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

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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.