Adaptation Früher Hominini im Südlichen Teil des Ostafrikanischen Grabens
Zusammenfassung der Projektergebnisse
In this ICDP DFG project, I developed a novel method to analyze nitrogen isotope values in fossil tooth enamel and produced important geochemical data from the Malawi Rift (Karonga Basin), the Gregory Rift (Manyara Basin, Tanzania) and Sterkfontein in the Cradle of Humankind (South Africa). Our stable carbon (δ13C), oxygen (δ18O), and clumped (∆47) isotope data on paleosols, hominins and selected fauna elucidates an unexpected diversity in Pleistocene hominin plant-based diet in various habitats of the East African Rift System (EARS). Food sources of early Homo and Paranthropus thriving in relatively cool and wet wooded savanna ecosystems along the NW shore of paleolake Malawi contained a large fraction of C3 plant material. Complementary water-consumption reconstructions suggest that ca. 2.4 Ma early Homo (H. rudolfensis) and Paranthropus (P. boisei) remained rather stationary near freshwater sources along the lake margins. Time equivalent P. aethiopicus from the Eastern Rift further north in the EARS consumed a higher fraction of C4 resources, an adaptation which grew more pronounced with increasing openness of the savanna setting after 2 Ma, while Homo maintained a higher versatility. Southern African P. robustus however followed - similar to the Malawi Rift individuals - C3 dominated feeding strategies throughout the Early Pleistocene. Collectively, our stable isotope and faunal data presented evidence that early Homo and Paranthropus were dietary opportunists in their plant-based resources, and able to cope with a wide range of paleohabitats, which clearly demonstrates a high behavioral flexibility in the early African Pleistocene. In the last year of this project, my work has focused on the development of a novel oxidationdenitrification method for measuring the nitrogen isotope composition of tooth enamel. The method was first designed to measure 15N/14N ratios of organic nitrogen in microfossils and we have adapted these protocols for the analysis of tooth enamel. Nitrogen isotope data (δ15N) are frequently used in conjunction with δ13C to reconstruct diet because δ15N values reveal information about an individual’s position in the food web. δ15N measured in collagen from fossil bone and dentin provide key insights into the dietary behavior of species in modern ecosystems and the recent geological past (<120 kyr). However, due to diagenetic alteration, such analyses have been limited to fossil sites with exceptional preservation. Unlike bone or dentin, organic matter in tooth enamel is protected from alteration by its highly mineralized structure, potentially preserving isotopic signals over millions of years, but low organic matter content in enamel has so far prevented nitrogen isotope analysis. We are the first to employ our new method as a proxy for reconstructing trophic level in terrestrial mammals. Our protocol includes a reductive-oxidative cleaning of enamel powder, followed by the oxidation of enamel-bound organic matter to nitrate, which is subsequently converted to N2O using the bacteria Pseudomonas chlororaphis. The isotopic composition of the N2O is then analyzed by a “SigBench” coupled to MAT253-Plus isotope ratio mass spectrometer. This automated system for the extraction and purification of the bacterially produced N2O performs nanomolar-scale, high-precision measurements (1 <0.1 ‰) of nitrogen isotopes of nitrate. The method requires 100-fold less N than traditional combustion approaches. With only 5 mg of enamel powder, we produce δ15Nenamel data with a standard deviation of <0.3 ‰, which is more than adequate to resolve the typical 3 to 5 ‰ trophic level enrichment. We established that enamel α15Nenamel records the isotopic composition of diet and preserves a trophic signal in a feeding experiment, as well as in natural ecosystems. Then, we utilize this novel biogeochemical method to analyze δ15Nenamel and δ13Cenamel data for Sterkfontein Member 4 (ca. 2.6 to 2.2 Ma) mammalian fauna, including seven australopithecines. Results represent the first δ15Nenamel data measured in any early hominin. Our data indicates a large variation in δ15Nenamel values between Australopithecus individuals, larger than in the other primate taxa analyzed from Sterkfontein Member 4. The values however do not overlap with carnivore δ15Nenamel data, pointing to a plant-based diet of these early Pleistocene hominins. Our dataset provides a first step towards understanding the trophic behavior of early hominins.
Projektbezogene Publikationen (Auswahl)
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(2018). Dietary Versatility of Early Pleistocene Hominins. Proceedings of the National Academy of Sciences, 115, 723-738
Lüdecke, T., Kullmer, O., Wacker, U., Sandrock, O., Fiebig, J., Schrenk, F., Mulch, A.
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(2021). Nitrogen isotopes in tooth enamel record diet and trophic level enrichment: Results from a controlled feeding experiment. Chemical Geology, 563, 120047
Leichliter, J.N., Lüdecke, T.; Foreman, A.D., Duprey, N.N., Winkler, D.E., Kast, E.R., Vonhof, H., Sigman, D.M., Haug, G.H., Clauss, M., Tütken, T.; Martínez-García
