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The Cambrian Explosion and the evolutionary origin of animals with Professor Paul Smith

Jun 06, 2021
Welcome everyone and what I want to talk about tonight is the

origin

of

animals

, this event that we call the Cambrian

explosion

and really look at what we mean by that and then focus on one particular location that, as Jack says, um I spent quite a bit of time looking at her as part of my Greenland research, so you'll be familiar with these references to the first animal exhibit now, sadly behind closed doors at Oxford's natural history museum, but luckily that's all. available online and if you want to explore the fossils that I'm going to talk about and the environments that I'm going to talk about in a little more detail, go and take a look at that website that has most of the exposition eh content and I'll repeat that URL at the end of the lecture, so what we're going to talk about tonight is not a new question.
the cambrian explosion and the evolutionary origin of animals with professor paul smith
I would not pretend that it was, in fact, one that Darwin identified when Darwin published On Origin. of species in 1859 in November 1859 just six months before the museum opened in Oxford, he recognized a real difficulty that the fossil record posed for him with his new theory of evolution by natural selection and that is that, as he said, there is another allied difficulty that is much more serious. I alluded to the way in which numbers of species in the same group suddenly appear in the lowest known phosphorous rocks, so what I was trying to say by that was that, strangely, there must be some Evolution missing from the record of Rock if multiple numbers of species of the same group appear at the same time rather than spaced across time and through the rock record, so it was a problem that Darwin was never able to solve in his lifetime and intermittently in his busy sciences. since 1859, but with a real acceleration in the past few decades, a great deal of research effort has been devoted to this question as the

origin

of species, and really, only in the last few years, I think we've started to do something real in ways to understand what the questions are and what are the different answers to those different questions, so if we think about a modern marine ecosystem, if we think about a place of the planet with a great diversity of

animals

, we could think of something like this. a modern crown with many different species of fish very visibly vertebrate animals the groups we belong to but also corals and lurking in those crevices and crypts many other species representing different groups of animals but if we go back before the Cambrian it is very different for the first three billion years of Earth's history a photograph equivalent to what would look something like this is a microbial film growing on a sediment surface and you might be able to see that there are little pustules, these little bumps which are visible and that's where the decomposition gases from the older mats as they rot are pushing against the bottom surface of the map which is methane eh bubbling but there are other bubbles there too one here and that's an oxygen bubble released by photosynthesis, so they are photosynthetic microbial masks created by cyanobacteria or blue-green algae, c As we used to call them, and they're building these movies as the storms tear at that surface. they break flakes out of the sediment and carry them away so it begins to become Rockets beginning to semi-lithify they certainly consolidate in such a way that they can be reworked by current action and that was what marine ecosystems were for the better part of three thousand millions of years until animals came along and changed things really radically and now these kinds of microbial systems are not very common they are present in only a few places in the world you might ask how do we have a picture of a pre

cambrian

ecosystem this is actually a puddle in the english lake district a long term puddle that doesn't dry out and just mimics those environments so we can understand the processes going on yes but if we go to the rock record and take a look at what what the rocks tell us we have similar features so now they are rocks that precamp off the east coast of Greenland at about 74 degrees north on a The island called Ella and these are microbial movies this time they've actually grown into a reef so we can get quite complex structures developed out of microbes and bacteria and if we zoom in that stick is a meter long the stick yellow if we zoom in you can see that in detail what we have is a series of columns of these bacteria competing with each other and like films and growing uh towards sunlight to capture as much sunlight as possible for their photosynthesis so that this is typical of rocks around 800 million years ago and if we zoom out from that scene, what we have here is a pretty complete succession from 800 million years ago to about 450 million years of what we would call the audition, so we pass to the final part of the rian pre-chamber in the Cambrian and Those Distant Hills here are the lower part of the Ore Divide and are tropical limestones almost as far as they go. the view except for this Cliff here and this Cliff here and in those two Cliffs something very different happens that is really significant for our history because in those cliffs we have rocks like these that don't look very limestone at all, they are actually little tills, They're glacial deposits and the red blocks you can see are granites, the gray blocks, um, are slightly limestones, the yellowish blocks are sandstones, they've all been picked up by the glaciers and deposited, so what we're looking at here is a large glacial event similar to the one that occurred in the northern hemisphere up to 10,000 years ago, but if we map these locations outside, they are absolutely global and it is an event that we call, as it says there, Earth snowball and reconstructions of Snowball Earth events, um, it looks something like this, a completely snowy planet.
the cambrian explosion and the evolutionary origin of animals with professor paul smith

More Interesting Facts About,

the cambrian explosion and the evolutionary origin of animals with professor paul smith...

There's a bit of debate about how much open water there is, in fact an article was published this week arguing that there was probably more open water and less glaciation than many people have thought, but for all intents and purposes, the planet it was locked solid for tens of millions of years, it's actually very hard to unlock when you do that. What you have to do or what the planet has to do is wait until enough volcanic heat builds up at the mid-ocean ridges and that gradually builds up enough temperature difference. because like a frozen planet it bounces off all sunlight and so there is very little heat gain from radiation alone so if we look at the geological record of these snowballing Earth events we begin to see an interesting pattern that really ends this very long period of microbial dominance that has lasted for three billion years there are three main events um at the end of the pre-Camorean uh the sturtium from 720 to about 660 million years uh the ma rinoan from 650 at 635 that section of rock I showed you was sturtium with Marino and on top of it and that closeup of The Rock was the marinoan and its global events are really global events um there is a third glacial event the gas gears which is less global but still a really significant glaciation event huh and that's in 5 18. that leaves a gap of only 40 million years huh between the gas gears and the base of the Cambrian and it's in that interval as we've heard in previous lectures interesting things start to happen yes we start to see fossils like these and these are the first evidence of really abundant multicellular life existing in quite complex ecosystems and we've heard Jack Matthews talk about this in the first lecture of the series and then frankie dunn uh talk about them a few lectures ago um and they've been very enigmatic for a long period of time over many decades since their first discovery but now there's more and more evidence that these are actually primitive animals and a One of the lines of evidence comes from Frankie Dunn's work that he talked about a few weeks ago about how these organisms grow and then he related it to the growth patterns of animals alive today and using that technique of Frankly, developmental biology was able to determine uh the most probable position on the

evolutionary

tree for these ediachrons, as we call them um organismos organis multicellular moses from India at the present time um is that they sit at the base of the animal tree and there are other supporting lines of evidence including conserved organic molecules that are beginning to support that hypothesis if we go a little further through the media Cara and during that time of postgascular glaciation then we started to see things like this: these are animal burrows and from their pattern we think they must have been made by uh organisms female-like organisms that have a plane of bilateral symmetry in half body like us so that's most animals except jellyfish and enemies and stuff like that and sponges so some evidence of slightly more advanced animals start to show up as we get further into the end of the edocarium and then as I heard at the last Duncan Murdock lecture right at the end of the idea bandwagon and we started to see evidence of animal s they make shells and they make what we call biominerals that make crystalline inorganic minerals um as part of their metabolism for protection and or um predation so if we put all of that together into a single overview of geologic time this is a pretty old diagram now , but it is still true in its essence that immediately after the gaseous glaciation we get the entrance of the edocarine biota, the idiocarine fauna and and at least some of them are animals, we can be pretty sure that, a few million years before the base of the Cambrian we get the first fossil remains that we think are made by animals and then we start to have animals with skeletons that arrived in the last few million years just before the Camry so you might ask if we have good evidence of animals before the base of the Cambrian.
the cambrian explosion and the evolutionary origin of animals with professor paul smith
What's the big fuss? Why? Is it called the Cambrian

explosion

? What is the Cambrian explosion? It's an event that replaces environments like this. This is a reconstruction that was part of the Martin Lysac exhibition. these primitive animals um sitting on microbial mats still dominated a microbial map um in pretty deep water and are replaced by really pretty dynamic ecosystems at the base of Cambria so we can define the Cambrian explosion a few different ways in green here we have the EB tagged, we have the occurrence of Ed, the educate, and the biota, and they have a reasonable number of attacks from different species, um uh, particularly towards the end of their time range, but then look at that really abrupt Transit, translate the transition to Cambrian Row the animal filter really reflects the highest level of body organization for example our own group is the Cordata um the echinoderms include the sea urchins and starfish and are unified by very um and very similar anatomies at the next level, by classes, we are seeing groups of organisms that are still very different, but for example, sea urchins form a class yeah, the starfish, an earlier class, the vertebrates, our own group forms a class, so while we can think about I mean, think about the number of endings and classes, it's the number of different body plans that are present and what we can see when we cross over into change is a sudden explosion in the number of different body plans that are present, so what is a push in evolution is not the origin of animals but the establishment of many of the body plans that we recognize today when we go down to the beach or when we go to an aquarium and I'll notice that that increase levels off a lot as we go through the Cambrian and into audition and since audition very few new endings or classes have been added to the animal complement, so that's one way of looking at it. the

cambrian

explosion another way is to think of it in terms of ecosystem change so we talked about what martin lysek's reconstruction of the media Face and biota on the left um sitting pre-fife for two million years ago base of the chamber sitting on these microbial mats a largely passive existence there were some who could move across that sediment surface but not many cross the chamber at the limit and as it says here they give it the fancy title the Substrate Agronomic Revolution , what it basically means is that the animals become much more dynamic and the interactions between the animals become much more dynamic, we get organisms that burrow into the sediments and start manipulating the sediment that the animals swim in the water column and these are newly evolved lifestyles that are associated with the Cambrian explosion, another way to look at it is to focus on those trace fossils, those ma burrows and the way organisms interact with sediment, uh, and that's something that Gabriella Mangano, who will talk about later in this lecture series, did in an article a few weeks ago about the number of different trace fossils thatwe get as we go, uh, from down in the, uh, the Precambrian, the crossover into the Cambrian. and look at the number of different trace fossils starting to show up and the way they're starting to modify the substrate they're starting to biologically modify their own habitats and that allows a number of different processes to interact and increases the diversity of organisms that can live in those spaces in another way this is quite a complex diagram but I'll just walk you through the gist of it another way to look at it is in terms of how it differs The ways animals build their skeletons just mentioned and this was what Duncan Murdoch talked about in the last lesson, so here we have geologic time from oldest on the left and the bar at the bottom to youngest on the right and we have an

evolutionary

tree from different groups of animals and sitting sideways um on top of that and the different colored bars represent different types of minerals that animals use and it's a painstaking assemblage of a large data set, but what we can tell from this is that biomineralization skeletal creation happened several different times Group B different groups chose different minerals in an evolutionary sense some chose calcite like starfish some like us they chose calcium phosphate and appetite some like sponges um chose silica very few groups of animals once they have made that evolutionary choice they redo that choice it becomes part of their developmental biology and so if organisms start to make their skeletons out of appetite they continue to make it out of appetite and in fact we can further break it down into different types of calcites also different types of calcium carbonate um and one of the other points is that evidence of tissue use hard skeletons for predation appears at more or less exactly the same time as for protection, so it is a coevolution, it's an evolutionary arms race between, um, hard tissues that evolve for predation and hard tissues that evolve for protection, so that's another way of looking at the Cambrian explosion and these are all equally valid ways of defining the explosion from the Cambrian; more recently people have started to think not in terms of individual aspects but really looking at a unified interdisciplinary approach and again this is from Rachel Wood who will be speaking later in the lecture series and what she has done with Phil Donahue and other co-authors is trying to piece together different data sets to look at patterns and processes at the base of the Cambrian the base of Fanner Thanos Zoe because it says here upper left linear protozoan so what you're trying to do here is unite, um, the evidence that we have from the genes on the left, um, the information is about three evolutionary is and um about the timing of the origins of the groups with geochemical evidence in the Middle with the sedimentary evidence the excavation evidence um indicated by the biothermation index with fossil evidence the largest and most exceptionally preserved fossils and if we start looking at the interaction of all those processes, it is likely that May we understand much better the dynamics of the Cambrian explosion.
the cambrian explosion and the evolutionary origin of animals with professor paul smith
This is something Dave Harper and I tried to do a few years ago and then in the green boxes we have uh biological processes in the blue boxes we have geochemical processes and in the red boxes we have geological processes and even though it's a very complex diagram what it indicates is that all of these processes are interacting and they're interacting by what we call feedback loops where the process goes round and round and starts to amplify the signal so this is another way of these interacting processes of looking at the camarina explosion how c and we get evidence for all this, what are the lines of evidence?
Well, one of the key tools that we have is that we're very fortunate in the Cambrian to have many exceptionally preserved fossil localities, and that's really the thing. from the first animal exhibit we call them lagostatin the same word that stands for lager beer storage and preservation um there are many locations and i've picked out a few of the key ones here um we'll be hearing about the Derrick Briggs burger in a few weeks and about the Chang Jiang, who is also part of the expo, also in a few weeks, but what I want to do is focus today on the lesser-known of these larger statins, the serious liability, huh. greenland biota this is a picture of the locality an exquisitely beautiful place on the north coast of greenland um discovered about the same time as the changing biota but much less known because people have been able to vis it is much less frequent and becomes much less materially noisy now i want to spend a little time talking about where is the Discovery um and how we amassed knowledge about the serious aesthetics of the record many people will be familiar with the story of the discovery of uh or at least the apocryphal story uh of the discovery of the outstanding reserve deposit Burgess Shale uh when a geologists horse Charles Dooley Walcott's horse stumbled and found the fossils and tracked them up the hill and founded I can't see where they came from um serious state discovery isn't that romantic but it's a story that worth looking at this is where the town is right on the northern tip of Greenland, practically e ain't no land further north than serious passages a little bit of Greenland and uh the smallest bit of Canada on the north shore of Ellesmere Island um but the rest is just the frozen arctic ocean right on the way to the North Pole, we're approaching that a bit of land in the far north of Greenland um it's hard to understand the scale actually the locality is around here this is a serious passerby indicated by the uh the red dot um the closest human habitation is a Nord hideout right on the east coast that's a weather station and it's actually 400 kilometers away, so those are the closest humans.
There's an alert on Ellesmere Island which is about the same distance away and then going north. The North Pole is about twice that distance. Leaving from the top of the diagram. the red dot on the left the red dot on the right is about 500 miles from the North Pole the serious passive locality is situated in the largest national park in the world and the next slide gives you an idea of ​​the scale of the terrain we're looking at , so North East Greenland National Park is a little over 970 000 square kilometers it occupies the red area deal hard to imagine of course what 970 000 square kilometers ters looks like but if I were to tell you that that red area is equivalent to the area of ​​france plus germany plus the netherlands plus belgium that gives you an idea of ​​the scale of the North East Greenland National Park um and is relatively recently explored early exploration um was summed up by louder um in a beautiful series of maps in 1940 and he looked at the survey of north Greenland and this was his summary of um the total knowledge of the north coast of Greenland you will see that the coasts were beginning to emerge at this point probably only 10 people had ever been to this locality uh surveying and mapping it of course there were many indigenous people who had passed through this area in earlier stages but the map was just beginning to come together in 1914, you'll see our Red Dot sits smack dab in the middle of a blank piece of land and it was only with the advent of aerial photography and then satellite imagery that I really began to get detailed maps of this area.
These two gentlemen found the serious pass in the fossils and were found during the systematic geological survey of North Greenland which I was fortunate to be a part of right after my PhD um Tony Higgins a British geologist but based for most of his career at the Greenland Geological Survey in Copenhagen a structural geologist but with a really encyclopedic knowledge of geology so happy doing basin analysis and sedimentology as I was doing structural geology Maps and was working with Jack Super who is very well known in the climbing community In rock. Basically, he was one of the founders of modern rock climbing, but also, in the 1960s, he was part of one of the last great heroic sledge surveys. sledge expeditions around the north coast of greenland making a geological map as they went along and they were working together and over the radio one afternoon in july 1984. we heard they got really excited saying they found fossils and they had found a lot of trilobites and a bunch of grass we tried to figure out what the grass bunch could be in fossil terms it definitely wasn't a bunch of grass that actually turned out to be a sponge um and then Jack came back the next season in 1985 and collected some bulk samples and on the back of those bulk samples sorry Tony came back in 1995 and on the back of the samples uh John peeling in Copenhagen one of the paleontologists in the survey agreed at that time they recognized soft body fossils fossils with soft tissue preserved in a style similar to the Burgess Shale and this led John Peel to raise the money for an expedition to going to collect the serious pass locality for the first time and that expedition took place in 1989 and I was part of that expedition there was a little logistical challenge the geological server is mapping a thousand kilometers further south on the east coast so we're really stretched in terms of logistics, we knew there was a little airstrip here, but the town is, as you can see from the red dot, it's 25 kilometers away, so if we could just land on that brain. airstrip we would have to carry all the equipment 25 kilometers through what became known as serious passes which were unnamed at the time um and then all the fossils all the way back so we were very interested in find a workaround um and that's where the icelandic pilots of the two otter short takeoff and landing aircraft really came into their own because we removed all the equipment in the brainfire and then looked for a location where we could get the twin otter down with the equipment um and we circled we circled we circled uh the pilot would go into a likely looking strip and hit the wheels to see if it would support the weight of the aircraft when it was at La Discover put the engines back spiral around spiral around hitting a one of the most nauseating experiences of my life and in the end they told us to hold on um and they landed the plane and it literally stopped in 50 meters ah now normally um yes we are working in these remote areas.
The ideal solution, like the one we had last summer, was to work with helicopters, but this time we only had the Twin Otter plane to support us, which meant we had to get in and out using the Twinata plane. and the place where the icelandic pilots managed to land was right on the edge of where these things can land now, you might think this is a cleverly posed photograph, like you're holding the camera at a tricky angle, but if you look, the pilot is standing perfectly upright and it's the plane that's a little lopsided leaning to the right Landing at an upward angle um they managed to get us down but it became clear to us there was no way they could land there again and take us with all the rock so one One of the upcoming challenges is that not only do we have to find the town, but we also had to build an airstrip before we could get out again, and the town menu was somewhere in those Hills in the far distance, but um, it was pre-GPS days and we didn't have an extremely accurate fix of where it was, so the plane dropped us off with all our gear about a ton of team and here is John Peel, who raised the money and led the expedition. waving funny goodbye um and then we had to take all our gear to a camp where we could build an airstrip yeah this was the photograph of the team and the team for this first exploration um it was john peel on the left then from the Geological Survey Greenland but um later uppsala university in the white coat Simon Conway Morris Cambridge University um in the middle the next to Simon Paul Schiller um who at the time was also with the Greenland Geological Survey but but then he went to work for the New Zealand Geological Survey and then me on the right and that's about a ton of equipment around us that we had to cross uh into the uh location before they could be picked up so this is an indication of the terrain the location it's very easy to spot in aerial photographs um it's this black and white white stripe on the right hand side um that you can see there and the plane landed It doesn't look very far it's only five or six kilometers huh but you'll notice there's a very substantial um river that runs down between the two and builds this big delta here um and a lot of water spills over and melts the ice um in the field, so then we had toNavigating the river is not insubstantial, particularly in the middle of the day when the melt is at its highest and that is a very perplexing Hands in Pockets.
I wonder how the hell we were going to get across. John Peale had come up with a fantastic plan to build what he called a tundra some wagons we set them up uh they broke down and we were able to put them together quickly um and it turned out they were a good way to cross terrain they're not ideal for crossing big rivers um so the only way to doing it was basically heavy, we spent a whole day, my notebook says we spent eight hours of continuous work to move the camp 200 meters and really it was absolutely exhausting work because once we got to the other side of the river, we had to get up the hill on the left side in those carts once we were on top of there it was relatively easy going and within a few days we were able to find a nice horizontal campsite huh that's the first of the carts we crawled over and then we were able to go and eagerly search for the serious passive locality on the hill above So This Is Us on the first morning walking up the hill in the vague direction of the locality that Tony Higgins has described for us not knowing exactly where to look and just combing the screws we look for any fossil and it turns out that the first fossil we found is one of the most iconic serious fossils as we were walking across a screen we noticed this particular specimen and now we know what it is a very primitive mollusk but a very unusual moss has a shell on each end and these um calcium carbonate spicules that cover the body so it's a slug-like animal um maybe two or two inches long and it was really the sign that we had tuned into the town huh and this was the town in 1989 a really snowy place uh working under this overhanging ledge that kept breaking off um and a pretty cold place to work too and couldn't look more different these days um, that's us trudging to the locality, um, a little later in the Expedition, and the locality is here, um, in e This hill, um, but you can see that this isn't just temporary. there is a recent snow storm in this picture but most of it is seasonal snow without melting and now the town looks like this it's covered in grass um the snow is pretty much gone there's pretty much no permanent snow that i can see uh for the jacob winter scale university bris tol they're just starting to transport some fossils there um so 20 years of rapid polar melting climate change has really changed serious cancer beyond recognition but it was an expedition pretty cold and snowy um and that meant a lot of time sitting in the tent um so again the Expedition team pumped the cello John peeled me off and Simon Conway Morrison noticed the old Greenland hands on the end of the tent she a has the candle B has the bottle of whiskey and then when the weather cleared up there was still the little matter of building a track so we could get out of there before winter set in, so one of the The least likely entries on my CV is Runway Construction Airstrip Construction, but that really opened up the town for future visits because now, um, we had a camp with a good water supply we had an airstrip right next to the camp um and it was a couple of kilometers walk and 400 meters of ascent um to the next location absolutely the location and this is the runway to a few years ago, ready to receive a door to door service from twin otters, more or less landing at the top top of the shop and picking up our Gear Up the next time I was able to go up was in 2009 in the meantime John Peale and Simon Conway Morris came back um in 1991 and 1994 and then um another short trip in 2006 and we went up in 2009 and in 2011 and a South Korean team with Jacob Winter and the University of Copenhagen were in 2016-17 so but Still only eight short trips to the Sirius pass so we don't know it as well as the other e largest stage of the Cambrian, so some geology back to some geology, we took a systematic approach in 2000 and 6 and 2009 that has been carried out. in later Expeditions there had been a mythology that you could only find the fossils on the screen, which isn't true, they are just as plentiful, but it's a bit harder to get out of solid rock, so while Jacob Vincent on the right um exceptionally looking to preserve fossils uh Emma ham on the left our geochemist from the University of London in 2011 is recording a section with me and as we build the sedimentary record she is collecting the geochemical samples that will be critical to our understanding of the environment in which lived serious animals and we'll get to and then once the section was searched it was basically rock breaking chain gang stuff um and this is the main expedition in 2011 Emma hamaland left Martin Stein in a Toyota Nielsen head down in the blue jacket and yelling at Rasmus and Jacob Valor and Dave Harper recording the notes and around the corner sitting on the step naughty uh Jacob came so it was a great team which meant we could make a lot of progress and and it really starts to tear um the passive locality would be both in terms of its fossils and in terms of its paleo and environments this just gives you an idea field work, but we can still take you.
Relatively small rock volumes because we are bounded by twin octopals. So what fossils occurred in a serious step? This is, in a way, one of my favorites because it is emblematic of the serious passive. of the serious personality um but of the soft bodied organisms that have real details in their anatomy uh arthro aspis here with a 20 centimeter notebook for scale um is it maybe uh really implemented uh and this is just a composite plate from the range of organisms um this is the trilobite bow and eye of ellis higgins uh named after tony higgins who discovered the locality these are the sponges um that were probably the pile of grass um and what i want to do is just take it through some of the faunal components, um, to give you an idea, it says there are 45 species and counting, but one of the tricks paleontologists use is to create what's called a collector curve and see whether you're starting to load yet you're collecting but you're not finding new species um and we're still at the point where we're finding new species so there's more to come out serious passive that's for sure it's not just that it's a foreign locality may not be as diverse as berger shell and xinjiang but certainly more diverse than fortified species huh this is a reconstruction first of all helkeria just to show you you know how slug it is with this armored top surface um and this foot on the bottom surface mouth to the right um and we'll see where it lived and how it was doing uh uh how we're getting its nutrition in a moment, one of the other common fossils of the fossils with a subbody.
When we used to talk about soft-bodied fossils, we mean those that do not have skeletons. mineralized skeletons. They are what we call logopods. They are more closely related. a periputus The velvet worms of today um a and on the left and on the right we have two of the different um Wolf pod Generas and species and we have been able to add more detail to um Kerry Michaela from the material we collected on the recent expedition which allowed a review anatomical reconstruction that you can see here that we published in Nature Communications a couple of years ago um of course one of the most imagined organisms that you see in both the shale bird and xinjiang are the anomalocarates here Illustrated with legania and these these were the apex predators of the Cambrian seas that grew up to three feet two meters long um with this radial mouth belong to a group called radiodons um and these appendages uh stuffing food into their mouths but but but not all anomalocodes were ferocious and the one that Jacob and his colleagues at Sirius Passa describe to us is actually very different in terms of their mode of feeding and you will see on the left rda that it has these feathery appendages that t stick out uh the main arm of the appendage um and that this appendage could flex and coil uh and the Reconstruction uh what Jacob and his colleagues thought most appropriate was that he's actually using them as a sieve mobile and that tamizia Caris was actually, the Cambrian equivalent of a bailing whale that was floating these giant energies through the water, filtering out plankton and stuffing them back into its mouth and then swimming along with um, we have some of the other characteristic organisms of a serious person it was big and multimeter long and gigantism is something we see in the serious past in other Cambrian localities um this is a thing called cyrilorica uh described by John Peale um it's closest are the closest living relatives we we'll be familiar with are things like nematode worms huh it starts to belong to a group called Lorry suffers um but the big difference actually is ad is they're tiny if you look at this scale bar down here try again uh scale bar down here that's 25 microns um 25,000 of a millimeter uh while cyrilorica is tens of centimeters long so um the representative of the Cambrian although anatomically really very similar it is orders of magnitude larger than the group that was swimming alongside timotyocaris is the group I am perhaps most interested in seriously veterans but there is much debate as to which is the most closely related here we have on the left we have a species that Jacob Dave Harper and I described in 2011 and it's a very distinctive veterinarian we have these these gill slits that open up the side we have a big mouth that opens up a big mouth so we think the water was coming in through the mouth and then out these slits, but at the back of that chamber, um, there's a tail that we can see that's segmented and capable of to flex so we think it was able to free swim like the esmond horn model in 10 terms indicates ates on the right and here for comparison is an example of chenjang so this is where the first described vegetables and you can see very clearly here that we're all opening up, um, since these slits have been flattened on the left and here are the gill slits where the water would come out, so this thing was sucking up large volumes of water again, it was filter feeding, um, and it was almost certainly pulling the food out of the water on the cilia of the fine hairs that line those.
The gills open on the side but propel themselves through the water column huh for maximum volume of water and food uh in that chamber that opens the chamber um yeah we reconstruct it and again this is one of Martin Luther's reconstructions of a chenjang fossil uh this is what some protection would look like ection at the opening, so the mouth and the right so I can close it off and protect it, but to feed it I would open those, um, and then the gill opens up the side and the mobile tail um the website for the exhibition also has some lovely animations um especially curly uh and swimming and feeding and these are actually quite plentiful they are present in fairly large numbers um they have not been found uh in the first few Expeditions but uh once you get a search pattern in your eye they are often quite broken down um, and now we have many hundreds and we're in the process of writing them down and describing them, so where did all these animals live?
What is the environmental setting that we were trying to understand through that sedimentary record and geochemical sampling, well this is a simplified geological map of northern Greenland, the serious locality is in JP cop Fjord, which is, um, it's here , you can ignore the red box which has a different purpose but the key point to take a message from this summarized geological diagram is that we can divide the geology into two parts we have the pale blue rocks to the south now those are the audition from the Cambrian and Siluri a continental shelf of shallow marine deposits deposits mainly limestones and is deposited for the most part to a few tens of meters depth of water, but then we cross the edge of the continental margin onto the continental slope into much deeper waters. fairly steeply into deeper water and there, um, we get mostly fine grained sediment deposition and some sediment that spill from the edge of the plant make such serious passes that they are practically at the limit between the continental shelf and the continental slope or as it says in this diagram the shelf and the channel if we draw a cross section uh more or less parallel to the east side of that red box looks like this so now we have a vertical cross section through the earth's crust and through the sedimentary deposits um and serious passive meet here so it's right on that Fletcher as as we move from the horizontal continental margin on the left to the deep water on the right um and you'll see on the left it indicates that there are sandstones there are continental shelf sandstones similar to depositors in the North Sea and west ofthe present day British Isles then we go into finer and finer deposits as we move out of the range of the sediment supply and down into mudstones and serious passive locality I actually drew this Arrow too high sits just above that boundary that transition boundary and that we can see there so it's at a transition point um and a point of change in sediment supply is the first thing we can conclude if we zoom in and look at the geological map that we made um you can see that point emphasized so in pale blue we have the oldest rocks the serious passive is sitting in the serious passerby locality is actually within a geologic unit called The Boon formation and the torus information itself changes radically as which runs over the edge of the continental shelf, so to the south, um, in yellow, we have the typical shelf sandstones that we saw in the last diagram; in the north, in pale green, um, we have the channel shales, um, and in the two darker shades of green, um, we have the Transitional Boon, as it's sometimes called um, which is where it's found The passive locality would be and it's all been a bit compressed because it's been crumpled by subsequent geological activity, but we can still unravel um really quite easily that original reservoir replacement ratio which is much harder to do with any other Camry in the counties. , so we have a lot more sedimentary information and paleoenvironmental information to play with. so the minerals have started to change, but we can still do the sedimentology.
This is the town facing east again. We have these Bowen platform sandstones at B on the right. I have the older portfield limestones which is what all settles in the locality is this black and white strip here um then we have the transition rocks um of the Shelf Slope Breaky then we come out into what is called the Frig Fjord mud Stones which are the stones of the months of the canal. If we zoom in on the locality itself, this is what it looks like, so this is the serious passive locality. here, the small quarry that has been opened to extract the fossils and measure the sedimentary section, these arrows here are actually young arrows and the v in the young direction, so in the white rocks they are young up, that's like would you do it. expecting the rocks to be the serious passive locality is actually backwards, it has been inverted by this later geological activity, but we can still read the rocks quite easily and this is what the locality looked like on that first trip before we started to dig into it so we can see the rib of the more fossiliferous material coming down the hill towards Simon Conway Morrison in the blue jacket um and if we get closer to that sediment it looks something like this it's pretty imperceptible uids as they settle it's stones very thin dark gray to black mud, but one of the really distinctive things is that they are coated in these yellow powders and these are iron oxides and hydroxides that are the result of oxidation. of pyrid iron sulfide and that's a really key part of our story so we put all of that together in a sedimentary record it looks like this it's a very thin section and the fossiliferous section is even thinner so you can see which in the Darkest browns are mudstones huh, going through the palace Brown Siltstones through intermediate silty mudstones and muddy siltstones it has for those of us who do sedimentary logs this is so boring as it gets frankly but really informative in terms of environments you'll see on the label that I've mentioned that there are abundant microbial mats and that's a key feature of the locality in red we have the horizons from which the soft tissues are recovered um and in yellow we have where these oxidized sediments are these yellow powders and on the far right, um, we have the sediment look like we just saw, but then e n the bottom right, a thin section through one of these individual shale layers and you'll see that it's a black and white stripe, but from where my pen is now to here, it goes from black to a sharp base, black gradations white gradually to black and what that tells us geologically is that these are quartz grains and those quartz grains are progressively replaced by mud so in other words we would say this is being refined upwards and that's indicative that geologists are slowing the currents.
We interpret this as the result of silts of sediments traversing the continental shelf, perhaps being uplifted by storms and depositing these very thin millimeter-thick horizons, but also carrying animals with them, so that leads us to a distinction in the Fossils we found in serious liabilities. we can identify, as I mentioned, the microbial mats and these are easily recognized by the fact that we can see burrows that run parallel to the map, so the horizontal burrows appear and go down through the mats, um and if they go under the mats lift up the mat like, uh, Jerry Wood in a Tom and Jerry cartoon, but then if they show up on the matte surface, they make slits so you can see this is a positive relief burrow, this is a negative relief office um and that's it and we can see the transition from one side to the other as we go so we follow the burial tracks um they often occur around uh fossils they seem to invade any decaying organic matter you might see in this image um segmentation this is one of those large osteoarthritis arthropods that I showed you a few slides ago now living on those microbial mats there is a very distinctive fauna that we call the guild of the microbial mats so top right we have one of these distinctive arthrospice b being extracted for its nutrients by these burrows the worms making these burrows um we have policky worms that live in the burrows they don't burrow in it there is no vertical elaboration here we have one of the arthro aspers in the middle a halcoria almost certainly skimming on that microbial mat top left and then a sponge sitting and filter feeding on the mat uh bottom left so that's what we call the microbial map gills and they're preserved at the base of these small storm layers below the sediment course they are suffocated they are killed by the ingress of these sediment columns um from the storms within the thin layers of sediment carried by the storms are the remainder of what we might call the typical fauna of the Cambrian we have phenomenal fragments nominal calories and the tunisian carus that we mentioned s we have um free-swimming policky annelids we have professional free-swimming vegetarians but it's also tearing up burrows um as well and some things that live on the surface so these are preserved in a much more typical shale type bird kind of way than things that live on the mats that tend to be more conserved in three foreign dimensions we can link that conservation to geochemistry and this is quite a complex diagram but I just want to focus on the one with this column on the left um next to the sedimentary record so that by looking at a number of deposits a technique has been developed to calibrate um what is the fehr called highly reactive iron to fet Total iron ratio so iron in sediments occurs in many different forms but the highly reactive form Iron is the reactive ion that occurs in oxides, hydroxides, and sulfides, now that it is used as an indicator of oxygenation. n of the water column.
If the fehr fet ratio is more than 0.38 we can say that that column of water where the sediment is is effectively without oxygen it is what we would call anoxic between 0.2 and 0.38 it is very low in oxygen eh we would say that it is hypoxic or dysoxic, you will see both terms on the slides that appear um and you'll see that the fauna that lives there and is transported a short distance we don't think any of the Fallen are traveling very far um it's quite frequent um within that low oxygen range and the low oxygen ranges are indicated by these horizontal rules, so how does that compare to the distribution of fossils?
Well actually if we open up that diagram and look at the abundance of fossils and the diversity in red, so this column here the abundance and in red the diversity and also the representation of the most common fossils in terms of the number of um of specimens that we found finding per unit area of ​​rock and you can see that the maximum fossil abundances um are coincident with the anoxic periods now you could say Well they're just being preserved because of that that's partly true but we also have good evidence that they are living there, so these organisms live with little oxygen. environments don't know it's not a big surprise because Emma Hamilton has also been looking at the changan deposit in china and the change looks like a beautiful beige limestone but actually the wells have shown it to be sedimentary almost identical logically to the serious facet what is these thin layers of stone um and the fehr Fe tote fet um the plots look almost identical to a serious person these organisms live and are preserved in low oxygen environments very low oxygen if you look at modern oceans um that's it pretty similar to the type of situation we find in what are called oxygen minimum results, they also occur at the edge of the continental shelves, oxygen is then trained in the seawater, in the photic zone, it's being produced by photosynthesis , has also been hit by wave action, but as we get out of the Turn on the depth to which the zone the lines can penetrate through photosynthesis in the photic zone stops and that means that the animals are only consuming oxygen. n respiration does not generate new oxygen and that results in a collapse in oxygen levels, but we still see a very characteristic fauna, as it says on the left, they occupy the margins of the oxygen minimum zones, they are frequently fairly dense aggregations. yes pretty abundant organisms but they have low diversity so they are opportunists that can survive there when not many other organisms can but they span a wide variety of different groups and we think this is not a bad model actually for the uh one comparison uh with what we are finding a serious person and that is quite contrary to a lot of previous ideas uh where people speculated that actually an increase in oxygenation of the oceans was what caused the chamber to explode and now we are starting uh to find evidence that actually the opposite is true that early animals are preferentially located in terms of their diversity, um, in low-oxygen environments and Emma has explained in this recent article that that shouldn't come as much of a surprise to us, we actually look at oxygenation from the perspective of successful oxygen-dependent terrestrial organisms, but in reality, a large part of the R eino Animal lives in much lower oxygen levels Marginal oxygenated levels um and as Emma says to the left she calls this the normal world and she's actually dealing with oxygen in many ways is what is challenging and then she refers Since the low-oxygen world has been an ancestral Niche and what we're used to is actually the Conquered Niche then we shouldn't be too surprised that early animals thrived on low oxygen levels, you know, we know, for example, that tumor cells in cancers can withstand very low levels of oxygen and still thrive, one of the tools that people have sought. to try to cure cancers is to deprive cancer cells of their oxygen, but in reality it turns out that they can withstand very low levels of oxygen, so perhaps we should reverse our thinking of animals and think of mo as the norm they evolved low in oxygen so in the last few slides we can put all of that together in a setting where the serious passive locality is indicated by the red star it's right at the limit of of um where sediment transport in these storms would reach , so we have shelf storms that increased considerably um exaggerated gradient um shelf storms Sandy kicking up sediment flows through a very gentle slope below the base of the storm wave into that oxygenated zone that buries our microbial mats that preserve our organisms serious um just off the shelf slope breaking abroad so if we look at what is was driving Cambrian Evolution and the Cambrian Explosion, we can be more or less sure that it wasn't oxygen because if it was oxygen that was held the key control will be on the inside shelf where there was a higher level of oxygen and yet, what we have is the sediment from the organisms that live here and are transported a short distance in that locality, so they are, as we've seen a pretty low oxygen um environment, if they were driven mostly by um supply of nutrients, they will also be further in, they will be within the photic zone where the maximum nutrients are somespecialists, some vertical burrowers called skeletonus um that live in um, the zoning of shallow water in this time interval where we've seen what was Scotland, for example, but one of the things that could be controlling where these early dwell organisms uh it's substrate mobility, it could be that they really weren't very tolerant of mobile substrates that would be moved by currents and sitting on microbial mats, um, like almost the more stable foreign and other larger substrains from the Cambrian. others exceptionally preserve Cambrian deposits as organisms that lived in deep, dark, and rather foul-smelling waters, rather than the crystalline tropical waters seen in some reconstructions and this rat. your nice Martin Lysette art diagram for the show I think characterizes this for Chang Jiang but this is pretty much the setting I envision for a serious bottom as well and I'll leave it at that thank you very much for listening thank you very much Paul for wonderful wonderful tour keep on chatting and we'll try to get as many answers as we can before we move on to that just a reminder that you can find and all of our previous chats and actually pulsar will be available in the next week or so on the museum's YouTube channel.
I just put a link in the chat right now and just a reminder that if you enjoyed tonight's talk then feel free to share that online. share the link with friends and family that you think might also be interested and then at that point we'll quickly switch to that because we're so happy to say that we've got our calendar sorted for the next few months so our next chat in two weeks time is going to be Professor Sarah Gabbert from the University of Leicester who will talk about some wonderful research she has done on experimental decay and what this tells us about fossil preservation and the link to sign up is now live and I just popped that for you, then two weeks later we have Professor Shuhai Zhao from Virginia Tech.
Two weeks later Professor Derek Briggs from Yale, we have a parade of

professor

s for you and then as Paul said in September . the ninth um Professor Gabriella Mangano from the University of Saskatchewan in Canada will be joining us and to finish it off on September 23rd we have Professor Rachel Wood from the University of Edinburgh again you get a little taste for what I could talk about one of the slides tonight, but write them down in your journal and as we get more details from our speakers we'll put some registration details on the website and of course share them in other talks and just before begin to answer some of your many questions, just a reminder that we love to get some feedback and would be especially uh pleased to hear your thoughts on this question has this lecture changed your view on the evolutionary origin of animals or been added to your understanding of the topic if so how and if you have any thoughts on that please blow it up in the chat but At this point let's move on to some questions and I thought that we'd start with some lovely questions about your fieldwork because it was a lovely insight into how fieldwork happens in these very challenging areas, so we had some let's group them all questions. together um or let's do them in two sorry uh first we have a question from Morrison how the transition from snow to grass due to global warming in May has made it easier or harder to find the fossils you are looking for and Margaret does a really good one he asks, he wonders if any of the indigenous people had stories or understanding of the locals, in terms of ease of finding, I guess that's what we would say, swings and roundabouts, you win. some you lose some so my overwhelming recollection of the first expedition was and the first Expeditions at the time were sitting in slightly cloudy conditions um really quite cold I couldn't feel your fingers but when you're looking for fossils in a serious pattern the good light is really critical um and on recent Expeditions it might seem but we have had much better light the downside is the increased grass and increased humidity has resulted in a lot of mosquitoes which we never used to have in that part from northern Greenland, um and there are days where, as an old arctic exploration said, um, story I was reading a few days ago, um, the only way you could fit more mosquitoes into a cubic meter would be if the mosquitoes they were smaller huh and that can be a little off putting at times but overall uh steady sunny weather like this Photograph would be my go to there any time I want to say they are still s It's only four degrees maybe but it's great weather to sit and company collecting fossils all day um in terms of the indigenous people there haven't been any indigenous people this far north for quite some time there are some uh archeological remains of paleo settlements Inuit were probably transient settlements um scattered along the coast they probably never got very far inland because that's not where the food was um but I'm not aware of any indigenous accounts of geology or super and get on with the fieldwork uh three more questions uh shawshark Laura wants to know if you have to worry about polar bears um Morrison wants to know how do you check or protect those specimens and if you have to worry about the cold um you know and transportation and then William asks us about these fossils this expedition at oxford museum take last first um yeah some are being studied so there are some in my office ina the The Bachelor Collins I mentioned and some were on display as part of the first animals and I You can see on the website of the exhibition the main collections of serious fossils are in Copenhagen at the national museum of natural history there but in They are actually only kept in custody because the ultimate goal is to get them back to a museum in Greenland in the prime of time huh so all the material we collected belongs to the geology of Greenland and the people of Greenland in the government um and that's where the material will come back and that's where it should remind me of the other questions again Jack so the other questions were how do you protect the specimens for transport and do you have to worry about the cold and Laura wants to know if you have to worry because of the polar bears, yes, so in terms of protecting them from the cold, that's not a big problem, but the problem is that they are reasonably fragile, so We pack them very carefully, either by wrapping them in cloth and cardboard.
John Peeler. the really cool system of taking a flat pack of cardboard boxes and rolls of foam um and then we'd just put a layer of foam a layer of fossils a layer of foam and then we'd fill the box and pack it well and you could kind of kick those on the runway and the fossils won't be disturbed um in terms of polar bears we haven't been worried about polar bears but they live there um I've seen them on the ice at JP cockfield that for you uh deep down huh from a helicopter which is a one of the best ways to see polar bears but we carry big big big color guns for huh caliber rifles with us and keep them in stores at all times in case we're disturbed more recently it's been wolves actually , wolves have started to become more plentiful in north greenland and there is a pretty active pack in serious passive but they keep out of our way they are pretty shy for the most part and on some questions about some particular specimens and the fossils themselves, we'll start with a question, my Jiang, which asks how curiously two shell-like segments suggest a close affinity to brachiopods or bivalves or whether the resemblance is superficial only, so it is in largely superficial when Simon first looked at him. that first specimen came up with the charming hypothesis that it was the missing link between brachiopods, amyloid worms and mollusks, we now know that they sit in very different parts of the animal evolutionary tree, but Jacob Winter's work as part of when i was a student actually a masters student proved that uh halkira is a primitive mollusk so the way it grows its shell is analogous to the way clams or bivalves make their shell um so the two shells end it are more similar to bivalve shells but they have all these spicules in the middle that are part of this arm and these sclerites as we call them arm parts and Joe botting wants to k Now how similar are the assemblies from one bed to another?
Well, Joe botting, the Sirius sponge expert, the man who posted about the Sirius passage sponges, uh, so it's not a completely naive question. Joe, thanks. sampled at 10 centimeter intervals across the entire Section just so we could do that census um and it's the same set of species um but but when it's um when it's a particularly high diversity interval, you only get the rarest elements that they go in, so there's not much, there's no particular gradation in the fauna of bottom-up questions and a nice open-ended question from Marc Jacobs who wants to know what your favorite find was.
I guess it would have to be Halkyria. I didn't say that during the conference, but um. I'm kind of stumbled upon it and so to pick that up and realize you know we found the locality and we found a pretty interesting fossil at the same time um but I think it's one of the best fossil discovery moments I've ever had. my career, actually, we always like to hear about favorite fossils or favorite areas of geology, moving on to some questions about trace fossils, um, I'll put two questions together here, um, Frederick would like to know. How can you tell that something is bilateral from its burrow shape? and Denver asks if the evidence for animals through trace fossils in the ediacran is still valid um since Mariotti et al have shown that microbial mats can form such tracts which are assumed to be made by animals yes that that was a very interesting article, um, I think it's one of those cases where you know exceptional claims require exceptional evidence and it's tempting to JUMP, um, into older deposits on your car and deposits and claim that things are done by animals I think there are undoubted um horizontal Burrows in Karen's latest idea that we would all be very happy with um and if Frankie were to speak now I would say I think there is some evidence that um in at least part of that idiot car and biota was able to move and disturb the substrate as well um so yeah I think from my perspective there is definitely good evidence for Burrows there is good evidence for districts in higher education u m in terms of the bilateral symmetry is the pattern of sinuosity and the fact that the city can deflect it um that kind of digging really depends on peristalsis the actions of swallowing we push a bolus of food down our throat which is peristalsis um and it's peristalsis that it's only possessed by bilaterally symmetrical organisms that allows for burrowing of that sort is also probably for what it's worth that allows for that primitive swimming that we see in some groups as well um so it's the evolution of peristaltic muscle movements is actually a key innovation in animals and Sid off asks a question about how we can calculate the age of the fossil, so I'm going to be a little more specific about how we know the age of the fossil.
The fossils in the Cirrus Passage, oh, that's a very, very good question, a very good one, and it's taken us a long time. It's much easier to describe a good soft-bodied fossil than to try to calculate the age. Biostratigraphy is difficult. um that's partly because we can't use precise arcs these little spores um we use frequently on this horizon because metamorphism the rocks have been heated to a point where they've burned it's just carbon the only thing that we have. can use is the trilobite doing Ellis Higgins Army um but it's only known from Serious Passage um so we have to take um a series of steps to correlate um Boone Ellis and his relatives in more complete sections in um Central North North America um, where we have a more complete stratigraphy, so that's one way we do it, but we can check it by mistake because what we can do is use sequential stratigraphy, which is the record of sea level rise that's in the sediment and there's a serious Liability because, and I didn't particularly talk about that, you're right at the base of a major sea level rise and that's a major sea level rise that we can take immediately across the entire North American continent and on other continents. it's also a very distinctive time that fits uh horizon um and they both give the same answer that he's essentially a serious person who's the same age as chain change and sitting on the base of cambrian series three ok I think some questions remain. and then we'll finish, but really nice one from Sarah, why do you think the Cambrian explosion happened when it did? ohso i think it was going to happen regardless um you know everything was in place my gut feeling is that what acts as the trigger for that actual acceleration we saw in the histograms is that sea level rise i just talked about for many tens to hundreds of millions of years the inner parts of the continents have not been flooded um and the sea level sat at or below the edge of the continental margin um but for a variety of geological reasons one of which is an increase in plate tectonic activity that raises global sea levels and floods the interiors of continents for the first time while increasing the area in which organisms can live within a given depth of water um on a slope , it's going to fit in a small area if it spills all that water across the low-gradient continental shelves, it has a much larger habitable area, and what ecologists know is that fun Species sity is closely related to habitable area so sea level rise increases habitable area which then provides the evolutionary drive to produce the chamber explosion in my opinion and let's ask a question from William do you think any Will we ever have a Snowball Earth again, yes, but not for a while, and so in closing, on to Eleanor Straw's final question, which asks if you had unlimited funding. would be the ideal place or thing for you to investigate to help you understand the Cambrian explosion.
I think what everyone would answer to that question is we need more locations, we need them in other places, um, we need them, so we have them. in australia we have them in china we have them in north america um we have some in russia but what we need is more locations now given my predilection for arctic stuff um and with my unlimited funding i would take a helicopter and jump along the formation Bowen in North Greenland and because the severe passive locality must occur elsewhere um and even though we've searched that little area around the locality and found some bits and pieces um that upwelling belt as we call it that rock band stretches across about 300 kilometers, so that's my fantasy helicopter ride.
Thank you very much for that final question. We look forward to your donations to Paul's field fund. I won't get to that, there were that many, but we hope to see you back here in two weeks for our conference with Professor Sarah Gabbert from the University of Leicester, who will talk about Experimental Decay and the wonderful world of rotten fish. and what that tells us about fossils and preservation should be really exciting so join us in two weeks and the link for that is in the chat but um and put your answer to the questions up on the screen now in the chat but um from me at the MU at the Museum and from Paul thank you once again Paul for a wonderful lecture and we hope to see you again in two weeks thank you very much thank you very much

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