Lost Worlds, Vanished Lives (1989) s01e02 Episode Script
Part 2
A fossil jaw, and little doubt about the animal to which it once belonged because similar animals with similar jaws are alive today.
The delicate imprint of a dragonfly in limestone.
It's so similar to a living dragonfly that it must have lived and flown in just the same fashion 150 million years ago.
A 50 million-year-old shell of a nautilus.
We can be pretty sure what kind of animal lived in it because nautilus still swim in the Pacific.
But many fossils are much more mysterious.
What could these bones have belonged to? Back at the beginning of the 18th century, a group of objects just like these were found near Nuremberg in Germany.
The man who discovered them was a doctor and he thought he knew exactly what they were.
They were, he said, part of a human backbone, the remains of a poor sinner who had died at the time of the biblical flood.
But, in fact, they're not shaped like human vertebrae.
However, a century later, this woman found some more on the south coast of England.
Her name was Mary Anning and she earned her living at Lyme Regis by selling fossils to visitors.
These new specimens of hers were particularly interesting because with the backbones were ribs and limbs and skulls.
She sold one of them to a London surgeon who was also a fossil collector.
He thought at first that they were some kind of fish.
Then he changed his mind.
He thought they were related, believe it or not, to the duck-billed platypus.
And finally he decided that their nearest living relative was a strange creature that occasionally appeared in the streams of Yugoslavia.
This odd animal and others like it were thought locally to be the tadpoles of dragons.
In fact, it's an olm, an amphibian related to salamanders.
But even its bones don't match the fossil ones.
Eventually, experts at the British Museum got to the truth of the matter: There was nothing alive today that was like the fossils of Lyme Regis.
But the skull seemed very reptilian and the paddle-like limbs showed that the animal swam.
So they invented a special name for it, ichthyosaur, "fish-lizard".
As more specimens were found, they tried to work out what the living animals looked like.
The spine always had a kink at the end.
That, they decided, was because the fleshy tail was so big that when the animal died, it drooped and broke.
The huge eye and the teeth suggested that it was a hunter.
Victorian illustrators began to picture ichthyosaurs in life, and this is how they saw them.
Then a lot more evidence came from Germany.
In the village of Holzmaden, near Stuttgart, there are thick deposits of black, slaty limestone of about the same age as the Lyme Regis rocks.
Careful examination showed that they were once mud on the floor of a wide bay in a tropical sea.
Most of the inhabitants in this sea swam in the sunlit upper waters, but the bay, it seems, was very tranquil and undisturbed by currents.
At the bottom, the water was still, stagnant, and very poor in oxygen.
Few scavengers could live down here and the processes of decay, which depend on oxygen, could only move very slowly.
So if the corpse of an animal that had been living in the waters above slowly drifted down here, it could settle on the bottom and remain entire, undecayed and undisturbed by scavengers, until mud settled down upon it and buried it.
And here are the remains of just such a corpse.
The tip of its snout lies beyond this natural joint in the rock.
These are its jaws, its eye is somewhere there, its neck, its backbone, a few vertebrae are displaced here, then the backbone runs through this rock here, past this imprint of an ammonite.
There it is in this crack again, a backbone, and past another ammonite, and there's its tail.
When such near-perfect specimens are carefully prepared, they may even show the outline of the flesh, as a dark, almost oily silhouette around the bones.
And from this it was discovered that the ichthyosaurs had a triangular fin on their back.
And that kink at the end of the backbone was not a break, but a strengthening of the lower fluke of the tail.
With the whole shape of the animal revealed, we can now work out just how it swam.
The joints between the bones of its spine showed that it beat its tail from side to side, and it was clearly capable of great speeds as it surged through the sea in search of its food.
No, not ichthyosaurs but their modern equivalent, dolphins.
There are, of course, differences.
Dolphins beat their tails not from side to side but up and down, and they are mammals, not reptiles.
But their lifestyle is certainly very similar.
Like ichthyosaurs, they breathe air and break the surface every now and then to do so.
After the ichthyosaurs died out, the seas, for a time, had no air-breathing hunters.
But then a group of mammals began to colonise the sea, just as a group of reptiles had done 100 million years earlier, and similar ecological demands have produced similar evolutionary responses.
Did ichthyosaurs, like dolphins, eat fish? Well, their teeth were sharp and easily capable of grabbing a wriggling fish, but they certainly ate other things as well.
This one's belly contained a number of small, horny hooks, and those, we know, came from squid-like animals.
But this is only one species.
There are lots of different kinds of ichthyosaurs, and each may have had its own particular diet.
This one was a giant, four or five times the length of the common ichthyosaur, and it was a cannibal, because here, between its ribs, where its stomach once lay, are the chewed-up remains of the backbones of smaller ichthyosaurs.
And in addition to this monster, there was another kind which is still something of a mystery.
Its jaws are extraordinary.
This is the upper one.
It's a long, thin spike.
The lower one is only a quarter of the length, and it's fully armed with teeth.
What could it have used them for? Well, there are two clues.
The first are its paddles, which are huge and very broad.
That suggests that they could only be moved very slowly.
Secondly, its eyes are gigantic.
They're the biggest of all known ichthyosaur eyes.
Big eyes are characteristic of animals that live in low light levels.
So maybe this, the rarest of the ichthyosaurs, lived in the darkness near the bottom of the sea and moved across the sea floor, propelling itself slowly with its huge paddles, stirring up the mud with its long upper jaw and snapping up what food it found with its lower.
The marvellously preserved specimens of Holzmaden reveal a further detail in the lives of these ancient reptiles.
Just emerging from the body of this female is a baby.
Most reptiles lay eggs on land, but the ichthyosaurs had broken this last link with the land and produced live young.
Ichthyosaur or dolphin? 150 million years ago, there must have been events just like this in Holzmaden lagoon.
While ichthyosaurs were swimming so efficiently through the water, other animals were moving around over the sand and mud of the sea floor.
Some were even managing to crawl out of the sea and up onto the land.
And here they left other evidence of their presence.
A track can tell you a lot about an animal; how many legs it has, in what order it moved them, how heavy it was and much else.
And tracks, too, can be preserved in sandstones.
0n the shores of the Isle of Arran in western Scotland, there are two parallel stripes in the rock.
At first they might appear to be some kind of stress mark or faulting in the stone, but look at them closely and you can see that they are tracks of some kind.
What is more, you can see that they were made by an animal with a very large number of legs.
There's an obvious candidate for what made them; a millipede.
Its multitude of legs, moving up and down in a wave passing along the body, leave just such parallel stripes in the mud behind it.
They match these tracks in Arran almost exactly.
The biggest millipede alive today is about ten inches long, and we call that a giant millipede.
But the animal that made these tracks, judging from their dimension, must have been about six feet long.
That was a real giant.
Marks in sand and mud, of course, can be made not only out of water but in it.
And one of the commonest of those underwater marks are the ones that are made when sand is moved across the bottom of the sea as the tide moves in and out - ripple marks.
These, too, are ripples in sand, but they are 500 million years old.
They were formed at the bottom of a sea which at that time covered most of western Europe.
Since then, continents have collided, and those sediments have been rucked up so that now they form these mountains in North Wales.
It's not only inanimate mechanical forces that create patterns in the sand of the sea floor, animals do so as well.
They burrow through the sediment, extracting nutriment from it, and they usually do so in a regular, systematic way, so that they don't miss patches of mud and don't process any of it twice, and this produces regular patterns of casts and burrows.
But many of these patterns are complicated, and it's not always easy to see exactly how the animal could have made them.
However, computers can help to solve this problem.
This is not a pattern that has been generated by the computer.
This is the tracing of an actual fossil, but it's rather puzzling.
Look, for example, at down here.
There's one ring there, but there is another ring on the inside.
How could that have been formed? Well, by looking at the actual fossil itself, you can see which ring, which track has been placed on top of which other track.
And by feeding that information carefully into the computer, you can then ask the computer to look at the pattern from a different point of view, and then what you see is this.
The animal was working in three dimensions, it was burrowing down in the mud, and it was when the rock was compacted that it produced this ring superimposed upon one another and that particular shape.
But although we know so much about this elegant burrow, we don't know what animal made it and may, in fact, never find out.
These rocks in North Wales, close by those ancient, 500 million-year-old ripple marks, are also covered with trails of many kinds.
One sort is like this.
They are long tracks which often criss-cross one another.
And this is another kind, a sort of large dimple.
What could have made them? Well, we have direct evidence as to what made this kind.
A fossil has been found that sits in it perfectly.
A trilobite, the most abundant of all the animals in the seas of this period.
The dimple is where it rested, the broad stripe the track it made as it trundled over the sea floor.
Trilobites have left no direct descendants, but we nevertheless know a lot about them.
Underneath their hard, jointed shells they had two rows of long, thin legs, as shrimps have.
Most trilobites were only an inch or so long, but a few were giants, over a foot in length.
Although their remains all accumulated on the bottom of the sea, they didn't necessarily all live there.
Some may have grubbed about on the bottom, but others could have swum quite a long way above the sea floor.
To find out which did what, casts are put in a tank of flowing water by Richard Fortey of the British Museum.
What kind of animal is this one? This is a typical bottom-living trilobite, which we think was rather poorly streamlined.
And we can show this quite graphically by turning on some dye.
There it goes.
And you can see that large wakes are created on the back of the animal, behind the eyes and behind the tail.
And if we turn the dye off, you can see how these wakes linger on for a long time, behind the eyes and on the back of the animal.
This is generally a bad design for active swimming, as we might expect of an animal that spent most of its time crawling along the sea floor.
If we look at this one, by contrast, you can see how well streamlined the animal is.
The dye proceeds over the back of the animal without the eddies we saw last time and the head of the animal, this end here, is prolonged into a kind of nose, and the eyes are recessed, it's almost like a dogfish head.
So that is proof, do you think, that this animal was free-swimming? I don't think we can ever talk about proof, but as far as we can test by experiment and looking at the shape of the animal, this was a free-swimming trilobite in the seas of 500 million years ago.
It's clear from such investigations that some trilobites, at any rate, were very active.
Active animals need good sense organs in order to find their way about, and trilobites had amazing eyes, the first complex eyes ever to gaze out on this world.
Each consisted of a mosaic of tiny, tightly-packed units, which produced separate spots of light or shade, and together formed a single picture.
Crabs have very much the same sort of eye today.
But some trilobites did even better.
Each element in their eye had a little lens over it which focused the light into a separate image.
This intricate structure was mounted on a kind of turret.
A pair of these on the head gave this trilobite a view that extended from its tail right round to its nose.
But why should it have needed such a detailed view of its surroundings? Well, there were hunters in those ancient seas.
Ancestors of cuttlefish were around, stalking trilobites, just as cuttlefish today hunt crabs.
Once the trilobites were alarmed, they had very good defences.
You find them preserved in many different postures.
From specimens like these, it's evident that those joints between the segments along the back were very flexible.
When danger threatened, they were able to protect their vulnerable undersides by rolling up.
They even had little knobs on their heads and sockets on their tails that enabled them to lock themselves into a ball.
They evolved into many thousand different species and then, 250 million years ago, they died out and left no descendants.
Yet from their remains we can still discover how they moved and protected themselves, what they ate, where they swam, even what they saw of that long-lost world.
The skies above the ancient seas were not empty either.
Today it's birds that fly over the ocean, scouring the surface for food of one kind or another.
But birds are relatively recent arrivals.
Millions of years before they appeared, the air had been invaded by flying reptiles.
The first to be discovered was named "wing-finger", pterodactyl, for its wing was supported by its greatly elongated fourth finger.
Now so many different kinds have been found that the group as a whole is called "winged reptiles" - pterosaurs.
Their slim jaws are lined with teeth and they had a skinny membrane that stretched from that long finger to the side of their body.
This wing was powered by muscles attached to the breastbone.
The fact that this is of a reasonable size and had a small keel down the middle shows that the pterosaurs were able to flap and not just glide.
But we have more than just bones of pterosaurs.
This is a very remarkable skull of one that was found in the north of England.
The front part of the snout is missing, and so is the lower jaw, but here is the huge orbit where the eye once was.
And at the back, the top of the skull is missing and you can see inside.
At some stage during fossilisation, sediment seeped in, and it's left a cast of the pterosaur's brain.
Brains can tell us a great deal about an animal's behaviour.
And this is not the only pterosaur brain we have.
One, separated from the skull and marvellously preserved, was found in Israel.
The lobes at the back of all brains coordinate the muscles, and those at the front link the muscles with the senses.
All these lobes are much bigger than in a similar-sized land-living reptile, which confirms that this animal had the speedy reactions necessary for manoeuvrability in the air.
The lobes at the side of the brain control vision and are also large, so the pterosaurs had excellent sight and probably flew during the day.
With their skinny wings and short feet, the pterosaurs may have looked more like bats than birds.
There's another way in which they may have resembled them.
Flying like this demands a lot of energy.
Bats can produce it because they have warm bodies insulated with fur.
What about pterosaurs? Could reptiles have warm blood? And if they did, how did they keep it warm? These remarkable pterosaur fossils from Kazakhstan in the Soviet Union provide an answer to that question.
Around the body of this one is the unmistakable imprint of fur, and what is fur for if it's not to keep a body warm? The pterosaurs first appeared 245 million years ago, and they populated the skies for the next 170 million years.
The earliest ones were about the size of sparrows and had bony tails, but, as time passed, they got bigger and bigger.
Judging from their teeth, they had a wide variety of diets.
Some of the smaller ones, with well-spaced, simple teeth like this, may have fed on insects, but this one, from the rocks of Bavaria, is very different.
Its teeth are so long and thin that they're little more than bristles.
Did it use them to filter food from the water, as a flamingo does? Nearly a hundred different kinds have been found already, and there are undoubtedly a great number still to be discovered.
One of the most productive areas in recent years has been Brazil.
Some extremely bizarre forms have come from there, like this one.
It's very big, the skull alone is over two feet long, and at the end of its upper jaw there is this extraordinary flange.
Peter Wellnhofer, a pterosaur expert working in Munich University, has been investigating these new finds, trying to work out what possible purpose such extraordinary features could have.
It cannot be an aerodynamic stabiliser.
It probably would not make much sense on the very end of the snout.
So no use in flying.
They can't use it to steer with or anything.
But probably it had a function when it was diving and skimming in the water, and during that time it was necessary to stabilise this long and narrow skull in the water.
As you can see here in this restoration, the skull must bend back when it dives down, but it still flies and it's moving through the water and it has to come up again.
Frigate birds pick up food from the water with just this sort of action.
The pterosaur's membranous wings probably gave it less control than feathered wings, so maybe a flange on the beak was essential for the pterosaur if it was going to do this trick.
I asked Peter Wellnhofer how he reconstructed the appearance of these pterosaurs.
This requires some degree of imagination, of course.
0n the other hand, we know that pterosaurs, for example, had hairs.
And so we put hair on the skull in the restorations, as you can see here.
And so you get a fairly good picture of what the animal looked like in life.
And what an extraordinary portrait gallery he has produced.
This is one of the filter feeders, with bristles on its lower jaw only.
This one, pteranodon, like many of the later kinds, had no tail, but its wings were 18 feet across.
Its wing muscles, judging from its breastbone, were not particularly powerful, so that it's likely that it was primarily a glider.
But you can get a long way gliding over the sea.
Pelicans show what can be done if you are able to exploit the updraughts created by the rolling waves.
And pteranodon was probably just as expert.
But perhaps the most extraordinary, indeed almost unbelievable pterosaur was found here in the badlands of southern Texas.
In 1971, a group of students working with Professor Wann Langston were down here looking for dinosaur bones when one of them, Douglas Lawson, found something very strange.
Late one hot July afternoon, after he had spent an almost fruitless day, he was walking up this dry arroyo and began to see postage stamp-sized fragments of petrified bone down in the sand.
And as he followed on up the valley, the fragments became more numerous and larger, and eventually he arrived over here at this bank and there he found a few pieces of bone projecting from the rock, still in place, and other, larger pieces that had weathered out were lying around on the surface.
This is a replica of the upper arm-bone in the wing.
As it turned out, this was the only piece that was nearly complete and still embedded in the rock, but it gives an idea of the size of the wing and taken together with all the fragments that were picked up, we've been able to piece together a reconstruction of the entire wing.
I just happen to have a diagram here that will give us some idea about the size of this object.
So this is the reconstruction of the entire wing.
The dark areas represent the pieces that we actually have found as fossils.
And from the shoulder joint out to this tip is a length of about 18 feet.
And remember this is only one wing, so you double the 18 feet and add a couple of feet for the body in between and you come up with an animal that had a wingspan of maybe 35 to 40 feet, which is larger than some small private aircraft.
How could such a huge creature have flown? Wann Langston studied the bones of a smaller individual of the same species in his laboratory to try and find out, suspending them in position to see just how they could move and how they couldn't.
We can take the humerus and because of the configuration of the head, fitting into the shoulder socket, we can move the humerus up to its maximum possible elevation.
We can also depress it to the limit and we can move it backward and forward in this plane, which also was possible for the animal.
And every move that we make with the humerus has an effect, of course, on the rest of the wing.
With all this detailed information about the mechanics of the wing available, the Smithsonian Institution in the United States decided to commission a model of one that would actually flap its wings and fly.
The cost of making one with a 40-foot wingspan would have been astronomic, so they decided to make a half-grown one, but even that is immense.
It was built from carbon-fibre materials which are very light and extremely strong.
It was coated with foam and then covered with latex, which is very flexible and allows the wing to make all the necessary movements.
The man who took on this job is aeronautical engineer and inventor Paul Macready.
What was your reaction when you first saw the fossils and the reconstructions made by palaeontologists of a thing like this? Did it seem that it could possibly fly, to you as an aeronautical engineer? Well, we knew it did fly, but it didn't seem possible because it was reputed to have a wingspan of 35 to 50 feet and that's so beyond anything that exists now that it almost seemed impossible, but you knew nature had done it.
So you, when you had to try and make something of the same shape that flew, what were your immediate problems? First you had to figure out what the shape was.
You pleaded with the palaeontologists, "Tell us what it looked like.
" The main thing was a big head stuck way out in front of a long neck and no tail to provide stability.
Trying to have this fly is like trying to shoot an arrow with the feathered end in front.
It's very unstable.
The earliest pterosaurs, little ones, had tails in the rear and they were stable, but it's kinda like riding a bicycle with training wheels.
When it's small and you're early in your training, you need that.
When nature got to these, it didn't need training wheels any more.
Everybody ready? The first experiments were with small models, fitted with tails to give them some stability while the designers wrestled with the basic aerodynamic problems.
Radio controls enabled them to move the head and wings.
With each flight, and each crash, a new lesson was learnt.
The damage caused by these crash-landings was often severe, but slowly the engineers were able to improve their design.
Even with the aid of computers and advanced aeronautical skills, this particular problem was so tricky that much of the progress was by trial and error.
After months of work, a half-sized, tailless, wing-flapping pterosaur was ready to take to the air.
Power on.
Motion check.
Left, right.
Forward, aft.
Take up the slack.
Clear.
Go.
Once airborne, the tail and the undercarriage needed for take-off are shed.
Although major movements are controlled by radio, the model controls itself to a considerable degree.
Sensors in the wings react to the varying wind currents and automatically feed signals to a small computer, a brain, which then activates tiny motors to adjust the posture of the head and wings, so preventing stalls and sideslips.
The last time such a shape flapped its way across the skies of North America, the animals watching it were dinosaurs.
You could hardly go farther than this in bringing long-dead bones back to life.
The delicate imprint of a dragonfly in limestone.
It's so similar to a living dragonfly that it must have lived and flown in just the same fashion 150 million years ago.
A 50 million-year-old shell of a nautilus.
We can be pretty sure what kind of animal lived in it because nautilus still swim in the Pacific.
But many fossils are much more mysterious.
What could these bones have belonged to? Back at the beginning of the 18th century, a group of objects just like these were found near Nuremberg in Germany.
The man who discovered them was a doctor and he thought he knew exactly what they were.
They were, he said, part of a human backbone, the remains of a poor sinner who had died at the time of the biblical flood.
But, in fact, they're not shaped like human vertebrae.
However, a century later, this woman found some more on the south coast of England.
Her name was Mary Anning and she earned her living at Lyme Regis by selling fossils to visitors.
These new specimens of hers were particularly interesting because with the backbones were ribs and limbs and skulls.
She sold one of them to a London surgeon who was also a fossil collector.
He thought at first that they were some kind of fish.
Then he changed his mind.
He thought they were related, believe it or not, to the duck-billed platypus.
And finally he decided that their nearest living relative was a strange creature that occasionally appeared in the streams of Yugoslavia.
This odd animal and others like it were thought locally to be the tadpoles of dragons.
In fact, it's an olm, an amphibian related to salamanders.
But even its bones don't match the fossil ones.
Eventually, experts at the British Museum got to the truth of the matter: There was nothing alive today that was like the fossils of Lyme Regis.
But the skull seemed very reptilian and the paddle-like limbs showed that the animal swam.
So they invented a special name for it, ichthyosaur, "fish-lizard".
As more specimens were found, they tried to work out what the living animals looked like.
The spine always had a kink at the end.
That, they decided, was because the fleshy tail was so big that when the animal died, it drooped and broke.
The huge eye and the teeth suggested that it was a hunter.
Victorian illustrators began to picture ichthyosaurs in life, and this is how they saw them.
Then a lot more evidence came from Germany.
In the village of Holzmaden, near Stuttgart, there are thick deposits of black, slaty limestone of about the same age as the Lyme Regis rocks.
Careful examination showed that they were once mud on the floor of a wide bay in a tropical sea.
Most of the inhabitants in this sea swam in the sunlit upper waters, but the bay, it seems, was very tranquil and undisturbed by currents.
At the bottom, the water was still, stagnant, and very poor in oxygen.
Few scavengers could live down here and the processes of decay, which depend on oxygen, could only move very slowly.
So if the corpse of an animal that had been living in the waters above slowly drifted down here, it could settle on the bottom and remain entire, undecayed and undisturbed by scavengers, until mud settled down upon it and buried it.
And here are the remains of just such a corpse.
The tip of its snout lies beyond this natural joint in the rock.
These are its jaws, its eye is somewhere there, its neck, its backbone, a few vertebrae are displaced here, then the backbone runs through this rock here, past this imprint of an ammonite.
There it is in this crack again, a backbone, and past another ammonite, and there's its tail.
When such near-perfect specimens are carefully prepared, they may even show the outline of the flesh, as a dark, almost oily silhouette around the bones.
And from this it was discovered that the ichthyosaurs had a triangular fin on their back.
And that kink at the end of the backbone was not a break, but a strengthening of the lower fluke of the tail.
With the whole shape of the animal revealed, we can now work out just how it swam.
The joints between the bones of its spine showed that it beat its tail from side to side, and it was clearly capable of great speeds as it surged through the sea in search of its food.
No, not ichthyosaurs but their modern equivalent, dolphins.
There are, of course, differences.
Dolphins beat their tails not from side to side but up and down, and they are mammals, not reptiles.
But their lifestyle is certainly very similar.
Like ichthyosaurs, they breathe air and break the surface every now and then to do so.
After the ichthyosaurs died out, the seas, for a time, had no air-breathing hunters.
But then a group of mammals began to colonise the sea, just as a group of reptiles had done 100 million years earlier, and similar ecological demands have produced similar evolutionary responses.
Did ichthyosaurs, like dolphins, eat fish? Well, their teeth were sharp and easily capable of grabbing a wriggling fish, but they certainly ate other things as well.
This one's belly contained a number of small, horny hooks, and those, we know, came from squid-like animals.
But this is only one species.
There are lots of different kinds of ichthyosaurs, and each may have had its own particular diet.
This one was a giant, four or five times the length of the common ichthyosaur, and it was a cannibal, because here, between its ribs, where its stomach once lay, are the chewed-up remains of the backbones of smaller ichthyosaurs.
And in addition to this monster, there was another kind which is still something of a mystery.
Its jaws are extraordinary.
This is the upper one.
It's a long, thin spike.
The lower one is only a quarter of the length, and it's fully armed with teeth.
What could it have used them for? Well, there are two clues.
The first are its paddles, which are huge and very broad.
That suggests that they could only be moved very slowly.
Secondly, its eyes are gigantic.
They're the biggest of all known ichthyosaur eyes.
Big eyes are characteristic of animals that live in low light levels.
So maybe this, the rarest of the ichthyosaurs, lived in the darkness near the bottom of the sea and moved across the sea floor, propelling itself slowly with its huge paddles, stirring up the mud with its long upper jaw and snapping up what food it found with its lower.
The marvellously preserved specimens of Holzmaden reveal a further detail in the lives of these ancient reptiles.
Just emerging from the body of this female is a baby.
Most reptiles lay eggs on land, but the ichthyosaurs had broken this last link with the land and produced live young.
Ichthyosaur or dolphin? 150 million years ago, there must have been events just like this in Holzmaden lagoon.
While ichthyosaurs were swimming so efficiently through the water, other animals were moving around over the sand and mud of the sea floor.
Some were even managing to crawl out of the sea and up onto the land.
And here they left other evidence of their presence.
A track can tell you a lot about an animal; how many legs it has, in what order it moved them, how heavy it was and much else.
And tracks, too, can be preserved in sandstones.
0n the shores of the Isle of Arran in western Scotland, there are two parallel stripes in the rock.
At first they might appear to be some kind of stress mark or faulting in the stone, but look at them closely and you can see that they are tracks of some kind.
What is more, you can see that they were made by an animal with a very large number of legs.
There's an obvious candidate for what made them; a millipede.
Its multitude of legs, moving up and down in a wave passing along the body, leave just such parallel stripes in the mud behind it.
They match these tracks in Arran almost exactly.
The biggest millipede alive today is about ten inches long, and we call that a giant millipede.
But the animal that made these tracks, judging from their dimension, must have been about six feet long.
That was a real giant.
Marks in sand and mud, of course, can be made not only out of water but in it.
And one of the commonest of those underwater marks are the ones that are made when sand is moved across the bottom of the sea as the tide moves in and out - ripple marks.
These, too, are ripples in sand, but they are 500 million years old.
They were formed at the bottom of a sea which at that time covered most of western Europe.
Since then, continents have collided, and those sediments have been rucked up so that now they form these mountains in North Wales.
It's not only inanimate mechanical forces that create patterns in the sand of the sea floor, animals do so as well.
They burrow through the sediment, extracting nutriment from it, and they usually do so in a regular, systematic way, so that they don't miss patches of mud and don't process any of it twice, and this produces regular patterns of casts and burrows.
But many of these patterns are complicated, and it's not always easy to see exactly how the animal could have made them.
However, computers can help to solve this problem.
This is not a pattern that has been generated by the computer.
This is the tracing of an actual fossil, but it's rather puzzling.
Look, for example, at down here.
There's one ring there, but there is another ring on the inside.
How could that have been formed? Well, by looking at the actual fossil itself, you can see which ring, which track has been placed on top of which other track.
And by feeding that information carefully into the computer, you can then ask the computer to look at the pattern from a different point of view, and then what you see is this.
The animal was working in three dimensions, it was burrowing down in the mud, and it was when the rock was compacted that it produced this ring superimposed upon one another and that particular shape.
But although we know so much about this elegant burrow, we don't know what animal made it and may, in fact, never find out.
These rocks in North Wales, close by those ancient, 500 million-year-old ripple marks, are also covered with trails of many kinds.
One sort is like this.
They are long tracks which often criss-cross one another.
And this is another kind, a sort of large dimple.
What could have made them? Well, we have direct evidence as to what made this kind.
A fossil has been found that sits in it perfectly.
A trilobite, the most abundant of all the animals in the seas of this period.
The dimple is where it rested, the broad stripe the track it made as it trundled over the sea floor.
Trilobites have left no direct descendants, but we nevertheless know a lot about them.
Underneath their hard, jointed shells they had two rows of long, thin legs, as shrimps have.
Most trilobites were only an inch or so long, but a few were giants, over a foot in length.
Although their remains all accumulated on the bottom of the sea, they didn't necessarily all live there.
Some may have grubbed about on the bottom, but others could have swum quite a long way above the sea floor.
To find out which did what, casts are put in a tank of flowing water by Richard Fortey of the British Museum.
What kind of animal is this one? This is a typical bottom-living trilobite, which we think was rather poorly streamlined.
And we can show this quite graphically by turning on some dye.
There it goes.
And you can see that large wakes are created on the back of the animal, behind the eyes and behind the tail.
And if we turn the dye off, you can see how these wakes linger on for a long time, behind the eyes and on the back of the animal.
This is generally a bad design for active swimming, as we might expect of an animal that spent most of its time crawling along the sea floor.
If we look at this one, by contrast, you can see how well streamlined the animal is.
The dye proceeds over the back of the animal without the eddies we saw last time and the head of the animal, this end here, is prolonged into a kind of nose, and the eyes are recessed, it's almost like a dogfish head.
So that is proof, do you think, that this animal was free-swimming? I don't think we can ever talk about proof, but as far as we can test by experiment and looking at the shape of the animal, this was a free-swimming trilobite in the seas of 500 million years ago.
It's clear from such investigations that some trilobites, at any rate, were very active.
Active animals need good sense organs in order to find their way about, and trilobites had amazing eyes, the first complex eyes ever to gaze out on this world.
Each consisted of a mosaic of tiny, tightly-packed units, which produced separate spots of light or shade, and together formed a single picture.
Crabs have very much the same sort of eye today.
But some trilobites did even better.
Each element in their eye had a little lens over it which focused the light into a separate image.
This intricate structure was mounted on a kind of turret.
A pair of these on the head gave this trilobite a view that extended from its tail right round to its nose.
But why should it have needed such a detailed view of its surroundings? Well, there were hunters in those ancient seas.
Ancestors of cuttlefish were around, stalking trilobites, just as cuttlefish today hunt crabs.
Once the trilobites were alarmed, they had very good defences.
You find them preserved in many different postures.
From specimens like these, it's evident that those joints between the segments along the back were very flexible.
When danger threatened, they were able to protect their vulnerable undersides by rolling up.
They even had little knobs on their heads and sockets on their tails that enabled them to lock themselves into a ball.
They evolved into many thousand different species and then, 250 million years ago, they died out and left no descendants.
Yet from their remains we can still discover how they moved and protected themselves, what they ate, where they swam, even what they saw of that long-lost world.
The skies above the ancient seas were not empty either.
Today it's birds that fly over the ocean, scouring the surface for food of one kind or another.
But birds are relatively recent arrivals.
Millions of years before they appeared, the air had been invaded by flying reptiles.
The first to be discovered was named "wing-finger", pterodactyl, for its wing was supported by its greatly elongated fourth finger.
Now so many different kinds have been found that the group as a whole is called "winged reptiles" - pterosaurs.
Their slim jaws are lined with teeth and they had a skinny membrane that stretched from that long finger to the side of their body.
This wing was powered by muscles attached to the breastbone.
The fact that this is of a reasonable size and had a small keel down the middle shows that the pterosaurs were able to flap and not just glide.
But we have more than just bones of pterosaurs.
This is a very remarkable skull of one that was found in the north of England.
The front part of the snout is missing, and so is the lower jaw, but here is the huge orbit where the eye once was.
And at the back, the top of the skull is missing and you can see inside.
At some stage during fossilisation, sediment seeped in, and it's left a cast of the pterosaur's brain.
Brains can tell us a great deal about an animal's behaviour.
And this is not the only pterosaur brain we have.
One, separated from the skull and marvellously preserved, was found in Israel.
The lobes at the back of all brains coordinate the muscles, and those at the front link the muscles with the senses.
All these lobes are much bigger than in a similar-sized land-living reptile, which confirms that this animal had the speedy reactions necessary for manoeuvrability in the air.
The lobes at the side of the brain control vision and are also large, so the pterosaurs had excellent sight and probably flew during the day.
With their skinny wings and short feet, the pterosaurs may have looked more like bats than birds.
There's another way in which they may have resembled them.
Flying like this demands a lot of energy.
Bats can produce it because they have warm bodies insulated with fur.
What about pterosaurs? Could reptiles have warm blood? And if they did, how did they keep it warm? These remarkable pterosaur fossils from Kazakhstan in the Soviet Union provide an answer to that question.
Around the body of this one is the unmistakable imprint of fur, and what is fur for if it's not to keep a body warm? The pterosaurs first appeared 245 million years ago, and they populated the skies for the next 170 million years.
The earliest ones were about the size of sparrows and had bony tails, but, as time passed, they got bigger and bigger.
Judging from their teeth, they had a wide variety of diets.
Some of the smaller ones, with well-spaced, simple teeth like this, may have fed on insects, but this one, from the rocks of Bavaria, is very different.
Its teeth are so long and thin that they're little more than bristles.
Did it use them to filter food from the water, as a flamingo does? Nearly a hundred different kinds have been found already, and there are undoubtedly a great number still to be discovered.
One of the most productive areas in recent years has been Brazil.
Some extremely bizarre forms have come from there, like this one.
It's very big, the skull alone is over two feet long, and at the end of its upper jaw there is this extraordinary flange.
Peter Wellnhofer, a pterosaur expert working in Munich University, has been investigating these new finds, trying to work out what possible purpose such extraordinary features could have.
It cannot be an aerodynamic stabiliser.
It probably would not make much sense on the very end of the snout.
So no use in flying.
They can't use it to steer with or anything.
But probably it had a function when it was diving and skimming in the water, and during that time it was necessary to stabilise this long and narrow skull in the water.
As you can see here in this restoration, the skull must bend back when it dives down, but it still flies and it's moving through the water and it has to come up again.
Frigate birds pick up food from the water with just this sort of action.
The pterosaur's membranous wings probably gave it less control than feathered wings, so maybe a flange on the beak was essential for the pterosaur if it was going to do this trick.
I asked Peter Wellnhofer how he reconstructed the appearance of these pterosaurs.
This requires some degree of imagination, of course.
0n the other hand, we know that pterosaurs, for example, had hairs.
And so we put hair on the skull in the restorations, as you can see here.
And so you get a fairly good picture of what the animal looked like in life.
And what an extraordinary portrait gallery he has produced.
This is one of the filter feeders, with bristles on its lower jaw only.
This one, pteranodon, like many of the later kinds, had no tail, but its wings were 18 feet across.
Its wing muscles, judging from its breastbone, were not particularly powerful, so that it's likely that it was primarily a glider.
But you can get a long way gliding over the sea.
Pelicans show what can be done if you are able to exploit the updraughts created by the rolling waves.
And pteranodon was probably just as expert.
But perhaps the most extraordinary, indeed almost unbelievable pterosaur was found here in the badlands of southern Texas.
In 1971, a group of students working with Professor Wann Langston were down here looking for dinosaur bones when one of them, Douglas Lawson, found something very strange.
Late one hot July afternoon, after he had spent an almost fruitless day, he was walking up this dry arroyo and began to see postage stamp-sized fragments of petrified bone down in the sand.
And as he followed on up the valley, the fragments became more numerous and larger, and eventually he arrived over here at this bank and there he found a few pieces of bone projecting from the rock, still in place, and other, larger pieces that had weathered out were lying around on the surface.
This is a replica of the upper arm-bone in the wing.
As it turned out, this was the only piece that was nearly complete and still embedded in the rock, but it gives an idea of the size of the wing and taken together with all the fragments that were picked up, we've been able to piece together a reconstruction of the entire wing.
I just happen to have a diagram here that will give us some idea about the size of this object.
So this is the reconstruction of the entire wing.
The dark areas represent the pieces that we actually have found as fossils.
And from the shoulder joint out to this tip is a length of about 18 feet.
And remember this is only one wing, so you double the 18 feet and add a couple of feet for the body in between and you come up with an animal that had a wingspan of maybe 35 to 40 feet, which is larger than some small private aircraft.
How could such a huge creature have flown? Wann Langston studied the bones of a smaller individual of the same species in his laboratory to try and find out, suspending them in position to see just how they could move and how they couldn't.
We can take the humerus and because of the configuration of the head, fitting into the shoulder socket, we can move the humerus up to its maximum possible elevation.
We can also depress it to the limit and we can move it backward and forward in this plane, which also was possible for the animal.
And every move that we make with the humerus has an effect, of course, on the rest of the wing.
With all this detailed information about the mechanics of the wing available, the Smithsonian Institution in the United States decided to commission a model of one that would actually flap its wings and fly.
The cost of making one with a 40-foot wingspan would have been astronomic, so they decided to make a half-grown one, but even that is immense.
It was built from carbon-fibre materials which are very light and extremely strong.
It was coated with foam and then covered with latex, which is very flexible and allows the wing to make all the necessary movements.
The man who took on this job is aeronautical engineer and inventor Paul Macready.
What was your reaction when you first saw the fossils and the reconstructions made by palaeontologists of a thing like this? Did it seem that it could possibly fly, to you as an aeronautical engineer? Well, we knew it did fly, but it didn't seem possible because it was reputed to have a wingspan of 35 to 50 feet and that's so beyond anything that exists now that it almost seemed impossible, but you knew nature had done it.
So you, when you had to try and make something of the same shape that flew, what were your immediate problems? First you had to figure out what the shape was.
You pleaded with the palaeontologists, "Tell us what it looked like.
" The main thing was a big head stuck way out in front of a long neck and no tail to provide stability.
Trying to have this fly is like trying to shoot an arrow with the feathered end in front.
It's very unstable.
The earliest pterosaurs, little ones, had tails in the rear and they were stable, but it's kinda like riding a bicycle with training wheels.
When it's small and you're early in your training, you need that.
When nature got to these, it didn't need training wheels any more.
Everybody ready? The first experiments were with small models, fitted with tails to give them some stability while the designers wrestled with the basic aerodynamic problems.
Radio controls enabled them to move the head and wings.
With each flight, and each crash, a new lesson was learnt.
The damage caused by these crash-landings was often severe, but slowly the engineers were able to improve their design.
Even with the aid of computers and advanced aeronautical skills, this particular problem was so tricky that much of the progress was by trial and error.
After months of work, a half-sized, tailless, wing-flapping pterosaur was ready to take to the air.
Power on.
Motion check.
Left, right.
Forward, aft.
Take up the slack.
Clear.
Go.
Once airborne, the tail and the undercarriage needed for take-off are shed.
Although major movements are controlled by radio, the model controls itself to a considerable degree.
Sensors in the wings react to the varying wind currents and automatically feed signals to a small computer, a brain, which then activates tiny motors to adjust the posture of the head and wings, so preventing stalls and sideslips.
The last time such a shape flapped its way across the skies of North America, the animals watching it were dinosaurs.
You could hardly go farther than this in bringing long-dead bones back to life.