Legacy of the Cambrian Explosion

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Search for and follow hostile history on Spotify, Apple podcasts, Amazon Music, or wherever you find your favorite podcasts fiveive hundred thirty eight million years ago. somethingomething mysterious happenens. in the murky depths of our seas O planet came to life It's known today as Biology's Big Bang Cambrian exxplosion Simple organisms gave way to complex, mobile creatures Eyes, limbs, shells, Predators and prey emerged And for the first time Life on Earth really began to take shape A sudden burst of evolution So practically all major animal species begin to appear in the fossil record But's why. What sparked this burst of complexity Why did evolution move so slowly for so long Only to erupt Like this. Welcome to the Ancients I'm Tristan Hughes, your host And this is the story of the Cambrian explosion Biologies big Our guest is a fan favorite returning expert paleontologist, evolutionary biologist, author and editor. The one The only and reaching Henry G What a pleasure it is to see you in person for the very first time. Well, it is Tristan. I mean, here we are actually together simultaneously, both at once and at the same time. Who thought who have thought him? Wh' have thought? I've got to ask first of all, are the chickens doing this? There' chickens, There are two of them left. Two of them left Bluebell and Poppet and they're still squawking and laying eggs, so that's nice But today we're going far beyond the origins of chickens, which in itself is a fascinating story isn't it? It takes millions years But the Cambriian explosion And this has been described the Cambriian explosion as life's bigig bang, as the biological big bang. Yes, today we're going to explode the Cambrian. And it's always been a big mystery. If you cast your mind back to the Victorian times, to the days of Darwin and pioneering geologists like Hutton and Lyle, who got an idea of which rocks came before what, but of course they had no idea how long the lengths of time that these rocks had taken to sediment And the lowest rocks in the sequence with fossils in was called the Silurian. I mean, it's all since been divided up into flats with a kind of retail outlet underneath. Now it's called the Cambrian. But before the Cambrian, there was nothing. After the beginning of the Cambrian, there were lots of fossils Cambs, lots of trilobites, which are these animals that look a bit like woodlice or pill bugs full of feelers and antennae and legs and eyes and armour and lots of other animals like that. So people wondered How is it that at the beginning of this period, there's lots of life, lots of loss, but immediately before, absolutely nothing. And Darwin was worried about this. He wrote in the Origin of Species that this particular gap was the chief difficulty of his theory of evolution. So this is the period when I mean the fossil record, I guess basically becomes a thing when we start actually seeing skeletons in the surviving record, in the soil and so on. That's right. It was the first time we actually saw Animals big enough to see with the naked eye with hard parts armour Jaw's teeth skeletons shells. and of course, it's the hard parts that tend to be fossilised. It's only very rarely that you get fossilisation of the soft parts of an animal and that really is remarkable. So if the world if the Earth is some four point five billion years old, How far back do we need to cast our minds for the story of the Cambrian. The Cambrian They keep changing their minds about the beginning of the Tambrian. There are two ways to decide this. One is when particular fossils occur. Traditionally the beginning of the Cambrian is seen as the occurrence of a kind of burrow called trepticus So when animals started to be able to burrow into the sediment, that caused a big change in the global ecology rather than skating over the surface. Once they started mixing up the sediment, that caused a great deal of change to the Earths system But the other one is directly dating it using not carbon dating, that runs out, that's useless before about forty five thousand recent history. That's quiteent recent history So there are various radioisotope methods that you can use to date the beginning of the Canan, but they keep changing their minds. I mean, I looked up this morning and the latest agreed The beginning of the Cambrian was five hundred thirty eight point eight million years ago. In fact, the reason we're having this today, listeners is because it's the five hundred thirty eight point eightion millionth anniversary next Tuesday. R So that's why while we're doing it. So the Cambrian period as a period or what they call geology called a system of rocks started about them, but they keep changing their minds because it's very fluid, it's a subject of Major research, not just in paleontology, but in geology and geophysics, trying to work out What changed in the system Before we had an idea of the absolute age, people wondered if there was a period before the Cambrian which was completely lost. It had been completely eroded away to nothing, in which all this evolution happened so that That being eroded away, you would then afterwards get the impression of nothing and then lots of things But it turns out that it's real. There is a definite gap Well, we're going to explain that in a second, but first of all, just so we really get it in our minds, I mean how far back we're going How much earlier are we talking with the Cambrian? How much later are the dyoss? Oh gosh Well, the Cambrian was say half a billion years ago, The dinosaurs didn't appear until two hundred million years ago. So that's just to emphasize just how much the earliest. But of course, when the Cambrian had happened, eight ninths or nine tenths of the Earth history had already happened and still the pre Cambrian We know very little about it. I mean, we know a lot more than we did in Darwin's Day, but there's still enormous gaps in our knowledge of what went on before the Cambrian. Well can we now explore this briefly? Can we almost kind coover what is known all a theory around the story of animals up to the point, up to that three hundred thirty eight million years ago. I'll try and keep this a huge story brief twoo billion years ago was an event called the Great Oxidation event. Well, that happened between two point four and two billion years ago when for reasons nobody is quite sure a lot of oxygen appeared in the atmosphere. Now before then there was almost no oxygen Now this caused a revolution in biosphere and that precipitated the evolution of what we call the eukaryotic cell, that is the kind of cell from which you and I are made up of as opposed to bacteria. Now bacteria had got together to create that And then Nothing much seemed to happen for a billion years. It's what geologists who don't get up in the morning for anything less than apocalyptic disaster called the boring billion. But things were going on in the background. Now, most eukaryotes that live today are single cell amoebas, paramecia flagellates, dinoflagellates that cause these blooms many horrible diseases, malaria, they're single celled, but there were signs of multi cellularly Ukiak cararyotes. about one point eight billion years ago seaweeds. About a billion years ago, there were early seaweeds, early fungi, but nothing animal like until breakup of a huge supercontinent Now we know about the supercontinent of Panga. and I remember we chatted about that. That in the Triasse Tass. Well, there is a supercontinent cycle that the Earth breathes on a period of about five hundred million years So the continents tend to glom together into a big supercontinent and then they break up and then they glom together again. And a friend of mine, a geologist called Ted Ned, has written about this in a book called Supercontinent and I owe it to him to tell everybody that it's not about the importance of pelvic floor exercises, it's about the the super confonfence cycle Well, before Panga, the supercontinent before that was called Rhodiniaodia And that started to break up about eight hundred million years ago. and as a consequence of that, there were two or three snowball Eth episodes where they were ice agges so severe that they covered the whole of the earth Now, just before the Great oxidation event, there was another of these snowball earth events, which was even more severe, but that was so long ago we don't need to worry about it. but Partly to do with the snowball earth events, animal life appeared and these were large enough to see with a naked eye. But the first flush of animal life was very strange. and this was before the Canban These were the Ediacran fauna. Now, a fellow, I think his name was Spriggs in Australia discovered the diacar and fauna in South Australia in some sandstone Very, very coarse impressions of things that look like jellyfish and other things squashy sea creatures that were very hard to sign to Any. particular group of animals, they have been thought to be lichens, they have been thought to be Their own thing, some strange creature some have been tentatively associated with more modern groups of animals But since then, Ediacar and fauners have been found in all sorts of exotic locations from the White Sea coast of Russia to Namibia Newfoundland to Bradgate Park near Leicester. If you go to Bradgate Park in Leicester, it's a public park and in the middle there are these enormous great rocks, which are pre Cambrian. It's a little splot of pre Cambrian in the middle of the English Midlands and it's got diacar and fossils on them, but they're very, very hard to see I mean, some of them are huge. I mean, they're not tiny. There is big as a pair of trousers, you know, spread along the rocks. There's what they called Charniiaiscus is one and they look like fronds but you really need to see them at dawn or dusk when the lummet is slanting. I mean I remember being there trying to look for them and I went on a very sunny day, midday and even though they were right in front of me and I knew this because I was I was doing face face timing. my colleague Emily Mitchell in Cambridge,' an expert on iaca and forwarders and she knew exactly where I was. So she was in Cambridge and I was in Bradgate Park and we said, no, left a bit, left a bit, right a bit there it is So the Eiacaran fossils They lived just before the Camrian and then They disappeared I'm still getting over the fact that you can go to Bragggate Park near Leicester today and look at the remains million six hundred million year old an. And there's people climbing around and walking their dogs and playing football and there they are. I mean, it is mind blowing. That's amazing. That is so amazing. And most people don't know they're there because they're very hard to spot unless you really know what you're looking for They were actually discovered by a small boy who was, I don't know, playing football oralking his dog. I haveve no idea And is it the fact so back then You know, these animals they have mouths. they' An Anus as well we're thinking that noobody really knows with the Ediacaran what they were like. I mean, some of them might be kind of colonial. They're these Ediacaran creatures called Rangom morphs which look like platid loaves. And some of them seem to have little smaller plaatid lobes around them. They grew like strawberry plants by shooting out runners and grew baby ones. These are mostly known from Newfoundland. Now people have split up the ediacaran into various substages. The earliest one part is found in Newfoundland and I think probably Leicestershire But the later part is in Namibia and also in the White Sea where you see signs of things that look a bit like mollusks, in other words, more modern animals. So there were signs of animal life happening just before the Ediacaran period finished and before the Camberan explosion. And I've just got this last thing in my notes is that people describe it as the Garden of Ediaca. Yeah. So this idea that there weren't predators or prey at that time, they all just coexisted. Yes, It was hard to know what the ecology was like, but there doesn't seem to have been any predation as far as we can see. Nobody knows how they lived. Maybe they had symbiotic algae like corals do today. So it's hu a huge amount of unanswered questions about how the Ediacaran lived and people think You know, it was a kind of blissful time of u of uh things just getting on, but I'm sure that a lot of the animals were probably slurping up even smaller things that don't appear in the fossil record. like larvae or bacteria or tiny eukaryotic cells because even though Multiellular creatures had evolved, there were still, as there are now, lots of single celled creatures around So there was probably a lot of filter feeding and deposit feeding, but nothing chasing each other with nasty long pointy teeth. But that comes soon after. it does ye. So What happens roughly around five hundred fifty million years ago, That is the spark explosion in life? There are lots of different theories and they're probably all connected. One is that Sponges evolved the earlier sponges are about nine hundred million years old, but sponges do something great. They slurp up a lot of deterritus from the ocean. And once the sponges did that, there was less for decay bacteria to decay. Deay bacteria suck up all the oxygen from the sea waterater, so without them the sea water became more oxygenated the way down, which was more space for large oxygen breathing creatures to live in to occupy Another one which is related is perhaps there was more oxygen in the atmosphere which tends to happen during ice aggey type times. But another one which I think is the clincher was that suddenly a lot. of minerals appeared in the seawater, particularly calcium Calcium is the element from which you create bones. calcium carbonate and invertebrates it calcium phosphate, but certainly all mollusk shells are made of calcium carbonate. suugary skeletons, kiting of jointed limbed creatures are reinforced with calcium carbonate. I mean, just think of you know, big lobsters, that sort of thing where do all these minerals come from Well, it looks like there was some huge episode of continents banging into each other the formation of Gondwana, the great southern continent It seems that two large continents slammed into each other creating the most enormous mountain range, four thousand kilometers long, at least a thousand kilometers wide And who knows how high? I mean, perhaps the greatest mountain ranges that ever existed on the planet I mean The Himalayas today are still being created by the collision of India with Southern Asia. Now this started fifty million years ago and it's still going on and it's created these enormous mountains, But mountains can only go so high because of gravity and rocks and everything. So what happened when these enormous mountains were created on land five fifty million years ago or also wasas they eroded really quickly in geological terms Until you it wasn't that long, a few tens of million years ago, they were eroded flat. Now where did all that stuff go? It went into the sea So in a relatively short order in terms of geology, all this mineral stuff was in the sea. this happened. it was a perfect storm that happened alongside anotherother major episode in evolution And you're going ask me what that is, aren't you I guess I should. Go on, Henry, what is this other major event? Well This is a family podcast, isn't it? This is a family It was It was the u an evolution of the anus A you know what? Be I know I asked that question earlier and it might have come out of the blue, but there was a reason I thought something Yeah. Go inhe and say the The evolution of the anus. Well, the evolution of the anus, Well, what happened was most early animals and on primitive animals they kind of absorb and excrete all their stuff through the skin because they're very small. Now some creatures such as jellyfish and hydra, they have one opening that leads to a bag like gut. So everything that goes in comes out the same way, and it's usually a kind of dissolved wash of stuff a major Innovation was the through gut. where there's a mouth at one end and an anus at the other end. Now of course biology loves its exceptions. There are these amazing things called comb jellies Tenafce they have four anuses, which is amazing. but we'll forget about them. they're another like chickens or another whole thing. But so there was a mouth at one end and an anus at the other. And so animals for the first time had a direction of travel So animals started doing things that they hadn't done before. Most of the time, previously they just stayed in the same place waving tentacles in the air. I mean diacar and animals are rather like that. They just stayed in the same place. They started burrowing. Now as we've talked about, the origin of the Cambrian is marked when burrowing animals happened. There's a particular kind of burrow called trepicmus that was made by a burrowing animal Now there are many ways to borrow. One way is to inflate yourself and to make yourself kind of hydrostatically rigid like an earthworm. but another way is to Clothhe yourself Clothhe your body in armor. So because of theseese things happening at the same time bilateral body plan with the mouth and the anus and all that calcium coming into the sea. And if animals are moving in a particular direction of travel, eyes evolved in the cambrian. There's a guy called Andrew Parker who's written and talked about this a lot about how eyes happen to the anus. So when something happens, when animals have got eyes and they're moving in one direction They're usually looking for something and what that something is is food. So they start to eat each other. And of course, what with all the calcium? that led to the evolution of teeth and the evolution of armor. Now one of the very earliest Cambrian fossils as opposed to just a burrow, which is what we call a trace fossil is an animal called cllaodina It's very, very small and it looks like a stack of ice cream cones. And one of the very earlyest cloudiners has bite a bite crunched out of it. So even then Back at the very earliest Cambrian, there are signs that animals were taking partes that. So from that fossil record, we have an example of that particular animal with a bite taken out of it. Yes, and it's one of the earliest Cambrian fossils. And there are plenty records of trilobites with bites out trilobites very quickly.. They're nice hemispherical, you know semicircular bites. So whatever they were, they were very tidy eaters Well shall we get to trilobytes now because they're perhaps the most iconic Fossil from the Cambrian period And they also exemplify These new changes that you've just described that allow for this development of life at the time Yes, triiler bites are absolutely beautiful and I would say that most fossil collectors will have bites in their collection Trilobes evolved early in the Cambrian their AMe was maybe in the Cambrian or the succeeding or division After the Devonian period, they went into a bit of a decline And they finally peetered out during the end Permian mass extinction of the Great Dying. but with the tririlobites that was really a art in a minor key. they were by that time quite minor components. But earlier there were trilobytes everywhere. I mean, some of them are virtually microscopic, some of them areot or too you know a foot or too long, someome of them had enormous eyes, compound eyes like insects do. some of them were blind, some of them burrowed, some of them skittered along the surface and some of them swam. So there were trilobyites for every occasion Right, so trying to get an idea of what exactly a trilobite was, we can get a general sense with the shell and that kind of woodlice look. But there is also once again, harkening back to why this is such an important time in the explosion of life There is a lot of diversity in the shape and size of the trilobites. Oh yes, they were a marvevelously adaptable form. I mean, if you can think of a pill bug or a woodlice, the reason they're called trilobites is they were divided into three parts longitudinally, a bit like a church with a nave Yeah, the side bitits at each side and at the front they had a very particular head but also like Jointed limbed animals like insects and crustaceans today, they molted So there are even fossils of trilobites molting or the actual molted skeleton of a Tla bike when it grew to become bigger and Very occasionally there are tririlobite fossils with soft part preservation. So the underneath of the trilobites you can see the gills that are attached to the legs, very much like crustaceans. They weren't particularly closely related to crustaceans like wlice crustaceans. They were the kind of their own thing There's a lot of debate about which jointed limbed animals they were most closely related to, but they kind of exemplify that kind of spiny leggy creature with a skeleton that they could shed with big eyes. they're even fossils now of the internal digestion of trialobites showing what they eat They kind of snarled up things and digested them. They don't really have a mouth with jaws crustations they do have a mouth, but it's surrounded by all kinds of mouth partots and they just stuff stuff in. and groined it up. They were great because, you know, like one of my favoritees fossils Lystosaurus, which was a goo anywhere, eat anything fossils from the tririassic. trilobes were a bit like that only in the Cambrian, which may have been why they were so successful. And so I from the surviving fossil record, then it seems like trilobites are front and center. you can normally recognize if you're at the Cambrian laayir because you'll find trilobite remains. Are there any particular sites in the world where we do have a really apart from Right outside Leicester Are there any particular examples? particular rock faces where they are just full to brim. different Cambian animals, trilobites, but also all these other animals that emerge at this time Well, the Cambrian is named after Cambria, Wales, so that's full of Canbrian Fners, but there was a lot more to the Canbrian than trialerys a century ago or so There was a fellow called Walcott who was a geologist, and he used to take his family on vacation to British Columbia. And high up on a mountain in British Columbia, he and his family discovered what are now known as the Burgess shales, which are actually quite a series of quite small exposures. Very high up. I mean, I've not been there. There was a field trip I didn't go on because I knew I was not going to be fit enough to get there. I mean it's like mountaineering to get there We're high up in the roockies It just shows you the power of the earth. They're these deposits that happen under in the deep seas five hundred and eight million years ago something like that So picture the scene Cental shelf, a mud slide, buries all these animals all at once and they go down to the deep sea and they' because of not very much oxygen, they're preserved perfectly, including their soft parts. And what a menagerie they are. They're lots of spiny skinned animals various sorts. There are some famous ones like Hallucagenia. Yes, what's this? Hallucienia was named after a friend of mine, Simon Conway Morris from the University of Cambridge, who I don't think he'd mind me saying he's a bit of an old hippie He named it and it says something in the paper on account of the strange and dreamlike appearance.ucinogenic, o. Yeah. So it's basically a worm with enormous spikes stipping out of its back and it's since been discovered quite a lot of these. They're called lobopods. They kind of closely related to arthropods, these armoud worms. And there is a relic of those animals living today on land, the Onicophores or velvet worms, which are strange little like worms with michelinand stumpy legs that go around forest flos And so there was that But there were a lot of sort of shrimpy like things, but there was a big reditor. we're gonna teap up that one because I've got two names here I like to do the smaller one first and I hope I'm on the right track when I say the word in Oapinia. Oinaina. Oabina It's very hard to describe what upper binia looks like If you've got small children, the closest thing is like the Nunu from the teletub. was the teletub. Okayes the sucking up the ye thing ye. It was Oapinia was a strange shrimp like creature. It was a swimming creature, It had lots of fins And it had five eyes on stalks And it had this long hose pipe mouth with jaws at the end that was a real weirdo. I mean, but that's Obscurely related to all these jointed limbs, so that was one of them. The other one though, and I think this is the big predator and I hope I get this pronunciation right Anomalo Corus. Anomalo chorus, yes, now. Anomalo chorus has a very checkered history Charles Walcott described a lot of different fossils turned out to be different bits of what we now know as a Loma Corus Now, it had a circular garbage grinder mouth with circular plates. Warcott described a fossil which was just as circular mouth as a kind of jellyfish called Pyoya. It also had segmented, spiny pinser type things at the front to stuff things into its mouth. and these were described as some kind of shrimp. and it wasn't until people found the whole thing So this enormous shrimp like thing with big googly eyes and this circular mouth and pincers to shove things into its mouth They could be a meter long which was huge. Back then that is like that T rex the Mar. Yeah, that was the big predator of the time A normala cararis means kind of weird shrimp really and The Anomal carids in the Cambrian were very successful. In fact, they survived the Cambrian because there's some Wonderful fossils coming out of Morocco, more recently the Fzuata formation in Morocco, which is not Camban, it's audo vision, it's the succeeding period. and that includes the latest known anoma carids They were also an nomalular carris that were filter feeders, a bit like the versions of basking sharks So they were big, but were filter feeders. And so they specialize in various ways, these phenomenal cars land a Viking Lship on island shores, scramble over the dunes of ancient Egypt and avoid the poisonous's cup in Renaissance Florence. Each week on Echoes of History, we uncover the epic stories that inspire Assassin's Creed. We're stepping into feudal Japan in our special series Chasing Shadows, where samurai warlords and Shinobi spies teach us the tactics and skills needed not only to survive, but to conquer. Whether you're preparing for Assassin's Creed Shadows or fascinated by history and great stories, listen to Echoes of History, a Ubisoft podcast brought to you by History Hit. There are new episodes every week Since the dawn of time, humanity has been at war. It has shaped the world around us. And if it somehow feels like we've been here before, it's because we have I'm David Boris. I'm a military historian, and on my new podcast Hostile History, I take us inside history's most defining wars and rebellions. From Gangghis Khan to the war in Iran, find out how the past can explain the present. seearch for and follow hostile history on Spotify, Apple Podcasts, Amazon Music, or wherever you find your favorite podcasts D you mentioned earlier those triobiotes which had bites taken out of them, circular bites. Yeah. Does that align then with that kind of circular malthe? Possibly posossibly, but there were lots of other things there at the time. I mean, there were all sorts of Athropods which are known as greatreat appendage Athropods. These had these were more like if you can imagine lobsters but with imense, much more immense claws sticking right out of from the front end of the animal these have been found these are very kind of Cambrian Athropods. So There are loads and loads and loads of arthropods from the Cambrian From which. Evolved That from a small selection the althropods we get today such as collaliserates, which is scorpions and spiders and crustations. from which the insects are actually an offshoot of crustaceans. They're the kind of land living crustaceans in the same way that tetrapods are land living fish and Things like horseshoe crabs that look kind of pre astoning These were all options, but a lot of different kind of arthropods became extinct. They didn't survive the cambria and they maybe lived a bit longer. But there were also a lot of amazing worms Tambrian In Cambridge some time ago, the great student of the Burger Sales was the guy called Harry Whittington and his students, his it were Simon Conway Morris, who I mentioned and also Derek Briggs, they're both still active Derek mostly does the arthropods on Simon did all the worms, but there are lots of worms Now there's an obscure group of worms now priapilids, which The classically trained listeners of the ancients will titter because it means basically penis worms And they look like penises And these were major, major players in the forauna digging stuff in the seabed and filtering out guns from the seabed. There're not many of them around now, but they still do exist, but there were many more of them thenen So it seems like this very diverse, very quite frankly, bizarre world on the seabed at the time of the Cambrian explosion, all these different arthropods and worms and so on. I've got one other in my notes because it seems Really interesting because of the quality of the fossils that have survived Fukxian Hu Ha Yes, I'm never quite sure how to pronounce this. It's Chinese Now Burgish Sales was it was for a long time, the poster boy of these Cambrian deposits, which preserved creatures including their soft parts in incredible detail a later one was discovered in China in South China, the Chengjhiang foraunner. Now if you want to go and discover new forauners for things, go to China. It's just amazing. in southern China was the Chenzhiang fauna and the other since. The Chenzhang fauna is older than the Burgish Sales by a few million years. And that included Lots of similar things to the Burgish Sals, but the other ones Fuxian Huia, I apologize I don't know how to pronounce it either. Now some of these are preserved so beautifully that you can even see the nervous systems Wow. That's amazing. Yeah you can reconstruct the nervous systems of Fuxian Huia to see how their brains were similar or different from modern arthropods and you get an idea. Now this is quite important for anatomy geeks because stududents of insects And alsothopods Oh by what's known as the Athropod head problem. Now anthropes of fgmented animals. And nobody's quite sure how many of the original segments went to make the head Now this is a problem that perplexed people back to Geta But once you've got the nervous system inside as well as the statements on the outside, you can get a better idea. I think people may inrose into the Athappod head problem, but I sincerely hope they never they never solve it because it's a wonderful problem. it's a nice problem to have We've covered all these various types of arthropods so far. And so far, Henry, we've covered They've all been invertebrates. But This is also such a big time because this is when we see the emergence of vertebras and what do we mean first of all by vertebras? bates are the animals group of animals to which we belong These are animals with backbones. back. So that rather than have an external hard skeleton like the arthroplods and the invertebrates, they vertebrates have an internal skeleton, the backbone now The origin of vertebrates is a subject that is close to my heart because When I was a graduate student in Cambridge, I had to teach early vertebrate history to undergraduates. Now in Oxford and Cambridge most of the actual teaching is given to graduate students. So I had to teach these undergraduates But I found that all the lend the notes from the lecturers were very, very old fashioned. so I had to do a lot of work to try and understand this myself and I got sucked in down that rabbit hole So it became it's a subject that's very close to my heart. and I've written now two books about the origins of vertebrates I can't help myself. I don't want to write another one. I did write one and then people kept asking me to write another one and I said, ' No, I'm not a scientist, you scientists, you write one. And then I was cornered in a room by two of these scientists and my publisher So there was no excuse. So I had to take spend sixteen months writing another book about the origin of erttebraes because a lot has been discovered in terms of genetics, in terms of molecular biology, and of course in fossils. Now It was the Chenjang faunner of China that produced the things that were that kind of solve the problem But I'll have to go back to one of these strange worms That' Simon Conway and Morr. can't help yourself, can you I go back to the strange worms. I got a str. Well, there was this kind of strange worm thing called Picia which looked like a segmented fish fillet. Because it wasn't an Athropod, Simon got to study that I written an initial description a long time ago Many more fossils have been found since And he kept not writing the definitive monograph and I asked him why he done it, he said, because the more you look at it, the weirder it get the less and less like a vertebrate ancestor. Now but in the changang So Picara is N the earliest vertebrate. It's an offshoot somewhere because there were all sorts of weird things that weren't vertebrates but the earliest vertebrates and we could call them fish We're at the Changeang forauna. There's one called Hikokis and there's another called Millo Comingia And these were the earliest known Th is the first fish the first world they had no paired fins They had If they had a backbone, it was just cartilaginous. They had no hard parts. And this is why it took exceptional preservation in places like the Changeang for Wner to show them up at all. They were you know about the size of an anchoivy or maybe small real tiddlers like' you know wide bait thighs sadd and something. Yeah, even smaller And they had eyes, but more than that, they had our eyes Two pairs of eyes In addition to the regular pair of eyes there had another accessory pair next to them of smaller eyes So Millo Kuningia, the earliest vertebrates had four eyes What happened to these other two? they eventually went inside the head and became the pineal gland which is still you know, we have pineal glands in the middle of our heads. but they're connected by nerves to the eyes and the optical centers of the brain. and these are the glands that help us regulate our biar rhythms. They produce melatonin and they keep our day and night cycle. They They are what goes out of sync when you fly a long way and get jet lag So But originally these were eyes with lenses and retinas and there were four of them in the earliest fishes. So these were the earliest vertebrates from from Chen hang, they weren't armored at all There Pain an idea that they were armoured fishes in the Cambrian. That has been debunked The problem with the armorered fishes in the Camron was they're just shown from fragments, tiny fragments, is if you took an armored fish and you stomped on it and rolled over it with a steam roller and scattered all the bits, and then you found one bit Of course these tiny fragments of Ohh you could study under a microscope. The problem is they're indistinguishable from arthropod skeletons. So these fragments that had been attributed to fossil fish were probably some kind of arthropoto. So the fish that we see in the Cambrian are unarmoured. It was only later in the Oivision that they became armoured And so with the evolution of the backbone to get to those earliest fish Is this the thing that people are still debating how you got from that strange worm to the eariest fish with a clear backbone yeah, the origin of vertebrates has been a really big problem for a long time because vertebrates are so different invertebrates in many, many ways This internal skeleton is very, very unusual So the history goes back a long way and that's another episode, The origin of vertebrates. Oh, yes, let's do that But our closest relatives are things called, believe it or not, sea squirts. These are creatures that live in one place, squirting seaweed in a seaweed They live in one place squirting seawater in an hour. did they wr? Our closest ancestors Our closest relatives. Our closest relatives are sea squirts. Yeah Okay, Well s sea squirts have larvae And these have little heads and tails like tadpoles. Tails have the nototor chord in, the nototor chord is the precursor of the bank. and they have the muscles on the otherer side. And then what these things do that in their heads, they've just got one eye spot Not four, just one All it can do is det take light and dark. And it's got a little gravity sensing or organ And all it does when it hatches, it goes on a very short journey with its tail just to find somewhere that's deep and dark and then it sticks onto the rock with its head end. And then it ressorbs the tail and then balloons out into this giant pharynx That's this giant balloon mouth and stomach, which is the sea squid So Verttebrates are basically these two things in one the mobile tail and the jaws and the visera behind it So A famous paleontologist called Al Roma One of his last papers in nineteen seventy two conceived of vertebrates as a mixture of two animals, the somatico visceral animal, that we have the muscles and the brain and the backbone of the mobile animal, which is represented by the little wholeo lava And the visceral part, which is the stomach, the intestines, all the squishy mixed grill part which are represented by the adult tunicade So it could be that the common ancestor of vertebrates and tunicates. was an animal which was motile And it had a segmented swwishy tail and it had a front end with jaws and a pharynx But then we went all separate ways. Verttebrates have integrated the two So they're almostly seamlessly joined. Tunicates have kind of deconstructed themselves. so the somatic part is the lather and the visceral part is the adult And on my desk several years ago, appeared a paper Morphon enjiang of something called the ticoleium And I looked at these and I thought Goodness me, Expletive Deleted. These look like Romas somatico visceral animals And these Vuleons do indeed have a blobby head with little gill gill slits and a kind of circular mouth and a segmented tail and these not universally, are generally seen as somewhere in the ancestry of vertebrates and tunicates together So And there is another animal called the amphioxus, which is a swimmy animal with gill slits That used to be seen as the closest relative to vertebrates, but now it's been demoted further back because of the all sorts of genetic things. Now, medical scientists loved tunicates because they had a perfect little heart but only made out of a few cells, So they were excellent for experimenting ideas on the development of the heart And the amphioxis doesn't have one And medical scientists said Really, the tunicates should be closer to vertebrates than they are But the genetics now reveals that they are. we are closely related to tunicates. We have many of the same genes, many of the same processes. It's just that tunicates have evolved in this strange deconstructing direction and have also cut down on how many cells they've got, so they don't have actually many cells Land a Viking longship on island shores, scramble over the dunes of ancient Egypt and avoid the poisoners' cup in Renaissance Florence. Each week on Echoes of History, we uncover the epic stories that inspire Assassin's Creed. We're stepping into feudal Japan in our special series Chasing Shadows, where samurai warlords and Shinobi spies teach us the tactics and skills needed not only to survive, but to conquer. Whether you're preparing for Assassin's Creed Shadows or fascinated by history and great stories, listen to Echoes of History, a Ubisoft podcast brought to you by History Hit. There are new episodes every week Since the dawn of time, humanity has been at war. It has shaped the world around us. And if it somehow feels like we've been here before, it's because we have I'm David Boris. I'm a military historian, and on my new podcast, Hostile History, I take us inside history's most defining wars and rebellions. From Gangghis Khan to the war in Iran, find out how the past can explain the present. seearch for and follow hostile history on Spotify, Apple podcasts, Amazon Music, or wherever you find your favorite podcasts ust to refresh, when you say tunicates, what kind of animals should we be thinking? These are the seaquirres Th are the sea squres. I apologize you but some of them. Some of the sea squirts live in as Alvs live in one place, someome of them float around in huge colonies in the sea. There're some called pyrosomes that have these huge colonies that are kind of made trumpet shapes I mean and divers can swim inside them I So they emerged at the time of the Cambrian exxplosion. Yeah and they're still visible today. Yes, there are fosite tunicates from the Cambrian explosion But some of the tunicates have evolved to be really, really strange. I mean, they're these tiny ones called larvations, which are still tiny, the size of a grain of rice and they are still divided like a tadpole into a switchy tail and a head. and they filter feed from the sea do this they secrete this enormous mucer structure called a house. which is Unbelievably intricate and it's made out of mucus that they secrete in huge amounts using genes and proteins that are seen nowhere else in nature And they use these for a few hours and then shed the lot and grow another one And these creatures have a life cycle of a day, a week or so. And these mucus houses drift to the bottom of the sea and they are a major, major part of the carbon cycle of the Eth. And yet not many people know about these because all this happens way way out in the open sea and these things are very fragile. so most tunicates, most of these tiny tunicates they're the size of a grain of rice and their house is the size of a walnut But there are ones that are maybe fossils that are known where they were, you know, fairly big animals and the house was the size of a football. And you can imagine shoulders for belief So our nearest relatives the Tunicates have gone on to be an amazingly diverse and weird set of creatures and they go back to the Canbrian explosion as well. I've never heard of them before. I'm just trying to picture it. So you've got trilobites on the floor, and on a Laris once in a while hunting. Th then you got these tunicates there and then the beginning, you know that the first vertebrates these very, very small fish mayaybe in shoals altogether P. Yeah in big shoals are these small earliest fish With four eyes. withith four eyes As the cambion goes on millions and millions of years, more and more oxygen, do these earliest fish do they get bigger Yes, they do and they also acquire armour Armour Right. So this is when we get the first armoured def. Yes. now in the succeeding Older Vision period, from the Older Vision through to the Dvonian They're more and more armoured fish. Mostly these are jawless fish. They just had mouths. they didn't have you know up and down crunching jaws Some of them they had very boxy armoud skeletons, so the front end was pretty much solidly boxed end had a sishy tail. Sometimes they had fins on each side and sometimes they didn't. And do we think this is an evolutionary grade to help fend off things like Anomala cararis Yes, but also a later arthropods, which were even more Night marish These were called the Euryptterids, which were relatives of spiders and scorpions. So these are the original scorpions. Y, Scorpion kind And these could be, you know six to eight feet long enormous googly eyes and they really did have snapping pincers Al Roma the same guy who came up with the idea of the dual origin of vertebrates. He published a paper in science in nineteen thirty three that's a classic, which is he said that maybe vertebrates evolved armor to escape the snapping jaws of Euryptterids. Now it's kind of fanciful But the unusual thing about vertebrates is the armour is not calcium carbonate, it's calcium phosphate. It's called hydroxy appetite. and it's the same our bones are made of hydroxy appetite Now, strangely enough, even though vertebrates had the notor chord, we had external armor more like in invertebrates Only later did the backbone become mineralized And the armour evolved in various ways. There're some of these fossil fish where the armour is broken up into scales, a kind of chagreen of scales. There're these beautiful little fossil jawless fish called Pelodonts, which have all sorts of amazingly stylish shapes Some of them come from this romantic locality called Moth It stands for manan on the hill. it's out in the northwest territies of the Jawless fish are known from all over the place. In fact, they're quite a from quite a lot have been described in the UK in Wales and the west of England where they're audo visioned Soleur in Devonian rocks. You know, the clues in the name, the Odoisian and the Silurian were named after the Roman tribes in Wales and the Babyonians li. So there were a lot from there. and They were escaping predators, but also Phosphate is quite rare. on earth and important in the biology of all animals. So there is an idea that bone was a kind of accessorory store of phosphate for very active animals, which vertebrates are much more active than most others. So that was the origin of bone and fishes. And then at some point in the silurian Jaws were invented That's Geors. That's alm the next stage in the story though because now we're going well past Yeah we' well past theion. That's another episode. The origin of Jaws. The origin of Jeors and it's not sharks, is it? No, no, noerms But let's go back to the Camrians. so How long shall we say the Cabian explosion lasts? How long before we do have this real diversity of life that we've covered in this episode today, the first vertebrates, anomalacaris, trilobites and so on. When we call the Cambrian explosion an explosion, it's more of a kind of extended detonation. It's a more of a difficult title to sell if we call it the Cambrian extended detonation. Y the Cambrian slow digestive rumble, right But in terms of geology, it was use That hiatus in the fossil record that so worried Darwin is real I mean, there was a step change in evolution partartly motivated by the input of calcium minerals into the sea And the whole thing lasted about fifty million years which is less than the time between the dinosaurs and now And that was time in which almost in fact all modern filer that is large categories of animals appeared in the Cambrian except one But even that's been cleared up now. So what's that? That's the briozoa or moss animals. These are tiny, tiny colonial creatures that live in little boxes and tentacles coming out. And that was thought to be the kind of slacker that didn't appear in the Cambrian, but now some fossils were found and some people said yes, these are brazoa and somebody said, no these aren't Brazoa, they're seaweed. me F first lot came up with some moren and said, yes, they're Brazoa. so that's been settled, which is nice. So just how rich and teeming in life the seas, I could say and the oceans of the Eth have been back during the Cambrian. And we should, as it's probably clear already, but I'll just state because I don't think I've stated once during this chat at a time before life is on land. I mean So how just rich and diverse and just flourishing would the seas have been? Yes, Well, the difference between land and sea would be quite stark. I mean, there have been some suggestions that some life was As sure in the Cambrian. In fact, before the Cambrian, there are some deposits in Northwest Scotland, which are a billion years old which are fresh water deposits and they're signs of encrusting mosses, lichens in ponds, so on land but not above the surface of the water There are in in some Cambrian deposits. This was shown to me in the Smithsonian by a lovely fellow called Ellis Yokelon. he's gone over the Rainbow Bridge since there are some Cambrian beach deposits with tracks on that look like motorcycle tyre tracks I mean, they're the same width as motorcycle tyre tracks and they look like motorcycle tyre tracks. It's as if some prehistoric motorcyclist came out of the sea and did wheelies and then went back under the sea So nobody knows what these creatures were, maybe some kind of slug like creature And there are thoughts that some of the ediacaron creatures were maybe intertidal, maybe on the beach occasionally. but really for animals and plants in those days to venture above the surface of the sea would be as inimical to life as going into empty space So It was a very long time before life came on to land. That would be another one hundred hundred fifty million years after the Cambrian explosion. I love doing episodes like this, whether it is the Cambrian as we've done, we've done dinosaurs in the past, going to do terrorirds in the future and hopefully also the carboniferous when insects got really big. because they're defined by all of these different types of animals that to us nowadays feel so strange and so weird And yet That was just the story of evolution. the creation of these animals to try and deal with their habitats and There has never been, has there a time in the Earth's history like the Cambrian where you see such an, I can use the explosion word again, but you know what I mean? such a diversity of life emerging because of all of these inccreasing calcium, increasing oxygen and so on that you have at this one period in time. such an amazing combination of different bizarre, weird and wonderful creatures that roamed the seabeds of the world some five hundred million years ago. I should say though that over time, biodiversity has increased be because of the pull of the recent, because the more recent the rock, the more of them and be so. But there does it does seem to be a real effect So just because the Cambrian was really weird and strange, it shouldn't blind us to the weird and strange things that go on around us today, the interactions between creatures. I mean, I've been learning a lot about parasitism and things For example