The large hippopotamus common in Africa today Hippopotamus amphibius is believed to be the probable ancestor of the Malagasy dwarf hippos.
Hippopotamus amphibius is likely to have got to the island of Madagascar by swimming across the 430 km Mozambique channel that separated Madagascar from the African mainland. This would have been a rare event but it may have happened several times over the last million years. Large mammals that become isolated on islands commonly evolve to be much smaller in body size relative to their mainland ancestors.
Both species of dwarf hippopotamus from Madagascar possess morphological characteristics
that are only shared with species attributed to the genus Hippopotamus.
In the past hippopotamine taxa were more diverse and attributed to four other genera
The tetraprotodont (4 incisor teeth) genus Hippopotamus, with derived anterior dentition
Hippopotamus species can be distinguished relatively easily from other hippopotamines and the monophyly of this taxon is well supported.