Taphonomic analysis of the level 3b fauna at BK, Olduvai Gorge
Introduction
The African Plio-Pleistocene witnessed the first stone tool assemblages associated with bones from several animals. Sites such as Ain Boucherit, dated to 2.4 million years ago (Ma) (Sahnouni et al., 2018), Gona dated to 2.5–2.1 Ma (Domínguez-Rodrigo et al., 2005), and Lokalalei 2C (2.34 Ma) (Roche et al., 1999) all show evidence of butchery marks on bones belonging mainly to medium and small carcasses. Nevertheless, all these assemblages are not in primary context or the samples are too small to fully ascertain the socio-economic behavior of early hominins. From 2 Ma onwards several archaeological sites that preserve stone artifacts and cut-marked fossil bones belonging to different taxa from the same level are documented. These sites are referred to as “Type C″ sites (Isaac, 1978, 1984) and are found at several localities, including Koobi Fora (1.95 Ma) (Bunn, 1994), FLK Zinj (1.84 Ma) (Leakey, 1971), El-Kherba (1.78 Ma) (Sahnouni et al., 2013), FLK W (1.7 Ma) (Yravedra et al., 2017b), the ST site complex at Peninj (1.5–1.3 Ma) (Domínguez-Rodrigo et al., 2002), SHK (∼1.5 Ma) (Domínguez-Rodrigo et al., 2014a), and BK (1.35 Ma) (Domínguez-Rodrigo et al., 2009a, 2014b; Organista et al., 2015, 2017). The growing sample of Type C sites now allows us to better characterize their relationship with the behavior of early Homo. At the Bell's Korongo (BK) site in particular there is strong evidence for repeated carcass butchery throughout a deep stratigraphic sequence that spans a significant amount of time, which offers us the opportunity to understand in some detail the socio-economic behavior and evolution of early Homo.
Early access (implying bulk defleshing) by hominins to large carcasses has now been demonstrated at several Early Pleistocene sites such as Kanjera South (e.g., Ferraro et al., 2013), Koobi Fora: FxJj50 (Bunn, 1994) and FwJj20 (Braun et al., 2010), El-Kherba (Sahnouni et al., 2013), Buia (Fiore et al., 2004), and the ST Site Complex (Domínguez-Rodrigo et al., 2002). To date, at Olduvai Gorge, the archaeological record preserves only limited taphonomic evidence for the manipulation by hominins of megafauna during Bed I times at FLK North (Domínguez-Rodrigo et al., 2010) and during lower Bed II times at SHK (Domínguez-Rodrigo et al., 2014a) and FLK West (Yravedra et al., 2017b). This situation changes during middle and upper Bed II times, where hominins' systematic exploitation of megafauna is thoroughly documented throughout the stratigraphic sequence of BK (Domínguez-Rodrigo et al., 2014b; Organista et al., 2015, 2017; Yravedra et al., 2019 accepted). In the current study, we present the taphonomic results of a new archaeological level with evidence for anthropogenic activity, level 3b at BK, which was initially excavated by M. Leakey (1971) and reopened by The Olduvai Paleoanthropology and Paleoecology Project (TOPPP) in 2006.
Section snippets
Site context
Bell's Korongo (BK) is located on the south bank of the Side Gorge, ∼3 km upstream from the junction of the main and side branches. The site was first recorded in 1935 at the top of Bed II in lateral connection with Tuff IID (Leakey, 1971; Hay, 1976). In the 1950s and 1960s, the Leakeys excavated a total of 10 trenches at BK, which revealed a rich fossiliferous assemblage (Leakey, 1971). Since 2006 TOPPP has excavated a 55 m2 surface through five archaeological levels, each of which represent
Site integrity
Due to the fluvial depositional context of BK, level 3b (BK3b) has been analyzed for potential fluvial distortion. Since flowing water may modify the spatial position of archaeological materials and generate preferential orientation of specimens, compasses and clinometers were used to measure the horizontal and vertical orientations of each specimen with a longitudinal axis at least twice as long as its width (Voorhies, 1969; Fiorillo, 1991; Alcalá, 1994; Howard, 2007). Measurements were taken
The integrity of the assemblage
The orientation of archaeological items (bones and lithics) shows a horizontal trend (Fig. 3a). The mean direction is about 50° east - 230° west as shown by the 95% confidence interval of the stereogram but, as the rose diagram shows (Fig. 3b left), the azimuth confidence interval shows clearly identifiable anisotropic orientations. The Woodcock diagram shows an isotropic fabric for the assemblage with a von Mises distribution k concentration value lower than 0.2 (Fig. 3c). The Rayleigh test
Discussion
To date, five archaeological levels have been excavated at BK, all of them preserved in a fluvial deposit of low to moderate energy. The anisotropy documented is probably the result of a local reorganization of the materials rather than sustained water flow. The lower frequency of small specimens suggests that the spatial properties of the assemblage probably have been lost due to rearrangement by water. However, the presence of shaft fragments with good preservation corresponding to all
Conclusion
The taphonomic study of Level 3b at BK provides convincing evidence for the systematic accumulation and exploitation of animals of different sizes and taxa by hominins. The frequency and distribution of cut and percussion marks on specimens corresponding to large animals suggest that hominins had early access to large quantities of meat and marrow. This exploitation of megafauna underscores the importance of meat to the diets of our ancestors -possibly because groups were larger and, thus, had
Acknowledgments
We thank the Tanzanian Commission for Science and Technology (COSTECH), the Department of Antiquities, the Ngorongoro Conservation Area Authority in the Ministry of Natural Resources and Tourism and the National Museums of Tanzania for permission to conduct research at Olduvai Gorge and at the National Museum in Dar es Salaam. We also thank the Spanish Ministry of Economy and Competitiveness for funding this research (HAR2017-82463-C4-1-P) and the Ministry of Culture for funding our research
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