0:00:02 > 0:00:06Bones. They offer structure,
0:00:06 > 0:00:10support and strength.
0:00:10 > 0:00:14But they have a much bigger story to tell.
0:00:17 > 0:00:23Vertebrates may look very different on the outside, but one crucial thing
0:00:23 > 0:00:26unites them all - the skeleton.
0:00:30 > 0:00:33I'm Ben Garrod - an evolutionary biologist,
0:00:33 > 0:00:36with a very unusual passion.
0:00:36 > 0:00:37This is unbelievable!
0:00:37 > 0:00:40There are too many skeletons for me to look at all at once!
0:00:40 > 0:00:43As a child, I was fascinated by bones.
0:00:44 > 0:00:46Now skeletons have become my life.
0:00:49 > 0:00:54And I put them together for museums and universities all over the world.
0:00:56 > 0:01:02I'm going to explore the natural world from the inside out.
0:01:04 > 0:01:10To see how the skeleton has enabled animals to move, to eat
0:01:10 > 0:01:12and even find a mate.
0:01:13 > 0:01:18I will take you on a very personal journey to discover how this one bony
0:01:18 > 0:01:23blueprint has shaped such massive diversity across the animal kingdom.
0:01:24 > 0:01:26This time, we'll discover the way
0:01:26 > 0:01:29bones allow animals to perceive the world.
0:01:31 > 0:01:35Looking at each sense in turn, we'll find out how vertebrates have
0:01:35 > 0:01:38evolved to see, hear and smell.
0:01:38 > 0:01:42This tiny little bone that is unique to the species has radicalised
0:01:42 > 0:01:45the way it feeds, the way it forages, the way it survives.
0:01:47 > 0:01:51And even use senses that appear supernatural.
0:01:53 > 0:01:57What you've got in effect is a 40 or 50-tonne, rigid, swimming radar gun.
0:01:57 > 0:02:01I'm going to reveal the Secrets Of Bones.
0:02:12 > 0:02:16I've been building the skeleton of a lowland gorilla, and when
0:02:16 > 0:02:20thinking about how it senses the world, it strikes me that there's
0:02:20 > 0:02:25one part of its skeleton that's more important than any other - the skull.
0:02:26 > 0:02:31Skulls evolved for one function - and that was to house the brain,
0:02:31 > 0:02:34at all costs, to protect the brain inside.
0:02:34 > 0:02:38But since then they've changed, and they've adapted and evolved
0:02:38 > 0:02:42specifically to become a sensory hub. They allow a sense of smell,
0:02:42 > 0:02:45hearing and, importantly, the sense of sight.
0:02:48 > 0:02:51On the outside, it might look like the weird
0:02:51 > 0:02:53and wonderful sensory organs
0:02:53 > 0:02:56are formed just from skin and soft tissue,
0:02:56 > 0:03:00but that couldn't be further from the truth.
0:03:03 > 0:03:06The bone itself is absolutely vital,
0:03:06 > 0:03:11and the skull is at the centre of the bony adaptations for sensing.
0:03:11 > 0:03:13These adaptations are so clear
0:03:13 > 0:03:17that I can often work out how an animal hunts,
0:03:17 > 0:03:21navigates and avoids being eaten, just from looking at its bones.
0:03:24 > 0:03:26First, I'm going to look at sight, which is
0:03:26 > 0:03:28the gorilla's most important sense -
0:03:28 > 0:03:33and that's evident by the large orbits or eye sockets in the skull.
0:03:34 > 0:03:38Now what they do, they allow these incredibly complex,
0:03:38 > 0:03:41delicate sensory structures, the eyes, to be housed
0:03:41 > 0:03:42and protected in a way
0:03:42 > 0:03:45that won't allow them to be damaged or knocked or squished.
0:03:45 > 0:03:48I mean, the last thing you want is your eye to be ruptured.
0:03:48 > 0:03:50But more than that, also it allows a direct
0:03:50 > 0:03:53transfer of information from the outside world, from the eye,
0:03:53 > 0:03:57through these little optic canals, right into the brain itself.
0:03:59 > 0:04:03So, at a basic level, the orbits house and protect the delicate eyes.
0:04:05 > 0:04:08But there's more to these bony sockets than that.
0:04:09 > 0:04:12Where they're placed in the skull plays a key role in sight.
0:04:21 > 0:04:25So, in my bag I happen to have two very different skulls -
0:04:25 > 0:04:30the first of which is a sheep, and I also have a wolf.
0:04:30 > 0:04:34The thing that interests me most is where their eyes are.
0:04:34 > 0:04:37Now, on the sheep here you can see the eyes, the eye sockets,
0:04:37 > 0:04:40are situated right on the side of the head, really far back.
0:04:40 > 0:04:44And that's because this animal spends a lot of its life head down,
0:04:44 > 0:04:46on the ground, eating, grazing,
0:04:46 > 0:04:50and what's going to happen is something's going to sneak up to it.
0:04:50 > 0:04:54By having these eye sockets situated way back
0:04:54 > 0:04:58on the side of its head, it can see almost 360 degrees around it
0:04:58 > 0:05:02and this gives amazing peripheral vision.
0:05:02 > 0:05:05The opposite end of the scale is something like the wolf.
0:05:05 > 0:05:07Now the wolf is an apex predator.
0:05:07 > 0:05:10It doesn't need to see behind it, nothing's going to sneak up
0:05:10 > 0:05:14and eat it, but what it does need is a set of eyes, a set of eye sockets,
0:05:14 > 0:05:19at the front of its skull where it has amazing stereoscopic vision.
0:05:19 > 0:05:23Now this means it has a huge overlap between what each eye can see
0:05:23 > 0:05:25and this gives it great depth perception,
0:05:25 > 0:05:28so it can see exactly how far away something is.
0:05:30 > 0:05:34And this is the case throughout the animal kingdom.
0:05:34 > 0:05:37Prey animals tend to have eyes on the side of their heads.
0:05:41 > 0:05:45And predators usually have forward facing eyes to help them hunt.
0:05:47 > 0:05:50So the position of the eyes and sockets has become
0:05:50 > 0:05:53an evolutionary trade-off for both predator and prey.
0:05:55 > 0:05:59As one evolves massive peripheral vision, the other evolves amazing
0:05:59 > 0:06:02stereoscopic vision, and what they're both trying to do is out-compete
0:06:02 > 0:06:06the other one in terms of staying off the dinner plate and having dinner.
0:06:16 > 0:06:19So the orbits can usually tell me whether an animal
0:06:19 > 0:06:21is predator or prey.
0:06:23 > 0:06:25But that's not all.
0:06:25 > 0:06:28The size of those eye sockets gives a clue
0:06:28 > 0:06:31about when and where an animal hunts.
0:06:32 > 0:06:36I have two skulls here from animals roughly the same size, now they're
0:06:36 > 0:06:41both primates and they're about the size of a big kitten, I guess.
0:06:41 > 0:06:43The first one is from a marmoset, which is
0:06:43 > 0:06:47a monkey from South America, and you can see the orbits,
0:06:47 > 0:06:50and therefore the eyes, are roughly the same sort of size
0:06:50 > 0:06:55I guess you'd expect from an animal with a body this sort of size.
0:06:55 > 0:06:59What's really special is this little fella here.
0:07:00 > 0:07:02Now this is a tarsier skull,
0:07:02 > 0:07:07and instantly you can see it's got these absolutely massive orbits.
0:07:07 > 0:07:10And it tells me that this animal is nocturnal.
0:07:14 > 0:07:17These huge orbits house a pair of enormous eyes that
0:07:17 > 0:07:21let as much light in as possible, enabling the tarsier
0:07:21 > 0:07:22to hunt at night.
0:07:24 > 0:07:28Tarsiers have the largest eyes in comparison to body size
0:07:28 > 0:07:29of any mammal.
0:07:29 > 0:07:34And, remarkably, each eye is larger than their own brain.
0:07:34 > 0:07:39If you were to somehow scale my eyes up to be the same size
0:07:39 > 0:07:42proportionally as the little tarsier here
0:07:42 > 0:07:45then each would be the same size as a grapefruit.
0:07:46 > 0:07:50But having such colossal eyes does pose a problem.
0:07:52 > 0:07:54The eyes are so large
0:07:54 > 0:07:58they can't actually move within their own eye sockets like ours can.
0:07:59 > 0:08:03To get around this, the little animal has an amazing
0:08:03 > 0:08:07skeletal adaptation where it can move its skull on the top
0:08:07 > 0:08:11of its vertebrae, almost 180 degrees in each direction.
0:08:13 > 0:08:16It does this by having specialised joints between
0:08:16 > 0:08:20its neck vertebrae so that it can rotate its head right around
0:08:20 > 0:08:23and see in all directions.
0:08:23 > 0:08:24Like an owl.
0:08:27 > 0:08:30Many animals that operate in low light conditions rely on
0:08:30 > 0:08:34extra large eye sockets, like sea lions,
0:08:34 > 0:08:36that fish in murky water,
0:08:36 > 0:08:40or the tiger, which hunts in dark forests.
0:08:42 > 0:08:44It even translates to humans.
0:08:44 > 0:08:49Polar regions receive much less light than equatorial areas,
0:08:49 > 0:08:52so people with Arctic ancestry can have eye sockets
0:08:52 > 0:08:5520% larger than those from the equator.
0:08:58 > 0:09:01So, just looking at a skull can reveal how
0:09:01 > 0:09:03an animal senses the world.
0:09:06 > 0:09:09Whilst the tarsier relies on sight,
0:09:09 > 0:09:12other vertebrates depend on different senses.
0:09:17 > 0:09:20I'm on my way to see an animal with extraordinary hearing,
0:09:20 > 0:09:23thanks again to the unusual structure of its skull.
0:09:27 > 0:09:31And to demonstrate just how effective this adaptation is,
0:09:31 > 0:09:33I've got a test for the animal in question.
0:09:35 > 0:09:36I've got three buzzers here and I'm
0:09:36 > 0:09:40going to hide them in three different locations amongst these leaves.
0:09:51 > 0:09:54These buzzers are controlled by this little box here
0:09:54 > 0:09:58and each of these buttons controls an individual buzzer.
0:09:58 > 0:09:59When I press it...
0:09:59 > 0:10:00BUZZING
0:10:02 > 0:10:05..even though I've only just hidden these buzzers,
0:10:05 > 0:10:08already I'm having huge difficulties in deciding
0:10:08 > 0:10:11where each buzzer is and which one is buzzing.
0:10:11 > 0:10:14That's because if I needed to find them I'd actually have to go
0:10:14 > 0:10:17and look for them because, as a human, my main sense is my vision.
0:10:17 > 0:10:21But there's one animal that can hear much better than I can
0:10:21 > 0:10:24and it will be able to find these buzzers instantly.
0:10:26 > 0:10:27BUZZING
0:10:35 > 0:10:37Perfect, straight to the buzzer.
0:10:37 > 0:10:38This is a great grey owl.
0:10:41 > 0:10:43This is a hand-reared owl,
0:10:43 > 0:10:47kept here at the International Centre For Birds Of Prey.
0:10:47 > 0:10:49I'm going to see if he can go to the second buzzer.
0:10:49 > 0:10:50BUZZING
0:10:50 > 0:10:54He can't see these buzzers, they're too well hidden.
0:10:54 > 0:10:56So he's relying totally on his ears.
0:10:58 > 0:11:01He got there, you found your second buzzer!
0:11:01 > 0:11:02You're such a clever bird!
0:11:02 > 0:11:06He's been trained to come to the buzzers to illustrate just
0:11:06 > 0:11:09how accurate his hearing is by curator Holly Cale.
0:11:13 > 0:11:16We've seen already that this bird has an amazing ability
0:11:16 > 0:11:19to hear, is that its main sense?
0:11:19 > 0:11:22It's definitely up there, it's probably its most
0:11:22 > 0:11:25important sense, but the eyesight is also very good.
0:11:25 > 0:11:29They're very good at seeing fine changes down in the undergrowth,
0:11:29 > 0:11:33they combine that with the hearing, when they need to.
0:11:33 > 0:11:37Great grey owls usually hunt by perching on branches or
0:11:37 > 0:11:40tree tops, watching and listening for prey below.
0:11:42 > 0:11:45But the Arctic habitat of these owls means their prey is often
0:11:45 > 0:11:48hidden under the snow, rendering their eyesight useless.
0:11:50 > 0:11:53And that's why they've developed such sensitive hearing - they can
0:11:53 > 0:11:57detect a tiny mouse under half a metre of snow
0:11:57 > 0:11:59from over ten metres away.
0:12:01 > 0:12:03Underneath all of the insulation that he needs to stay
0:12:03 > 0:12:06warm in the Arctic he's actually not a huge owl.
0:12:06 > 0:12:09The most striking thing about it is he's got this beautiful round facial
0:12:09 > 0:12:15disc and that's there to funnel sound into the ears as best he can.
0:12:15 > 0:12:19If I can pop by finger in the side here, very gently, roughly where
0:12:19 > 0:12:21his ear is and stop when I get to his skull -
0:12:21 > 0:12:26there we go - that shows you he's got a good inch of insulation.
0:12:26 > 0:12:27A lot of feather.
0:12:27 > 0:12:31And an inch of facial disc angling and funnelling sound into those ears
0:12:33 > 0:12:36But this facial disc is just part of what gives
0:12:36 > 0:12:39the great grey owl its auditory prowess.
0:12:41 > 0:12:44Like most vertebrates, it has ear openings
0:12:44 > 0:12:46on either side of its skull.
0:12:46 > 0:12:49This means that sound reaches the two ears at
0:12:49 > 0:12:51slightly different times,
0:12:51 > 0:12:54allowing it to detect the direction the noise is coming from.
0:12:56 > 0:12:59What's special about certain species of owl is that
0:12:59 > 0:13:01one ear is slightly higher than the other.
0:13:02 > 0:13:06This asymmetry means the height of a sound can be pinpointed,
0:13:06 > 0:13:09making their hearing even more accurate.
0:13:11 > 0:13:14He's being very well-behaved but he's constantly looking around,
0:13:14 > 0:13:19he's restless it seems - is he listening all the time?
0:13:19 > 0:13:22He is constantly aware of what's going on around him,
0:13:22 > 0:13:25so every time there's a noise, a background noise,
0:13:25 > 0:13:27bits and pieces going on, he'll turn his head,
0:13:27 > 0:13:31he'll face his facial disc to where he thinks that noise is coming from
0:13:31 > 0:13:35to get a better idea of what's going on in his surroundings.
0:13:35 > 0:13:38Is it important, is it something he needs to worry about,
0:13:38 > 0:13:39is it something worth hunting?
0:13:39 > 0:13:42I genuinely think I'm in love with this guy.
0:13:42 > 0:13:44He's such a wonderful little character,
0:13:44 > 0:13:48but he's like this hunting, flying, predatory satellite dish.
0:13:48 > 0:13:50He's perfect, isn't he?
0:13:50 > 0:13:54He is, all of those things combine to make him a little star.
0:14:04 > 0:14:07Whilst an asymmetrical skull allows these owls to isolate
0:14:07 > 0:14:09sounds more accurately,
0:14:09 > 0:14:13bone has an even more fundamental role to play in hearing.
0:14:14 > 0:14:15Because without it,
0:14:15 > 0:14:19most vertebrates wouldn't hear much of anything at all.
0:14:22 > 0:14:23As a sound wave hits the inner ear,
0:14:23 > 0:14:2899.9% of its energy would be reflected away -
0:14:28 > 0:14:32and almost all sounds would go unheard - if it wasn't for bones.
0:14:34 > 0:14:38Most vertebrates have developed tiny, delicate ear-bones -
0:14:38 > 0:14:39or ossicles.
0:14:40 > 0:14:43And mammals have three of them.
0:14:44 > 0:14:47These are the human ossicles,
0:14:47 > 0:14:49and as well as being very fragile,
0:14:49 > 0:14:51they're the smallest bones
0:14:51 > 0:14:54in our body.
0:14:55 > 0:15:00They're made up of
0:15:00 > 0:15:01the malleus,
0:15:01 > 0:15:04incus and stapes.
0:15:05 > 0:15:11These bones work together to form a vibrating chain, passing
0:15:11 > 0:15:14sound waves from the malleus
0:15:14 > 0:15:16to the incus to the stapes.
0:15:19 > 0:15:22And because the ossicles are arranged as a system of levers, a small
0:15:22 > 0:15:28force at one end becomes a larger force at the other, so not only is
0:15:28 > 0:15:32a sound wave passed through to the inner ear, the sound is amplified.
0:15:35 > 0:15:39And what's more, the composition of these tiny bones is different
0:15:39 > 0:15:41to every other bone in the human skeleton.
0:15:43 > 0:15:45Bone is essentially made up of two components -
0:15:45 > 0:15:51an organic part - collagen - which provides the flexibility
0:15:51 > 0:15:55and a mineral one - calcium phosphate - which gives the bone
0:15:55 > 0:15:56rigidity.
0:15:56 > 0:16:00These different compounds are found in varying degrees in almost
0:16:00 > 0:16:03every bone in our body.
0:16:03 > 0:16:06Now, these little bones here are really mineral rich,
0:16:06 > 0:16:10and this makes them really hard but quite fragile.
0:16:10 > 0:16:12This would be useless in something like our femur, in our thigh,
0:16:12 > 0:16:17because with all that weight bearing and twisting it would simply shatter.
0:16:17 > 0:16:20But whereas these little bones are protected deep within the skull,
0:16:20 > 0:16:27by being very hard allows them to transfer and conduct sound perfectly.
0:16:28 > 0:16:31So the chemical composition of bone
0:16:31 > 0:16:33and the way the three ossicles work together
0:16:33 > 0:16:38makes an extremely efficient hearing system, transmitting 60% of
0:16:38 > 0:16:42the sound energy that hits the eardrum to the inner ear.
0:16:44 > 0:16:47Whilst most vertebrates have just one ossicle,
0:16:47 > 0:16:48only mammals have three,
0:16:48 > 0:16:52helping them have some of the sharpest hearing on the planet.
0:16:56 > 0:16:59There's another key sense housed in the skull,
0:16:59 > 0:17:02which has more of a connection with bone than might first appear.
0:17:02 > 0:17:05The sense of smell.
0:17:07 > 0:17:10All skulls have an opening for the nostrils.
0:17:10 > 0:17:12They're even found on birds' beaks.
0:17:13 > 0:17:16Nostrils occur in different positions,
0:17:16 > 0:17:19just like the eye sockets and ear openings.
0:17:19 > 0:17:23And one animal has taken this to the extreme.
0:17:25 > 0:17:27Kiwis are the only birds
0:17:27 > 0:17:30with nostrils right on the tip of the beak.
0:17:36 > 0:17:39They're nocturnal, and virtually blind
0:17:39 > 0:17:42so rely on their sense of smell to find food.
0:17:44 > 0:17:49As they walk, kiwis tap the ground with their beak, probing the soil
0:17:49 > 0:17:51to sniff out their prey - earthworms,
0:17:51 > 0:17:54insects, fallen fruits and seeds.
0:17:57 > 0:18:00Having nostrils at the end of the beak means that,
0:18:00 > 0:18:04when poked underground, they can smell an earthworm 15cm down.
0:18:08 > 0:18:10Even at this basic level,
0:18:10 > 0:18:14changes to the skeleton help the kiwi detect its prey.
0:18:16 > 0:18:20But hidden inside the skull is another bony structure that
0:18:20 > 0:18:23can turn an animal's sniffing into a supersense.
0:18:27 > 0:18:29Here at the Oxford Museum of Natural History,
0:18:29 > 0:18:31there's a perfect example.
0:18:37 > 0:18:40If you look inside the nose here you can see this elaborate,
0:18:40 > 0:18:43honeycomb-like structure.
0:18:43 > 0:18:45These structures are actually very delicate bones,
0:18:45 > 0:18:47known as turbinates.
0:18:47 > 0:18:50These turbinates, along with this really long muzzle here,
0:18:50 > 0:18:53tells me that this animal has an incredibly good sense of smell.
0:18:55 > 0:18:57This is the skull from a polar bear.
0:19:01 > 0:19:03Their eyesight is about the same as ours
0:19:03 > 0:19:08but it's estimated their sense of smell is 100 times greater.
0:19:10 > 0:19:14Polar bears have been reported as travelling 20 kilometres
0:19:14 > 0:19:16in a straight line to reach a carcass,
0:19:16 > 0:19:19which they've located by following their nose.
0:19:24 > 0:19:25By sniffing the ice,
0:19:25 > 0:19:28they can detect where a seal is using a breathing hole.
0:19:30 > 0:19:34And can even find a seal pup hidden under a thick layer of ice
0:19:34 > 0:19:36from over a kilometre away.
0:19:40 > 0:19:43And it's because their prey is spread out over huge distances,
0:19:43 > 0:19:47that a polar bear's sense of smell needs to be exceptional.
0:19:49 > 0:19:52This extraordinary ability is down to the turbinate bones
0:19:52 > 0:19:57in their nose, which form a sophisticated system for smelling.
0:20:00 > 0:20:04The turbinates are separated into three very distinct areas, the first
0:20:04 > 0:20:06of which are the maxilloturbinates, and they're at the front,
0:20:06 > 0:20:11and are actually responsible for warming air as it enters the nose.
0:20:11 > 0:20:14This is kind of essential if you're living up in the Arctic.
0:20:14 > 0:20:17Behind those you have the nasoturbinates
0:20:17 > 0:20:18and the ethmoturbinates
0:20:18 > 0:20:22and these are the ones that are associated with a sense of smell.
0:20:23 > 0:20:27This delicate bony structure is covered in sensory cells
0:20:27 > 0:20:31which detect smell and transmit information to the brain.
0:20:33 > 0:20:35In the polar bear, the turbinates' large size
0:20:35 > 0:20:39and intricate honeycomb structure provides a huge surface area
0:20:39 > 0:20:43to house a vast number of these sensory cells.
0:20:43 > 0:20:46And this is what's key to giving the polar bear
0:20:46 > 0:20:48such an amazing sense of smell.
0:20:58 > 0:21:02There's one last nose which has to be the most bizarre
0:21:02 > 0:21:04when it comes to bony adaptations for smelling.
0:21:08 > 0:21:10This nose is unique
0:21:10 > 0:21:12and very few people have ever seen it,
0:21:12 > 0:21:15because it belongs to one of the rarest mammals on
0:21:15 > 0:21:20the planet, found only on the island of Hispaniola in the Caribbean.
0:21:23 > 0:21:26I've come to the Zoological Society of London to meet
0:21:26 > 0:21:31Dr Sam Turvey, who can show me what this nose can do and the animal
0:21:31 > 0:21:32it belongs to.
0:21:34 > 0:21:37It's an animal called Hispaniolan Solenodon.
0:21:37 > 0:21:39And they are a type of insectivorous mammal
0:21:39 > 0:21:41they are distantly related to shrews.
0:21:41 > 0:21:43They're very distinct from anything,
0:21:43 > 0:21:46they diverged from all other living mammals about 76 million
0:21:46 > 0:21:48years ago, that's during the time of the dinosaurs.
0:21:48 > 0:21:51Looking at its snout, it looks like it's broken it,
0:21:51 > 0:21:55but I'm guessing that's not the case, it's got this kink in the middle - what's going on?
0:21:55 > 0:21:57We know very little about solenodons,
0:21:57 > 0:22:00they're extremely threatened with extinction and there have
0:22:00 > 0:22:02been very few ecological studies conducted on them.
0:22:02 > 0:22:04But what we do know is that they're active at night
0:22:04 > 0:22:06and also at dawn and dusk.
0:22:06 > 0:22:09In fact, it will navigate around and find its prey
0:22:09 > 0:22:11using that very, very elongated snout.
0:22:11 > 0:22:13If you're lucky enough to see one in the wild you'll
0:22:13 > 0:22:17see the snout's constantly twitching around like this,
0:22:17 > 0:22:21so they're almost comic, very cute looking characters if you see them.
0:22:23 > 0:22:25The selenedon is ground-based,
0:22:25 > 0:22:28hunting mostly insects and other invertebrates.
0:22:31 > 0:22:33It uses its snout to explore cracks
0:22:33 > 0:22:36and crevices where its prey hides.
0:22:38 > 0:22:41It then shoves its nose into the soil to retrieve its food,
0:22:41 > 0:22:44creating holes in the ground called "nose pokes".
0:22:47 > 0:22:52This strong, flexible snout is down to its peculiar skeletal structure.
0:22:54 > 0:22:57And the only way to see that properly is to X-ray a rare
0:22:57 > 0:23:01specimen the institute has in its collection.
0:23:01 > 0:23:03So, have you had this X-rayed before?
0:23:03 > 0:23:05No, it's the first time it's been X-rayed
0:23:05 > 0:23:08and I can't think of many or any other times solenodons have
0:23:08 > 0:23:11ever been X-rayed, so it's really interesting to see what we find.
0:23:17 > 0:23:19You can see here this white area, that's
0:23:19 > 0:23:23the bone of the skull and this greyer shadow, that's the soft
0:23:23 > 0:23:26tissue, so you've got the snout coming down here, and this
0:23:26 > 0:23:30little thing here, that is the key to the solendon's flexible snout.
0:23:30 > 0:23:31What do you think that is?
0:23:31 > 0:23:33I'm guessing it's an extra bone.
0:23:33 > 0:23:39Yes, it's an os proboscis or a nose bone. And it's the only mammal
0:23:39 > 0:23:42in the world, as far as we know, to have this unique bone and this
0:23:42 > 0:23:45is what gives the solenodon that little extra edge in having
0:23:45 > 0:23:48a really flexible wiggly snout.
0:23:48 > 0:23:51You can see it's a ball and socket joint.
0:23:51 > 0:23:55So like I get in my shoulder or my hip, it's the same thing there.
0:23:55 > 0:23:56That's brilliant.
0:23:56 > 0:24:00Yes, and it provides both support for this large, heavy snout
0:24:00 > 0:24:04but also flexibility and leverage at the same time.
0:24:04 > 0:24:06So this tiny little bone that's unique to this species
0:24:06 > 0:24:10has really radicalised the way it feeds, the way it forages,
0:24:10 > 0:24:12the way it survives.
0:24:12 > 0:24:14It's so nice to see it as well because I've been
0:24:14 > 0:24:16working on these species for so many years and I've never seen
0:24:16 > 0:24:21a nice X-ray exposure of this, it's the first time for me, it's lovely.
0:24:21 > 0:24:22Really interesting.
0:24:24 > 0:24:29Having looked at sight, sound and smell, it might
0:24:29 > 0:24:32seem that's the end of the story for bones and senses.
0:24:34 > 0:24:37But some animals use bone to take their senses
0:24:37 > 0:24:39to a whole new level.
0:24:42 > 0:24:47This is the mighty sperm whale - a multiple record breaker.
0:24:47 > 0:24:51It's the largest of the toothed whales, with some males reaching
0:24:51 > 0:24:5220m in length.
0:24:54 > 0:24:57What's more, it's the deepest diving mammal,
0:24:57 > 0:25:02reaching depths of 3,000m - that's two miles down.
0:25:03 > 0:25:07And it's during these super deep dives that it uses its
0:25:07 > 0:25:10extraordinary sensory capabilities.
0:25:11 > 0:25:14At those depths, it's almost pitch black,
0:25:14 > 0:25:18so sperm whales navigate and hunt using echolocation.
0:25:19 > 0:25:22And it's their bones that enable them do this.
0:25:23 > 0:25:27The sperm whale has a truly massive head filled with a specialised oil
0:25:27 > 0:25:30called spermecetti.
0:25:30 > 0:25:34Now, at the front of the head, round about here somewhere, it would
0:25:34 > 0:25:38produce a series of very quick pulsed clicks.
0:25:38 > 0:25:42These travel back through this spermecetti to this part of the skull
0:25:42 > 0:25:44and this is very concave,
0:25:44 > 0:25:47it's effectively the whale's forehead, I guess.
0:25:47 > 0:25:52Once these pulses are channelled and focused they shoot out.
0:25:52 > 0:25:56The clicks are the loudest sounds ever recorded from an animal
0:25:56 > 0:25:58and can travel for ten kilometres.
0:25:59 > 0:26:01If they hit something,
0:26:01 > 0:26:04the pulses bounce back towards the whale.
0:26:04 > 0:26:07The whale doesn't receive these echoed return pulses
0:26:07 > 0:26:09in the top of its head again.
0:26:09 > 0:26:13Instead, it receives them in the lower jaw, in this area here.
0:26:13 > 0:26:17The lower jaw has evolved to have this grooved channel running
0:26:17 > 0:26:18all the way through the bone,
0:26:18 > 0:26:21and this is filled with a jelly-like, fatty substance.
0:26:21 > 0:26:24It's this that picks up these returned echoes.
0:26:24 > 0:26:28It transfers it through this channel, right through the lower jaw
0:26:28 > 0:26:31into this area here, and eventually into the inner ear.
0:26:32 > 0:26:34After that it goes into the brain,
0:26:34 > 0:26:37and this is where the animal builds up a 3D picture
0:26:37 > 0:26:38of the world around it.
0:26:38 > 0:26:42And there's one further skeletal adaptation which makes
0:26:42 > 0:26:44this system even better.
0:26:44 > 0:26:47It's in the neck vertebrae. Now, like most mammals,
0:26:47 > 0:26:50sperm whales have seven vertebrae in their neck, just like we do.
0:26:50 > 0:26:54But the special adaptation here is that most of them
0:26:54 > 0:26:58are fused together in one large bone, you can just see there.
0:26:58 > 0:27:02This serves to hold the whole head rigid.
0:27:02 > 0:27:05This makes sense when you think that it's got a massive head with
0:27:05 > 0:27:08a really sensitive sensory organ attached to that.
0:27:08 > 0:27:12When it's firing out these little pulses and receiving the echoes,
0:27:12 > 0:27:15the last thing it wants is a head that's all over the place and wobbly.
0:27:15 > 0:27:18By being held in one position ensures that these
0:27:18 > 0:27:21pulses are received as accurately as possible.
0:27:21 > 0:27:25So what you've got in effect is a 40 or 50-tonne, rigid,
0:27:25 > 0:27:27swimming radar gun.
0:27:28 > 0:27:31It's a combination of skeletal adaptations
0:27:31 > 0:27:35which add up to create a deadly and sophisticated sensory capability.
0:27:38 > 0:27:41This is just one of the countless methods vertebrates use
0:27:41 > 0:27:43to sense the world.
0:27:44 > 0:27:48Underneath muscle and soft tissue, bone is evolving
0:27:48 > 0:27:52to enable them to do this in an ever increasing number of ways.
0:27:55 > 0:27:59Be that with enormous eye orbits and a specialised neck joint,
0:27:59 > 0:28:02asymmetrical ear openings, or complicated nasal turbinates.
0:28:04 > 0:28:10Bone is vital for finding food, detecting predators and navigation.
0:28:13 > 0:28:16Next time, we uncover how the skeleton is essential
0:28:16 > 0:28:18for capturing and devouring food.
0:28:18 > 0:28:20From the enormous...
0:28:21 > 0:28:24Each one of these molars can weigh up to 5kg.
0:28:25 > 0:28:26..to the bizarre...
0:28:27 > 0:28:31It's more alien than it is animal, and it's one massive killing
0:28:31 > 0:28:33machine head, with a little tail.
0:28:34 > 0:28:38..as we delve even deeper into the Secrets Of Bones.