Middle Pleistocene paleoclimate and paleoenvironment of central Italy and their relationship with hominin migrations and evolution

Abstract

To investigate the paleoclimate and paleoenvironment of central Italy during the Middle Pleistocene, we analyzed the carbon and oxygen stable isotope composition of the carbonate component of sequential enamel samples from twenty-four rhinoceros (Stephanorhinus spp.) teeth. The samples come from two key archeological and paleontological sites located in the Molise region: Isernia La Pineta (ILP; ∼600 ka) and Guado San Nicola (GSN; ∼400 ka).Carbon isotope ratios of enamel from both ILP and GSN indicate feeding in a pure C3 ecosystem that consisted predominantly of woodlands and/or mesic C3 grasslands with the possible sparse presence of closed canopy forests at or near ILP ∼600 ka. The average (± 1 σ) enamel δ13C for ILP (−13.6 ± 0.6‰) is lower than that for GSN (−12.1 ± 0.4‰), suggesting higher mean annual precipitation and lesser aridity ∼600 vs. ∼400 ka. Average intra-tooth variability in enamel δ13C from both sites is low (∼1‰), likely indicating seasonally uniform diets, plant carbon isotope compositions, and precipitation amounts. However, the low intra-tooth variability in enamel δ13C may also reflect amplitude attenuation of the isotopic signal of the plants into tooth enamel.With respect to oxygen isotopes, the average (± 1 σ) enamel δ18O for ILP (24.2 ± 0.7‰) is slightly lower than that for GSN (25.0 ± 0.7‰), likely reflecting the higher elevation of ILP as well as lesser aridity and/or slightly lower mean annual temperature in the region ∼600 vs. ∼400 ka. The δ18O values of meteoric precipitation (∼-7‰) calculated from enamel compositions are indistinguishable from the modern values, suggesting that mean annual temperatures were broadly similar to today (∼13°C). Both sites exhibit a moderate average intra-tooth variability in enamel δ18O (∼2‰), likely indicating a temperature seasonality similar or slightly decreased relative to today. The temperate climate and the increase in aridity that occurred sometime between ∼600 and ∼400 ka were potentially important factors for the human colonization of the Italian peninsula and for the cultural and behavioral evolution of the early hominins during the Middle Pleistocene.