†Trilobophorus Geze, 1985 Hippopotamidae is a family of stout, naked-skinned, and semiaquatic artiodactyl mammals, possessing three-chambered stomachs and walking on four toes on each foot.

The number of incisors varies even within the same species, but the general dental formula is given in the table below: The hippopotamids are descended from the anthracotheres, a family of semiaquatic and terrestrial artiodactyls that appeared in the late Eocene, and are thought to have resembled small- or narrow-headed hippos.

[2] After the appearance of the hippopotamids, the remaining anthracotheres went into a decline brought about by a combination of climatic change and competition with their descendants, until the last genus, Merycopotamus, died out in the early Pliocene of India.

[3] Hippopotamidae's placement within Artiodactyla can be represented in the following cladogram:[4][5][6][7][8] Tylopoda (camels and kin) Suina (pigs and kin) Ruminantia (ruminants) Hippopotamidae (hippopotamids) Cetacea (whales) The lower canine teeth of hippopotamids are similar in function and structure to the tusks of elephants.

While hippopotamids and elephants are only very distantly related within the Mammalia, the lower canine teeth of both groups are long and have a slight curve, and species of both families use this structure when fighting.