Simplify the following text for a Grade 7 native English-speaking person.
Original: The hippopotamus ( Hippopotamus amphibius ) , or hippo , from the ancient Greek for `` river horse '' , is a large , mostly herbivorous mammal in sub-Saharan Africa , and one of only two extant species in the family Hippopotamidae ( the other is the Pygmy Hippopotamus . )
Simplified: The other is the Pygmy Hippopotamus .