Vegetation and climate dynamics in the northwestern Altai (MIS 9–MIS 2): Implications for archaic hominin ecology

The Altai Mountains preserve a nearly continuous archaeological and paleoanthropological record spanning the second part of Middle and the entire Late Pleistocene, making the region key to understanding the coexistence and ecological adaptation of archaic hominins. We present new pollen data from the South Chamber of Denisova Cave and integrate them with previously published palaeoecological evidence from the Main and East chambers, as well as from other key sites in the region (Chagyrskaya, Okladnikov, Verkhnaya Sibiryachikha, Ust-Karakol, Anui-2). Using this combined record, we reconstruct vegetation and climate dynamics in the northwestern Altai from MIS 9 to MIS 2 and characterize the environmental conditions that accompanied the presence of Denisovans and Neanderthals. The record shows pronounced glacial–interglacial cyclicity with an overall trend of long-term climatic deterioration: birch and pine forests with variable broad-leaved and dark coniferous admixtures during the warmer phases of MIS 9–5 were progressively replaced by open herb-dominated steppe and tundra-steppe landscapes during MIS 4–2. Denisovans, present from at least MIS 9 to early MIS 3, occupied a wide range of environments — from mixed forests to periglacial tundra-steppe — suggesting that they were ecological generalists. In contrast, late Neanderthals, present during late MIS 4 – early MIS 3, occupied open steppe landscapes, while the ecology of the earlier Neanderthal population that coexisted with Denisovans during MIS 6–5 remains poorly known. The coexistence of both groups was likely facilitated by local environmental heterogeneity, which provided sufficient ecological space for each.