0:00:03 > 0:00:05'Of all the animals that live on our planet,
0:00:05 > 0:00:09'one extraordinary group dominates.
0:00:10 > 0:00:12'It has produced the largest...'
0:00:12 > 0:00:15The blue whale!
0:00:15 > 0:00:17'..the fastest,
0:00:17 > 0:00:19'and the most intelligent creatures
0:00:19 > 0:00:21'that have ever lived.
0:00:21 > 0:00:24'They're known as the vertebrates,
0:00:24 > 0:00:28'and they all share one vital feature.
0:00:28 > 0:00:30'A backbone.
0:00:33 > 0:00:37'Now, I want to travel back in time to explore their ancient origins.
0:00:40 > 0:00:45'And investigate the key advances that led to their amazing success.'
0:00:46 > 0:00:48Advances that can also reveal
0:00:48 > 0:00:52how we came to acquire the characteristic features
0:00:52 > 0:00:54of our own vertebrate bodies.
0:00:54 > 0:00:59Jaws that bite, lungs that breathe, ears that can hear.
0:00:59 > 0:01:02Because the story of the rise of animals
0:01:02 > 0:01:07is also the story of how you and I came to be as we are.
0:01:10 > 0:01:16'I will find evidence in a series of spectacular fossil discoveries
0:01:16 > 0:01:19'around the world and within living animals.'
0:01:21 > 0:01:23That's it.
0:01:23 > 0:01:25'With the latest scientific analysis,
0:01:25 > 0:01:29'we can bring our ancient ancestors back to life.'
0:01:31 > 0:01:35And understand how, over 500 million years,
0:01:35 > 0:01:41they developed the bodily features needed to master the seas...
0:01:42 > 0:01:47..colonise the land, and take to the skies.
0:01:50 > 0:01:54This is the story of the rise of animals.
0:02:16 > 0:02:18The history of life on Earth
0:02:18 > 0:02:21has been known in outline for many years,
0:02:21 > 0:02:25but there were a number of tantalising gaps in it,
0:02:25 > 0:02:28particularly in the history of animals with backbones.
0:02:28 > 0:02:33When, for example, did the first signs of a backbone appear?
0:02:33 > 0:02:37And is it really true that dinosaurs developed feathers
0:02:37 > 0:02:39and turned into birds?
0:02:39 > 0:02:41Well, in recent decades,
0:02:41 > 0:02:45answers have been found to those extraordinary questions,
0:02:45 > 0:02:49here, in China, and I'm here to look at them.
0:02:54 > 0:02:58China is the new frontier for fossil discoveries.
0:03:01 > 0:03:04Excavations here are unearthing links in the story
0:03:04 > 0:03:07of the vertebrates that have so far eluded us.
0:03:15 > 0:03:19I have long wanted to see this sensational evidence for myself.
0:03:21 > 0:03:25I will be travelling to the frozen north of the country,
0:03:25 > 0:03:27and to the capital, Beijing.
0:03:30 > 0:03:33But to search for the first step in our journey,
0:03:33 > 0:03:37I'm heading south, to Yunnan Province.
0:03:41 > 0:03:46This is the site of a thrilling discovery that has given us
0:03:46 > 0:03:48new evidence for the very first vertebrates.
0:03:53 > 0:03:57Excavators here are exposing a rich seam of rocks
0:03:57 > 0:04:01known as the Chengjiang fossil beds.
0:04:01 > 0:04:05Remarkably, they contain the remains of creatures that once swam
0:04:05 > 0:04:08in the ancient seas 525 million years ago.
0:04:11 > 0:04:15'Palaeontologist, Hou Xianguang, was the first to discover
0:04:15 > 0:04:17'the unique features of these beds,
0:04:17 > 0:04:20'an astonishing perfection of preservation.'
0:04:20 > 0:04:21Are these mouth parts?
0:04:21 > 0:04:25- Yeah.- That's very beautiful.
0:04:25 > 0:04:27You can see it's got striations on it.
0:04:29 > 0:04:32'To find complete bodies like this is extremely rare.'
0:04:35 > 0:04:37When an animal dies in the sea,
0:04:37 > 0:04:41normally bacteria destroy the soft parts very quickly
0:04:41 > 0:04:46so that all we can find afterwards are the hard parts, bone or shell.
0:04:46 > 0:04:49Why that didn't happen here in this particular part
0:04:49 > 0:04:52of this particular sea is something of a mystery.
0:04:52 > 0:04:55It may be something to do with the lack of oxygen,
0:04:55 > 0:04:59but whatever it was, it has given us a privileged view
0:04:59 > 0:05:01into one of the most exciting chapters
0:05:01 > 0:05:03in the whole history of life.
0:05:06 > 0:05:11The beds have so far yielded over 200 separate species.
0:05:13 > 0:05:17This was a time period known as the Cambrian.
0:05:19 > 0:05:22The land was still bare and lifeless,
0:05:22 > 0:05:26but, underwater, it was exploding into a multitude of forms.
0:05:34 > 0:05:38The major animal groups we know today were appearing on the planet
0:05:38 > 0:05:40for the very first time.
0:05:44 > 0:05:48They built their bodies entirely of soft tissue.
0:05:48 > 0:05:51Some protected and supported it with a hard outer casing.
0:05:55 > 0:05:59But none had anything that resembled a backbone.
0:05:59 > 0:06:02These were the invertebrates.
0:06:07 > 0:06:12'Then, Professor Hou and his team found one intriguing exception.'
0:06:14 > 0:06:15Oh, yes, yes, yes.
0:06:16 > 0:06:20It's a fossil called Myllokunmingia.
0:06:20 > 0:06:22But to examine it in detail,
0:06:22 > 0:06:25you've got to look at it under the microscope.
0:06:28 > 0:06:32Its features reveal evidence of a new type of support,
0:06:32 > 0:06:35not outside the body, but inside.
0:06:37 > 0:06:42This is one of about 30 specimens that have already been found
0:06:42 > 0:06:45of this tiny little creature.
0:06:47 > 0:06:53Under the microscope, it contains an extraordinary amount of detail.
0:06:56 > 0:07:02Those marks are marks that have been made by the excavator's needle.
0:07:02 > 0:07:07This is the animal itself. This is its head, the top of its back.
0:07:07 > 0:07:12And nearly every one of them have these two little black spots
0:07:12 > 0:07:16at the front, eye spots.
0:07:16 > 0:07:18Looking farther down the animal,
0:07:18 > 0:07:21there are just some striations here,
0:07:21 > 0:07:25little bars which are thought to have been the gill bars,
0:07:25 > 0:07:29the little constructions that carry blood vessels
0:07:29 > 0:07:31which enabled the animal to extract oxygen
0:07:31 > 0:07:34from the waters it flowed over and breathe.
0:07:34 > 0:07:40And behind them, farther down the animal, there are these bars...
0:07:41 > 0:07:48..bands of muscle, and they were probably attached to a gristly rod
0:07:48 > 0:07:51somewhere in the middle there.
0:07:51 > 0:07:54This is called the notochord,
0:07:54 > 0:07:57which was the forerunner of the backbone.
0:07:59 > 0:08:03Myllokunmingia is the earliest creature we know of
0:08:03 > 0:08:07that we can truly call a vertebrate.
0:08:07 > 0:08:11And it seems clear that it used its strong inner rod
0:08:11 > 0:08:15to move in an entirely new way.
0:08:15 > 0:08:20As the muscles contract, they bend the rod from side to side.
0:08:20 > 0:08:24This movement pushes against the water and creates forward thrust.
0:08:35 > 0:08:38Here was a revolutionary new way to get around.
0:08:38 > 0:08:43It allowed Myllokunmingia to roam far and wide and escape
0:08:43 > 0:08:47the dangerous invertebrate predators that were prowling the seas.
0:09:00 > 0:09:04The vertebrates would diversify over millions of years
0:09:04 > 0:09:08to create the spectacular variety of backboned creatures we see today
0:09:08 > 0:09:11in every environment on the planet.
0:09:19 > 0:09:22Fish dominate the seas, lakes and rivers.
0:09:23 > 0:09:26The amphibians live in both water and land.
0:09:28 > 0:09:32The reptiles can survive in the driest places on Earth.
0:09:32 > 0:09:35The birds rule the skies...
0:09:37 > 0:09:40..and the mammals have insulated their bodies
0:09:40 > 0:09:42to adapt to every climate.
0:09:45 > 0:09:50We humans have used our greater intelligence to overrun the planet.
0:09:53 > 0:09:55This astonishing journey
0:09:55 > 0:09:58was built on a series of key evolutionary steps
0:09:58 > 0:10:02that helped our ancient ancestors to exploit their environments
0:10:02 > 0:10:04and overcome huge challenges.
0:10:07 > 0:10:10The first of these advances was the development
0:10:10 > 0:10:13of that inner support - the notochord.
0:10:17 > 0:10:20Back in Europe, you can find a creature that represents
0:10:20 > 0:10:23the next critical step in our story.
0:10:27 > 0:10:30It lives unobtrusively and often ignored in British rivers.
0:10:32 > 0:10:37And it sheds light on the challenges those first vertebrates faced.
0:10:40 > 0:10:41Ah, there it is!
0:10:46 > 0:10:49This is a lamprey.
0:10:50 > 0:10:57You might think at first sight that it was a kind of fish, but it's not.
0:10:57 > 0:11:02It's something much, much more primitive.
0:11:02 > 0:11:07It has no fins, and even its tail
0:11:07 > 0:11:11is nothing more than a flattened blade.
0:11:13 > 0:11:16But what is most remarkable about it
0:11:16 > 0:11:19is that it doesn't really have a true mouth.
0:11:20 > 0:11:24Its mouth is just a simple hole
0:11:24 > 0:11:26with little bristles about it.
0:11:26 > 0:11:31And it feeds by sucking in water through that mouth
0:11:31 > 0:11:35and then filtering out little particles of food.
0:11:38 > 0:11:42So this little animal takes us right back to the time
0:11:42 > 0:11:46when the first animals with backbones appeared on Earth.
0:11:46 > 0:11:48It's a true living fossil.
0:11:57 > 0:12:01The first vertebrates seem to have had the same kind of mouth
0:12:01 > 0:12:03and they were almost certainly limited
0:12:03 > 0:12:05to the same kind of simple food.
0:12:08 > 0:12:12Over time, other forms evolved with different shapes and sizes,
0:12:12 > 0:12:15many of them rather larger than Myllokunmingia,
0:12:15 > 0:12:19but all of them had that very simple mouth,
0:12:19 > 0:12:23an opening at the front of the body as the lamprey has today.
0:12:23 > 0:12:26If the early vertebrates were going to really take advantage
0:12:26 > 0:12:30of the variety of food that was available in those early seas,
0:12:30 > 0:12:33they were going to have to develop a much more complex
0:12:33 > 0:12:35and powerful form of eating machinery.
0:12:39 > 0:12:43Scientists on the east coast of the United States are seeing evidence
0:12:43 > 0:12:48of this evolutionary advance, not in fossils but in living creatures.
0:12:52 > 0:12:54Maine, New England.
0:13:04 > 0:13:07Marine biologists at the University of New England
0:13:07 > 0:13:10are studying a group of fish with a very ancient ancestry.
0:13:12 > 0:13:16They build their skeletons with the same strong material
0:13:16 > 0:13:19that formed the gristly rod of the first vertebrates - cartilage.
0:13:21 > 0:13:24They're the sharks, skates and rays.
0:13:27 > 0:13:30This group appeared among the vertebrates
0:13:30 > 0:13:31over 420 million years ago.
0:13:33 > 0:13:35And that means we can use them
0:13:35 > 0:13:39to examine the development before that split of a remarkable piece
0:13:39 > 0:13:43of engineering that changed the course of evolutionary history.
0:13:44 > 0:13:46The jaw.
0:13:53 > 0:13:56If you look back on the evolutionary tree,
0:13:56 > 0:13:59you'd find that a jaw is a really important feature to have
0:13:59 > 0:14:02and it's one of the features that have made skates
0:14:02 > 0:14:06and sharks apex predators in the environments in which they live.
0:14:08 > 0:14:13A jaw hinged to the skull brought the new ability to grab food,
0:14:13 > 0:14:17then rip or grind it into digestible pieces.
0:14:19 > 0:14:22But where did this amazing piece of equipment come from?
0:14:24 > 0:14:25Scientists have found an answer
0:14:25 > 0:14:30by studying the way living vertebrates develop as embryos.
0:14:31 > 0:14:34Skates lay their fertilized eggs on the sea bed
0:14:34 > 0:14:38inside leathery cases called mermaid's purses.
0:14:38 > 0:14:43Scientists can open these up and observe them as they develop,
0:14:43 > 0:14:45fed by a generous supply of egg yolk.
0:14:49 > 0:14:52The skate embryo has a simple structure
0:14:52 > 0:14:54shared by all embryonic vertebrates
0:14:54 > 0:14:57that served as the basis of the first jaw.
0:14:58 > 0:15:01What we see are these folds...
0:15:02 > 0:15:04..and what's really interesting about this,
0:15:04 > 0:15:07is that this skate is in about...
0:15:07 > 0:15:09four months of its development.
0:15:09 > 0:15:12If we take a close look at another vertebrate,
0:15:12 > 0:15:14we can see it looks very similar.
0:15:14 > 0:15:19Here we have the head, as you can follow it down to the body.
0:15:19 > 0:15:21You also see the folds.
0:15:22 > 0:15:24Now, this is actually a human being.
0:15:27 > 0:15:31It's thought that the embryos of the earliest vertebrates looked
0:15:31 > 0:15:35much like this and that each fold developed into a gill.
0:15:38 > 0:15:42In a skate embryo, the folds furthest from the head
0:15:42 > 0:15:47keep to their original purpose and form the rigid arches of its gills.
0:15:48 > 0:15:50But the nearest fold has been adapted to form
0:15:50 > 0:15:52an upper and lower jaw.
0:15:55 > 0:15:59In a human embryo, the lower folds develop into structures that
0:15:59 > 0:16:01include the larynx and the throat.
0:16:04 > 0:16:06But the top fold, once again,
0:16:06 > 0:16:08constructs the jaw.
0:16:14 > 0:16:20The development of the jaw improved the ability to collect food,
0:16:20 > 0:16:23and those that lacked it, with a few exceptions like the lamprey,
0:16:23 > 0:16:25died out.
0:16:25 > 0:16:28But in order to collect food, you have to find it
0:16:28 > 0:16:31and that led to an improvement in swimming.
0:16:34 > 0:16:37In the Chinese capital, Beijing,
0:16:37 > 0:16:39I've been given special access
0:16:39 > 0:16:42to a newly identified missing link.
0:16:45 > 0:16:50'This tiny fossil holds clues that are just fragments and hard to spot.
0:16:50 > 0:16:53'But it's the earliest example yet found of a creature
0:16:53 > 0:16:56'with two pairs of fins.'
0:16:59 > 0:17:02It's called Parayunnanolepis and
0:17:02 > 0:17:06it's about 410 million years old.
0:17:06 > 0:17:08Its front part, like many other fish at the time,
0:17:08 > 0:17:10was covered by armour plating
0:17:10 > 0:17:12to protect it from predators.
0:17:20 > 0:17:25Underneath, you can see that it has a mouth,
0:17:25 > 0:17:29and although the lower jaw is missing,
0:17:29 > 0:17:33you can tell from marks on the upper jaw that it was once there.
0:17:35 > 0:17:40But what is most important about this is its fins.
0:17:41 > 0:17:43Just their stumps are visible.
0:17:45 > 0:17:48It had two fins at the front -
0:17:48 > 0:17:49petrol fins.
0:17:53 > 0:17:56They were shaped rather like the wings of an aeroplane,
0:17:56 > 0:17:58and they had the same effect,
0:17:58 > 0:18:01creating upwards lift through the water.
0:18:03 > 0:18:05Front fins have been found on older fish.
0:18:05 > 0:18:10But what's interesting is this is the earliest example which
0:18:10 > 0:18:13has another pair of fins at the back -
0:18:13 > 0:18:15the pelvic fins.
0:18:18 > 0:18:22This second smaller pair brought much more stability,
0:18:22 > 0:18:25helping the fish to hold its course through the water.
0:18:29 > 0:18:34This system was hugely successful
0:18:34 > 0:18:39and it made the sharks the skilful swimmers that they are today.
0:18:39 > 0:18:43So now, the vertebrates had jaws and four fins.
0:18:51 > 0:18:54To see evidence of the next crucial development,
0:18:54 > 0:18:58I'm heading out onto Lake Fuxian, in southern China.
0:19:02 > 0:19:05These waters are home to living descendants of a group
0:19:05 > 0:19:08that developed a new kind of inner support,
0:19:08 > 0:19:12a support that would have huge significance for later life.
0:19:18 > 0:19:21Here they get a lot of fish
0:19:21 > 0:19:23like this.
0:19:23 > 0:19:26It's a carp and it's very different
0:19:26 > 0:19:27from the sharks
0:19:27 > 0:19:28we've been looking at,
0:19:28 > 0:19:31because instead of having cartilage skeletons,
0:19:31 > 0:19:34carp and others like it, have skeletons that are strengthened
0:19:34 > 0:19:36with calcium phosphate.
0:19:36 > 0:19:40They're bony and most fish today have bony skeletons.
0:19:43 > 0:19:46Bone contains the main material found in cartilage,
0:19:46 > 0:19:49a long stringy protein called collagen.
0:19:51 > 0:19:54Hard crystals of calcium phosphate add strength.
0:19:56 > 0:19:58But the collagen can still flex slightly
0:19:58 > 0:20:02and prevent the bone snapping under pressure.
0:20:08 > 0:20:13These bony fish could subject their skeletons to the far greater
0:20:13 > 0:20:17forces that come from increases in speed and agility.
0:20:21 > 0:20:23They added mobile fan-shaped fins
0:20:23 > 0:20:26and assumed a multitude of different forms.
0:20:34 > 0:20:37From their simple origins over 500 million years ago,
0:20:37 > 0:20:39the sharks and bony fish
0:20:39 > 0:20:41diversified to dominate
0:20:41 > 0:20:44every underwater environment on Earth.
0:20:49 > 0:20:53There are over 35,000 species alive today.
0:21:03 > 0:21:07The strong inner bony support to the body had evolved in water,
0:21:07 > 0:21:11but it would prove most spectacularly successful,
0:21:11 > 0:21:13in a completely new environment.
0:21:22 > 0:21:25For most of the Earth's history until now,
0:21:25 > 0:21:27the land had been empty and barren.
0:21:29 > 0:21:35But around 450 million years ago, first plants, then worms
0:21:35 > 0:21:38and then the ancestors of insects began to colonize it.
0:21:40 > 0:21:44Here were rich pickings for any vertebrate that could reach them.
0:21:45 > 0:21:48The stage was set for one of the most astonishing
0:21:48 > 0:21:50leaps in evolutionary history.
0:21:52 > 0:21:55The vertebrates move onto land.
0:21:58 > 0:22:02But to achieve this remarkable feat, they would need to make
0:22:02 > 0:22:04a major modification.
0:22:06 > 0:22:10To move around on land without the support of water,
0:22:10 > 0:22:13these fish needed a way to lift their bodies
0:22:13 > 0:22:15up from the surface of the ground.
0:22:15 > 0:22:17They needed limbs.
0:22:20 > 0:22:23Scientists have recently found the earliest evidence for this
0:22:23 > 0:22:26key moment in Eastern Europe.
0:22:31 > 0:22:33Zachelmie, Poland.
0:22:37 > 0:22:40Once a quarry for building stone,
0:22:40 > 0:22:43today this is a hugely significant fossil site.
0:22:46 > 0:22:51But palaeontologist Per Ahlberg and his team aren't looking for bodies,
0:22:51 > 0:22:55they're looking for the marks the bodies left behind.
0:23:01 > 0:23:04393 million years ago,
0:23:04 > 0:23:06this was the soft muddy floor
0:23:06 > 0:23:08of a tropical lagoon.
0:23:08 > 0:23:11You can still see mud cracks here from an episode
0:23:11 > 0:23:14when the lagoon dried out and the mud all flaked up.
0:23:17 > 0:23:20Over millions of years, the mud solidified into layers of rock,
0:23:20 > 0:23:24which were then tilted by movements in the Earth's crust.
0:23:27 > 0:23:31By carefully exposing each layer, Per and his team have been
0:23:31 > 0:23:34able to uncover a series of intriguing tracks.
0:23:36 > 0:23:38There are three big dimples in the rock.
0:23:38 > 0:23:43There's one here, one here and one down by my feet.
0:23:49 > 0:23:51These are not erosional hollows,
0:23:51 > 0:23:53it's not like rock has been scooped away, something's been
0:23:53 > 0:23:56pressed into the surface of the mud while it was still soft.
0:23:56 > 0:23:59You can see that from the internal texture here,
0:23:59 > 0:24:03but also from the fact that you've got a slightly raised rim
0:24:03 > 0:24:06round the edge where the mud has been displaced.
0:24:06 > 0:24:11So a large heavy animal, presumably a vertebrate of some sort,
0:24:11 > 0:24:13pushed an appendage into the mud here,
0:24:13 > 0:24:16once, twice, three times in succession.
0:24:18 > 0:24:21The marks suggest a creature floating
0:24:21 > 0:24:23and pushing itself around in the shallows.
0:24:29 > 0:24:32But Per and his team have found a more detailed set of prints
0:24:32 > 0:24:35that show an animal doing something even more radical.
0:24:38 > 0:24:41This is one of the most important specimens from the entire site,
0:24:41 > 0:24:44and the reason for that is the pattern that these prints make.
0:24:44 > 0:24:47You can see, easily I think, that they make pairs,
0:24:47 > 0:24:50one in front of another, in this kind of diagonal arrangement.
0:24:50 > 0:24:53In order to be able to produce this,
0:24:53 > 0:24:56you need to have limbs that stick out to the side
0:24:56 > 0:24:59and which can be swung forwards and backwards rather freely
0:24:59 > 0:25:01while you're flexing your body from side to side.
0:25:01 > 0:25:03Then, you can generate this kind of pattern.
0:25:03 > 0:25:07A fish crawling trace would not look like this.
0:25:10 > 0:25:13Another extraordinary slab has even preserved the imprint
0:25:13 > 0:25:16of what Per believes is a fully-formed foot
0:25:16 > 0:25:18complete with toes.
0:25:21 > 0:25:25So, how did the vertebrates make this astonishing transition
0:25:25 > 0:25:30from fish swimming to animals with four legs walking on land?
0:25:33 > 0:25:36In search of clues, I'm heading to London
0:25:36 > 0:25:39and the Natural History Museum, home to the largest
0:25:39 > 0:25:42collection of plant and animal specimens in the world.
0:25:46 > 0:25:49I'm here to see the remains of an ancient creature,
0:25:49 > 0:25:53once hailed as a missing link that would answer such questions.
0:25:56 > 0:26:00This is a type of bony fish called a Coelacanth.
0:26:00 > 0:26:04Its fossilized skeletons have been found in rocks even older
0:26:04 > 0:26:05than those in Poland.
0:26:08 > 0:26:14Its fins have an intriguing feature not seen in other kinds of fish.
0:26:14 > 0:26:18Their base is a rounded fleshy stump that looks
0:26:18 > 0:26:21tantalizingly like the beginnings of a leg.
0:26:23 > 0:26:26So scientists thought that this might well be
0:26:26 > 0:26:29the ancestor of all land-living vertebrates.
0:26:30 > 0:26:32And then, a sensation.
0:26:33 > 0:26:38A living coelacanth was hauled up from the depths of the Indian Ocean
0:26:38 > 0:26:41and the museum has acquired several of them.
0:26:44 > 0:26:48Here is the body of a baby coelacanth.
0:26:48 > 0:26:51The coelacanth female retains the egg in her body
0:26:51 > 0:26:53until it's fully developed.
0:26:53 > 0:26:55There's its yolk sack,
0:26:55 > 0:26:57and here's its fin,
0:26:57 > 0:27:02and you can see this fleshy base to it here and then its fin rays.
0:27:02 > 0:27:07The question is, was that strong enough to enable a fish like this
0:27:07 > 0:27:11to haul itself out of the water and up onto land?
0:27:17 > 0:27:19Now, living coelacanths have been
0:27:19 > 0:27:20filmed in the depths of the sea.
0:27:23 > 0:27:25Its fleshy, muscular fins
0:27:25 > 0:27:27do certainly help it to
0:27:27 > 0:27:30manoeuvre its five-foot-long body.
0:27:32 > 0:27:37There is even the hint of a walking pattern,
0:27:37 > 0:27:41but detailed analysis has revealed that their fins
0:27:41 > 0:27:44are still a long way from being legs.
0:27:48 > 0:27:52The ancient coelacanth marked a crucial early stage in that
0:27:52 > 0:27:56transition, but some characteristics ruled it out as a direct
0:27:56 > 0:27:58ancestor of the land vertebrates.
0:28:02 > 0:28:07All land-living backboned animals have limbs which have a basic
0:28:07 > 0:28:10similar bone structure.
0:28:10 > 0:28:13There is one bone at the top,
0:28:13 > 0:28:16then there are two bones
0:28:16 > 0:28:19and a group of bones, followed with digits.
0:28:21 > 0:28:25And the coelacanths didn't have that structure.
0:28:25 > 0:28:30And then, recently, another fossil discovery was made.
0:28:34 > 0:28:37Ellesmere Island lies in the icy waters
0:28:37 > 0:28:40between northern Canada and Greenland.
0:28:44 > 0:28:48A team of American palaeontologists, who shot this footage,
0:28:48 > 0:28:52believed that the rocks here were deposited in the right
0:28:52 > 0:28:55sort of environment for the vertebrates move to land.
0:28:58 > 0:29:00We learned about a sequence of rocks
0:29:00 > 0:29:03that formed in ancient stream systems.
0:29:03 > 0:29:07Our hypothesis was that it was in those sorts of environments,
0:29:07 > 0:29:11where limbs were being favoured over fins.
0:29:17 > 0:29:22The arrival of plants on land had stimulated a surge in life
0:29:22 > 0:29:24in and around fresh water swamps
0:29:24 > 0:29:28and this created new opportunities for the fish that lived here.
0:29:32 > 0:29:35One of the nitches that was being developed at the time,
0:29:35 > 0:29:38was for shallow-water predators.
0:29:38 > 0:29:42You know, which fish could find other fish that were living
0:29:42 > 0:29:46in the shallows, the swamps, the productive eco systems
0:29:46 > 0:29:50that were just starting to appear on Earth at that time?
0:29:52 > 0:29:56Ted Daeschler and his colleagues believed that limb-like fins
0:29:56 > 0:29:59could have helped a fish to hunt in this kind of environment.
0:30:03 > 0:30:06And then, on the slopes of a barren valley,
0:30:06 > 0:30:08they made a thrilling discovery.
0:30:14 > 0:30:17This was the fossil that got us really excited.
0:30:17 > 0:30:20We couldn't have dreamed actually that we would find
0:30:20 > 0:30:22something as well preserved as this one.
0:30:22 > 0:30:24It's about the front
0:30:24 > 0:30:26two-thirds or half of the body,
0:30:26 > 0:30:27as you can see,
0:30:27 > 0:30:29a very complete skull,
0:30:29 > 0:30:31and a large piece of the body,
0:30:31 > 0:30:34including parts of the fin.
0:30:36 > 0:30:39The team found features that matched the profile
0:30:39 > 0:30:41of a shallow-water predator.
0:30:42 > 0:30:46Eyes placed on the top of a flattened head...
0:30:48 > 0:30:50..and ranks of sharp teeth.
0:30:53 > 0:30:57They gave it a local Inuit name -
0:30:57 > 0:30:58Tiktaalik.
0:31:01 > 0:31:05We can now work out from its bones how Tiktaalik
0:31:05 > 0:31:07moved around in those swamps and shallows.
0:31:20 > 0:31:24In deep water, it must have swum like any other fish.
0:31:29 > 0:31:33But further examination of its bones showed that it could also
0:31:33 > 0:31:36move its body in a far more radical way.
0:31:38 > 0:31:41One of the really amazing aspects
0:31:41 > 0:31:43of Tiktaalik that we've noticed
0:31:43 > 0:31:46is this evolution of the neck.
0:31:46 > 0:31:49There was not a rigid connection between the skull
0:31:49 > 0:31:51and the rest of the body.
0:31:51 > 0:31:53Tiktaalik is the first vertebrate
0:31:53 > 0:31:57we see that has freed up the neck. And when you think about it,
0:31:57 > 0:32:01all limbed animals, including ourselves, would not be able
0:32:01 > 0:32:05to move our head independently of our shoulders if it were not
0:32:05 > 0:32:10for these innovations that were occurring in a form like Tiktaalik.
0:32:10 > 0:32:16A flexible neck allowed Tiktaalik to point its jaws at its prey
0:32:16 > 0:32:19when space was too cramped to manoeuvre its whole body.
0:32:20 > 0:32:23But it was the fins that provided the team
0:32:23 > 0:32:25with the most exciting evidence.
0:32:30 > 0:32:34Behind the spiny rays, there were lobe-like stumps,
0:32:34 > 0:32:36like those of the coelacanth.
0:32:36 > 0:32:40But Tiktaalik's bones revealed a pattern that was much
0:32:40 > 0:32:44closer to the basic structure of limbs.
0:32:46 > 0:32:48We learned a lot
0:32:48 > 0:32:51about the fin of Tiktaalik
0:32:51 > 0:32:52from this specimen.
0:32:52 > 0:32:56Now, this is a cast of all the different bones that we found
0:32:56 > 0:33:01in association, including the shoulder girdle here.
0:33:01 > 0:33:03But that is the complete fin skeleton
0:33:03 > 0:33:05from the front fin so...
0:33:05 > 0:33:11I'm a lobe-fin fish, here is my front fin, we call it a limb now,
0:33:11 > 0:33:14but here is Tiktaalik's front fin.
0:33:14 > 0:33:17We've got a shoulder joint
0:33:17 > 0:33:19and it's very important that there's a shoulder joint
0:33:19 > 0:33:22which is oriented a little bit laterally,
0:33:22 > 0:33:24a little bit down in Tiktaalik.
0:33:24 > 0:33:27Very different from an animal that's just swimming with its fin
0:33:27 > 0:33:32and paddling along, this fin seemed to be oriented beneath the body.
0:33:32 > 0:33:33So this is the humerus.
0:33:33 > 0:33:38We all have a humerus, that's the first bone in the front appendage.
0:33:38 > 0:33:41We have an ulna and a radius.
0:33:41 > 0:33:43So you and I, all limbed animals,
0:33:43 > 0:33:45have an ulna and radius.
0:33:45 > 0:33:47We have some wrist bones
0:33:47 > 0:33:49and we actually then have something
0:33:49 > 0:33:51which, like a wrist, could
0:33:51 > 0:33:54bend together and allow this fin
0:33:54 > 0:33:56to sit down and to contact
0:33:56 > 0:33:59a surface with a surface area.
0:33:59 > 0:34:03And so, when we see all of these features,
0:34:03 > 0:34:06we see a structure which is very much like our limbs.
0:34:06 > 0:34:11So here is a fish using its fin in a very limb-like way.
0:34:13 > 0:34:17Tiktaalik's heavy-duty fin still helped it to swim.
0:34:20 > 0:34:22But if it hit the shallows,
0:34:22 > 0:34:25the bones and joints would help to
0:34:25 > 0:34:27push itself up and punt around.
0:34:31 > 0:34:35But this new limb didn't just help mobility in the water.
0:34:42 > 0:34:45It became the driving force behind one of the most spectacular
0:34:45 > 0:34:48events in evolutionary history...
0:34:51 > 0:34:55..the arrival of the first vertebrate animals on land.
0:35:24 > 0:35:27Over time, creatures evolved
0:35:27 > 0:35:30that spent most of their time out of water.
0:35:32 > 0:35:35They formed a new group we call amphibians.
0:35:35 > 0:35:39And to survive on land, they had to solve a new challenge.
0:35:39 > 0:35:42They had to be able to extract oxygen
0:35:42 > 0:35:46not from water, like their fish ancestors, but from the air.
0:35:47 > 0:35:52Fish use gills to absorb oxygen into the body.
0:35:55 > 0:35:59In air, gills quickly dry out and stop working.
0:36:04 > 0:36:08China is the home of a rare and fascinating creature
0:36:08 > 0:36:12that can show us how the ancient amphibians overcame this problem.
0:36:16 > 0:36:22Today, the biggest amphibian alive is this creature -
0:36:22 > 0:36:25the Chinese giant salamander.
0:36:26 > 0:36:33It breathes partly through its skin which has these long flaps on it,
0:36:33 > 0:36:36and that absorbs oxygen from the water...
0:36:38 > 0:36:41..but it also breathes air.
0:36:45 > 0:36:52It's going to come up, and as it does, it snatches a gulp of air,
0:36:52 > 0:36:54blows a few bubbles...
0:36:58 > 0:37:00..and sinks down again.
0:37:03 > 0:37:08Its jaw acts as a pump, forcing air down into the body.
0:37:10 > 0:37:14Here, oxygen is absorbed into the bloodstream
0:37:14 > 0:37:18from two inflatable sacks with permeable walls - lungs.
0:37:21 > 0:37:25Because they're enclosed inside the body, they don't dry out.
0:37:27 > 0:37:31The lungs it uses are just simple pouches
0:37:31 > 0:37:33coming from the back of the throat.
0:37:33 > 0:37:38But nonetheless, they were the first kind of lungs that animals had.
0:37:38 > 0:37:43The forerunners of the air-breathing organs that all of us
0:37:43 > 0:37:46land-living vertebrates now have.
0:37:59 > 0:38:00From their origins,
0:38:00 > 0:38:03around 365 million years ago,
0:38:03 > 0:38:06the amphibians took on many different forms.
0:38:09 > 0:38:13Over 7,000 species now live in a variety of habitats
0:38:13 > 0:38:15on land and in water.
0:38:22 > 0:38:23They include salamanders...
0:38:26 > 0:38:27..frogs...
0:38:31 > 0:38:33..and newts.
0:38:36 > 0:38:39But two things tie the amphibians to water.
0:38:39 > 0:38:43First - their skins are moist and if they dry out, they die.
0:38:43 > 0:38:48And secondly - their eggs, like this frogspawn,
0:38:48 > 0:38:51are covered in nothing more than jelly.
0:38:51 > 0:38:54And they have to be laid in water or at the very least,
0:38:54 > 0:38:56in moist conditions.
0:38:56 > 0:39:00And until the vertebrates could solve those two problems,
0:39:00 > 0:39:04they would not be able to colonise the dry parts of the land.
0:39:11 > 0:39:14Then, a group of pioneers appeared
0:39:14 > 0:39:17with an amazing new feature to their bodies.
0:39:19 > 0:39:22We can find the evidence for this next step
0:39:22 > 0:39:25by looking at animals that can survive far from water today.
0:39:32 > 0:39:34This little creature is a lizard.
0:39:34 > 0:39:37They call it in these parts a tree dragon.
0:39:37 > 0:39:42And its body is very much the same shape as an amphibian.
0:39:42 > 0:39:47Long body with a backbone and two pairs of limbs.
0:39:47 > 0:39:48But there's one crucial difference
0:39:48 > 0:39:51between an animal like this and an amphibian.
0:39:51 > 0:39:54Its skin is not moist, it's dry.
0:39:56 > 0:40:00We can see what has changed by putting the two types of skin
0:40:00 > 0:40:02under the microscope.
0:40:04 > 0:40:06The skin of an amphibian
0:40:06 > 0:40:08is smooth with living cells
0:40:08 > 0:40:09visible on the surface.
0:40:11 > 0:40:14A lizard's skin is much rougher
0:40:14 > 0:40:17because it contains large amounts of keratin -
0:40:17 > 0:40:21a protein similar to that from which our own fingernails are formed.
0:40:24 > 0:40:29Keratin-filled cells dry out and layer up to form scales.
0:40:34 > 0:40:38This creates a barrier, sealing water inside the body.
0:40:40 > 0:40:45We humans have inherited this keratin barrier in our skin,
0:40:45 > 0:40:49allowing us to maintain up to 70% of our bodies as water.
0:40:54 > 0:40:57Animals with this body plan became a huge success.
0:40:57 > 0:41:02They evolved into a great number of species big and small.
0:41:02 > 0:41:04We call them reptiles.
0:41:07 > 0:41:11But the reptiles still had to overcome a second challenge -
0:41:11 > 0:41:14how to lay their eggs out of water.
0:41:21 > 0:41:25'I have come to Lufeng, in southern China, to see evidence
0:41:25 > 0:41:30'gathered by local scientists of the ingenious solution.'
0:41:30 > 0:41:32Thank you very much.
0:41:36 > 0:41:39These eggs were laid by a reptile,
0:41:39 > 0:41:41and as you might imagine,
0:41:41 > 0:41:43a pretty big one at that.
0:41:43 > 0:41:48The first reptilian eggs almost certainly had a leathery covering,
0:41:48 > 0:41:51rather like those a turtle lays today.
0:41:51 > 0:41:57But these eggs are different, they have a hard covering - a shell.
0:41:57 > 0:42:00And you can see where the weight
0:42:00 > 0:42:02of the sand that eventually
0:42:02 > 0:42:03covered them and fossilized them
0:42:03 > 0:42:06bore down upon them, they crushed that shell,
0:42:06 > 0:42:09but the pieces are still in place.
0:42:11 > 0:42:13From examining modern reptile eggs,
0:42:13 > 0:42:17we know that this shell must have been made of hard calcium carbonate
0:42:17 > 0:42:20and it must have supported an inner fibrous membrane.
0:42:22 > 0:42:25Together, they made the egg water-tight.
0:42:25 > 0:42:29And that meant that the animals that laid them no longer had to
0:42:29 > 0:42:34go back to the water to lay their eggs, as all amphibians had to do.
0:42:34 > 0:42:40Instead, they could go to the driest part of the land and breed
0:42:40 > 0:42:43and nest and lay their eggs.
0:42:43 > 0:42:46So all the dry land was open to them.
0:42:50 > 0:42:55The amphibians had spearheaded the move to land.
0:42:55 > 0:42:57Now, their descendants, the reptiles,
0:42:57 > 0:43:00were able to establish themselves
0:43:00 > 0:43:01in its driest parts.
0:43:08 > 0:43:12Over 9,500 species now inhabit our planet.
0:43:18 > 0:43:21But the limbs that helped the vertebrates
0:43:21 > 0:43:24emerge from the water began to present problems
0:43:24 > 0:43:28when it came to walking efficiently on dry land.
0:43:28 > 0:43:31Because they projected sideways,
0:43:31 > 0:43:34it took a lot of effort to hold their bodies off the ground.
0:43:37 > 0:43:40Then, around 230 million years ago,
0:43:40 > 0:43:44one set of reptiles developed an amazing solution.
0:43:46 > 0:43:50These eggs were laid by an animal belonging to the most
0:43:50 > 0:43:53successful of all reptile groups,
0:43:53 > 0:43:57a group that dominated the world for 100 million years -
0:43:57 > 0:43:59the dinosaurs.
0:44:19 > 0:44:23More than 150 different species of dinosaur have been
0:44:23 > 0:44:28found in the rocks of China alone, and over 1,000 worldwide.
0:44:36 > 0:44:40And they too depended on a crucial advance.
0:44:40 > 0:44:44A radical modification of the bone that connects the leg to the body -
0:44:44 > 0:44:45the hip.
0:44:50 > 0:44:54This is Lufengosaurus, a plant-eater.
0:44:56 > 0:45:01The early reptiles had legs which splayed out from either side
0:45:01 > 0:45:04of the body and left the body very close to the ground.
0:45:04 > 0:45:08But a change in the shape of the hips of the dinosaurs
0:45:08 > 0:45:11enabled them to bring their hind legs underneath the body
0:45:11 > 0:45:16and so, lift them up and give them greater freedom of movement.
0:45:16 > 0:45:19And some of them, including Lufengosaurus,
0:45:19 > 0:45:23were able to support the entire weight of the body on the hind legs.
0:45:28 > 0:45:33This new hip, along with sturdier leg joints, allowed the dinosaurs
0:45:33 > 0:45:35to take longer strides...
0:45:39 > 0:45:41..and support heavier bodies.
0:45:43 > 0:45:48They became the largest animals that have ever lived on land.
0:45:49 > 0:45:53But this new way of walking was also the first step on the road to
0:45:53 > 0:45:56an even more radical evolutionary advance.
0:45:58 > 0:46:04It was from this group of two-legged dinosaurs that there came a truly
0:46:04 > 0:46:09astonishing development that we are only just beginning to understand,
0:46:09 > 0:46:12and that was to lift the vertebrates to a completely new level.
0:46:15 > 0:46:21The backboned animals had colonized the seas and invaded the land.
0:46:21 > 0:46:26But there was one final habitat to explore - the skies.
0:46:28 > 0:46:32Another extraordinary Chinese fossil bed is providing the missing
0:46:32 > 0:46:38evidence for one of the great mysteries in evolutionary science -
0:46:38 > 0:46:41the intriguing link between dinosaurs and birds.
0:46:47 > 0:46:53I'm heading for Liaoning province to fulfil a long-held dream
0:46:53 > 0:46:57and see the site of these discoveries for myself.
0:47:01 > 0:47:05These rocks are about 125 million years old.
0:47:05 > 0:47:09At that time, this part of China was tropical
0:47:09 > 0:47:13and the land was covered with a lot of freshwater lakes.
0:47:13 > 0:47:16And in those lakes was washed sediment
0:47:16 > 0:47:19which formed these bands here.
0:47:19 > 0:47:23But every now and again, the sediment changes colour.
0:47:23 > 0:47:28And that is ash that was spewed out from a nearby volcano
0:47:28 > 0:47:31so that about that level there,
0:47:31 > 0:47:35there were a lot of skeletons waiting to be discovered.
0:47:35 > 0:47:40And when they were discovered, they revealed some sensational facts
0:47:40 > 0:47:44about dinosaurs, the most sensational for a very long time.
0:47:47 > 0:47:48This fossil was one of
0:47:48 > 0:47:51the most remarkable to emerge.
0:47:51 > 0:47:53A two-legged dinosaur
0:47:53 > 0:47:54about the size of a cat.
0:47:54 > 0:47:58It's been named Sinosauropteryx.
0:48:00 > 0:48:03Its discovery revealed an intriguing feature
0:48:03 > 0:48:05never seen before on a dinosaur.
0:48:07 > 0:48:09Up its tail and down its back,
0:48:09 > 0:48:12a covering of what looks like fur.
0:48:15 > 0:48:20Fresh finds have revealed that a wide range of two-legged dinosaurs
0:48:20 > 0:48:24had skin covered by very similar hair-like filaments.
0:48:26 > 0:48:27But what were they for?
0:48:30 > 0:48:34In Beijing, there are the crucial specimens
0:48:34 > 0:48:36that answered those questions.
0:48:39 > 0:48:43This is one of the world's leading institutions in the study
0:48:43 > 0:48:45of dinosaur evolution.
0:48:48 > 0:48:52Professor Xu Xing and his colleagues have been analysing another
0:48:52 > 0:48:55larger specimen of Sinosauropteryx.
0:48:59 > 0:49:02It too retains traces,
0:49:02 > 0:49:04just fragments of the mysterious filaments.
0:49:07 > 0:49:14If you look near the tail, the dark things there near the tail,
0:49:14 > 0:49:16they are single filaments, just like our hair,
0:49:16 > 0:49:18which are very, very simple.
0:49:19 > 0:49:23Xu Xing has been puzzling over their function.
0:49:23 > 0:49:27Together, these filaments create a covering like fur,
0:49:27 > 0:49:29so the most likely answer is that they served
0:49:29 > 0:49:32to keep these dinosaurs warm.
0:49:32 > 0:49:37But detailed examination has suggested an additional
0:49:37 > 0:49:38and very different function.
0:49:41 > 0:49:44Experts at the institute have taken minute samples
0:49:44 > 0:49:48and examined them under powerful magnification.
0:49:49 > 0:49:52They contain intriguing structures.
0:49:53 > 0:49:56Some are lozenge-shaped,
0:49:56 > 0:49:59some spherical.
0:49:59 > 0:50:03Investigators identified them as melanosomes -
0:50:03 > 0:50:08microscopic capsules that contain pigment.
0:50:08 > 0:50:13They would have given the filaments on Sinosauropteryx's tail colour.
0:50:14 > 0:50:17Based on our analysis, you see stripes.
0:50:17 > 0:50:23- One like white, brown, white, brown. - Really?
0:50:23 > 0:50:27Yes, definitely. It's a beautiful pattern. Of course you can't see all,
0:50:27 > 0:50:31that's maybe for display or communication or...
0:50:31 > 0:50:33Do we know how it held its tail?
0:50:33 > 0:50:36Uh, tails definitely can move in different directions.
0:50:36 > 0:50:39In most cases, I would guess is up or horizontal.
0:50:39 > 0:50:43So it's like a ring-tailed lemur waving its tail around as a display.
0:50:45 > 0:50:47Dinosaurs may have used
0:50:47 > 0:50:50these coloured furry bands to signal
0:50:50 > 0:50:51to other members of the species
0:50:51 > 0:50:54or to act as camouflage.
0:50:54 > 0:50:58But then came a discovery that suggested another far more
0:50:58 > 0:51:00significant function.
0:51:03 > 0:51:07I've been granted privileged access to the underground vaults
0:51:07 > 0:51:11of the Beijing Museum of Natural History, to look at one of the most
0:51:11 > 0:51:15important creatures yet to be found in the fossil beds of Liaoning.
0:51:47 > 0:51:53This is Anchiornis, a creature that's clearly a dinosaur.
0:51:53 > 0:51:57It's got powerful legs here ending with toes with sharp claws
0:51:57 > 0:52:00on them, and its head,
0:52:00 > 0:52:03which has been detached, lies here
0:52:03 > 0:52:07upside down but you can see the jaw,
0:52:07 > 0:52:08which has teeth in them.
0:52:11 > 0:52:15But what is spectacular about this particular specimen
0:52:15 > 0:52:20is the perfection of the preservation of these structures.
0:52:20 > 0:52:23They show that the simple filaments have developed into something
0:52:23 > 0:52:25far more complex.
0:52:26 > 0:52:29The central stalk has tiny strands
0:52:29 > 0:52:31branching out on either side.
0:52:31 > 0:52:34The filaments have become feathers.
0:52:37 > 0:52:43Analysis of them has shown that the crest here on the head
0:52:43 > 0:52:45was a rufous red colour
0:52:45 > 0:52:48and the body feathers
0:52:48 > 0:52:50were striped black and white.
0:52:54 > 0:52:57There are feathers all down the legs.
0:53:00 > 0:53:05And looking at the density of them on the forearms here,
0:53:05 > 0:53:08it does look very like a wing.
0:53:08 > 0:53:10So the question is,
0:53:10 > 0:53:13could this animal fly?
0:53:13 > 0:53:20Could this be the moment when a dinosaur became a bird?
0:53:26 > 0:53:30A clue to the answer could come from the environment in which it lived.
0:53:30 > 0:53:36At this time, this area of northern China was covered in lush forests.
0:53:38 > 0:53:42Animals that could climb trees would be able to collect food
0:53:42 > 0:53:44that was not available on the ground.
0:53:45 > 0:53:49They could also find safety from ground-living predators.
0:53:51 > 0:53:56Xu Xing and his colleagues see evidence that Anchiornis adapted
0:53:56 > 0:54:01to a tree-living way of life, by putting its feathers to a new use.
0:54:03 > 0:54:07Anchiornis has some features suggesting a tree-living lifestyle.
0:54:07 > 0:54:12For example, you look at the Anchiornis' toe,
0:54:12 > 0:54:14they have very curved claws.
0:54:14 > 0:54:18And also, they have big feathers attached to their feet.
0:54:18 > 0:54:22If Anchiornis is a tree-living animal, then I have good reason
0:54:22 > 0:54:26to believe that flight started from tree down.
0:54:26 > 0:54:32Which means that the birds' ancestor can take advantage of gravity
0:54:32 > 0:54:34and then start their journey to the sky.
0:54:37 > 0:54:39Because Anchiornis lived high up,
0:54:39 > 0:54:42it could use its feathers to glide.
0:54:58 > 0:55:02It must have needed all the feathers growing along its front limbs,
0:55:02 > 0:55:07hind limbs and tail to create a large enough surface to catch
0:55:07 > 0:55:09the air and slow its descent.
0:55:21 > 0:55:27It wasn't capable of flapping flight but, at 160 million years old,
0:55:27 > 0:55:32it's now the earliest creature we know to have used feathers to fly.
0:55:39 > 0:55:41The gliding dinosaurs would eventually give rise to
0:55:41 > 0:55:44a whole new group of vertebrates...
0:55:45 > 0:55:47..the birds.
0:55:52 > 0:55:56Over 9,000 species crowd our skies today.
0:55:59 > 0:56:03An astonishing evolutionary journey had enabled the vertebrates
0:56:03 > 0:56:06to dominate every corner of the planet.
0:56:10 > 0:56:15It was a journey that began in the Cambrian seas
0:56:15 > 0:56:17over 500 million years ago,
0:56:17 > 0:56:19and that led to the development of
0:56:19 > 0:56:24a set of body parts that we ourselves would ultimately inherit.
0:56:26 > 0:56:29Jaws and a bony skeleton from the early fish...
0:56:34 > 0:56:37..limbs and lungs from the amphibians...
0:56:39 > 0:56:42..water-tight skin from the reptiles.
0:56:45 > 0:56:47By the time the birds appeared on the planet,
0:56:47 > 0:56:52the early pioneers of another major vertebrate group had also evolved.
0:56:55 > 0:56:59At first, they were tiny but they were destined eventually to
0:56:59 > 0:57:02dominate the Earth -
0:57:02 > 0:57:03they were the mammals.
0:57:06 > 0:57:10Most, I dare say, were little better than snack food
0:57:10 > 0:57:14for the dinosaurs, but all that was about to change.
0:57:19 > 0:57:22A devastating meteor strike,
0:57:22 > 0:57:25that many believe triggered a mass extinction.
0:57:29 > 0:57:31We don't know exactly what happened,
0:57:31 > 0:57:36but certainly, 65 million years ago, all the dinosaurs disappeared.
0:57:38 > 0:57:41But some of the birds and mammals survived
0:57:41 > 0:57:47and with the bigger dinosaurs gone, the world was up for grabs.
0:57:53 > 0:57:59Next time, I'll be investigating the extraordinary rise of the mammals
0:57:59 > 0:58:03to discover how they developed a remarkable set of new bodily
0:58:03 > 0:58:08features to become the most complex and successful vertebrates yet.
0:58:10 > 0:58:13Powerful senses,
0:58:13 > 0:58:16a radical new way of producing their young,
0:58:16 > 0:58:18and monstrous bodies.
0:58:20 > 0:58:23We will also see how we humans finally
0:58:23 > 0:58:25arrived on the tree of life
0:58:25 > 0:58:30with hugely advanced brains that would allow us to out-compete
0:58:30 > 0:58:32all other species on the planet.
0:58:57 > 0:59:00Subtitles by Red Bee Media Ltd