Re-examining the earliest evidence of human presence in western Europe: New dating results from Pirro Nord (Italy)

We present the results of the first dating study of site P13 at Pirro Nord, Italy, which documents some of the earliest evidence for hominin presence in western Europe. Our multi-technique dating approach is based on a combination of palaeomagnetism, electron spin resonance (ESR), thermally-transferred optically stimulated luminescence (TT-OSL) and combined U-series/ESR applied to both fossil material and host sediment. It provides ages ranging from 627 ± 59 to 1006 ± 126 ka and clustering around 0.8 Ma. One additional fossil tooth collected from the nearby P10 site also returns an age within this range. Ordinarily, this outcome would naturally lend itself to the straightforward conclusion that Pirro Nord has a late Early Pleistocene age of ∼0.8 Ma. However, this interpretation is complicated by the fact that these numerical dating results are in contradiction with the biochronological evidence, which suggests a much older age on the order of 1.3–1.7 Ma. Consequently, we explore the various potential sources of bias that could have influenced the numerical dating methods and the biochronological inferences. In particular, the critical evaluation of the palaeomagnetic data available for various sites belonging to the younger Colle Curti Faunal Unit (FU) indicates that there is non-negligible age uncertainty on the allegedly minimum age of ∼1.1 Ma traditionally assigned to the Pirro FU. Moreover, while the combined U-series/ESR dataset could accommodate an older age for the fossil remains if uranium uptake in the dental tissues occurred relatively rapidly before the closure of the system (CSUS model), the ages obtained from the two semi-independent quartz dating methods (ESR and TT-OSL) both appear to indicate that the sediment was last exposed to sunlight about 0.8 Ma. This disparity opens up the possibility that the sediment and fossil assemblage may not be coeval. In other words, it is possible that the fossil remains may have been reworked into younger deposits that entered the karst about 0.8 Ma. Though feasible from a karst sedimentary dynamics perspective, this hypothesis is not consistent with previous taphonomic studies that indicate an absence of evidence for fossil reworking after entering the karst. At the very least, our dating results indicate that site formation processes at Pirro Nord site P13 are more complex than previously considered.