, they're made up of simple filaments.
16:53And their function is not for flight, but insulation to keep this little creature warm.
17:00And back in the Jurassic period, long before the arrival of true birds,
17:05very similar looking feathers appeared on very different animals, reptiles,
17:11dinosaurs, to be precise.
17:13To find evidence for that astonishing statement, which not so long ago was highly controversial,
17:23we're heading for China.
17:24And here I was able to see the evidence for myself.
17:33Some truly sensational fossils.
17:35Some truly sensationalism.
17:55North-east of China's Great Wall, near the borders of Mongolia, lies the Chile province of Liaoning.
18:02Here, there are great areas of rocks that were laid down as mud in the bottom of immense freshwater lakes.
18:14The bodies of animals that were swept down into these lakes were slowly entombed
18:20by the fine-grained sediment that preserved them entire and in exquisite detail.
18:25And from these rocks have come specimens that solve one of the most hotly debated of evolutionary arguments,
18:36the origin of the birds.
18:41The key specimens are now in Beijing, where they've been delicately prepared under the microscope.
18:47They have been studied here by one of the world's greatest dinosaur experts, Professor Xing Shu.
18:59First, he showed me one of his oldest specimens, part of a dinosaur's arm.
19:06But thanks to the fineness of the mud of those ancient lakes, there is more here than just bones.
19:12If you see it, you see it, this species is called a Beipyalthaurus.
19:16So Beipyalthaurus is an animal of like two or three meters long, so quite a big animal.
19:22And here's the arm, hand, you see here, dark, fundamental structures,
19:31along the arms and the hand, actually primitive feathers.
19:36And those feathers are very simple, very, very simple.
19:42So we believe they represent the very primitive stages for feather evolution.
19:49These simple strands were made of the same material as the feathers of today's birds.
19:55They were relatively thick and must have been quite stiff,
19:59so they would have stuck out beyond the dinosaur's arm.
20:02Behind them were shorter strands that covered its whole body.
20:07Like the down on the chick, these might have kept the dinosaur warm.
20:12But those longer strands most likely had a different function.
20:17Clues to what that might have been can be found on an even more extraordinary fossil.
20:24These claws and finger bones belong to a creature called Chordypteryx.
20:28The long dark shapes around them are the remains of feathers.
20:37The single strands are here rather more complex.
20:42They had barbs, thin filaments, attached to either side of a central rod.
20:48This looks more like a bird's feather.
20:51Chordypteryx had around 26 of them along each arm.
20:55This may look like a wing, but the feathers were not very long.
21:03And when you compare them to the size of this creature's body and its long legs,
21:09it's clear that they weren't big enough to enable Chordypteryx to fly.
21:15So what were these feathers for?
21:19Microscopic examination has revealed that they were colored and patterned.
21:24So maybe they were used for display, perhaps to wave around during courtship to attract a mate.
21:32But then it seems that they also helped the dinosaur in a different way.
21:40We can find a hint of how they might have done this
21:43by watching the way some young birds use their first feathers today.
21:47These are 10-day-old pheasant chicks.
21:55Their feathers are not yet fully developed.
22:01At this stage, they're similar in structure to the feathers on that dinosaur,
22:05Chordypteryx, and grow in a line along each arm in much the same way.
22:09But these early feathers are also too short to enable these creatures to fly.
22:19Nevertheless, they're very helpful.
22:21Pheasant chicks hatching nests on the ground, but they soon need to roost high up,
22:28where they'll be safe from predators.
22:30Pheasant chicks hatching nests on the ground, but they'll be safe from the ground.
22:38Flapping these simple wings gives the chicks a little extra lift to help them climb into a tree.
22:44And when the time comes to return to the ground, those first feathers again are a help.
23:09They don't provide a large air-catching surface, but they're enough to slow a chick's fall.
23:15And make that landing just a little softer.
23:23Maybe the feathers that had initially kept the dinosaurs warm now also helped them to get into the air.
23:34And then, only a few years ago, the mudstones of Liaoning produced yet another extraordinary fossil.
23:44It's been named Microraptor, and it's clearly a small dinosaur.
24:02But this specimen is particularly exciting because of its feathers.
24:10Feathers on the forearms there, feathers on its hind limbs,
24:15and even feathers right at the end of its very long tail.
24:22But there's something that makes these feathers different from any other feathers we've seen
24:27on dinosaurs before.
24:30They are narrower on one side of the quill than on the other, just like bird feathers.
24:40Microscopic structures within them suggest that they had flashes of iridescence.
24:45So these feathers were probably used for display.
24:50But their asymmetric shape is characteristic of flight feathers.
25:02The air flowing over the narrow front of the feather can produce lift.
25:07So could this strange-looking dinosaur with feathers all over it actually fly?
25:29Some people think that those feathers on its hind legs would have made it rather difficult for it
25:40to walk around on the ground, and that it would have been more at home climbing.
25:44And those claws on the fingers and toes were obviously very helpful in climbing up tree trunks.
26:02But those aerodynamically shaped feathers certainly suggest that its arms were being used as wings.
26:21This four-wing dinosaur must have been a really extraordinary animal.
26:34Its front wings were broad enough to enable it to collide,
26:38and its muscles on the chest were sufficiently strong to enable it to flap every now and then
26:45and help it on its way.
26:46But the wings on the hind legs were probably not held spread out,
26:52but kept beneath the body to help the animal to steer.
27:01Now, clearly, these dinosaurs were on their way to join the pterosaurs in the sky.
27:07And then, around 130 million years ago, the true birds appeared.
27:21And here, on a loch in Scotland, are some of the most majestic of those that are around today.
27:29Hooper swans.
27:37Hooper swans.
27:38These particular birds were in contact with human beings from the very first moment that they hatched.
27:45So they allow me to get really close to them.
27:52The small feathers on their bodies are still essential for keeping their owners warm.
27:55But this one is a wing feather.
28:00It's extremely strong, but very light.
28:03And the filaments on either side of the quill, the barbs, zip together to form a continuous surface,
28:11which is strong enough to hold the air.
28:14But if the air is to support a big bird as it flies, it has to move over the wing very fast.
28:22And in order for that to happen, these swans will move at speed across the surface of the water,
28:30like an aircraft taxiing before takeoff.
28:52And if the air is to support a big bird as it flies, I'm waiting to drop a bullet.
28:54And then the air comes to the ice.
28:56If it fires, I'm in trouble.
29:00And then to hear a little bit of the air coming out of the mountain,
29:07when I see the air coming out of the岸, then I see the air coming out of the sea.
29:15And I see that amazingasses were so complicated.
29:16When you're close up to a flying bird like this, you can see how the wonderful piece
29:35of complex engineering their wings are, able to change their shape and their beat to respond
29:41to every little change in the currents of the air around them, and so propel them forward
29:48and lift them upwards.
29:58So how do birds' wings actually work?
30:03If we slow them down, we can watch in detail the many subtle changes they make as they move
30:08up and down.
30:11The feathers overlap to form a smooth, contoured surface that extends far beyond the bones
30:17within.
30:23With a curved leading edge at the front and a sharp trailing edge at the back, they have
30:28the classic aerodynamic shape that produces lift.
30:32They are aerofoils.
30:41With each downward beat, the air pressure above is reduced so that the bird is sucked upwards.
30:52Wings like these, consisting of jointed bones covered with closely fitting feathers, can make
30:58very subtle, delicate movements.
30:59The feathers slide over one another so that when the wing changes shape, there is no loss
31:08of smoothness and the contour.
31:10When the swan slightly retracts its wings in between beats, the sliding feathers ensure that the aerofoil still
31:23produces lift.
31:24And the birds' bodies have become modified in another way.
31:35They've become lightweight.
31:37The dinosaurs' heavy bony jaws lined with teeth have been reduced to a lightweight beak of horn.
31:48The bony tail has shrunk to a stump, merely an attachment point for the tail feathers.
31:53And many of the bones within the body have become hollow, so reducing weight even further.
32:05The result is an extremely efficient, lightweight flyer.
32:11We're travelling around 30 miles an hour now, and yet these birds could easily accelerate
32:18and leave us behind if they wanted to.
32:20So feathers, since their first appearance on the bodies of dinosaurs, have acquired
32:49several different functions.
32:52Initially, they served to keep their owners warm.
32:56Then, some grew large and acquired colour, and were probably used in courtship displays.
33:06And only then, after millions of years, were they used to help their owners get into the air.
33:11But the birds were not the last animals to acquire the ability to fly.
33:25When the tennosaurs vanished, together with the dinosaurs, there was room in the skies for yet another aeronaut.
33:32And one appeared with yet another kind of wing.
33:43Animals on our planet have flown for over 320 million years.
33:49First came insects, then a group of winged reptiles, pterosaurs, and next, birds.
33:55Then, around 66 million years ago, came the global catastrophe that triggered the disappearance of a vast proportion of the animal life of this planet.
34:12An asteroid hitting the Earth was the most likely cause of this mass extinction.
34:25In the devastation that followed, the dominant creatures of that age, the dinosaurs, disappeared.
34:36The pterosaurs were completely wiped out.
34:39And only a few of the birds survived.
34:45The skies, for a short period, must have been relatively empty.
34:49But then, a new kind of flying animal appeared.
35:00Now was the chance for a group of furry, warm-blooded little creatures
35:05that had been scampering around the feet of the dinosaurs for several million years.
35:10They were the mammals.
35:14The first of them to take to the air were doubtless gliders.
35:17And one mysterious creature, still alive today, can give us an idea of what they were like.
35:27It lives in the rainforests of Borneo, and it's called the kubong.
35:35It has an enormous blanket of furry skin that stretches from the side of its head
35:40right down to the very tip of its tail.
35:42But to see how it travels through the air, we must wait until nightfall.
35:46To see how it travels through the air, we must wait until nightfall.
36:16As soon as it lands, it regains the height it's inevitably lost by clambering up the trunk.
36:19As soon as it lands, it regains the height it's inevitably lost by clambering up the trunk.
36:23As soon as it lands, it regains the height it's inevitably lost by clambering up the trunk.
36:30As soon as it lands, it regains the height it's inevitably lost by clambering up the trunk.
36:36It's by far the most skilful of the forest gliders and can travel over a hundred meters in one leap.
36:55It's undoubtedly a very ancient animal, and some believe that it may well have survived virtually unchanged,
37:18from that time long ago when mammals first took to the skies as gliders.
37:24But soon the mammals did better than that.
37:45This is a fossil that dates from about 52 and a half million years ago.
37:56It has its head with very well-developed teeth, backbone and ribs, and long tail, hind legs,
38:05and most important of all, from our point of view, hands with enormously elongated fingers.
38:12And there was skin between those fingers.
38:16These were wings and they could flap.
38:19This is the earliest fossil yet discovered of a bat.
38:26We have no evidence to show exactly how bats' fingers first began to lengthen to support their wings.
38:33But we can understand how those early bats flew by looking at their modern descendants.
38:50These are some of the largest.
38:53They're so big that they're often called flying foxes.
39:10And they have a wingspan of over a meter.
39:13When you slow a bat's flight down like this,
39:23you can see that its four fingers are spread wide on the downstroke,
39:27keeping the membrane wide and taut,
39:29and then come together on the upstroke with just the thumb at the top free.
39:36Boy.
39:37The Bayouva will stand before it is its protruding towards the top free.
39:40This folding of the wings reduces the bat's air resistance between each beat.
39:50.
40:05To maximize the size of its wing,
40:08the back edge of the wing membrane is attached to the ankles.
40:15That's roost by hanging upside down.
40:20And this is how they tend to spend their days.
40:26It's thought that the first mammals were nocturnal.
40:29That, doubtless, was the best thing to be,
40:31out of the way of the dinosaurs
40:33that were rampaging around during the day.
40:37So the bats continued the nocturnal habit of their ancestors.
40:41And they had also inherited the acute senses
40:44needed to move around at night.
40:46Eyes specially adapted to operating well in low light.
40:50And an acute sense of smell
40:52that enables them to find food in the dark.
40:55In any case, birds already dominated the daytime skies.
41:06With their wings of skin and nocturnal senses,
41:09the bats became a huge global success.
41:12Today, there are over 1,100 species of them.
41:18That's over a fifth of all mammals.
41:24So by 50 million years ago,
41:26three groups of large, backbone animals
41:29had joined the insects in the air.
41:32The pioneers were reptiles, pterosaurs,
41:41with membranes of skin stretched from elongated fingers.
41:52Then came a group of dinosaurs
41:55that acquired feathers and became birds.
41:58But when the pterosaurs and dinosaurs were swept away
42:03in a global extinction event,
42:06the stage was set for the birds
42:08and the newly-emerged bats between them
42:11to take command of the skies.
42:15Each of these two groups had evolved its own techniques
42:18for getting into the air,
42:20and each was destined to bring their skills
42:23to astonishing extremes.
42:27Next time, we'll see how birds adapted and diversified
42:31to become the remarkable creatures we see in our skies today.
42:40Lethal hunters.
42:48Formation flies.
42:50And aerial acrobats.
42:56We explore how the bats developed a new super-sense
43:00that enabled them to hunt in the pitch-blackness of the night.
43:05And we visit one spectacular place
43:08where the battle for the skies
43:10between insects, bats, and birds still continues.
43:20It's fair to say nobody does it better than Sir David Attenborough.
43:32He returns to Sky 1 HD and Sky 3D next Thursday at 8
43:36for the concluding part of Conquest of the Skies.
43:39And if you're looking for a bit of spice to your Thursday night,
43:42we've got high drama in the brand-new season of Scandal.
43:45It starts at 10 on Sky Living HD.
43:47and if I ask them,
43:48I'm a mystery to my mother,
43:50who is a mystery to my master.
43:50But we are not used in the way I should look for it.
43:52And I'm a mystery to you,
43:52the way I have seen these things.
43:52That is a blessing.
43:53And through the weekend,
43:54I'm a mystery to the sky,
43:54I see a mystery to my master,
43:56and a hacker,
43:57and a professor said master.
43:57So that is an amazing thing,
43:58it's a special thing.
43:59So that has a great night on your side,
43:59because I look for a heart,
44:00and I see you on my side.