The barren-ground caribou ("R. t. groenlandicus") is found in western Greenland, but the larger herds are in Alaska, the Northwest Territories and Nunavut. According to Grubb, based on Banfield and considerably modified by Geist, these subspecies and divisions are considered valid: the "caribou" or woodland caribou division, which includes "R. t. buskensis", "R. t. caribou", "R. t. dawsoni", "R. t. fennicus", "R. t. phylarchus" and "R. t. valentinae" ("R. t. osborni" is a transitional subspecies between the "caribou" and "tarandus" divisions), the "tarandus" or tundra reindeer division, which includes "R. t. caboti", "R. t. groenlandicus", "R. t. pearsoni", "R. t. sibiricus" and "R. t. terraenovae" and the "platyrhynchus" or dwarf reindeer division, which includes "R. t. pearyi" and "R. t. platyrhynchus". Some of the "Rangifer tarandus" subspecies may be further divided by ecotype depending on several behavioural factors – predominant habitat use (northern, tundra, mountain, forest, boreal forest, forest-dwelling, woodland, woodland (boreal), woodland (migratory) or woodland (mountain), spacing (dispersed or aggregated) and migration patterns (sedentary or migratory). The "glacial-interglacial cycles of the upper Pleistocene had a major influence on the evolution" of "Rangifer tarandus" and other Arctic and sub-Arctic species. Isolation of "Rangifer tarandus" in refugia during the last glacial – the Wisconsin in North America and the Weichselian in Eurasia-shaped "intraspecific genetic variability" particularly between the North American and Eurasian parts of the Arctic. In 1986 Kurtén reported that the oldest reindeer fossil was an "antler of tundra reindeer type from the sands of Süssenborn" in the Pleistocene (Günz) period (680,000 to 620,000 BP).