The intraruminal papillation pattern indicates the degree of rumen contents stratification, and is related to the feeding niche of a ruminant. Muskoxen (Ovibos moschatus) display a variety of morphophysiological adaptations typical for grazers. We investigated the intraruminal papillation of 22 free-ranging muskoxen from 5 different months, by comparing the surface enlargement factor both between seasons, and between individual rumen regions. The seasonal pattern of rumen papillation indicated a distinct seasonality in food quality. The intraruminal papillation indicated a moderate degree of rumen contents stratification typical for intermedate feeders. The nutritional ecology of muskoxen is characterized by specific morphophysiological adaptations to a grass-dominated diet that nevertheless allow extensive seasonal use of browse forage.