 I'm really pleased to have this opportunity to tell you a little bit more about some very interesting results that I obtained during my PhD. And this is just a small part of the overall project that was looking also at contemporary animals like the previous presentation. And we were looking at the isotopic variability in these contemporary animal tissues across the environmental gradients of South Africa. And we were doing this to better understand the paleo data sets. And the piece of research that I'm going to be presenting today is more about the methodological aspects of our tooth position and isotopes. So as most of you probably know, stable isotope analysis of animal tissues is a major tool in ecological and environmental studies. And this is because carbon can tell us about whether or not animals are eating C3 or C4 food and oxygen. As we've just heard, we'll tell us about the body water in an animal, the drinking water and the water found in food. And each of these is influenced by climate or by dietary preference. But researchers working on fossil assemblages are often constrained by the limited number of teeth found and then are available for analysis. So we don't often find the whole manual, we're often constrained by isolated teeth. So it becomes very important to know whether the isotopic composition along different teeth in the tooth flow of an individual are consistent, so that different measurements are directly comparable. And if they're not consistent, then are there systematic differences between the teeth so that we can apply a correction factor before making these comparisons? So here's an example of a tooth flow of an ungulate. This is the spring buck and didocus mossupialis. So tooth formation takes place very early on in the life of mammals, as most of you probably know. That isn't species that don't have continuously growing teeth. So this means that the isotopic composition of teeth therefore reflects the diet of this early part of the individual's life. And the sequence of tooth formation from initial mineralization, crown completion and root development and finally emergence. He's very similar across all mammals. So here you can see a table. I have the eruption sequence of various species. There we've got antidocus that we were just looking at, but also giraffe, aqueous. And what you can see is consistent is that the M1 consistently erupts before the M2 and then finally the M3 is the last of molars to emerge. So this sequence can then be used to construct a life history of each animal. So this slide, this publication shows quite nicely how the different molars form and erupt over a period of time. So here's the birth of the animal with the M1 crown and root formation followed by the M2. Then we've got the premolars and so on. And so changes in isotopic value of these teeth might then reflect residential mobility or change in diet. So for this reason, the inter-tooth variation within individuals can be used as a valuable source of information. So as I mentioned, the stable isotope composition of tooth enamel reflects this early part of the time when the tooth was forming. So compared with plants, milk tends to be enriched in 180 and depleted in 13C due to the presence of depleted 13C lipids. So teeth that formed early on in life like the M1, like we just saw, which typically mineralizes while the animal is still sucking from its mother might therefore be expected to have higher Delta 18O values and lower Delta 13C values when you compare it to teeth that formed post-weaning. Of course, the lipid content of the milk might also play a role. For example, the lipid content of ungulate milk, as we know, is about 3.7%, so the effect of Delta 13C might be negligible. But the effect will be much higher in animals like marsupials, kangaroos, because the lipid content is much higher. There aren't many studies that have done actual inter-tooth analysis, most have done serial sampling and a lot of serial sampling teeth. And these are some of the studies that have investigated inter-tooth differences in carbon and oxygen, and we'll just look quickly at them. The first one is Gadbury, who is investigating fossil bison. He found quite a nice pattern. This is the expected pattern. Here we've got the molar running along here and the Delta 13C value. You can see that the M1 is lower as a lower Delta 13C value, which is as we expected. Oxygen is not nearly as clear with a lot more variation. Again, you've got the molars and it isn't a systematic offset. Zaza was also working on fossil bobbins, so they did serial sampling, but they also did it along the molars, which is why I've included it here. Here you can see these are the boxes for the M1s, the boxes for the M2s and the M3s, with the Delta 13C running along here. So you can see that the Delta 13C starts at a lower value, and then there isn't much variation for the M2 or M3. The oxygen, funnily enough, also seemed to have quite a nice pattern across the five specimens. They only looked at five specimens, but you can see that the Delta 18C started higher in the M1 and then some variation in the M2s and the M3s. Two studies that found the pattern to be less clear for oxygen is Murphy and Wang, and this is the Delta 13C for Wang. They were looking at modern goats, horses and yaks, and you can see that for the key pre-molars and remolars, the Delta 13C is rather stable. Then finally DeAmbrios was working on equids, and they found quite variable patterns, which they attribute to varying birth seasons, and particularly for oxygen, which is up here. So here you can see the Delta 18O of the precipitation running along here. They fitted their Delta 18O of the two individuals as examples over this timeframe. And in both of these examples, you can see the M1 has the same value, but in the example A, if they say that if the M2 has a lower value than the M1, then it's most likely following this pattern, and the animal is most likely born in autumn. And here if the M2 has a higher value, then it's most likely following this pattern, and the animal was born in spring. So the Delta 18O of the individual teeth will correspond with the time of the year, so it can be quite complex. And this is just a summary, and what the bottom line about this slide is that what's in the literature seems to be quite inconsistent. So we wanted to test what the situation was in our region. So here is the African continent, and there you've got South Africa in the southern tip of Africa. Our study focuses on larger mammals from areas of near and natural vegetation. And here are the collection sites in green, and they extend across the winter rainfall zone and near-round rainfall zone of South Africa. South Africa, as many of you probably know, has a lot of national parks, which means we could collect animals from relatively undisturbed natural environments. And since the region is predominantly a winter rainfall region, it's characterized by C3 plants, and that will include the grasses. So all the plants are C3. In some areas around wetlands you might get some C4 grass within this winter rainfall zone. And then in the year-round rainfall zone, the trees and the shrubs are C3, but the grasses are both C3 and C4. So the animals included in this study are the arid-adapted spring work, some two rotissera species, two gator species, and the true browser, the kudu. And we sampled as many teeth as were present, usually three to five teeth, and the teeth were drilled along the line extending from the occlusal surface down to the cervix. And this ensured that the enamel collected was representative of the entire period of crown formation, and this was to average out any possible seasonal variation. I should mention this was a conscious decision not to do serial sampling, because we wanted to see if we could pick up these broad environmental or mobility changes between teeth. So these are the charts for the four groups of species. You can see the delta-13C running along here, and the teeth, P3, P4, M1, M2, and P3, and each of these lines is a different individual. And for those of you who don't know these species, I've just included a little picture. So the first thing to note is that M1s are not always more depleted in 13C than other molars. But there are differences between species, which we're going to look at now. And the amount of variation along the tooth row will depend on factors such as whether the food sources were available throughout the year or not, and how much C3 versus C4 plants are being consumed during the year as well. So the spring buck is an example of fluctuations along the tooth row probably being explained by fluctuations in the amount of C3 food sources that are available throughout the year. You can see this is a tree, it's eating mainly browse. So this animal is living in quite a dry area, and so that's probably why it has these rather larger variations. The stem buck, which eats both grass and browse, has quite a large delta-13C range, and this is probably because of fluctuations in the amount of C3 and C4 plants that it's eating throughout the year. So it's more of a mixed feeder. For both of these wrapper series species, you can see that the M1 are consistently lower than the other molars. Other animals that strongly prefer browse like this kudu and to a lesser extent the deca are going to show less variation, and that's because their food source is available throughout the year. Then looking at the oxygen variation, this will reflect the seasonal variation in the delta-18I of food and drinking water. Looking at the species individually, there doesn't seem to be any systematic differences between the delta-18I of the molars. So the M1 is not consistently higher as we would have expected, and this may be because wild animals suckle less than these domesticated animals where good seasonal patterns have been shown. Season of birth is also playing a role. So any seasonal changes in delta-18O of the available water are possibly bigger than the weaning signal in these animals, and so the weaning signal is undetectable. The variation within the individuals is also quite large. It's much larger than you see in carbon. Here is the largest range. It's a six-part per mole between the P3 and the M3. And of course the range of delta-18O of rainfall in Cape Town has been shown to vary up to 11 parts per mole. So this would contribute to this larger amplitude that we see when we compare it to carbon. Of course the delta-18O of faunal tissues will average out this precipitation signal to some extent. Not only because of the averaging during tissue synthesis, but also because there's octoduses not only being derived from water, it's also being derived from the food. So our study showed that there's limited systematic offset for carbon along the tooth row, but it's quite specific, so some species show a more systematic offset than others, but almost none for delta-18O. And for animals with tightly constrained birth seasons, it will depend on whether or not there are seasonal fluctuations in the oxygen. And also it will depend on seasonal fluctuations in the availability of food and water. Thank you, and I'd just like to thank our funders.