- 8 months ago
Secrets of Bones episode 5
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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.
00:47As a child, I was fascinated by bones.
00:50Now, 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.
01:23I 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'll see how bones have helped vertebrates to capture and devour practically every type of food on the planet.
01:48We'll look at extreme jaws.
01:55Bizarre teeth.
01:58It really is a bonkers adaptation.
02:01Highly specialized bony tools.
02:04And one small appendage that has had an immense impact.
02:08It may not look much, but it changed the course of our evolutionary history.
02:15I'm going to reveal the secrets of bones.
02:19This is a jewel from the largest living tooth predator on the planet.
02:40At five metres long, it's from a sperm whale that was nearly 30 metres in length.
02:46The teeth can be 20 centimetres long, and they're all roughly the same in terms of their shape.
02:54This makes them perfectly adapted for grabbing and killing.
02:58Now, teeth and jaws absolutely fascinate me because they reveal so many of the secrets behind the animal's life and their success.
03:07Sperm whales may have a spectacular set of jaws, but there are more than 60,000 species of vertebrate,
03:13and each has evolved its own special way of feeding.
03:18Jaws first appeared around 420 million years ago.
03:24Important tools for catching and consuming food, their shape and size adapted to exploit whatever was available.
03:32This evolutionary change can take place surprisingly quickly.
03:44And to understand the story of rapid jaw evolution, I need to get an MRI scan of my skull.
03:51The information is processed to create a model in plastic.
04:07I'm more than a little curious to see what my own skull looks like.
04:10I've been working with bones for 20 years, but this is a first.
04:22I'm quite shocked.
04:24It's so weird to look at your own skull whilst you're still alive, I think, really.
04:30Even though I study bones, you look in a mirror and you don't see all these little lumps or this massive brow ridge I apparently have.
04:41Or this quite large jutting jaw.
04:52Weird.
04:54I'm taking my skull to Dr Carolyn Rando, an archaeologist at University College London, who's been conducting some fascinating research into how human jaws are adapting to our ever-changing diet.
05:12You've got an impressive array of skulls here, Carolyn. What can they tell us about the evolution of our jaws?
05:16Well, what we have here is we have a selection of skulls going all the way back from Neanderthal man to Cro-Magnon and then medieval London and post-medieval London here.
05:27And so, while these give us a cross-section of essentially kind of human evolutionary history, my main interest is with these two here.
05:35And what I found through my research is that jaws have gotten significantly smaller since the medieval period up until the modern period.
05:42We're talking just several hundred years here, aren't we?
05:45Absolutely. So the medieval period ends in 1550 and post-medieval, we're talking 17, 1800s, 1900s.
05:52When you say the jaws are changing, how?
05:54Well, what's happening is that, for one, in this individual, we have what we call an edge-to-edge bite, which means that his front teeth line up perfectly with each other.
06:03It's a really nice top and bottom together.
06:04And what we have here is that his top teeth and his bottom teeth, they don't fit together at all.
06:09That's massive there. I'm closing mine now. Mine do the same, so is that typical of modern man now?
06:16Absolutely. And in this individual here, you can see that they fit together so poorly that I can put an entire finger in between his upper and lower teeth.
06:25How would my diet make my jaw become smaller?
06:28Throughout human evolution, we've had a very specific type of diet, which is lots of rough, hard foods.
06:35It's tough and fibrous, isn't it?
06:37Exactly, yeah. We really have to chew hard to make our food work for us.
06:41And all of that work is stimulating our jaws to grow.
06:46It stimulates our teeth, which stimulates the jaws, and then the whole face responds in kind to these things.
06:51And so what happened then is we switched from a very traditional agriculturalist diet to one that was soft and sticky and very sweet and something that's almost identical to what we have now.
07:02Processed foods, I guess. Absolutely. Right.
07:05We don't have that same type of interaction between the food and the jaws anymore. They just tend to become smaller through inactivity.
07:13Yeah.
07:15Although the trend is towards an increasing overbite, the severity differs between individuals, and this is largely down to their particular eating habits.
07:24So where does that leave me?
07:28Now, I have another skull for you. I just happen to have it in my bag, as I often do.
07:34Now, I want to see what you make of this one.
07:37And if it looks familiar, that's because it's mine.
07:40Oh, Ben, that's amazing. It looks just like you.
07:46We're very attached.
07:48Now, this is the skull that I've had printed off from a 3D image, but where does this fit with the jaw story?
07:55Well, if we compare it to our two gentlemen here, what we can see is that while you're not quite as bad as our modern individual over here, you do still have quite a bit of an overbite here.
08:09So I think you're going more towards modern, but not quite as bad as this gentleman here.
08:14It's reassuring.
08:15Can we predict what will happen to humans in the future? Will this carry on? Will it get smaller?
08:20I think it's a bit hard to say because who knows what our diet is going to be like 50 or 100 or 200 years from now.
08:28We could have a liquid-based diet or maybe something that's pill-based instead of actually chewing our food.
08:34And then I imagine that our jaws would start getting smaller yet again.
08:37Yet again, yes.
08:38I love this because it really emphasises yet again just how malleable, changeable, adaptable not only the skull but bones and skeletons in general really are.
08:48Dr Rando believes that due to the lack of tough, fibrous foods in our diet, there's no longer a need for large, powerful jaws.
08:57This is evolution in action, as we can see it, and it is happening to us. We are not outside of our environment.
09:02We are still evolving and adapting to everything around us.
09:10Diet has shaped the vertebrate jaw.
09:13In some cases, to the extreme.
09:18Snakes' flexible mandibles allow them to consume enormous prey.
09:26Some species can open their jaws 180 degrees.
09:30Stretching so wide, they can eat prey five times larger than their own heads.
09:47So just how do they do this?
09:50Well, the old idea that they dislocate their jaws, that's a load of rubbish.
09:54What they actually do is far more interesting.
09:57You can see here that each side of the lower jaw is made up of different bones that are connected together.
10:03And both lower jaws aren't even attached to one another.
10:08This all goes together to make a very flexible lower jaw.
10:12And it's connected through a whole network of very tight but elastic-like ligaments.
10:17Imagine that my two arms are the lower jaw bones or the mandibles of the snake.
10:24And these two elastic bands are the ligaments that hold the jaws together.
10:31When the snake is trying to eat something, these ligaments stretch, allowing the jaw bones to spread massively.
10:37This is how a snake can eat something much larger than you might expect.
10:44It's very simple but effective.
10:46Snakes are the ultimate binge eaters.
10:54They're ectothermic, relying on the environment to warm their bodies.
10:59And so need to conserve energy wherever possible.
11:02By eating huge meals every few weeks, snakes can maximise food intake whilst minimising energy expenditure.
11:10To achieve this, their bones have had to adapt spectacularly.
11:18Once they've secured their prey, they move one mandible forward at a time to swallow it.
11:26It can then take several days for their food to be dissolved by strong acids in their stomach.
11:32But the African egg-eating snake has found a more immediate bony solution to breaking up its prey.
11:43It feeds exclusively on birds' eggs.
11:48And its skeletal secret is revealed by this video x-ray.
11:54With a superbly flexible jaw, it can consume an egg many times bigger than its head.
12:07Knife-like bony spikes in its vertebrae protrude into the body cavity.
12:13When the egg reaches the part of the backbone with downward-pointing spines, the snake arches and squeezes.
12:20The spikes first pierce the shell and then slip the membrane inside, releasing a highly nutritious meal.
12:32A backbone that can break up your food is an ingenious skeletal adaptation.
12:37But most vertebrates use a more conventional method.
12:47Teeth.
12:52They're mostly made up of enamel and dentine and are similar in composition to bone.
12:58But as they contain little or no collagen, they're much harder.
13:02Teeth do different jobs.
13:05From biting and ripping to crushing and nibbling.
13:12A wide variety of foods has led to a diverse range of tooth shape and size.
13:19Carnivores have particularly impressive teeth.
13:23They use their canines for puncturing, carnassials for shearing and incisors for tearing flesh.
13:37However, it's a herbivore that holds the record when it comes to tooth size.
13:42The animal with the largest teeth on the planet is the elephant.
13:51First up, teeth for chewing.
13:54They're massive.
13:56Each one of these molars can be 30cm in length and can weigh up to 5kg.
14:02Their flattened surface is ideal for grinding.
14:05They're also heavily ridged on the top.
14:08And this is a perfect adaptation for a vegetation diet which is really tough and fibrous.
14:17An elephant gets six sets of these teeth throughout its lifetime.
14:21And as each one is worn down, new ones are pushed forward from the back of the mouth.
14:25A bit like a conveyor belt.
14:27As the last one is worn down and is finally lost, the elephant can no longer eat.
14:31And this marks the end of the animal's life.
14:37The elephant's biggest teeth are its tusks.
14:40And they can grow to be more than three metres long.
14:44They're actually modified incisors, like the front teeth in humans.
14:49Unlike ours, they keep growing, as much as 17cm a year.
14:55Made from ivory, a kind of dentine, tusks are important for display and defence.
15:03And as tools for helping elephants collect their food.
15:09But there's a marine mammal that has independently evolved tusks that aren't used for feeding at all.
15:16The walrus has these enormous tusks.
15:21Now these are actually specialised canine teeth which erupt from the upper jaw here.
15:26Now these tusks can be over one metre in length.
15:29Their scientific name, Odobenus, means tooth walker.
15:32And walruses use their teeth to haul their one-ton bodies out of the icy water and onto ice flows.
15:44Their tusks are also used for dueling.
15:48And defence.
15:49If they're not used for eating, how do they feed?
16:02Walruses produce jets of water to uncover clams, hidden in the silt on the seabed.
16:10They can consume 6,000 in one feeding session.
16:15Exactly how they were able to prise open the shells, puzzled researchers for years.
16:29Looking at the jaws, they noticed that the teeth are very worn.
16:33Now this you might expect from an animal that's eating and chewing and crushing lots of shellfish.
16:37But when scientists looked in the stomachs of walruses, they found that they can have up to 70 kilograms of shellfish meat and not a single shell.
16:51What researchers discovered is that walruses are able to turn their mouths into powerful suction devices.
16:59And they do this through some very specific skeletal adaptations.
17:03The first of which is in the roof of the mouth.
17:06Now you can see here, it's highly arched and domed.
17:09And this allows them to put their thick, muscular tongue right at the front of their mouths.
17:14They grind their jaws together so tightly that this is what wears the teeth down.
17:19So they've got a shellfish at the front of their mouths and their lips.
17:23Their teeth are held together very tightly.
17:25And this tongue is pushed forward.
17:27They'll pull this back so quickly that it forms a vacuum.
17:31And the vacuum power is so strong that it sucks the meat clean out of the shellfish.
17:37In captivity, walruses have been seen to suck a hole through plywood board.
17:42Vertebrates have evolved many novel ways of using their mouths to feed.
17:51But there is one specialist feeder with the most bizarre looking teeth I've ever seen.
17:58And a specimen is kept in the stores of Dublin's Natural History Museum.
18:03A close relative of the walrus, it's one of the most abundant large mammals on Earth.
18:13It's the crab-eater seal.
18:17There are estimated to be 15 million of them found in Antarctic waters.
18:23As they primarily live on free-floating pack ice in remote and inhospitable locations,
18:29they are rarely seen and little studied.
18:33Much of their lives still remain a mystery.
18:36Now, the crab-eater seal, you assume they eat crabs.
18:40And even the scientific name Lobadon carcinophagia means lobe-toothed crab-eater.
18:46But more than 95% of their diet is made up of Antarctic krill,
18:53a shrimp-like crustacean.
18:54They can consume 20 kilograms of them per day.
18:59It's said to have the most complex teeth of any carnivore.
19:06Like the walrus, the crab-eater seal uses suction to feed, but in a very different way.
19:13As it swims, it sucks water and krill into its mouth,
19:18then filters the tiny crustaceans through its teeth.
19:24I genuinely love these teeth. They fit together perfectly.
19:28And by being shaped with all these little lobes and nooks and crannies,
19:33the teeth can fit together and form an amazing sieve.
19:36It really is a bonkers adaptation.
19:41And these teeth are perfectly adapted feeding tools.
19:52Using a mouth to capture and manipulate food works for most vertebrates.
19:57Sometimes, however, jaws and teeth just aren't enough.
20:05And more sophisticated bony tools are needed to secure a meal.
20:12Particularly when you live in a challenging environment where food can be hard to come by.
20:18The monkfish is one of the ultimate ambush predators.
20:23It's the stuff of nightmares. It really is.
20:26It's more alien than it is animal.
20:27And it's one massive killing machine head with a little tail attached to the back of it.
20:33This hefty beast of a fish sits on the seabed where it's dark and murky for very long periods of time.
20:41There's not much down there and food is few and far between.
20:44So it's got a set of skeletal adaptations that really help maximise any chance of getting some grub.
20:52The most peculiar of which is a lure.
20:57The monkfish is a species of anglerfish.
21:02The lures of anglerfish come in a variety of cunning shapes to entice prey within jaw's reach.
21:08Some deep-sea species even have ones that glow in the dark.
21:14On the monkfish, the lure is a specialised dorsal filament on its head made of bone.
21:22And its excess, I think, is almost entirely down to this one little bony appendage.
21:27Now, fish are quite inquisitive, so something will swim past, it will have a good look, and then that's the start of the end.
21:34The monkfish has a clever strategy to bring food straight to its mouth.
21:45There are other vertebrates that have evolved even more sophisticated ways to gather food.
21:51And the most advanced example of this is in the human body.
21:57It's a bony feature that has totally revolutionised the way we collect our food.
22:04And is found in the skeletons of most primates, including this gorilla.
22:11When you compare my hands to those of the gorilla here, you can see they're similar.
22:25Not only the shape of the bones, but their orientation, the number of bones, everything.
22:30But more than that, we share this wonderful, unassuming, opposable thumb.
22:36It may not look much, but it changed the course of our evolutionary history.
22:45An opposable digit enabled primates to move their thumb freely and independently,
22:51giving them a precision grip to grasp branches, pick leaves,
22:58and use tools to obtain food normally out of reach.
23:02But around three and a half million years ago, something happened in our evolutionary history
23:09that set us apart from our primate cousins.
23:12Primates mainly walk on all fours.
23:16But when our early human ancestors started walking upright on two legs,
23:21it freed up their hands, allowing them to use their opposable thumbs to carry and manipulate tools,
23:27including weapons for hunting.
23:32With arms freed up, they became skilled at throwing, helping them hunt big game at a distance,
23:39enabled by a set of skeletal adaptations.
23:42The human shoulder has an amazing ability to release stored energy from the huge criss-crossing network of tendons and ligaments right across this area.
23:55It acts like a slingshot, and this allows us to be such good throwers.
23:59Today, top-class baseball pitchers can throw accurately at speeds of over 100 miles an hour.
24:06There are three key skeletal adaptations, the first of which is having a really high and mobile waist,
24:17and this allows a lot of torsion in the torso.
24:21Secondly, and really importantly, is the very low position of the shoulder blade up on the body.
24:26Our humerus, our upper arm bone here, has the ability to twist and turn as well.
24:34This all happened about two million years ago, way before we existed as Homo sapien,
24:40back in the day when Homo erectus roamed the Earth.
24:43Our ability to throw, and our success as hunters, is an important part of why we have thrived as a species.
24:58But there's one primate that stands out as having the most highly specialised hands that it uses in an unparalleled way.
25:19This lemur from Madagascar is the world's largest nocturnal primate.
25:33It's the aye-aye.
25:36Feeding on insects and larvae hidden deep inside tree trunks, it needs very specialised digits to extract them.
25:44Now like most primates, it has this wonderful opposable thumb, allowing it to grasp and manipulate objects.
25:52But unique to the aye-aye, it has a very, very specialised finger.
25:59So you can see this wonderful third digit here, which is a very long needle-like structure,
26:04with this great little hook claw on the end.
26:06To try to find where the grubs are hiding, the aye-aye uses its highly sensitive, bony finger to sound them out by tapping.
26:17It'll tap up to ten times a second, much faster than I can do.
26:23This is called percussive foraging.
26:25The aye-aye uses its large ears to listen for the echo produced from the tapping, to locate where the grubs are hiding.
26:36It's the only primate to use echolocation.
26:39Once it's pinpointed a grub, it gnaws a hole in the wood with its chisel-like teeth, and uses its spiky, long finger to search for it.
26:53This finger has a ball and socket joint, which is unique in the primate world.
27:02Now I've got one in my hip, but nothing else has one in its fingers.
27:07And it gives the aye-aye's finger great flexibility to explore inside wood cavities.
27:13Once it's found the little grub, you use this third finger again, drag it out, eat it.
27:20With its sophisticated and specialised hands, the aye-aye is, in my opinion, the most extraordinary predator on planet Earth.
27:39The skeleton has allowed vertebrates to capture and devour practically every type of food on the planet.
27:46Using a diverse range of jaws, teeth, and other sophisticated bony tools.
27:59Next time, I'll be investigating what role bones play in the three crucial things needed for reproduction.
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