New paleoecological inferences based on the Early Pleistocene amphibian and reptile assemblage from Dmanisi (Georgia, Lesser Caucasus).

Dmanisi (Georgia) is one of the oldest Early Paleolithic sites discovered out of Africa. In addition, it is the best site to understand the first Homo deme out of Africa and the first hominin occupation of Central to Western Eurasia. It has produced more than 40 hominin remains, including several very informative skulls, found in direct association with faunal remains and numerous lithic artifacts. To date, fossil amphibians and reptiles are one of the few proxies that have been used to propose quantitative climate reconstructions for the time where the hominins were living at Dmanisi. The aim of the present study is to review and amplify the previous paleoclimatic interpretation given by Blain et al. (2014), with an enhanced methodology using geographic information system and based on uncertain distribution area-occupied distribution area discrimination technique. This procedure permits to approach to a more precise common species distribution area and then using the WorldClim v. 2.1 climate database to propose for the first time monthly reconstructions for temperature and rainfall, in addition to annual parameters. The same technique is used to infer dominant ecoregions through the study area and potential tree coverage. Dmanisi climate is newly reconstructed as warm and semi-arid, similar to the present-day Mediterranean climate. New estimates however suggest warmer temperatures than previously reconstructed, together with a slightly higher but much more irregular amount of rainfall. The aridity indexes suggest a six months dry period, from May to October. Associated regional paleoenvironment is mainly characterized by Mediterranean forests, woodlands, and scrub, and the potential tree coverage is around 25%, that is, much less forested than today. New estimates agree with the 'Iberian' hominin ecological model, and with other proxies (large mammals, small mammals and archaeobotanical remains) that indicate a period of increased aridity contemporaneous with human occupations of the site.

Coping with arid environments: A critical threshold for human expansion in Europe at the Marine Isotope Stage 12/11 transition? The case of the Iberian Peninsula.

Archaeological remains have highlighted the fact that the interglacial Marine Isotope Stage (MIS) 11 was a threshold from the perspective of hominin evolution in Europe. After the MIS 12 glaciation, considered one of the major climate-driven crises experienced by hominins, the archaeological records show an increasing number of occupations, evidence of new subsistence behaviors, and significant technical innovations. Here, we used statistical and geographic techniques to analyze the amphibian- and reptile-based paleoclimate and habitat reconstructions generated from a large data set of the Iberian Peninsula to (1) investigate if temperature, precipitation, and/or forest cover may have impacted the hominin occupation of the territory during the Early and Middle Pleistocene, (2) propose an 'Iberian' ecological model before and after the MIS 12/11 transition, and (3) evaluate, based on this model, the potential hominin occupation at a European scale. The results indicate the existence of climatic constraints on human settlement related to rainfall and environmental humidity. The Early Pleistocene and the first half of the Middle Pleistocene are dominated by the occupation of relatively humid wooded areas, whereas during the second part of the Middle Pleistocene, a broadening of the earlier ecological niche is clearly observed toward the occupation of more open arid areas. Based on the estimated occupational niche for hominins, a maximum potential distribution for early hominins is proposed in Europe before and after 426 ka. Results also indicate that parts of the Iberian Peninsula may not have been suitable for early hominin occupation. Our ecological model is consistent with the pattern of hominin occupation observed in northern and central Europe, where the earliest evidence reflects only pioneering populations merely extending their ranges in response to the expansion of their preferred habitats, as compared with a more sustained occupation by 400 ka.