Easily recognized by their nose horns and thick armor-resembling skin, rhinoceroses are familiar to wildlife enthusiasts everywhere. Found throughout Africa and southern Asia, these massive animals are intimidating fauna of their local environments. Of the five species of rhinoceros, two inhabit Africa, the black rhino, and the white rhino. The other three species, the Javan rhino, Sumatran Rhino, and Indian rhino are found throughout southern Asia, with each species' range encompassing the geographic location of its name.

The word rhinoceros literally means "nose horn", derived from the Greek rhis, meaning nose, and keros, meaning horn. All rhinos have horns, but two species, the Indian rhino and Javan rhino, have but one horn, while the black rhino, white rhino, and Sumatran rhino have two horns. Rhino "horns" are not true horns. True horns consist of a bony core, covered by a keratin sheath. Rhinoceros horns are composed of keratin, but lack a bony core. They are simply a group of highly compacted keratin fibers on a roughened area of the skull.

Despite their horns and armored appearance, one may expect rhinos to share close ancestry with elephants. But rhinoceroses are actually related to horses and tapirs, in the Mammalian Order for odd-toed ungulates, Perissodactyla. Like the other perissodactyls, rhinos have mesaxonic feet, which means the center toe bears much of the weight. Rhinos have three toes, which are large and splayed out to support their bulky body. Also like horses, rhinos are hindgut fermenters, bearing the ability to eat less nutritious vegetation than ruminants because digestion is faster. All species of rhino are herbivorous, either grazing on grasses or browsing on shrubbery.

Rhinos are primarily solitary, found together only to breed, with calf, or at a shared resource. Males are territorial, defending their territory aggressively. The two African rhino species joust with their horns, while the Asian rhino species battle with their lower inscisors, and in the case of the Sumatran rhino - its lower canines. Females travel throughout different territories, using resources as needed.

Rhinoceros eyesight is very poor. A motionless person at 100ft (30m) is undetectable to a rhino. However, what rhinos lack in sight is accounted for in audition and olfaction. A rhino's hearing is extremely sensitive, capable of noticing the slightest of sounds. But a rhino's cardinal sense is smell. The volume of olfactory passages in the snout exceeds that of the brain!

Unfortunately, not even the keenest sense of smell can save the rhino from human hunters. Poached for its magnificent horn, all species of rhino are in danger of extinction. Rhino populations are now increasing due to protection from national park systems and captive breeding programs in zoos throughout the world.