Adam Clarke on Genesis 41:2

There came up out of the river seven well-favored kine - This must certainly refer to the hippopotamus or river horse, as the circumstances of coming up out of the river and feeding in the field characterize that animal alone. The hippopotamus is the well-known inhabitant of the Nile, and frequently by night comes out of the river to feed in the fields, or in the sedge by the river side.