Reindeer and small animal remains do not preserve, but reindeer excrement has been found in sediment.[2] In the most arid regions of the mammoth steppe that were to the south of Central Siberia and Mongolia, woolly rhinoceros were common[3][6] but woolly mammoths were rare.[4][6] Reindeer live in the far north of Mongolia today and historically their southern boundary passed through Germany and along the steppes of eastern Europe,[5][6] indicating they once covered much of the mammoth steppe.[6] Mammoths survived on the Taimyr Peninsula until the Holocene.[6][6] A small population of mammoths survived on St. Paul Island, Alaska, up until 3750 BC,[7][8] and the small[9] mammoths of Wrangel Island survived until 1650 BC.[10][11] Bison in Alaska and the Yukon, and horses and muskox in northern Siberia, have survived the loss of the mammoth steppe.[6] One study has proposed that a change of suitable climate caused a significant drop in the mammoth population size, which made them vulnerable to hunting from expanding human populations.