0:00:02 > 0:00:03Our planet is the greatest
0:00:03 > 0:00:05living puzzle in the universe.
0:00:05 > 0:00:06A collection of worlds
0:00:06 > 0:00:08within worlds,
0:00:08 > 0:00:10each one a network
0:00:10 > 0:00:13of relationships and connections
0:00:13 > 0:00:14between all their living parts,
0:00:14 > 0:00:17leading to the diverse
0:00:17 > 0:00:19and complex world we live in.
0:00:21 > 0:00:23And at the heart of many of these worlds
0:00:23 > 0:00:26is a very special group of animals -
0:00:26 > 0:00:29the insects, and their close relatives -
0:00:29 > 0:00:32the arachnids and crustaceans,
0:00:32 > 0:00:36classed together as the arthropods.
0:00:36 > 0:00:39Together, they account for 80% of
0:00:39 > 0:00:42all animal species on our planet.
0:00:42 > 0:00:44In these three specials,
0:00:44 > 0:00:47we're going to explore the connections and relationships
0:00:47 > 0:00:49that they have with us,
0:00:49 > 0:00:51our planet...
0:00:52 > 0:00:54..and with each other,
0:00:54 > 0:00:57ultimately, to understand how this group
0:00:57 > 0:01:03hold the key to life itself inside nature's microworlds.
0:01:11 > 0:01:13Arthropods are the most abundant
0:01:13 > 0:01:15and diverse
0:01:15 > 0:01:16group of animals in the world.
0:01:18 > 0:01:19They inhabit
0:01:19 > 0:01:22every continent and every ocean...
0:01:24 > 0:01:26..from the harsh climate
0:01:26 > 0:01:28of Antarctica...
0:01:29 > 0:01:33..to the driest of deserts around the equator.
0:01:34 > 0:01:37From the lushest jungles
0:01:37 > 0:01:40to the highest mountain peaks.
0:01:46 > 0:01:49There are an estimated ten million species.
0:01:51 > 0:01:54More than all the other animal groups combined.
0:01:57 > 0:02:00But what is the secret of their success?
0:02:02 > 0:02:04What is the single key to their global domination?
0:02:07 > 0:02:11To understand this, we need to unpick, one by one,
0:02:11 > 0:02:15the factors that influence the lives of arthropods.
0:02:19 > 0:02:22First, we need to understand what arthropods are
0:02:22 > 0:02:23and where they came from.
0:02:28 > 0:02:29And to do that,
0:02:29 > 0:02:31we must travel to Delaware Bay,
0:02:31 > 0:02:33on the east coast of America.
0:02:40 > 0:02:43400 million years ago,
0:02:43 > 0:02:44the first land animals
0:02:44 > 0:02:46pulled themselves out of the sea.
0:02:49 > 0:02:53They were the ancestors of the arthropods
0:02:53 > 0:02:54who dominate our planet today.
0:03:00 > 0:03:04And each spring, on the highest tides of the full and new moons,
0:03:04 > 0:03:06a similar spectacle still occurs.
0:03:10 > 0:03:11These are horseshoe crabs -
0:03:11 > 0:03:15some of the most primitive arthropods alive today.
0:03:17 > 0:03:19They're here to breed.
0:03:21 > 0:03:25The males are two-thirds the size of their mates
0:03:25 > 0:03:29and cluster along the water's edge as the females arrive.
0:03:29 > 0:03:32Clinging to the female's shell,
0:03:32 > 0:03:34he's pulled up the beach,
0:03:34 > 0:03:35fertilising her eggs as she lays.
0:03:45 > 0:03:46For these crabs,
0:03:46 > 0:03:49breeding on land is only possible
0:03:49 > 0:03:51because of the arthropod blueprint.
0:03:58 > 0:04:00Their basic body plan
0:04:00 > 0:04:03is the same as all arthropods -
0:04:03 > 0:04:06a hard exoskeleton,
0:04:06 > 0:04:09segmented body,
0:04:09 > 0:04:11and jointed legs.
0:04:13 > 0:04:18A body plan that's persisted unchanged for 400 million years.
0:04:18 > 0:04:22A body plan as adaptable as it is simple.
0:04:25 > 0:04:29The key design feature is no doubt the exoskeleton.
0:04:31 > 0:04:34A hard external skeleton,
0:04:34 > 0:04:38largely made of chitin, that provides protection,
0:04:38 > 0:04:40support for muscles,
0:04:40 > 0:04:44but most importantly, prevents water loss from the body.
0:04:48 > 0:04:51The ability of the exoskeleton to retain water
0:04:51 > 0:04:53is the factor that allows these crabs
0:04:53 > 0:04:55to lay their eggs on land
0:04:55 > 0:04:57and ultimately allowed arthropods
0:04:57 > 0:05:00to be the first animals to colonise the land.
0:05:05 > 0:05:08But even this master of design,
0:05:08 > 0:05:10the exoskeleton, has a weakness.
0:05:11 > 0:05:15How do you grow inside a suit of armour?
0:05:22 > 0:05:24To see that,
0:05:24 > 0:05:26we must travel 400 miles south
0:05:26 > 0:05:30to a freshwater microworld in South Carolina.
0:05:42 > 0:05:47This crayfish is getting ready to transform -
0:05:47 > 0:05:49something all arthropods must do
0:05:49 > 0:05:51to increase their size.
0:05:56 > 0:05:59In preparation, he withdraws calcium from his shell
0:05:59 > 0:06:03and stores it in little white tablets on the side of his head.
0:06:05 > 0:06:08His hard exoskeleton then splits,
0:06:08 > 0:06:12and the larger soft-bodied crayfish emerges.
0:06:15 > 0:06:17It can take up to a few days for
0:06:17 > 0:06:20the new exoskeleton to fully harden,
0:06:20 > 0:06:21and before this occurs,
0:06:21 > 0:06:23the crayfish is vulnerable.
0:06:29 > 0:06:32This queen snake is on a hunt for a meal.
0:06:36 > 0:06:38The hardened armour of the crayfish is too much for her,
0:06:38 > 0:06:42but she can detect the chemicals
0:06:42 > 0:06:44given off by the soft body
0:06:44 > 0:06:46of a freshly moulted crayfish
0:06:46 > 0:06:49and knows this is her chance.
0:07:03 > 0:07:05As soft as a doughnut,
0:07:05 > 0:07:08this crayfish provides a hearty meal.
0:07:12 > 0:07:14So the exoskeleton,
0:07:14 > 0:07:17vital to their success,
0:07:17 > 0:07:20also leaves them vulnerable.
0:07:23 > 0:07:28And it has another significant defining effect on all arthropods.
0:07:30 > 0:07:32It restricts their size.
0:07:38 > 0:07:43This is the largest terrestrial arthropod - the coconut crab.
0:07:45 > 0:07:47This crab will moult each year,
0:07:47 > 0:07:50and can live until he's 60,
0:07:50 > 0:07:54yet is still no larger than a newborn baby.
0:07:54 > 0:07:56If you must transform
0:07:56 > 0:07:58every time you need to grow,
0:07:58 > 0:08:02then there's a limit to how big you can get.
0:08:04 > 0:08:06But this apparent size disadvantage
0:08:06 > 0:08:08can be seen as an asset.
0:08:11 > 0:08:14It opens up a whole new world for the arthropods.
0:08:24 > 0:08:25And to see how,
0:08:25 > 0:08:27we must travel to
0:08:27 > 0:08:29the Flow Country, in Scotland.
0:08:40 > 0:08:42This is the fairy wasp,
0:08:42 > 0:08:44a quarter of a millimetre long.
0:08:44 > 0:08:46They spend nearly all their lives underwater.
0:08:49 > 0:08:54She is one of the smallest known arthropods alive on the planet
0:08:54 > 0:08:56and almost invisible to the naked eye.
0:08:56 > 0:08:58She makes a tiny water flea
0:08:58 > 0:09:00look like a giant.
0:09:01 > 0:09:03This female is looking for
0:09:03 > 0:09:06a very specific place to lay her eggs.
0:09:08 > 0:09:09She positions
0:09:09 > 0:09:11her microscopic ovipositor
0:09:11 > 0:09:13to pierce into the stem of a plant,
0:09:13 > 0:09:16where the eggs of a water beetle have been laid.
0:09:18 > 0:09:20She deposits up to 100 eggs
0:09:20 > 0:09:22inside a single beetle egg.
0:09:28 > 0:09:31When the young hatch, they have a ready source of food -
0:09:31 > 0:09:34the water beetle's undeveloped young.
0:09:37 > 0:09:39It's only the size of this wasp
0:09:39 > 0:09:42that opens up this niche for her to exploit.
0:09:46 > 0:09:49In fact, the arthropods' diminutive size
0:09:49 > 0:09:52gives them a real trump card in the game of life.
0:09:52 > 0:09:56It allows them to exploit microhabitats.
0:09:57 > 0:09:59Be it an egg,
0:09:59 > 0:10:02a gall on an oak tree,
0:10:02 > 0:10:03or a single leaf.
0:10:04 > 0:10:06The wealth of habitats and niches
0:10:06 > 0:10:10available to them is virtually infinite.
0:10:15 > 0:10:18But being small also makes them vulnerable.
0:10:21 > 0:10:22Their size and abundance
0:10:22 > 0:10:25makes them an ideal food source
0:10:25 > 0:10:27for a whole host of other animals...
0:10:33 > 0:10:37..including the biggest animal to have ever lived.
0:10:39 > 0:10:41The blue whale.
0:10:46 > 0:10:50So if size is not the ultimate key to their success,
0:10:50 > 0:10:54we must look elsewhere and examine
0:10:54 > 0:10:56why the diversity of arthropods
0:10:56 > 0:11:01has evolved so much faster than in all other animal groups.
0:11:03 > 0:11:06How do the arthropods speed up their evolution?
0:11:10 > 0:11:13To find out, we must travel to a microworld
0:11:13 > 0:11:16in our very own back gardens.
0:11:20 > 0:11:23This is a female cabbage aphid.
0:11:25 > 0:11:28In spring, she produces
0:11:28 > 0:11:31100 offspring in just a week.
0:11:32 > 0:11:35Her offspring already have babies inside them,
0:11:35 > 0:11:36so this mother aphid
0:11:36 > 0:11:38is nurturing her granddaughters
0:11:38 > 0:11:40even before they're born.
0:11:43 > 0:11:45If all her descendants survived and bred,
0:11:45 > 0:11:47by the end of the summer,
0:11:47 > 0:11:53there'd be 1,560 billion trillion aphids!
0:11:56 > 0:11:59She is the ultimate breeding machine.
0:12:01 > 0:12:04This ability to reproduce prolifically
0:12:04 > 0:12:06is a real trait of the arthropods.
0:12:10 > 0:12:14Having lots of offspring and a quick life cycle
0:12:14 > 0:12:17increases the chances of genetic mutations occurring.
0:12:19 > 0:12:21And it's these mutations,
0:12:21 > 0:12:23however bizarre they seem,
0:12:23 > 0:12:26that increase the diversity of the gene pool.
0:12:28 > 0:12:32They can provide novel solutions
0:12:32 > 0:12:33to life's challenges...
0:12:41 > 0:12:43..and ultimately lead to
0:12:43 > 0:12:45the evolution of new species.
0:12:48 > 0:12:52This means that arthropods have the ability to respond to opportunities
0:12:52 > 0:12:56and potentially fill niches faster than any other group of animals.
0:12:58 > 0:13:01This does gives them a winning hand
0:13:01 > 0:13:04and provides another vital piece in our jigsaw.
0:13:08 > 0:13:10But it's not the whole story.
0:13:17 > 0:13:24We've seen how arthropods have been around for over 400 million years,
0:13:24 > 0:13:26how their winning body plan
0:13:26 > 0:13:28has stood them in good stead for all this time.
0:13:31 > 0:13:35We've seen how their size enables them to exploit microhabitats,
0:13:35 > 0:13:39and rapid reproduction has accelerated their evolution.
0:13:41 > 0:13:44All factors that have enabled them to fly,
0:13:44 > 0:13:47squelch, crawl,
0:13:47 > 0:13:49and scuttle
0:13:49 > 0:13:51into the myriad of forms we see today.
0:13:55 > 0:13:57But there's a twist in the tale.
0:14:00 > 0:14:04For the real key to their global success and diversity,
0:14:04 > 0:14:06we must look much closer to home.
0:14:09 > 0:14:10To really understand
0:14:10 > 0:14:13the diversity of the arthropods,
0:14:13 > 0:14:15we must examine how the presence
0:14:15 > 0:14:17of other arthropods affects them.
0:14:20 > 0:14:23Firstly, let's look at what can be achieved
0:14:23 > 0:14:25when arthropods work together.
0:14:37 > 0:14:39This colony of 40,000 bees
0:14:39 > 0:14:42is focused on a single task -
0:14:42 > 0:14:44the production of honey.
0:14:47 > 0:14:48They have a single queen,
0:14:48 > 0:14:51who is the only bee to lay eggs.
0:14:52 > 0:14:54She can lay up to 2,000
0:14:54 > 0:14:55in a single day.
0:14:58 > 0:15:01Each bee is roughly a centimetre and a half in length.
0:15:01 > 0:15:04Their exoskeleton prevents them from growing any further
0:15:04 > 0:15:06in this adult form.
0:15:08 > 0:15:13But there's an animal over a million times its weight on the prowl...
0:15:16 > 0:15:18..and he's after their honey.
0:15:23 > 0:15:26To lose their honey now would be fatal for their colony.
0:15:26 > 0:15:29It'll be their only source of food
0:15:29 > 0:15:31during the cold winter months.
0:15:31 > 0:15:34But this super society won't give up
0:15:34 > 0:15:37its hard-won prize without a fight.
0:15:39 > 0:15:43They attack and sting en masse.
0:15:43 > 0:15:46The first stinger releases an alarm pheromone
0:15:46 > 0:15:49that tells other bees to join in.
0:15:49 > 0:15:51The stings are barbed
0:15:51 > 0:15:54and hook into the skin of the bear.
0:16:01 > 0:16:04Each sting has its own nervous system
0:16:04 > 0:16:07and pumps venom into the attacker.
0:16:10 > 0:16:12Worker bees can only sting once...
0:16:14 > 0:16:16..and then they die.
0:16:17 > 0:16:20It's the ultimate sacrifice for their colony.
0:16:22 > 0:16:25But the bees are victorious.
0:16:25 > 0:16:27The bear is repelled.
0:16:30 > 0:16:31Teamwork enables these bees
0:16:31 > 0:16:34to defend their precious honey
0:16:34 > 0:16:38against an intruder many thousands of times their own size.
0:16:42 > 0:16:46So working together can offer great advantages for defence.
0:16:48 > 0:16:52But it's one thing if your attacker is an animal like a black bear
0:16:52 > 0:16:55and quite another if it's the environment itself.
0:17:00 > 0:17:04So how does working as a team allow you to live in
0:17:04 > 0:17:07one of the toughest environments in the world?
0:17:09 > 0:17:11To find out, we must travel 9,000 miles
0:17:11 > 0:17:14to the mangroves of Australia.
0:17:16 > 0:17:19They may look like a benign place to live,
0:17:19 > 0:17:21but they're actually packed with
0:17:21 > 0:17:24potentially deadly natural forces.
0:17:27 > 0:17:30Hot tropical sun, salty water,
0:17:30 > 0:17:33and the risk of drowning with every high tide.
0:17:38 > 0:17:40But in the mangrove mud is where these ants
0:17:40 > 0:17:43have chosen to build their nest.
0:17:43 > 0:17:48And teamwork has turned the tide to their advantage.
0:17:51 > 0:17:53Each high tide brings a fresh bounty of food
0:17:53 > 0:17:55that the ants can harvest.
0:17:59 > 0:18:01But this tide also brings the threat of drowning
0:18:01 > 0:18:05and the precious ant larvae being swept away.
0:18:06 > 0:18:08The ants have a cunning strategy.
0:18:20 > 0:18:23Every tide, these ants combine their forces
0:18:23 > 0:18:26and move the entire nest, larvae and all,
0:18:26 > 0:18:28into bell-shaped chambers they've built,
0:18:28 > 0:18:32which trap the air, keeping them safely above the waterline.
0:18:34 > 0:18:38Here, they'll remain for several hours, until the tide retreats.
0:18:44 > 0:18:48So cooperation between arthropods of the same species
0:18:48 > 0:18:51offers great advantages.
0:18:55 > 0:18:57But we must look elsewhere
0:18:57 > 0:19:00for the ultimate key to the success of the arthropods.
0:19:02 > 0:19:04We must examine the idea
0:19:04 > 0:19:07that diversity stems not only from cooperation,
0:19:07 > 0:19:10but also exploitation.
0:19:16 > 0:19:19A female bolas spider.
0:19:19 > 0:19:21She's hunting for food...
0:19:23 > 0:19:26..and she's got a pretty unique way of doing it.
0:19:29 > 0:19:33She spins a single thread of silk,
0:19:33 > 0:19:34thinner than a human hair,
0:19:34 > 0:19:36with a sticky globule on the end.
0:19:38 > 0:19:42And from special glands on her abdomen,
0:19:42 > 0:19:44she produces a pheromone to attract her prey.
0:19:48 > 0:19:49She waits.
0:19:52 > 0:19:54An approaching moth,
0:19:54 > 0:19:57but she hasn't quite got her eye in.
0:20:04 > 0:20:06She doesn't miss twice.
0:20:13 > 0:20:16So arthropods affect their own diversity
0:20:16 > 0:20:18by providing a food source.
0:20:20 > 0:20:23And necessity being the mother of all invention,
0:20:23 > 0:20:26they've evolved some diverse and ingenious ways
0:20:26 > 0:20:27of catching each other.
0:20:33 > 0:20:38But the exploitative relationships between them don't end there.
0:20:41 > 0:20:43The Mojave desert in California.
0:20:45 > 0:20:48This is a female blister beetle.
0:20:52 > 0:20:54She lays her eggs in the scorching sand of the desert,
0:20:54 > 0:20:57a few centimetres below the surface.
0:20:59 > 0:21:01The perfect temperature for incubation.
0:21:03 > 0:21:05When the larvae hatch,
0:21:05 > 0:21:08they need to find food - and fast.
0:21:10 > 0:21:12En masse, they climb the nearest stem of grass
0:21:12 > 0:21:14and form a cluster.
0:21:17 > 0:21:19They release a pheromone
0:21:19 > 0:21:22identical to that produced by a female digger bee,
0:21:22 > 0:21:24and it isn't long before they're noticed.
0:21:27 > 0:21:32This is a male digger bee and he's come to mate,
0:21:32 > 0:21:34but instead of an amorous reception,
0:21:34 > 0:21:36he's boarded by hundreds of larvae.
0:21:39 > 0:21:41Temporarily stunned,
0:21:41 > 0:21:42he falls to the floor,
0:21:42 > 0:21:44but quickly regains his composure...
0:21:45 > 0:21:48..and heads off in search of another female.
0:21:50 > 0:21:52While he's mating,
0:21:52 > 0:21:54his stowaways jump ship.
0:22:01 > 0:22:04The female then returns to her burrow,
0:22:04 > 0:22:06where she's secreted pollen
0:22:06 > 0:22:08for her unhatched young.
0:22:13 > 0:22:16The blister beetle's larvae have reached safety
0:22:16 > 0:22:19and a ready supply of food,
0:22:19 > 0:22:22and when the pollen is finished,
0:22:22 > 0:22:24they'll consume the young of the digger bee.
0:22:28 > 0:22:29So we know that predation
0:22:29 > 0:22:32and exploitation lead to diversity.
0:22:36 > 0:22:38But there's one final factor
0:22:38 > 0:22:41that affects the success of the arthropods.
0:22:41 > 0:22:44One final vital key that unlocks a greater understanding
0:22:44 > 0:22:47of their world, and without which,
0:22:47 > 0:22:49the array of life we see today
0:22:49 > 0:22:52would not be present,
0:22:52 > 0:22:55and it's diversity itself.
0:23:08 > 0:23:12Diversity breeds diversity.
0:23:12 > 0:23:16Arthropods are part of a constant arms race
0:23:16 > 0:23:20to outmanoeuvre and exploit each other,
0:23:20 > 0:23:22a process called coevolution.
0:23:22 > 0:23:25To see coevolution at work,
0:23:25 > 0:23:26we must head to a meadow
0:23:26 > 0:23:28in the Swiss Alps.
0:23:33 > 0:23:37This is a female Alcon Blue butterfly.
0:23:39 > 0:23:42She lays her eggs on the gentian plant,
0:23:42 > 0:23:44and when they've hatched into caterpillars
0:23:44 > 0:23:47and eaten their fill, they drop onto the ground.
0:23:49 > 0:23:51Surrounded by foraging ants,
0:23:51 > 0:23:54you'd think they'd be at risk,
0:23:54 > 0:23:56but the ants dutifully collect them
0:23:56 > 0:23:58and transport them back to their nest,
0:23:58 > 0:24:00where they're cleaned and fed.
0:24:06 > 0:24:09The Alcon Blue caterpillars have bewitched the ants.
0:24:11 > 0:24:13They emit chemicals that convince the ants
0:24:13 > 0:24:15they're one of their own larvae,
0:24:15 > 0:24:17even producing noises
0:24:17 > 0:24:20similar to those made by the queen ant,
0:24:20 > 0:24:22to ensure the royal treatment.
0:24:23 > 0:24:27They've checked in to a five-star ant hotel.
0:24:30 > 0:24:34But the ingenuity of this butterfly species
0:24:34 > 0:24:38presents an opportunity to any other species canny enough to exploit it.
0:24:43 > 0:24:46This is an ichneumon wasp.
0:24:48 > 0:24:50Out of hundreds of ants' nests,
0:24:50 > 0:24:52she's able to detect the one
0:24:52 > 0:24:55that contains an Alcon butterfly caterpillar.
0:25:00 > 0:25:02The ants' response to any invader is to attack...
0:25:05 > 0:25:07..but she releases a pheromone
0:25:07 > 0:25:09that deranges the ants.
0:25:11 > 0:25:13They begin to attack each other...
0:25:16 > 0:25:19..and this buys her the time she needs.
0:25:25 > 0:25:27The wasp makes a beeline for
0:25:27 > 0:25:29the butterfly larvae,
0:25:29 > 0:25:31where she will lay her eggs.
0:25:41 > 0:25:44Job complete, she leaves the nest.
0:25:48 > 0:25:51The ants' nest, released from the wasp's spell,
0:25:51 > 0:25:53returns to normal.
0:25:59 > 0:26:02The caterpillars remain in the nest
0:26:02 > 0:26:03until the following summer,
0:26:03 > 0:26:05when they transform into a pupa,
0:26:05 > 0:26:06and after about a month,
0:26:06 > 0:26:09the adult butterflies emerge.
0:26:19 > 0:26:21But not every pupa contains
0:26:21 > 0:26:23an Alcon Blue adult.
0:26:25 > 0:26:27A young ichneumon wasp.
0:26:40 > 0:26:43The exploiter has become the exploited.
0:26:48 > 0:26:52Diversity has presented opportunity.
0:26:56 > 0:27:00The wasp has evolved to exploit the butterfly...
0:27:01 > 0:27:04..who exploits the ants.
0:27:04 > 0:27:06Their lives are intricately linked.
0:27:06 > 0:27:09They have coevolved.
0:27:11 > 0:27:14And this is the final vital key
0:27:14 > 0:27:15to the abundance
0:27:15 > 0:27:17and diversity of the arthropods.
0:27:17 > 0:27:20The process of coevolution.
0:27:22 > 0:27:23All over the world,
0:27:23 > 0:27:26the opportunities presented by other arthropods
0:27:26 > 0:27:29are creating the pressure to innovate and evolve.
0:27:31 > 0:27:33No doubt this diversity wouldn't exist
0:27:33 > 0:27:37if it weren't for that winning body plan,
0:27:37 > 0:27:39small size,
0:27:39 > 0:27:42ability to reproduce,
0:27:42 > 0:27:43work cooperatively,
0:27:43 > 0:27:47and finally, predate and exploit each other.
0:27:50 > 0:27:52But it's this snowballing effect
0:27:52 > 0:27:54of diversity itself
0:27:54 > 0:27:55that raises arthropods onto
0:27:55 > 0:27:57a whole new level.
0:28:01 > 0:28:02The arthropods have lived,
0:28:02 > 0:28:05survived and thrived on Earth
0:28:05 > 0:28:08for 400 million years...
0:28:08 > 0:28:10THUNDER BREAKS
0:28:12 > 0:28:14..through extreme climate change,
0:28:14 > 0:28:16volcanic events,
0:28:16 > 0:28:20ice ages,
0:28:20 > 0:28:22and the extinction of the dinosaurs.
0:28:25 > 0:28:29In fact, arthropods have survived and thrived
0:28:29 > 0:28:32when 99.9% of all species
0:28:32 > 0:28:35that ever lived have become extinct.
0:28:37 > 0:28:39They are the most successful
0:28:39 > 0:28:43and diverse group of animals to have ever lived.
0:29:05 > 0:29:09Subtitles by Red Bee Media Ltd