The only living members of the family Hippopotamidae are the modern hippopotamus and the pygmy hippopotamus. Anthracotheres and hippos are included in the superfamily Anthracotheroidea by some taxonomists. The order Artiodactyla includes Hippopotamidae and other even-toed ungulates. 39–40 Closeup of the head Five subspecies of hippos have been identified based not only on differences in their geographical range but also on morphological differences in their skulls: 3  The nominate subspecies of H. a. amphibius can be found in the Gambia, Ethiopia, Mozambique, and as far north as Egypt in the past; It has a slightly smaller preorbital area, a bulging dorsal surface, an elongated mandibular symphysis, and larger teeth for chewing.
H. a. kiboko, which is found in Somalia and Kenya; was noted to be smaller and lighter colored than other hippos, with wider nostrils, a snout that was a little longer, and orbits that were more rounded and relatively raised, with an incurved space between them.
H. a. capensis, which can be found in South Africa and Zambia; characterized by wider orbits.
H. a. tschadensis is found in Niger and Chad; featured prominent, forward-facing orbits and a face that was slightly shorter but wider.
H. a. constrictus was found in Namibia, Angola, and the southern Democratic Republic of the Congo; skull portrayed by a thicker preorbital district, more limited nose, compliment dorsal surface, diminished mandibular symphysis and more modest biting teeth.