Titolo della tesi: Late Pleistocene Palaeoenvironment, Palaeoclimate, and Land Use Patterns: A Multi-isotopic Study of the Gotera site, Southern Ethiopia
The Late Pleistocene saw major developments in human behaviour, including technological transitions, behavioural complexities, range expansions, and dispersal within and beyond Africa. These developments in the Late Pleistocene are thought to coincide with ecological and climatic fluctuations. Despite eastern Africa’s significance in biocultural change and human dispersal, little is known about the ecological and environmental underpinnings, as well as the land use patterns through which our species thrived, expanded, and contracted. Understanding the interplay between natural systems and human adaptability requires examining the Late Pleistocene environmental, climatic, and land-use patterns linked with cultural and behavioural changes. The Gotera area, the subject of the present study and dated to Marine Isotope Stage 3 (MIS 3), yields rich archaeological finds including Middle Stone Age (MSA) assemblages, fireplaces, ochre, post holes, and faunal remains, reflecting intense human occupation in lower-elevation settings associated with technological innovation and elements of behavioural complexity. Because most eastern African MSA sites were distributed at higher altitudes during MIS3, the presence of Gotera in the southern section of the Main Ethiopian Rift (MER) provides a unique opportunity to explore human adaptations and palaeoecological conditions.
In this study, stable carbon (δ13C), oxygen (δ18O), and strontium (87Sr/86Sr) isotope analyses of mammalian tooth enamel from Gotera mainly the GOT10 site and other selected MSA sites in Ethiopia dated to the Late Pleistocene were performed to understand the dietary ecologies and environmental contexts of MSA hunter-gatherers, palaeoclimatic conditions, and inter-annual seasonality and human palaeoecology across a varied landscape and topographic settings of Ethiopia. This study has also produced a bioavailable Sr isoscape of southern Ethiopia using environmental samples to enhance our knowledge of the mobility patterns and landscape use of faunal and human communities in Gotera.
The δ13C isotope analysis of faunal tooth enamel from Gotera suggests a palaeoecological niche of a more open, and C4 - dominated grassland environment. Some extent of woody habitat structure, possibly riverine vegetation, would have also existed, as inferred from the δ13C values of some taxa. The δ13C values were in agreement with the δ18O values, suggesting that semi-arid climatic conditions may have prevailed during site use. The ecosystem at Gotera would have had to support a savannah-like environment with riverine vegetation and a semi-arid climate, akin to, yet slightly more humid than, today’s Gotera environment of the Borena area in southern Ethiopia.
Stable δ13C and δ18O isotope analyses of intra-tooth samples of herbivores from the Late Pleistocene sites of Gotera and Porc Epic reveals the prevalence of seasonal environments at both sites. However, the different cyclicity patterns observed in the δ13C and δ18O values at both sites may have resulted in different behavioural responses. While hunter-gatherers in Gotera were probably residentially stable during site occupation, faunal and human groups in Porc Epic may have been seasonally mobile across the immediate highlands. A further comparative study of δ13C and δ18O isotope analysis of bulk samples of faunal tooth enamels from three Late Pleistocene sites, namely Gotera, Mochena Borago and Porc Epic suggests the expansion of C4 grasses and occupation of open environments across different topographic and occupational contexts while human groups would have had to adapt cooler and wetter climates at higher elevation sites such as Mochena Borago.
This present study produced the first strontium (Sr) baseline isoscape map of southern Ethiopia through the analysis of environmental samples, including soil, plants, water, and microfauna, coupled with 87Sr/86Sr isotope datasets from previous studies. 87Sr/86Sr isotope analysis of faunal remains from the Gotera area revealed that the faunas are of predominantly local origin, suggesting residential stability and exploitation of locally available resources. The 87Sr/86Sr isotope study is the first of its kind to demonstrate its potential as a future research avenue to produce bioavailable 87Sr/86Sr isoscapes of Ethiopia and the Horn of Africa using more samples and multiple modelling approaches.
Sedimentological deposits with fluvial-lacustrine settings, indicative of marshy and river-fed environments, may have been critical for the animal and human groups in Gotera. I argue that the Gotera area may have offered lake-side refugia for hunter-gatherers by providing locally available resources, such as water, raw materials, fauna, and open and semi-arid environmental settings. This would have likely furnished opportunities for foragers in Gotera to be residincially stable, technologically innovative, and behaviourally complex, as evidenced by archaeological and isotope records. The empirical evidence in this study suggests that Late Pleistocene human groups exploited and adapted to heterogeneous environments in Ethiopia.
Keywords: palaeoenvironment, palaeoclimate, landscape use, multiple isotopes; MSA; Gotera; southern Ethiopia