Pygmy hippopotamus occur. The common hippopotamus gives birth and mates only in the water, but pygmy hippos mate and give birth on both land and water. Young pygmy hippos can swim almost immediately. At birth, pygmy hippos weigh 4.5–6.2 kg (9.9–13.7 lb) with males weighing about 0.25 kg (0.55 lb) more than females. Pygmy hippos are fully weaned between six and eight months of age; before weaning they do not accompany their mother when she leaves the water to forage, but instead hide in the water by themselves. The mother returns to the hiding spot about three times a day and calls
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