Paleontology and paleoecology of the late Miocene Mpesida Beds and Lukeino Formation, Tugen Hills succession, Baringo, Kenya

The hominin lineage is known to have diverged from the Pan lineage ~7–5 Ma, and despite being one of the most researched and debated events in the history of life, explanations of how, why, and even where this occurred remain elusive. Characterizing the environmental backdrop to this event is key to understanding behavioral and morphological traits that characterize the emergence of the tribe Hominini. This thesis presents a high-resolution record of faunal change through a key interval of time in order to develop an environmental framework from which we can generate hypotheses for hominin origins, addressing those questions by considering the dynamic backdrop of changing climate and landscapes in late Miocene Africa. The Tugen Hills succession, Baringo, Kenya, offers a remarkable opportunity to reconstruct the paleoenvironment of the earliest hominins and place their evolution in broader geographic and ecological context. Alongside diverse faunal assemblages, several important hominin specimens have been discovered, including the ~6 million-year-old Orrorin tugenensis. A refined stratigraphic framework incorporating >30 fossil-bearing localities in the succession, and analysis of paleoenvironmental change across time and space using faunal guild composition, ecometrics, and enamel isotopes is presented. An exceptionally preserved in situ fossil forest dated to ~6.4 Ma is analyzed using modern forest ecology techniques that utilize tree distribution data to infer forest type and faunal ecology, providing an unprecedented snapshot of an extinct ii ecosystem at this crucial time. The establishment of a precise faunal chronology provides a means of establishing trends within lineages and faunal assemblages through time, as well as the use of these localities as a biochronological yardstick by which other late Miocene fossil localities can be compared. Importantly, a number of sites from the previously poorly-understood Kaperyon facies – from which paleontologically significant specimens have been recovered – are temporally constrained for the first time to 6.4-6.1 Ma, bridging the shift in faunal assemblages between Mpesida and Lukeino. The result is the refined placement of the emergence of hominins in the broader context of faunal distribution and dispersal, and a better understanding of their partitioning on the paleolandscape