Lost Worlds, Vanished Lives (1989) s01e03 Episode Script
Part 3
(SPEAKS TUAREG) We're looking for a dinosaur.
At the time when the dinosaur first appeared, about 200 million years ago, all the land on the earth was grouped together in one supercontinent and the dinosaurs roamed all over it.
And so today their remains can be found in the fragments of that supercontinent, in Australia, in North America, in Europe and here in Africa.
We're on an expedition in the southern fringes of the Sahara and the reason we've come here is that in a desert there's very little vegetation to cover the rocks, so that if there are dinosaurs in them, we'll be able to see them.
One of the expedition leaders, Dick Moody, showed me their first find.
I'm sure you'll find this one, which we haven't touched, quite a superb specimen, quite exciting.
0h, it is absolutely magnificent.
This is obviously the backbone, but which way is it lying? It's running in that direction, we believe, towards the head and towards the east.
And in this direction, generally, back towards the tail.
- And the ribs? - The ribs are running off.
As you can see, they're slightly disarticulated and slightly broken up, but they are running in that general direction down the sand dune.
And how long do you think the complete animal was? Between 20 and 30 metres.
- What, that's 90 feet? - Yes.
- That's enormous.
- It's a large animal, yes.
How complete do you think it might be? We're hoping to find some skull material and obviously limb material underneath here.
If we clear these just a little The weathered shales in which the bones were embedded were so soft that we could brush them away with our hands.
After only half an hour, we already had some idea of how much of the animal was preserved.
But it was a further day before all the bones at this site were exposed.
There weren't as many as we had first hoped.
The base of the tail and the lower spine was there, but the legs and most of the body were missing.
But half a mile away, the rest of the expedition was working on another group of bones.
These were leg bones and probably belonged, if not to the same animal, then at least to the same kind.
The huge carcass, whatever it was, had clearly already been dismembered before it was buried.
Perhaps other scavenging dinosaurs had pulled it apart.
Perhaps the rotting body had disintegrated as it lay in the river that eventually buried it in mud.
The expedition was from the Natural History Museum and Kingston Polytechnic in London.
Before the bones could be transported back, they had to be protected by wrapping them with strips of sackcloth soaked in plaster.
This will harden into a solid jacket that will hold the whole specimen together.
The expedition dug up and plastered almost 100 bones in the four weeks they worked in the Sahara.
But this was only the start.
Indeed, it won't be until the team gets the bones back to London and has cleaned them, studied them and pieced them together, that they will know for sure exactly what kind of dinosaur they've got.
But one thing is certain - it's a giant.
These bones, too, in the museum in East Berlin, came from Africa back in 1912.
When pieced together, they proved to belong to the most massive land animal known up to that time.
It was 74 feet, 22½ metres long, it stood 39 feet, that's 12 metres, high, and it was estimated to weigh 77 tons, which is as much as 12 bull elephants put together.
This is brachiosaurus.
It's head, perched on top of its immensely long neck, was comparatively tiny, less than three feet long, but it has huge nostrils, high on its forehead and they led some people to suggest that this animal lived in lakes, with its head and nostrils above the surface while it walked along the bottom with the water supporting its huge body.
But that, we now know, would have been impossible.
If its nostrils were open at the surface, the water pressure 30 or so feet below the surface would have been so great that its lungs would've collapsed.
Furthermore, the shape of its legs and its deep, narrow chest all suggest an animal that lived on land.
So now, it seems, we have to think of brachiosaurus as a kind of gigantic reptilian giraffe, browsing the tops of the trees.
Brachiosaurus may be the biggest mounted dinosaur in the world, but it may not be so for long.
In New Mexico, they've found remains of an animal that may be even bigger.
They've already given it a name, seismosaurus, the "earth-shaker".
But the rock in which it is embedded, unlike the soft shales of the Sahara, is almost as hard as concrete, and excavating it is a laborious and time-consuming business.
The excavation leader, Dave Gillette, told me the story.
This is where we found the first set of vertebrae in 1979.
We finally excavated in 1985.
How much of it was showing? Only the upper part.
It was showing as though it had been carved out of the rock in bas-relief.
It was perfectly exposed just in this fashion.
- And then? - Then, when we looked closer in the ground, we found a total of eight vertebrae along this line, all in perfect articulation, and they're from the basal part of the tail, leading into the pelvic region.
There's another vertebra here.
Then we took out two large blocks, one here, another here at the base of the tail, that led right up to the hip region.
- What's that? - This is a rib, which has been displaced from the proper anatomical position when the animal died.
- The rock looks awful.
- It is terribly hard around the bone.
- It takes for ever for us to excavate the bones.
- Does the animal go on in there? We think the animal continues right into the hill to the north for another 60 or 70 feet.
- Under the rock? - About eight feet deep.
We're using sophisticated and experimental remote-sensing techniques to try to see those bones before we excavate.
The site is only a few miles from Los Alamos atomic research station, and the scientists there, on their days off, come out to use the most advanced techniques of nuclear physics to help Dave locate his dinosaur bones deep in the rock.
This sledge carries a still-experimental remote-sensing device, a kind of radar that looks into the ground.
It's dragged along carefully-plotted tracks across the rock and already readings from it are beginning to confirm the gigantic size of the animal.
I asked Dave how long he thought seismosaurus might eventually prove to be.
My best estimate is 140 feet in length, from the snout to the tip of the tail.
How does that compare? The previous record-holder was diplodocus at 87 feet.
We're approaching twice that length.
When will you actually know whether this is a world-beater? We know now.
We have good confidence in our calculations.
Dinosaurs certainly include some gigantic animals.
Stegosaurus, bigger than a rhinoceros.
Allosaurus, tall as a giraffe.
But they weren't all huge.
Some were no bigger than a dog.
Nonetheless, many were very big indeed and they certainly include some of the most spectacular animals ever to walk the earth.
They dominated the world for over 160 million years.
But what did a dinosaur like this actually look like when it was alive? Did it have hide like an elephant, or was it covered in scales like a lizard, or perhaps hair, like a horse? The skin, of course, like the rest of the soft parts, is very rarely fossilised, but in this exceptional example, it has been.
This is the fleshy pad on the underside of its foot.
And behind you can still see the wrinkles in the skin on its belly.
This particular individual was, most unusually, entombed in the hot sand of a desert, and although its flesh decayed and disappeared, its tough hide was baked and mummified.
You can even see the impressions of the scales in the skin.
From remarkable specimens like this, we can deduce that dinosaur skin was thick and tough, probably not unlike an elephant's hide.
But was it grey and colourless like an elephant's? 0r was it, perhaps, brightly coloured, as are the skins of many reptiles today? Animal pigments don't fossilise, so it's anyone's guess as to whether the dinosaurs were coloured or not, but it's tempting to think that they were.
But we can go further than simply investigating the size and appearance of dinosaurs.
What did the dinosaurs eat? Well, flowering plants didn't develop until about 100 million years ago.
That means that for most of the time dinosaurs were on earth, there were very few of the kinds of plant that dominate the land today.
There were no oak trees or hazel in Europe, on which deer feed.
In Africa there was no thorn scrub or acacia, on which elephant and giraffe browse.
Most important of all, there was no grass, on which horses or bison or antelope graze.
Instead there were plants like these.
These are cycads.
Today they grow wild in only a very few places, and mostly in the tropics.
But when the dinosaurs first evolved, they were spread worldwide.
In addition to these, there were also tree-ferns and primitive conifers like pines.
But all these plants had tough, fibrous leaves, almost indigestible, you might think.
To make matters more awkward, the early dinosaurs were poorly equipped with teeth.
Diplodocus had only these small, peg-like teeth that could have done little more than just nip off the fronds.
It certainly couldn't have chewed them.
So how did it avoid terrible indigestion? Clues to the answer were eventually found lower down in the skeleton.
Between the ribs of specimens that had been fossilised more or less complete are sometimes found great heaps of small, highly polished pebbles.
It seems these had been swallowed and stored in a muscular pouch of the dinosaur's stomach, a gizzard, which served as a kind of internal mill to grind up its fibrous meals.
Even so, it must have taken a very long time for a dinosaur's digestive juices to break down the woody stems and trunks of plants like these.
If you have to keep your food in your stomach a long time, then you need a very big stomach to serve as a storage vat.
That, in turn, means you need a very large body to carry it.
So the ancient pastures of tree-ferns may be one of the main reasons why plant-eating dinosaurs grew so big.
As millions of years passed, however, evolution brought changes.
The first flowering plants appeared, and so did new kinds of plant-eating dinosaurs.
These are hadrosaurs.
They had no teeth at all in the front of their jaws.
Instead, the rounded bone was almost certainly covered with a horny sheath.
With this, they could have done little more than just nip off leaves and twigs.
But inside the mouth, at the back of the jaws, they had an enormous battery of teeth, row upon row.
This particular jaw had over 200.
As these crushed and ground the tough fibres, they were inevitably worn down.
But new ones grew in the bone of the jaw beneath and moved up to replace the old ones.
But could they use them to chew? Mammals like this camel can chew by moving their lower jaw from side to side, so they are able to break down the toughest of plant foods.
The dinosaurs were reptiles, and no reptile can do that.
They can only move their jaws up and down, and that puts a real limit on what they can eat.
The hadrosaurs dealt with that problem in a most remarkable way.
The highlighted upper jaw could actually hinge outwards.
When a hadrosaur's skull is examined closely, it reveals an elastic joint between the upper jaw and the roof of the snout.
This means that as the lower jaw moves up, it pushes aside the upper jaw, in effect, chewing without any sideways movement of the lower jaw at all.
The most powerful grinding battery of all was that possessed by triceratops, one of the last of the dinosaurs.
This, the product of 100 million years of development in the technique of chewing, is perhaps the most powerful chewing device ever possessed by any animal.
A huge beak in the front served as shears which could probably slice clean through a tree trunk.
The branches were then moved to the back of the mouth, where the massive grinders reduced them to pulp.
But these teeth belong to a very different sort of animal.
These are not thin pegs for nipping off bits of leaves.
These are daggers, finely serrated along the edge like steak knives, adapted to slicing through flesh and hide.
In life, much of the empty space in the skull here would have been filled by massive muscles, which gave an enormously powerful bite to these huge jaws.
This is Tyrannosaurus rex, the biggest of all the meat-eating dinosaurs, measuring over forty feet long and weighing about seven tons, surely the most terrifying hunter ever to roam the earth.
With long, curved claws and sharp teeth, the carnivorous dinosaurs must have been terrifying and highly efficient predators.
But other kinds of dinosaurs evolved that had no teeth at all.
This one seems to have been rather like the ostrich of today.
So perhaps, like an ostrich, this dinosaur, called struthiomimus, picked up and swallowed anything, animal or vegetable, it considered remotely edible.
So the bones of dinosaurs, carefully pieced together, can tell us a great deal about how big they were, what they fed on, and therefore their relationships with one another, and how their limbs articulated.
But how fast could they move? To answer that question, you have to come to a place like this.
150 million years ago, there was a mudflat here, around the margin of a freshwater lake.
The lake filled and eventually sediments covered the whole area, and the mudflats turned into mudstones.
In them are preserved huge footprints - dinosaur footprints.
These, nearly a yard across, can only have been made by a huge plant-eater like a brontosaur such as diplodocus.
No other had such a huge foot.
Here the animal has trodden on a small shell, a kind of freshwater mussel.
Molluscs virtually identical to this still live today, but only in water that is less than three feet deep.
So these little shells confirm that these dinosaurs that day were splashing through the shallows.
If you can measure an animal's stride from its tracks, and also know the length of its legs, it's possible to calculate the speed at which it was moving.
The brontosaurs had legs that were about nine feet long, as we know from their skeletons.
But this animal's right hind leg, which was printed here, is only about six feet from the next print in the sequence.
So we can be pretty sure the animal that was moving along here was moving fairly slowly, as perhaps you'd expect if it was just plodding along, looking for food around the margin of a lake.
But, in fact, although thousands of these prints have now been found, not one of them has a stride longer than 12 feet.
So we can be pretty certain that these animals were fairly slow-moving.
These prints, though, are very different, not circular but with three prominent toes.
At the end of each, there is a deep, sharp mark that can only have been made by a claw.
They match the three-toed feet of theropods, medium-sized, carnivorous dinosaurs.
From tracks like these, it's been calculated that some of these hunters could run at up to 30 miles an hour.
Moving at such speeds demands a great deal of energy, and an animal can only produce enough if it has a warm body.
So did the dinosaurs get their energy directly from the sun, as reptiles do today, or could they generate warmth internally, like birds and mammals? That is a question of great debate.
This is how Tyrannosaurus rex may have moved, in the opinion of one of the new generation of dinosaur interpreters, Robert Bakker of the Museum of Colorado.
0K, Tyrannosaurus rex, the most famous dinosaur, the most popular dinosaur, and here it is, running at 40 miles per hour, faster than a rhino, faster than an elephant.
This T.
Rex is going faster than a lion.
Yes, but that's your animation.
How do you know? Because of the way the muscles were hung on those leg bones, the way the calf muscles were hung on that knee, and the way the massive thigh muscles were hung on that ilium.
- But why does that prove it was warm-blooded? - Let's look at the real one, eh? Could it really have reared up like that and lifted its immense length? Absolutely, and more.
It could jump, it could run fast.
This is a T.
Rex, a real one, a cast, with a bloody big knee, right? - But why does that make it warm-blooded? - Actually, it's the other way around.
Unlike the Pentagon, evolution doesn't build more strength than the animal needs.
This animal is immensely strong.
It has a strong knee and a bloody big drumstick of calf muscle to run fast, because warm-bloodedness demands speed.
This animal has to cruise fast and it needs great bursts of speed because it has to kill more often than a cold-blooded animal.
There is no cold-blooded animal today with this great strength.
None.
This is not a scaled-up lizard or a scaled-up tortoise.
This is an enlarged, five-ton, meat-eating roadrunner, that's what it is.
And like a roadrunner, it's eating frequently.
There's another message about speed in the skeleton, not in the legs but in the chest, because in the chest, in the first three ribs, in that space, there is only one organ housed, the cardiac chamber, the heart.
And in modern cold-bloods, the heart is very small, because cold-blooded animals need only a weak cardiac organ.
But look at this: The first rib, the second rib, the third rib.
Look how long that is.
There was housed in these ribs, without doubt, a gigantic heart designed to pump, designed to put out blood flow at emphatically warm-blooded levels.
So maybe we should get rid of the image of dinosaurs as slow, lumbering plodders and think of them instead as nimble and agile in spite of their size.
(BL00D-CURDLING R0AR) The truth is almost certainly that some were warm-blooded and others were not.
A skeleton can not only give clues about the temperature of an animal's blood, it can, perhaps even more surprisingly, reveal something about the animal's social life.
This is the skull of a hadrosaur.
Like all hadrosaurs, it has a rounded front to its jaws, lacking in teeth, which in life were probably covered with a horn, and which give the family as a whole the name duck-billed dinosaurs.
At the back there is a battery of powerful, plant-crushing teeth.
In fact, the skulls of all hadrosaurs are very much the same, except for one feature - this, a crest.
And this varies amazingly.
This one is thin and forward-pointing, this one is long and goes right down the front of the skull and this one is broad and plate-like and sits on top of the skull.
So these are three separate species.
But this is almost certainly a male, because here's another one with very much the same shape of crest on top of the skull, but slightly smaller, so it's probably a female.
And there is a third in which the same shape of crest is only just developing, so that's probably half-grown.
So crests in hadrosaurs served to proclaim an individual's sex, age and species.
And since such adornments that do that elsewhere in the animal kingdom are very often made more obvious with colour, we can speculate that the dinosaurs were indeed quite spectacular-looking animals, as the character of their scaly skin has already suggested.
But these crests were more than visual signals.
Inside, there are air chambers, which must have acted as resonators when the animals bellowed.
Since the air chambers vary in size and shape as much as the crests, each species must have had its own characteristic call.
(GRUNTING) And they probably roared in deafening choruses, for we know that plant-eating dinosaurs lived in herds, as wildebeest do today.
In Montana, deposits have been discovered where the bones of hadrosaurs are piled up in vast numbers.
Jack Horner, the researcher who discovered the remains of the herds, has also found in Montana even more extraordinary evidence of the social life of dinosaurs.
He's actually found their nests and eggs, and he showed me where I, too, could pick up bits of the shell.
(ATTENBOROUGH) Is that anything? (HORNER) Just eggshell.
(ATTENBOROUGH) What do you mean, just? (ATTENBOROUGH) Really? (HORNER) Well when we're looking for a nest, what we want to see is Eggshell is important.
- Is it always black? - Yep.
In this formation it's always black.
In other formations it can be other colours.
If the piece is big enough, you can see the texture of the egg and then, with a microscope, you can see the pores.
Is this the sort of size you get normally? Well, in a nest where there's babies, the eggshell will be really tiny because the babies were in the nest, they trampled the eggs and so it gets broken up quite bad.
But if we find a nest that was deserted after the eggs had been laid, then we'll find big pieces.
Jack has even discovered complete clutches of unhatched eggs which he's taken back to his lab.
Now this nest is actually upside down, isn't it, because that's the top of the jacket.
And so these are the eggs? These are the eggs, yeah.
This is the centre egg in the nest.
The centre egg is always laid upright and then each egg out from the centre becomes more and more inclined.
- They were laid spirally? - Spiral, uh-huh.
- This was the first? - That was the first, I assume.
- Are they loose? - Yes, this one's loose.
You can see the pointed end of the egg, and the top of the egg has been smushed down.
- And is there shell on there? - Yeah, this is all shell.
This whole nest, presumably, was deserted by the parents.
Apparently so, yeah.
- Do you think there's anything in that? - Yes.
- I don't think there is, I know.
- How do you know? They've been x-rayed and CAT-scanned, and there are indications of little ones in there.
How can you wait? Why don't you hit it with a spoon and take it out? I would like to do that.
My preparators tell me I'm not supposed to.
- Have you got an opened egg? - Yes, we have one from another nest.
- This was a clutch of nineteen eggs.
- Nineteen? Nineteen, and all nineteen have embryos.
This is one of the better ones.
What you see here is the thigh-bone, the femur, the tibia and then the ankle joint with the foot underneath.
Very carefully open it up.
- And what can we see there? - What we're looking at is the right leg.
There's the left leg, the tibia.
And then between the knees is the skull, sitting right in here.
So we can see that tiny little teeth had erupted in the jaw.
(ATTENBOROUGH) So it could give you a nip as soon as it hatched, just like young alligators can today.
What about individual bones, do you ever get them out? Yeah.
One of the eggs I took completely apart and just took out this.
It's a humerus, the upper arm-bone of the embryo.
Just for comparison, so you get some idea of what it looks like, here's a sub-adult.
- So you can see, it had a little growing to do.
- Beautiful.
The bones of young a few weeks old also reveal a great deal about the hadrosaur's habits.
They are found inside the nest, implying that the young stayed there.
That means their parents must have brought back food to the nest to feed them, and there's confirmation of that in their teeth, which are already slightly worn.
The hadrosaurs flourished around 75 million years ago.
In Montana, the climate was much warmer than it is there today, and there were swamps fringing an inland sea.
The dinosaurs had reached the pinnacle of their evolution and many different kinds lumbered through the swamps which, then as now, were also the home of many other reptiles and birds.
But 64 million years ago, the hadrosaurs and all the other dinosaurs vanished.
The reign of the dinosaurs had ended.
There are many theories as to why the dinosaurs finally became extinct.
One of the most recent is that an asteroid collided with the earth, creating such an immense explosion on impact that the skies filled with dust, blotting out the sun.
In the darkness, the plants all died, and the dinosaurs, with nothing to eat, starved to death.
There are two problems with that or any other theory which depends upon a single catastrophe as the explanation.
The first is that the dinosaurs didn't die out in a year or a decade but over thousands of years.
The second is that, although the dinosaurs died out, many other creatures didn't.
These alligators are reptiles, just as the dinosaurs were.
They evolved on earth long before the dinosaurs, yet they've survived to the present.
It seems unlikely that they would have lived through a sudden global catastrophe in which the dinosaurs perished.
A more likely explanation, to my mind, is a gradual change in the earth's climate.
Some animals, birds, for example, were better able to cope with this than the dinosaurs, with their less-than-perfect control over their body temperature.
The early birds, like birds today, were protected by their superbly efficient insulating coats of feathers, so they survived.
Small reptiles were able to take refuge against the cold in nooks and crannies, and reptiles that lived in water were cushioned against extreme temperature changes.
So the earth still retains representatives from all these animal groups.
But for me, the most exciting thing about the dinosaurs is not how they died, but how they lived.
Their dynasty, after all, lasted for nearly 200 million years, compared with a mere two or three million years that human beings have been on earth.
When the hadrosaurs were at the height of their success, much of North America was covered with swamps very like these.
In the 64 million years since then, the shallow seas that covered much of North America drained away from the margins of the continent.
Rivers deposited layers of mud over the fallen trees and finally the swamps became dry land.
This is the richest dinosaur graveyard in the world, Drumheller in Alberta, Canada.
This light-coloured rock is composed of sand that was laid down in a river channel.
The dark layer at the top is the remains of mud deposited when the whole area was submerged in a flood.
It's in between these layers in these particular cliffs that dinosaur bones are most commonly found.
Almost 500 skeletons of 50 different species have come from these cliffs, the remains of a whole community of dinosaurs.
And here, too, in the Tyrrell Museum of Palaeontology more of them have been reconstructed and displayed than anywhere else in the world.
They daily astonish thousands of visitors, who come both to marvel at the bones and to learn about the vanished lives of these spectacular animals.
So today, less than 200 years since we discovered that these animals even existed, we've learnt so much about them that we can almost hear the champ of these huge jaws, visualise the glint in the eye that once revolved in this empty socket, clothe this immense skeleton with leathery skin and muscles and picture in our imaginations in almost as much detail as if they were alive today these bellowing, battling, browsing, nesting, courting, scavenging, fighting creatures that disappeared from the earth over 50 million years before mankind appeared upon it.
At the time when the dinosaur first appeared, about 200 million years ago, all the land on the earth was grouped together in one supercontinent and the dinosaurs roamed all over it.
And so today their remains can be found in the fragments of that supercontinent, in Australia, in North America, in Europe and here in Africa.
We're on an expedition in the southern fringes of the Sahara and the reason we've come here is that in a desert there's very little vegetation to cover the rocks, so that if there are dinosaurs in them, we'll be able to see them.
One of the expedition leaders, Dick Moody, showed me their first find.
I'm sure you'll find this one, which we haven't touched, quite a superb specimen, quite exciting.
0h, it is absolutely magnificent.
This is obviously the backbone, but which way is it lying? It's running in that direction, we believe, towards the head and towards the east.
And in this direction, generally, back towards the tail.
- And the ribs? - The ribs are running off.
As you can see, they're slightly disarticulated and slightly broken up, but they are running in that general direction down the sand dune.
And how long do you think the complete animal was? Between 20 and 30 metres.
- What, that's 90 feet? - Yes.
- That's enormous.
- It's a large animal, yes.
How complete do you think it might be? We're hoping to find some skull material and obviously limb material underneath here.
If we clear these just a little The weathered shales in which the bones were embedded were so soft that we could brush them away with our hands.
After only half an hour, we already had some idea of how much of the animal was preserved.
But it was a further day before all the bones at this site were exposed.
There weren't as many as we had first hoped.
The base of the tail and the lower spine was there, but the legs and most of the body were missing.
But half a mile away, the rest of the expedition was working on another group of bones.
These were leg bones and probably belonged, if not to the same animal, then at least to the same kind.
The huge carcass, whatever it was, had clearly already been dismembered before it was buried.
Perhaps other scavenging dinosaurs had pulled it apart.
Perhaps the rotting body had disintegrated as it lay in the river that eventually buried it in mud.
The expedition was from the Natural History Museum and Kingston Polytechnic in London.
Before the bones could be transported back, they had to be protected by wrapping them with strips of sackcloth soaked in plaster.
This will harden into a solid jacket that will hold the whole specimen together.
The expedition dug up and plastered almost 100 bones in the four weeks they worked in the Sahara.
But this was only the start.
Indeed, it won't be until the team gets the bones back to London and has cleaned them, studied them and pieced them together, that they will know for sure exactly what kind of dinosaur they've got.
But one thing is certain - it's a giant.
These bones, too, in the museum in East Berlin, came from Africa back in 1912.
When pieced together, they proved to belong to the most massive land animal known up to that time.
It was 74 feet, 22½ metres long, it stood 39 feet, that's 12 metres, high, and it was estimated to weigh 77 tons, which is as much as 12 bull elephants put together.
This is brachiosaurus.
It's head, perched on top of its immensely long neck, was comparatively tiny, less than three feet long, but it has huge nostrils, high on its forehead and they led some people to suggest that this animal lived in lakes, with its head and nostrils above the surface while it walked along the bottom with the water supporting its huge body.
But that, we now know, would have been impossible.
If its nostrils were open at the surface, the water pressure 30 or so feet below the surface would have been so great that its lungs would've collapsed.
Furthermore, the shape of its legs and its deep, narrow chest all suggest an animal that lived on land.
So now, it seems, we have to think of brachiosaurus as a kind of gigantic reptilian giraffe, browsing the tops of the trees.
Brachiosaurus may be the biggest mounted dinosaur in the world, but it may not be so for long.
In New Mexico, they've found remains of an animal that may be even bigger.
They've already given it a name, seismosaurus, the "earth-shaker".
But the rock in which it is embedded, unlike the soft shales of the Sahara, is almost as hard as concrete, and excavating it is a laborious and time-consuming business.
The excavation leader, Dave Gillette, told me the story.
This is where we found the first set of vertebrae in 1979.
We finally excavated in 1985.
How much of it was showing? Only the upper part.
It was showing as though it had been carved out of the rock in bas-relief.
It was perfectly exposed just in this fashion.
- And then? - Then, when we looked closer in the ground, we found a total of eight vertebrae along this line, all in perfect articulation, and they're from the basal part of the tail, leading into the pelvic region.
There's another vertebra here.
Then we took out two large blocks, one here, another here at the base of the tail, that led right up to the hip region.
- What's that? - This is a rib, which has been displaced from the proper anatomical position when the animal died.
- The rock looks awful.
- It is terribly hard around the bone.
- It takes for ever for us to excavate the bones.
- Does the animal go on in there? We think the animal continues right into the hill to the north for another 60 or 70 feet.
- Under the rock? - About eight feet deep.
We're using sophisticated and experimental remote-sensing techniques to try to see those bones before we excavate.
The site is only a few miles from Los Alamos atomic research station, and the scientists there, on their days off, come out to use the most advanced techniques of nuclear physics to help Dave locate his dinosaur bones deep in the rock.
This sledge carries a still-experimental remote-sensing device, a kind of radar that looks into the ground.
It's dragged along carefully-plotted tracks across the rock and already readings from it are beginning to confirm the gigantic size of the animal.
I asked Dave how long he thought seismosaurus might eventually prove to be.
My best estimate is 140 feet in length, from the snout to the tip of the tail.
How does that compare? The previous record-holder was diplodocus at 87 feet.
We're approaching twice that length.
When will you actually know whether this is a world-beater? We know now.
We have good confidence in our calculations.
Dinosaurs certainly include some gigantic animals.
Stegosaurus, bigger than a rhinoceros.
Allosaurus, tall as a giraffe.
But they weren't all huge.
Some were no bigger than a dog.
Nonetheless, many were very big indeed and they certainly include some of the most spectacular animals ever to walk the earth.
They dominated the world for over 160 million years.
But what did a dinosaur like this actually look like when it was alive? Did it have hide like an elephant, or was it covered in scales like a lizard, or perhaps hair, like a horse? The skin, of course, like the rest of the soft parts, is very rarely fossilised, but in this exceptional example, it has been.
This is the fleshy pad on the underside of its foot.
And behind you can still see the wrinkles in the skin on its belly.
This particular individual was, most unusually, entombed in the hot sand of a desert, and although its flesh decayed and disappeared, its tough hide was baked and mummified.
You can even see the impressions of the scales in the skin.
From remarkable specimens like this, we can deduce that dinosaur skin was thick and tough, probably not unlike an elephant's hide.
But was it grey and colourless like an elephant's? 0r was it, perhaps, brightly coloured, as are the skins of many reptiles today? Animal pigments don't fossilise, so it's anyone's guess as to whether the dinosaurs were coloured or not, but it's tempting to think that they were.
But we can go further than simply investigating the size and appearance of dinosaurs.
What did the dinosaurs eat? Well, flowering plants didn't develop until about 100 million years ago.
That means that for most of the time dinosaurs were on earth, there were very few of the kinds of plant that dominate the land today.
There were no oak trees or hazel in Europe, on which deer feed.
In Africa there was no thorn scrub or acacia, on which elephant and giraffe browse.
Most important of all, there was no grass, on which horses or bison or antelope graze.
Instead there were plants like these.
These are cycads.
Today they grow wild in only a very few places, and mostly in the tropics.
But when the dinosaurs first evolved, they were spread worldwide.
In addition to these, there were also tree-ferns and primitive conifers like pines.
But all these plants had tough, fibrous leaves, almost indigestible, you might think.
To make matters more awkward, the early dinosaurs were poorly equipped with teeth.
Diplodocus had only these small, peg-like teeth that could have done little more than just nip off the fronds.
It certainly couldn't have chewed them.
So how did it avoid terrible indigestion? Clues to the answer were eventually found lower down in the skeleton.
Between the ribs of specimens that had been fossilised more or less complete are sometimes found great heaps of small, highly polished pebbles.
It seems these had been swallowed and stored in a muscular pouch of the dinosaur's stomach, a gizzard, which served as a kind of internal mill to grind up its fibrous meals.
Even so, it must have taken a very long time for a dinosaur's digestive juices to break down the woody stems and trunks of plants like these.
If you have to keep your food in your stomach a long time, then you need a very big stomach to serve as a storage vat.
That, in turn, means you need a very large body to carry it.
So the ancient pastures of tree-ferns may be one of the main reasons why plant-eating dinosaurs grew so big.
As millions of years passed, however, evolution brought changes.
The first flowering plants appeared, and so did new kinds of plant-eating dinosaurs.
These are hadrosaurs.
They had no teeth at all in the front of their jaws.
Instead, the rounded bone was almost certainly covered with a horny sheath.
With this, they could have done little more than just nip off leaves and twigs.
But inside the mouth, at the back of the jaws, they had an enormous battery of teeth, row upon row.
This particular jaw had over 200.
As these crushed and ground the tough fibres, they were inevitably worn down.
But new ones grew in the bone of the jaw beneath and moved up to replace the old ones.
But could they use them to chew? Mammals like this camel can chew by moving their lower jaw from side to side, so they are able to break down the toughest of plant foods.
The dinosaurs were reptiles, and no reptile can do that.
They can only move their jaws up and down, and that puts a real limit on what they can eat.
The hadrosaurs dealt with that problem in a most remarkable way.
The highlighted upper jaw could actually hinge outwards.
When a hadrosaur's skull is examined closely, it reveals an elastic joint between the upper jaw and the roof of the snout.
This means that as the lower jaw moves up, it pushes aside the upper jaw, in effect, chewing without any sideways movement of the lower jaw at all.
The most powerful grinding battery of all was that possessed by triceratops, one of the last of the dinosaurs.
This, the product of 100 million years of development in the technique of chewing, is perhaps the most powerful chewing device ever possessed by any animal.
A huge beak in the front served as shears which could probably slice clean through a tree trunk.
The branches were then moved to the back of the mouth, where the massive grinders reduced them to pulp.
But these teeth belong to a very different sort of animal.
These are not thin pegs for nipping off bits of leaves.
These are daggers, finely serrated along the edge like steak knives, adapted to slicing through flesh and hide.
In life, much of the empty space in the skull here would have been filled by massive muscles, which gave an enormously powerful bite to these huge jaws.
This is Tyrannosaurus rex, the biggest of all the meat-eating dinosaurs, measuring over forty feet long and weighing about seven tons, surely the most terrifying hunter ever to roam the earth.
With long, curved claws and sharp teeth, the carnivorous dinosaurs must have been terrifying and highly efficient predators.
But other kinds of dinosaurs evolved that had no teeth at all.
This one seems to have been rather like the ostrich of today.
So perhaps, like an ostrich, this dinosaur, called struthiomimus, picked up and swallowed anything, animal or vegetable, it considered remotely edible.
So the bones of dinosaurs, carefully pieced together, can tell us a great deal about how big they were, what they fed on, and therefore their relationships with one another, and how their limbs articulated.
But how fast could they move? To answer that question, you have to come to a place like this.
150 million years ago, there was a mudflat here, around the margin of a freshwater lake.
The lake filled and eventually sediments covered the whole area, and the mudflats turned into mudstones.
In them are preserved huge footprints - dinosaur footprints.
These, nearly a yard across, can only have been made by a huge plant-eater like a brontosaur such as diplodocus.
No other had such a huge foot.
Here the animal has trodden on a small shell, a kind of freshwater mussel.
Molluscs virtually identical to this still live today, but only in water that is less than three feet deep.
So these little shells confirm that these dinosaurs that day were splashing through the shallows.
If you can measure an animal's stride from its tracks, and also know the length of its legs, it's possible to calculate the speed at which it was moving.
The brontosaurs had legs that were about nine feet long, as we know from their skeletons.
But this animal's right hind leg, which was printed here, is only about six feet from the next print in the sequence.
So we can be pretty sure the animal that was moving along here was moving fairly slowly, as perhaps you'd expect if it was just plodding along, looking for food around the margin of a lake.
But, in fact, although thousands of these prints have now been found, not one of them has a stride longer than 12 feet.
So we can be pretty certain that these animals were fairly slow-moving.
These prints, though, are very different, not circular but with three prominent toes.
At the end of each, there is a deep, sharp mark that can only have been made by a claw.
They match the three-toed feet of theropods, medium-sized, carnivorous dinosaurs.
From tracks like these, it's been calculated that some of these hunters could run at up to 30 miles an hour.
Moving at such speeds demands a great deal of energy, and an animal can only produce enough if it has a warm body.
So did the dinosaurs get their energy directly from the sun, as reptiles do today, or could they generate warmth internally, like birds and mammals? That is a question of great debate.
This is how Tyrannosaurus rex may have moved, in the opinion of one of the new generation of dinosaur interpreters, Robert Bakker of the Museum of Colorado.
0K, Tyrannosaurus rex, the most famous dinosaur, the most popular dinosaur, and here it is, running at 40 miles per hour, faster than a rhino, faster than an elephant.
This T.
Rex is going faster than a lion.
Yes, but that's your animation.
How do you know? Because of the way the muscles were hung on those leg bones, the way the calf muscles were hung on that knee, and the way the massive thigh muscles were hung on that ilium.
- But why does that prove it was warm-blooded? - Let's look at the real one, eh? Could it really have reared up like that and lifted its immense length? Absolutely, and more.
It could jump, it could run fast.
This is a T.
Rex, a real one, a cast, with a bloody big knee, right? - But why does that make it warm-blooded? - Actually, it's the other way around.
Unlike the Pentagon, evolution doesn't build more strength than the animal needs.
This animal is immensely strong.
It has a strong knee and a bloody big drumstick of calf muscle to run fast, because warm-bloodedness demands speed.
This animal has to cruise fast and it needs great bursts of speed because it has to kill more often than a cold-blooded animal.
There is no cold-blooded animal today with this great strength.
None.
This is not a scaled-up lizard or a scaled-up tortoise.
This is an enlarged, five-ton, meat-eating roadrunner, that's what it is.
And like a roadrunner, it's eating frequently.
There's another message about speed in the skeleton, not in the legs but in the chest, because in the chest, in the first three ribs, in that space, there is only one organ housed, the cardiac chamber, the heart.
And in modern cold-bloods, the heart is very small, because cold-blooded animals need only a weak cardiac organ.
But look at this: The first rib, the second rib, the third rib.
Look how long that is.
There was housed in these ribs, without doubt, a gigantic heart designed to pump, designed to put out blood flow at emphatically warm-blooded levels.
So maybe we should get rid of the image of dinosaurs as slow, lumbering plodders and think of them instead as nimble and agile in spite of their size.
(BL00D-CURDLING R0AR) The truth is almost certainly that some were warm-blooded and others were not.
A skeleton can not only give clues about the temperature of an animal's blood, it can, perhaps even more surprisingly, reveal something about the animal's social life.
This is the skull of a hadrosaur.
Like all hadrosaurs, it has a rounded front to its jaws, lacking in teeth, which in life were probably covered with a horn, and which give the family as a whole the name duck-billed dinosaurs.
At the back there is a battery of powerful, plant-crushing teeth.
In fact, the skulls of all hadrosaurs are very much the same, except for one feature - this, a crest.
And this varies amazingly.
This one is thin and forward-pointing, this one is long and goes right down the front of the skull and this one is broad and plate-like and sits on top of the skull.
So these are three separate species.
But this is almost certainly a male, because here's another one with very much the same shape of crest on top of the skull, but slightly smaller, so it's probably a female.
And there is a third in which the same shape of crest is only just developing, so that's probably half-grown.
So crests in hadrosaurs served to proclaim an individual's sex, age and species.
And since such adornments that do that elsewhere in the animal kingdom are very often made more obvious with colour, we can speculate that the dinosaurs were indeed quite spectacular-looking animals, as the character of their scaly skin has already suggested.
But these crests were more than visual signals.
Inside, there are air chambers, which must have acted as resonators when the animals bellowed.
Since the air chambers vary in size and shape as much as the crests, each species must have had its own characteristic call.
(GRUNTING) And they probably roared in deafening choruses, for we know that plant-eating dinosaurs lived in herds, as wildebeest do today.
In Montana, deposits have been discovered where the bones of hadrosaurs are piled up in vast numbers.
Jack Horner, the researcher who discovered the remains of the herds, has also found in Montana even more extraordinary evidence of the social life of dinosaurs.
He's actually found their nests and eggs, and he showed me where I, too, could pick up bits of the shell.
(ATTENBOROUGH) Is that anything? (HORNER) Just eggshell.
(ATTENBOROUGH) What do you mean, just? (ATTENBOROUGH) Really? (HORNER) Well when we're looking for a nest, what we want to see is Eggshell is important.
- Is it always black? - Yep.
In this formation it's always black.
In other formations it can be other colours.
If the piece is big enough, you can see the texture of the egg and then, with a microscope, you can see the pores.
Is this the sort of size you get normally? Well, in a nest where there's babies, the eggshell will be really tiny because the babies were in the nest, they trampled the eggs and so it gets broken up quite bad.
But if we find a nest that was deserted after the eggs had been laid, then we'll find big pieces.
Jack has even discovered complete clutches of unhatched eggs which he's taken back to his lab.
Now this nest is actually upside down, isn't it, because that's the top of the jacket.
And so these are the eggs? These are the eggs, yeah.
This is the centre egg in the nest.
The centre egg is always laid upright and then each egg out from the centre becomes more and more inclined.
- They were laid spirally? - Spiral, uh-huh.
- This was the first? - That was the first, I assume.
- Are they loose? - Yes, this one's loose.
You can see the pointed end of the egg, and the top of the egg has been smushed down.
- And is there shell on there? - Yeah, this is all shell.
This whole nest, presumably, was deserted by the parents.
Apparently so, yeah.
- Do you think there's anything in that? - Yes.
- I don't think there is, I know.
- How do you know? They've been x-rayed and CAT-scanned, and there are indications of little ones in there.
How can you wait? Why don't you hit it with a spoon and take it out? I would like to do that.
My preparators tell me I'm not supposed to.
- Have you got an opened egg? - Yes, we have one from another nest.
- This was a clutch of nineteen eggs.
- Nineteen? Nineteen, and all nineteen have embryos.
This is one of the better ones.
What you see here is the thigh-bone, the femur, the tibia and then the ankle joint with the foot underneath.
Very carefully open it up.
- And what can we see there? - What we're looking at is the right leg.
There's the left leg, the tibia.
And then between the knees is the skull, sitting right in here.
So we can see that tiny little teeth had erupted in the jaw.
(ATTENBOROUGH) So it could give you a nip as soon as it hatched, just like young alligators can today.
What about individual bones, do you ever get them out? Yeah.
One of the eggs I took completely apart and just took out this.
It's a humerus, the upper arm-bone of the embryo.
Just for comparison, so you get some idea of what it looks like, here's a sub-adult.
- So you can see, it had a little growing to do.
- Beautiful.
The bones of young a few weeks old also reveal a great deal about the hadrosaur's habits.
They are found inside the nest, implying that the young stayed there.
That means their parents must have brought back food to the nest to feed them, and there's confirmation of that in their teeth, which are already slightly worn.
The hadrosaurs flourished around 75 million years ago.
In Montana, the climate was much warmer than it is there today, and there were swamps fringing an inland sea.
The dinosaurs had reached the pinnacle of their evolution and many different kinds lumbered through the swamps which, then as now, were also the home of many other reptiles and birds.
But 64 million years ago, the hadrosaurs and all the other dinosaurs vanished.
The reign of the dinosaurs had ended.
There are many theories as to why the dinosaurs finally became extinct.
One of the most recent is that an asteroid collided with the earth, creating such an immense explosion on impact that the skies filled with dust, blotting out the sun.
In the darkness, the plants all died, and the dinosaurs, with nothing to eat, starved to death.
There are two problems with that or any other theory which depends upon a single catastrophe as the explanation.
The first is that the dinosaurs didn't die out in a year or a decade but over thousands of years.
The second is that, although the dinosaurs died out, many other creatures didn't.
These alligators are reptiles, just as the dinosaurs were.
They evolved on earth long before the dinosaurs, yet they've survived to the present.
It seems unlikely that they would have lived through a sudden global catastrophe in which the dinosaurs perished.
A more likely explanation, to my mind, is a gradual change in the earth's climate.
Some animals, birds, for example, were better able to cope with this than the dinosaurs, with their less-than-perfect control over their body temperature.
The early birds, like birds today, were protected by their superbly efficient insulating coats of feathers, so they survived.
Small reptiles were able to take refuge against the cold in nooks and crannies, and reptiles that lived in water were cushioned against extreme temperature changes.
So the earth still retains representatives from all these animal groups.
But for me, the most exciting thing about the dinosaurs is not how they died, but how they lived.
Their dynasty, after all, lasted for nearly 200 million years, compared with a mere two or three million years that human beings have been on earth.
When the hadrosaurs were at the height of their success, much of North America was covered with swamps very like these.
In the 64 million years since then, the shallow seas that covered much of North America drained away from the margins of the continent.
Rivers deposited layers of mud over the fallen trees and finally the swamps became dry land.
This is the richest dinosaur graveyard in the world, Drumheller in Alberta, Canada.
This light-coloured rock is composed of sand that was laid down in a river channel.
The dark layer at the top is the remains of mud deposited when the whole area was submerged in a flood.
It's in between these layers in these particular cliffs that dinosaur bones are most commonly found.
Almost 500 skeletons of 50 different species have come from these cliffs, the remains of a whole community of dinosaurs.
And here, too, in the Tyrrell Museum of Palaeontology more of them have been reconstructed and displayed than anywhere else in the world.
They daily astonish thousands of visitors, who come both to marvel at the bones and to learn about the vanished lives of these spectacular animals.
So today, less than 200 years since we discovered that these animals even existed, we've learnt so much about them that we can almost hear the champ of these huge jaws, visualise the glint in the eye that once revolved in this empty socket, clothe this immense skeleton with leathery skin and muscles and picture in our imaginations in almost as much detail as if they were alive today these bellowing, battling, browsing, nesting, courting, scavenging, fighting creatures that disappeared from the earth over 50 million years before mankind appeared upon it.