The Cambrian Explosion: When Life Began?

538 million years ago, life on Earth changed forever. In an evolutionary burst known as the Cambrian Explosion, complex animals rapidly appeared in the oceans, laying the foundations for almost every major animal group alive today. Tristan Hughes is joined by the mighty Henry Gee to explore biology’s 'Big Bang'. What triggered this extraordinary leap in evolutionary complexity? Why did creatures with eyes, shells and limbs emerge so suddenly in the fossil record? And what can the Cambrian Explosion reveal about the origins of animal life and the history of our planet? MORE Rise of Humans Listen on Apple https://podcasts.apple.com/gb/podcast/the-ancients/id1520403988?i=1000702067254 Listen on Spotify https://open.spotify.com/episode/1vXxIXCruQh4w90EuawE6E?si=C_kRYYqdSfWYa134dL74Tw The Age of Dinosaurs Listen on Apple https://podcasts.apple.com/gb/podcast/the-ancients/id1759820234?i=1000753155493 Listen on Spotify https://open.spotify.com/episode/1yXsjOGcPzF7f4F8iiI4Wy?si=mcnna0i1RzqS4sKxZcbKlA We're going on *TOUR* to Australia and New Zealand! - grab your tickets here https://fane.com.au/whats-on/an-evening-with-tristan-hughes/. The Ancients is now on YouTube! Watch here: @TheAncientsPodcast https://www.youtube.com/@TheAncientsPodcast Presented by Tristan Hughes. Audio editor is Aidan Lonergan. The producer is Joseph Knight. The senior producer is Anne-Marie Luff. All music courtesy of Epidemic Sounds The Ancients is a History Hit podcast. Sign up to History Hit for hundreds of hours of original documentaries, with a new release every week, PLUS early access, ad-free podcasts. Sign up at https://www.historyhit.com/subscribe. Hosted on Acast. See acast.com/privacy https://acast.com/privacy for more information.

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:00Tristan Hughes?

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• 0:45Tristan Hughes?

  538 million years ago, something mysterious happened in the murky depths of our seas. Our planet came to life. It's known today as biology's Big Bang, the Cambrian Explosion. Simple organisms gave way to complex, mobile creatures with eyes, limbs, shells, and teeth. Predators and prey emerged, and, for the first time, life on Earth really began to take shape. A sudden burst of evolution saw practically all major animal species begin to appear in the fossil record. But why?

• 1:30Tristan Hughes?

  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, biology's Big Bang. Our guest is a fan-favorite returning expert, the paleontologist, evolutionary biologist, author, and editor, the one, the only, Dr. Henrichi.

• 2:05Tristan Hughes?

  Henry G, what a pleasure it is to see you in person for the very first time.

• 2:10Speaker 01

  Well, it is Tristan. I mean, here we are actually together simultaneously, both at once and at the same time.

• 2:18Tristan Hughes?

  Who thought this was possible?

• 2:20Speaker 01

  Who'd have thought it?

• 2:20Tristan Hughes?

  I've got to ask first of all, are the chickens doing all right?

• 2:22Speaker 01

  They're chickens, there are two of them left.

• 2:24Tristan Hughes?

  Two of them left.

• 2:25Speaker 01

  Bluebell and Poppet, and they're still squawking and laying eggs, so that's nice.

• 2:29Tristan Hughes?

  But today we're going far beyond the origins of chickens, which in itself is a fascinating story, isn't it? It takes millions of years. But the Cambrian explosion, and this has been described, the Cambrian explosion, as life's big bang, as the biological big bang.

• 2:44Speaker 01

  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, that it's all since been divided up into into flats with a kind of retail out underneath. Now it's called the Cambrian. But before the Cambrian, there was nothing.

• 3:24Speaker 01

  After the beginning of the Cambrian, there were lots of fossils, clams, and 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 and lots, 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.

• 4:01Tristan Hughes?

  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

• 4:12Speaker 01

  That's right. It was the first time we Actually saw animals big enough to see with the naked eye with hard parts, armour, jaws, teeth, skeletons, shells. And of course, it's the hard parts that tend to be fossilized. It's only very rarely that you get fossilization of the soft parts of an animal, and that really is quite remarkable.

• 4:36Tristan Hughes?

  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?

• 4:46Speaker 01

  The Cambrian, they keep changing their minds about the beginning of the Cambrian. 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 treptichnus. 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 earth system. But the other one is directly dating it, using, not carbon dating, that runs out, that's useless before about forty five thousand.

• 5:28Tristan Hughes?

  It's recent history.

• 5:29Speaker 01

  It's quite recent, recent, recent history. So there are various radioisotope methods that you can use to date the beginning of the Cambrian. But they keep changing their minds. I mean, I looked up this morning and the latest agreed date for the beginning of the Cambrian was five hundred and thirty eight point eight million years ago. In fact, the reason we're having this today, listeners, is because it's the five hundred and thirty eight point eight millionth anniversary next Tuesday. So that's why, why we're doing it. So the Cambrian period as a period or what they call, geologists call a system of rocks,

• 6:10Speaker 01

  started about then, but they keep changing their minds because it's a, 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 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 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.

• 6:52Tristan Hughes?

  Well, we're going to explain 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 dinosaurs?

• 7:02Speaker 01

  Oh, gosh. Well, the Cambrian was, say, half a billion years ago. The dinosaurs didn't appear until 200 million years ago.

• 7:11Tristan Hughes?

  So that's just to emphasise just how much.

• 7:12Speaker 01

  At the earliest. But of course, when the Cambrian had happened, like eight ninths or nine tenths of the Earth's 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.

• 7:34Tristan Hughes?

  Well, can we now explore this briefly? Can we almost kind of cover what is known, all the theory around the story of animals up to the point, up to that 338 million years ago?

• 7:48Speaker 01

  I'll try and keep this huge story brief. About 2 billion years ago was an event called the Great Oxidation Event. Well, that happened between 2.4 and 2 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 the 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.

• 8:26Speaker 01

  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, um, most eukaryotes that live today are single-celled amoebas, paramesia, flagellates, dinoflagellates that cause these blooms, many horrible diseases, malaria, they're single-celled. But there were signs of multicellular eukaryotes about 1.8 billion years ago. Seaweeds, about a billion years ago, there were early seaweeds,

• 9:06Speaker 01

  early fungi, but nothing animal-like until the breakup of a huge supercontinent. Now, we know about the supercontinent of Pangaea, and I remember we chatted about that. That's in the Triassic area, it's much later, yeah. Well, there is a, a supercontinent cycle, that the Earth breathes on a period of about 500 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 Neild, 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,

• 9:50Speaker 01

  it's about the, the supercontinent cycle. Well, before Pangaea, the supercontinent before that was called Rodinia, uh, and that started to break up about 800 million years ago, and as a consequence of that, there were two or three snowball Earth episodes, where they were ice ages 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 event, animal life appeared, and these were large enough to see with the naked eye, but the first flush of animal life was very strange.

• 10:35Speaker 01

  And this was before the Cambrian. These were the Ediacaran fauna.

• 10:39Tristan Hughes?

  Hmm.

• 10:40Speaker 01

  Now, a fellow, I think his name was Spriggs in Australia, discovered the Ediacaran fauna in South Australia in some sandstone, very, very coarse impressions of things that look like jellyfish and and other things, squishy sea creatures that were very hard to assign to any particular group of of animals. Uh, they have been thought to be lichens, they have been thought to be their own thing, some strange creature. Um, some have been tentatively associated with more modern groups of animals. But since then, Ediacaran faunas have been found in all sorts of exotic locations on the, from the White Sea coast of Russia, uh, to Namibia, to, uh, Newfoundland,

• 11:26Speaker 01

  to Bradgate Park near Leicester.

• 11:29Tristan Hughes?

  Brilliant.

• 11:29Speaker 01

  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 a splot of pre-Cambrian in the middle of the English Midlands, and it's got Ediacaran 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's there was a, um, big as a pair of trousers, you know, spread along the rocks. There's what are called Charnia discus is one. And they look like fronds. But you really need to see them at dawn or dusk when the light is slanting. I mean, I remember uh, being there, trying to look for them. And I went on a very sunny day at midday, and e- even though they were right in front of me.

• 12:10Speaker 01

  And I knew this because I was do- uh, I was doing the face, FaceTiming my colleague Emily Mitchell in Cambridge. She's an expert on Ediacaran faunas, and she knew exactly where I was. So she was in Cambridge and I was in in Bradgate Park, and she said, no, left a bit, left a bit, right a bit, right. There it is. So the Ediacaran fossils, they lived just before the Cambrian, and then they disappeared.

• 12:32Tristan Hughes?

  I'm sorry, I'm still getting over the fact that you can go to Bradgate Park near Leicester today and look at the remains

• 12:39Speaker 01

  Six hundred million.

• 12:41Tristan Hughes?

  Six hundred million year old.

• 12:42Speaker 01

  And there are people climbing around and walking their dogs and playing football, and there they are. I mean, it is mind blowing.

• 12:48Tristan Hughes?

  That's amazing. That is so amazing.

• 12:49Speaker 01

  And most people don't know they're there because they are very hard to spot unless you really know what you're looking for. They were, they were actually discovered by a small boy who was, I don't know, playing football or walking his dog. I've no idea.

• 13:00Tristan Hughes?

  And is it the fact, so back then, you know, these animals, they had mouths, they have an anus as well, we're thinking that kind of thing.

• 13:07Speaker 01

  Well, nobody 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 Ranger Morphs, which look like plaited loaves. And some of them seem to have little small, smaller plaited loaves around them. They, they grew by like strawberry plants, by shooting out runners. Uh, and grow, grew baby ones. These are mostly known from Newfoundland. Now, people have split up the Ediacaran into various sub-stages. The earliest one part is found in Newfoundland, and I think probably Leicestershire, but the later part is in Namibia.

• 13:45Speaker 01

  And also on 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, and before the Cambrian explosion.

• 14:01Tristan Hughes?

  And I've just got this last thing in my notes is that people describe it as the Garden of Ediacaria.

• 14:07Speaker 01

  Yeah.

• 14:08Tristan Hughes?

  So this idea that there weren't predators or prey at that time, they all just coexisted.

• 14:13Speaker 01

  Uh, yes, they, um, they, i- i- 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 knew, knows how they lived. Maybe they had symbiotic algae like corals do today. Uh, so it's huge, a huge amount of unanswered questions about how the Ediacaran lived. And people think, you know, it was a kind of blissful time of, uh, of, uh, things just getting on. But, um, I'm sure that a lot of the animals were probably slurping up even smaller things that don't appear in the fossil record. Uh, like larvae or bacteria or tiny eukaryotic cells.

• 14:57Speaker 01

  Because even though multicellular 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, um, deposit. Feeding, but nothing chasing each other with nasty, long, pointy teeth.

• 15:13Tristan Hughes?

  But that's comes soon after.

• 15:15Speaker 01

  It does, yeah.

• 15:16Tristan Hughes?

  So what happens roughly around five hundred and fifty million years ago, that is the spark, what's explosion in life?

• 15:23Speaker 01

  There are lots of different theories and they're probably all connected. One is that that sponges had evolved, the earliest sponges are about nine hundred million years old. But sponges do something great, they slurp up a lot of detritus from the ocean. And once the sponges did that, there was less for decay bacteria to decay. Decay bacteria suck up all the oxygen from the sea water, so without them, the sea water became more oxygenated. All 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.

• 16:08Speaker 01

  Which tends to happen during ice agey type times. But another one, which I think is the clincher, was that suddenly a lot of minerals appeared in the sea water, particularly calcium. Now, calcium is the element from which you create bones, calcium carbonate. And also invertebrates calcium phosphate, but certainly all mollusk shells are made of calcium carbonate. The sugary skeletons, chitin, of jointed limbed creatures are reinforced with calcium carbonate. I mean, just think of, you know, big lobsters, that sort of thing. Now, where did all these minerals come from?

• 16:50Speaker 01

  Well, it looks like there was some huge episode of continents banging into each other. Um, 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 range that ever existed on the. Plan in. 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.

• 17:31Speaker 01

  And it's created these enormous mountains, but mountains can only go so high because of of gravity and and and rocks and everything. So what happened when these enormous mountains were created on land five fifty million years ago or so? Was they eroded really quickly in geological terms? Until, you know, 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 re- in a relatively short order, in terms of geology, all this mineral stuff was in the sea. And this happened, it was a perfect storm.

• 18:11Speaker 01

  That happened alongside another major episode in evolution. And you're going to ask me what that is, aren't you?

• 18:20Tristan Hughes?

  I guess I should. Go on, Henry. What is this other major event?

• 18:23Speaker 01

  Well, this is a family podcast, isn't it?

• 18:26Tristan Hughes?

  This is a family.

• 18:27Speaker 01

  It was the, it was the um, the evolution of the anus.

• 18:31Tristan Hughes?

  Ah, you know what? Because I know I asked that question earlier and it might have come out of the blue, but.

• 18:36Speaker 01

  It certainly came out of something, yeah.

• 18:40Tristan Hughes?

  Come on then, so the the the evolution of the anus.

• 18:43Speaker 01

  Well, the evolution of the anus, well, what happened was most early animals and pr- on primitive animals. Um, 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 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. But 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 cone jellies, uh, tinafores.

• 19:25Speaker 01

  They have four anuses, which is amazing, but we'll forget about them. That's they're another like chickens are 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. Uh, most of the time previously, they just stayed in the same place waving tentacles in the air. I mean, Ediacaran. Uh, animals were rather like that. They just stayed in the same place. They started burrowing now as as we've talked about. The origin of the Cambrian is marked when burrowing animals happened. There's a particular kind of burrow. Called treptichus that was made by a burrowing animal.

• 20:06Speaker 01

  Now, there are many ways to burrow. Once, uh, one way is to inflate yourself and uh, to make yourself kind of. Hydrostatically rigid like an earthworm. But another way is to clothe yourself in clothe your body in armour. So because of these things happening at the same time. The 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. Uh, there's a guy called Andrew Parker who's written and talked about this a lot about how eyes happened.

• 20:42Tristan Hughes?

  The earliest.

• 20:42Speaker 01

  So when 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 armour. 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 Cloudina. It's very, very small and it looks like a stack of ice cream cones. And one of the very earliest Cloudinas has got a bite, a bite crunched out of it. So even then. Back at the very earliest Cambrian, there are signs that animals were taking bites out of each other.

• 21:20Tristan Hughes?

  So from that fossil record, we have an example of that particular animal with a bite taken out of it.

• 21:26Speaker 01

  Yes, and it's one of the earliest Cambrian fossils. And there are plenty records of trilobites with bites taken out of it.

• 21:32Tristan Hughes?

  We'll get the trilobites very quickly, don't worry.

• 21:33Speaker 01

  Yeah, they're nice hemispherical, you know, semicircular bites. So whatever they were, they were very tidy eaters.

• 21:39Tristan Hughes?

  Well, shall we get to trilobites 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.

• 21:53Speaker 01

  Yes, trilobites are absolutely beautiful and I would say that most fossil collectors will have trilobites in their collection. Trilobites evolved early in the Cambrian. Their acme was maybe in the Cambrian or the succeeding Ordovision. After the Devonian period, they went into a bit of a decline and they finally petered out during the end Permian mass extinction, the great dying. But with the trilobites, that was really a departure in a minor key. They were by that time quite minor components. But earlier, there were trilobites everywhere. I mean, some of them are virtually microscopic, some of them are a foot or two, you know, a foot or two long. Some of them had enormous eyes,

• 22:38Speaker 01

  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 trilobites for every occasion.

• 22:50Tristan Hughes?

  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.

• 23:05Speaker 01

  Oh, yes. They were a marvelously adaptable form. I mean, if you can think of a pillbug or a woodlice, they were, the reason they're called trilobites is they were divided into three parts longitudinally, a bit like a church with a nave.

• 23:19Tristan Hughes?

  Oh, true.

• 23:19Speaker 01

  Yeah, the side bits 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 were even fossils of trilobites molting or the actual molted skeleton of a trilobite when it grew to to become bigger. And very occasionally, there are trilobite 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 woodlice, woodlice or crustaceans. They were the kind of their own thing.

• 24:00Speaker 01

  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 with a skeleton that they could shed with big eyes. They're even fossils now of the internal digestion of trilobites showing what they ate. They kind of snarfed up things and digested them. They don't really have a mouth with jaws, crustaceans. They do have a mouth, but it's surrounded by all kinds of mouth parts and they just stuff stuff in and grind it up. They were great because, you know, like one of my favourite fossils, Lystosaurus, which was a go anywhere, eat anything fossil from the Triassic.

• 24:45Speaker 01

  Trilobites were were a bit like that, only in the Cambrian, which may have been why they were so successful.

• 24:52Tristan Hughes?

  And so, I mean, from the surviving fossil record, then it seems like trilobites are front and centre. You can normally recognise if you're at the Cambrian layer 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?

• 25:08Speaker 01

  Hmm.

• 25:09Tristan Hughes?

  Are there any particular examples, like particular rock faces, where they are just full to brim of different Cambrian animals, trilobites, but also all these other animals that emerge at this time?

• 25:21Speaker 01

  Well, the Cambrian is named after Cambrian whales, so that's full of Cambrian horners. But there was a lot more to the Cambrian than trilobites. 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 a 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 Rockies. It just shows you the power of the earth.

• 26:04Speaker 01

  They're these deposits that happened under in the deep sea.

• 26:10Speaker 01

  Five hundred and eight million years ago, something like that. So picture the scene, continental shelf, a mudslide, buries all these animals all at once, and they go down to the deep sea. And they're because of not very much oxygen, they're preserved perfectly, including their soft parts. And what a menagerie they are. There are lots of spiny skinned animals of various sorts. There are some famous ones like halucogenia.

• 26:41Tristan Hughes?

  Yes, what's this?

• 26:42Speaker 01

  Halucogenia 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.

• 26:58Tristan Hughes?

  Hallucinogenic, okay.

• 26:59Speaker 01

  Yes. So it's basically a worm with enormous spikes tipping out of its back. And it's since been discovered that there are quite a lot of these. They're called lobopods. They're kind of closely related to arthropods, these armored worms. And there is a relic of those animals living today on land, the onychophores or velvet worms, which are strange little, like worms with meachlan man's stumpy legs that go around forest floors. So there was that. But there were a lot of sort of shrimpy like things, but there was a big, big predator.

• 27:36Tristan Hughes?

  Well, we're gonna, we're gonna tee 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 opabena.

• 27:46Speaker 01

  Opabena.

• 27:47Tristan Hughes?

  Opabena, okay, right.

• 27:48Speaker 01

  Opabena. It's very hard to describe what opabena looks like. If you've got small children, it, the closest thing is like the Nunu from the Teletubbies.

• 27:58Tristan Hughes?

  The Teletubbies, okay, yes, the sucking up thing, yeah.

• 28:01Speaker 01

  Was a, opabena was a strange shrimp like creature. It was a swimming creature, had lots of fins, and it had five eyes on stalks, and it had this long hosepipe 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.

• 28:26Tristan Hughes?

  The other one, though, and I think this is the big predator, I hope I get this pronunciation right, anomalocaris.

• 28:33Speaker 01

  Anomalocaris, yes. Now, anomalocaris has a very chequered history. Charles Walcott described a lot of different fossils that turned out to be different bits of what we now know as the Anomalous Caris. Now, it had a circular garbage grinder mouth with circular plates, but Walcott described a fossil which was just this circular mouth as a kind of jellyfish called Paitoya. It also had segmented, spiny, pincer-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

• 29:15Speaker 01

  with big googly eyes and this circular mouth and pincers to shove things into its mouth, they could be a metre long, which was huge.

• 29:24Tristan Hughes?

  Back then, that is like the T-Rex of the days.

• 29:26Speaker 01

  Big mama, yeah, that was the big predator of the time. Anomalous Caris means kind of weird shrimp, really. And the Anomalous Carids in the Cambrian were very successful. In fact, they survived the Cambrian because there are some wonderful fossils coming out of Morocco, more recently the Fezouata Formation in Morocco, which is not Cambrian, it's Ordovician, it's the succeeding period, and that includes the latest known Anomalous Carids. There were also Anomalous Carids that were filter feeders, a bit like the versions of basking sharks, so they were big but were filter feeders. And so they specialised in various ways, these Anomalous Carids.

• 30:19Speaker 02

  If you love a good story, why aren't you listening to Dan Snow's History Hit Podcast? It's a show where we tell you every amazing, crazy and important thing that's ever happened in human history, from the perilous voyages of the first Polynesians, the discoveries of Captain Cook, the deadly Viking raids on Britain and Ireland, the rise and fall of the great English kings and queens. We'll tell you how Waterloo was won, the Alamo was lost, and all the history in between. So make sure you check it out, Dan Snow's History Hit, for the best true stories ever told, wherever you get your podcasts.

• 31:10Tristan Hughes?

  And you mentioned earlier those trilobites which had had bites taken out of them, circular bites.

• 31:15Speaker 01

  Yeah.

• 31:16Tristan Hughes?

  Does that align then with that kind of circular mouth?

• 31:18Speaker 01

  Oh, possibly, possibly, but there were lots of other things there at the time. I mean, there were all sorts of arthropods which are known as great appendage arthropods. These had, these were more like, if you can imagine lobsters, but with immense, much more immense claws sticking right out of the, from the front end of the animal. These have been found, these are a very kind of Cambrian arthropods. So there are loads and loads and loads of arthropods from the Cambrian, from which evolved us from a small selection, the arthropods we get today such as calycerates, which is

• 31:59Speaker 01

  scorpions and spiders and crustaceans, from which the insects are actually an offshoot of crustaceans, they're the kind of land living crustaceans in the same way that tetrapods, the land living fish, and things like horseshoe crabs that look kind of prehistoric. These are all offshoots, but a lot of different kind of arthropods became extinct, they didn't survive the Cambrian, they maybe lived a bit longer. But there were also a lot of amazing worms in the Cambrian. In Cambridge, some time ago, the great student of the Burgess Shales was a 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.

• 32:43Speaker 01

  Derek mostly does the arthropods and Simon did all the worms, but there are lots of worms. Now, there's an obscure group of worms now called priapylids, which...

• 32:54Speaker 01

  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 fauna digging stuff in the seabed. And filtering out gunge from the seabed. There are not many of them around now, but they still do exist, but there were many more of them back then.

• 33:18Tristan Hughes?

  So it seems like this is 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. Fuxian Hu Huiya.

• 33:36Speaker 01

  Yes, I'm never quite sure how to pronounce this. It's Chinese. Now, the Burgess Sails was, it was the, 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 Chenzang fauna. Now, if you want to go and discover new faunas for things, go to China. It's just amazing. So in Southern China was the Chenzang fauna and their other sins. The Chenzang fauna is older than the Burgess Sails by a few million years. And that included lots of similar things to the Burgess Sails.

• 34:21Speaker 01

  But the other ones, Fuxian Hu Ya, I apologize, but 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.

• 34:32Tristan Hughes?

  Wow, that's amazing.

• 34:33Speaker 01

  Yeah, you can reconstruct the nervous systems of Fuxian Hu Ya 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.

• 34:48Speaker 01

  Students of insects and arthropods are perplexed by what's known as the arthropod head problem. Now, arthropods are segmented 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 Goethe. But once you've got the nervous system inside as well as the segments on the outside, you can get a better idea. I think people are made inroads into the arthropod head problem, but I sincerely hope they never did. They never solve it because it's a wonderful problem. It's a nice problem to have.

• 35:27Tristan Hughes?

  Well, 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 vertebrates. And what do we mean first of all by vertebrates?

• 35:45Speaker 01

  Vertebrates are the animals, the group of animals to which we belong. These are animals with backbone.

• 35:51Tristan Hughes?

  The backbone.

• 35:51Speaker 01

  So that rather than have an external hard skeleton like the arthropods and invertebrates, they have, or 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 the graduate students. So I had to teach these undergraduates. But I found that all the lecture, 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.

• 36:34Speaker 01

  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 16 months writing another book about the origin of vertebrates. Because a lot has been discovered in terms of genetics, in terms of molecular biology, and of course in fossils. Now.

• 37:13Speaker 01

  It was the Chenzang fauna of China that produced the things that were that that kind of solved the problem. But I have to go back to one of these strange worms that Simon Conway and Morris.

• 37:27Tristan Hughes?

  You can't help yourself, can you? You've got to go back to the strange worms.

• 37:30Speaker 01

  Well, there was this kind of strange worm thing called Pikaia, which looked like a segmented fish fillet. Because it wasn't an arthropod, Simon got to study that. He'd 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 hadn't done it. He said, because the more you look at it, the weirder it gets, that the less and less like a vertebrate ancestor. Now, but in in the Chenzang, so it Pika is not the earliest vertebrate. It's it's an offshoot somewhere because there were all sorts of weird things that were weren't vertebrates.

• 38:15Speaker 01

  But the earliest vertebrates, and we could call them fish, were at the Chenzang fauna. There's one called Hikoikis, and there's another called Milokmingia. And these were the earliest known fish.

• 38:31Tristan Hughes?

  These are the first fish in the world.

• 38:33Speaker 01

  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 the Chenzang fauna to to show them up at all. They were in a small, about the size of an anchovy, or maybe small, real tiddlers, like a, you know, whitebait size.

• 38:56Tristan Hughes?

  Sardines.

• 38:57Speaker 01

  Yeah, or even smaller. And they had eyes, but more than that, they had four eyes. They had two pairs of eyes. In addition to the regular pair of eyes, they had another accessory pair next to them of smaller eyes. So Milokmingia, the earliest vertebrates, had four eyes.

• 39:17Speaker 01

  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, to the eyes and the optical centers of the brain. And these are the glands that help us regulate our biorhythms. They produce melatonin and they, they keep our day and night cycle. And 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 Chiang Chiang.

• 40:01Speaker 01

  They weren't armored at all. There had been an idea that there were armored fishes in the Cambrian, but that's been debunked. The problem with the armored fishes in the Cambrian, it 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 steamroller and scattered all the bits, and then you found one bit.

• 40:29Speaker 01

  But of course, these tiny fragments of armor, you could study under a microscope. The problem is they're indistinguishable from arthropod skeletons. So that these fragments that had been attributed to fossil fish were probably some kind of arthropod. So the fish that we see in the Cambrian are unarmored. It was only later in the Ordovician that they became armored.

• 40:56Tristan Hughes?

  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 earliest fish with a clear backbone?

• 41:07Speaker 01

  Uh, yeah, the origin of vertebrates has been a really big problem for a long time because vertebrates are so different from invertebrates in many, many ways. This internal skeleton is very, very unusual. So the the history goes back a long way, and that's another episode, the origin of vertebrates. Oh, yes, let's do that, please. But our closest relatives are things called, believe it or not, sea squirts. These are creatures that live in one place squirting seaweed, a seaweed. They live in one place squirting seawater in an hour.

• 41:44Tristan Hughes?

  Sorry, did I hear, did I write, our closest ancestors?

• 41:46Speaker 01

  Our closest relatives.

• 41:48Tristan Hughes?

  Our closest relatives are sea squirts.

• 41:50Speaker 01

  Yeah.

• 41:51Tristan Hughes?

  Okay.

• 41:52Speaker 01

  Well, these sea squirts have larvae, and these have little heads and tails like taples. And the tails have the notochord in, the notochord is the precursor of the backbone. And they have the muscles on the other side. And then what these things do, they're in their heads, they've just got one eye spot, not four, just one. And all it can do is detect light and dark. And it's got a little gravity sensing organ, 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 resorbs the tail and then balloons out into this giant pharynx.

• 42:35Speaker 01

  That's this giant balloon mouth and stomach, which is the sea squirt. So vertebrates are basically these two things in one. The mobile tail and the the jaws and the viscera 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 the brain and the backbone of the mobile animal, which is represented by the little tadpole larva. And the visceral part, which is the stomach, the intestines, all the squishy mixed grill parts,

• 43:21Speaker 01

  which are represented by the adult tunicae. So it could be that the common ancestor of vertebrates and tunicae was an animal which was motile. And it had a segmented squishy tail and it had a front end with jaws and a pharynx. But then we went our separate ways. Vertebrae have integrated the two, so they're almost seamlessly joined. But tunicae have kind of deconstructed themselves. So the somatic part is the larva and the visceral part is the adult. And on my desk several years ago appeared a paper morphing changjang of something called Vertulicolians.

• 44:04Speaker 01

  And I looked at these and I thought, goodness me, expletive deleted. These look like Rhomosomatico visceral animal. And these Vertulicolians do indeed have a blobby head with little gill gillslets 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 tunicae together. So, and there is another animal called the Amphioxus, which is a a swimmy animal with gillslets. That used to be seen as the closest relative to vertebrates, but now it's been demoted further back because of the of all sorts of genetic things.

• 44:49Speaker 01

  Now, medical scientists loved tunicae 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 Amphioxus doesn't have one. And medical scientists said, really, the tunicae should be closer to vertebrates than they are. But the genetics now reveals that they are. We are closely related to to tunicae. We have many of the same genes, many of the same processes. It's just that tunicae 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.

• 45:38Speaker 02

  If you love a good story, why aren't you listening to Dan Snow's History Hit Podcast? It's a show where we tell you every amazing, crazy and important thing that's ever happened in human history. From the perilous voyages of the first Polynesians, the discoveries of Captain Cook, the deadly Viking raids on Britain and Ireland, the rise and fall of the great English kings and queens. We'll tell you how Waterloo was won, the Alamo was lost, and all the history in between. So make sure you check it out, Dan Snow's History Hit, for the best true stories ever told, wherever you get your podcasts.

• 46:29Tristan Hughes?

  Just to refresh, when you say tunicae, what kind of animal should we be thinking?

• 46:33Speaker 01

  These are the sea squirts.

• 46:34Tristan Hughes?

  These are the sea squirts, I'm sorry.

• 46:36Speaker 01

  But some of them, some of the sea squirts live in, as albatross live in some, one place, some of them float around in huge colonies in the sea. There's some called pyrosomes that had these huge colonies that are kind of made the trumpet shaped. I mean, and divers can swim inside them.

• 46:54Tristan Hughes?

  So they emerged at the time of the Cambrian explosion?

• 46:56Speaker 01

  Yes.

• 46:57Tristan Hughes?

  And they're still visible today?

• 46:58Speaker 01

  Yes, there are fossil tunicae from the Cambrian explosion. But some of the tunicae have evolved to be really, really strange. I mean, they're these tiny ones called larvations, which, 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, the sea. But to do this, they secrete this enormous mucus 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.

• 47:43Speaker 01

  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 earth. 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 this, where they were, you know, fairly big animals and the house was the size of a football. And you can imagine shoals of these. So our nearest relatives, the tunicates, have gone on to be

• 48:26Speaker 01

  an amazingly diverse and weird set of creatures and they go back to the Cambrian explosion as well.

• 48:33Tristan Hughes?

  I'd never heard of them before. I'm just trying to picture, so you've got trilobites on the floor, anomalous caris once in a while hunting. Then you've got these tunicates there. And then at the beginning, you know, the, the first vertebrates, these very, very small fish, maybe in shoals altogether.

• 48:48Speaker 01

  Oh, probably, yes.

• 48:49Tristan Hughes?

  Probably in big shoals of these small earliest fish.

• 48:52Speaker 01

  With four eyes.

• 48:53Tristan Hughes?

  With four eyes. As the Cambrian goes on, millions and millions of years, more and more oxygen. Do these earliest fish, do they get bigger?

• 49:02Speaker 01

  Yes, they do. And they also acquire armour.

• 49:05Tristan Hughes?

  Armour, right. So this is when we get the first armoured fish.

• 49:07Speaker 01

  Yes, now, in the succeeding Ordovician period, from the Ordovician through to the Devonian, there are more and more armoured fish. Mostly these are jawless fish. They, they just had mouths. They didn't have, you know, up and down crunching jaws. Some of them, they had very boxy armoured skeletons. So the front end was pretty much solidly boxed. And the back end had a swishy tail. Sometimes they had fins on each side and sometimes they didn't.

• 49:37Tristan Hughes?

  And do we think this is an evolutionary upgrade to help fend off things like anomalous caris?

• 49:42Speaker 01

  Yes, but also a later arthropods, which were even more.

• 49:48Speaker 01

  Nightmarish. These were called the Euripterids, which were relatives of spiders and scorpions.

• 49:54Tristan Hughes?

  So these are the original scorpions, scorpion kind of.

• 49:56Speaker 01

  And and and these could be, you know, six to eight feet long, enormous googly eyes, and they really did have snapping pincers. And 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 armour to escape the snapping jaws of of Euripterids. 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 hydroxyapatite, and it's the same arm, our bones are made of hydroxyapatite.

• 50:41Speaker 01

  Now, strangely enough, even though vertebrates had the notochord, we we had external armour more like in invertebrates. Only later did the backbone become mineralized. And the armour evolved in various ways. There are some of these fossil fish where the armour is broken up into scales, a kind of chagrin of scales. There are these beautiful little fossil jawless fish called thelodonts, which have all sorts of amazingly stylish shapes. Some of them come from this romantic locality called Moth, which stands for Man on the Hill. It's out in the northwest territories of Canada.

• 51:19Speaker 01

  But jawless fishes are known from all over the place. In fact, they're quite a lot from, quite a lot have been described in in the UK. In the in Wales and the west of England, where there are Ordovician, Silurian, Devonian rocks. You know, the the clues in the name, the Ordovician and Silurian were named after the Roman tribes in Wales and the Devonian is Silurian. So there are a lot from there. And they were escaping predators, but also phosphate is quite rare on earth and it's important in the biology of all animals. So there is an idea that bone was a kind of accessory store of phosphate

• 52:01Speaker 01

  for very active animals, which vertebrates are much more active than most others.

• 52:07Speaker 01

  So that was the origin of bone and fishes. And then at some point in the Silurian jaws were invented.

• 52:14Tristan Hughes?

  So that's jaws. That's almost the next stage in the story, though, because now we're going well past.

• 52:18Speaker 01

  Yeah, we're well past the Cambrian. And that's another episode, the origin of jaws.

• 52:22Tristan Hughes?

  The origin of jaws. And it's not sharks, is it?

• 52:25Speaker 01

  No, no, no.

• 52:26Tristan Hughes?

  Good terms. But let's go back to the Cambrian. So how long shall we say the Cambrian explosion lasts? How long before we do have this real diversity of life that we've covered in this episode today? The first vertebrates, anomalous caris, trilobites and so on.

• 52:44Speaker 01

  Well, when we call the Cambrian explosion an explosion, it's more of a kind of extended detonation.

• 52:51Tristan Hughes?

  It's a more of a difficult title to sell if we call it the Cambrian extended detonation.

• 52:55Speaker 01

  Yes, or the Cambrian slow digestive rumble.

• 52:58Tristan Hughes?

  Right.

• 52:59Speaker 01

  But in terms of geology, it was because that hiatus in the fossil record that so worried Darwin is real. I mean, there was a step change in evolution, partly 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 a time in which almost, in fact, all modern phyla, that is, large categories of animals, appeared in the Cambrian. Except one, but even that's been cleared up now.

• 53:41Tristan Hughes?

  So what's that?

• 53:42Speaker 01

  That's the Bryozoa 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 brassoa and somebody said, no, these aren't brassoa, they're seaweed. And the first lot came up with some more and said, yes, they're brassoa. So, so that's been settled, which is nice.

• 54:08Tristan Hughes?

  So just how rich and teeming in life would the seas, I can say, and the oceans of the earth have been back during the Cambrian? And we should, as is 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?

• 54:32Speaker 01

  Yes, well, the, the difference between land and sea would be quite stark. I mean, there have been some suggestions that some life was ashore in the Cambrian, in fact, before the Cambrian. There are some deposits in North West Scotland, which are a billion years old, which are freshwater 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 Yokelson.

• 55:10Speaker 01

  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 Ediacaran creatures were maybe into tidal, maybe on the beach occasionally.

• 55:47Speaker 01

  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 hundred, hundred and fifty million years after the Cambrian explosion.

• 56:10Tristan Hughes?

  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 terror birds 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, 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 ex, I'm going to use the explosion word again, but you know what I mean, such a diversity of life emerging because of all of these increase in calcium, increase

• 56:49Tristan Hughes?

  in 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.

• 57:04Speaker 01

  I should say, though, that over time biodiversity has increased. Now, that could be because of the pull of the recent, because the more recent the rock, the more of them and so, but it 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, one of the most successful and species-rich groups of animal today are what's called parasitoid wasps. They are tiny, tiny, tiny, and we don't notice them. And they lay their eggs on the larvae, the maggots and the grubs

• 57:48Speaker 01

  and the caterpillars of other insects. And they develop inside the caterpillar or whatever, and eat it from the inside. Sometimes two different parasitoids lay their eggs on the same caterpillar, and the larvae grow up into tiny little soldiers that actually fight wars inside caterpillars. But the

• 58:09Speaker 01

  These things get their just desserts because they're all infected by different kinds of bacteria. And some of these parasitoid wasps have parasitoids that parasitize them called hyper parasitoids. So, you know, big fleas have little fleas and these things go on all around you. In every garden, in every forest, i- in every woodland, even today. A teaspoonful of soil contains an unbelievable richness of life. Life is absolutely everywhere, from the depths of the ocean up into the atmosphere. So the Cambrian is where animal life really had its first flowering.

• 58:51Speaker 01

  But once life gets established, it's very, very hard to get rid of. I mean, there have been, the earth has tried many times to get rid of life and us humans are also having a good go at trying to get rid of a lot of life. But it, it usually bounces back and the amazing interconnections that are formed by creatures that we hardly know exist. I mean, everyone knows about tigers and pandas and rhinos and, and dogs and cats, but these tiny, tiny creatures. Like each fungus has a fungus fly that only lives on that fungus. And each fungus has fungi that grow on the fungi and each of those fungi that grow on the fungi have their own fungi and fungus flies. It's kaleidoscopic, man.

• 59:33Tristan Hughes?

  Could there still be some Cambrian relics out there in the depths of the oceans?

• 59:36Speaker 01

  Well, who knows? I mean, there have been all sorts of changes that have been done. So back in the Cambrian, there were these shellfish-like things called brachyopods, which had two shells. But they were an up and a down shell. There were a, a dorsal and a ventral. They, they're called lampshells because they look like the kind of lamps that Aladdin had. And these were the shellfish type analog. They had a amazing structure inside called the lofo four, beautiful structure that were a Greek lyre. Which was full of gills and that would filter stuff away. And their competitor were bivalves, which also had two shells, but their shells side to side rather than.

• 1:00:19Speaker 01

  And these go back to the Cambrian too, but were always quite rare. But it was only after the end Permian extinction when almost all the brachyopods were wiped out. But there are still brachyopods today and there are some that are quite successful and some are only found in the deep sea. But there are also ancient echinoderms, the starfish and sea urchins and allies also go back to the Cambrian where they had some really, really weird versions, which we haven't had a chance to talk about. And some really ancient type of chondomes have been found in the depths of the deep sea.

• 1:00:56Tristan Hughes?

  Henry, you're teeing up so many more episodes we could do in the future about these weird and wacky animals of the Cambrian and so on. But it just goes to me to say now, it has been a pleasure to see you in person for the first time and to have you on the show.

• 1:01:10Speaker 01

  Well, thank you. As always, it's a great pleasure and it's a lot of fun to be here, actually in person for once. May there be many more.

• 1:01:23Tristan Hughes?

  Well, there you go. There was the one and only Dr. Henry G shining a light on biology's big bang on the Cambrian explosion. I hope you enjoyed the episode. If you want more episodes with Henry on the evolution of life on our very, very, very distant prehistoric past, then you are in luck. We have done episodes with Henry on the origins of life on earth and also several on dinosaurs as well. So we'll put a link to a couple of those episodes in the show notes if you want more of the legend that is Dr. Henry G. In the meantime, thank you so much for listening to this episode of the ancients. If you are enjoying the show, please make sure to follow us on Spotify or wherever you get your podcasts. That really helps us.

• 1:02:08Tristan Hughes?

  You'll be doing us a big favour. If you'd be kind enough to leave us a rating as well, we'd really appreciate that. Don't forget, you can also sign up to History Hit for hundreds of hours of original documentaries with a new release every week. Sign up at historyhit.com/subscribe. That's all from me. I'll see you in the next episode.