ISOTOPIC ANALYSES OF FOSSIL BONES AND TEETH OF HERBIVORES AND CROCODILES FROM UPPER BED I, LOWER BED II, AND UPPER BED II OF THE OLDUVAI GORGE, TANZANIA

The evolution, radiation, and extinction of early East African vertebrate fauna, including early hominins, has been linked to key climatic fluctuations that occurred around 2.8, 1.7, and 0.5 Ma. These events were recorded in marine and continental sediments and soil carbonate isotopes. Isotope Ratio Mass Spectrometry can be used to analyze the stable isotope compositions of the bioapatite of vertebrate fauna that lived throughout these climatic events, and can help determine the dietary and climatic changes and stresses that acted on them. This research focuses on the drought event that occurred at the end of Lower Bed II times of the Olduvai Gorge (1.7 Ma, ±0.1 Ma), and evaluates the effects of paleoclimatic changes on vertebrates in East Africa. This study analyzes the oxygen and carbon isotopic compositions of bones and teeth from Upper Bed I, Lower Bed II, and Upper Bed II layers from the Olduvai Gorge, Tanzania, a site of paleoanthropological importance where early hominin remains have been found. These geological intervals document critical biological and cultural developments of early hominins in Africa.

In this study, vertebrate bioapatite carbon and oxygen isotope compositions are found to be similar to those of pedogenic carbonates, showing similar trends that reflect a drying environment that was changing from C₃ woodland dominated habitats to C₄ grasslands from Bed I to Lower Bed II times. In spite of a return to more humid conditions in Upper Bed II times based on pedogenic isotope data, however, herbivores retained mostly the drought-resistant C₄ plant diet. This shows that the paleoenvironment change from woodland to grassland was sudden and directly affected by increasing aridity levels, whereas a recovery back to woodland habitats was protracted.