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Listen: Sigma Xi Guest Lecture on “Life in the Cambrian and Beyond: An Explosion of Biodiversity”

Listen: Derek Briggs

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In this talk, G. Evelyn Hutchinson Professor of Geology and Geophysics Professor Derek Briggs talks about the explosion of biodiversity in early Cambrian deposits.  He says, “if we look at the Burgess Shale fauna in a cartoon this is the diversity of organisms. And if we extract everything that's soft body and normally not fossilized this is what we're left with. So this is the 40%. And we're missing the other 60%. So that's my justification, if you needed one, for working on exceptionally preserved soft body fossils.”

The fossils of the Burgess Shale of British Columbia and similar Cambrian deposits have acquired iconic status as weird forerunners of marine life today which lived more than 500 million years ago. Fortunately, sites preserving soft bodied animals also occur, albeit more rarely, in younger Paleozoic rocks, and here we find more familiar fossils that lead directly to modern groups. Without such exceptional preservations we would only have evidence of about 40% of ancient biodiversity through the record of shells and other hard parts. New fossil discoveries around the world continue to reveal the origins and early evolution of biodiversity in the oceans.

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Audio Transcript:

Speaker 1: Hello everyone. Thank you all for coming. My name is Debra. I'm the president of Swarthmore College chapter of Sigma Xi this year. I just want to tell you a little bit about Sigma Xi before I introduce our speaker. Sigma Xi was founded at Cornell University in 1586. It's a scientific research society. An international organization with the mission and I quote from their website, "To honor scientific accomplishments. To encourage and enhance the worldwide appreciation and support of original investigation in science and technology. And support the original investigation in science" ... oh sorry, "and to foster worldwide creative, dynamic interaction among science and technology and society."

Speaker 1: One of the things I like about it is that a year after it was founded, they're already inducted five women in 1887. The Swarthmore college chapter was founded in 1922. The first wholly undergraduate chapter. One of over 500 chapters worldwide. Our chapter sponsors lectures, dinners. We help to support student travel to present research at conferences. And every September, we sponsor a poster session which many of you have probably witnessed. And there are lots of pictures out there in the lobby from this past year's poster session.

Speaker 1: I also just wanna mention, because I'm really good at Greek. The letters Sigma Xi, stand for the Greek words and I apologize to those of you ] Greek speakers, Spaldon [Xinones 00:01:35] which allegedly translates to companions in [inaudible 00:01:40] research. So, that's what we all are.

Speaker 1: Alright, so now, I am very happy to welcome Professor Derek [Briggs 00:01:50] who is our speaker today. He has his BA from The University of Dublin and his higher degrees include a PhD from The University of Cambridge. He's held positions at Cambridge and The Universities of London, Bristol and Chicago, having come across the pond. He has been at Yale since 2003 where he is the G. Evelyn Hutchinson professor of geology and geophysics. And the curator of the Yale Peabody Museum of Natural History.

Speaker 1: Professor Briggs is also a fellow of The Royal Society, that's The Royal Society, but holds medals and memberships in other royal societies; Dublin, the Irish Academy. You guys have lots of royal societies, that's impressive. But numerous other memberships and [inaudible 00:02:45] across the pond and in the United States and elsewhere. His research focuses on preservation and evolutionary significance of exceptionally preserved fossil biota. And here's something for you guys to ... you students to strive for. Of over 18,000 Google citations of his work. This work includes research on soft body fossils which are key to seeing the bio diversity of the past in addition to the more traditional hard body fossils. So today, you're gonna hear from Professor Briggs on life in the [Cambrian 00:03:29] and beyond. An explosion of bio-diversity.

Speaker 1: Please join me in welcoming ...

Prof. Briggs: Thank you. Do you think I need to use a microphone? Alright, holler if you can't hear me. That's not a contradiction in terms. I'm delighted to share the room with companions in zealous research ... In essence what we do. And I'm also honored to be your Sigma Xi speaker. This is my first trip to Swarthmore and I'm not responsible for the weather. Let's cap that straight away. Right away. I had a very enjoyable evening last night with the [inaudible 00:04:17] society thanks to Rick Hellman who is here. And I enjoyed talking to Vince[inaudible 00:04:23] this morning. And one or two of you have decided to come back which is very reassuring.

Prof. Briggs: So life in the Cambrian. An explosion of diversity. Let me start, unapologetically, with a diagram from 1981 by the late Jack Sepkosky, who was at the University of Chicago and was one of the first people to develop metrics for looking at the history of life, through time, in terms of diversity. This diagram is based on number of families, so taxonomic families, but these are families of shelly fossils in marine sediments. So it's a somewhat selective database. And you'll see V is Vendium, the old Russian name for Ediacaran, let's call it pre-Cambrian. Here's the Cambrian explosion, and here's the increase in diversity through the [inaudible 00:05:25] to a kind of plateau through much of the Paleozoic.

Prof. Briggs: And then there's a major decline. This is what's commonly called "the mother of all extinction". I'm not quite sure why it has to be the mother of all extinction. It could be the father of all extinctions, if you prefer, or alternatively, when life nearly died. But fortunately, it didn't, and of course we have this dramatic increase in diversity through to the present day and then we're doing horrendous damage to the current [inaudible 00:06:00] which is something I'm not going to talk about. I'm going to be staying down here, in the early part of the fossil record.

Prof. Briggs: So this diagram I've just shown you is based on the shelly fossil record. And my primary concern, as Deb has suggested, is in exceptional fossilization in the soft body fossil record. So why should we care about the soft body fossil record? Isn't the shelly fossil record adequate for our purposes. Well back in 1978 the late Tom Schoff, again at the University of Chicago where this kind of research really started out, did an interesting ... let's call it an experiment. It was really observations at Friday Harbor Labs; University of Washington on the West Coast. If you ever get a chance to go, do. It's a marvelous place. And he surveyed mud, sand, and rock formers. Modern formers. The modern beach, rock pools and sandy biotas and he compared the organisms he found with their representation in the fossil record. And he found that about 56% of the mud fallout, 68% of the sand fallout, 61% of the rock fallout are not represented in the fossil record. And if we turn that around, it means of course that the shelly fossil record is about 40% of total diversity through time in marine settings.

Prof. Briggs: So I started out my zealous research career, like all you Sigma Xi folks, but in my case on the Burgess Shale which is a famous, now famous Cambrian locality in British Columbia. And this is [inaudible 00:07:50] here, and here is fossil ridge, and this little band of snow here is the Burgess Shale Quarry, the original Walcott Quarry, which was discovered in the 1900's. And actually I did an entire PhD without going there. Simply mined the collections in the Smithsonian Institution in Washington which were a legacy of Walcott's endeavors back in the early part of the 20th century.

Prof. Briggs: But in the early 1980's I had the opportunity to do field work there with the Royal Ontario Museum. So this is a somewhat younger now Professor Briggs, with his then graduate student colleague Simon [inaudible 00:08:33] only outcrop in the Burgess Shale. And we went up there in early July, I think in 1982 if I remember correctly. The quarry was full of snow. We had permission to camp in the quarry and no where else. And of course we were brilliantly equipped British/Royal Ontario Museum group team so we had nothing to dig the snow out with. So I still have this clear memory of taking metal plates and scouring out the snow and pitching the tent on top. And then it rained overnight and we could hear this slippery sound of snow falling down the sides of the tent. So it was a somewhat baptism ... I was going to say baptism of fire but that would be wrong analogy. Quite the opposite.

Prof. Briggs: But we certainly had great fun up there and if we look at the Burgess Shale fauna in a cartoon this is the diversity of organisms. And if we extract everything that's soft body and normally not fossilized this is what we're left with. So this is the 40%. And we're missing the other 60%. So that's my justification, if you needed one, for working on exceptionally preserved soft body fossils.

Prof. Briggs: Lots of people are still working on the Burgess Shale. The Royal Ontario Museum still sends out expeditions, sometimes every year, sometimes every other year. And they're discovering new localities in British Columbia and new fossils. Because in essence they're exploiting different pockets of life on the Cambrian sea floor. Probably of slightly different ages. So last year I had the privilege of collaborating with Jean Bernard Caron, who's the curator of the Royal Ontario Museum of invertebrates, and we describe this animal here which is a ketones and ketones are arrow worms because they look vaguely like arrows, they are very common in the modern marine biota and they are really quite vicious predators cause they have this apparatus of spines at the front for grasping prey. But fortunately they are generally only a couple of centimeters all in dimension. So they don't give us any trouble. The Cambrian worms, fortunately, are much bigger and therefore much easier to work on. So this particular animal is about 10 cm long.

Prof. Briggs: I've also been working on a Cambrian locality in northern Vermont where fossils were first discovered in the 1880's and the locality was considered worked out or lost and this gentleman here, Giovanni Perry, who's an advocational paleontologist, he collects fossils for fun, has leased and opened the quarry again, primarily because he's interested in trilobites. And this locality yields spectacular trilobites, rare but very often complete, and he started turning up soft body fossils. This is a worm. This is the appendage of a giant [inaudible 00:11:34]-like predator called [inaudible 00:11:36]. And he's availed me that much trouble I'd have to say into a collaboration looking at this particular quarry, which if you like is the first discovered example of one of these unusual Cambrian Burgess Shale-type preservations. And here's one of Giovanni's trilobites. I went up in the autumn and did a couple of days collecting with him. He's been there all week, he slices out huge slabs of [inaudible 00:12:07] for fossils; he discovered precisely 3 specimens in the entire week. So this is dedication. Dedication, zealous researchers, is required for doing science.

Prof. Briggs: So if this is our Burgess Shale community, many of these organisms look rather odd. They are peculiar to our eyes, and Steve Gould who was well know writer on things science, now sadly deceased, used to refer to these bizarre looking animals as "weird wonders". And we have a number of these weird wonders in the Burgess Shale and indeed in Burgess Shale type deposits in other parts of the world. And let me introduce you just to 3 and then you'll see where I'm going with this.

Prof. Briggs: So here's my first one. This is a thing called microdochium. And microdochium first turned up in residues of limestones, Cambrian limestones, dissolved in acid. So these little structures here are microscopic, just 2 or 3 mm across. They come out when you dissolve Cambrian rocks with lots of other things, little shells and the like. And the question is, what on earth are they? Can you make sense of it? And here are some of the ideas that were put out in the literature. Some sort of support for an organism that lives attached to rocks, might be a colony, might be somewhere almost like an egg box to house early larval stages. Or, perhaps they could be sclerites, little plates that serve to toughen the skin.

Prof. Briggs: So in the Burgess Shale there is an odd looking animal, what's called a lobopod because it has lobe shaped limbs called ischia. And ischia was redescribed by my graduate student supervisor and he demonstrated that this thing is commonly associated with sponges and may well have lived by eating sponge tissue and was probably not quite parasitic. I doubt the sponges died, but it probably stuck these little tentacles into the sponges and sucked out the soft tissues. This is the paleontologist's dream. The animal crawls out of the rock and becomes alive on the desk and you don't have to worry about reconstructing it, you can just describe what you see. Sadly it doesn't happen. Only in the movies.

Prof. Briggs: So these lobopod like animals, these Cambrian animals which are marine and 540 or 30 odd million years ago, 25 million years ago, it turns out are quite closely related to a group of living organisms, also lobopods, with the scientific name [inaudible 00:15:07] they are sometimes called velvet worms. These things live on land in damp rotting wood and forest litter in the Southern Hemisphere. So they are about as far a move from Cambrian marine environments as you could imagine. Lo and behold, one of these Cambrian lobopods turns up in China, in a slightly older deposit than the Burgess Shale I introduced you to at the beginning, and microdochium is on the side of it in pairs, so it looks as if they're actually sperites that might have protected the organism. Now they don't look very good as pseudo armor because if you're a half sensible predator you'll just go into the caps between the position of the sperites. So part of it's protected, part of it is clearly not.

Prof. Briggs: Can we really infer that these are for protection or anything to do with protection? Well we can, if we think about this in the context of other kinds of organisms, microdochium here, [inaudible 00:16:15] at least has little spines and if we turn our attention to something in the Burgess Shale here, hallucogenia, which was described by my co-graduate student Simon Calmay Morris who I introduced you to early on. And reconstructed in this manner here is a kind of bizarre worm like animal walking on stilts on the Cambrian sea floor. So do the thought experiment, folks, can you make this thing walk on a muddy substrate? I challenge you to do it, and I challenge this thing to stay upright even in the slightest bottom current.

Prof. Briggs: So unfortunately, of course, this was based on only partial evidence and further specimens showed that these structures here are not actually separate tentacles which might have separate jaws at the end. This is the thing of nightmares. But they actually turn out to be one set of those lobopods. So unfortunately due to the absence of full evidence Simon had this thing upside down and probably back to front as well. We now know that [inaudible 00:17:28] looks like this. And now you can see the link to microdychtium because we have a series of plates along the side and in this case they have spines, not stilts for walking on, spines for protection. So clearly you can see the link and you can see that there's a group of these things and here they are reconstructed in a paper by Chinese paleontologists and you can being to see the relationships and the possibilities here. So this starts out as a weird wonder, and it turns out to be pretty peculiar but it's actually quite closely related to a modern group of lobopod organisms which just happens to be a survivor that's now living in terrestrial environments.

Prof. Briggs: So here's my second weird wonder. And this actually turned out to be something I described in my PhD thesis. When I went to Cambridge to do a PhD I was allocated the bivalve arthropods from the format. Now the bivalve arthropods, things that look like shrimps but have just 2 valves with a hinge that protects the anterior part of the animal. So why was this part of the bivalved arthropods? Well, because this was assumed to be the body of a shrimp like organism even though the carapays had not been found in association, and it was reconstructed and here is Charles Knight's famous restoration of the Burgess Shale from National Geographic in 1942 and here is that structure here sticking out of the back of something that has 2 valves, a shrimp like organism.

Prof. Briggs: I should say that if you ever find a bundle of National Geographics in a store where they're selling used books or somebody's clearing out this one has always gone because they have a whole other dinosaur reconstruction as well. And somebody always gets there first. Very frustrating.

Prof. Briggs: So, another fossil which is related to this story is this structure here. Turns out to be a [inaudible 00:19:40] as you'll see in a moment or 2, but was reconstructed by [inaudible 00:19:44] as a kind of floating pineapple ring in the Cambrian ocean. Because they assumed that because of its radial symmetry it had to be some kind of Medusa or jellyfish. But if you look at it carefully, here seen in reflected light it doesn't take much imagination to realize this is rather unlikely to be a jellyfish. You've probably all met these things on the beach at some time or another and you're perfectly aware that they do not have teeth. They are actually stinging organisms. So it turns out that what in turn my advisor had borrowed a series of specimens from the National Museum, from Walcott's collection and had them in Cambridge and in these specimens are jellyfish, no, an jawlike structure in the anterior of the animal and limbs up here which are rather hard to see which give you a reconstruction like this.

Prof. Briggs: So here's my shrimp trunk, which turns out to be an appendage and I managed to figure that out before we found the complete specimen I'm delighted to say. Here's our jellyfish, which turns out to be the jaw. Extrapolating up in terms of size this thing gets to half a meter, maybe even larger, so it's a giant Cambrian predator and occasionally it bit trilobites. Because we find trilobites with W shaped bites out of the rear of them and of course you only find, needless to say, the ones that survived, you don't find the ones that were completely consumed. And sometimes they have a little ridge of scar tissue which implied that they were covered, molted again, and somehow managed to deal with this loss of part of their protection. And here is a model. We did a little work with NHK which is the Japanese television company, the equivalent of PBS here or the BBC in the United Kingdom and I'll show you a little clip from this, with apologies to anybody who actually speaks Japanese.

Speaker 3: [Japanese speaking]

Prof. Briggs: So these are thoughtfully provided by the television company. [crosstalk 00:22:13]

Speaker 3: [Japanese speaking]

Speaker 4: My advisor. Strip away here but the shale is not very different from ... it has this double shale. Plausible. [crosstalk 00:22:44] what happens if you try and [inaudible 00:22:47]

Prof. Briggs: So there you go. These things were thoughtfully filled with some jello substance so they have this gooey interior. And if you play with it long enough you eventually produce a bite that looks roughly W shaped and is rather like the bite you see in the trilobite I showed you moments early. Which of course pleased the Japanese television company to no end because they got something that actually resembled a comparison. They also produced this here, which was much more exciting to me because they managed ...no I don't have a movie of this, you'll be relieved to hear but they managed to make essentially a model which swam and we spent a delightful afternoon in an expensive house close to Cambridge that had a swimming pool playing with this thing. Swimming up and down the lanes and demonstrating that it did indeed swim in the way that I'd figured out it probably did.

Prof. Briggs: So I have these giant predators in the Cambrian oceans, we have them all over the world now. This is an example from the Emu Bay Shale in Australia and this is a particularly fierce example from China. These things are widely distributed and since we put the thing together in the 1980's many different kinds have been discovered and I'll show you 1 or 2 a little bit later on.

Prof. Briggs: So we have a number of these weird things in the Cambrian alongside everything else but in terms of where they sit they're essentially part of the stem group. And I don't want to dwell on this too much but some of you may be familiar with the idea. Here's today. Here's one major group or phylum. Here's another. And what we're sampling in the Cambrian for the most part are early offshoots of these lines that lead to our modern groups that actually went extinct. So they don't tell us a whole lot about the evolution of modern marine organisms. They are, if you like, stem groups. And if we want to get closer to the crown which is where we are now, and which will interest us as biologists, we have to go into younger rocks.

Prof. Briggs: So, we move into the next part of this diversity curve which I showed you in [inaudible 00:25:04] 1980's version at the beginning. And we call this GOBE, and this is a terrible abbreviation. It actually means Great Ordivision Biodiversification Event. Try saying that quickly after a few beers. GOBE is much simpler although it's a really rather ugly term. So if we go to GOBE our problem with GOBE is that there are rather few exceptional preservations. For reasons which it's not appropriate to go into here there are many and this is only a very small sample of the classic localities. There are many exceptionally preserved faunas in the Cambrian. It's probably about ocean chemistry and the composition of Cambrian clays that buried these organisms and may have inhibited decay.

Prof. Briggs: But fortunately there are 1 or 2 in the ordivision, as we move into the Great Ordivision Biodiversification Event. And there in mind we are trying to find the other 60%. We've only got 40 in the shelly record. So we can go to Fez or Otta in Morocco where we've been working recently. And this is a spectacular place to work, we're talking about the northern edge of the Sahara. South of the Atlas Mountains. The scenery is spectacular and it's particularly excellent because there's no vegetation and vegetation is a menace for geologists because it conceals the rocks. So we are concerned with collecting; we can follow beds along a particular series of little spurs or bluffs and collect at several localities. And coming out of here are other exceptionally preserved fossils and some of them are rather similar to our Cambrian Burgess Shale examples.

Prof. Briggs: So here's a Burgess Shale [inaudible 00:26:53] a Cambrian one. Here are specimens from Phesolata, which are much younger, we are talking about something that's several 10's of millions of years younger, and here are appendages which look very similar to the appendages that we pick up in the Cambrian examples. What we were particularly excited about this specimen here and unless you are a paleontologist you probably find it difficult to understand why we are particularly excited about this specimen. It looks like a brown blob. Well, this is anomolacaradid and it's actually, you can get the impression of scale from the anomolacaradid it's the largest complete one ever found. And it's in a huge concretion, I parted the rock body that's been cemented very early in this case by silica and retains the thing more or less in 3 dimension and certainly intact. Unfortunately the concretion doesn't include those grasping appendages at the front but they occur separately and we can reliably associate them in the shales and they look like this.

Prof. Briggs: So this is the appendage at the front end of this particular anomolacaradid which is an ordivision 4 and you can see what we're looking at. Here's the limb, slightly squidged. These are blades descending down. And these are other blades and other blades, so this is an arrangement that is reminiscent of fractiles. It's a sort of series of smaller versions of the same arrangement and if we reconstruct this animal it looks like this. It really does look like that. Probably not that color. So, this is a different kind of anomolacaradid and you already figured out how this was feeding. This is an autopredator, it doesn't have a big circular jaw with teeth in it. It's actually an early example of a large organism that was flipper feeding. And this array of comb like projections is for that purpose. So it was flippering small swimming arthropods out of the ocean and consuming them. So this gives us an indication that these things were not only diverse morphologically but they were diverse ecologically in terms of what they did.

Prof. Briggs: Where they sit on a scheme of relationships, details not important here I hasten to add, here's our lobopod animal down here, here are the anomolacaradids and here are trilobites and other modern arthropods. So this thing is still on the stand. It's not giving us much in the way of information about the ancestors of living groups. And we have another very neat animal from Pheso ... we have many neat animals from [inaudible 00:29:52] here's another one I'll just introduce you to which is also on the stand but in this case it's not an arthropod and you may or may not be able to figure out what it is. It has a single large valve at the front. These are 2 illustrations of the part and counterpart, one transposed, and then it has a series of fine spines or sterites over the rear part of the animal. What's interesting, if we look at the anterior of the shell in detail it has clear indication of the rasping teeth that make up a baradula.

Prof. Briggs: The biologists among you may realize that a baradula is the jaw structure of a snail or other kind of mollusk. So this is clearly a mollusk. We call it Calvapalosa. Here is a model which is slightly larger than life size. It shows you the valve on the front and the spiny structures and the underside is not so easily reconstructed because the details aren't entirely there but most of them are. And again, if we look at the relationships here, don't be alarmed by the complexity of the diagram, here are modern shelled mollusks; snails, clams, octopus, keflapod etc. here is Calvapalosa down here in the ordivision which is essential an ancestral morphology and then there are a bunch of odd looking modern mollusks which you're probably not familiar with. Including chitons, coded male shells which come off on another line. So this again is on the stand, but by the time we get to phesaloto we have things that are not in the stand and you can see straight away what this is; this is a horseshoe crab. And you can all identify this if you've ever seen [inaudible 00:31:41] on the seashore. So this is clearly something that indicates that modern groups are present in the ordivision and indeed this exceptional record that phesaloto provides for us indicate that the modern groups went further back in time than we formerly realized, and some of the Cambrian groups went further forward in time likewise.

Prof. Briggs: So if we want to think about the origins of the crown, the living groups of organisms, we have to go into younger rocks, we have more trouble finding exceptional preservations and one of the [inaudible 00:32:17] localities that it's not becoming is in the middle [inaudible 00:32:21] England and it's about 430 million years ago and we call it our herefiture biota. So this is yet another another type of [inaudible 00:32:32] and in this case we do have vegetation, but we're in a formerly worked quarry and we can actually get earth moving equipment in there. And what this is, is a volcanic ash horizon on the surface of a former reef. We're not sure whether its Pompeii like but certainly a large amount of ash was dumped in the ocean. It may have been dumped directly on the animals we find, or it may have been dumped and reworked by currents. And then buried the animals. And I've done this project for 20 or so years now and we're still producing papers with a pair of twins, David and Derek Senator, one in Leicester, one in Oxford, and Mark [inaudible 00:33:17] who's at Imperial College in London.

Prof. Briggs: So this is what you collect. Now this is not very satisfying to the average fossil collector. It would barely send Rick's pulse racing up. But it's very satisfying to an Irishman because it's just like picking potatoes out of the field. And then you take them back to the lab and you crack the concretions and when you crack the concretions you get images like this and this. So the outer part of the concretion is slightly weathered, which gives you this brownish color and the central part is the original gray, and then there's a bunch of calcite in the middle which if you look very closely at it seems to be some kind of [inaudible 00:34:03]. So you get cross sections like this. This is about 4 [inaudible 00:34:10] long from one end to the other. Nobody has any idea what it is, unless you've seen the papers which I very much doubt. So it turns out this is actually a sea spider. So here's our sylearian animal, here's our modern sea spider. They are not strictly spiders but they are related to literates, and they are quite common in the morror oceans. This one's dried out of course, they don't normally look quite so sad. But needless to say one would have terrible trouble figuring what this looked like and discovering it was like that. So let's see how you would do it.

Prof. Briggs: Well when we started out 20 years ago in the 1990's, we just cracked concretions, and here's a little arthropod, a little horseshoe crab like thing. Which we call offocolus. And here's one section, you can imagine you're cracking concretions in the lab with a little vise, here's one section probably front to back, here's another one front to back but this time sideways. Here's once coming out of the screen at you. And here's one that's been sliced so you actually have a single appendage with a few little bristles behind. But based on this kind of evidence you'd have extraordinary difficulty in figuring out what the thing looks like in 3 dimensions. So you all know how you do this; you'd say okay, do computer aided tomography. Take it to a cat scan machine and it'll produce images right through, essentially like an xray in 3 dimensions. And then you can reconstruct what it looks like.

Prof. Briggs: But sadly there's a problem with this. Cat scanning only works if there's a striking density contrast between the fossil of interest and the matrix. And in this case, there isn't. Because the matrix, albeit volcanic ash, is cemented by calcite and the infullig mineral is also calcite. So there's no density contrast and these things are invisible to cat scanning. So we have to destroy it. This is a little worrying but this is in effect what we did. So you cut a little square out to include your fossil and bear in mind these things are generally only a centimeter or a couple of centimeters in size, you mount it in a holder which has a graded wind out if you like. So you can literally wind out 30 or 40 microns at a time. You put it on a grinding surface, you essentially extend it out 40 microns, you grind it away, you wash it, you take a photograph, you extend it out 40 microns, you grind it away, you wash it, you photograph, using the you to me Carralot Lewis current operator in Oxford. And the one saving grace is that you can partially automate it and you can put several examples in one holder so you can do them all at the one time.

Prof. Briggs: You get spectacular results. So this is that animal that I just showed you in 4 section now extracted from the rock and reconstructed using the kinds of methods you would use to reconstruct cat scans. It's fine with this one because we have multiple specimens. We might have slight reservations about doing some of the rarer things. The saving grace is of course that I can put this information on a file for you and I can send it to anybody who wants it. And we publish the papers the date of our there so anybody can resolve the problem. And we've plenty of concretions left. So come the day the guys work out how to deal with a difference in density such as the one we have maybe we'll have a way forward to do this in an automated fashion.

Prof. Briggs: In the meantime we scratch our heads when we split concretions and we try and figure out what things are. So, could you have figured out what this is? Probably not. It reconstructs like that, so it's a brachiopod, this is a shell here's the stalk and you can make movies of these if you're so minded. And I can tell you that in the normal fossil record just the shell survives. This stalk is soft, certainly the little looplets that anchored in the sediment are not preserved nor are very often any sort of encrusting organism that's attached to the brachiopod.

Prof. Briggs: Here's one we did recently. Guesses? Well, you'd probably say perhaps it's an arthropod and you'd be right. This is what it looks like. We christened this thing "The Kite Runner" after the Khaled Hosseini novel. And you can see it's an arthropod, and you can see the kites, these structures here which are attached to the carapes at the end of the spines. And then the question is what on earth are the kites? And you are scratching your head. Are they just hitching a ride? In which case is the animal likely to tolerate them because they would create drag as it moves through the water and it has these nice long antenna which I can imagine it would sweep behind it and knock these things off before they got established. Could they be parasites? I think not because the threads that attach them are much too long to make it efficient to extract nutrients and for the most part they are attached to spines right on the edge of the carapes.

Prof. Briggs: So we think these things are juveniles and this is a bizarre kind of brooding strategy and there's something to support that. When you section the ends of the kites, so to speak, you can see appendages so they look like little capsules that might have enclosed a juvenile arthropod that then emerged after a time. And there are problems with this interpretation. For example, what happens when the arthropod molts, does it cast its skeleton and all the kites? It would mean that it would have to go through the entire process of becoming mature before the other molted. And there are other issues with how it got those things attached but were recently happy that the kite runner is a bizarre kind of [inaudible 00:40:48] breeding strategy.

Prof. Briggs: So what about animals that actually give us some insights into modern groups? This is the old problem. Until you reconstruct it you have no idea what it is. These are actually ostrocods and ostrocods are just millimeter size tiny little crustaceans and we can reconstruct not only the carapes but all the interior appendages. And if we do this we get an organism that's extraordinarily similar to living ostrocods. These particular ones come from the Japan Sea, and they are a group called zenolaparids. Here we have something that's quite clearly related to a modern group. And we not only have males, indeed the last one was a male, we have females and this is a female example of an ostrocod we called Nymphatalina and we know it's female because it has egg masses at the rear and a brood chamber inside the carapes which is rather similar to the egg masses you get in the brood pouch of modern ostrocods. And just bear in mind that this thing is about 2 or 3 mm long and you will recall how spectacular the information is.

Prof. Briggs: We get parasites attached to these things. We thought this might be a new ostrocod because it has this strange tail like structure emerging at the rear of the hinge. But here you can see the reconstruction, here it is in dorsal view, here you see it side on, this is just the ventral part of the ostrocod. And here's another one, inside, attached to the eggs. This is almost certainly a Silurian Tongue worm, or pentastomid. Here you see it isolated. These are rather disgusting little parasitic crustaceans and people working on modern biology have had terrible trouble in figuring out what they are even in the living form because they look so different to any kind of living crustacean. And the saving grace here of course, is gene sequencing and molecular phylogenies.

Prof. Briggs: And nowadays tongue worms, or pentastomids, tend to be found mainly in vertebrates, mainly in terrestrial vertebrates who swallow them as part of the life cycle and they engage themselves in the internal organs, often in the lungs of living mammals and reptiles. In this case we see a stage, perhaps in the evolution of this group where they attached in marine settings to other arthropods and parasitized their egg structures. And we get in some modern ostropods too, not pentastomids specifically but little isopods for example and that one is in here, feeding on the egg mass of this particular living arthropod.

Prof. Briggs: And we have pretty much no evidence of these things in the fossil record, apart from very early Cambrian forms, microscopic, phosphatized, but probably larvae so this is fill the gap in a group that's pretty much not represented in the fossil record at all and it belongs to this group of pentastomids, the [inaudible 00:44:07].

Prof. Briggs: So can we say anything at all about the process cause we're now clearly dealing with groups that are closely related to things that are around today. It will be nice if we can say something about how these things evolved and how perhaps evolutionary development influenced changes in morphology in fossil lineages.

Prof. Briggs: So this is my final example from [inaudible 00:44:32]. And this is a horseshoe crab. Its a thing called diversterium. So just to remind you, or to instruct you, this is modern limulis, horseshoe crab of today. This is a molt. You can see the way the carapes are split along the margin. And you can see the limbs include the little claw at the front, the chela, or chelicera and then 2, 3, 4, 5, 6 and then a reduced appendage right at the rear called settle. And these things have spines at the base of the appendages. They feed and eat trilobites, well they essentially eat with their elbows. They have spines at the base of the appendage which round up the food, and the little claws push it into the mouth. And then at the rear, the posterior part of the animal they have gills. This is the way they essentially work.

Prof. Briggs: So here's our diversterium which is a slightly different kettle of fish, this might spin ... I think this one spins very slowly so it's dangerous at this stage of the lecture because people say oh, I'll go to sleep now. Bu you get the idea.

Prof. Briggs: So when we start exploring this array of limbs and you can see straight away that there are too many of them. It just don't seem to make sense, it's as if somebody stuffed a few extra ones in there. We've no idea why. So when we look at individual limbs we find that there are pairs and the pairs correspond to 2 branches of the same limb. And in modern arthropods this is a very common way of doing things, particularly in aquatic forms, where there will be a walking branch and a gill branch attached at the base of the limbs. We call it a biramous or 2 branch limbs. The bizarre situation in diversterium is that these 2 branches insert in different places on the ventral body wall. So let's compare this with limbulis. We have one, it's rather different of a claw but it's essentially the same and it has a little pincer at the end. Then we have 2 branches corresponding to 2, 2 branches corresponding to 3, 2 corresponding to 4, 2 corresponding to 5, just one corresponding to 6 and then 7 is essentially equivalent.

Prof. Briggs: Now during the evolution of modern horseshoe crabs they started out with a biramous limb, with 2 branches and then produced the number of branches in the front part for walking and feeding and in the rear part as gills. And we imaging the same things probably happened in fossil horseshoe crabs. So can we find any evidence of the second branch in a modern horseshoe crab? And I went to one of my colleagues at the University of New Haven who works on horseshoe crabs and I said, "do you ever get mutants, strange developments where you get 2 branches instead of 1" and the answer sadly so far is, no.

Prof. Briggs: But there's a limited amount of work on the evolutionary development. The embriology of modern horseshoe crabs and these are 2 of the earliest stages in limulis. Early and late embryo. And what you can do, of course, is to stain tissues to produce a fake map so you get some kind of idea of what these might have developed into. And the evolutionary development people among you will say, well this is a slightly coarse and rather crude way of looking at it. But in this case if you stain for distillus which is a gene involved in many things including appendage development you get a small additional stain outside the main limbs in the head in more or less the position that you have that second isolated branch in the fossil horseshoe crab. And lo and behold by the time you get to a late embryo it's gone. So this may indicate that evolutionary development,i.e. the suppression of this gene here may indeed account for the loss of that pandation in fossil horseshoe crabs sometime after the Silurian.

Prof. Briggs: If we think about exceptional preservation over time, we know that it represents the 60% as opposed to just the 40% that we get in the shelly fossil record. It gives us insights, therefore, into a whole range of groups and bear in mind that many major groups are almost entirely soft and therefore would have no fossil record at all. But if we want to worry about the origin of the modern biopath we have to go past the Cambrian, even though I've spent large part of my research working on it and it's very exciting, we have to go past the Cambrian into the ordivision at least but arguably even to the Silurian to understand the kinds of processes that may have led to the groups living today.

Prof. Briggs: And just as a final slide, this is an array, a cast of characters from our Silurain [inaudible 00:49:58] in the United Kingdom, many of them arthropods, mollusks, worms, and so forth. And we're still producing these things. We can't write them up fast enough. So we get a few out every year. So you can watch this space if you're so inclined. Anyway. Thank you.

 

 

 

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