Out from the shadow of the dinosaurs? : dietary diversity and niche partitioning in Cretaceous and Paleocene mammals

The first mammals evolved as small-bodied insectivores in the shadow of the dinosaurs during the Mesozoic, but truly large body sizes and dominance of terrestrial ecosystems were only attained by mammals in the Cenozoic after the end-Cretaceous mass extinction. Yet, the extent and trajectory of mammalian palaeoecological diversity through the Late Cretaceous before the mass extinction and in its immediate aftermath in the early Paleocene remain incompletely understood despite centuries of fossil collecting and study. Recent developments in palaeodietary reconstruction using robust, quantitative proxies provide a timely opportunity to examine these issues. This thesis uses the well-resolved record from North America to test hypotheses related to mammalian dietary palaeoecology through the Late Cretaceous and early Paleocene. Firstly, a new quantitative review of dietary interpretations for Late Cretaceous mammals is presented, which reveals support for a rejection of the traditional Mesozoic 'suppression hypothesis'. However, the quality and consistency of interpretations are variable, highlighting the need for robust palaeodietary work in future. Secondly, a diverse set of extant herbivorous mammals is used to explore the benefits of applying and combining two dietary proxies: multi-proxy dental morphology analysis (MPDMA) and dental microwear texture analysis (DMTA). This study shows for the first time that multivariate metrics from both techniques are significantly but variably correlated and that dietary classification improves by combining both methods. Thirdly, MPDMA and DMTA are then applied to early Paleocene 'condylarths' (so-called 'archaic ungulates') from the San Juan Basin in New Mexico, providing strong support for the rapid recovery and radiation of placental mammals in the aftermath of the mass extinction. Finally, a novel multi-comparator approach to DMTA sheds new light on mammalian responses to an abrupt hyperthermal event in the early Paleocene, which has important implications for assessments of extinction risk amidst the current climate and biodiversity crises facing our planet.