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  • 2 days ago
Secrets of Bones episode 3

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Learning
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00:00Bones. They offer structure, support, and strength. But they have a much bigger story to tell.
00:17Vertebrates may look very different on the outside, but one crucial thing unites them all. The skeleton.
00:35I'm Ben Garrett, an evolutionary biologist with a very unusual passion.
00:42This is unbelievable. There are too many skeletons for me to look at all at once.
00:46As a child, I was fascinated by bones. Now, skeletons have become my life.
00:58And I put them together for museums and universities all over the world.
01:06I'm going to explore the natural world from the inside out
01:12to see how the skeleton has enabled animals to move, hunt, and even sense the world.
01:22I will take you on a very personal journey to discover how this one bony blueprint has shaped such massive diversity across the animal kingdom.
01:32And how it has come to dominate life on planet Earth.
01:38This time, we're going to uncover how bones...
01:41Oh, wow. That's absolutely amazing.
01:43...have enabled animals to do the most remarkable thing of all.
01:49Take to the air.
01:50Take to the air.
01:51I'm going to reveal the secrets of bones.
01:57Take to the air.
02:06Pretty much every group of animals, from fish...
02:10...to frogs...
02:13...and mammals...
02:15...to snakes have had a go at getting airborne.
02:17are getting airborne.
02:22But only a few have dramatically changed their skeleton and truly mastered powered flight.
02:31The ultimate fliers have to be the birds.
02:37Their bones have adapted not only for a life up in the sky, but also down in the ground.
02:45And even under the water.
02:49How did the skeleton enable birds to become so successful?
02:57First up, the evolution of wings.
03:03Surprisingly the blueprint for all vertebrate wings can be seen in the primate skeleton,
03:10like this gorilla, and you and me.
03:15These five digits are known as the pentadactyl limb, and first appeared in land animals
03:21over 300 million years ago.
03:24Basically, it was from five fingers like ours, the winged flight has evolved independently
03:30three times.
03:32And to see how these bones first helped animals take to the skies, I'm going back to the time
03:41of the dinosaurs.
03:45The first vertebrates to become true fliers with fully formed wings and sustained flight
03:50were a type of flying reptile, the pterosaurs.
03:55This is a fossil cast of Pterodactylus antiquus, a young pterosaur, about as big as a starling.
04:03The smallest though were only the size of sparrows.
04:08But the biggest pterosaurs, they were massive.
04:11They had a wingspan of over 10 metres.
04:17They were the largest flying animals to have ever lived.
04:21Their wings would fill this room.
04:32Pterosaurs dominated the skies for 150 million years, and had wings modified from the original
04:39five-fingered blueprint.
04:48This is clear when compared alongside a human hand.
04:53The first three digits adapted as grasping claws, and the fifth digit was lost.
04:59But the fourth digit grew really long as a support for the wing membrane, and in some species could
05:05be several metres in length.
05:08The word pterodactyl comes from Greek origins, and actually means wing finger.
05:16When pterosaurs were wiped out around 65 million years ago, other flying animals flourished.
05:25Including bats.
05:28They developed a completely different method of taking to the air.
05:33They evolved a second way of flying.
05:37Once again, based on the pentadactyl limb.
05:42Unlike the pterosaurs, in the bats, only their first digit, or thumb, became hooked for grasping.
05:49The other four fingers grew extremely long, giving them superb control over the shape of their wings in flight.
05:55Now, on this fruit bat here, also known as one of the megabats, sounds cool, doesn't it?
06:08You can see some amazing skeletal adaptations.
06:11The first, and most obvious, is up here, is this wonderful forelim, the wing.
06:16You can see the very long bones here.
06:18But they end in these four very, very elongated digits, and these serve to open up as much skin and soft tissue as possible, allowing for these very broad, strong wings.
06:30The bones are also very flexible, which helps cope with the extreme forces acting on the skeleton during flight.
06:40Basically, the whole skeleton works together to become as aerodynamic and as lightweight as possible.
06:45Now, I'll be honest, bats amaze me, because to me, they're fat, little, hairy mammals that manage to stay up in the air, and they do it very well.
06:55But more impressive to me is the fact that there are approximately 1,000 species of bats across the globe, and this accounts for nearly a quarter of all mammal species on Earth.
07:06The success of bats can largely be attributed to their flying prowess, and that is mainly down to their skeleton.
07:22Flexible wings allow them to catch highly acrobatic prey.
07:28They can turn 180 degrees in less than half a wingspan.
07:35Bats may be brilliant flyers, but birds are the true masters of the sky, with almost ten times more species inhabiting practically every habitat on the planet.
08:00So, what's special about their wings?
08:05They developed an entirely independent third way of flying.
08:10And again, it all began with five fingers.
08:15Rather than the elongated digits found in bats and pterosaurs, some bird bones fused together.
08:22Others disappeared completely.
08:25This gave rigidity to the wing and provided a platform for feathers to generate lift.
08:31But it's not all about wings.
08:35Birds had to make other significant changes within their skeletons to become such successful flyers.
08:42In order to overcome gravity, it's important to become both lightweight and strong.
08:48This is exactly what birds have done.
08:51You can see on this pheasant how many of their bones have fused together for strength.
08:57The first of which is this area here where they've fused a load of their vertebrae and their pelvis into one big superstructure.
09:06And you can very clearly see this at the edge of the wing where you've got not only a loss of some of the digits, but also a fusion of several bones into one yet again.
09:14There's another skeletal adaptation which I love, and it's these little processes you get between the ribs, linking one rib to the next, to the next.
09:24And this all serves to stiffen the whole rib cage, again, making it really, really strong.
09:30Now, you're a bird.
09:31You can fly.
09:32You've got these big wings.
09:33You've got these massive muscles.
09:35You need somewhere to attach these things to.
09:37And what birds have evolved and developed is this wonderful structure here as well.
09:41So this is the breastbone or the keel.
09:43This big flattened projection you can see here serves to anchor all of these big muscle attachments, which ultimately allows the bird to fly.
09:54One other crucial adaptation has helped birds take to the air.
10:00And this time, the secret is inside their skeleton.
10:05Their bones have evolved to be as light as possible.
10:12Here we've got a wonderful image from a scanning electron microscope from within a bird's bone.
10:19And you can see this whole network of rigid internal strap-like supports, which actually prevent the bones from buckling during flight.
10:28Compare this to human bone, and you can see the difference instantly.
10:32It's much thicker.
10:33It's very dense.
10:34There's lots of marrow.
10:35Ultimately, it's incredibly heavy.
10:37It's the last thing you want when you're trying to fly.
10:43To see how all these adaptations to the skeleton have come together, I'm going to look at an extraordinary
10:50bird that we see every day and is often taken for granted.
10:57The humble pigeon.
10:59It's hugely successful.
11:02There are over 10 million pigeons in the UK alone.
11:07And there are thought to be around 260 million in the world.
11:12There's one particular survival technique that has allowed the pigeon to thrive.
11:20Bird handler Lloyd Buck is going to reveal the secret with a very short and simple flight.
11:26We're ready?
11:27Yeah.
11:28There's a pea there.
11:29I'll try and get out of the way.
11:31OK.
11:32Pssh.
11:33By filming Smudge in slow motion, we can see how pigeons have an explosive takeoff,
11:44able to fly vertically upwards for more than 20 metres.
11:50This exceptional flying ability is down to their complex physiology.
11:54So when they do their vertical takeoff, what's going on?
11:58Well, it's amazing to watch, isn't it?
12:00And when you see it slow down, you get more of an idea what's happening.
12:04And you see she's putting all of her energy into that one purpose, to clear the ground,
12:09isn't she?
12:10And go up as fast as she possibly can.
12:11Yeah.
12:12This slow, you can see how Smudge first bends her knees.
12:21Then pushes off the ground, whilst flinging her wings above her head.
12:27This powerful jump allows her to clear the ground enough to make a complete downward stroke
12:34without her wings touching the floor.
12:40She can accelerate from zero to 60 miles an hour in less than two seconds.
12:47To see how pigeons are such skilled fliers, we need to take a closer look at their bones.
12:53I thought it'd be nice to have a real good comparison between the live bird and, well, my sort of bird.
13:00The first thing that sticks out is this massive keel.
13:02Quite big for a bird that size.
13:04I'd never seen a pigeon skeleton before today.
13:07I never used to seeing live ones like Smudge here.
13:09When I first looked at it, I thought, that's not quite right, is it?
13:13But then actually, when you look at Smudge, look.
13:15Yeah, right down there.
13:16Yeah.
13:17I really see it.
13:18And there are so many adaptations that just points to this being an absolute powerhouse of muscle and flight.
13:23I mean, if you look at the bones in the upper arm here, the humerus, they're really short.
13:26Having that short, stubby, stocky little bone there really allows that power again.
13:30Even that one bone says, this is a very strong bird.
13:33Incredible.
13:34It's brilliant.
13:35You can see these massive legs, they just keep going up.
13:38Yeah.
13:39And they're really strong, aren't they?
13:40Yeah.
13:41You can tell this bird is one hell of a flyer, to be honest.
13:44Yeah.
13:48Their stocky yet flexible legs, big muscular keel and short manoeuvrable wing bones allow them to perform powerful vertical takeoffs.
13:58But why do they need this skill?
14:02It's Smudge being a feral pigeon.
14:04Yeah.
14:05Spend a lot of time feeding on the ground.
14:06Mm-hm.
14:07So, if a ground predator or an aerial predator come in to try and kill them, they need to be able to get away as quickly as possible.
14:14Makes sense.
14:15And the vertical takeoff is a brilliant method.
14:18Yeah.
14:19They can out-climb a peregrine if they need to.
14:22A peregrine has no chance of matching them for climbing speed.
14:28And also, they could just keep going over distance, getting close to 100 kilometres an hour.
14:32They could do up to 800 kilometres in a day.
14:34One day.
14:35It needs to be.
14:36That's phenomenal, isn't it?
14:37It really is.
14:39Smudge.
14:40Come here.
14:42The pigeon is the ultimate all-rounder.
14:47But the basic bird skeleton has adapted in other species for extremely specialised forms of flight.
14:58For speed.
14:59Maneuverability.
15:00And long-haul travel.
15:01At more than three and a half metres, the albatross has the longest wingspan of any bird.
15:19They require a good run-up to allow enough air to move over their wings to generate lift.
15:27Once airborne, they rarely need to flap their wings, using a soaring technique to glide on wind currents for thousands of kilometres.
15:37How can they undertake such epic journeys?
15:45The wing bones are very, very long and very, very straight.
15:48And this wing allows the animal to soar and glide in much the same way that an aeroplane's wing would.
15:54On top of that, there's another very specific adaptation.
15:59And that's a very large tendon that sits in the shoulder area and travels all the way down the humerus, up and over the elbow.
16:08This allows the wing to be locked into place.
16:13This ability to effectively lock their wings during gliding allows them to fly effortlessly, conserving valuable energy.
16:23You can see from this X-ray image that part of their tendon has also become hardened bony.
16:31Known as a spreader bone, it offers stability and support to the wings during long periods of flight and reduces muscle fatigue.
16:42This bird can glide like almost no other, and it can travel for 15,000 kilometres from the moment they take off to the moment they return to the ground.
16:54As one of the heaviest flying birds, the albatross needs a colossal wingspan to cope.
17:02But some big birds have tiny wings.
17:08I'm on my way to the Royal Veterinary College near London to understand why their skeletons have specialised in this way.
17:19Hello. Be careful here, it's really muddy as you go in.
17:24Professor John Hutchinson is an expert in animal locomotion.
17:29It's safe. Hello.
17:31They're pretty mellow.
17:34Cheeky animals too.
17:36So the peck won't hurt you, it's the kick you've got to worry about, but they won't use it unless they're threatened.
17:41Why do you have a field full of emus?
17:43Yeah, yeah, so emus are just really cool birds.
17:46Although they look kind of dinosaur-like and they don't fly, so that seems primitive.
17:50Actually, they're specialised, they're advanced for a bird, because most birds fly.
17:55They've lost their flight and become an extreme runner, a real athlete on land.
18:00Whoa, okay.
18:02John and his team have been studying how the emu's anatomy is adapted for running and not flight.
18:13Being this close, you can really see there's almost no wing.
18:17Yep.
18:18Where is it?
18:19Well, it's just a little nubbin dangling down in front of the knee here.
18:23They're really small, really fragile.
18:24I happen to have their wing of an emu.
18:29Check that out.
18:30Isn't that cool?
18:31It's so small.
18:32Cool but tiny, yeah.
18:33There's the humerus, forearm bones, radius and ulna, and there's the wrist and the hand,
18:38very, very short hand, and the claw finally, so they don't get much bigger than that.
18:43It really shows you close up just how small they are, just that massive reduction they've had.
18:48It makes sense to lose flight when it's no longer favoured by natural selection.
18:54Because flight is energetically expensive.
18:56Yeah, I guess so.
18:57They're almost like a trade-off, isn't it?
18:58They've lost the ability to fly, but they've compensated by having massive legs.
19:02Exactly.
19:03A bird can't be both a super fast runner and a great flyer.
19:07It's one or the other, and emus really are at the one extreme of being a great runner, not a flyer at all.
19:15Okay, show us the wings.
19:18Emus aren't alone when it comes to being superb runners.
19:21Ostriches are the fastest birds in the world when it comes to sprinting.
19:27They can reach speeds of over 40 miles an hour.
19:31And once again, the secret is in their bones.
19:35These are the leg bones of five different land animals.
19:43Now, they're the femur, which is the bone in the upper thigh.
19:46And we've got a camel, a horse, dog, ostrich, and emu.
19:53Now, they all look incredibly similar to each other.
19:56That's because, technically, they all have the same functional role, which is support and a lot of weight bearing at the top of the leg.
20:03But what's weird and quite interesting is that these two from the flightless birds here, the ostrich and the emu,
20:09they look really heavy, robust, thick-set, but they're actually, they're actually really light.
20:15To understand why, I need to saw one open and take a close-up look.
20:27Oh, wow.
20:47Look at that. That's absolutely amazing.
20:50Now, this ostrich bone perfectly demonstrates why it's so light.
20:55These big, flightless birds have retained so many of the characteristics that you see in the original flying birds.
21:01These bones genuinely are more air than they are bone.
21:05That same honeycomb structure found in flying birds is still here in one that lives on land.
21:12But what happens when birds take to the oceans?
21:24Penguins lost flight around 65 million years ago.
21:34About the same time as when the dinosaurs died out.
21:40It's thought they lost this ability because they no longer had any sort of land predators.
21:46You can see from this little guy, he's really not too fussed that I'm next to him.
21:52Exactly.
22:04But it wasn't just the lack of land predators that led to penguins becoming flightless.
22:10It was also their need to swim.
22:24Penguins can travel at over 20 miles an hour.
22:27They need to be fast to dodge predators like leopard seals and hunt down their prey.
22:41To be this manoeuvrable underwater, something happened to their bones that then made it impossible to fly.
22:50It's only when you look at their skeletons and their bones specifically that you can really see the actual story behind what's going on here.
22:58Every single bone is heavier than you'd expect in a bird.
23:03When you've got flying birds, they've got very dynamic and lightweight bones and that's perfect for them.
23:09But if you live underwater a lot of the time and you hunt underwater, you need heavy bones.
23:14This allows the skeleton to act as ballast.
23:17If you take a close-up look at a penguin bone under a microscope, you can see just how dense it is compared to that of a flying bird.
23:28If you look at specific areas of the skeleton as well, you can see there are some perfect adaptations for this hunting underwater lifestyle.
23:36First of all, if you look at the wings.
23:38Now, they're not very long, but they're very broad and the leading edge and trailing edge are actually quite sharp.
23:43This allows the penguin to have a very, here they come, the penguin to have a very rigid wing that you can see here.
23:50And again, this is perfect for slicing through the water.
23:53One of my favourite adaptations on the penguin, though, are these things.
23:58Now, these are massive scapulae. These are the shoulder blades.
24:02They're huge. They're absolutely monstrous.
24:05You watch a penguin power through the water, they're constantly paddling and paddling and paddling.
24:10And because water offers much more resistance than air, they really need a lot of power up in the shoulder areas to really pull themselves through the water.
24:20With their large scapulae, paddle-like wings and heavy bones, penguins have traded the ability to fly in the air to effectively fly underwater.
24:32You see one shoot past and they look like a little fat feathered torpedo.
24:41It's only when you finally see the bubbles, you kind of remember they're underwater.
24:48We see penguins in almost comedy light, and it's wrong because they're not.
24:56They're predators, and they're good predators.
24:59They live in the Southern Oceans around Antarctica, and it's not easy to live down there.
25:03They're tough, tough animals.
25:05One bird has adapted for life underwater, on land, and in the sky.
25:25It really is my ultimate bird skeleton.
25:31This little bird is such a paradox.
25:35It doesn't look as though it's very good at flying, and it doesn't look as though it's very good at swimming.
25:42But actually, this wonderful little interesting bird is both.
25:49It's the Gillimot.
25:51Gillimots live in large colonies on coastal cliffs.
26:05Although they appear quite clumsy when taking off, they're surprisingly good fliers, capable of speeds of over 40 miles an hour.
26:20And when they hit the water, their versatility really becomes apparent.
26:25You'd think that their wings would be too cumbersome for diving.
26:31But they swim with them half closed to reduce turbulence.
26:37Gillimots can reach depths of over 150 metres.
26:42This puts them amongst the deepest divers of all birds.
26:47To really understand how they can be both skilful fliers and impressive divers, you have to look at their bones.
26:57Now we've got a specialist flier, the pigeon here, and we've got a specialist diver, the penguin.
27:06We've just got a few bones of the wing, but that's enough.
27:10I think probably my favourite way to look at the differences here, and I love this technique, is to get a torch and shine it through the bones.
27:18And you can see if I shine it through the pigeon, this light shines through them perfectly.
27:24And you can really see that they're almost translucent.
27:28And this is what you'd associate with an animal that has lightweight bones, which is essential for flight.
27:33If we go to the opposite end of the scale and look at the wing bones from a penguin, you can barely see that light coming through.
27:39And this is because they're incredibly dense bones to counteract buoyancy.
27:43Where will the Gillimot fit?
27:45Now you can see, if you have a good look with a torch, it's somewhere between the two.
27:49It's a happy medium.
27:51You can see through slightly, but it's much more dense.
27:54It's not as dense as the penguin, but it's definitely more dense than the pigeon.
27:58This amazing adaptation, bones light enough to fly and yet heavy enough to dive,
28:05makes this one of the most impressive birds on the planet.
28:11My little Gillimot here really is the ultimate flyer.
28:14And for that reason, I'm in love with this bird. It's brilliant.
28:23The skeleton has enabled birds to conquer the sky.
28:28And also the land.
28:31And even the sea.
28:35Next time, we'll discover how bones have evolved to detect prey.
28:40What you've got in effect is a 40 or 50 ton rigid swimming radar gun.
28:45And to sense the world around us.
28:52These eyes are so large that each one is larger than the animal's own brain.
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