- 6/21/2025
Secrets of Bones episode 4
Category
đ
LearningTranscript
00:00bones they offer structure support and strength but they have a much bigger story to tell
00:13vertebrates may look very different on the outside but one crucial thing unites them all
00:23the skeleton I'm Ben Garrett an evolutionary biologist with a very unusual passion this
00:36is unbelievable there are too many skeletons for me to look at all at once as a child I was
00:41fascinated by bones now skeletons have become my life and I put them together for museums and
00:51universities all over the world I'm going to explore the natural world from the inside out
01:02to see how the skeleton has enabled animals to move to eat and even find a mate I will take you
01:14on a very personal journey to discover how this one bony blueprint has shaped such massive diversity
01:21across the animal kingdom this time we'll discover the way bones allow animals to perceive the world
01:28looking at each sense in turn we'll find out how vertebrates have evolved to see here and smell
01:37this tiny little bone that's unique to the species is really well radicalized the way it feeds wait for
01:43forages and even use sensors that appear supernatural what you've got in effect is a 40 or 50 ton rigid
01:55swimming radar gun I'm going to reveal the secrets of bones
02:00I've been building the skeleton of a lowland gorilla and when thinking about how it senses the world it strikes
02:19me that there's one part of its skeleton that's more important than any other the skull skulls evolved for
02:28one function and that was to house the brain at all costs protect the brain inside but since then they've
02:35changed and they've adapted and evolved specifically to become a sensory hub they allow sense of smell
02:42hearing and importantly the sense of sight on the outside it might look like the weird and wonderful
02:52sensory organs are formed just from skin and soft tissue but that couldn't be further from the truth
03:02the bone itself is absolutely vital and the skull is at the center of the bony adaptations for sensing these
03:12adaptations are so clear that I can often work out how an animal hunts navigates and avoids being eaten just
03:20from looking at its bones first I'm going to look at sight which is the gorillas most important sense
03:28and that's evident by the large orbits or eye sockets in the skull now what they do they allow these
03:36incredibly complex delicate sensory structures the eyes to be housed and protected in a way that won't
03:42allow them to be damaged or knocked or squished and the last thing you want is your eye to be ruptured
03:46but more than that also it allows a direct transfer of information from the outside world from the eye
03:53through these little optic canals right into the brain itself so at a basic level the orbits house and
04:01protect the delicate eyes but there's more to these bony sockets than that where they're placed in the skull
04:10plays a key role in sight so in my bag I happen to have two very different skulls the first of which
04:26is a sheep and I also have a wolf the thing that interests me most is where their eyes are now on the
04:34sheep here you can see the eyes the eye sockets are situated right on the side of the head really far
04:39back that's because this animal spends a lot of his life head down on the ground eating grazing and
04:46what's going to happen is that something is going to sneak up to it by having these eye sockets situated
04:53way back on the side of its head it can see almost 360 degrees around it and this gives amazing peripheral
05:00vision the opposite end of the scale is something like the wolf now the wolf is an apex predator it
05:07doesn't need to see behind it nothing's going to sneak up and eat it but what it does need is a set of
05:12eyes set of eye sockets at the front of its skull where it has amazing stereoscopic vision now this
05:19means it has a huge overlap between what each eye can see and this gives a great depth perception so it
05:25can see exactly how far away something is and this is the case throughout the animal kingdom prey animals
05:34tend to have eyes on the side of their heads and predators usually have forward-facing eyes to help
05:45them hunt so the position of the eyes and sockets has become an evolutionary trade-off to both predator
05:52and prey as one evolves massive peripheral vision the other one involves amazing stereoscopic vision
06:00and what they're both trying to do is out-compete the other one in terms of staying off the dinner
06:04plate and having dinner
06:05so the orbits can usually tell me whether an animal is predator or prey
06:20but that's not all the size of those eye sockets gives a clue about when and where an animal hunts
06:30i have two skulls here from animals roughly the same size and they're both primates
06:36and they're about the size of big kitten i guess the first one is from a marmoset which is a monkey from
06:43south america and you can see the orbits and therefore the eyes are roughly the same sort of size i guess
06:51you'd expect from an animal with a body this sort of size what's really special is this little fella
06:58here this is a tarsier skull and instantly you can see it's got these absolutely massive orbits and it
07:07tells me that this animal is nocturnal
07:13these huge orbits has a pair of enormous eyes that let as much light in as possible enabling the tarsier to hunt at night
07:24tarsiers have the largest eyes in comparison to body size of any mammal and remarkably each eye is larger than their own brain
07:33if you were to somehow scale my eyes up to be the same size proportionally as the little tarsier here
07:41then each of my eyes would be the same size as a grapefruit but having such colossal eyes does pose a problem
07:52the eyes are so large they can't actually move within their own eye sockets like ours can
07:57to get around this the little animal has an amazing skeletal adaptation where it can move
08:06its skull on the top of its vertebrae almost 180 degrees in each direction it does this by having
08:14specialized joints between its neck vertebrae so that it can rotate its head right around and see in all
08:21directions like an owl many animals that operate in low light conditions rely on extra large eye sockets
08:32like sea lions that fish in murky water or the tiger which hunts in dark forests
08:41it even translates to humans polar regions receive much less light than equatorial areas so people with
08:49arctic ancestry can have eye sockets 20 percent larger than those from the equator
08:58so just looking at a skull can reveal how an animal senses the world
09:06whilst the tarsier relies on sight other vertebrates depend on different senses
09:12buzzers
09:16i'm on my way to see an animal with extraordinary hearing thanks again to the unusual structure of its skull
09:27and to demonstrate just how effective this adaptation is i've got a test for the animal in question
09:34I've got three buzzers here, and I'm going to hide them in three different locations amongst these leaves.
09:51These buzzers are controlled by this little box here, and each of these buttons controls an individual buzzer.
09:57When I press it, even though I've only just hidden these buzzers, already I'm having huge difficulties in deciding where each buzzer is and which one's buzzing.
10:10That's because if I needed to find them, I'd actually have to go and look for them, because as a human, my main sense is my vision.
10:17But there's one animal that can hear much better than I can, and it will be able to find these buzzers instantly.
10:27Perfect. Straight to the buzzer. This is a great grey owl.
10:41This is a hand-reared owl, kept here at the International Centre for Birds of Prey.
10:46I'm going to see if he can go to the second buzzer.
10:50He can't see these buzzers. They're too well hidden, so he's relying totally on his ears.
10:57He got there.
10:59You found your second buzzer. Oh, you're such a clever bird.
11:03He's been trained to come to the buzzers to illustrate just how accurate his hearing is by curator Holly Kale.
11:13We've seen already that this bird has an amazing ability to hear. Is that its main sense?
11:18It's definitely up there. It's probably its most important sense.
11:22But the eyesight is also very good.
11:24They're very good at seeing fine changes down in the undergrowth.
11:29They combine that with the hearing when they need to.
11:33Great grey owls usually hunt by perching on branches or treetops, watching and listening for prey below.
11:39But the Arctic habitat of these owls means their prey is often hidden under the snow, rendering their eyesight useless.
11:49And that's why they've developed such sensitive hearing.
11:53They can detect a tiny mouse under half a metre of snow from over ten metres away.
11:59Underneath all of the insulation that he needs to stay warm in the Arctic, he's actually not a huge owl.
12:06The most striking thing about it is he's got this beautiful round facial disc.
12:09And that's there to really funnel sound into the ears as best you possibly can.
12:14If I can pop my finger in the side here, very gently, roughly where his ear is, and stop when I get to his skull.
12:21There we go.
12:22That shows you he's got a good inch of insulation there.
12:26A lot of feather.
12:27And an inch of facial disc angling and funneling sound into those ears.
12:31But this facial disc is just part of what gives the great grey owl its auditory prowess.
12:41Like most vertebrates, it has ear openings on either side of its skull.
12:46This means that sound reaches the two ears at slightly different times, allowing it to detect the direction the noise is coming from.
12:54What's special about certain species of owl is that one ear is slightly higher than the other.
13:02This asymmetry means the height of a sound can be pinpointed, making their hearing even more accurate.
13:11Now, he's being very well behaved, but he's constantly looking around.
13:14He's restless, it seems. Is he listening all the time?
13:18He's constantly aware of what's going on around him.
13:21So every time there's a noise, a background noise, bits and pieces going on, he'll turn his head, he'll face his facial disc to where he thinks that noise is coming on to get a better idea of what's going on in his surroundings.
13:35Is it important? Is it something he needs to worry about? Is it something worth hunting?
13:39I genuinely think I'm in love with this little guy.
13:41He really is such a wonderful little character.
13:44But he's like this hunting, flying, predatory satellite dish, isn't he? He's perfect.
13:49He is. He is. All of those things combine to make him a little star.
14:03Whilst an asymmetrical skull allows these owls to isolate sounds more accurately, bone has an even more fundamental role to play in hearing.
14:12Because without it, most vertebrates wouldn't hear much of anything at all.
14:21As a sound wave hits the inner ear, 99.9% of its energy would be reflected away, and almost all sounds would go unheard, if it wasn't for bones.
14:32Most vertebrates have evolved tiny, delicate ear bones, or ossicles.
14:40And mammals have three of them.
14:43These are the human ossicles, as well as being very fragile.
14:49They're the smallest bones in our body.
14:53And they're made up of the malleus, incus, and stapes.
15:05These bones work together to form a vibrating chain.
15:11Passing sound waves from the malleus, to the incus, to the stapes.
15:16And because the ossicles are arranged as a system of levers, a small force at one end becomes a larger force at the other.
15:27So not only is a sound wave passed through to the inner ear, the sound is amplified.
15:34And what's more, the composition of these tiny bones is different to every other bone in the human skeleton.
15:41Bone is essentially made up of two components.
15:46An organic part, collagen, which provides the flexibility.
15:50And a mineral one, calcium phosphate, which gives the bone rigidity.
15:56These different compounds are found in varying degrees in almost every bone in our body.
16:02Now these little bones here are really mineral rich.
16:06Now this makes them really hard, but quite fragile.
16:09This would be useless in something like our femur, in our thigh, because with all that weight-bearing and twisting, it would simply shatter.
16:16But whereas these little bones are protected deep inside the skull, by being very hard, allows them to transfer and conduct sound perfectly.
16:26So the chemical composition of bone, and the way the three ossicles work together, makes an extremely efficient hearing system,
16:36transmitting 60% of the sound energy that hits the eardrum to the inner ear.
16:41Whilst most vertebrates have just one ossicle, only mammals have three, helping them have some of the sharpest hearing on the planet.
16:52There's another key sense housed in the skull, which has more of a connection with bone than might first appear.
17:03The sense of smell.
17:05All skulls have an opening for the nostrils.
17:09They're even found on birds' beaks.
17:13Nostrils occur in different positions, just like the eye sockets and ear openings.
17:19And one animal has taken this to the extreme.
17:25Kiwis are the only birds with nostrils right on the tip of the beak.
17:30They're nocturnal and virtually blind, so rely on their sense of smell to find food.
17:44As they walk, kiwis tap the ground with their beak, probing the soil to sniff out their prey.
17:50Earthworms, insects, fallen fruits and seeds.
17:53Having nostrils at the end of the beak means that when poked underground, they can smell an earthworm 15 centimetres down.
18:08Even at this basic level, changes to the skeleton help the kiwi detect its prey.
18:15But hidden inside the skull, there's another bony structure that can turn an animal sniffing into a super sense.
18:23Here at the Oxford Museum of Natural History, there's a perfect example.
18:37If you look inside the nose here, you can see this very elaborate honeycomb-like structure.
18:43But these structures are actually very delicate bones, and they're known as turbinates.
18:46These turbinates, along with this really long muzzle here, tells me that this animal has an incredibly good sense of smell.
18:54This is the skull from a polar bear.
19:01Their eyesight is about the same as ours, but it's estimated their sense of smell is 100 times greater.
19:08Polar bears have been reported travelling 20 kilometres in a straight line to reach a carcass, which they've located by following their nose.
19:23By sniffing the ice, they can detect where a seal is using a breathing hole.
19:28And can even find a seal pup hidden under a thick layer of ice from over a kilometre away.
19:38And it's because their prey is spread out over such huge distances, that a polar bear's sense of smell needs to be exceptional.
19:46This extraordinary ability is down to the turbinate bones in their nose, which form a sophisticated system for smelling.
20:00The turbinates are separated into three very distinct areas, the first of which are the maxilloturbinates.
20:05Now, they're at the front, and are actually responsible for warming air as it enters the nose.
20:11This is kind of essential if you're living up in the Arctic.
20:13Behind those, you have the nasoturbinates and the ethmoturbinates, and these are the ones which are associated with a sense of smell.
20:23This delicate, bony structure is covered in sensory cells which detect smell and transmit information to the brain.
20:32In the polar bear, the turbinate's large size and intricate honeycomb structure provides a huge surface area to house a vast number of these sensory cells.
20:43And this is what's key to giving the polar bear such an amazing sense of smell.
20:47There's one last nose which has to be the most bizarre when it comes to bony adaptations for smelling.
21:04This nose is unique, and very few people have ever seen it, because it belongs to one of the rarest mammals on the planet, found only on the island of Hispaniola in the Caribbean.
21:19I've come to the Zoological Society of London to meet Dr Sam Turvey, who can show me what this nose can do, and the animal it belongs to.
21:31It's an animal called a Hispaniola and Selenodon, and they are a type of insectivorous mammals.
21:38They are distantly related to shrews, but they're very distinct from anything.
21:42They diverge from all other living mammals around 76 million years ago, so that's during the time of the dinosaurs.
21:48Looking at his snow, it looks like he's broken up, but I'm guessing that's not the case.
21:52It's got a kink in the middle. What's going on here?
21:54We know very little about selenodons. They're extremely threatened with extinction, and there have been very few ecological studies conducted on them.
22:01But what we do know is that they're active at night and also at dawn and dusk.
22:05And in fact, it will navigate around and find its prey using that very, very elongated snout.
22:11And if you're lucky enough to be able to see one in the wild, you can see the snout's always constantly twitching around like this.
22:16So they're kind of almost comic, very cute-looking characters if you see them.
22:20The selenodon is ground-based, hunting mostly insects and other invertebrates.
22:30It uses its snout to explore cracks and crevices where its prey hides.
22:37It then shoves its nose into the soil to retrieve its food, creating holes in the ground called nose pokes.
22:44This strong, flexible snout is down to its peculiar skeletal structure.
22:53And the only way to see that properly is to x-ray a rare specimen the Institute has in its collection.
23:01So have you had this x-rayed before?
23:03No, it's the first time the specimen's been x-rayed.
23:05And I can't think of many or any other times that selenodons have ever been x-rayed.
23:08So really interesting to see what we find.
23:10Really?
23:11Really.
23:14As you can see here, this white area, that's the bone of the skull.
23:20And this kind of greyer shadow, that's the soft tissue.
23:23So you've got the snout coming down here.
23:25And this little thing here, that is the key to the selenodons' flexible snout.
23:30What do you think that is?
23:31I'm guessing it's an extra bone.
23:33It's an extra bone, yeah.
23:33It's an osproposis, or nose bone.
23:36Nose bone, brilliant.
23:37It's the only mammal in the world, as far as we know, to have this unique bone.
23:41And this is what gives the selenodon that little extra edge in having a really flexible, wiggly snout.
23:48It allows, it's actually, you can see, it's a ball and socket joint.
23:51So, like I get in my shoulder, my hip, it's the same thing there.
23:55That's brilliant.
23:55Yes, and it provides both support for this large, heavy snout, but also flexibility and leverage at the same time.
24:03So this tiny little bone that's unique to this species has really radicalised the way it feeds, the way it forages, the way it survives.
24:11It's so nice to see it as well, because I've been working on these species for so many years, and I've never seen a nice X-ray exposure of this.
24:19It's the first time for me.
24:20It's lovely, really interesting.
24:21Having looked at sight, sound and smell, it might seem that's the end of the story for bones and senses.
24:33But some animals use bone to take their senses to a whole new level.
24:41This is the mighty sperm whale, a multiple record breaker.
24:46It's the largest of the toothed whales, with some males reaching 20 metres in length.
24:53What's more, it's the deepest diving mammal, reaching depths of 3,000 metres.
25:00That's two miles down.
25:03And it's during these super deep dives that it uses its extraordinary sensory capabilities.
25:09At those depths, it's almost pitch black, so sperm whales navigate and hunt using echolocation.
25:19And it's their bones that enable them to do this.
25:21The sperm whale has a truly massive head, and it's filled with a very specialised oil called spermaceti.
25:30Now, at the front of the head, around about here somewhere, it would produce a series of very quick pulsed clicks.
25:38These travel back through this spermaceti to this part of the skull.
25:42And this is very concave, and it's effectively the whale's forehead, I guess.
25:46And once these pulses are channelled and focused, they shoot out.
25:52The clicks are the loudest sounds ever recorded from an animal, and can travel for 10 kilometres.
25:59If they hit something, the pulses bounce back towards the whale.
26:04The whale doesn't receive these echoed, returned pulses in the top of its head again.
26:09Instead, it receives them in the lower jaw, in this area here.
26:12Now, the lower jaw has evolved to have this grooved channel running all the way through the bone.
26:18And this is filled with a jelly-like, fatty substance.
26:21It's this that picks up these returned echoes.
26:23It transfers it through this channel, right through the lower jaw, into this area here.
26:29And eventually, into the inner ear.
26:32After that, it goes into the brain, and this is where the animal builds up a 3D picture of the world around it.
26:37And there's one further skeletal adaptation, which makes this system even better.
26:44It's in the neck vertebrae.
26:45Now, like most mammals, sperm whales have seven vertebrae in their neck, just like we do.
26:50But the special adaptation here is that most of them are fused together in one large bone.
26:56You can just see there.
26:58Now, this serves to hold the whole head rigid.
27:02This makes sense when you think that it's got a massive head with a really sensitive sensory organ attached to that.
27:08When it's firing out these little pulses and receiving the echoes, the last thing it wants is a head that's all over the place and wobbly.
27:15By being held in one position ensures that these pulses are received as accurately as possible.
27:21So what you've got in effect is a 40 or 50 tonne rigid swimming radar gun.
27:28It's a combination of skeletal adaptations which add up to create a deadly and sophisticated sensory capability.
27:37This is just one of the countless methods vertebrates use to sense the world.
27:44Underneath muscle and soft tissue, bone is evolving to enable them to do this in an ever-increasing number of ways.
27:51Be that with enormous eye orbits and a specialised neck joint, asymmetrical ear openings or complicated nasal turbinates.
28:03Bone is vital for finding food, detecting predators and navigation.
28:10Next time, we uncover how the skeleton is essential for capturing and devouring food.
28:19From the enormous...
28:20Each one of these molars can weigh up to 5 kilograms.
28:25To the bizarre.
28:27It's more alien than it is animal and it's one massive killing machine head with a little tail.
28:33As we delve even deeper into the secrets of bones.
Recommended
28:51
|
Up next
29:21
29:20
29:36
28:36
37:55
49:56
48:15
47:01
58:13
59:01
58:52
59:06
43:39
29:00
29:07
59:05
43:33
59:08
58:03