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Abstract

Mammals are a charismatic and taxonomically diverse radiation of vertebrates with unique ecological adaptations. Connecting patterns of mammalian morphological evolution observed the fossil record to the processes that produce and sort phenotypic variation has the potential to illucidate general evolutionary rules. Here I investigate the evolutionary dynamics of two groups with exemplary fossil records within the mammal radiation, primates and equids (fossil and modern horses), using phylogenetic comparative methods. Chapter 1 introduces the subject matter of this disseration. Chapters 2 and 3 investigate the evolution of primate historical biogeography and body size respectively, and test how inferences derived from analyses that include data from both living and extinct taxa differ from those that do not incorporate fossil data (as is the case in many comparative evolutionary studies). To generate a phylogenetic framework for these analyses, in Chapter 2, I first infer the largest tree of living and fossil primates to date (900+ species) using a formal meta-analytical pipeline. Chapter 2's analyses of primate historical biogeography shed light on where the major groups of primates originated and ancient patterns of cross-continental dispersal. Comparison of ancestral range estimates derived from the complete dataset of living and extinct primate species to those derived from an extant-only dataset demonstrates that ancestral ranges at older nodes in primate phylogeny are significantly more likely to be mis-estimated than younger nodes. This pattern of age-dependent incongruence is not observed when comparing results derived from total-group and extinct-only datasets. Chapter 3 uses the primate phylogeny from Chapter 2 to investigate the tempo and mode of primate body size evolution. I find that rates of primate body size evolution slowed over the Cenozoic, and that at the ordinal level and across many different primate subgroups this decline in evolutionary rates was likely mediated by changing global temperatures. Results from extant-only analyses were frequently not congruent with those derived from the complete dataset. Chapter 4 investigates the evolution of the equid skull through the lens of craniofacial evolutionary allometry (CREA), a pervasive pattern of morphological evolution which seems to broadly characterize mammalian skull proportions, and is thought to be linked to patterns of growth observed over ontogeny. I find equids deviate from the CREA pattern and that the evolution of hypsodont dentition had little influence on patterns of skull evolution within the group. These results are only apparent when appropriately accounting statistically for species non-independence due to shared evolutionary history. Chapter 5 addresses areas for future study. As a whole, this dissertation contributes to the understanding of the evolutionary history of primates and equids, presents comprehensive phylogenies for both groups that may be employed for future studies, and emphasizes that incorporation of fossil data and choice of statistical methods (phylogenetic versus non-phylogenetic regression), can dramatically change results of comparative analyses and correspondingly our understanding of evolutionary dynamics.

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