Genomic insights from a final Bronze Age community buried in a collective tumulus in an Urnfield settlement in Northeastern Iberia.

The transition from the Bronze Age (BA) to the Iron Age (IA) on the Northeastern Iberian Peninsula is characterized by the emergence of cremation as the main funerary practice. Cultural attributes of a group, known as the Urnfield Culture, expanded from Central Europe to Northeastern Iberia during the Final Bronze Age (FBA), from ~1300 to ~850 cal BCE. Various hypotheses on the group's emergence exist, but cremations hinder DNA preservation. Here, we present genome-wide data from 24 inhumed individuals from a collective burial mound at the site of Los Castellets II (Spain), where inhumations and cremations co-occurred during the FBA, and one Early Iron Age (EIA) individual from Los Piojos (Spain). The results show that two source populations are required to explain the ancestry at Los Castellets II: one enriched in steppe-related ancestry and distantly related to Central European BA populations, and a second source similar to local Southeastern Iberian BA. Additionally, two-thirds of the individuals from the same collective tumulus were closely biologically related from 1st to >6th degree, with a man having the highest number of genetic relatives. We detected signs of inbreeding within the family group, all together suggesting the tumulus was used as a family mausoleum.