 All right, good morning. So any questions about the previous lecture or lectures? Nothing? OK. So the few announcements. So the last lecture for me, or actually the last lecture for evolution is next Wednesday, this coming Wednesday. And it'll be a guest lecture. So my office hours on that day won't be from 9 to 10. They'll be 1 to 2 in 2013. So don't expect to see me after that lecture. OK. Since there's no questions, I'm going to start today's lecture. I'm going to do two things today. I want to just finish up and talk about phylogeny. I basically described to you how phylogenetic trees are estimated last time. I talked about the combinatorics of trees. That is the number of possible ways you can't explain the relationships of organisms. I talked about the parsimmonic criterion, which is a method for giving each possible tree a score and then that orders those trees from the best explanation of some data to the worst. And then the idea is to find the best explanation of the data, the tree that minimizes the number of changes. That's the parsimmonic method. What I'd like to do to start off today with is just explain or show you a couple of examples of phylogenies. So this is a phylogeny that includes all of life. Over here, we have different bacterial groups. Let's see, where is human? There is human right there. And where should be? There's the corn is right there. So this is a tree that's very inclusive. This is sort of like one of those t-shirts you sometimes see of the galaxy with the arrow you are here. Well, you are right there in the tree of life. Just want to give you some acute examples of phylogeny. This is one that was a little bit surprising. These are hermit crabs. Anybody here ever had a hermit crab as a pet? I never did. Anyways, these are hermit crabs. They're little crabs that take over a snail's shell and live in a snail's shell. And oops, wrong way. And here, this is a Laskin king crab. You probably haven't had one of these as a pet, but you might have had one of these on your dinner plate. So it turns out that there are people that are interested in crustacean phylogeny, how different crustaceans are related to one another. And one of the big surprising things that came out is that the king crab is just a hermit crab that changed its lifestyle of living in a snail's shell. So once it sort of gave up that lifestyle, it was unconstrained to grow quite large. So here's a king crab nested nicely within all the hermit crabs in a phylogeny. Now, this is an interesting result that came out about, well, 10, 15 years now ago. And it was based on DNA sequence data collected from hermit crabs and from king crabs as well as other crabs. And the interesting thing is that even though the phylogeny was decisively confirmed by DNA sequences, there were these 100-year-old manuscripts of people that studied crustacean embryology, where one of these guys said, well, maybe these king crabs have larvae that look very much like hermit crabs. So it was actually hinted at 100 years before this result came out. So a little bit about dinosaurs, since I figured you might like dinosaurs, at least I did as a kid. So here's your typical dinosaurs. This is a Tronosaurus rex skeleton that's at the Field Museum in Chicago. You might have seen it. It's one of the most complete skeletons ever found. Nicknamed Sue is also quite an expensive purchase by that museum. Here is an example of a bipedal. Most dinosaurs were bipedal ancestrally. A dinosaur, a dromiosaur, knows it has what looked like feathers on its arms. So paleontologists have worked out the phylogeny of dinosaurs. And of course, they're not using DNA sequence information. They're using traits that are preserved in the skeleton. And this is just to give you an idea of the part of the dinosaur tree that is closely related to birds. So here are, let's see, micro raptors. There's archaeopteryx. These down here are things like velociraptors, if you remember seeing Jurassic Park with the dinosaurs that were hunting humans. They're over here. You have a lot of other dinosaurs, some of which had feathers. There's archaeopteryx. I'll talk more about archaeopteryx here, but a very famous fossil find from Germany in a Solonhofen limestone. And basically, the most spectacular of these fossils actually preserve the imprints of the feathers that this creature had. And interestingly, people later went into the paleontologists' interest in dinosaurs, went through a lot of museums in Europe. They found other examples of archaeopteryx, but they'd been misclassified as dinosaurs, or they'd been put in the dinosaur bin, basically, a shelf, because they just happened to be more typically preserved archaeopteryx skeletons that didn't have the feathers. If you take away the feathers from archaeopteryx, it looks like a dinosaur. Here's some other ancient birds, and here are the modern birds. And what I've done along here is I've just plotted out some of the characteristics that all the organisms above this point in the tree share. So simple feathers is something that all these dinosaurs share, complex feathers, a breastbone with a prominent ridge, and so forth. If you go further down this way, you'll find other characteristics of birds, such as hollow bones. This is something that Tyrannosaurus rex shares with birds. So even though you would think of hollow bones as being a characteristic that evolved for flight, it actually is not a characteristic that evolved for flight, it evolved for some other reasons. So many of the adaptations for flight were pieced together from other pre-existing adaptations for some other feature. For instance, feathers evolved down here, and these are creatures that could not have flown there, much too large, and clearly did not fly. So some of the characteristics that we think of as uniquely evolved for flight clearly evolved for some other purpose and were co-opted for flight. So the adaptations for flight were pieced together from other adaptations for some other reason that occurred for some other reason. So just remember that when you eat, like Thanksgiving is what, one month away now, when you go home, you can tell your parents that you guys are eating a dinosaur, and you are. Because the birds evolved from dinosaurs, so according to some people who believe that you should group things by monophylletic groups, birds are dinosaurs. I already explained what that is, and these are just some of the snapomorphies for dinosaurs that you're not, I'll remove this from the slides before I release them. So another enigma in mammalian phylogeny at least was the position of whales. And the problem is that whales are so derived, are so specialized for living in a purely aquatic environment that they've lost, or it's very difficult to compare their features to other mammals and decide with whom they're most closely related. You know, they've reduced their hind limbs significantly, they've fused a lot of the vertebra in their nexa and so forth. So who are whales most closely related to? And for a long time, the fossil record for whales was quite spotty too. That's not the case anymore. There've been some spectacular finds in Egypt and in North Africa that show conclusively the closest relatives of whales, but the molecular evidence was the first that was used to sort of pin down where whales are, to whom whales are related. So there's whales. Notice they're the sister species to hippopotamus, hippos, that's pretty cool. Nobody would have guessed that beforehand. So whales are like big swimmin' hippos, if you will. And here's the phylogeny of some other mammalian groups. There we are, right there. Okay, I'll go, when I talk about fossils a little bit later, we'll be looking at some of the whale fossils and looking at some of the characteristics in these whales' fossils that also put them with organisms like whales and cows and pigs and so forth. And this is a, one last thing I wanna talk about with phylogeny is this hypothesis for the origination of eukaryotic cells. So remember, you should remember from your high school biology that there's two different types of cells out there, the simple cells and prokaryote cells that things like bacteria, where you don't have lots of organelles inside the cell. And the eukaryotic cell, which is much larger and is quite complex, as in a complex internal organization where you have lots of compartments in the cell called organelles. And the endosymbiosis hypothesis for the origin of organelles is that these organelles, such as the mitochondria, actually evolve from some ancient symbiosis between bacteria. So the idea is that the organelles, like the chloroplastin plants, or the mitochondrion in all of life, all eukaryotes, actually evolve from some ancient, it's actually a little ancient bacterium, okay? That's given up a free lifestyle. So this is just to remind you what the cell looks like. These little blue things in this picture, there's a mitochondrion, then you can see that there's a nucleus where most of the DNA in the organism is stored. So there's lots of evidence that was used to point out that the endosymbiosis hypothesis is probably well supported. And this is just a list of some of them. So for instance, I'll just highlight some of them. The mitochondria and some of these other organelles are superficially like bacterium size. They're about the right size to be bacteria. And they have circular DNA. The mitochondria have a circular genome, just like bacteria do. It's got the same stark codons that bacteria use. That's interesting. They also have chloroplastomitochondria have their own replication machinery for making proteins. Like I just said that they use the same amino acid, stark codon is bacteria do. But it's also interesting the antibiotics that inhibit translation or protein synthesis in bacteria also inhibit protein synthesis in mitochondria. That's suggestive. But this is obviously, there's no phylogeny evidence here. So what is the phylogenetic evidence say? Well, what people did is so obvious. It's one of these experiments or one of these things you wish you had done. So basically this is a tree of life again, just sort of like I showed you before. There's humans, there's corn, there's a bunch of eukaryotes over here. And here's a lot of what we would call bacteria. Bacteria are a very large ancient group that are actually more subdivided than what we're gonna say in class. But what they did is they took one of the genes from the mitochondrial genome. Remember the mitochondria has its own genome. So circular genome, like I said, they took a gene, a ribosomal gene that you can compare across all of life. It's such a conserved gene that you can compare this particular gene in bacteria and humans and corn with anybody. And look at where the mitochondria in the chloroplasts fall out. They fall out over here with bacteria. And not only that, this closest relatives of the mitochondria are bacteria that have this endocellular lifestyle. There's some bacteria, most bacteria live outside of their cells. There's some bacteria that get inside a eukaryotic cell and well, they're actually quite interesting, but things like Wolbachia that parasitize lots of insects and actually bias their sex ratios and stuff. And Rickettsia, these mitochondrial and chloroplast genomes actually more closely related to endo, into bacteria that live inside other cells, which is quite interesting. So this is a phylogenetic evidence supporting the endosymbiosis hypothesis for the origin of mitochondria and these other organelles. Wait, I wasn't done with phylogeny after all. So I wanted to give an example of how phylogeny can be used to study speciation. And so what I've got here, there's a gopher, a very bad picture of a gopher. And these are much better pictures of the lice that infest the gopher, okay? So gopher is like a lot of mammals have lice, parasites that specialize in living in the skin and in the hair. And what this fellow, Mark Hafner, who is at Louisiana State University did is he made a phylogeny of the gopher. So here's the gopher's over here and this is how they're related to one another. And then these gopher's often have unique species that live only on that gopher. So here's an example of the lice that live on the gopher. So what I've done with these bars is I've shown you which lice parasitize which gopher. So this louse parasitizes that gopher and so forth across the board here. And the point here is that although it's not a perfect matchup, the phylogenies of the hosts over here and the parasites over here closely match up. And you can really see that on the top part of the phylogeny. Look at this, the topology of the gopher's and the lice is perfectly matched up. And not only that, this is a phylogram so the lengths of the branches means something. So it means that in this case, this speciation event occurred before this speciation event and over here the speciation event leading to the different lice, this speciation event predates this one just as it does in the host phylogeny. So this is evidence that the gopher's, the speciation of the gopher's is also causing speciation in the associated lice. It's a form of allopatric speciation where the gopher's species speciate. It's as if the lice were on different continents, right, that were spreading apart from one another. And so the lice also speciate with the gopher's. This is called co-speciation and there's numerous examples of this. So here's an example of co-speciation in ants and the fungus that they cultivate inside. These are leaf-cutting ants, I mentioned them earlier, and they basically bring these leaves into their nest and they mash them up and they cultivate fungus and it's the fungus that they actually eat. And here is an example of an ant phylogeny on the right and the fungal phylogeny on the left. And once again, you have this matchup of the phylogeny of the ants and the funguses that they cultivate. One guy that they cultivate, whatever. All right, and maybe I'll talk about this too. Phylogenies are also used in epidemiology. So epidemiology is the study of how diseases spread in a population. And you guys are all probably familiar with HIV, the virus that causes AIDS. And in other primates, they don't call it HIV, they call it SIV. It's the same virus, you know, closer-related virus, I should say, but it's a simian immunodeficiency virus. And so the idea is that phylogenies have actually given us insight into where the transfer of HIV into humans occurred from it. It looks like it occurred from chimpanzees. So here's the chimpanzee viruses, SIV. And then you can see the human HIV viruses clustered within the viruses leading to, for the, within the SIV, the chimpanzee SIV viruses. Now how did that spread? It's not like what some of you are probably thinking. It's probably the bush meat trade, actually. So people go out and they kill a chimpanzee and they butcher it. And if you have an open wound on your hand, that's a prime way that you can become infected with HIV, with SIV from the chimp. And occasionally the SIV infection takes over, establishes itself in that person, that person can then transfer it to other individuals. Now the interesting thing about this phylogeny, because you notice down here, it's also found in macaques and manganese, the human viruses, HIV, HIV2 is more close related to some other monkeys, or some monkeys rather, is it implies that there were multiple invasions of HIV into humans. It wasn't a single instance that caused this pandemic or this infection in humans, but rather multiple infections into humans by, from close relatives of their primates. Phylogeny gave us insights into that. And they've even been used in a quarter of law. So here's an example of a phylogeny that was used to establish or suggest that a particular dentist infected his patients with HIV. So this was a case that came up almost 20 years ago now. It was a dentist in Florida. And what happened is a lot of his patients started to get HIV, they became infected. And yet they didn't have any of the other risk factors that are usually associated with becoming infected by HIV. And so the thought was that maybe this dentist was the guy who, for some reason, was infecting his patients. Now it turns out the dentist also had HIV and died before anything could be done about it, before he could be put into jail, for instance. But what they did is they took a particular gene from the HIV in the patients, and they also sequenced the same, the virus from the dentist, okay? Now they also sequenced people in Florida that were HIV positive, but who had never visited the dentist. They called these the so-called local controls and they're marked LC in this phylogeny. And the point is that the patient and the dental sequences clustered together on the phylogeny, except for this one patient down here, this patient F, who was later found to have other risk factors for getting HIV. So this was taken as evidence that HIV, the infection for these patients probably did come from the dentist, who's probably, you know, inoculated them with the virus when maybe he was injecting them with nobikane or something like that. Nice guy. And this is just an example of a phylogeny of viruses sampled from one single individual over time. So this was a study that was completed in the late 90s. And what happened is these men came in about three months after the HIV was established as an infection, and they came in every couple of months and they gave a blood sample to this clinic. And then what they did is they sequenced maybe half a dozen, a dozen of the viruses from that each blood sample. And they did that basically every three months until the patient died. And what you see here is a phylogeny of the DNA sequences taken from one particular patient over time. And you can't really see the labels, but in general these samples taken early in the infection are those on the left and those on the right were those that were taken late in the infection. The point is that HIV has such a rapid rate of evolution that even an infection over the course of one patient, infection in a patient over the course of one infection looks almost like a mammalian phylogeny. You get almost that amount of diversity within one person over the course of an infection. But anyways, these phylogenetic methods have been quite useful in establishing all sorts of useful things about how disease spread in population. And that's probably one of the most practical use in biology. Now, that always takes me longer to talk about these things than I anticipate. I want to talk a little bit about the fossil record now and I'd have half an hour to do so. I want to talk about first, the first thing I want to talk about is the context in which fossils are found. I mean fossils are found in rocks, we all know that. And they're found in specific types of rocks. They're found in rocks that form through the deposition of sediment, one on top of the other. That's called sedimentary rocks. They're not found in volcanic rocks like you'd find in Hawaii. They're not found in ash. Well, okay, so you can find some fossils, what we call fossils in ash. Hopefully the next lecture will show you an example of that. But for the most part, fossils are found in sedimentary rocks, not in igneous rocks, not in metamorphic rocks, that is to say rocks that were later deformed. And there's a few things I want to talk about. Also these rocks have been dated. We know the sequence in which rocks were formed and we can even nowadays at least put or assign specific ages in terms of millions of years before the present two rocks. So how is this done? Well, there's a number of principles that people have used to establish the sequence of rocks in the rock record. I want to go over those. So just a few things. Talk about two principles first off. These were principles that were discussed several hundred years ago. The principle of superposition and original horizontality. So when we go out and we look at the rock record, especially the sedimentary rocks at least, we see a layer cake, right? They don't call it a layer cake, but what you see is you see different strata that are deposited one on top of the other, okay? The law of superposition says something fairly obvious. The strata, the layers that are the lowest in the rock column, they're also the oldest. And that's because these rocks formed from the deposition of rocks on top of one another. They have to be that way. The other principle, the second one I listed is that when these rocks were laid down, they were originally horizontal. So if later, like you go up Claremont Boulevard, for instance, up to Grizzly Peak and you see rocks that are tilted, well, the idea is that these rocks were originally laid down horizontally and the tilting must have occurred afterwards. So the tilting occurred after the original deposition. So this principle of lateral continuity says that, well, when you have these rocks deposited, they're deposited over a wide area, okay? So the area in which, I mean, this is a term you'd get in a geology course here, but the area over which these rocks are deposited, that's called a depositional basin, okay? That's the area like it would be a lake or the end of the Mississippi River and the Gulf of Mexico, that's a depositional environment, okay? So you're gonna have rocks formed in one area. And if later on you see, this is how the rocks were originally formed, now imagine you have a valley of roads out, all the stuff in the middle, okay? So maybe I'll erase this part in the middle. So if you're a geologist and you're looking at rocks on one side and you see, for instance, here's that red rock and here's that greenish rock and so forth. And then the other side of the valley you have this. This principle says that originally, even though they're discontinuous now, there's a separation between them. Originally, the layers were continuous with one another. That's what the principle lateral continuity says. And similarly, this rock must be been deposited at the same time as this rock over here. There's another obvious one, cross cutting relations. So if you also look out in real rocks, you'll find that they're often fractured, especially around the Bay Area. They'll have faults in them. So you'll see faults, that is to say, places where the rocks have slipped one against the other. And this cross cutting relationship says that the faulting must have occurred after the rocks were deposited. This is not rocket science. These are all very obvious principles that I'm talking about. But using these principles, you can piece together a great deal of history, geological history. Unconformities. So what's an unconformity? Well, unconformity, so let's go ahead and put the rocks back here. Unconformity forms like this. You have rocks formed, so they pile one on top of the other, and then rocks also erode down. So the erosion will actually cause rocks to disappear, so now we're gonna erode away some of these rocks. I'll make it kind of wiggly here. There's our eroded rocks. And now we have a new surface. There's our eroded rocks. I don't know why I made it wavy like that. But afterwards, you can have more rocks being deposited on top of these. So you can have periods during which you have rocks deposited, rocks eroded, and then more deposition of rocks. This part is called the unconformity. And you can think of unconformities as being indicative of missing time. They're big hiatuses in the rock record. So some of these hiatuses, the time between when these rocks are formed and the rocks above them were formed, that could be a billion years, right? That's the type of unconformities we can talk about. I'll show you some pictures of unconformities in a bit. And the last principle I wanted to talk about was faunal succession. One of the most practical uses of fossils, I mean, as evolutionary biologists, you think about fossils as being cool because they document the evolutionary history of life. But if you're a petroleum geologist, the coolest thing about fossils is that they help you date rocks. And if you know that one rock of a certain date, you found oil underneath it, it would be really useful if you could find another rock of the same date and then you could explore there to see if you can find oil as well, okay? So faunal succession basically says that you have different species alive at different times. And so you might find one type of species, this guy here, and these rocks. And then you might find a snail over here. These are really lousy fossils, but I'm a theoretical biologist, so what do you expect? And then you find the X fossils up here, okay? This is the pattern we see. We don't see fossils of a species randomly distributed through the rock record. They tend to be clustered in certain rock strata. And so the idea is if you find this fossil here, and you find the same fossil in a rock over here, then these rocks must be the same age. That's how people actually match up rocks from different continents. And we're able to say these rocks here are from a certain time as are those over there using this principle of faunal succession. These are ways, all these principles I talked about, these are all ways of establishing the relative ages of rocks in the events you see documented in rocks. These principles don't tell you that the rocks are 10 million years old or 100 million years old or a billion years old. They just tell you that this rock is older than that rock. It was only in the 1950s that people were able to assign absolute ages to rocks. And the way they use this is they use the radioactive decay of different isotopes. That turns out when these types of methods only work on igneous rocks, that is to say rocks that form from the cooling of molten rock. So you can only use this on the Hawaiian islands, where you have rocks being formed through the cooling of lava. It only works in igneous rocks. And the idea is that when you have these isotopes that go from a parent isotope to a daughter isotope. I'll give you some examples in a table of parent-daughter isotope relationships. But basically you have the spontaneous decay of some isotope into another isotope. And this decay occurs at a constant rate that can be measured in the laboratory. So we know the rate at which different isotopes of atoms will decay. And I'll show you those decay rates. Typically the decay rate is measured in terms of what's called a half-life. It's basically the amount of time that you have to wait before half of the parent isotope is left. So that's the rate at which this decay is measured, usually in terms of half-lifes. So the idea is that when you have igneous rock form, it preserves 100% of the parent isotope and 0% of the daughter isotope. Now over time as the rock ages, you have more and more of the daughter isotope accumulates and you'll have a decrease in the amount of the parent isotope. So if you can measure the fraction of the parent to the daughter isotope, that gives you an idea of how old the rock is. I'm not gonna expect you guys to be able to calculate this, but I want it to be an intuitive. The more the daughter isotope that you can find in the rock, the older the rock is. Because remember it started off 100% parent, 0% daughter. And if you have 1% parent, 99% daughter, the rock must be older than a rock that has 50% parent, 50% daughter. That's the extent to which I want you to understand rate of metric age dating. But it allows us to put an absolute time on the geological time scale. So what is the geological time scale? Well the geological time scale is an easy way for you to earn some points on the next exam. It's basically what geologists came up with in terms of the time of different rocks. So the geological time scale basically is a division of Earth's history into different periods of time. And the part of Earth's history that we're interested in isn't all 3.5 billion years, only the last 540 million years. It's over the last 540 million years that we see evidence of fossils with hard parts, shells and whatnot being preserved. So what is this geological time scale? Well we'll start off at 540 million years ago. And the first period is the Cambrian. You have the Ordovician, the Slurian, the Devonian, the Mississippian, the Pennsylvania, and the Permian. This is 250 million years. These periods, Cambrian, Ordovician, Slurian, Devonian, Mississippian, Pennsylvania and Permian, these are called the Paleozoic. We see the first organisms with hard parts, shelly, shells, trilobites and whatnot, appearing at the base of the Cambrian. Each one of these periods basically marks an extinction. Basically we have a pretty, not complete, but a lot of species die at the end of these periods and that's what makes it easy to mark the different boundaries of these. The largest extinction in Earth's history occurred at the end of the Permian. 90% of marine organisms went extinct at the end of the Permian. So what's up here? We have the Triassic, Jurassic, Cretaceous, 65. These are the Mesozoic. This is the Age of Dinosaurs, okay? The Triassic, Jurassic, and Cretaceous. So the Mesozoic goes from 250 million years to 65 million years ago. 65 million years ago is also a very large extinction event in Earth's history. This is the one that wiped out, well, most of the dinosaurs, the birds looked through it, right? And I'm not that tall. So we're gonna write the last era over here. So we have 65 here. So here we are today. Yippee. All right. So that's the last 65 million years of Earth's history is the Senozoic. So this is Earth's history. It's useful to actually have this in your mind, believe it or not, through your entire life. Now whenever you see a newspaper article, and you know how often newspaper articles refer to the different periods of time, you'll know exactly what they're talking about. And there is actually an easy way of remembering this. I don't know if you remember the one I gave you, King Philip came over from German shores for remembering the different Linnaean hierarchies. Well, this one's, can Oliver see down my pants pockets? Tom Jones can, Tom's queer. Meaning that... Meaning he's strange. But this is one way of remembering it. That's how I remembered it. The last thing I wanna say about the fossil record, the last thing I wanna say about the fossil record is that it's a very biased one, okay? The fossil record is biased. How is it biased? Only certain types of organisms typically can find their way into the fossil record. If you're a worm, that is to say, you don't have any skeleton, you're mostly out of luck, okay? Unless you just happen to be really, really, really lucky. So for the most part, organisms that don't have hard parts, skeletons, shells, don't find their way into the fossil record. It's, the fossil record is very heavy on marine organisms. That is, if you already live in your depositional environment, a place where rocks are formed, you have a much better chance of becoming preserved yourself, okay? And it's also biased in terms of how things are presented to us. So there's an entire field of paleontology. So we should also talk about what are fossils. What is a fossil? A fossil is any trace of a living organism. So it can be a direct evidence of a living organism, like you have a skeleton. That's a direct evidence, that's a fossil. That's the one you usually think of. But we also have lots of indirect evidence. We have burrows, traces of burrows. We have footprints often. We even have what are called coprolites. Does anybody know what a coprolite is? It's what paleontologists call preserved poop, okay? We have coprolites. That's obviously evidence of pre-existing organisms. And there's a field, a sub-discipline within paleontology called tephonomy. Tephonomy is the study of the biases in the rock record, in the fossil record, rather. It's basically the study of everything that can occur to an organism from the time it dies to the time it's found in a museum drawer. Okay, so let's see if I can give you some examples. Screen down. So this is just to illustrate some of the points I made early on about rocks. Here's an example of a typical formation of rocks. You can see the different layers of the strata. These aren't very good. Here's, I'll go over here. Here's an example of a fault. This is, it gives you an idea of the cross-cutting relationships. Here's examples of extrusions of molten lava, molten rock into a pre-existing rock. These are called dikes, but obviously the dikes, these extrusions must be younger than the rocks that they extruded into. I didn't want to take that out. Here's an example of some unconformities and some spectacular ones. The unconformity here is this bed right here. You have a bunch of rock down here than this erosional surface than with new rocks deposited above it. Here's what's called an angular unconformity right here. Notice that you have rocks below it that must have originally deposited horizontally, but then later they tilted. Then they eroded, and then you have horizontally deposited rocks on top of it. Sometimes you hear people argue about the age of the Earth, right? And this took a long time, right? Even without absolute age dating, events like this did not occur in a couple days. This is something that documents millions, tens of millions, hundreds of millions of years of Earth's history. This is basically repeating what I said about radiometric age dating, but now it's in your notes as well. This is the table I wanted to show you. Here are the parent and daughter isotopes in their half-life. So people can actually measure the fractions of these two different parent and daughter isotopes for all these different methods of dating, these different systems. And basically which parent isotope combination you use depends on how old the thing you're trying to date. So carbon-14 dating works really well for material that isn't fossilized, that's not too old, because it's half-life is only 5,700 years. Potassium argon dating is a very popular one. It's had the half-life of potassium argon is 1.3 billion years. So this is a quite useful method for dating rocks that are on the order of millions of years. Here's the geological timescale showing you a lot more detail than you really need to know. I'm only really expecting you to know the different periods and the eras, but you can see that the rock record has been divided up into even smaller bits called epics. And then paleontologists have even, or geologists have even divided these epics into smaller intervals still. I'm not gonna talk about paleomagnetics. I'm not gonna talk about that. Let's go right to fossils. So I will exclude some of the material I just skipped over. So here's an example of a fossil, a trilobite from the Cambrian period. So just to remind you that fossils are any preserved recognizable evidence of preexisting life. So talked about preserved material and trace fossils, things like burrows and whatnot. And the important point here is that fossils are the only direct evidence of what organisms look like in the past. You can think about phylogenies as providing some indirect evidence because you can often reconstruct what the common ancestor looked like, but you can imagine that's probably not the most reliable method compared to actually having the organism in your hand. So the fossil record is the only direct evidence we have. And like I said, it's a biased record. So here is the study of, basically giving you a flow chart showing me what happens in an organism from the time it dies to the time it appears in a museum drawer. But basically you die, you decay, you have scavengers come around, they spread your bones apart, they gnaw on your bones, if you're hyenae, you might gnaw on the bones. So you have this period if the remains are exposed, they can become scattered and gnawed upon before they're buried. The only way to become a fossil is you have to be buried in an aquatic environment. That's pretty much the only way it happens. So you have to be dead and then the best thing that can happen in terms of becoming a fossil is you're dead and you are immediately buried with sediment and then you have a really good chance of being a beautiful fossil when you grow up. Otherwise, it's much more typical and things are scattered and gnawed upon or eroded or worn. So these are some of the biases I talked about, only hard parts, only organisms that are likely to be preserved with the ones that lived in good depositional environments. You can have things like postmortem transport that is, your body floats down a river, say, before it's actually made a fossil and so forth. So let's go ahead and talk about some of the different types of fossils that are out there. And then I want to cut to the chase and talk about some of the more interesting fossils out there out there. So these are examples of microfossils, some of which are quite beautiful. These are diatoms and foraminifera. Certain class of paleontologists called micro paleontologists study these. They're not small paleontologists. They're paleontologists of normal size who study small fossils. But microfossils are incredibly useful for all sorts of reasons, but they've been very useful for a very fine scale dating of rocks. Here's what people call invertebrates, but they're basically organisms without backbones, as you can imagine, that's a large number of organisms. Here's a fossil oyster from central Texas, which I like a lot. And this is what's called a blendite. It's a backbone of a squid, okay, from the Cretaceous period. You can find these types of fossils if you're from New Jersey. There's all sorts of, there's a lot of Cretaceous deposits there, and you can find all sorts of oyster and blendite fossils there. You have vertebrate fossils. Here's that spectacular suet, the Field Museum. Now let's talk a little bit about the sequence in which the fossils occurred. They're not a random jumble of organisms or species out there. Generally speaking, the very oldest fossils we have document the first traces of life, which go back about 3.4 billion years, okay? They're traces of bacteria, basically. The first real obvious, you know, is to say fossils you can see with your eye are bacterial mats, okay? They're basically mats of bacteria called stromatolites. Here's examples of stromatolites from the fossil record. Today's stromatolites are only found in places where you don't have grazing invertebrates like snails and stuff, graze on bacteria that are on the bottom. So you can find them in places that are hypersaline, that is lots and lots of salt that exclude the grazing invertebrates. And so this is Shark's Bay, Australia, where you can actually see living, or modern stromatolites, bacterial mats. But you can see the oldest stromatolites are 2.7 billion years or maybe 3.4 billion years. There's some unclear examples. So fossils can be used to document the earliest traces of life. And like I said, you don't really see a really abundant fossil record until the beginning of the Cambrian, but even before the Cambrian, we have evidence of metazones that is to say multicellular organisms, mostly through their trace fossils. It looks like something happened about the base of the Cambrian, which selected for having hard parts, shells and whatnot. It probably has something to do with predation. That's probably where you had an ecological system had enough layers in it with predators that actually forced the guys that are being preyed upon to have hard parts. But the other interesting thing about fossils is some of them preserved intermediate forms, transitional forms between what we might call considered major groups. This is archaeopteryx. Here's the example of one of the famous archaeopteryx skeletons with the feathers preserved. Archaeopteryx you can think of as a transitional form between dinosaurs and birds. Now, one thing about transitional fossils, there's two things. Most people think about transitional fossils just in terms of preserving intermediate traits or traits that are a blend of both groups. Now they're not, it's not like the, well, let's give an example. So for instance, archaeopteryx, unlike modern birds, has teeth, okay? Has a jaw with teeth and it has a tail, okay? Modern birds have just a little stub. So those are some characteristics that archaeopteryx have that are not bird-like, that are more dinosaur-like. So often these fossils, these transitional forms are sort of a mosaic. There's some characteristics that share still with one group and other characteristics that it shares with the, let's say, birds. But they also occur at a very specific time, okay? So going back to Haldane, remember the guy that has always came up with the right response at the right time? At one point somebody asked him, well, is there any observation that would make you not believe evolution? And his quip was brilliant. It was says, yeah, a Cambrian rabbit. So what does it mean, a Cambrian rabbit? That means a rabbit that's found in the Cambrian rocks, okay? And why would that be so disturbing? Because what you see are everything we know about the history of life, everything we know about phylogeny, for instance, is that rabbits are very derived. They're very young organisms. And to find a rabbit in the Cambrian rocks, 500, or 550, 520 million years before we should expect them, would be very disturbing. These transitional forms not only occur, they don't only have the right combination of features, but they occur at the right time, okay? This archeopteryx was not found in rocks that are 10 million years old, which would be way too young, or rocks that were 500 million years, which were way too old. They basically occur at the time we'd expect them to occur, which is about the beginning of the dinosaurs, okay? I'll give you some other examples. Vassalosaurus, this is a fossil whale. And this is an example of some of the different fossil whales we have. Here's a duradon, it has more modern whale-ish type thing. We also have whales that have fully developed hind limbs. So why would that be important? Well, remember I said that whales are so weird that it's very hard to find any characteristics that link them with other mammals. We found molecular evidence that says that there's, you know, like there are cows and hippos and pigs, right? They're in that group. Arteodactyls. But you don't see any morphological characteristics that would unite modern whales with arteodactyls. But there are some characteristics you find in the fossils that have hind limbs. And one of them is details of the hind leg. So here is a detail of the ankle bone of one of these fossil whales, rhodocetus. Here is a modern, what is it, antelope or pronghorn, I guess. And arteodactyls have this unique double pulley system in their ankle. That's what makes them spring around, okay? So they have this double pulley astragalus. It's not important to know the details of the morphology, they have this unique characteristic in their ankles. These whales have that double pulley astragalus. Pretty cool. So not only does molecular evidence put them with the arteodactyls, so does the morphological evidence that you can see from the most primitive whales. These primitive whales not only do they have the right morphology, but they occur at the right time. And the last kind of most spectacular and recent example is a primitive tetrapod, an organism with four limbs. This is a recent discovery by a paleontologist at University of Chicago, Tic-Talic. I can never pronounce this right. What he did is he was interested in the origins of tetrapods. He knew that in certain rocks of one age, you found fully developed tetrapods. That is to say, organisms with fully developed fingers and four limbs and whatnot. And in rocks just 10 million years older, you didn't. You found things that looked more fish-like but had, you know, they looked more like the sila-canth type of limbs. So he thought to himself, well, the intermediate form must be in that 10 million year interval. So what he did is he looked over the geological map, looking how old the rocks were on the surface of the earth, and he looked for rocks that were of the right age. Then he went there and he found this, okay? This is that intermediate form that has, this is the reconstruction, obviously. But this is Tic-Talic, and this is the things that were just 10 million years older, but they have, or no, this is Tic-Talic too, but you can see it has this modern structure of one bone followed by two bones, followed by a bunch of little bones and fingers, okay? So that is all I'm gonna say. See you, or have a good next lecture.