The Great Transitions in Evolution with Neil Shubin

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- [Announcer] This program is a presentation of UCTV for educational and noncommercial use only. (gentle music) - Good afternoon, my name is Ellen Gobler. I manage the Graduate Council Lectures, and we're pleased to have all of you here today. Thank you so much for joining us. It's my pleasure to introduce Andrew Szeri. (audience applauding) - Good afternoon. My name is Andrew Szeri, I'm Dean of the Graduate Division, and we're pleased along with Graduate Council to welcome you to the Charles & Martha Hitchcock lecture series. Our speaker today is Neil Shubin. The story of how the endowment came to Berkeley is a nice example of the ways in which this campus is linked to the history of California and of the Bay Area. Dr. Charles Hitchcock was a physician for the army and came to San Francisco during the gold rush, where he opened a thriving private practice. In 1885, Charles established a professorship here at Berkeley as an expression of his long-held interest in education. His daughter, Lillie Hitchcock Coit, still treasured in San Francisco for her personality as well as her generosity with respect to Towers, greatly expanded her father's original gift to establish a professorship at Berkeley, making it possible for us to present a series of lectures. The Hitchcock Fund has become one of the most cherished endowments of the University of California, recognizing the highest distinction of scholarly thought and achievement. Now I would like to invite William Lester, Professor of Chemistry and Chair of the Hitchcock Professorship Committee, to say a few words about our speaker, Professor Neil Shubin, thank you. (audience applauding) - Well thank you, Dean Szeri. Good afternoon. Although you've heard it before, I'm William Lester, Professor of Chemistry and Chair of the Hitchcock Professorship Committee. On behalf of the Hitchcock Committee, I'm pleased to welcome Neil Shubin as this year's speaker and the Charles M. and Martha Hitchcock Lecture Series. Neil Shubin is a distinguished paleontologist whose research seeks to understand the mechanics behind the evolutionary origin of anatomical features of animals. His work focuses mainly on the Devonian and Triassic periods, to understand the pivotal ecological and evolutionary shifts that occurred during that time. In 2004, after scouring the Canadian Arctic for six years, Shubin and his team unearthed Tiktaalik roseae crae, a fossil fishapod, which despite its fishlike features, had a neck, skull, ribs, and parts of limbs similar to land animals. This discovery represents the transition between fish and four-legged mammals that occurred over 350 million years ago. His announcement about the discovery of this phenomenon on April 6, 2006 in the journal Nature made front page news in newspapers worldwide. Finding the 375 million year old fossil also spurred Shubin to write the recent book, Your Inner Fish: A Journey Into The 3.5-Billion-Year History Of The Human Body, arguing that fish provide an important evolutionary step in human history. Shubin received his BA from Columbia University in 1982, he earned his PhD from Harvard University in Organsimic and Evolutionary Biology in 1987, and in 1996 he was awarded an Honorary MA from the University of Pennsylvania. He was a Miller postdoctoral fellow at UC Berkeley from 1987 to 1989 and held positions as an assistant, associate, and full professor of biology at the University of Pennsylvania before joining the faculty at the University of Chicago in 2000. Shubin in currently the Robert R. Bensley Professor of Organismal Biology and Anatomy. He serves as the Associate Dean of the Biological Sciences division and as a member of the committee on evolutionary biology. Shubin has been honored with a Guggenheim Fellowship, the Marcus Singer Award, and was named Person of the Week by ABC News for the week of April 7th, 2006. In addition, he has appeared on the Colbert Report and Public Radio International. Please join me in welcoming Professor Neil Shubin. (audience applauding) - Thank you Dean Szeri, Professor Lester, members of the Hitchcock Committee, my hosts in the Department Of Integrative Biology here at Berkeley. Thank you for the honor of being a Hitchcock Professor and thanks also for giving me the opportunity to return to Berkeley, which is the place of my intellectual roots. Much of what I do is really sort of flowed from the concepts, ideas, and approaches that I learned during my time here at Berkeley. So today we're gonna talk about the great transformations. And if you take the four and a half billion year history of our planet, you can begin to visualize in a number of different ways. And one of the most common ways to visualize the history of our planet, is as some sort of linear series of events. And so this is one taken from a textbook. It's from Press and Siever, a very prominent geology textbook. And what you see is this linear series is depicted as sort of a corkscrew so they can fit it on the page. And you see the various events and the trajectory in the history of our planet, and the history of life on our planet from the presence of the first rocks, the earliest visible life in the fossil record, the origin of bodies and plants and animals, and then you see sort of the major events in the history of vertebrate life, creatures with bones, the shift from water to land, the shift to the origin of dinosaurs and so forth. When you look at the world this way, in this sort of linear way, from beginning to present, what you sort of see is there are times that kind of look revolutionary or the sort of revolution in the air where there are big things happening. And those time periods have always attracted my attention for one reason or another. And that's why I've ended up focusing on two time periods in the history of life, the Triassic and the Devonian, time periods from 200 million years ago and about 375 million years ago. But anyway, I'm gonna show you how this kind of way of depicting the history and the sequence of events in our world, actually it gets in the way of really understanding and decomposing some of the main events we see in the history of our planet and life on our planet. And what I'm gonna do is I'm gonna take one particular example, one major transformation, the shift from fish that lives in water to limbed animals that live on land. I'm gonna take that shift and really analyze it in detail to show you how an integrative approach, integrating fossils, and studies with living organisms, can tell us a lot about how this transformation happened. And I'm gonna use that as a microcosm, an example really of how we can approach all the other transformations that are out there. So let's start with the transformation from water to land. So here what we have the transformation from water to land. And you see here, I've shown a cartoon. This is a complete caricature of the situation. And if you were to sort of blue sky this thing, on the back of an envelope, and you know look at a fish, and look at a land living vertebrate animal with bones, you can sort of say wow geesh, life in water is vastly different from life on land. Almost every single system of these creatures had to change. And I just showed you several here, I mean, respiration, feeding, locomotion, and head mobility. And if you look at the end states of this transition it looks really large and indeed almost impossible. Now just take a few of them, take respiration, and you have a shift from creatures that are largely water breathing to creatures that are air breathing. This involves whole sweeps of changes to organs and the ways that organs develop, and circulatory systems, and lungs and so forth. Feeding, feeding in water is very different from feeding in land. You go from where you have water where you can suck the food into the mouth by changing the volume of the mouth cavity to biting, where on land you can't suck in unless you're a Hoover Dustette or a vacuum cleaner. It's really more of a biting approach to the capturing and chewing food. Locomotion is completely different on land from water. I mean, here you have water supported, where you basically have to support yourself in gravity, it's not gravity supported, but it's basically you're dealing with gravity as a force. And the skeleton had to change from a water supported to actually dealing with gravity as a force, on the ground, on the substrate. And there's all kinds of other changes associated with this. Head mobility, you know fish have heads that are largely connected to the body by a series of bones so when you move the head you move the rest of the body. They don't have necks whereas land living creatures have necks, their head can move independently to the body. Now for this whole talk I could have gone through a whole long list of things from excretion, reproduction, and all kinds of different systems that would have to change. And when you look at these systems, you'd say golly gee, I don't see how this transformation could ever happen. So my sort of goal for the last 20 years has really been to look at this in detail. To try to collect new fossils, to try to collect understandings from living recent creatures that tell us a lot about how fish achieve this important shift in evolution. This was sort of the state of affairs in 1987. This is a textbook written by one of my predecessors at the University of Chicago, Len Rodinsky. And I saw this in 1987 in a graduate seminar and it really attracted my interest. 'Cause what he showed is a lobe-finned fish on the top. This is a creature from about, the first ones of these appeared about 380 million years ago. And on the bottom you see an early limbed creature. This is a creature from Greenland, at least that's what we thought it looked like at the time, from about 365-ish or so million years ago. And I remember looking at this and saying, "Golly gee, this is a big transition. "There's a lot for features that have to change." And to approach this, it became pretty clear that if we wanted to address this, we had to find new fossils. In fact if we wanted to find new fossils that bridge this gap, we had to find whole new places to look for fossils. So off we went to start looking for places to find new fossils to tell us about this important anatomical shift. And so like paleontologists everywhere, there are actually some simple rules to go when you want to design a new expedition to look for fossils. We look for places in the world that have sort of a convergence of three things. The first is you look for places in the world that have rocks of the right age to answer the question that you're interested in. I mean so I'm interested in the shift from water to land and fish, so it's no mystery that I'm interested in rocks around 380 to 365 or so million years old. The next thing is you look for rocks of the right type. Not every kind of rock preserves fossils. Sedimentary rocks preserve fossils better volcanic or metamorphic ones. And indeed within the sedimentary rocks there are certain depositional environments, environments where those rocks were formed which are more likely to preserve fossil bone than others for a variety of reason. One because they might reflect areas where creatures lived. The other is, because they were formed in very gentle environments with little erosion so that whatever fossils were there were preserved in some detail. The third variable is really important. Actually it's one of the most important ones. It does me no good if my wonderful rocks of the right age and the right type are buried five miles underground. I mean these rocks have to be exposed to the surface. I mean what we do as paleontologists is walk over rocks for long days, just to find bones weathering out. So it's really exposures, rocks of the right age, and rocks of the right type. There's a third variable when I stated out on this quest. And that was lack of money. And so I started on my, this is really true. I started my first academic job after leaving Berkeley as a Miller Fellow, I moved to Philadelphia as a young assistant professor here in the southeastern portion of the state. And what I wanted really was a field program that I could do on the cheap, or on weekends out of my car. You know paying like turnpike tolls and gas money. And the first thing I did was obviously pulled out a geological map of New York and Pennsylvania and the first thing you see when you pull out a geological map of New York and Pennsylvania is you see that the place is just littered with Devonian Age rocks. So I basically stripped out everything unimportant out of the state of Pennsylvania and what's left here is the Devonian. (laughs) And you can see, I mean it's loaded with Devonian Age rocks. And these span an age pretty much in the late Devonian is the ones I was interested in. And these are rocks about 365 million years old from the Catskill Formation and they extend into New York and into the Catskills, hence the name. So it's pretty clear, from about a three hour drive from Philadelphia, you know I had access to Devonian Age rocks. Got even better when we started to look at the geology of these rocks and what geologists knew. The Pennsylvania State Geological Survey was mapping these rocks for years and concocted a cartoon really version of what Pennsylvania was like at this time. If you wanna think what Pennsylvania was like in the Devonian, get Pittsburgh, Harrisburg, and Philadelphia out of your brain and think Amazon Delta. This is really just a cartoon of the reconstruction. Essentially a series of highlands to the eastern part of the state of Pennsylvania, and an inland sea to the west, called the Catskill Sea. So if you look at the Devonian rocks of Pittsburgh or Cleveland, you'll find they're marine rocks from this inland sea. And a series a rivers that drain from east to west. Now if you're a paleontologist interested in the transition from fish to limbed animal, and you wanna find fossils along those lines, this is perfect. Because you can sample if you're lucky, ancient seas, ancient estuaries, all the way up the stream if you're lucky. I was also lucky in this regard because a graduate student started working with me. This is Ted Daeschler here, this is a picture of us last year, not when he was a graduate student. We were a lot younger when this whole thing started. But Ted and I have been working ever since and Ted really has been a major, major, major part of much of the work, fossil work, you're gonna hear about. But Pennsylvania has a problem, I mean it has two of these variables, it has rocks the right age and rocks of the right type, but unfortunately it's not renowned for its exposures. Pennsylvania's not a desert. And so it turns out the best exposures for us were areas where the Pennsylvania Department Of Transportation decided to put in new roads. What would happen, or where there are streams, but it's actually the road cuts that were kind of a critical thing. What happens is, you know Penn DOT will come through and you know when they want to put a road or a bend in a road or widen a road, what would they do, they'd blow it up, they blow up rock. When they blow up rock, if we were really lucky, they'd blow up rock in the Devonian. And if you're super really lucky, they'd blow up rock in you know the right part of the delta system of the Devonian rocks. And to his was one area which was widened in the 70s. It's a road about an hour north of State College, Pennsylvania. It's a road cut called, don't be surprised, Red Hill, 'cause it's a red hill. A large road cut and when it was widened in the 70s, it exposed a series of the strata, the beds here which you can see going up. This is really a fluvial river environment. And what you see as you walk through here are cross-sections of ancient streams. Ancient streams, their overbank or marginal deposits, sometimes you'll see point bars, these streams look like they meander, it has a very classic sort of deltaic even part of, and some meandering streams within this area. So it's a really rich area. And you see the scale here. There's a car and there's a human being for scale. What is actually our research program was, was to climb up and down the sides of these hills. It got a little tricky but pretty soon, by about 1991 we started to find all kinds of fossils. I mean the first things we started to see were like teeth the size of railroad spikes coming out of the hills here. We started to find jaws to these creatures. This is Ted holding one of our first jaws we found out of this thing. It was just the front end of the jaw. These jaws are like long as your arm and you know with teeth the size of your thumb. So these are really big monstrous fish that are about 16 feet long, up to 16 feet long. So large carnivorous fish coming out of the rocks here. We have lots of other kinds of fish, invertebrate animals. This is the sidewall of a fish, you can see its body armor, it's got a squashed head here. Tons of these kinds of things. And then by about 1993 we started to find bits and pieces of early limbed animals. And this was one that was particularly important at the time. It's an upper arm bone, the humerus, and we started to find a femur, which is an upper leg bone. We found other bones of the skull and so forth. And this humerus is particularly important because it was very similar to a humerus known from a Devonian limbed animal from Greenland. The one actually I showed you in a cartoon earlier. So it was pretty successful. We started to find by the mid-90s, a whole ecosystem really. And I'm not describing the plants. Some of the earliest known forests, with trees, we found their leaves and trunks and so forth. Land was loaded with lots of life, scorpion-like and spider-like creatures, and many of those from these sites, and then tons of fish from within here. And this is what this road cut, Red Hill road cut in Pennsylvania looked like when we reconstructed it with National Geographic. You know you got that large fish, you know with the teeth the size of railroad spikes. You have lots of little armored fish around here, and then you had these limbed animals with the tetrapods, literally four legged creatures of which there are about three or four types coming out of here. It's really remarkable. But it became really clear that to get to the problem that I was interested in, this transition, we weren't making a ton of headway. We were finding tons of fossils, but these rocks are about 365 million years old. And what we were picking up at this point were mostly really well formed tetrapods. We were picking up some of these creatures as well. But from our knowledge of the rocks and faunas around the world, it was pretty clear we were probably in rocks too young. We would have to move back in time. Because to move back in time, we begin to understand some of the transition here and I just want to run through some of the anatomy that's different. And here you see the lobe-finned fish on top, which we knew was closely related to limbed animals. And just look at the head. You see basic differences in the architecture of the head. You know here at the top you see, you know these creatures have like a conical head with eyes on either side. The early limbed animals have got almost like a crocodilian kind of head. It's a flat head with eyes on top. And the architecture of the bones in here actually is somewhat different than the fish on top as well. If you look at the neck, fish don't have a neck. Again as I said before, the head is actually connected to the shoulder via sort of linkages of bones and the head is not independent movable, whereas in early limbed animals, like all their descendants, you and I, have a neck with a head that's separate from the shoulder and there's a series of joints at the base of the skull. And you know finally, and I can make a long list here, the thing that was really interesting to me was to understand the shift from fins to limbs. Fish had fins with fin webbing, you lose the fin webbing when you get to these early limbed animals, and you gain fingers and toes and wrists and ankles okay. And we weren't making a whole ton of headway in understanding this transition. And it became very clear from what we knew and this is what we were finding. This is the family tree more or less. Here's limbed animals up here. These are the fish that are successfully mostly related to them. If we wanted to make any headway, we had to find creatures that were sort of more on this branch, which would really be able to very clearly tell us the sequence of keys or the origin of key features that led to the origin of limbed animals. And to do that, when we look at the age of these things, these things, many of these first appear back around 380, 390 million years ago. Some of them continue all the way up. The earliest limbed animals, tetrapods, appeared around 363, 365 million years ago, the good scalable material. At the time, that's what we knew. But there is a big gap in our knowledge. We didn't have many faunas or floras at this age really here about 375 million years ago. So we had to move back in time. And so we began our hunt again right. So you look, remember we\ look for rocks the right age, rocks the right type and exposures. And going through it, it became pretty clear we had to, we were thinking about going to Brazil, we were thinking about working in Colorado. Everything changed for us one day in the winter of 1998, in my office at the University Of Pennsylvania. Ted and I were having an argument and to settle the argument, I pulled out a college undergraduate geology textbook. (laughs) This is I think, the one that I had was the second edition of Dott and Batten, Evolution Of The Earth. I believed it was pre-plate tectonic when it was written. This book is now I think in the 11th edition or something like that. We settled the debate and as I was thumbing through the book, after that little set to, I came upon this figure in the textbook in like chapter 14. And it stopped me in my tracks and basically defined my research, at least in the field for the next six years. So I want to spend a second on this diagram, it's that important. It says, Upper Devonian Sedimentary Facies. Which means, you know rocks more of less the right age and you know maybe rocks of the right type. And what you see here is a map of North America, here's the United States, here's Mexico, here's Canada, Greenland, Canadian Arctic. And superimposed on that, is a map of the depositional environments, or the environments of rock formation in the Devonian. And the western part of North America was mapped as an ancient ocean. The rocks there were formed, the Devonian at least, were formed in the ancient ocean. But these authors, Dott and Batten, with their citations, identified three areas around the world that were formed in ancient Delta systems, like the Amazon Delta today. One of them, the first one I showed and right here, we know about that one right, that's the Catskill project. That's where Ted and I were already working and finding fossils. The second one is up in Greenland, this is East Greenland, I already showed you a limbed animal form there. This is well known. But there's a third area that stopped me in my tracks, and it's an area extending about 1500 kilometers east to west across the Canadian Arctic, which was mapped by these guys and said to be Devonian Age rocks, like Devonian Age rocks, formed in ancient delta systems, completely unexplored. And that, you know, that literally stopped us. So we ran to the library, and this all happened one morning. Ran to the library, and there we started to uncover a really wonderful story. And just indulge me as I spend a second or two on this little story. The story begins in 1890s in Norway where the Norwegians wanted to run to the North Pole. There's a race to get to the North Pole. And the Norwegians had a really bright idea to design a ship, a really strong wooden boat, and that this wooden boat would be sitting in the Arctic and get carried by currents up to the North Pole. That was their idea. And they had an explorer named Nansen who was a remarkable individual in many ways, who helped design this boat. And this boat's called the Fram, which means forward in Norwegian, and it's truly a remarkable ship. This is a boat that took Nansen furthest North, it didn't get him to the North Pole but it got him close in the 1890s, it was eventually to take Amundsen to the South Pole around 1910, so it went from north to south. In the interim, it went to the Canadian Arctic with this crew. And this is the crew led by Otto Sverdrup, he doesn't look like he's a very funny guy, but you know what they did was for three or four years, they went up to the Canadian Arctic overwintered there on the ship, the sole purpose being to understand the flora, the fauna, and the rocks of the Canadian Arctic. On the boat was this gentleman here, Per Schei, he's the hero of the story. So what they did was, they went to Southern Ellesmere Island, from 1898 to 1902. And they went to these fjords down here overwintering, and it's a pretty harsh place to overwinter, I can tell you that much. And Schei would get off the boat and start mapping the geology. This is Per Schei. He started mapping the geology and you can see, here's a fjord he went to called Goose Fjord, and he started mapping it out and he started to pull out bones of fish. And these were the species of fish, the fauna list that he brought about. Little pieces, rhino flex and this and that. This was actually to be lost. No one really was to cite this. Per Schei passed away tragically after the return of the Fram, he died at age 30. And this work was subsequently just picked up by a guy named Keran in 1915, who described it and then this paper sort of sat in the literature, never really, never really cited until 1974. This gentleman comes along, Ashton Embry, who mapped, who was partly responsible for running a mapping project in the Canadian Arctic, mapping the rocks of the Arctic for a variety of economic reasons. And what Ashton did, is a map in the Arctic, he really did a precise map which basically told us that we had to work there, and where we had to work. And the paper that did it is this, and it was published in 1976. And the reason why I'm showing you this paper is there's a single page in the paper that basically told us we had to go immediately to the Canadian Arctic. And this is the page. It doesn't look like much, a lot of words on the page, but I'll blow up two areas for you. Where he talks about age, blow it up it says, the available data indicate an age of Early to Middle Frannian. You remember the question mark I showed you before, that's the question mark. Then it really, where we lost it, (laughs) was essentially when we saw what he described as the Fram Formation. The Fram Formation is similar to the Catskill Formation of Pennsylvania. So here we had rocks at the question mark that were similar to the Catskill Formation of Pennsylvania. This all happened in the morning in 1998, in you know, in my office in a library at the University of Pennsylvania. We were shaking, there was nothing else we could do, we went to get some Chinese food. So um, we went for Chinese food, I had my kung pao chicken, and this really sealed the deal. I opened my fortune cookie, and it said, soon you will be at the top of the world. (laughing) So I was like, okay we're out of here. Anyway so that got us there. So um, so this is what, so we're dealing with Nunavut territory, here's the North Pole, we're 600 miles or 700 miles from the North Pole, this is Ellesmere Island right here, here's Ellesmere. This is what Ashton maps as the exposures of the, of the Devonian the Canadian Arctic. He named the key formation, the one that's most like the Catskill Formation, after that boat The Fram, and it's called the Fram Formation right here. So it's actually right at that right edge, the question mark. The earliest-known tetrapods, limbed animals at the time, were from up here, so we're significantly earlier in time. And again just to show you the cartoon, he mapped it as a Delta system, with a series of Highlands to the east and north, and Inland Sea to the west, and the series of streams and rivers draining from east to west, so off we go. It was a little bit of challenge because the places up there right, it's not here where I could drive with my Subaru to, you know Pennsylvania, it's up here which creates problems, I mean logistic problems. So the nearest town to us where we ended up working, is a couple hundred miles away, and this is a picture of that town, with a population of about 170 people in spring. It's Grise Fjord, Grise Fjord, Nunavut. It's not, you know, not a hotbed of activity. So it's quite remote you know, so everything we bring is fairly precious, we bring a small crew as I'll show you in a second, because we get around through this ferry operation of helicopters and planes since we're so, we're farther than a tank of gas could take us in a helicopter, so fuel has to be ferried in to get us to where we want to go. So we take these planes which land actually on the rock and Tundra here, it's pretty thrilling actually, and then, if you define that term loosely, and then the helicopters take us into our camps. Because of that it really affects the science we can do, we can't bring big crews and importantly, when we find something, and ie fossils, which are very heavy, we can't bring a lot of them back. And so we leave a lot of what we find out there, and we, you know it's a real decision. We're out there for five or six weeks, and we're making sort of, hard choices about what stays and what comes with us. So we started in 1990, the fortune cookie was in 1998, it took us about a year to raise money, and so we went to the western part of the Arctic first, this is what camp looks like, it's the personal tents, main tent. What we do is basically, these are the Devonian rocks, and since you have this freeze thaw in the Arctic, the bones come weathering out, quite nicely. And you know we walk over the rocks, and when you find bones, you look for the layers that they're coming from. In 1999 we didn't find much, we had terrible weather, and it turns out we were actually in much deeper ocean ancient deeper ocean, than we wanted to be. So following the Delta model, we had to move upstream, and what that meant geologically, is moving east. And when we moved east to southern Ellesmere Island here, that's when we started to find lobe-finned in abundance, bits and pieces of them at least, along these sort of cliff things, as we walk up and down the cliffs. The big discovery was made by a college undergraduate Jason Downes, who joined us one year to sort of apprentice. This is the site Jason was to discover in the morning before he discovered it. So about three hours later, Ted took this picture. About three hours later Jason was to walk over this little patch here, I don't know if you can see it, it's sort of a greenish gray patch. We didn't know it at the time, but Jason had discovered, an enormous quantity of bone. He was late back to camp, it was actually quite a worry, but he returned to camp with pile after pile of bone. So what we did that night was, since it's daylight 24 hours a day in the Arctic, this is us that night around midnight or 1:00 in the morning, actually crawling Jason's site, to find the layer that Jason's bones were coming from. Now this grayish green carpet here was formed, I mean I should say a carpet, of thousands and thousands and thousands of fish bones of which you're seeing like lungfish tooth plates, and things like that here. It took us about a year I should say, I mean a whole year, to actually find that layer, it was actually quite hard, but when we found it, we were able to isolate it, this is Ted here and the crew, the layer was exposed as a series of fish skeletons buried one on top of the other. So Jason's little carpet of fish fragments was formed by skeletons, mostly you know half skeletons, occasionally a full skeleton, but it was really articulated material that was coming out. So we opened up the hole fairly large, and this is what it looked like in 2006 actually after a while, and the big discovery happened here, with the my colleague Steve Gatesy who was cracking rock and discovered this, I don't know if you're going to see it but you the Devonian rock here, see this little V and there's a little slash there. This little V, he said, "Hey guys what's this?" We looked at it, turns out it's the snout of a fish, and not just any fish, a flat-headed fish. You could tell it was flat-headed snout. So remember I showed you before, conical head, flat head? Here I had a flat head sticking out of the cliff, looking me in the eye right. So I kind of knew we'd found what we were looking for. And so what it became then, was to remove these things very carefully. As we remove this one, we found about four more of these flat headed fish, we now have about 20 of them, in various states, from individual bones to whole skeletons, to the skeletons we have about five. So come home on the bottom of the helicopter anyway. So when these came back, it was in the fall of 2005, the preparators take over and these are people who work with a needle and pin, and these things come back encased in plaster. And this is Steve's specimen, they sit for months of the time, this took several months, Fred Mollison in Philadelphia did this, removing the rock grain by grain. And here you can see after about six or seven weeks, a top of a head was revealed. This is one orbit where an eye would be, this is another orbit where an eye would be, looks like you're dealing with the top of a flat head. A few more months go by, and this was starting to be exposed, here's the head showing itself, here's one orbit, here's the other, this is a shoulder, and this is a shoulder, it looks like we have a neck with no connection of bone to the shoulder, this thing got really interesting. As this was happening, a trial was going on in Pennsylvania, the Dover trial, Kitzmiller case where intelligent design. And some people were saying during that trial, that whether that there are no transitional fossils with transitional features in the fossil record, and here sitting on our desks, both in Chicago and Philadelphia, were these things exposing themselves. So as we began to prepare it, you know here's a fish from about 380 million years ago, here's a early limbed animal, from about 365 million years ago, here's the new fish, I use that term for lack of a better word. What it is, we have the extended size from about a foot and a half long to nine feet long. The creature here is 4 feet long, and only I'm showing you the front half. You can see it had scales on it's back, these have been squashed in, scales on it's back and a fin, fins with fin wedding, yet it has a flattish head with eyes on top. It has a real neck so it's lacking an operculum, which most fish have. So it has a mosaic of features of both fish and land living creatures. So you see as a mosaic like a lobe-finned fish, it has fins and scales and primitive jaws. Like a land-living animal, it has a neck, wrists, flat head and expanded ribs. So here we have a wonderful fossil with transitional features, limbs, heads and so forth. So being the discoverers of this creature, we got to name it, and so we wanted the name to reflect its Inuit heritage. We worked there with the permission of the Inuit government, and the Inuit elders, they were very helpful to us, and we wanted the name to reflect it's provenance. And so we had a naming project where we engaged the Nunavut elders, these are the Nunavut elders here, to come up with a name to meet two criteria. Criterion number one, was a name that was meaningful to them and to us. And number two, was a name that we could pronounce. And this is the name of the committee, so that secondary, didn't lend for a lot of confidence that we have a name it yeah. Anyway so um, talked to one of these people, I believe it's this guy here, I'm not totally sure. But we were talking on the phone over about a month, trying to describe what it was, and you know I'd said, well you know we have a fish, and it comes in rock you know, long pause, well no, hunters don't find fish in rocks, they're in the streams or ocean. Like no no no, it's a fossil, and there were so many gaps in the way to communicate here, they had no concept for fossil and so forth. So eventually one conversation I'll never forget he said, "You know, just what is it, "tell me what it is and where it lived." I said, "Oh it's a it's a large freshwater fish." He says, "Why didn't you just say so, "you have yourself a Tiktaalik." I said, "A Tiktaalik, what's that?" He said, "It's a large freshwater fish in our language," So that was the, um, how the name stuck. But anyway back to the biology here. The um, so we had several of these things, and we were very fortunate to have several specimens, because that means we can now take them apart, to begin to understand, how did the bones work, how did the joints work, how does, and then, put the animal together again to figure out, how it compares to creatures along the evolutionary tree. And how does it tell us about how this great transformation happened. And this is what this is all about. And so here you're looking at one of our large specimens, about nine feet long, and you see here's a lower jaw, here's another lower jaw so you're looking at it like this, two jaws like yay. And it was one specimens like these, that we started take limb bones apart. So we found here's an upper arm bone, a humerus, and here's a shoulder. And so we took all these things out and we were really fortunate in that not only did we have many of the bones of the of the fin, so you take off the fin webbing, this thing had fin webbing, and then you see, just like our arm, if you were look at your own arm in the skeleton, you have one bone, upper arm bone, two bones in the forearm, a series of joints here, that as they go distally, they can flex and extend, and those joints go all the way out to your fingers. And that's essentially what you have here. One bone, two bones, you have a series of joints that are capable of flexion, just like like your wrists and fingers. And indeed, we can compare these bones, this bone here and this bone here, to bones that are actually in amphibians, creatures for lack of a better word. And we can compare them up and down the file in the evolutionary tree. What got really interesting is when we took the bones apart, we were able to take each joint apart. So what we did was, we took the shoulder apart. And here's the shoulder of Tiktaalik. Here's the socket on the shoulder, here's the ball on the humerus. And we can see from the detailed shape, what the likely and unlikely patterns of kinematics, of motion of one bone on the other would be at the shoulder. Very unusual shoulder in some ways, it has a ball, but has a sort of cam-stop here, which would prevent it from this action of protraction. We could see the elbow of Tiktaalik. Here's the radius and here's the ulna, and you can see the sockets, where they'd fit on the elbow joint of the distal humerus. This is the arm bone and you can see where they'd fit on, and you can see how this one facet, which sort of rotates this down this side here. That means this bone could rotate far down into the plane of the slide, that's important, I'll show you later. And then we can do it for every other joint in the thing. It was really remarkable to be able to do that, and what we're doing now is actually modeling it digitally, to see how these bones would move on one another. But to give you a sense of all this, let's just look at the shoulder. And I have three creatures here. I have one, a lobe-finned fish, this is a Eusthenopteron, here's an early limbed animal Acanthostega, and you're seeing the shoulders here from from the side. Okay so you're like looking at the animal from the side like this, and here's Tiktaalik. One of the things is, you can see the shoulder socket, here in Acanthostega and you can't see it in Eusthenopteron. Well if you pop on the humerus you can see the upper arm bone you can see what that means. In Acanthostega, this early limbed animal, the humerus or upper arm bone is coming out at you, like this, like a crocodile, so the limb is held to the side of the body. Whereas in fish like Eusthenopteron, the humerus is facing backwards like this. In Tiktaalik it's different it's rotated, that whole joint is rotated, so it's sort of intermediate in position between the bone that faces to the side in Acanthostega, and backwards in Eusthenopteron. And then you just add the other bones in. If you add the forearm bones, the radius and ulna, turns out that the radius and ulna in Tiktaalik, just like Acanthostega, are capable of flexion like yay. And indeed the radius can rotate inwards, and work with a motion called pronation, like moving your thumb inwards. And when you add the other bones in, we can begin to see what Tiktaalik was able to do. Tiktaalik is specialized into a form of a push-up, with elbow bent and wrist extended, with a small set of palmish bones it could, and remember the fin webbing is sticking out here as well, you can support the body in a form of a push-up with a palm-equivalent flush against the ground. What was nice about these specimens too, and it's something we haven't really published it, is the notion that we can begin to see how the fin webbing changes during this change. So you're looking at the type specimen, one of the better specimens of Tiktaalik, from the top, and here you see the fin with its fin webbing. We have several these specimens that are intact, which show the relationship between the limb bones I just showed you, and the fin webbing. And that's really important, because, if you look at a fish like Eusthenopteron and Acanthostega, you see the big shift in the fin webbing, they lose it. fish have fin webbing, limbed animals do not. If you look at Tiktaalik, it's reduced the fin webbing, but it's done so in a very important way. It's done so, not from the outside in, but from the inside out. It's done it over the joints. So where it's lost the fin webbing and these big rods, is over the elbow joint and over the wrist joint. Which totally makes sense, those are the areas where the fin would bend. So this is a sort of more or less what we think what the fin of Tiktaalik was able to do, function like a paddle, or like a prop, enabling the creature to do a push up. This is the reconstruction of Tiktaalik as it was in 2006, as a flathead with eyes on top, pair of nostrils, has a neck where the head is separate from the shoulder, and key in this, is the loss of many bones, including the opercular bone which the, a whole series of opercular bones. It has a fin webbing and inside that fin webbing is an upper arm bones, forearm bones the equivalence, and both proximal carpal and distal carpal bones that is the equivalence of a wrist, big expanded ribs. We now know a lot about the hind fin, with the pelvis and so forth, we're lacking the femur so that's why I haven't drawn it in yet. One of the key things here is really understanding Tiktaalik as a living animal, because then we can begin to see this transformation, And that's what we are going to get to. One of things about Tiktaalik, is if it's supporting itself as the appendanges suggest, on the ground like in a push-up, that's when the neck becomes comes quite handy. If you look at a fish, it has a head fused to the shoulder, and it does so by a series of bones at the back of the skull, and a series of opercular bones, a whole opercular series that connect the cheek to the shoulder. These bones, I should say the opercular bones, have several functions, they actually connect the head to the shoulder. They function in breathing in fish as well. They're pumps that draw water across the gills. One of the big changes in the transition to tetrapods, the limbed animals, is the loss of all these bones, so not only do you have a neck, but you've lost the operculum as well. And it turns out Tiktaalik is much the same. It's evolved the ability to do push-ups, and at the same time it's lost this whole series of bones here. And what this shows is, with this opercular series, is how one change, loss of simple bones, can affect several traits of the creature, from head mobility, which is important for locomotion and the variety of behaviors it has, to breathing as well. Because as you lose the operculum, there are new ways that have to come about to bring water through the mouth. So what's Tiktaalik specialized to do? Here's the reconstruction it's a benthic animal, able to live on the water bottoms, with a flat head with eyes on top, looking at prey as they go by. It's also an animal that's able to live at the margin of water and land, and to feed as a carnivore, to feed either on fish or on the large variety of invertebrates that are present on land, and in the air at this time as well. So if you look at the family tree and you plot with all the various characters that we can do, Tiktaalik turns out to be very closely related to limbed animals. And so no surprise given all the features that we found. Now to really make sense of this, and to get back to the whole point of the talk, which is really understanding great transformations. Remember I opened with up the fact that this is an integrative discipline, this is something we have to pull in data from many different lines of inquiry. When it really comes down, we have to think of ways to integrate these studies of fossils. And I should say right off the bat, that Tiktaalik only gains meaning in relationship to the other fossils that we have in this sequence in this series here okay. It alone doesn't tell us anything. It's this whole batch of things which tell us how this transition happened. But we really have to begin to think about what living fish can tell us, and how they can, what lessons can we learn from them about how fish evolved to walk on land and to live on land. And there's a couple things, I'm just gonna to isolate three. One is, we can study their genes and genetics. That is, we can look at the genetic recipe that builds the bodies of fish, and builds the bodies of land living animals and we can ask the question what's different among them, and we can do that at the level of organs, we can do that the level of tissues, we can do that at a variety of different levels, with increasing precision every year. We can look at appendage support, how do fish support themselves with their appendage, what are the models of living organisms that do this kind of thing today, and we can look at air breathing. How does air breathing happen in fish? And you know we can do with, this is arbitrary, I could add in another four or five things on here, but I wanted to give you some take-home messages about what we can learn from living fish. Well if you look at it, what I'm going to show you here is, what you can see are limbs, these are fins up here and limbs down here. If you take living creatures alone, with no fossils, we have limbs with one bone, two bones, little bones and fingers, and I'm showing you a chicken and a human, and they have a one bone, two bone, sort of finger arrangement as well, despite the fact that it's in a fin, and if you're compare to fish fins that are alive today they don't look a whole lot alike. Here's a lungfish here, a creature Neoceratodus from Australia, and it has one bone okay down here, but it doesn't have any other bones that look very limb-like, neither do any of these other fins here. Where the comparison gains meaning are when we add the fossils to this evolutionary tree, that we begin to see this one bone two bone limb pattern appearing and evolving in our own lineage. So if you just take living creatures, this transition from fin, I'm sorry from fin to limb, looks vast. But when we start to add in the fossil taxa, the fossil creatures and species, you begin to see the links between them. but really where it's important is we can study the genetics and developmental biology of living creatures, in a way that we can't do with the ones that have been dead for 375 million years. And when we do that, what we can begin to understand is the genetic toolkit and the recipe that builds the skeleton of an appendage. We can begin to ask the question is, what are the set of genetic interactions that build the pattern of one bone two bones, little bones, fingers? We begin to ask the question, what's the genetic recipe that controls the number of bones in different parts of the body? It's size and shape and so forth. And if we do that we can begin to see, and by about the late 90s we began to see that there's a very characteristic set of patterns of gene activity and gene function, genes called the Hox genes and others, I'm not going to go through them all, that characterized the development of limbs. It's a cascade of events, of cellular events and genetic events, that produced the pattern of limbs, I'm going to talk about that more tomorrow. However what was really interesting is we knew what this stuff was, how it was happening in chickens and mice and frogs. The real surprise came when we started to look at these genetic interactions and processes acting in fish fins, and what was truly remarkable, is that many of the genetic processes that build the fins and the skeleton of the fins of fish, and indeed that pattern them, are very similar to those that pattern the limbs of limbed animals. And in fact it's very clear that you know, if you were to ask the question, are there any new genes that are patterning the limbs of limbed animals that aren't in present in fins. The answer's likely no. That is it's not like the origin of limbs involved, necessarily involved the origin of whole new sets of genes, it involved whole new sets of genetic interactions, and new ways of genes being turned on and off in new places and so forth. so it's using existing genes in new ways, and reconfiguring them. So the genetic, if you want toolkit, that's necessary to build appendages, was already present when a lot of these fossils hit the scene. So the repertoire was already there. If we look at appendage support in extant creatures, what you'll find is a lot of fish actually support themselves with their appendages. Most famous among this is the mudskipper. Mudskippers can live on land for a period of time, about 24 hours about the max in the mud, and they have appendages but the little type of elbow. And if you look at frog fish, the frog fish is a creature that can walk in the water, this is actually an aquatic creature they can walk around. It even has a little sort of elbow and a distal paddle. What's remarkable about all these creatures that have evolved to sort of walk or support themselves with their appendages, is oftentimes they do it with equivalent kinds of joints. shoulders and and paddles and so forth. But in each case that they do it, they do it with different bones. So here is the frogfish fin, and you remember we have this one bone two bone little bone ray pattern, this is nothing like that. This is three bones, a big old plate, a big old rod, a big old rod here and a bunch of spikes coming off. That's very different from the limb pattern in early, in limbed animals. So what you see is when fish, that are distantly related to Tiktaalik and other creatures evolved appendage support, they evolved similar kinds of joints but they do it with different sets of bones. Only one lineage did it our way, and that's the Tiktaalik lobe-finned fish of ourlineage. Finally you can ask the question you know, the creatures that are doing appendage support and walking in mud and so forth, how they breathe? Well if you look at the evolutionary tree of fish, and you ask the question, how many of these things are air breathers? There are about 30,000 different species of fish, say 29,000 of them or so. Of those that are looked at so far, in the last major monograph somebody identified 375 species of air breathing fish, which is what's been looked at, there are certainly a whole lot more, in 49 different families and if you map it to a tree, it evolved at least 24 times. That likely is about three times to love, based on if you look at the trees that mapped on. So air breathing in fish has evolved many times independently in living extant fish. And how do they do it? The most common way that fish breathe air, at least in the evolutionary tree, is they use lungs. In fact lungs are primitive, lungs are primitive to this thing here, a Polypterus, to lung fish, indeed if you look at Tiktaalik and where it fits on this tree, Tiktaalik's right about here. So lungs hit the scene well before Tiktaalik, and even its distant relatives were around in Devonian streams. They evolved in each case like in the lung fish they evolved to allow creatures to breathe when water gets anoxic and oxygen poor, they go up and gulp air in many different ways. And there other examples as well, there are diverse air breathing organs in this group here which is very specious. Some of these creatures vascularize their swim bladders, they vascularize their mouths there are numerous strategies for air breathing in fish, but lungs are the ones that are actually primitive to our own lineage. So returning to the initial sort of challenge. With air breathing evolving multiple times independently in fish, with the genes necessary to build limbs, already present in fish fins, with appendage support appearing in numerous kinds of fish independently, with intermediates in the fossil record at just the right time in the fossil record, you, you know don't ask the question, how could this transition ever have happened. Ask the question, why did it happen only once. It's so, this barrier between water and land seems to be very porous, at least for creatures that are specializing for the interface between water and land. And why did it evolve only once, I can only speculate. In our lineage and only evolved once. Perhaps it's some sort of ecological king of the hill situation where, you have an incumbent, and it sort of displaces any other lineages that would evolve to walk on land, 'cause there's already an incumbent set of species there. So all this is in terms of its extrapolating to great transformations. You know one way of thinking about great transformations, is the popular one you see day-to-day in cartoons and oftentimes in texts, which is as a ladder-like notion of change that is, you know one species leads to another species leads to another species. That's not how it works. that's not how the water to land transition works, that's not how any of the other great transitions works. It's not like Tiktaalik and its kin were sitting around thinking, oh golly I wanna to evolve lungs so I can walk on land, I wanna evolve wrists to walk on land. It was adaptation to life in water, it was diversification in life in water, finding new strategies to live on the water bottom in the shallows, in the interface between water and land, on the mud flats and so forth, that led to the diverse adaptations which became useful when the need came to walk on land. And so what we think about is evolution not as this ladder, but as Darwin originally proposed, as a tree. As a tree of evolution with a diverse set of strategies evolving. And I should say that there is a unifying theme to many of the great transformations, I'm gonna just close with a series of these. You can think of the transformation from something like you know the common ancestor of an acorn worm and the earliest fish with a skull. If you look at this change, if you look at creatures both living and long dead, what you'd find is a wonderful series of creatures with transitional features between acorn worm and fish and I should say, some of the most important species in this transformation have just been discovered in the last 30 years. You could say the same thing with any other great transformation. Take whales and their derivation from four-legged creatures about 50 million years ago, you could find fossils that have a series of transitional features leading to whales, devise a family tree well supported by characteristics which show how this sequence of changes happened. And again the major fossils that support this transformation discovered in the last 20 years. And the same thing is true with the shift from reptiles to mammals, to the evolution of our own species Homo Sapiens from our primate relatives, from birds to dinosaurs, when underlying all these transformations is this, that some of the most important fossils and understanding the great transitions in the history of life, have been discovered in the last 30 years. and when you think about this field, these are the great times in understanding great transformations. Nowhere has it become easier to find fossils from around the world, to analyze them in new ways with new imaging and new quantitative techniques, to study living creatures with understanding their genes and genomes and sequencing in an ever rapid clip, to understand the the genes that build bodies, and control development, to understand the biomechanics of the features that these creatures use to walk and to live, to understand the ecosystems and the systems that function as ecosystems and the food webs, the ways these creatures would have interacted. Nowhere, at no other time in the history of our science has it been a better time to study the great transformations because this is now a fundamentally integrative field, and an integrative biology. Thank you very much. (audience applauding) (gentle music)
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Channel: University of California Television (UCTV)
Views: 37,508
Rating: 4.7917571 out of 5
Keywords: neil, shubin, fossil, findings, anatomical, transformations
Id: Dilq0JKDgRc
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Length: 56min 8sec (3368 seconds)
Published: Thu Apr 30 2009
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