Evolution
Map of Madagascar indicating distribution of extinct hippopotamus species.
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
- upper canine teeth with a very shallow posterior groove
- lower canine teeth with strong and convergent ridges
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
- Choeropsis,
- Saotherium,
- Hexaprotodon
- Archaeopotamus
The tetraprotodont (4 incisor teeth) genus Hippopotamus, with derived anterior dentition
includes
- the extant Hippopotamus amphibius,
- Hippopotamus gorgops, Hippopotamus kaisensis from Africa,
- the Malagasy Hippopotamus spp.
- the Quaternary European Hippopotamus
- Mediterranean island Hippopotamus spp.
Hippopotamus species can be distinguished relatively easily from other hippopotamines and the monophyly of this taxon is well supported.