The results are reported of a study of plant remains from the gastrointestinal tract of large herbivorous mammals, i.e., horse, mammoth, bison, which perished, according to C14data, during various periods of the Kargin interglacial in the Indigirka River basin (corresponding to the mid‐Wisconsin, 45,000 to 30,000 BP). At that time, the forest reached the coast of the Arctic Ocean, and bogs spread. This led to a reduction of herbaceous communities serving as pastures. The qualitative composition of the food of the animals changed. Plants of moist and waterlogged communities, sedges, cotton‐grass, grasses, and green and sphagnum mosses, began to predominate in their fodder. These communities differ considerably in their content of major nutrients (protein, albumin, fats) and mineral composition from plants of dry habitats and meadow forbs. This was the main reason for the reduction in the population of some animals and the final extinction of others.