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A 14C chronology for the Middle to Upper Palaeolithic transition at Bacho Kiro Cave, Bulgaria


The stratigraphy at Bacho Kiro Cave, Bulgaria, spans the Middle to Upper Palaeolithic transition, including an Initial Upper Palaeolithic (IUP) assemblage argued to represent the earliest arrival of Upper Palaeolithic Homo sapiens in Europe. We applied the latest techniques in 14C dating to an extensive dataset of newly excavated animal and human bones to produce a robust, high-precision radiocarbon chronology for the site. At the base of the stratigraphy, the Middle Palaeolithic (MP) occupation dates to >51,000 yr bp. A chronological gap of over 3,000 years separates the MP occupation from the occupation of the cave by H. sapiens, which extends to 34,000 cal bp. The extensive IUP assemblage, now associated with directly dated H. sapiens fossils at this site, securely dates to 45,820–43,650 cal bp (95.4% probability), probably beginning from 46,940 cal bp (95.4% probability). The results provide chronological context for the early occupation of Europe by Upper Palaeolithic H. sapiens.

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Fig. 1: Bacho Kiro Cave.
Fig. 2: A selection of bone specimens from Bacho Kiro Cave with anthropogenic surface modifications that were radiocarbon dated in this study.
Fig. 3: Bayesian chronological models for Bacho Kiro Cave.

Data availability

All data are available in the manuscript and supplementary materials.

Code availability

OxCal script is included in the supplementary information.


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The re-excavation of Bacho Kiro Cave is a joint project between the National Institute of Archaeology and Museum, Bulgarian Academy of Sciences, Sofia and the Department of Human Evolution at the Max Planck Institute for Evolutionary Anthropology, Leipzig. This work was funded by the Max Planck Society. Graphitization and AMS dating in Switzerland were funded by ETH Zürich. The AixMICADAS and its operation are funded by the Collège de France and the EQUIPEX ASTER-CEREGE (Principle Investigator: E.B.). S.T. is funded by the European Research Council under the European Union’s Horizon 2020 Research and Innovation Programme (grant agreement No. 803147-951 RESOLUTION, awarded to S.T.). We acknowledge The National Museum of Natural History (Sofia), the Archaeology Department at New Bulgarian University (Sofia), the Regional Historical Museum in Gabrovo, the History Museum in Dryanovo and the guest house Platex in Dryanovo for their assistance in this project. We acknowledge the vital contribution of all the excavators who have worked at Bacho Kiro Cave since 2015.

Author information

Authors and Affiliations



The study was devised by J.-J.H., S.T., S.P.M., T. Tsanova, N.S. and H.F. Archaeological excavation was undertaken by T. Tsanova, N.S., Z.R., V.A. and S.P.M., who all contributed contextual information. The 2015–2017 excavation laboratory and collection was organized by V.S.-M. Lithic analysis was performed by T. Tsanova, N.S., S.S. and S.P.M. Zooarchaeological analysis was performed by G.M.S. and R.S. N.L.M. classified the bone tools in the sample set. Stratigraphic and micromorphological analysis was carried out by V.A. ZooMS was carried out by F.W., L.P. and V.S.-M. Sample pretreatment and EA-IRMS analyses were carried out by H.F. FTIR analyses were carried out by H.F. and R.M. Graphitization and AMS dating at ETH Zürich was carried out by L.W., B.K. and H.F. Dating with the AixMICADAS was carried out by E.B., Y.F. and T. Tuna. Bayesian modelling was carried out by H.F. and S.T. H.F. wrote the paper with input from all authors.

Corresponding author

Correspondence to Helen Fewlass.

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Extended data

Extended Data Fig. 1 Photograph of Bacho Kiro Cave excavations in 2019.

View of the Niche 1 (left) and Main Sector (right), looking toward the south in the cave. The concrete floor in the centre covers the 1970s excavation area.

Extended Data Fig. 2 Bacho Kiro Cave, excavation 2015-2018.

a, Plan view of the entry hall and the excavated area, with the grid system of the recent excavations (black letters) and those of the 1971-75 excavations (grey letters). Red lines indicate the locations of the profile columns from Niche 1 (b) and Main Sector (c). b, Stratigraphic section-log in the Niche 1 in 2018. Layer attributions in the Niche 1 have an ‘N1-‘ prefix. c, Initial stratigraphic section-log in the Main Sector in 2015. Numbers in parentheses show the layer attributions from the 1970s excavations. Legend for the stratigraphic units shown on the left.

Extended Data Fig. 3 Collagen yields (%) of pretreated bones.

a, Main Sector and b, Niche 1, separated by layer and layer contact zones (I/J, N1-J/K, N1-I/J, N1-H/I). The dashed line shows the minimum level of collagen preservation generally considered suitable for 14C dating.

Extended Data Fig. 4 Comparison of radiocarbon dates of Homo sapiens bones F6-597 and BK-1653.

a, F6-597 comes from Layer B of the new excavations and b, BK-1653 comes from the 1970s collection (Layer 6a/7) that is stored in the National Museum of Natural History in Sofia. The purple range shows the weighted mean age and error of all the dates measured from graphite targets and directly from CO2 gas (shown in Supplementary Table 6), calculated using the R_Combine function in OxCal 4.345.

Supplementary information

Supplementary Information

Supplementary Text 1–6, Figs. 1–6 and Tables 1 and 6.

Reporting Summary

Supplementary Tables

Supplementary Tables 2–5 with pretreatment information, AMS data and modelling output.

Supplementary Data

OxCal code for Bayesian models (Main Sector and Niche 1) presented in the paper.

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Fewlass, H., Talamo, S., Wacker, L. et al. A 14C chronology for the Middle to Upper Palaeolithic transition at Bacho Kiro Cave, Bulgaria. Nat Ecol Evol 4, 794–801 (2020).

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