Is hippopotamus a proper noun or a common noun?

"Hippopotamus" is a common noun, as it refers to a general species of large, mostly herbivorous mammals found in sub-Saharan Africa. Common nouns name general items, while proper nouns identify specific names or titles. For example, "Hippopotamus amphibius" is the scientific name of the species, but "hippopotamus" on its own remains a common noun.