There are five living species of rhinos in Africa and Asia. The largest, the White Rhino, is about twice the size and weight of the smallest, the relatively diminutive Sumatran Rhino. All have much in common regarding their behavior and anatomy. Still, there are significant differences as well, indicating how, over time, the individual species have adapted to their environmental circumstances.
RHINOS—A QUICK INTRODUCTION
The ancestors of the rhinos emerged about 55 million years ago. Today five species survive. Little more than 200 years ago, rhinos in their hundreds of thousands—if not millions—still roamed through much of Africa and large parts of Asia. By the early 1900s, the Asian species and Africa’s Southern White Rhinos were on their knees. Towards the century’s end, the Black Rhino and the Northern White Rhino also faced extinction. Then, from 2008 through to the present, the Southern White Rhinos, which had recovered remarkably, again suffered huge losses and the hand of poachers. Indian and Black Rhino numbers are increasing steadily, but the Javan and Sumatran Rhinos remain in great peril.
Click the sections below to find out more and what is to be done to ensure the survival of rhinos.
RHINOS IN BRIEF
Explore the lives, behavior, and habits of the five living rhino species in Africa and Asia. Learn about their population numbers, ranges, habitats, outstanding features, biology, diet, mobility, calls and communication, social behavior, and conservation status.
The rhino’s most outstanding anatomical feature is its horn. In many respects, rhino physiology and anatomy function like any other mammal, but they have several adaptations, other than their horns, that are particularly beneficial to their way of life. Roll your cursor over the labels in this infographic to find out how rhinos “work.”
In most horned mammals, the horn has a living, bony core covered by a thin keratin sheath. Rhino horn differs in that it is almost entirely made up of keratin. See “All About Horn” to learn more about the composition and structure of rhino horn, its much-debated medicinal properties, and the many myths and legends surrounding it.
The rhino’s brain is on the small side for a creature of its size. It typically weighs 14–21 ounces (400–600 grams), but it’s similar to that of any other mammal in its general structure and organization. The rhino brain has not been well studied in detail. However, South African scientists have observed some interesting differences in the brains of Black and White Rhinos. Learn more about this study in “Rhino Brains—Different Strengths for Different Lifestyles.”
Ears & Hearing
The rhino has an excellent sense of hearing. Its cup or tube-shaped ears are sensitive to the slightest sound and can be rotated to pick up audio signals from any direction with equal intensity.
Rhinos have powerful, well-developed shoulder and neck regions, a feature most pronounced in White Rhinos which have noticeable “nuchal humps.” There are three components to these humps: a thick, outer covering of skin tissue, an underlying layer of fat, and a mass of muscles and ligaments joining the base of the skull to the last vertebrae in the neck. The nuchal hump is absent or poorly developed in many mammals, but for those adapted for running, a well-developed it helps support the head, preventing excessive stress on the muscles of the region. Therefore, given their overall bulk, need for mobility, and comparatively massive heads, it makes sense that this ligament in rhinos is particularly strong, especially in White Rhinos which, for much of the time, carry their heads close to the ground while they eat grass.
The Indian and Javan Rhinos have pedal glands that almost continuously exude a thick secretion used to scent-mark along their trails. This passes on important signals to other rhinos moving through the same area. The Sumatran Rhino and the two African species lack these glands.
Rhinos are vegetarians and either grazers or browsers or a combination of both. Because plant matter has a high cellulose component, the rhino’s gut needs to break down this fibrous matter before nutrients can be absorbed into the body. Learn more in “Coping With a Rhino Diet.”
It would be hard to describe any aspect of a rhino as dainty, but they have relatively small feet for their overall size.Scientists at the Royal Veterinary College in the UK are trying to work out how one of the heaviest land creatures on earth manages on such comparatively tiny feet. Notwithstanding their small feet and short stumpy legs, rhinos are remarkably agile and fast. The Black Rhino is a real speedster and can reach 35 miles per hour (55 kilometers per hour) over short distances.
The White Rhino has a distinctive wide or square-lipped mouth profile ideal for cropping the grasses that make up its diet. By contrast, the Black Rhino (a specialist browser) and the Asian species (mixed feeders) have pointed, prehensile upper lips, enabling them to grasp and strip leaves, twigs, and small branches.
Nose & Smell
The rhino’s sense of smell is vital to its safety and for finding its way around its territory, as it helps the animal be aware of things it may not be able to see or hear. The large nostrils are positioned at the tip of the snout. Each one is richly supplied with millions of highly sensitive sensory cells able to register subtle odors in the air and then relay them to the brain’s olfactory center for interpretation.
Rhinos have powerful molars and premolars in the upper and lower jaws to grind the coarse plant material that makes up their diet. The two African rhino species lack incisors, but the Asian species are armed with long, sharp, tusk-like incisors in the lower jaw. These are present in males and females but are longer in males. They can reach a length of more than five inches (13 centimeters) in dominant male Indian Rhinos. They are not used for feeding but as potentially lethal weapons when competing for access to breeding females. African rhinos spar with their horns in dominance battles.
Eyes & Eyesight
Rhinos have small eyes for their body size, and their positioning on the side of the head means that they lack binocular vision. But are rhinos as poor-sighted as they are made out to be? Learn more in “Shortsighted? Not Really”.
The rhino is a big animal, and it needs a big pump to circulate blood to and from all parts of its body. The White Rhino—the largest of all the living rhinos—has a heart weighing about 22 pounds (10 kilograms), almost double that of the comparatively small Sumatran Rhino. By comparison, an elephant’s heart can weigh between 26 and 46 pounds (12–21 kilograms), while our human heart weighs in at a puny 11 ounces (312 grams). The creature with the biggest heart of all is the blue whale—a mighty 400 pounds (181 kilograms).
Rhino skin is tough and thick. In White Rhinos, for example, it can be nearly two inches thick (50 millimeters) in places – that is thicker than hippo skin and substantially more so than an elephant’s hide, which is little more than half an inch thick (about 17millimeters).
We have African rhinos (Black and White) and Asian rhinos (Indian, Javan, and Sumatran), and surely these names are enough to separate them accurately? In everyday terms, they are, but science needs to be more precise than that. And so, a whole branch of biology known as taxonomy is devoted to naming, describing, and classifying all the world’s life forms—plants, fungi, animals of the land, sea, and sky, and millions of microorganisms. Rhinos are no exception.
WHITE RHINOS—ONE SPECIES…OR TWO?
Things are never quite settled in science—it’s all part of an ongoing, rigorous process of questioning and challenging what we know and then changing when the evidence suggests we should. There has been an ongoing dispute regarding its taxonomic classification regarding the White Rhino. Presently the Northern and Southern White Rhinos are described by the IUCN as subspecies of Ceratotherium simum. But it has been argued that the differences between the two and other factors are sufficient for them to be recognized as two separate species altogether.