Pygmy hippopotamus the pygmy hippopotamus, are considered dwarf hippopotamuses, rather than pygmies. They are likely descended from a full-sized species of European hippopotamus, and reached their small size through the evolutionary process of insular dwarfism which is common on islands; the ancestors of pygmy hippopotami were also small and thus there was never a dwarfing process. There were also several species of pygmy hippo on the island of Madagascar (see Malagasy hippopotamus). Pygmy hippos share the same general form as a hippopotamus. They have a graviportal skeleton, with four stubby legs and four toes on each foot, supporting a portly frame. The
Mammal scheme used, are the [[Primate]]s including the [[ape]]s, [[monkey]]s and [[lemur]]s; the [[Cetartiodactyla]] including [[whale]]s and [[even-toed ungulates]]; and the [[Carnivora]] which includes [[cat]]s, [[dog]]s, [[weasel]]s, [[bear]]s, [[Pinniped|seals]] and allies. According to "[[Mammal Species of the World]]", 5,416 species were identified in 2006. These were grouped into 1,229 [[genus|genera]], 153 [[family (biology)|families]] and 29 orders. In 2008, the [[International Union for Conservation of Nature]] (IUCN) completed a five-year Global Mammal Assessment for its [[IUCN Red List]], which counted 5,488 species. According to a research published in the "[[Journal of Mammalogy]]" in 2018, the number of recognized mammal species is 6,495