Etymology

Etymology
The Latin word hippopotamus is derived from the ancient Greek ἱπποπόταμος, hippopótamos, from ἵππος, híppos, “horse”, and ποταμός, potamós, “river”, meaning “horse of the river”.[4][5][6] In English, the plural is “hippopotamuses”, but “hippopotami” is also used.[7]

Taxonomy and origins
Classification
Hippopotamus is the type genus of the family Hippopotamidae. The pygmy hippopotamus belongs to a different genus in Hippopotamidae, either Choeropsis or Hexaprotodon. Hippopotamidae are sometimes known as hippopotamids. Sometimes, the subfamily Hippopotaminae is used. Further, some taxonomists group hippos and anthracotheres in the superfamily Anthracotheroidea.[8]:39 Hippopotamidae are classified along with other even-toed ungulates in the order Artiodactyla. Other artiodactyls include camels, cattle, deer and pigs, although hippos are not closely related to these groups.

Detail of the head
Five subspecies of hippos have been described based on morphological differences in their skulls and geographical differences:[8]:3

Great northern hippopotamus or Nile hippopotamus H. a. amphibius – (the nominate subspecies) which stretched from Egypt, where they are now extinct, south up the Nile River to Tanzania and Mozambique
East African hippopotamus H. a. kiboko – in Kenya in the African Great Lakes region, and in Somalia in the Horn of Africa. Broader nasals and more hollowed interorbital region
Cape hippopotamus or South African hippopotamus H. a. capensis – from Zambia to South Africa, most flattened skull of the subspecies
West African hippopotamus or Tchad hippopotamus H. a. tschadensis – throughout Western Africa to, as the name suggests, Chad, slightly shorter and wider face, with prominent orbits