Order Artiodactyla Author Wilson, Don E. Author Reeder, DeeAnn text 2005 The Johns Hopkins University Press Baltimore Mammal Species of the World: a Taxonomic and Geographic Reference (3 rd Edition), Volume 1 637 722 book chapter 0-8018-8221-4 10.5281/zenodo.7316519 Hippopotamidae Gray 1821 Hippopotamidae Gray 1821 , London Med. Repos., 15: 306 . Synonyms: Choeropsinae Gill 1872 . Genera: 2 genera with 2 species: Genus Hexaprotodon Falconer and Cautley 1836 (1 species with 2 subspecies) Genus Hippopotamus Linnaeus 1758 (1 species with 3 subspecies) Discussion: Hexaprotodon † madagascariensis (Guldberg, 1883), Hippopotamus † lemerlei Grandidier, 1868, and H . † laloumena Faure and Guerin, 1990 were present in the Holocene on Madagascar ( Stuenes, 1989 ), but have not been shown to have survived into the last 500 years.