PALEOECOLOGICAL RESPONSES TO LACUSTRINE VARIABILITY IN OLDUVAI GORGE, TANZANIA AND ITS IMPLICATIONS ON HOMININ EVOLUTION

Olduvai Gorge, Tanzania is a valuable landscape for hominin evolution research, in part because of associated climatic and geomorphic responses to active rift tectonics. A changing climate caused the environment to shift from a tropical forested environment to an arid grassland. Active rifting and paleoclimatic shifts resulted in changes to the position, size, and salinity of the local paleolake, a major resource for hominins and their associated fauna. Olduvai fossils span 2 Ma-60 ka and are distributed across several well-described units. Previous work has established the approximate extent of the paleolake in each unit. The largest paleolake margin occurred during the oldest Bed I and shifted to a fluvial /playa lake system in the upper, younger beds. Major changes in the environment and the landscape likely contributed to changes in local paleoecology and hominin adaptations.

During this period, hominins had changes in taxonomic diversity, population size, and geographic distribution. These changes can be seen by the number and position of hominin fossil localities in relation to the size and location of the paleolake in the region. Bed I had the largest lake margin with over 37 hominin fossils and the greatest amount of diversity. The fewest hominin fossils were found in Bed III, when the paleolake shrank and shifted 3 km NE. These fluctuations affect all aspects of the local paleoecology. The decline of hominin fossil material could reflect a decline in hominin activity. Alternatively, sedimentation rates had a ~60% decrease between Bed I and Masek and fewer lacustrine deposits are present in the upper beds, potentially influencing taphonomic processes and the number of recovered fossils. Additional controls on within-bed fossil hominin diversity and temporal changes in diversity are currently unresolved. By mapping paleolake margins and overlying fossil localities through time, we can better understand the relationship between extent of suitable habitat and behavioral and dietary changes that facilitated hominin co-occurrence within a bed and occurrence between beds. We will combine paleolake data and fossil distributions across units with paleoclimate data from cores to fully understand the ecological response to tectonic and paleoclimatic changes.