Classification

Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Perissodactyla
Family: Rhinocerotidae

Overview

Rhinoceroses, otherwise known by the shortened form "rhinos", are a group of five species of odd-toed ungulates, the group containing horses and tapirs. Even-toed ungulates include cattle, deer and antelopes amongst others.

Feeding on an exclusively herbivorous diet, rhinos grow very large and are some of the largest animals on Earth. They are characterised by their thick, grey, collagen reinforced hide and large facial horns. Like most other ungulates they have an efficient digestive system which can break down tough plant matter.

Horns

Rhino horns are made from keratin, the same substance that makes up your fingernails and the spines on a hedgehog.

Unlike most other horned animals, like antelope and sheep, rhino horns lack a central bone core, which means that they can sometimes fall off given the necessary stress - something which has been observed in captive animals who regularly brush their horn against their enclosure. However, just like your fingernails, rhino horns grow continuously and the shed horn will grow back eventually.

Species

Both the African white and black rhinos and the Sumatran species have two horns, while Indian and Javan rhinos have a single horn. The Indian rhino's binomial name, Rhinoceros unicornis, points to this single horn, although this is about all it shares with the mythical unicorn.

White and black rhinos aren't as contrasting in shade as you may imagine - both are a similar shade of grey. It is a common belief that the white rhino (seen at the very top of the page) is so-named because "white" is a distortion of either the Afrikaans word "wyd", meaning "wide", corresponding to their square lips which they use for grazing on grass. In contrast the black rhinos have a pointed, prehensile top lip which they use for grasping foliage, displaying their very different feeding habits.

Conservation and Poaching

Three species of rhino are listed as critically endangered on the IUCN Red List, black, Javan and Sumatran rhinos. Of these one sub-species of black rhino was declared extinct in 2011, there are now less than 60 Javan rhinos are still alive and Sumatran rhinos, the smallest of the rhinos, are down to only 275 individuals.

Of the other two species the Indian rhino is declared vulnerable, while the white rhino is now listed as near threatened, having made a come-back in recent years.

The major threat to wild rhinos is the illegal trade in rhino horn which is sold on the black market, commonly east Asia, for use in traditional medicines or fashioned into ornaments.. A good deal of the reduction in population sizes is due to poaching for horn, with the dead or dying rhinos stripped of their horns.

Some managed populations in parks and reserves are routinely stripped of their horns in order to reduce their value to poachers. There has also been calls in recent years to open up the trade of rhino horn in order to combat poaching, however this is a contentious issue.

Quick Facts

• Rhinos have relatively small brains at around 500g.
  
• No predators, although young rhinos can be predated on by big cats and crocodiles.
  
• Rhinos have been around for over 20 million years.
  
• White rhinos are the largest rhino and the fourth largest land animal.
  
• Sumatran rhinos are the smallest, averaging less than a tonne.