 So today's lecture is gonna cover most of the same interval of time that we looked at in the last lecture. The big difference is going to be that in today's class, instead of concentrating on what was going on in the marine realm, we're gonna be heading on to land and seeing what is happening on the terrestrial realm with ultimately our destination being this big mass extinction event over here which is mostly a marine event. So we're gonna kinda jump back to the marine realm. All right, that is the goal for where we are going. So before I start though talking about the Ordovician, the Silarian, the Devonian, we've gotta go way back in time and think about what does land actually look like up until that point? At what point do we start getting organisms on land? Well, we probably had organisms on land pretty much as long as we had organisms of any kind at all, but they weren't very interesting organisms to most people anyways. They would have looked something like this. I mean, I think this is actually a lot of algae in here, but originally this would have just been bacteria. So anywhere you had damp environments on the earth, you had the potential for mats of bacteria to form and they likely did for most of earth history. By the time we get into the Cambrian, we get some evidence that at least periodically some organisms are moving up onto land. So we have things like here, this is from a Canadian masters thesis and this is a track way of something moving on and the sediments in this case were interpreted as being terrestrial or at least marginal marine sediments. Over here, you can see these little footprints moving along here, these little paired footprints. This is an atheropod of some kind. This is its tail dragging along. So this might have been a trilobite or something like that moving out. So these are marine organisms that are periodically moving up onto land and then they're probably heading right back to the ocean afterwards. So this is not evidence of actual inhabitation. It's kind of brief journeys on potentially lay eggs or to escape from predators or for some other reason. So at least periodically, by the time we get to the Cambrian, organisms are probably crawling up onto land and then probably going back. But there's no actual fossil evidence that we have organisms continually living on land by the Cambrian. By the time we get into the Ordovician, things change. But it's worth asking, why is that the case? I mean, by the time we are in the Ordovician, we've got fully fleshed out oceans with levels of diversity that pretty much approach or pretty close to approaching the diversity we get today. So why did it take so long for organisms to adapt to life on land? Well, there's a bunch of answers to this or components to the answers. But the basic answer is that it's actually really hard to live on land. And we take for granted because we are very well adapted to living on land and the plants we grow in our houses and our gardens, they're all really well adapted to living on land, but it's not an easy go. It's much easier, especially if you are originally a marine organism to just continue living in the water. So when I say that, what do I actually mean? What are the difficulties involved? Well, let's take plants. And we're gonna journey back to land organisms later on. We'll talk about animals, but right now I just wanna talk about plants. So here are problems that you're going to encounter. You start off and you are a green algae, which we've got evidence, remember going back a billion years. So you're a green algae, you're floating around in the water. Now you wanna come out, you wanna be a land plant. Well, what's the problem? Well, the first thing is that it's really hard to actually support yourself. If you're just floating in the water, it's no big deal. You just float there. But if you wanna actually maintain structure on land, you've gotta figure out some way of building up a hard, rigid element of your body that's capable of keeping yourself erect. So that means you've gotta evolve wood functionally. Well, if you're in the water, no problem, you're not gonna dry out, but if you are on land, you've gotta come up with some way of maintaining your moisture when it's not actively raining. So you need some kind of a cuticle, a waxy material to stop evaporation, or at least to control evaporation. At the same time, though, you need to be exchanged gases, right? This CO2 oxygen exchange. You need to not only have some part of your body which stops water, but it has to still allow gases to come in and out. So you need stomata is what leaves on modern plants have, tiny little holes that allow gas exchange. You need some way eventually, although this is not a prerequisite, but for most of your habitation in something like a desert environment of reproduction, you need something like a seed, some way of exchanging sperm and eggs and retaining a moist capsule that has your reproductive, your embryonic material within it. And finally, if you wanna get big, if you wanna make something which is tree-like, you need some way of moving water, of moving, let's get our water, we're moving our water down here up to the branches. How do you actually get your water up there? Well, you need a vascular system which is essentially a pump that pumps water all the ways up to your leaves. And we have a similar thing, so the cardiovascular system is how our heart pumps water around our body. Well, trees and all plants or all vascular plants have a similar system which allows them to pump water up and into all of their extremities. Each one of these requires a fair amount of evolutionary engineering. So when does this happen? Well, it happens probably, as you'll see in a second, by the Cylurian, maybe the Ordovician. But interestingly, the earliest examples of organisms living on land aren't plants at all and they certainly aren't continuously on land, they certainly aren't animals. The earliest examples we have in terms of fossils are fungi. And so this is a little guy here called Tortotubus and he is the earliest example of a land-dwelling, continuously land-dwelling, body fossils. We have this trace fossil evidence, remember? And this is a fungus. And we're gonna come back to this, but fungus still plays an incredibly important role as a decomposer, right? Cycle minerals or to cycle nutrients within modern ecosystem. And so these guys have gotta evolve in lockstep with plants. They are a really important part of the carbon cycle. And we've got this guy by the early Cylurian. So Ordovician, no direct evidence of body fossils, but we have our earliest example by the early Cylurian of things continuously living on land. Now we do have evidence, though, going back further. All the way is back to the Ordovician. Now they're not directly fossils themselves, but we've got both trace fossil evidence in the form of burrows that are probably from millipedes, this kind of stuff up here. And we also have spores of things that we take to be liverworts or similar non-vascular plants. These are not organisms that are capable of pumping water up. These are things that are still around today, but they're very simple, very simple plants. So we don't actually have the plants themselves at this point, but we've got their spores, which strongly suggests that these things were on land already by the Ordovician. Now in fact, there's some evidence that goes back even further. Remember our molecular clock evidence. So this looks at the genetic kind of dissimilarities between different lineages and tries to calculate the point of departure, the evolutionary separation of two lineages based on accumulated mutations. And so if you look at this molecular clock evidence, it suggests that the earliest land plants might have actually shown up by the Cambrian. So perhaps as early as 500 million years ago. This is somewhat controversial as all the molecular clock data always is. We'll see what happens with it, but it wouldn't be far out if we found evidence as far back as the Cambrian of spores or land plants. But at this point, the earliest evidence is around the Ordovician. That looks like when we start getting land plants showing up based on their spores. All right, so what are the earliest land plants look like? Well, they're really simple little things, but we are interested in building up trees and then eventually building up kind of forest ecosystems. So we wanna look at what are the earliest examples of a vascular plant. And you will find that they are wholly unimpressive. So the Devonian in New Brunswick in Quebec is actually one of the best spots in the entire world to look at this stuff, this early evolution of forest ecosystems. I mean, this is not a forest at this point. These are very, very small things, maximum 10 centimeters. So an inches, this thing here is, I mean, almost a scale actually on my computer screen right now. These are gonna be very small organisms. This is Cuxonia. It's one of the more famous ones. This is a reconstruction of the American Museum of Natural History. So you could find these things in New Brunswick. It's one of my goals is to go out and find some of these in the field. I have never personally done that, but you can. And here are some examples. This is from Quebec, and these are examples here of a different genus of very simple, very simple vascular plants. You can click on that link and you can see some beautiful images. This is from Megosha. So this point I'm gonna show you a quick video that showcases a worker who's doing some important stuff up in those rocks in New Brunswick and Quebec. I've always been really interested in what the earliest plants were like and how they relate to living forms. And this is one of the very best places in the world to come and collect fossils that would give us that kind of information. The plants are very abundant and they're extremely well preserved. And we found a lot of very early plants here. One thing is that they differ from modern ones mostly by lacking any leaves. So what we find are stems and we find their little reproductive bodies and they have different kinds of architecture so we can tell different tacks of the part and we find that there's actually a pretty good diversity of early plants that are represented in this deposit. Actually here's the kind of plant that we get out. And this one has, there are many, many stems that have been preserved in the rock. They seem to be lined up. This might be actually due to the action of currents when they were being deposited. They have little tiny spines all over the sides of them and I can recognize this as a genus that we find in several parts of the world called Saudonia. If you were to walk through a landscape in the, in this case this is the Silurian, this is what the landscape might look like. It might look like something like this. So these are all these little Cuxonia, these little very early vascular plants and they would have been just a few inches tall. These are the rocks hanging out here. Anyways, this has a little CGI reconstruction to give you an idea of what these things, what these things would have looked like. By the time we get into the late Silurian, things start to get big. Okay, they don't really get big. This is a foot tall by this point. This is a, still a small organism. This is Barigwanathia, that pronunciation may not be correct. And this is a really famous early or sorry, late Silurian organism. And the reason for that is that this shows some increase in size. But more importantly, this is a reconstruction over here. You can kind of see it if you squint over here. But these little guys here are some of the earliest examples of leaves. I mean, they're very simple leaves you can see, but that's a big, a big step forwards. So this is our next kind of big step towards something that looks like a tree. So I'm gonna actually make a real forest. We've got some increase in height, but more importantly, we've got the presence of leaves at this point here. All right, so that gets us to the late Silurian. Now I wanna show you something which is growing within these forests around the same time. And this stuff goes through showing up in the late Silurian and continuing through the Devonian. And this has another cool connection to New Brunswick and Quebec and a Canadian connection as well. There's a guy named Dawson who was a very famous early Canadian paleontologist. He started the Red Path Museum. He's from Nova Scotia, actually, originally. So he originally described this thing over here and gave it the name Prototaxides. So what is Prototaxides? These are actually some of his original illustrations from the 1850s. This is a modern microscope image of a thin section through this thing as well. And so what Dawson thought he was looking at is a big stump which had been colonized by fungus that was decomposing it. So as of 2000, we have around 2001, we've changed our interpretation of this thing. And we think now, and this is super weird and a good reminder that although the present is a key to the past, the past was sometimes incredibly weird and the present sometimes is not a good reflection on what the past was like. It was a wholly different place in many cases. So this thing here, which got up to 26 feet tall, this is a two and a half story building is how big this thing was, a meter in diameter. This is a tree-sized thing. So it's totally reasonable Dawson thought this thing was a tree. It turns out that our modern interpretation of it, looking actually at it in microscope image here, this thing here seems not to be a dead tree colonized by fungus, but in fact, the entire thing was a fungus. So this is a giant fungus, we think. There is nothing like this in the world today. This is the kind of thing that you see when you watch sci-fi movies, when you go to a planet and there's these giant mushrooms. This was a giant mushroom. So if you were walking around the landscape in the late Silarian, early Devonian, what you would see is a landscape filled with very small vascular plants and potentially house-sized giant mushrooms protruding from the land. It would have been an eerie and quite literally alien landscape. So the role of mushrooms, both these weirdo guys here, but also mushrooms as decomposed is super important. So now we're gonna take another quick little break and I wanna show you a quick little video produced by PBS that shows this stuff, social and mood constructions and also really highlights the role of fungal evolution in the advancement of these early forest ecosystems. 420 million years ago, a giant rose along the river banks of what would become North America. It feasted on the dead, growing slowly into the largest living thing on land. This towering colossus was an animal, plant or mineral. Instead, it belonged to an unlikely group of pioneers that ultimately made life on land possible, the fungi. If you're anywhere on land right now, like not on a fishing boat or some floating oil rig, then all the life that you see around you right now is there because of fungi. Fungi like the small, unassuming little decomposer known as prototubus protuberans. It's one of the earliest known fungi in the fossil record, dating back 440 million years to the early Sulurian period. Prototubus grew near coastlines and rivers on the supercontinents of Gondwana and Laurentia and regions that would eventually become New York, Saudi Arabia, Sweden and Scotland. But back then life in these places was anything but lush on land, signs of life for sparse. There were bacteria, algae, early plants like liverworts and possibly some of the first terrestrial arthropods. But if it weren't for fungi, things probably would have stayed that way. Because even though they weren't very big, early fungi like prototubus had a superpower, the ability to break down almost anything using digestive enzymes. Fungi eat by releasing enzymes that break down organic matter. This allows them to take the nutrients they need from their material while helping the rest to decompose. But these enzymes could be so powerful that they could eat into solid rock. Given enough time and some help from erosion, many fungi can weaken rocky earth and eventually form fertile soil that plants can sink their roots into. So big complex life on land, like vascular plants, probably wouldn't have been possible if prototubus and its fungal predecessors hadn't prepared the land first. Once plant life started to spread and diversify on land in the Devonian period, fungi were there to help. Again, some scientists think that the first land plants use symbiotic fungi on their roots to help them gather and transport nutrients. In fact, most plants still do this today. If you pull a plant out of the soil, you'll probably see a lot of dirt sticking to little white hair things on the roots. Those hair things are actually bundles of nutrient-absorbing tendrils called hyphae from fungi living symbiotically with the plant. And these fungal structures are incredibly important for making arable soil that plants can grow in. They help stabilize soil, retain moisture, and hang on to nitrogen. So without fungi, soil would just be non-nutricious dirt. But you know what's weird? Despite their starring role in making life on land possible, ancient fungi haven't been studied much by scientists. That's probably why back in 1800s, when paleontologists discovered a fossil that was eight times taller than the tallest plants of its time, no one expected it to be a fungus. Geologists first discovered this enormous fossil in 1843 during a coal survey in Gaspe Bay, Canada. It was more than eight meters tall. She had to kind of like a tree trunk. And it came from a layer of earth that dated back 420 million years when the Salurian period gave way to the Devonian. A good 20 million years after tortoitupus first appears in the fossil record. And for a long time, researchers were totally stumped by this specimen. Stumped, is that some kind of tree trunk joke? The fossil remained unstudied in a museum collection for years before paleontologist John William Dawson found more new specimens in the 1850s and tried to classify them. Dawson thought this thing might be a primitive conifer tree with some sort of fungus growing on it. So he named it prototexides, which means first you after the tree he thought it most resembled. Then in 1872, botanist William Carruthers wrote a paper saying that prototexides couldn't possibly be a plant. He said it was probably a giant mound of algae like maybe kelp. And to his credit, English botanist Arthur Harry Church also studied prototexides in 1919. And he said it probably was a fungus, but nobody really paid attention to him at the time, which is too bad. So based on Carruthers' findings, prototexides was filed under probably weird algae for more than a century. Until the 1990s, when Francis Huber, a curator at the Smithsonian Museum of Natural History, took yet another look. And he focused on a feature of prototexides that had long puzzled scientists, these strange rings. They look kind of like growth rings, like what you'd find in modern trees, but the rings and prototexides were lopsided and not always concentric. So Huber examined them under the microscope and found long tube-shaped cells that were similar to the hyphae found in modern fungi. He concluded that prototexides wasn't a plant at all, but rather a member of team fungus. And this was the same conclusion of another study done in 2007 that looked at the chemical makeup of the fossils. Now, how can chemistry tell you whether something's a fungus? The answer, as always, is carbon. We talk about carbon a lot around here because carbon is the stuff of life and different kinds of living things can be identified by how much carbon and in what kinds of fossil contains. The thing that researchers focus on here is a ratio of various isotopes of carbon, like carbon 12 and carbon 13. Now, plants have pretty consistent ratios of carbon 12 to 13 because they all get their carbon from the same place, the CO2 in the air. But things that eat instead of photosynthesize, like animals and fungi, pick up carbon isotopes from their food so their ratios can vary a lot. In the 2007 study, compared the isotopes and several fossils of prototexides from different eras, it found that those ratios changed radically over time, probably as its food sources changed. This means prototexides was not a photosynthesizer but an eater. It got its food from other living things. Now, there's still a chance that this enormous not-plant thing was something else, like a lichen. Despite looking like weird plants, lichens are actually fungal hybrids that house their own algae or photosynthetic bacteria. So far, no one's come up with a good way to prove whether prototexides was a pure fungus or a lichen. But either way, it was a giant in its day and it marks the peak of fungi's reign over life on land. When they first appeared in the early Devonian, the fungal spires of prototexides towered over everything else that grew, burrowed, and crawled around them. Like the humble tortoitubus, prototexides fed on dead stuff. But unlike its tiny predecessor, the giant fungus sent out huge networks of hyphae in all directions, sending food back to its central pillar. And in turn, it may have been a source of food and shelter for early invertebrates. Scientists have even found little boreholes and tunnels that look like insect burrows in some of its fossils. All told, the heyday of the giant fungus spans 70 million years, a short time that saw a lot of change. When prototexides first arrived on the scene 420 million years ago, vascular plants had just begun to colonize the land. But by the time they vanished 350 million years ago, the first trees started to tower over the fungi that had paved the way for them. No one's sure why the giant fungus went extinct. And I, for one, am bummed that I will never get to see one. Some speculate that it grew too slowly to recover from being chewed on by invertebrates all the time. Others suggest that the rise of the land plants brought too much competition for nutrients. Either way, ever since the demise of prototexides for hundreds of millions of years, fungi have continued to thrive but with a much lower profile. Today they're mostly found in the dark, close to the surface and even underground. But the world we live in was made possible by these fungal pioneers with their ability to digest rock to create soil and to derive life from death. Okay, let's continue on in the production of the evolution of our forests. At this point, we've got something that looks like a real tree. I mean, you can see that that's got a canopy here. These things are quite large. This is arguably the world's oldest proper tree. This is a thing called Watizia. It was described in terms of all the components of it. You know, were found and combined together to get a full idea of what this thing looked like. Relatively recently, you can go check out this article 2007. This thing is mid-Devonian. The particular fossils here are from New York. So there is Watizia. Here's another example of a thing. This is Archaeopteris. Now I want to be clear. This is not Archaeopteryx, which is a completely different organism. That is an early bird. This is Archaeopteris. And this is a very famous, fairly widespread genus of early tree. What's important, you can find these things at McGuasha as well, at the State Park. There's a beautiful collection of flora in addition to all of the amazing marine deposits up there. So this is what a forest might look like by the time we get into the late Devonian. The early Devonian, the late Silurian, it would have been just, you know, tiny little things like this with giant towering, you know, mushrooms poking up out of the ground, these big giant mushrooms poking up like this. By the time we get into the late Devonian though, you can walk around and you can see tree-sized actual trees, right? Now there's still not the towering redwoods that we have today, right? But these things are getting up to be fairly large by the time we get into the late Devonian. Now importantly, everything here is still super weird. None of the modern groups that make up trees are in existence at this point. These are all essentially giant versions of things that today remain really small. So all of this stuff down here just got big, right? It got big during the Devonian, but we still haven't produced any of the modern tree groups. And really importantly, we haven't produced any group of organism which is capable of doing something that we just take for granted that trees do, which is make seeds. Seeds by this point do not exist. Instead, what we are seeing is a bunch of things that are all reproducing like ferns do today or like horsetails do today. So these are giant versions of spore reproducing organisms. Now there's a limitation that comes with spore reproduction. If you guys think about where ferns occur, where do they occur, they occur in moist ground. And the reason for that is they need the moisture as do horsetails. If you think about where horsetails occur, you see them in swamps and things like that, club mosses, all of these things are still around today. The tree ferns over here are not, but all these other things are. And they all today occur in moist ground or actually where you've got, you know, growing on the edge or slightly into the water. And the reason for that, we are not gonna get into this in detail, is these things reproducing a really weird way, which is that they produce these spores, the spores then actually grow into a separate life stage. This is a little plant that we don't think of as being part of a fern, but it is. And this separate little kind of stage of life, the separate little kind of plant actually produces sperm that just swim around free in the water. These are my little sperms and they're just cruising around free in the water. So they need a moist environment where they're gonna go and directly encounter eggs and then they produce eventually a new sporophyte, which is the thing we're used to thinking about as the plant entirely. So this stage of the evolution or the evolution of the reproduction of the life cycle of these things requires access to water, at least, you know, some water on the ground. So that means that you cannot inhabit, you can't colonize most of the world. Where you think about trees growing today, like pine forest, none of these guys are gonna be able to hang out in the pine forest. And therefore all of these early inhabitants of these early Devonian forests aren't capable of colonizing most of the earth. So that big colonization step is gonna require another big step, which is the production of seeds. And we get our first seed producing organism actually showing up around the same time, is the Toritosperms, the seed ferns. These are not actually technically ferns, we just call them that because the branches of them look a lot like ferns. And you can find examples of these pretty much anywhere you find shales or sandstones within the Sydney area. Come down to the lab and I'll show you tons of examples of tree ferns. Now the rocks around Sydney are of course younger than the late Devonian. They're into the carboniferous. We'll talk about these late class, but next class. But these things continue on, and seed ferns continue on, and they're common organisms well into the kind of coal era, the carboniferous era that we're in. But this allows plants to suddenly move outside of the water. So originally we had organisms that had to actually, the plants had to live in the water itself. And then eventually with vascularity, they're able to move a little ways away and they can start colonizing moist areas around the water. And they start to get bigger eventually, but they are still trapped close to the water. They can't move a long ways away because they need that water, or at least moist, moist ground for the reproductive stage. So the trick of learning how to produce seeds allows these guys to suddenly colonize whole areas of the world that they were not able to do before. So they're able to start sweeping out across the world, and they massively increase in abundance. And we'll come back to what impact that massive increase in abundance of these things in the late Devonian is having on surprisingly things like the ocean and the atmosphere. Okay, but we want to keep going. So here is the late Devonian. What are the forests like? Well, we've got these tree-sized things over here, some of them which are actually producing material by seeds. We've got still all of these other organisms that existed before, they're still there. So this is a bizarro forest, but some of these things are getting pretty big by this point. You could walk through, and you could hide behind some of these things. So it's still, it's an odd environment. It's an odd environment, but it's an environment that's starting to look a lot more like a forest that you are used to. So here is where we are. What is this doing? Well, this turns out to be not only altering the climate. So we'll talk about precisely how they do that, but the most obvious thing is remember, all of these things are literally built of CO2. Their bodies are made of sequestered CO2, but they're also having more important, their roots down here are also having important effects on carbon cycling as well. But importantly, what's happening here is these things are creating a habitat, and that's a habitat that what can live in, well, us, well, not us directly, as you'll see in a second, but the earliest tetrapods. So a little bit of foreshadowing. The earliest tetrapods, that is our group, things that have one, two, you know, you can't see the other one, three, four, four legs coming off of them, that's our group here, the tetrapods. They show up in the late Devonian. We'll come back to that in a second. Before we get to them, I want to remind you about fishes. So fishes, remember this idea that we are all low-fin fishes? Well, what do I mean by that? So we've got all these different groups of fishes. These are the groups that things like sharks are in. Pretty much everything modern is in here. Remember that when we're in the Devonian, we have less total number of species, but we have more individual groups around at the same time. So this is the age of fishes in the Devonian. It is also the age of the beginning of us, right? So the beginning of tetrapods is gonna be in here in a second. I'm gonna try to write tetra in here. So tetrapods is showing up in here. And we are a branch, which is just coming off of the low-fin fishes over here. We are a type of low-fin fish. So low-fin fishes are not a group that we think about very much. Because as you can see here, there are not very many species of them left. There are very few species, in fact. But the ones that exist are pretty cool. And you should see when I show them to you that if you kind of squint and expand your mind a little bit, you should see that they have some characteristics, even just with superficial examination, that suggests that they are a bit weird in terms of fish. And are a lot more like us in some ways than they are other fish. So the first is the silo canth. And the silo canth, if you don't know the story, stop this video right now and Google the silo canth. This is a thing that's often referred to as a living fossil, that these beautiful blue fish. When you see them preserved, they lose their blue color. But when they're alive, these beautiful blue fish. We thought these things died out with the dinosaurs. And eventually, off the coast of Africa, one was pulled up by a fisherman. The fisherman there knew they existed. They caught them periodically. But it came to the attention of a local, of a woman who was running a local kind of museum and had a deal with a fisherman that she would take weird specimens. She drew a sketch of it, sent it off to a, to an ichthyologist in, I think Britain, I don't recall. And just based on her pencil drawing, you can look at the pencil drawing. It's actually a pretty good drawing. He immediately went, oh my God, because it's like you just drew a picture of a T-Rex and said, hey, I found one of these, right? That's how we thought it was dead for 65 million years. But it turns out, no, there are populations of these things that are still around. They exist off of the coast of Africa and they also exist, now we know, off the coast of Indonesia as well. We found them there. There's some hints they may exist in other places as well, potentially off the coast of Mexico. But as far as we know, the only place they exist now today is off the coast of Indonesia and Australia. So look them up. But what you're interested in seeing is these really robust fins they've got here. And when we look at the actual underlying skeleton of these, they've got these rays coming off here, but this component of it here is a really robust bony element that has a lot of similarities to our own limbs. And those similarities are not by accident. Then we've got these guys here. And these guys are super weird. They're super weird for a couple of reasons. One, they've got lungs. So they actually breathe through lungs. Lungs are actually a relatively primitive condition. Lots of things have lungs. Lungs get co-opted and they turn into swim bladders and things. But importantly, if you see these things, they've got these long kind of gangly arms on them. And that combination of these arm-like appendages, I mean, these are just heavily modified fins, but they really do look like really weak little arms and the presence of lungs. These are lung fishes, not surprisingly. These things really do start looking like something you might be able to build a tetrapod out of. I started to be able to build an amphibian out of. The primitum was primitive of the tetrapods. So we've got these guys. And then importantly, we've got, well, these guys. This group down here, that's us. Looks like a picture of, I don't know why they put an old man that's Darwin or something down here. And then the question is, how do you get from this stuff down here to this guy right down here? And I said that these limbs here are superficially similar to the kinds of limbs you're seeing here, the kind of things you're seeing here. But you know that they are really superficially similar. So how do I get down here? These things, they have some similarities, but they are super different. And the question of how you get down here really was a mystery for quite a long time. Now there's another group that I have not thrown in, and this takes us back to Quebec, and it's this guy right here. So this is a thing called Eustonopteran. And this guy here, they call him the Prince of Maguasha. This thing here is an amazing fossil. And the land plants from Maguasha are really important, but I told you the fish are really the reason why that is such an important locality and why it's recognized as a spot of international importance, as UNESCO designation. And it's largely for this particular fish right here, which is reasonably common in Maguasha. So this is the third group of the lobe fin fishes. So expect I might ask a question like, what are the three groups of the lobe fin fishes? So what are they? They are the sea locants. They are the lung fishes, and they are the tetrapodomorphs. So this guy is a tetrapodomorph. And guess what? So are we. This guy over here is also a tetrapodomorph. So that is the line I did not put in. There's Maguasha. This is a very stylized picture of a Eustonopteran. I don't know, this kind of looks like a spaceship to me. This is the locality. I have not been there. It's on my dream spot to go. You can go up there as well. It's been a UNESCO site since 1999. And here is a fossil of Eustonopteran. You can see these robust limbs on it. But when you actually look, I said limbs, I meant fins in it. When you look within the fin, what's amazing about this one is not only is this thing really robust, but we can actually pick out specific bones that correlate to specific bones in our own arm. So there's the humorous over there, the funny bone, quote unquote. There's the radius. There is the ulna right there. So these are components of our own arms. And there are, it probably has lungs because it had not only external nostrils, but nostrils are not the technical term for this, but it also had a nasal opening inside of its, inside of its, the inner part of its head as well, which suggests it was breathing through there. So it most likely had lungs. It had fins that are very similar to our limbs, at least superficially. It even had bone marrow. This is the earliest example of a vertebrate that had bone marrow. So these things are super cool and they've got a ton of them and they're preserved like this. So you can see why this place is a place of international importance. So I'm gonna remind you of this idea here that we talked about earlier on, this idea of homology. So homology, remember, is when we see structures which are similar because they have a similar evolutionary origin, but are being used, right? They're being used often for different functions. So you can see these seen components here. There's your humorous, there's your radius, there's your ulna right here and here it is in a bird. You know, here's these same things in a bird. Here it is in a frog. You can see them all over here in a frog and here it all is. These are these same bones within eustenopteran. So this is an example, a beautiful example of homology, but you're gonna just go, Jason, look, I can obviously see these things in here. This thing here, yeah, it kinda looks like one, but this is really primitive. I need a lot more steps to get to here. This is not a convincing path at this point. So that is kind of true and this is where we sat for quite a little while. Now, Greenland offers some additional information in terms of fossils. Remember that in paleontology, we can't just do, we can do some experiments on things like how things decompose or how they preserve mineralogically, but a lot of the time we just have to patiently wait or go actively looking, as you'll see in a second, to find particular fossils. So there are fossils that come from Greenland very early, very early tetrapods and tetrapod-like organisms. And they've been known for quite a while, but they were really collected in large amounts and also studied and their significance was really identified by this paleontologist here. This is Jenny Clack. She's sometimes referred to as the diva of the Devonian. That's by British tabloids. She was a researcher in England. She actually just really unfortunately passed away. I just found this when I was building this lecture. She literally passed away three days ago. So you can read, I think this is an obituary I put up, if not just you can Google it and you can read her journey. It's really amazing, both her scientific contributions but also the kind of background sexism that a paleontologist would face, a female paleontologist even as far back as or as recently as the 1980s when she was doing her important fieldwork. So she went up to Greenland in 1987, I believe and brought back several tons of material, including some really excellent examples of this beast right here. This is a thing that had been described previously but she was able to get really good information about its limb architecture, how that connects to the pelvis and to the shoulder blades here, the head, all the rest of this. This is a thing called a cantostega. There's another thing called ichthyostega. I don't remember if I put it in this PowerPoint as well that she also famously studied but we're gonna talk about, oh, there's ichthyostega right there. A cantostega is what we're interested in here. So a cantostega, the ichthyostega by this point, this thing is getting pretty similar to a modern kind of salamander or an amphibian or something like that. In many ways it's still quite primitive here but let's jump down to this thing here, the cantostega. So this thing it's got these big tail rays off of this. So this is very fishy in terms of its tail apparatus. It's clearly living in the water. It still has a very streamlined swimming body. If you look at the limbs here, these things have eight digits and it's not capable. There's no way that this was able to support itself. It simply could not stand up in any way at all. On the other hand, these paddle-like things look a lot more like hands than they do look like the fins of Eustenopteran, for example. Its neck right here was separate from its kind of shoulder blades, was able to move its head around kind of like we do. You can wiggle your head right now. So this thing is still a fish but it really is a transitional thing. It's kind of half fish and half amphibian. So that's a cantostega. So we go from Eustenopteran to a cantostega and we've got ichthyostega on the far end. This thing is something that's capable of dragging itself up onto land. This thing is really quite tetrapoddy at that point. So what else have we got? Well, here's our cantostega. I'm not gonna, I just went over this. But you can review this later on if you want. These are fish-like characteristics. These are amphibian-like characteristics. All right, so here's our Eustenopteran. If you look at the architecture of its limbs, right? This is clearly a fish. This is clearly a fish. There's a cantostega over here. Here's a cantostega. This thing has a number of characteristics which are pretty amphibian-y but it is still clearly a very fish-like organ. This is more fish than it is amphibian. And this guy over here is tulipotan. Apologies again. The pronunciation may not be correct on these guys. I'm sure the vertebrate paleontologists are squirming every single time I try to say these things out loud. So this thing here is undeniably an amphibian. This is a perfectly normal amphibian. And so we've got a fish over here with rigorous bones. We've got a fishapod over here, right? This is not something that's gonna be able to haul itself around. And then we've got a proper amphibian over here. The question is what separates these things or what unites these things, rather? I mean, getting from here to here is still a pretty large step. So how do we do that? Well, let's see what else we've got. Turns out we've got this thing. So this is a thing called pandericthes and you can see this is a, we've got a more robust. We've eliminated some of these finer, ray-like components of it. And we've got a thing here that looks a lot more like your own arm does. Your upper arm and your lower arm bones here, right? Starting to look a lot more like that. But it's still a very large jump in between the two of these. If you look at its skull, it's starting to look a lot more like the skull of an amphibian, a lot less like a fish, et cetera. So there's pandericthes. And this is where we end up as of just a few years ago. So here's Eustenopteran, here's pandericthes. And we jump over to Acanthostega. And then on the other side of Acanthostega, we have stuff which is very clearly an amphibian. And we've got this big chunk though, of missing time. So sometimes people say that paleontology is, you know, not a, you know, it's a non-falsifiable or evolution is a non-falsifiable science. It's not a real science. It can't make predictions, it can be falsified. That just isn't true. So the beauty as we looked at in class of looking at these kind of, you know, phylogenetic trees is that we are able to make predictions. So a prediction should be that if we know the time interval that this thing lived and the time interval this thing lived and the time interval that this thing lived, that we should be able to find some organism that has features that are intermediate between these two organisms at a time which is intermediate between these two organisms. And that's a prediction. And so that is a prediction that some American paleontologists actually followed up on. So this is Neil Shubin here and Neil Shubin and Ted Daishler, they wanted to try to find that missing link. So they set out to try to find it. They started first in America and America has lots of great Devonian deposits and they looked out and they found this thing here which is cool but also very clearly an amphibian. This is not the transitional fossil. This is not the quote unquote missing link. So instead they turned to Canada and Canada has a vast expanse of rocks of the correct time interval. So they went looking along and it took their grant money and they went up north and the first spot they went looking is up in Nunavut and they went to Nunavut starting in 1999 and they spent an entire field season there and they found nothing. They did not find what they were looking for. And so they headed up to Ellesmere Island. If you guys have done field work and you haven't but I have actually my supervisor did a bunch of work up here in Ellesmere Island. My field work area is all over here as I told you last class. This is crazy expensive. Everything's got to get flown in by float plane. It is insanely expensive to operate up here. So these guys were blowing through money even though it was a relatively small operation. You'll see it in a video. And so they went up there and they found nothing and they found nothing and then they found nothing and then on their fourth season they were going up part way through the fourth season they hit Paytard. They hit Tiktalic and Tiktalic is now that fossil that is going to fill in that gap. It's another Canadian contribution to the flushing out of the great kind of tree of life. And I'm going to let you see how it was discovered the story of its discovery in a short video now. This part of the Arctic has rocks of the right age and the right type to hold evidence of a great transition when our ancient fish ancestors moved from water onto land. It's hard to believe when you look at this frozen landscape that once this was a warm, watery world swimming with life. This valley 375 million years ago was a giant floodplain and that floodplain was filled with rivers that swelled their banks and sometimes shrunk but in those conditions formed swamps and streams of all different sizes. And inside those streams was diverse life. And somewhere out there, our distant relatives sank into muddy graves which would preserve them for 375 million years. At the end of our stay in 2000, we found a hill loaded with fossils and over the next four years, we dug hoping to find the fossils we were looking for. Well, it was the second week of July in 2004 we're all working in series in this halt where my head is right next to Farish's feet and Farish's feet is next to Steve Gates. We're digging together and Steve says, Hey guys, what's this? Ted and I go running over to see what Steve was referring to and what we saw was this V here. It was covered with rock. And as soon as we saw this V and we saw these teeth under it, it became very clear that this little V we're seeing is the tip of a snout and that this was a snout of a flat-headed fish. Based on other fossils from slightly younger rocks, this feature alone suggested we might have a transitional fish. Okay, we get home. We knew we had a flat-headed fish, but how much of it did we have? Then about a month and a half goes by and they start to find the orbits, the eye holes. And then we see the shoulder and then we see the fins and then we see more and more and more and more until we see pretty much the entire top side of the body. So you can not only say, okay, what did this animal look like, but we can begin to ask, you know, how did it work? How did it move about in these 375 million-year-old streams? The local Inuit people came up with the name Tectolic for our fossil. It means large freshwater fish. But although this creature had the scales and fin of a fish, it also had the flat head and rotating neck of a land animal. And when we looked at its fins, we realized it had the beginnings of the bone structure that's shared by all four limbed vertebrates today. It had versions of an upper arm, forearm, even parts of a wrist. This was a fish from a pivotal moment in evolutionary history. Descendants of fish like Tectolic would go on to spawn reptiles, mammals, and eventually, us. Alright, so this is where the tree looks like after Tectolic. Here's our Eustonopteran. Here's Pandaricthes. There's Icathostega. Sorry, Icthiostega. Icathostega. And there is Tectolic. And so Tectolic's often referred to as a fishapod in that this thing was still a fish. It lived in the water. But it wouldn't have been able to kind of do planks. Like it wouldn't have been able to do push-ups, right? To kind of prop itself up and kind of take a look around, right? It's got a head, which is kind of a crocodile-looking head, which is on the way towards this kind of head up here and a lot less like this head down here. It is a classic transitional fossil. And the more detail you actually understand of the skeletal architecture of modern tetrapods, the more you see that this thing actually does have a lot of very subtle features that really unite it as a fantastic transitional fossil. You've got this beautiful sequence now, going through it like this. Okay, so that is where we end up. We've got something now, which is kind of filling up this gap. And we'll flesh this gap in with lots more of other things. This is not to say, by the way, this is actually the direct ancestor of a cathastega, whether the cathastega is a direct ancestor, but these are representatives of what the thing that would have been the ancestor would have looked like. The form that gave rise would have been something like these things, right? They are kind of placeholders for those points in evolution. So this is where we are now, this beautiful transitional sequence. And I put a few more. I didn't. I mean, this diagram I stole. I put a few more things in there. These are all these kind of things that are definitely in the amphibian area. Here's our tick-tock, and here's the actual timeline moving through it like here till we get the proper amphibians over here. We've got all these. We've got tons of these things. It's a really well fleshed out tree now. It's a fantastic record. What are the classic stories now in paleontology? But it begs a question, which is if they are coming out in the Devonian, this is when we finally get things that are fish to jump out onto land. They've been swimming around, you remember, since the Cambrian. Why did they come out in the late Devonian? And why not come out hundreds of millions of years beforehand? At this point, we are getting into around 400 million years. They could have come out potentially, well, not hundreds, but 800 million years before. We had fish swimming around, no problem, more than 100 million years before. So what is it that is driving them to come out at this point in time? The simplest answer is the answer we've already given you, which is that by the Devonian, by the late Devonian in particular, we've got forests, really weird forests, but forests. And inside those forests, you have a whole ecosystem of organisms. These are relatively simple insects. You don't have things like ants. You don't have bees. A lot of the things we take for granted don't exist yet, but a lot of the more primitive groups are hanging out at this point. And we've got things like this, the early Devonian. They are coming out coinciding with those very early, very, very short, you know, proto forests. And by the late Devonian, notice these are detritivores. That means they eat material, which is the decomposing material. So they're eating all these bits of plants, along with the fungus. This is all part of the recycling system. Now, if you've got these things out, then you've got things like this. This is a gigantic organism. Look, it's built into its name right here. This is not. I mean, if you were this little mite over here, this thing is terrifying to you. But for a scale, this is less than a centimeter long. So this is, you know, as long as your baby fingernail, something like that. But in the world of, this is a primitive, a very archaic spider, right? Probably not technically a spider, but it's an arachnid. Anyways, you can click on this link here. So we've got predators coming out. So the insect ecosystem is also fleshing out, and it's getting bigger as well. And what that means is that at this point, right, where we started with the, we started with the plants and the plants acted as, the plants are acting as food for these things. And those things are then acting as food for these kinds of things, which means that you've got what? It means you've got food for these kinds of things, right? And you've got this whole kind of co-evolution, whereas the plant matter gets more abundant and larger. It starts to support an ecosystem of insects, of arthropods. And they're co-evolving along with it. They're performing important ecological roles, helping them as well. But more importantly, they're just eating it up, right? So now you've got biomass in the form of animals on land. We've had biomass in the form of animals in the water since the, well, I mean, in terms of fleshed out ecosystems, since the Cambrian, but there wasn't really sufficient nutrients available on land to support animals until that point. If you were, you know, you were a horseshoe crab, or, you know, a trilovite, whether you might come crawling out onto land, take a look around, lay your eggs, but there's no real purpose to stick around until we get really into the Devonian. Now the Devonian, now we've got stuff to eat, which means that we start evolving this ecosystem of insects. And where we've got an ecosystem of insects, we have a lot of biomass, and that biomass can support ever larger organisms. So really what you're seeing here is the trees, the evolution of flora, driving the evolution of animal ecosystems by providing both, you know, environments they can live within and crawl upon, but more importantly, providing both through their living bodies and their decomposing bodies food for arthropods, for insects, and once we start to build up larger insects, that provides an incentive for fish to start coming out. There are other things, maybe dry and get up, try climate change or things like this, but the most likely, the most likely driving force is simply that this guy is competing for food, and not this guy, in the early fishapods, there is a fine-in amount of food in the water, they're all competing for it, so if you're able to come out and eat some of this guy over a year, then you've got an advantage over everything in the water, and so that puts, you know, impetus to come on out and eat the material on land, and as they start making brief little sojourns, they start to get more and more and more of all. Now that's a simple version of the story, but it's most likely what's going on, is that the colonization of the land by tetrapods is simply the chasing of nutrients as the expansion of the arthropod and the floral communities create, you know, the ability to do it. You can't live on a land that's devoid of nutrients. So we have this, I put a garden of Eden up here, I mean it's not a garden of Eden if you're, you know, this mite and this thing is trying to eat you, but we've got this, you know, our first real fleshed-out ecosystem of plants and, you know, all these things, we don't have things like this here yet, we've got amphibians wiggling around out of the water by the late Devonian, and then of course everything dies. So this is our second big mass extinction right here, the Devonian extinction. Now this is a bit weird in terms of our extinction. So you can arguably say that this is not actually a mass extinction at all. I mean it's mass in the sense that we lose a lot of groups, but the problem is it is not really an episode at all. It is a prolonged interval of extinction, probably with a series of more intense pulses, one a little bit further back from the end and one really obvious one right up close to the end. So whether you want to include this along with these other guys is still actually a point of contention. There's a new paper that just came out relatively recently that really brought higher resolution to the timeline here and really demonstrated this thing is not even probably, this is probably more like 50 million years right, the timeline of this extinction. So it's a, there are pulses of severity within, that's supposed to be a five, but it is a prolonged interval of biodiversity loss over the Devonian. So this is our event. What do we lose? Well we lose all of those cool armor jawless fishes, the astrachoderms, they're all gone. We lose our placoderms, they're all gone. Goodbye, Dunkley-Austias. We hit really hard, pretty much everything in the marine realm. Acrotarks are a boring little microfossil group, but the cool big guys, trilobites, the cephalopods, the gastropods, the snails, all of these things are getting hit hard, hard, hard. The reefs though take the biggest hit in terms of long-term effect because remember that up until this point we had magnificent reefs. In fact the reefs in the Devonian are the greatest that they have ever or will ever be in the history of life and they never recover. And I mean never, I mean we are literally even today even with things like the Great Barrier Reef we are still not in the world of reefs that used to exist in the Devonian. But for a long interval after they hadn't even recovered at all. So I'll show you back to this guy here and you see that we go through an interval for the entirety of the rest of the Paleozoic. Paleozoic, Mesozoic boundary right here. We don't actually have any true reefs and I'll talk about this in a second, right? They just get hammered. They get hammered at this point. We lose all of these amazing things and it's not until we get into the Mesozoic that we actually see reefs come back in terms of proper reefs again. Alright, so there's our no true reefs. So this is a paper you can click on this link in the PowerPoint version that just did a really high resolution look through 26,000 year time slices through the Cambrian all the way through to the very beginning of the Mesozoic. And this paper suggests that it's probably actually about a 50 million year interval. This interval of extinction activity. So is this an event? I mean it depends on what you want to do. It's certainly a thing. It's an episode, I mean whatever you want to do. So people argue about this, you know, semantics really. But this extinction is a prolonged interval of crisis. It still requires an explanation because things are different, right? The rate of extinction and the rate of diversity loss and the rate at which new species are arising are different than they were in the background. They are radically different. And so that requires some kind of invocation of something which is if not difficult different in kind, at least different in magnitude, a scale of what the normal background events are in Earth history. So causes like with all the mass extinction events are still relatively uncertain. They are argued about, but the longest standing explanation and probably the most convincing explanation is that it is climate change. And the climate change could have been due to volcanism. This is now the trend everywhere is everyone starting to look for evidences or lips as an explanation. And I told you that this was one that was invoked for the Ordovician pretty convincingly based on mercury data. And then that mercury data has just become pretty questionable. I haven't followed up on this to see what's going on with the Devonian. But this was a kind of a new hypothesis. I mean, it's not new, but the mercury one is pretty new. So could it have been enhanced volcanism is messing with the climate system by adding or subtracting greenhouse gases? Or it could have been. We've got something else that's more important and more obvious going on. And again, these mechanisms they're often presented in the media as if you know, new thing, new cause but these causes don't have to be mutually exclusive. You could have volcanism as well as this. But trees are actually the most likely mechanism causing this. So how are trees causing a mass extinction event? Well the first thing to remember is that trees are themselves made of CO2. And if you are sequestering CO2 in massive amounts of plant biomass that means you're going to have less CO2 all of the things being equal in the atmosphere. And so just the production of all this biomass might actually have drawn down CO2. But it's not just as simple as that. Because when we start actually adding plants to the system they are going to be enhancing the rate of weathering and they're going to be changing how erosion takes place. So where you've got your tree and we've got the tree that's actually got roots, those roots are going through and they're capable of actually breaking apart the rocks. And that's going to start increasing. It's going to increase the rate of weathering. But also all of this organic matter that is coming off of here as well as the roots holding this stuff together, they start to produce soil. And soil hosts this whole microbiome of organisms. And they're respirating as well. And so this ends up being a very chemically active environment. A very acidic environment relative to just dry dirt. It retains moisture. So this combination of more acids down here as well as more water down here means that the chemical processes that break down rock in an environment with trees are also going to be amplified. Those are greater than I could put pluses in here as well. Pluses just remind you it's an increase in amount. So the idea is this is all pumping out or pulling down CO2. And then at the same time as these things are pulling down CO2, this on the other hand is enhancing weathering which means you've got more nutrients that are going to be cruising on off to the ocean where they're doing what in the ocean. They're going in and they are fertilizing the ocean which means you've got plants that are growing in the ocean. Those plants now are built of what? They're built of CO2 too. So that enhanced biological productivity in the oceans perhaps due to this enhanced weathering is also going to pull down CO2. So you've got CO2 here and you've got CO2 here coming out. Now where you've got all this biomass, what happens? Well it's going to die and it's going to fall down as it decomposes. Remember that loses up oxygen and so you're going to end up with less oxygen in the ocean. So we probably have a combination of glaciation and marine anoxia. And as we saw with the Ordovician, if you kill the oxygen and you cool things down that's not a good environment. The killing the oxygen part for the Ordovician that was the second phase of that two pulse extinction. So we think that that's probably most likely what's going on but it's of course complicated. So here's just the story that I talked about as well. Increase chemical weathering which means more nutrients which means you trophic oceans which means anoxia. So that is the most likely explanation for what is happening at this point. But regardless we go through the interval of millions of years of decreased biodiversity. And that sets the stage though for rebound in the Carboniferous which is going to be the point of next class, the topic of next class. We start to talk about these giant bugs here. And they are having a showdown with one of our distant relatives here, this tetrapod. This is the environment that you would encounter if you went into a time machine. If you're in the Sydney and most of Cape Breton, this is what the background environment was like. This is the coal interval. This is our own unique history and we will talk about this next class.