So the thing that I want to talk to you about is we can have trees, but, and those trees may be drawn to scale, they might not be drawn to scale, and how we particularly rotate a particular set of branches doesn't matter. It may make it more readable. But the thing that I want you to look at here is actually a story about characters.
So, we're characters. What do I mean by that? These characters?
The different animals? No. Characters are a word that biologists and paleontologists use to refer to how we infer trees like this, right? Like, we don't just dream this up.
We actually have evidence that we have to use in order to actually figure this out. And in fact, we do a lot of arguing about this sort of thing and where particular groups come out on this particular tree. So, the synapsids back here, they're united by a particular trait. And often we draw this, you know, we'll draw this as maybe like a line or a little box that we show on the brush.
branch leading to that group. And then we'll say something about what that trait is. So what do synapsids have? Synapsids. Sounds like things are being kind of like maybe glued together or something like that.
Well, that's right. They actually have a fused skull. Unlike the other groups of terrestrial vertebrates, synapsids sort of close up their skull so they don't have as many holes in the skull as dinosaurs do.
You've probably seen a tyrannosaur or another dinosaur skull at some point in the museum and you've probably thought to yourself, man, it looks like it's got a lot of holes in it. Yeah, that's right. That's a very big difference that goes all the way back. Dimetrodon has a... more like us where all the different parts of the skull are more fused together and there aren't as many holes.
And you might think to yourself, why would you ever want to have holes in your skull? Well, here's the funny thing. Your skull can be entirely closed off and that might provide better protection for what's in it. However, that makes it more difficult for there to be be places for your muscles to attach to. And you're like, well, why do I need muscles on my skull?
I don't need muscles. I got muscles right here. Look at these guns. No, the muscles that are really important in your skull, really important to all of our skulls is vertebrates.
The thing that we all do is chew. Our jaws actually have to have really powerful muscles attached to them. And figuring out how to design a skull so that you have a place for attaching this enormous muscle that connects to your jaw, really difficult actually.
Dinosaurs, crocodiles, Dimitridon, us, all sorts of different ways and solutions of trying to solve this problem, but we're attaching those muscles. All right. The synapsid way of doing it. closing off the skull and figuring out some other way of attaching a really large muscle to the outside of the skull. The dinosaur way of doing it, actually allowing that muscle to pass through into the inside of the skull.
So synapsids, they have that fused skull. So that's a character. It's a type of character that once it's gained, it's not really lost.
And it's a character that is a change from how things were previously, going all the way back to fish and amphibians. The different pieces of what we will call skull are all different bones, actually. The skull even of a modern fish really is still multiple bones, kind of not entirely fused together in the same way that our skulls are fused together.
So this was really a change, a change from an ancestral condition, a change from how it was from the previous lineages. So these few skulls, that's a change. That's what we call a, so this condition, we call that an apomorphy.
All right. So an apomorphy. And because it's shared by this particular group, it's something that unites that group.
We call it a syn. Whoops. Syn, as in the.
the German word for same, it is a synapomorphy. syn with an N. Synapomorphy. All right.
Now there's obviously some conditions that develop, but we only ever see them in one particular taxon. So for example, humans, relative to all other living animals at least, humans, you know, you compare us to a chimpanzee, for example. We have lots of morphological adaptations that make us very different from chimpanzees. So for example, let's just take one particular one, the way that our legs are constructed is bizarre for an ape, alright? You ever go to the museum, compare a human, look at a human skeleton, look at ape skeletons, look at monkey skeletons, our legs look completely different.
In order to see a leg that looks like a human leg, you're gonna have to walk probably across the hall and go look at the elephants. The human leg looks like an elephant leg in terms of how it's constructed. So we have sort of this big upright leg that's great for standing around, for walking at sort of a slow pace.
We in fact are masters of it biologically. The thing that humans are really great at, the thing that makes us incredible from an animal kingdom point of view that is, you know, outside of our intelligence or other stuff like that, we can walk for really long distances for a really long time. Most animals are designed for moving very quickly and then needing to rest for a really long time.
So they might be faster than us over short distances, but we are really great at long distance walking just like elephants are. Now that trait's only held by our lineage really, right? So I'm not going to consider any of the sort of extinct lineages of hominids here, so I'm just going to talk about that that trait here is an So what is this ought there?
So this is all coming actually from German. The Germans were really involved in figuring out these sort of how to classify different characters back in the 50s and the 60s. So they invented the word ought. So what is this ought there? So this is all coming actually from German.
The Germans were really involved in figuring out these sort of how to classify different characters back in the 50s and the 60s. So they invented the word ought. So what is this ought there? So this is all coming actually from German. The Germans were really involved in figuring out these sort of how to classify different characters back in the 50s and the 60s.
All the words, ought apomorphic means that that is an evolutionary change, but we only see it in one lineage. So individual, ought, it means individual in this case. Sin shared, ought, individual. And you might think to yourself, oh, they must have been really into fossils.
No, they were really into insect relationships. One guy in particular named Hennig, he was really into figuring out how insects were related to each other. And not like...
groups of insects, how individual species of insects were into each other. So that's what these words were all invented for originally. But we now apply them to any sort of biological group. All right, so we've got syn-apomorphies, we've got aut-apomorphies, we've got things like ancestral conditions.
So for example, legs? Well, there are groups of non-avian dinosaurs that essentially lose their arms. One particular, let's just take here, well actually it would actually look like it's more of a bird, but it's a non-avian dinosaur. It's Mononychus. We'll talk about it later.
It's basically lost its arms. It maybe has one little arm digit with a claw attached on each side, depending on how you interpret it, but Mononychus basically has no arms. So it no longer has that ancestral condition. Whales no longer have four legs or four limbs, right? They have little bones that are deep, deep inside their bodies that still indicate where the legs used to develop, where the legs used to exist within the whale form.
So those little vestigial bones represent the traces of a whale. So let's just draw that. So whales. And so whales will look like this.
They got big front fins, right? But then deep inside their bodies are little vestigial bones. There we go.
Whales, right? The condition in this case of not having four limbs, that's convergence. That's what we actually call a homoplastic or homoplasy character.
We can easily tell in this particular case that mononychus and whales have nothing to do with each other. One is a giant creature creature that lives in the ocean and has front flippers. The other is a large ostrich-like reptile thing that maybe had some feathers and looked maybe like an ostrich with maybe somewhat less feathers and no arms.
So very, very different. But this ancestral condition, that's the important thing right now, that's what we actually call a plesiomorphy. Ancestral. Or we might also call it a primitive.
condition. We don't want to group things together based upon primitive conditions or based on just not having the primitive condition. That's how you end up with, you know, whales getting put with fish because whales are aquatic, right? Whales are marine. Only fish are marine or aquatic.
So clearly these two things are the same. No, not true. Whales and dolphins are actually quite different from fish.
We want to try to figure out what those evolutionary relationships are. And so separating out plesiomorphies versus apomorphies, which we also call derived traits, that's a really important part, a big aspect of how we figure out evolutionary relationships. Because what we really want to do is we want to separate out homoplastic or homoplasy from Homology. What is homology? Homology means this is the same trait because of a shared history of ancestry.
So homology represents sort of an assumption of ancestry. What we're trying to do, what we're trying to sort out, how do we do this? groups are related to each other is we're trying to identify cases of traits that can be homology, homology, h-o-m-o-l-o-g-y, homology, there we go. We're trying to identify those cases of homology and separate out cases of homoplasia. or cases of plesiomorphy.
Why? Because those characters can then allow us to figure out how things are related. So for example, there's a character that defines when we start calling something a dinosaur versus being a diapsid or a dinosaur-like diapsid or a dinosauromorph. You know, those are all words we use to refer to the stuff that happens back here.
Just some branches for you. That origin, this is a little too late, but whatever, I'm gonna, this isn't, the origin of dinosaurs isn't the Jurassic, somewhere here in the early Triassic, but whatever. That is, there is the acetabular foramen.
What is the acetabular foramen? It's a hole in your hip. All the dinosaurs have that.
Non-avian, anavian, or they have lost the acetabular foramen secondarily. And that happens a lot. Evolution isn't forever.
In fact, that's the very definition. of evolution is that you are in a state of changing. That's what the word evolution means. It means changing. So just because you develop a particular trait doesn't mean you then keep it forever.
And so birds have changed a lot. I wouldn't be surprised if there's birds that don't have an acetabular foramen. But in terms of us being able to distinguish what was a dinosaur and what is a dinosaur, the acetabular frame is really useful.
And it probably had something to do with the fact that the earliest dinosaurs were all bipedal. That was sort of the big innovation for them, was being bipedal, being able to run around two legs. Yes, you know probably a lot of four-legged dinosaurs, like the big sauropods, stegosaur, triceratops, etc. Those four-legged dinosaurs all became quadrupedal secondarily.
We'll come back to this tree in a little bit, and we're going to talk more about the history of dinosaurs and vertebrates. And we're going to sort of lay out a roadmap about how this class is going. going to go and we'll talk, we'll review some of the concepts we've covered already about synapomorphies and homology and paraphily and I'm going to and we're gonna start off with a question that is really interesting I think which is, where are turtles on this tree?