Evolutionary radiations of Ruminantia (Mammalia: Artiodactyla)

Ruminant artiodactyls diversified throughout the Neogene to become a dominant group of large terrestrial herbivores. Ruminants are an ideal group with which to study taxonomic and morphologic diversity during evolutionary radiations, yet their rise to ascendancy had not been studied in a quantitative manner prior to this dissertation. This dissertation addresses three related aspects of the radiation of ruminants: their phylogeny, taxonomic radiation, and morphologic diversification.; The first part investigates the conflict among the results of previous phylogenetic studies using morphologic and molecular data by analyzing the phylogenetic signal of a new morphological data set. The results of these analyses suggest a weak morphological signal that is significantly different than that of the molecular data. This conflict is most likely due to homoplasy in suites of morphological characters due to functional convergence.; The second part of this study uses recently proposed survivorship methods to determine the temporal patterns of origination, extinction and preservation throughout the history of ruminants. Additionally, phylogenetic tree-based methods are used to determine if any particular ruminant subclades showed significantly higher rates of diversification. These methods have different strengths and weaknesses, but when used in conjunction offer a more complete view of taxonomic diversity. Results of these analyses suggest two independent radiations driven almost entirely by new origination. The first of these is in the Early Miocene and marks the diversification of the Pecora, or “higher” ruminants, and the second occurs in the Late Miocene and Plio-Pleistocene, and is restricted to the family Bovidae.; The third part of this study investigates patterns of morphological diversity of ruminant dentitions to determine if the taxonomic radiations were coupled with morphologic divergence. Morphological diversity was also subdivided among ruminant subclades to determine the pattern within subgroups, and to determine the proportion of overall disparity attributable to each. Overall ruminant dental disparity shows no significant temporal pattern, while patristic dissimilarity increases over much of ruminant history. This suggests appreciable morphological evolution that is not accompanied by an increased range of forms. Subdividing ruminant disparity into taxonomic components suggests that radiation of the Bovidae did involve significant morphological diversification.