Slab Grave expansion disrupted long co-existence of distinct Bronze Age herders in central Mongolia.

Dairy pastoralism reached Mongolia during the Early Bronze Age and flourished in the Late Bronze Age alongside the emergence of diverse mortuary practices, including the Deer Stone-Khirgisuur Complex and figure-shaped/Ulaanzuukh burials. While the spread of pastoralism has been widely studied, interactions between these pastoralist groups with distinct mortuary traditions remain underexplored due to challenges in obtaining both genomic and mortuary data. In this study, we analyzed genome-wide and mortuary data from 30 ancient individuals in central Mongolia, a key region where pastoralists with distinct mortuary practices converged. We identify two genetically distinct clusters persisting throughout the Late Bronze Age that correspond to separate burial types, suggesting limited genetic mixing and a maintenance of distinct mortuary practices despite their coexistence. These groups were eventually replaced during the Early Iron Age by the expansion of the Slab Grave population and the establishment of a new burial tradition. Finally, we refine the genetic origin of the Late Bronze Age Deer Stone-Khirgisuur Complex populations, tracing their minor western Eurasian ancestry back to the Eneolithic/Early Bronze Age Afanasievo and Early Bronze Age Khemtseg (Chemurchek) populations. This study provides fine-scaled genetic tracking of major mortuary transitions in prehistoric Mongolia, offering insights into the complex and divergent processes that shaped the ancient pastoralist societies of Asia.