The main difference between Hippopotamus and Rhinoceros is that the Hippopotamus is a species of pachyderm and Rhinoceros is a family of mammals.
The common hippopotamus (Hippopotamus amphibius), or hippo, is a large, mostly herbivorous, semiaquatic mammal native to sub-Saharan Africa, and one of only two extant species in the family Hippopotamidae, the other being the pygmy hippopotamus (Choeropsis liberiensis or Hexaprotodon liberiensis). The name comes from the ancient Greek for “river horse” (ἱπποπόταμος). After the elephant and rhinoceros, the common hippopotamus is the third-largest type of land mammal and the heaviest extant artiodactyl. Despite their physical resemblance to pigs and other terrestrial even-toed ungulates, the closest living relatives of the Hippopotamidae are cetaceans (whales, dolphins, porpoises, etc.) from which they diverged about 55 million years ago.
Common hippos are recognisable by their barrel-shaped torsos, wide-opening mouths revealing large canine tusks, nearly hairless bodies, columnar legs and large size; adults average 1,500 kg (3,310 lb) and 1,300 kg (2,870 lb) for males and females respectively. Despite its stocky shape and short legs, it is capable of running 30 km/h (19 mph) over short distances.
The common hippopotamus inhabits rivers, lakes and mangrove swamps, where territorial bulls preside over a stretch of river and groups of five to thirty females and young. During the day, they remain cool by staying in the water or mud; reproduction and childbirth both occur in water. They emerge at dusk to graze on grasses. While hippopotamuses rest near each other in the water, grazing is a solitary activity and hippos are not territorial on land. The hippopotamus is among the most dangerous animals in the world as it is highly aggressive and unpredictable. They are threatened by habitat loss and poaching for their meat and ivory canine teeth.
A rhinoceros (, from Greek, Modern rhinokeros, meaning ‘nose-horned’, from rhinos, meaning ‘nose’, and kerato/keras, meaning ‘horn’), commonly abbreviated to ‘rhino’, is one of any five extant species of odd-toed ungulates in the family Rhinocerotidae, as well as any of the numerous extinct species. Two of the extant species are native to Africa and three to Southern Asia. The term “rhinoceros” is often more broadly applied to now extinct relatives of the superfamily Rhinocerotoidea.
Members of the rhinoceros family are some of the largest remaining megafauna, with all species able to reach or exceed one tonne in weight. They have a herbivorous diet, small brains (400–600 g) for mammals of their size, one or two horns, and a thick (1.5–5 cm) protective skin formed from layers of collagen positioned in a lattice structure. They generally eat leafy material, although their ability to ferment food in their hindgut allows them to subsist on more fibrous plant matter when necessary. Unlike other perissodactyls, the two African species of rhinoceros lack teeth at the front of their mouths, relying instead on their lips to pluck food.Rhinoceros are killed by some humans for their horns, which are bought and sold on the black market, and used by some cultures for ornaments or traditional medicine. East Asia, specifically Vietnam, is the largest market for rhino horns. By weight, rhino horns cost as much as gold on the black market. People grind up the horns and consume them, believing the dust has therapeutic properties. The horns are made of keratin, the same type of protein that makes up hair and fingernails. Both African species and the Sumatran rhinoceros have two horns, while the Indian and Javan rhinoceros have a single horn. The IUCN Red List identifies the Black, Javan, and Sumatran rhinoceros as critically endangered.
A large, semi-aquatic, herbivorous (plant-eating) African mammal (noshow=1)
Any of several large herbivorous pachyderms native to Africa and Asia of the five extant species in the three extant genera in the family Rhinocerotidae, with thick, gray skin and one or two horns on their snouts.