Lost Worlds, Vanished Lives (1989) s01e04 Episode Script
Part 4
The sunlit waters of a shallow sea.
Life here is rich and varied.
Jellyfish, sea gooseberries and all kinds of larvae drift in the dappled waters.
On the bottom, sea anemones wave among the rocks and small worms wriggle within crannies.
Everywhere you look, there seems to be life of some kind.
Creatures like these have a very ancient ancestry.
They were among the first forms of life to appear on earth and they existed for several hundred million years before the development of fish, the first animals with backbones.
But when such creatures with no bones in them die, what remains of them? Almost nothing.
Their soft tissues simply disintegrate and dissolve in the water, and there's hardly anything left of them but a little slime in the mud.
Only a minority, a few molluscs with hard shells, crustaceans like crabs with external skeletons, only they leave any signs of their existence after their flesh has vanished.
So of all that multitude of creatures, only one or two could leave behind in the mud any evidence that they had ever existed.
This, too, was once mud at the bottom of a sea but that was over 500 million years ago and now it's mudstone and high in the Canadian Rockies.
And these rocks, too, contain the remains of the hard parts of sea animals, and very extraordinary animals, too.
They're now totally extinct and we call them trilobites.
But there's virtually nothing else but trilobites in these rocks, so what did the trilobites live on and, maybe, what hunted the trilobites? The answers to questions like those could only be guesswork until, that is, the year 1901.
In that year, an American geologist, Charles Walcott, was exploring here in the Rocky Mountains of British Columbia, travelling on horseback with a train of pack mules.
He was in his 60th year and coming towards the end of a long and distinguished career in which he had made a special study of the ancient fossil-bearing rocks of North America.
When he got to this precise point on the trail, where this slip of loose rocks crosses it, one of his horses stumbled.
Walcott dismounted to clear the path, and when he did so, he hit one of the boulders with his hammer, as he must have done ten thousand times before.
Only this time, when the boulder fell apart it revealed a fossil the like of which he had never seen before in all his experience.
To his amazement, he saw that it had its soft parts preserved: Tentacles, the head and a row of small legs on either side of its body.
If he didn't do so then, he must have realised very soon afterwards that this was the most important discovery of his life.
So the next season, he and his sons returned to this place to try and find out where that boulder had come from.
They climbed up the rock tip, looking for fossils as they went and knowing that the highest level at which they found any fragments with fossils in them must be the place from which all the fossils were coming.
And that proved to be just here, and this place has been the site of research ever since.
A band of these shales just seven foot thick produced all the fossils.
Walcott came here for the next eight seasons, and in that time he collected 61,000 specimens, and two-thirds of the species that he found proved to be new to science.
Animals such as these, with delicate legs, with tiny gills and threadlike antennae, must have been living throughout the seas of this very ancient period.
They had never been seen before because everywhere else, being soft-bodied, they had simply dissolved and disappeared without trace.
Only here, for some extraordinary reason, had they been preserved, and preserved, what's more, in amazing detail.
This was some kind of worm, presumably a burrower in the mud, with an extendible proboscis.
And here a most remarkable find, a worm with fleshy legs, a possible link between true worms and more complex invertebrates such as centipedes and insects.
These rocks are known as the Burgess Shales.
How is it that one thin band of them on this particular mountainside preserved signs of life that are found nowhere else in the world? That was one of the questions Walcott and his successors spent a long time trying to answer.
The latest group of scientists to work on the site here come from the Royal Ontario Museum and are led by Des Collins.
530 million years ago, this was a muddy sea floor about 400 feet deep and was directly in front of a massive, sheer cliff that you can see in this light-coloured material here.
The reef front rose in a sheer cliff about 300 feet high.
You can see at the top the bedded rock, which is where the animals lived in a lagoon about 100 feet deep or less.
Every so often, the mud at the top would come down in a slump, picking up the animals, bringing them down here, killing them and burying them and preserving them in the mud.
This happened at a time when complex animals had only just appeared, so the ultimate ancestors of all life today must therefore be among them.
This worm, with an internal rod running along its length, may be the ancestor of all backboned animals.
And this, with five pairs of claws on its head, may be the creature from which scorpions and spiders have evolved, for it shares some of their most significant characters.
This, with what seems a protrudable proboscis, is more of a puzzle.
It may be related to certain kinds of living worms.
And this bizarre creature is quite unlike anything alive today.
It had seven pairs of legs, seven tentacles on its back, each with a mouth.
It seems to have been one of evolution's experiments that simply didn't work very well, and it's left no descendants.
By examining the best of these specimens, it's possible to deduce from the flattened outlines what it was like before it was squashed flat, and to reconstruct it in three dimensions.
The liquid mud often penetrated the insides of the animals, separating each tiny organ from the other by a microscopic film of mud particles, and then it's possible to work out details of internal anatomy.
This creature swam by waving flaps beneath it and it sensed its food with long feelers.
But some specimens are so strange, it's difficult to make head or tail of them.
This, for example, three or four inches long, looks like some kind of shrimp, except that none has ever been found with a head.
And this, rather like a slice of pineapple.
Could this be some kind of jellyfish? Though there are still some speculations, we now have a picture of a large and varied community.
But if there were so many of these mud munchers and filter feeders, there must surely have been some hunter that preyed on them.
What was that? That question troubled a British palaeontologist, Harry Whittington, as he worked on some of Walcott's specimens.
Searching through many thousands of them, he found one in which that pineapple slice seemed to be attached to some other structure.
What is more, there were several other specimens rather like it, including one that was not completely cleared of matrix, and he started very carefully to investigate it.
if you think this is the underside of the body, to look and see, is there anything perhaps attached to the underside that goes down into the rock? And there was a little area here.
And using a little drill, you could very delicately work along the edge here and remove flakes of rock.
And gradually this thing became exposed and I realised, particularly when I got to this end and saw the characteristic spines on it, that was this thing that had been described many years before, anomalocaris, the strange shrimp, and people thought this was part of an animal and envisaged it having a little shell here, but no whole one had ever been found.
Now here was one attached under the front end of this animal.
Was that an accident? If there was one one side, there ought to be one the other.
Indeed, there was a layer in the rock here and I exposed parts of that chiselling around here, and there exposed is part of the companion one that was attached there.
That predator was revealed.
The headless shrimps were its claws and the pineapple slice was its muscular mouth.
This was the terror of the trilobites.
So now we have an even more complete picture of the life that flourished on the sea floor 530 million years ago.
We knew it must have contained the ancestors of all subsequent life, but now we have some idea of what they looked like.
The next exceptionally detailed glimpse we get of the progress of life comes from this valley in southern Germany, near a village called Solnhofen.
140 million years ago, that's 400 million years after the time of the Burgess Shales, this part of Europe lay under the sea, as we know because it's covered by limestone, but this valley is lined by cliffs of a special kind.
When you examine the rock of these huge towers, you see that it's composed not of thin, horizontal layers of sediment, but of curving plates.
And these are, in fact, the fossilised remains of sponges and other reef-building organisms which, growing one on top of the other, over centuries slowly built these huge, pillar-like reefs.
While they were living, beneath the sea, they sheltered the water lying between them and the shore from the waves and currents of the open ocean and they created a shallow lagoon.
Conditions then must have been rather like they are today in other shallow tropical lagoons where the water evaporates so fast that it becomes extremely salty, and calcium carbonate in solution starts to precipitate as an extremely fine, limy mud, layer upon layer.
Over millions of years, the mud compacted and turned to stone.
The land level rose and the sea drained away.
The river in the Solnhofen valley eroded much of it, exposing those coral cliffs again.
But elsewhere, the limestone remains.
And now, as stone, those layers can be separated, where it's weathered, into plates almost as thin as paper.
And where it's not weathered, it formed a magnificent building stone that's been worked in places like these since Roman times.
If the rock splits into plates an inch or so thick, it can be used for roofing.
Where it's more massive, it's cut into blocks for masonry of such quality that it has been used all over Germany.
In the 19th century, a local man discovered yet another use for it.
If you draw a picture on it with wax pencil, you can, using a special ink, take an almost unlimited number of copies from it.
He called the process lithography, and it was widely used to print illustrations for a hundred years or more, all over Europe.
But every now and again, when the quarrymen come to split a block, they open it and find that there's an illustration already printed within it, an illustration that's 140 million years old, like this one A fish.
Fossils are not abundant, for few animals could live in this inhospitable, near-sterile lagoon.
These fish were swept into it, past the reefs, by sudden storms.
But though there are few of them, their preservation is near-perfect, for the storm that carried them in also stirred up the mud and, as they died, that settled back and covered them like a shroud.
A fish with grinding teeth, like a parrot-fish of today, which presumably fed in the same way, pulverising coral to extract the little polyps.
A kind of garfish.
A bottom-living ray, a species that seems to have survived almost unaltered until today.
This lobster, too, had ancestors that strayed into the Solnhofen lagoon.
Crustaceans, with their hard external skeletons, make excellent subjects for preservation under these conditions.
And backboned animals, too, with their skeletons of bone, are also beautifully preserved.
A turtle, its flesh gone but its bones very clear.
Another reptile, with an amazingly long body and an even longer tail.
Yet, because of the infrequency of the currents in the lagoon, all its bones remained perfectly positioned while the flesh decayed around them.
And because of that extreme stillness, even a jellyfish settling gently on the limy mud has left the delicate impress of its soft body.
Tracks on the lagoon floor have also remained clear.
This one was obviously made by an animal with several long legs.
The scratches between the footprints suggest that it also had a spiky tail.
And it seems to have been lost, for it's wandering aimlessly about.
We're looking at the story of one small death that took place 140 million years ago, for here's the body, complete with that trailing tail.
It's a horseshoe crab, virtually identical with the horseshoe crabs that still today swim in the seas off North America.
Other tracks are not so easily interpreted.
What about, for example, this extremely rare but rather mysterious mark? Is it perhaps some kind of worm? Well, it seems to have been caused by an empty ammonite shell that fell down into the mud, making a dent, and then, carried by a current, rolled until it came to the mouth again, which caused it to leap up, fall again, and then roll again.
Insects flying over the lagoon sometimes flopped into the water and sank.
A dragonfly.
A winged grasshopper.
And a much bigger flying animal, a pterosaur, the membrane of its skinny wings plainly visible.
But there's one animal in particular, whose remains drifted down through the salty water and settled on the mud of the lagoon, that has made the name Solnhofen famous worldwide.
Its remains are so excessively rare, and so important to science, that they've been called "the most valuable fossils in the world".
The most perfect of them, which is kept here in East Berlin, is so valuable that it's kept locked away in a safe, away from public view, and exhibited only as a replica.
This is a rare privilege to see the real thing.
Archaeopteryx, a creature that represents a link between reptiles and birds.
It's birdlike because it's covered not by fur but by feathers.
Their intricate structure, each with a central quill and barbs coming off it on either side, can be clearly seen.
They are virtually identical to modern feathers.
Its wings are modified front legs, but not as greatly altered as the wings of modern birds, for three of their five toes still have claws at their tips, projecting from the front edge of the wings.
The feet had backward-pointing big toes, which gave the animal a firm grip on a branch, and that, too, is characteristic of birds.
The head, however, is not at all birdlike.
It had no beak, but a bony, reptilian jaw lined with teeth.
And here, reptilian and bird characteristics combined in one feature, the tail.
No bird has bones in its tail like this, and while reptiles do, none of them has feathers on it.
In recent years, the question was raised as to whether these really were feathers, but the closest examination of another specimen in London has proved conclusively that they certainly are.
So, thanks to the limy burial shrouds of Solnhofen we can make a detailed reconstruction of this key creature in the history of the evolution of life.
But reptiles were still, at this time, the dominant animals.
Gigantic seagoing crocodiles like this one roamed the seas.
Huge pterosaurs bigger than any eagle soared through the air.
And on land, there were the dinosaurs.
The reason we know so much about dinosaurs is that many were very big, with tough bones that could survive being washed down by the rivers and buried in the deposits of the delta.
But 67 million years ago, the last of the dinosaurs died.
For some time, the land was comparatively underpopulated, but then the early mammals began to spread.
But they were not big creatures with tough bones but small animals with delicate skeletons that were easily destroyed.
Neither did they live in a lagoon where there were regular deposits, but on land, where there was virtually none.
So they were comparatively poor candidates for fossilisation and we knew very little about them until, at last, another of these extraordinary fossil sites was discovered.
At Messel, near Frankfurt, in Germany, there's a deposit of shales so rich in oil that quite spontaneously, they catch fire and burn underground.
The oil comes from the tissues of animals and plants living in the lake that lay here 48 million years ago.
The shales were once worked commercially for their oil, but they contain much more valuable things than that.
48 million years is a comparatively short time for mud to turn to rock.
Solnhofen limestone is three times as old, the Burgess Shales over ten times, and these shales are still soft and moist.
The excavators have spotted the remains of a fish, but it mustn't be fully exposed to the air because if it dries out, it'll disintegrate, so the slab is carefully cut out and taken to a laboratory.
There it's kept moist while the compressed mud is delicately scraped from the flank of the fish.
Once that side has been cleaned as far as possible, liquid resin is poured over it.
When that sets, it's perfectly transparent, so now specimens treated in this way can be worked on from the other side.
Eventually, virtually all the mud can be removed, and the fragile bones are held firmly in a block of transparent plastic.
This is one of the early mammals for which Messel is now famous, a tiny horse that was no bigger than a spaniel.
Gerhard Storch, from the Senckenberg Museum in Frankfurt, is one of the team working on these finds.
Unlike recent horses, they possess four digits in the forefeet, one, two, three, four.
- Both legs are there, aren't they? - Yeah, there are both legs, side by side.
- And perfect little hooves.
- And perfect little hooves, yeah.
The grinding teeth are not tall and high in the jaw like those of a modern horse, but low, indicating that the animal ate soft leaves and fruit, and that's confirmed by examining the stomach.
With a scanning microscope, we can investigate the last diet of these horses.
In this specimen, the gut contained soft leaves from tropical plants.
- So it was living, what, in the woodlands? - It was living in a dense, tropical forest.
And there are even stranger things in the muds of Messel than spaniel-sized horses.
This is a mammal that belongs to a very archaic group close to insectivores and this group became extinct.
The forelimbs are very small, very reduced.
The hind limbs are long, elongated.
The tail is very long.
It's a world record for mammals.
It consists of about 50 single vertebrae.
And all of these body proportions tell us that this animal was moving on its hind limbs, but not in a way that is familiar to us from kangaroos or jerboas, running fast and very manoeuvrable on the hind limbs but with alternating steps.
(ATTENBOROUGH) So really there's no equivalent alive today? (STORCH) There is no analogue today.
There is also, believe it or not, an ancestor of hedgehogs.
The texture of bone on the front of the skull shows that the flesh there was particularly thick with blood vessels, which suggests that there was some kind of gland or shield on its forehead.
And there are true birds, many kinds, some so excellently preserved that almost the only detail you can't make out is their colour.
And not only birds, but bats, and several kinds of them as well.
But why should so many flying animals have fallen dead into the lake? Something must have happened to these bats while they were hunting on the wing, and my idea is that there were poisonous gases on the Messel lake and a bat which went down drinking came to such a gas bubble and fell down to the water's surface.
So, because of those freakish conditions 40 million years ago, the vanished lake of Messel now yields evidence about not only the animals that swam in its waters and lived in its forests, but even those that populated the skies.
Los Angeles, in America.
Hardly world-famous for its fossils, but it should be, for in the heart of this most modern of cities is a site that gives another wholly exceptional picture of a vanished world.
40,000 years ago, this was the appearance of the land on which hotels and freeways now stand.
Firm evidence for every single detail in this most detailed painting comes from a small park close by one of the city's main avenues, La Brea.
In one corner of it, through the harmless grass, oozes a substance that kills - la brea, tar.
It wells up from the ground here to form these black pools.
When it rains, water lies on top of it, and it looks like a place where you might get a drink.
But any animal that came here to do so would be lucky to escape alive.
Feet sink into the tar, feathers get entangled in it, and the animal is fatally trapped.
That's been happening for 40,000 years and more, and it's still happening today.
Tar, like oil, is derived from the bodies of animals and plants that accumulated in swamps.
The sand that was deposited on top of them squeezed their remains so that droplets of oil were expelled from their tissues.
That accumulated in basins within the texture of the porous sandstone and then, where there is a fault, this substance is forced up to the surface.
The earlier flows of tar, containing the most ancient animals, have now been covered by later flows, so to reach them, you have to dig down into the tar pit, and excavations which started back at the beginning of this century are now being carried on some 30 feet down, while the tar still rises around the excavating platform.
The work is supervised by trained scientists, but most of the team is made up of local volunteers.
(MAN) 0K.
This is ready to go.
Got the bag? (W0MAN) Yes, I do.
(MAN) That's a sabre-toothed cat femur.
(W0MAN) Right or left? (MAN) That's a right.
(W0MAN) And without his epiphysis.
(MAN) Right.
(MAN) What you got over there, Jerry? (JERRY) I've got this ulna uncovered here.
- What's it lying on top of? - It's lying right across a sabre-tooth cat skull.
The finds have been put on display in a museum recently built on the site, and very spectacular they are.
In addition to this magnificent imperial mammoth, the biggest of all the prehistoric elephants that lived in North America, there were extinct horses and camels which grazed on these plains.
Huge, long-horned bison.
There were over 20 species of eagles and falcons.
Ground sloths the size of small elephants.
These huge animals are now totally extinct.
They browsed the trees and, like the rest of these plant-eaters, only rarely and accidentally strayed into the tar pits.
But once an animal like this was mired and stuck, it made the pits a positive attraction to packs of wolves.
These dire wolves were about the same size as living wolves but with more massive heads.
Struggling, trapped animals were obviously something they couldn't resist, for wolves, in fact, are the commonest of all the victims of the tar pits.
The most frequently trapped grass-eaters were the bison, so there were probably big herds of them, but, again, the pits contain more bones of the animal that preyed on them, the American lion.
The females were about the same size as African lions, but the males were 25% bigger.
And there was an even more impressive cat, the sabre-tooth.
At one time it was thought that these extraordinary teeth were daggers for stabbing, but now it's believed that they were used to slit open the belly of the prey.
You might wonder how the animal managed even to close its jaws, and I asked a scientist at the museum, George Jefferson, to explain.
I think we can illustrate that best with the specimen here that was preserved closed.
That will give us an idea what that mouth looked like.
As you can see, the incisors actually interlaced, allowing the jaw to fully close.
I'm surprised how much space there is between those huge sabre teeth and the lower jaw.
That gap is the same gap as between the meat-slicing teeth on the side of the face.
What that meant is, the animal would disengage the incisors, drop the jaw down, move it slightly sideways, and guide the slicing blades here by running the inside of this flange against the canine tooth.
- Is that a new discovery? - It is.
In fact, we didn't know this gap was that way until we found this specimen.
As well as big animals, the tar preserved a whole range of organisms that lived here.
Even pollen grains can be obtained from it, and it's they that have enabled the artist who painted the reconstructed landscape to show the correct species of flowering bush, Californian sage.
The museum's laboratory is surrounded by glass windows, so that those working on the finds become exhibits themselves.
I think this rib's going in like that, and if you look at the top, the way it angles round, - I think there's probably a little edge.
- So it's going back under.
Once you've discovered what animals were present, why go on digging up more? Well, the museum has over 200 jaws of bison.
As George Jefferson explained, their sheer number gives new information.
With these three specimens here, we can see an animal three years old, two years old and one year old.
We can tell that from the eruption stage of the teeth.
Here we see this tooth being pushed out - this animal is three years old.
We don't have specimens representing intermediate ages between three years old and two years old, nor two and one year old.
That tells us that these animals are coming here periodically at a certain time of year.
We can determine that season by comparing the stage of wear on these teeth with modern bison who have a very restricted calving period.
They're here in the late springtime.
- So they're migrating? - Yes.
The multitudes of jaws, therefore, prove that once in California, great herds of bison made long migratory journeys, and that every year, after the rains, when the grass began to sprout on the Hollywood hills, there was great carnage around the tar pits.
The sheer abundance of the dire-wolf skulls also yields information.
They are not, of course, all the same, and the differences are not all due to age.
The lumps and distortions that are apparent, compared to the smooth forehead on this animal, indicate an infection in the frontal sinuses of the forehead, probably as the result of being kicked in the face, maybe by a bison or a camel.
This animal was obviously going after its prey and getting injured.
We also see injuries in the sabre cats.
We see chronic injuries to the back.
Here we have three lumbar or back vertebrae that have been fused together by a mass of bony tissue.
This bony tissue grows along the ligaments and muscles where they're injured and stretched while this animal is lunging for its prey.
In this hip we have a fairly normal hip socket here, but on this side you can see a lot of knobbly bone, a distortion and break, there are flanges of extra bone in here.
This animal was obviously in a lot of pain while this healing was going on.
We think it may have been butted by a bison, hit very hard, or even, possibly, by a mammoth elephant.
- So he's really a cripple.
- Yes.
It's astounding it lived as long as it did.
Some researchers believe this is evidence that the injured and infirm were being tolerated within the population and possibly cared for.
- So social behaviour among the sabre cats? - Social behaviour.
It seems almost miraculous that any remains of animals could survive for tens of thousands of years, let alone hundreds of millions.
In exceptional circumstances, like the tar pits of La Brea or the volcanic lake of Messel, the hot lagoons of Solnhofen and the muddy submarine avalanches of the Burgess Shales, they leave clues that tell us not only about their appearance, but their detailed internal anatomy, their daily habits, even their social life.
Fossils have been forming ever since life appeared on this planet and lie in the earth all around us.
They provide us with irrefutable and wonderful evidence of what existed before we did.
Sometimes the latest high-tech apparatus is needed to reveal it, sometimes it needs nothing more than a simple blow from a hammer and logical, clear-minded thought.
But slowly, piece by piece, we're putting together the history of the long procession of life that preceded mankind's appearance upon this planet, and of which, indeed, we are a part.
Life here is rich and varied.
Jellyfish, sea gooseberries and all kinds of larvae drift in the dappled waters.
On the bottom, sea anemones wave among the rocks and small worms wriggle within crannies.
Everywhere you look, there seems to be life of some kind.
Creatures like these have a very ancient ancestry.
They were among the first forms of life to appear on earth and they existed for several hundred million years before the development of fish, the first animals with backbones.
But when such creatures with no bones in them die, what remains of them? Almost nothing.
Their soft tissues simply disintegrate and dissolve in the water, and there's hardly anything left of them but a little slime in the mud.
Only a minority, a few molluscs with hard shells, crustaceans like crabs with external skeletons, only they leave any signs of their existence after their flesh has vanished.
So of all that multitude of creatures, only one or two could leave behind in the mud any evidence that they had ever existed.
This, too, was once mud at the bottom of a sea but that was over 500 million years ago and now it's mudstone and high in the Canadian Rockies.
And these rocks, too, contain the remains of the hard parts of sea animals, and very extraordinary animals, too.
They're now totally extinct and we call them trilobites.
But there's virtually nothing else but trilobites in these rocks, so what did the trilobites live on and, maybe, what hunted the trilobites? The answers to questions like those could only be guesswork until, that is, the year 1901.
In that year, an American geologist, Charles Walcott, was exploring here in the Rocky Mountains of British Columbia, travelling on horseback with a train of pack mules.
He was in his 60th year and coming towards the end of a long and distinguished career in which he had made a special study of the ancient fossil-bearing rocks of North America.
When he got to this precise point on the trail, where this slip of loose rocks crosses it, one of his horses stumbled.
Walcott dismounted to clear the path, and when he did so, he hit one of the boulders with his hammer, as he must have done ten thousand times before.
Only this time, when the boulder fell apart it revealed a fossil the like of which he had never seen before in all his experience.
To his amazement, he saw that it had its soft parts preserved: Tentacles, the head and a row of small legs on either side of its body.
If he didn't do so then, he must have realised very soon afterwards that this was the most important discovery of his life.
So the next season, he and his sons returned to this place to try and find out where that boulder had come from.
They climbed up the rock tip, looking for fossils as they went and knowing that the highest level at which they found any fragments with fossils in them must be the place from which all the fossils were coming.
And that proved to be just here, and this place has been the site of research ever since.
A band of these shales just seven foot thick produced all the fossils.
Walcott came here for the next eight seasons, and in that time he collected 61,000 specimens, and two-thirds of the species that he found proved to be new to science.
Animals such as these, with delicate legs, with tiny gills and threadlike antennae, must have been living throughout the seas of this very ancient period.
They had never been seen before because everywhere else, being soft-bodied, they had simply dissolved and disappeared without trace.
Only here, for some extraordinary reason, had they been preserved, and preserved, what's more, in amazing detail.
This was some kind of worm, presumably a burrower in the mud, with an extendible proboscis.
And here a most remarkable find, a worm with fleshy legs, a possible link between true worms and more complex invertebrates such as centipedes and insects.
These rocks are known as the Burgess Shales.
How is it that one thin band of them on this particular mountainside preserved signs of life that are found nowhere else in the world? That was one of the questions Walcott and his successors spent a long time trying to answer.
The latest group of scientists to work on the site here come from the Royal Ontario Museum and are led by Des Collins.
530 million years ago, this was a muddy sea floor about 400 feet deep and was directly in front of a massive, sheer cliff that you can see in this light-coloured material here.
The reef front rose in a sheer cliff about 300 feet high.
You can see at the top the bedded rock, which is where the animals lived in a lagoon about 100 feet deep or less.
Every so often, the mud at the top would come down in a slump, picking up the animals, bringing them down here, killing them and burying them and preserving them in the mud.
This happened at a time when complex animals had only just appeared, so the ultimate ancestors of all life today must therefore be among them.
This worm, with an internal rod running along its length, may be the ancestor of all backboned animals.
And this, with five pairs of claws on its head, may be the creature from which scorpions and spiders have evolved, for it shares some of their most significant characters.
This, with what seems a protrudable proboscis, is more of a puzzle.
It may be related to certain kinds of living worms.
And this bizarre creature is quite unlike anything alive today.
It had seven pairs of legs, seven tentacles on its back, each with a mouth.
It seems to have been one of evolution's experiments that simply didn't work very well, and it's left no descendants.
By examining the best of these specimens, it's possible to deduce from the flattened outlines what it was like before it was squashed flat, and to reconstruct it in three dimensions.
The liquid mud often penetrated the insides of the animals, separating each tiny organ from the other by a microscopic film of mud particles, and then it's possible to work out details of internal anatomy.
This creature swam by waving flaps beneath it and it sensed its food with long feelers.
But some specimens are so strange, it's difficult to make head or tail of them.
This, for example, three or four inches long, looks like some kind of shrimp, except that none has ever been found with a head.
And this, rather like a slice of pineapple.
Could this be some kind of jellyfish? Though there are still some speculations, we now have a picture of a large and varied community.
But if there were so many of these mud munchers and filter feeders, there must surely have been some hunter that preyed on them.
What was that? That question troubled a British palaeontologist, Harry Whittington, as he worked on some of Walcott's specimens.
Searching through many thousands of them, he found one in which that pineapple slice seemed to be attached to some other structure.
What is more, there were several other specimens rather like it, including one that was not completely cleared of matrix, and he started very carefully to investigate it.
if you think this is the underside of the body, to look and see, is there anything perhaps attached to the underside that goes down into the rock? And there was a little area here.
And using a little drill, you could very delicately work along the edge here and remove flakes of rock.
And gradually this thing became exposed and I realised, particularly when I got to this end and saw the characteristic spines on it, that was this thing that had been described many years before, anomalocaris, the strange shrimp, and people thought this was part of an animal and envisaged it having a little shell here, but no whole one had ever been found.
Now here was one attached under the front end of this animal.
Was that an accident? If there was one one side, there ought to be one the other.
Indeed, there was a layer in the rock here and I exposed parts of that chiselling around here, and there exposed is part of the companion one that was attached there.
That predator was revealed.
The headless shrimps were its claws and the pineapple slice was its muscular mouth.
This was the terror of the trilobites.
So now we have an even more complete picture of the life that flourished on the sea floor 530 million years ago.
We knew it must have contained the ancestors of all subsequent life, but now we have some idea of what they looked like.
The next exceptionally detailed glimpse we get of the progress of life comes from this valley in southern Germany, near a village called Solnhofen.
140 million years ago, that's 400 million years after the time of the Burgess Shales, this part of Europe lay under the sea, as we know because it's covered by limestone, but this valley is lined by cliffs of a special kind.
When you examine the rock of these huge towers, you see that it's composed not of thin, horizontal layers of sediment, but of curving plates.
And these are, in fact, the fossilised remains of sponges and other reef-building organisms which, growing one on top of the other, over centuries slowly built these huge, pillar-like reefs.
While they were living, beneath the sea, they sheltered the water lying between them and the shore from the waves and currents of the open ocean and they created a shallow lagoon.
Conditions then must have been rather like they are today in other shallow tropical lagoons where the water evaporates so fast that it becomes extremely salty, and calcium carbonate in solution starts to precipitate as an extremely fine, limy mud, layer upon layer.
Over millions of years, the mud compacted and turned to stone.
The land level rose and the sea drained away.
The river in the Solnhofen valley eroded much of it, exposing those coral cliffs again.
But elsewhere, the limestone remains.
And now, as stone, those layers can be separated, where it's weathered, into plates almost as thin as paper.
And where it's not weathered, it formed a magnificent building stone that's been worked in places like these since Roman times.
If the rock splits into plates an inch or so thick, it can be used for roofing.
Where it's more massive, it's cut into blocks for masonry of such quality that it has been used all over Germany.
In the 19th century, a local man discovered yet another use for it.
If you draw a picture on it with wax pencil, you can, using a special ink, take an almost unlimited number of copies from it.
He called the process lithography, and it was widely used to print illustrations for a hundred years or more, all over Europe.
But every now and again, when the quarrymen come to split a block, they open it and find that there's an illustration already printed within it, an illustration that's 140 million years old, like this one A fish.
Fossils are not abundant, for few animals could live in this inhospitable, near-sterile lagoon.
These fish were swept into it, past the reefs, by sudden storms.
But though there are few of them, their preservation is near-perfect, for the storm that carried them in also stirred up the mud and, as they died, that settled back and covered them like a shroud.
A fish with grinding teeth, like a parrot-fish of today, which presumably fed in the same way, pulverising coral to extract the little polyps.
A kind of garfish.
A bottom-living ray, a species that seems to have survived almost unaltered until today.
This lobster, too, had ancestors that strayed into the Solnhofen lagoon.
Crustaceans, with their hard external skeletons, make excellent subjects for preservation under these conditions.
And backboned animals, too, with their skeletons of bone, are also beautifully preserved.
A turtle, its flesh gone but its bones very clear.
Another reptile, with an amazingly long body and an even longer tail.
Yet, because of the infrequency of the currents in the lagoon, all its bones remained perfectly positioned while the flesh decayed around them.
And because of that extreme stillness, even a jellyfish settling gently on the limy mud has left the delicate impress of its soft body.
Tracks on the lagoon floor have also remained clear.
This one was obviously made by an animal with several long legs.
The scratches between the footprints suggest that it also had a spiky tail.
And it seems to have been lost, for it's wandering aimlessly about.
We're looking at the story of one small death that took place 140 million years ago, for here's the body, complete with that trailing tail.
It's a horseshoe crab, virtually identical with the horseshoe crabs that still today swim in the seas off North America.
Other tracks are not so easily interpreted.
What about, for example, this extremely rare but rather mysterious mark? Is it perhaps some kind of worm? Well, it seems to have been caused by an empty ammonite shell that fell down into the mud, making a dent, and then, carried by a current, rolled until it came to the mouth again, which caused it to leap up, fall again, and then roll again.
Insects flying over the lagoon sometimes flopped into the water and sank.
A dragonfly.
A winged grasshopper.
And a much bigger flying animal, a pterosaur, the membrane of its skinny wings plainly visible.
But there's one animal in particular, whose remains drifted down through the salty water and settled on the mud of the lagoon, that has made the name Solnhofen famous worldwide.
Its remains are so excessively rare, and so important to science, that they've been called "the most valuable fossils in the world".
The most perfect of them, which is kept here in East Berlin, is so valuable that it's kept locked away in a safe, away from public view, and exhibited only as a replica.
This is a rare privilege to see the real thing.
Archaeopteryx, a creature that represents a link between reptiles and birds.
It's birdlike because it's covered not by fur but by feathers.
Their intricate structure, each with a central quill and barbs coming off it on either side, can be clearly seen.
They are virtually identical to modern feathers.
Its wings are modified front legs, but not as greatly altered as the wings of modern birds, for three of their five toes still have claws at their tips, projecting from the front edge of the wings.
The feet had backward-pointing big toes, which gave the animal a firm grip on a branch, and that, too, is characteristic of birds.
The head, however, is not at all birdlike.
It had no beak, but a bony, reptilian jaw lined with teeth.
And here, reptilian and bird characteristics combined in one feature, the tail.
No bird has bones in its tail like this, and while reptiles do, none of them has feathers on it.
In recent years, the question was raised as to whether these really were feathers, but the closest examination of another specimen in London has proved conclusively that they certainly are.
So, thanks to the limy burial shrouds of Solnhofen we can make a detailed reconstruction of this key creature in the history of the evolution of life.
But reptiles were still, at this time, the dominant animals.
Gigantic seagoing crocodiles like this one roamed the seas.
Huge pterosaurs bigger than any eagle soared through the air.
And on land, there were the dinosaurs.
The reason we know so much about dinosaurs is that many were very big, with tough bones that could survive being washed down by the rivers and buried in the deposits of the delta.
But 67 million years ago, the last of the dinosaurs died.
For some time, the land was comparatively underpopulated, but then the early mammals began to spread.
But they were not big creatures with tough bones but small animals with delicate skeletons that were easily destroyed.
Neither did they live in a lagoon where there were regular deposits, but on land, where there was virtually none.
So they were comparatively poor candidates for fossilisation and we knew very little about them until, at last, another of these extraordinary fossil sites was discovered.
At Messel, near Frankfurt, in Germany, there's a deposit of shales so rich in oil that quite spontaneously, they catch fire and burn underground.
The oil comes from the tissues of animals and plants living in the lake that lay here 48 million years ago.
The shales were once worked commercially for their oil, but they contain much more valuable things than that.
48 million years is a comparatively short time for mud to turn to rock.
Solnhofen limestone is three times as old, the Burgess Shales over ten times, and these shales are still soft and moist.
The excavators have spotted the remains of a fish, but it mustn't be fully exposed to the air because if it dries out, it'll disintegrate, so the slab is carefully cut out and taken to a laboratory.
There it's kept moist while the compressed mud is delicately scraped from the flank of the fish.
Once that side has been cleaned as far as possible, liquid resin is poured over it.
When that sets, it's perfectly transparent, so now specimens treated in this way can be worked on from the other side.
Eventually, virtually all the mud can be removed, and the fragile bones are held firmly in a block of transparent plastic.
This is one of the early mammals for which Messel is now famous, a tiny horse that was no bigger than a spaniel.
Gerhard Storch, from the Senckenberg Museum in Frankfurt, is one of the team working on these finds.
Unlike recent horses, they possess four digits in the forefeet, one, two, three, four.
- Both legs are there, aren't they? - Yeah, there are both legs, side by side.
- And perfect little hooves.
- And perfect little hooves, yeah.
The grinding teeth are not tall and high in the jaw like those of a modern horse, but low, indicating that the animal ate soft leaves and fruit, and that's confirmed by examining the stomach.
With a scanning microscope, we can investigate the last diet of these horses.
In this specimen, the gut contained soft leaves from tropical plants.
- So it was living, what, in the woodlands? - It was living in a dense, tropical forest.
And there are even stranger things in the muds of Messel than spaniel-sized horses.
This is a mammal that belongs to a very archaic group close to insectivores and this group became extinct.
The forelimbs are very small, very reduced.
The hind limbs are long, elongated.
The tail is very long.
It's a world record for mammals.
It consists of about 50 single vertebrae.
And all of these body proportions tell us that this animal was moving on its hind limbs, but not in a way that is familiar to us from kangaroos or jerboas, running fast and very manoeuvrable on the hind limbs but with alternating steps.
(ATTENBOROUGH) So really there's no equivalent alive today? (STORCH) There is no analogue today.
There is also, believe it or not, an ancestor of hedgehogs.
The texture of bone on the front of the skull shows that the flesh there was particularly thick with blood vessels, which suggests that there was some kind of gland or shield on its forehead.
And there are true birds, many kinds, some so excellently preserved that almost the only detail you can't make out is their colour.
And not only birds, but bats, and several kinds of them as well.
But why should so many flying animals have fallen dead into the lake? Something must have happened to these bats while they were hunting on the wing, and my idea is that there were poisonous gases on the Messel lake and a bat which went down drinking came to such a gas bubble and fell down to the water's surface.
So, because of those freakish conditions 40 million years ago, the vanished lake of Messel now yields evidence about not only the animals that swam in its waters and lived in its forests, but even those that populated the skies.
Los Angeles, in America.
Hardly world-famous for its fossils, but it should be, for in the heart of this most modern of cities is a site that gives another wholly exceptional picture of a vanished world.
40,000 years ago, this was the appearance of the land on which hotels and freeways now stand.
Firm evidence for every single detail in this most detailed painting comes from a small park close by one of the city's main avenues, La Brea.
In one corner of it, through the harmless grass, oozes a substance that kills - la brea, tar.
It wells up from the ground here to form these black pools.
When it rains, water lies on top of it, and it looks like a place where you might get a drink.
But any animal that came here to do so would be lucky to escape alive.
Feet sink into the tar, feathers get entangled in it, and the animal is fatally trapped.
That's been happening for 40,000 years and more, and it's still happening today.
Tar, like oil, is derived from the bodies of animals and plants that accumulated in swamps.
The sand that was deposited on top of them squeezed their remains so that droplets of oil were expelled from their tissues.
That accumulated in basins within the texture of the porous sandstone and then, where there is a fault, this substance is forced up to the surface.
The earlier flows of tar, containing the most ancient animals, have now been covered by later flows, so to reach them, you have to dig down into the tar pit, and excavations which started back at the beginning of this century are now being carried on some 30 feet down, while the tar still rises around the excavating platform.
The work is supervised by trained scientists, but most of the team is made up of local volunteers.
(MAN) 0K.
This is ready to go.
Got the bag? (W0MAN) Yes, I do.
(MAN) That's a sabre-toothed cat femur.
(W0MAN) Right or left? (MAN) That's a right.
(W0MAN) And without his epiphysis.
(MAN) Right.
(MAN) What you got over there, Jerry? (JERRY) I've got this ulna uncovered here.
- What's it lying on top of? - It's lying right across a sabre-tooth cat skull.
The finds have been put on display in a museum recently built on the site, and very spectacular they are.
In addition to this magnificent imperial mammoth, the biggest of all the prehistoric elephants that lived in North America, there were extinct horses and camels which grazed on these plains.
Huge, long-horned bison.
There were over 20 species of eagles and falcons.
Ground sloths the size of small elephants.
These huge animals are now totally extinct.
They browsed the trees and, like the rest of these plant-eaters, only rarely and accidentally strayed into the tar pits.
But once an animal like this was mired and stuck, it made the pits a positive attraction to packs of wolves.
These dire wolves were about the same size as living wolves but with more massive heads.
Struggling, trapped animals were obviously something they couldn't resist, for wolves, in fact, are the commonest of all the victims of the tar pits.
The most frequently trapped grass-eaters were the bison, so there were probably big herds of them, but, again, the pits contain more bones of the animal that preyed on them, the American lion.
The females were about the same size as African lions, but the males were 25% bigger.
And there was an even more impressive cat, the sabre-tooth.
At one time it was thought that these extraordinary teeth were daggers for stabbing, but now it's believed that they were used to slit open the belly of the prey.
You might wonder how the animal managed even to close its jaws, and I asked a scientist at the museum, George Jefferson, to explain.
I think we can illustrate that best with the specimen here that was preserved closed.
That will give us an idea what that mouth looked like.
As you can see, the incisors actually interlaced, allowing the jaw to fully close.
I'm surprised how much space there is between those huge sabre teeth and the lower jaw.
That gap is the same gap as between the meat-slicing teeth on the side of the face.
What that meant is, the animal would disengage the incisors, drop the jaw down, move it slightly sideways, and guide the slicing blades here by running the inside of this flange against the canine tooth.
- Is that a new discovery? - It is.
In fact, we didn't know this gap was that way until we found this specimen.
As well as big animals, the tar preserved a whole range of organisms that lived here.
Even pollen grains can be obtained from it, and it's they that have enabled the artist who painted the reconstructed landscape to show the correct species of flowering bush, Californian sage.
The museum's laboratory is surrounded by glass windows, so that those working on the finds become exhibits themselves.
I think this rib's going in like that, and if you look at the top, the way it angles round, - I think there's probably a little edge.
- So it's going back under.
Once you've discovered what animals were present, why go on digging up more? Well, the museum has over 200 jaws of bison.
As George Jefferson explained, their sheer number gives new information.
With these three specimens here, we can see an animal three years old, two years old and one year old.
We can tell that from the eruption stage of the teeth.
Here we see this tooth being pushed out - this animal is three years old.
We don't have specimens representing intermediate ages between three years old and two years old, nor two and one year old.
That tells us that these animals are coming here periodically at a certain time of year.
We can determine that season by comparing the stage of wear on these teeth with modern bison who have a very restricted calving period.
They're here in the late springtime.
- So they're migrating? - Yes.
The multitudes of jaws, therefore, prove that once in California, great herds of bison made long migratory journeys, and that every year, after the rains, when the grass began to sprout on the Hollywood hills, there was great carnage around the tar pits.
The sheer abundance of the dire-wolf skulls also yields information.
They are not, of course, all the same, and the differences are not all due to age.
The lumps and distortions that are apparent, compared to the smooth forehead on this animal, indicate an infection in the frontal sinuses of the forehead, probably as the result of being kicked in the face, maybe by a bison or a camel.
This animal was obviously going after its prey and getting injured.
We also see injuries in the sabre cats.
We see chronic injuries to the back.
Here we have three lumbar or back vertebrae that have been fused together by a mass of bony tissue.
This bony tissue grows along the ligaments and muscles where they're injured and stretched while this animal is lunging for its prey.
In this hip we have a fairly normal hip socket here, but on this side you can see a lot of knobbly bone, a distortion and break, there are flanges of extra bone in here.
This animal was obviously in a lot of pain while this healing was going on.
We think it may have been butted by a bison, hit very hard, or even, possibly, by a mammoth elephant.
- So he's really a cripple.
- Yes.
It's astounding it lived as long as it did.
Some researchers believe this is evidence that the injured and infirm were being tolerated within the population and possibly cared for.
- So social behaviour among the sabre cats? - Social behaviour.
It seems almost miraculous that any remains of animals could survive for tens of thousands of years, let alone hundreds of millions.
In exceptional circumstances, like the tar pits of La Brea or the volcanic lake of Messel, the hot lagoons of Solnhofen and the muddy submarine avalanches of the Burgess Shales, they leave clues that tell us not only about their appearance, but their detailed internal anatomy, their daily habits, even their social life.
Fossils have been forming ever since life appeared on this planet and lie in the earth all around us.
They provide us with irrefutable and wonderful evidence of what existed before we did.
Sometimes the latest high-tech apparatus is needed to reveal it, sometimes it needs nothing more than a simple blow from a hammer and logical, clear-minded thought.
But slowly, piece by piece, we're putting together the history of the long procession of life that preceded mankind's appearance upon this planet, and of which, indeed, we are a part.