These guys are kind of a land dwelling version of a hippo but, unlike hippos, rhinos are odd-toed ungulates (three toes on each foot, a hippo has four). However, like hippos, rhinos can be just plain mean if you happen to be a human. Who can blame them when for years they have been persecuted - hunted because of being one of the big five (the most difficult animals in Africa to hunt on foot), and hunted for their horn simply because the Chinese believe that their horn when ground into powder is a cure for fevers and convulsions (not an aphrodisiac as is commonly believed).
There are two species in Africa. The "white rhino" (Ceratotherium simum simum), so called not because of its colour but simply because someone many years ago misinterpreted the Dutch word "weit", which means "wide", in reference to their wide nose (compared to the relatively narrower one of the black rhino) and the name "white" kind of stuck! In fact, the white rhino is also called the "square-lipped rhino" because of its nose. There are two sub-species of white rhino, the "southern" white rhino, which is the most endangered species, and the "northern" white rhino. White rhinos tend to prefer savannas with water holes and shadey glades.
The other African species is the "black rhino" (Diceros bicornis), also known as the "hooked-lipped rhino". This species tends to prefer dense, woody habitats.
Below are some excellent resources about rhinos: