The hippopotamus and rhinoceros are large, grayish wild herbivorous mammals known for their immense size. The rhino can be distinguished with a prominent horn on its snout.
There are five extant (existing biological) species of odd-toed ungulates (3 toes on each foot) in the family rhinocerotiae. The Javan, Sumatran and Black rhinoceros are critically endangered; the Indian one-horned rhinoceros is endangered; the white rhinoceros is vulnerable and lives in Africa.
There is only one species of Hippopotamus in existence: the Hippopotamus amphibius in the family Hippopotamidae. The other is the Pygmy Hippopotamus which is seen only in certain reserves in West Africa.
The rhinoceros family is characterized by its large size. It is one of the largest remaining megafauna alive today, with all of the species able to reach one ton or more in weight. The white rhino can exceed 3,500 kg, have a head-and-body length of 3.5–4.6 m. The fully grown Indian rhino males are larger than females in the wild, weighing from 2,500–3,200 kg. The Hippopotamus is the third largest land animal, after the elephant and white rhino.
The average weight for adult males hippos ranges from 1,500–1,800 kg with the females smaller at an average weight between 1,300–1,500 kg. Older males can get much larger, reaching at least 3,200 kg and occasionally weighing 4,500 kg. Male hippos appear to continue growing throughout their lives; females reach a maximum weight at around age 25.
The rhino is characterized by its keratin horn. It has an immense body and large head, a short neck and broad chest. The white rhino has a long face and a pronounced hump on its neck.
The hippopotamus has a stocky, barrel-shaped torso, enormous mouth and teeth, nearly hairless body, stubby legs and tremendous size. The eyes, ears, and nostrils of hippos are placed high on the roof of the skull. This allows them to be in the water with most of their body submerged in the waters and mud of tropical rivers to stay cool and prevent sunburn.
The color of white rhino can range from yellowish brown to slate gray. It is not white, it is named after the Dutch word for wide for its wide lip. The Indian Rhinoceros has thick, silver-brown skin which creates huge folds all over its body. The Javan rhino has hazy gray skin. The Black rhino is not black and is similar in color to the white rhino. Sumatran rhino's are reddish brown in color.
The hippopotamus has a grayish colored body.
edit Skin and Hair
Most of the white rhino's body hair is found on the ear fringes and tail bristles with the rest distributed rather sparsely over the rest of the body. The Javan rhino is hairless like the Indian rhino. The Indian Rhinoceros has thick, silver-brown skin which creates huge folds all over its body and is a pinkish color near the folds. Its upper legs and shoulders are covered in wart-like bumps. The Sumatran rhino's hair can range from dense, in calves to sparse.
The hippo's grayish body has very thick skin which is virtually hairless. The hippo has neither sweat nor sebaceous glands, relying on water or mud to keep cool. It does, however, secrete a viscous red fluid which protects the animal’s skin against the sun and is possibly a healing agent.
White Rhinos have the distinctive flat broad mouth which is used for grazing in contrast to the Black rhino's pointed lip which they use to grasp leaves and twigs. Rhino's have 24 to 34 teeth mostly premolars and molars used for grinding.
The hippo has sharp canines that are used as defence and also to attack mating rivals. It can open its mouth to an angle of 150 degrees, compared to 45 degrees in humans.
The most obvious distinguishing characteristic of the rhinos is a large horn above the nose. Rhinoceros horns, unlike those of other horned mammals – especially bovines - lack a bony core. The horn of a rhinoceros consists only of keratin, the same type of fibrous structural protein that makes up hair and fingernails.
All rhino's except the Indian rhino have two horns for which they are usually poached. The horn is used to make daggers or crushed and used as an aphrodisiac in traditional Chinese medicine. The two horns on the skull are made of keratin with the larger front horn typically 50 cm long, exceptionally up to 140 cm. Sometimes, a third smaller horn may develop. The black rhino’s horn is much smaller than that of the white rhino
The white rhino's front horn is larger than the other horn and averages 90cm in length and can reach 150cm. The greek word 'ceros' means horn. Both male and female Indian rhinos have only one horn. The horn which is made of keratin, the same substance of human fingernails, starts to grow after 6 years of age. In most adults the horn reaches about 25 centimeters, but has been recorded up to 57.2 centimeters in length. The nasal horn curves backwards from the nose. Its horn is naturally black. In captive animals, the horn is frequently worn down to a thick knob. The rhino's in Africa (white and black) use their horns for attacking while the Indian rhino uses its incisors.
The hippopotamus has no horn.
The white rhino needs open undulating woodland with plenty of grass and permanent water. Hippos are semi-aquatic mammals so rivers and lakes, not necessarily very deep, with pools of slow moving water and banks with good quality grazing is an ideal habitat. Both hippos and rhinos are herbivores. Almost 98% of the black rhino population is found in just four countries: South Africa, Namibia, Zimbabwe and Kenya when at one stage they were found all over the African continent. The white rhino is found in African countries including South Africa, Botswana, Zimbabwe and Namibia. The black rhino is found in South Africa, Rwanda and Zimbabwe. The Sumatran and Javan rhinos are found in Sumatra and Java respectively. The Indian one-horned rhino is found in the Assam region of India and in Nepal. Hippos are found all over Sub-Saharan Africa.
Both rhinos and hippos in the wild can be very aggressive to humans.
White rhinos are less aggressive and more sociable than black rhinos and can be seen in groups of ten or 15 and live according to a strict social structure. Black rhinos travel alone. The Indian Rhinoceros forms a variety of social groupings. Adult males are generally solitary, except for mating and fighting. Adult females are largely solitary when they are without calves. Mothers will stay close to their calves for up to four years after their birth. Male rhinos can greet each other in a very friendly manner and play with stick and twigs together.
Hippos spend most day soaking in water. They cannot swim but often submerge and resurface every 3 to 5 minutes to breathe. They can also sleep underwater and automatically resurface without waking.
There are estimated 17,500 white rhinoceros remaining in the wild and about 4240 black rhinos. In 2007 there were only 50 Javan rhinos in the wild, 200 Sumatran rhinos and 2620 one-horned Indian rhinos in the world. There are an estimated 125,000 to 150,000 hippos throughout Sub-Saharan Africa; Zambia (40,000) and Tanzania (20,000–30,000) possess the largest populations.
Since 1970 the world rhino population has declined by 90 percent, with five species remaining in the world today, all of which are endangered. The Javan and Sumatran rhinos are critically endangered. Hippos are not endangered although their population dramatically declined in Congo where their meat is sold illegal. Hippo populations are threatened due to loss of fresh water sources.