[MUSIC] So we're going to start today with the discussion of differentiated teeth which we have touched on all ready. But I want to continue a little bit deeper into what exactly that means. So again, un-differentiated teeth, we have kind of a comparison here, we can take a look at our reptile specimen, and what we notice about a reptile is that all of the teeth are generally shaped the same. So they all kind of start wide and they come down to a point, and we would infer, as scientists, that that's used for maybe ripping and shredding of flesh of their prey. So, but the thing to note about a reptile which is different from mammals is that all the teeth are generally shaped the same, and that's called un-differentiated teeth. So, we'll compare that to our mammal specimen here. Where again, just to briefly review, we have differentiated teeth on the mammal, and so, this is a canine, a dog specimen here. And what we'll quickly notice, is that there are different shapes of teeth. And that's called Differentiated Teeth. So, a quick review, we have incisors in the front. Canines is this large pointy one, has the main canine of dog there. We get back to premolars near the back of the mouth. And then molars are the big teeth all the way in the back of the mouth here. And so we can note the thing to note is that there's different shapes of teeth, and that's called Differentiated Teeth. So mammal paleontology has been based largely on examining these dental specimens basically. So even if there's an absence of a tooth we can sort of tell the shape of it or how deep the root is or how many roots there are? And so a lot of mammal Paleontology and evolution is based on fossilized teeth more or less. And as [LAUGH] you may notice, when you're biting into a lollipop or caramelized popcorn, teeth are very resistant to destruction, and so those are also better preserved or well preserved in the fossil record. So it's very advantageous to a paleontologist or an evolutionary biologist that teeth are resistive to destruction because we can start to think about, and hypothesize, and eventually theorize about the feeding modes of these different mammals. If we can't directly observe them in the modern day. If we have a dentary bone or a tooth socket even or a full jaw then we can really start getting specific about the feeding mode of those specific mammals. So digging a little deeper into differentiated teeth, we're going to start with the molars, because the molars can really start to distinguish different groups of organisms and different feeding modes. So we're going to start with a group called Browsers. And so if we can take a look here at a bear specimen actually, we're looking at the molars in the back of the mouth there. And browser teeth can be identified by a series of peaks and valleys actually. And those peaks and valleys as you can tell from this specimen, we have these little sharp peaks on the sides maybe and then we have some deeper valleys in the middle of the teeth or kind of running laterally across the teeth as well. But that's the key feature of a browsers tooth is that we have the series of peeks and valleys, and those are basically used to crush things to they could be used to grab, but largely kind of puncture fruits, leaves, sticks [LAUGH] twigs and sprouts. And a browser is often has a varied diet there. So this is a great example of a browsers tooth. So another group of mammals that we can distinguish based on their molar morphology, are the grazers. And grazer molars look like a series of ridges basically. And again, think of the function of those molars there. What their function is, is to grind up plant materials, so we kind of want a rough surface we can grind together and prepare for your stomach, right? For digestion, so here we have a rodent skull and you can see the presence of incisors here. No real canines, and then we can start to focus in on the molars here. And these are great examples of a grazer molar. And to kind of contrast to the browser molars, we have a series of ridges here. And with the browsers we had a series of peaks and valleys. So a little subtle there but as you start to look at the specimens a little bit more closely you'll see that there is definitely a difference there between the grazer molars and the browser molars. So another example of a grazers molar is this specimen here. And so if we could just take a look here and compare. So, we've already looked at this sample, and one of these teeth is representative of one of these back molars again, but again, largely different scale here. But what we can notice from this specimen is that you can see pretty clearly, because it's a little bit worn down because we can see this series of ridges. That constitutes a grazers molar that are utilized for grinding up plant material. Our last group of mammals that we can identify based on tooth morphology is the carnivores. So carnivores again they're going to be eating meat. Ripping and shredding flesh, and here we have a canine, again a dog specimen. And what you'll obviously notice right away is the presence of this long and sharp canine and that's actually a distinguishing skull feature that identifies a carnivore. Is this extension of this canine tooth here. And so it's long and sharp and you can even tell back towards the back with the molars that those are even sharp. So, that's indicating a very specialized diet. These teeth are made for ripping flesh. These are predators, carnivores, so just keep that in mind. If you start to identify these sharpened molars in back, these sharpened premolars and then definitely the existence of those large pronounced canine, then your going to want to think that it's going to be eating meat and that's a carnivore. So I'd like to take a little bit closer look at differentiated teeth and how we can deduce the feeding mode from those specific tooth morphologies. All right so we're going to start with, again our trusty canine here. And what I'd like to define is exactly the different types of teeth that mammals exhibit. And the function of those teeth. And how you can identify them if you find a skull or a fossil. So we'll start in the front of the mouth here with the incisors. So incisors generally have a single root and they're used for slicing or basically cutting through, biting into maybe an apple or something or a nice peach. So that's what those incisors are for. They're slicing into something, biting through food. Moving back toward the back of the mouth from our front incisors here, the next tooth that we would identify is the canine. And again, in this particular specimen it's long and sharp, it's pronounced and we would deduce that this is a [LAUGH] carnivore here. Ss again, if we have these long pronounced canines, which usually have a single root. It's usually deeper than the root of the incisors. But if we have this long pronounced canine here, you might start to think that this can be used for a throat bite. That's the kill bite, right? That's actually a function of this tooth. That's the function of that pronounced canine is that throat bite. Little scary there. [LAUGH] Right? All right. But these long and sharp canines, again, are pronounced in carnivores they can be absent in herbivores. You may not need that throat bite if you're eating grass or some corn, right? So that can actually be completely absent in a herbivore. So just something to note there. Moving towards the back of the mouth from the canine, our next group of teeth are the premolars. And the morphology of these teeth can actually vary widely based on the organism's diet, or the feeding mode. So with this particular specimen, you will notice quickly that they're sharp and so that's speaking to the specificity of this organism's diet which is, it's a carnivore. And so it's largely going to be eating meat, if not completely eating meat. And so, those teeth are very specific to the function that they're needed for. So premolars have two roots, again their molar-like in herbivores, and they're canine-like in carnivores, and in herbivores the pre-molars can be hard to distinguish from those grinding molars in the back. So just be aware of that. That differentiation between premolars and molars can be a little tricky with the herbivores. So continuing on towards our trek to the back of a mouth [LAUGH] of a mammal here, we're moving on to our molars, so molars can have two to four roots, so they're anchored in the back of your jaw there. And again, the morphology of those molars can be used to distinguish between our browsers, our grazers, and our carnivores. And again, here with our specimen. They're very sharp. We've got some high, high peaks there. They look like they're ready to cut and tear, and, so, we're just reiterating our deduction that this is a carnivore here. All right, we're going to continue on here discussing our differentiated teeth, and we're going to think about a very highly specialized development here called the Carnassial Complex. And the carnassial complex is specific to the order order carnivora, after named I'm sure. [LAUGH] Those are a group of carnivores, obviously. And the carnassial complex describes the occlusion of the last upper premolar and the first lower molar of these animals. So what you can tell, if I can articulate this jaw correctly here, is that the last upper premolar is going to sheer by, or kind of splice by, the lower molar. And so instead of occluding kind of surface to surface like that like most of the other teeth do, they actually cut by each other like scissors, for example, alluding to the function there obviously. So the carnassial complex is specifically designed to sliced flesh more or less. So you can tell that from our specimen here. In the order carnivora where that last upper premolar and the first lower molar are occluding sort of differently than the rest of the teeth. They're sliding by each other in a cutting fashion. All right so one of the convenient features of identifying the carnassial complex is that if you can figure out which teeth are involved in the carnassial complex here, you can actually define for yourself the border between the premolars and the molars. Which, that can be a little tricky in other organisms that don't have the carnassial complex. And so if you can find which teeth are slicing by each other here, you can identify that the upper tooth is the first premolar, and the lower tooth is the molar, and that's going to be useful when we put together our dental formula in just a moment. [MUSIC]
