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具有连锁效应，特别是大型食草性哺乳动物的丧失。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复制气候实验的实验室。 我的研究计划的长期目标是了解物种的特性，如物种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，以调节草食动物的多样性和形态变异。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说。 验证这一假设需要一棵完全分辨的进化树，但活着的偶指目动物的谱系与最早的化石之间的关系是有问题的，因为这些标本超出了成功进行古代DNA采样的年龄范围，而且所使用的形态特征非常收敛。利用CT扫描，我们将描述早期偶指目动物头骨底部的形态，这是有意义的，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，我们将检验关于偶指目动物早期辐射的几个假设：最早的偶指目动物谱系是代表一系列干群还是代表单一辐射；骆驼是属于与反刍动物关系更近的更广泛辐射的一部分(传统形态解释)，还是像分子数据所表明的那样，是与它们关系不密切(但表现出很强的形态趋同)的基本谱系的一部分。 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的变化模式和时间，以了解牙排区域的这些变化是否与牙齿功能的重大变化相关。哺乳动物的牙齿在不同的区域有不同的形状。这很可能是通过改变颌骨内基因表达的边界而进化的。在前牙“软化”的有蹄类动物中识别这些变化，将有助于测试这些变化是否与调控基因网络的变化有关，以及这些变化是否会改变牙齿功能和饮食。这些变化将被用来与哺乳动物牙齿区域基因调控的其他工作相结合，以提供对形态差异限制的综合理解。 我们将测试外部因素，如纬度、气候和植被变化对草食动物大小分布的影响，并继续收集萨斯喀彻温省的高纬度数据，以通过研究草食动物谱系和群落的大小进化来检验环境因素的影响，并探索较小草食动物的进化对较大草食动物的作用。

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.