howdy so uh today um let's not just focus so last time we talked about how to read a phylogeny today let's talk about how to draw a phylogen if you're given some information so let's just start off with some sort of uh very basic statements about relationships between a few groups and then we're going to draw those out and then we're going to see how to describe the different parts of the tree again and um a few more terms to learn about how to read a phylogeny and and how to look at it from the perspective of when you're drawing a phylogeny so first you know I've mentioned this before but as you might know actually a favorite Texan fossil dimitrodon which you know is this four-legged sail-backed Predator you see it quite often at museums and um other places in Texas it lived uh uh we know that I lived here in Texas it was originally discovered in Canada we find it actually over quite a geographic distance is most closely related to in this particular diagram that I'm going to draw that's true because there's actually three different lineages of vertebrates that evolve to live on land fully not in other words not to be amphibious and so one lineage we call this synapses the dimetrodon and us we're part of that lineage that's why Once Upon a Time demetran used to be called a mammal-like reptile we now know that in fact dimetrodon was probably a lot more like a mammal than you would even expect um another lineage is that T-Rex was most closely related to a pigeon so these statements are all relative it just means that the things that we're going to include on the tree are going to be just these particular things all right so T-Rex is most closely related to a pigeon and that's because that birds and dinosaurs not alien dinosaurs like T-Rex they're part of one of those three main lineages and it's the same lineage that crocodiles also belong to it's the lineage we call the diopsets and then there's a third lineage um we used to call these the antaspids that's maybe not the best name for them anymore but that's the snakes and lizards and they're all part of one group it doesn't necessarily include everything you might think of as snakes or Lizards but it's most of those things and um this group overall is more closely related to to uh the crackling Edge all right most related to The Croc lineage which by the way is the diopside lineage so now let's let's draw that out what does that actually look like when we're talking about a phylogenetic tree so if we just come over here we can say all right well if we go all the way back to the Carboniferous basically there was two big splits in vertebrate tetrapods in land rolling vertebrate tetrapods and one of those splits became the synapses the other split became the diaposins and the lizards and snakes the antasputs so with that information and we're gonna we're gonna just we're actually gonna let's give this a little bit of a time scale here I talked last time about how phylogenies can be drawn relative to time so we'll say that that's the carbon fris what's the carbon that first the carboniface is a period of geologic time when as you might guess from the name carbon it's when a whole bunch of coal actually got deposited into the Rocks um we actually split it up into the Mississippian and Pennsylvania because guess what Mississippi and Pennsylvania are full of coal from two different intervals of the Carboniferous it was a time when there was a lot of wet very uh very second very you know um uh what's the word um a very uh vibrous forests and these forests would flourish there'd be oblitiation the the sea levels would change um sediment would come over and bury the forests and then the forest would regrow and this happened many many times and that's why we have really rich coal deposits from that time all right so we're drawing this phylogeny to to time and so we're just going to say all right so this this lineage here this is going to be lizards and snakes and we'll call this the modern it's today time equals zero that does mean of course uh we're going towards zero here going from left to right I think that's a rather natural way to do a Time axis um some people they like to draw to zero over here on the left it doesn't really matter which way you do it but over here we've got our us maybe getting a little too up there on the video there we go there's us I won't draw anything too much up there and then we've got our our sale back friend the dimetrodon back here in the Permian so this here is our let's draw a snake now lizards snakes there's our snakes of course there's lizards and snakes today so they stretch all the way to the Monitor and this Branch here let's make that crocodiles let's draw a little crocodile here big long snout I let me go ahead all right that's a pretty good crocodile all right so crocodiles then we'll take this little Branch we'll extend this so This Branch becomes dinosaurs which then will split into non-avian dinosaurs and avian dinosaurs we don't really know when that particular split happened we don't have to be really too specific about it so the premium period ended about 200 whoops 250 million years ago and we'll maybe have a split back here this is the Cretaceous I'm just going to draw um kpg Cretaceous paleogene boundary what is that that was 66 million years ago that's when well when we believe a really big rock smashed into uh the Yucatan Peninsula and set off a series of events that caused the extinction of the non-aviant dinosaurs so between 250 million years ago and 66 million years ago will say that there was a split one of those became our pigeon friends hello there's our little pigeon friend and this split over here there's our T-Rex all right so let's look at what I've drawn here and just sort of consider that I've sort of drawn it rather small but that was actually kind of with an intent because we're going to add to it later all right there's our Dimetrodon Dimetrodon us all right so what do we see here so we see just like last time we see a phylogeny it's composed of branches I said before that it unless it's marked it as having a scale the scale doesn't matter in this case I actually did Mark a scale so where the splits happen is supposed to be sort of my rough guess about when the house particular group split apart from each other so we can see that dimitrodon isn't a direct ancestor of us but it's a close cousin you know it's a it's um a distant Uncle it was only one step away from our lineage maybe or you know just a few steps away from our lineage um obviously a lot more uncles than just one but uh um but it probably isn't too distant from the lineage that led directly to us crocodiles there was probably a lot of time there that between crocodile splitting and the diopsides that eventually became uh birds and dinosaurs um and then there was some time between the split between when T-Rex shows up and when that split happened where pigeons came off that happened that happened sometime in the Jurassic T-Rex was like 100 million years later all right um so this is sort of the the grand picture really about what's going on in terms of vertebrate Evolution that we're going to talk about in this particular class um so one thing to keep in mind is that for example when we say diopsids which is this group right here or when we say synapses which is that group right there um we're referring to a clade what is a clay a clade is a is what is a group that includes the ancestor of that group and all the descendants of that ancestor so we can actually we can pick a particular point on this tree and everything that comes off of it basically everything that is later than that point on the tree that's all one clade all right we're not snipping anything off um not avian dinosaurs those aren't really a clade right because we have to actually we have to say oh it's everything after this point but not the stuff that starts looking um more like an archeopter X or a chicken than uh looking like a velociraptor right the rules get a little more complicated claims are really what biologists really love to use as sort of biological units to when they want to refer to groups when they want to refer to tax that they really want them to be clades and this property of having an ancestor and all of its descendants is a term we call monophyletic what does that mean well as you can as you probably guessed phylogeny phyletic that means Branch it means tree okay mono means one one branch all right so if we're just picking off one branch then that means that it's um uh monophyletic so let's just add one little Branch here and we're going to have a little stegosaur branch now the fact that I've drawn it on the other side of the pigeons that doesn't matter remember the the even though I've got a time scale on this flipping around whether the T-Rexes are on one side or the birds are on one side that doesn't matter that's still the same tree so I've drawn a little stegosaur there splitting often yeah that's probably right you know T-Rex is more closely related to pigeons than stegosaurus but if we wanted to take the group that we know of the group that that we sort of think of instinctually as a dinosaur the non-avian dinosaurs that group isn't all of the descendants of the ancestor of dinosaurs so that group has a property to it and we call that property Para phyletic so that's when we've taken an ancestor but only some of its descendants where we've sort of sniffed off additional branches off of it um if we were to say for example monkeys monkeys are a paraphality group because we're snipping off Apes we're not we're not including when we say monkeys usually we don't mean Apes like gorillas or chimpanzees or orangutans or us so that's a thing to keep in mind is that paraphyletic groups they don't have as natural of a definition it's not the ancestor and all the descendants you're sort of are well arbitrarily or not you're sort of taking things off of that now I think there's an argument to me that there's some groups like not even dinosaurs that are too hard to think of right like the the change to a bird is a really significant transition we're going to spend a lot of time talking about that in this class actually about how non-avian dinosaurs evolved avian dinosaurs some of the non-eating dinosaurs evolved into alien dinosaurs so that's a really significant transition so there is in some way sort of a natural way of thinking about that division but it's not as easy not as simple as a monophyletic group and that's why biologists really love to talk about collates um now looking at this crocodiles lizards snakes things like dimetrodon things like T-Rex well those are the things stegosaur all of this stuff that's what we kind of mean when we're thinking about reptiles right when we use the word reptile that's what we mean we've been well actually kind of just going back here maybe going back all the way here you know trying to include the ancestor um maybe not right we don't really know exactly the the when that split between the diopsides an app spit group and the synapse bids really happened maybe that was more of an amphibian kind of thing rather than a reptile thing you know maybe we wouldn't include that in reptiles so like what is this thing back here question mark all right but however we Define reptiles it's really arbitrary maybe that's sort of a paraphyletic thing but maybe what we're actually doing is we're taking different branches off of the tree and we're putting them together into a box and if we do that if we're putting if we're not just saying it's an ancestor and all or some of its descendants we're actually taking different branches from different places on the tree and they don't all share a common ancestor that's in the box with them that group poly violetic those are really unnatural groups um a long time ago Sailors used to consider whales to be fish that would be a very polyphyletic group right all everything that we think of as a fish plus whales so we're not really we're sort of brand you know there's uh there is definitely an ancestor in there an ancestor of all fish but then whales those are part of mammals right now um so we would generally think of that as sort of a polyphyletic group right in fact actually when we use fish itself and sort of a modern common day parlance well fish itself is a paraphyletic group right because what is fish missing fish is missing amphibians fishes because amphibians are descendants of fish right well what else is also a uh a fish then all other vertebrates as well dimitrodon's a fish we're a fish lizards and snakes fish crocodiles fish T-Rex one very very large fish so the word fish is actually when we start thinking about it really in terms of a monophyletic label really expansive it applies to a lot of things we are not just people we're not just humans we're also Apes we are also synapses like dimitrodon and we are also fish like all the other invertebrates that walk on the Earth we're just fish that figured out to walk on earth so um fish itself is paraphyletic but the thing that really makes the old definition of fish with whales also many invertebrate groups you know like star fish uh or um uh various types of crustaceans or mollusks or whatever that that definition of fish was very polyphilitic it was taking different branches from all over the Tree of Life putting them together and saying that's a group all right we really strive not to try to use polyphyletic groups paraphyletic groups aren't great they're a little arbitrarily defined um uh they're not as natural as monophyletic groups which we also call