The limits and drivers of phenotypic variation and their effects on Cenozoic mammalian herbivore diversity and disparity

生物多样性的丧失对生态系统产生了级联效应，特别是大型食草哺乳动物的丧失。关于气候快速变化的长期反应的唯一数据来自化石记录，这是一个在没有人类影响的情况下重复气候实验的实验室。***我的研究计划的长期目标是了解物种的特性，如灭绝和物种分裂的速度以及新形态的起源，如何与环境因素相互作用，以调节食草动物的多样性和形态变化。一种假设是，分裂较慢的谱系比分裂较快的谱系积累了更多的形态差异。有蹄类动物的化石记录可以用来验证这一假设。***验证这一假设需要一个完全确定的进化树，但是现存偶蹄动物的谱系与最早的化石的关系是有问题的，因为这些标本超出了成功的古代DNA采样的年龄范围，并且所使用的形态特征是强烈趋同的。通过CT扫描，我们将描绘早期偶蹄龙颅底的形态特征，这是有信息的，因为这个区域发育得很早，似乎不太容易收敛。有了这些信息，我们将检验关于偶蹄动物早期辐射的几个假设：最早的偶蹄动物谱系是代表一系列茎群还是代表单一辐射；骆驼是否属于与反刍动物更密切相关的更广泛的辐射（传统形态学解释）的一部分，或者像分子数据显示的那样与反刍动物不密切相关的基础谱系（但表现出强烈的形态学趋同）。***我们将确定牙齿区域的主要发育变化，并记录食草动物进化过程中变化的模式和时间，以了解牙齿区域的这些变化是否与牙齿功能的主要变化相关。哺乳动物牙齿的不同部位形状不同。这可能是通过改变颌骨内基因表达的界限而进化的。在有“臼齿化”的有蹄类动物中识别这些变化，将允许测试这些变化是否与调节基因网络的变化有关，以及这些变化是否改变了牙齿功能和饮食。这些变化将被用于联系哺乳动物牙齿区域遗传调控的其他工作，以提供对形态差异限制的综合理解。***我们将测试纬度、气候和植被变化等外部因素对草食动物体型分布的影响，并继续收集萨斯喀彻温省高纬度地区的数据，通过研究草食动物血统和群落的体型进化来检验环境因素影响的生物地理学假设，探索小型草食动物的进化对大型草食动物的作用。

Loss of biodiversity has cascading effects on ecosystems, especially loss of large herbivorous mammals. The only data on long-term response to rapid changes in climate comes from the fossil record, a laboratory of replicate climate experiments without human influence.***The long-term goal for my research program is to understand how properties of species, such as rates of extinction and species splitting and the origin of new morphologies, interact with environmental factors to regulate diversity and morphological variation of herbivores. One hypothesis is that slower-splitting lineages accumulate more morphological differences than rapid ones. The fossil record of ungulates can be used to test this hypothesis.***Testing this hypothesis requires a fully resolved evolutionary tree, but the relationships of the lineages of living artiodactyls to the earliest fossils are problematic, because these specimens are beyond the age range for successful ancient DNA sampling, and the morphological characteristics used are strongly convergent. Using CT scans, we will characterize the morphology of the base of the skull of early artiodactyls, which is informative because this region develops very early and seems less prone to convergence. With this information, we will test several hypotheses about the early radiation of artiodactyls: whether the earliest artiodactyl lineages represent a series of stem groups or represent a single radiation; and whether the camels are part of a wider radiation that is more closely related to ruminants (traditional morphological interpretation), or a basal lineage not closely related to them (but showing strong morphological convergence) as molecular data suggest. ***We will identify major developmental shifts in tooth regions and document the pattern and timing of shifts in the evolution of herbivory to see whether these changes in the regions in the toothrow correlate with major changes in dental function. Mammalian teeth have different shapes in regions. This likely evolved by shifting the boundaries of gene expression within the jaw. Identifying these shifts in ungulates with “molarized” anterior teeth, will allow testing whether shifts are tied to changes in the network of regulatory genes, and whether these change dental function and diet. These changes will be used to tie to other work on the genetic regulation of the tooth regions in mammals to provide an integrated understanding of the limits on morphological disparity.***We will test the effects of external factors, such as latitude, climatic and vegetation changes, on herbivore size distributions, and continue to collect high latitude data from Saskatchewan to allow testing of biogeographic hypotheses testing the effects of environmental factors through studies of size evolution in herbivore lineages and communities, and explore the role of the evolution of smaller herbivores on larger ones.