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, but 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 arrived on the stage of life about 55 million years ago and over the passage of time, drifting continents, altering climate and sudden cataclysmic events have all presented this family of redoubtable pachyderms with challenges to their existence. At times, rhinos have flourished and at others, not. But their lineage has persisted, and today five species survive.
Little more than 200 years ago, rhinos in their hundreds of thousands—if not millions—roamed through much of Africa and large parts of Asia. A century later the Asian species were on their knees, while in Africa numbers had also fallen dramatically, and by the mid-1900s they too teetered on the brink of extinction.
To find out how and why this happened, where rhinos stand today and what is to be done to ensure their survival, click on the sections below.
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, contact with humans, and their conservation status.
Without doubt, the rhino’s most renowned anatomical feature is its horn—mostly for all the wrong reasons. In many respects rhino physiology and anatomy function as for any other mammal, but they do exhibit a number of 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 sheath of keratin. Rhino horn differs in that it is almost entirely made up of keratin. Find out more about the composition and structure of horn, its much-debated pharmacological attributes, and the many myths and legends that surround it—see “All About Horn”.
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 basically, it’s like that of any other mammal in its general structure and organization. That said the rhino brain has not been well studied in any detail, but recently, scientists at South Africa’s University of the Witwatersrand have observed some interesting differences in the brains of Black and White Rhinos. Find out 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 “humps”. There are three components to these humps: a thick, outer covering of skin tissue, an underlying layer of fat, and a mass of muscle and ligament joining the base of the skull to the last vertebrae in the neck. This ligament is absent or poorly developed in many mammals, but for those adapted for running, a well developed ligament helps to support the head and prevents excessive stress on the muscles of the region. It is logical, therefore, given their overall bulk, need for mobility and comparatively massive heads, that this ligament in rhinos is particularly strong, especially in White Rhinos which are specialist grazers and for much of the time carry their heads close to the ground.
The Indian and Javan Rhinos have pedal glands that exude a thick secretion almost continuously. In this way they scent mark along their trails—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—cellulose is the tough fibrous material that gives plants their strength—the rhino’s gut needs to break it down before nutrients can be absorbed into the body. Find out more in “Coping With a Rhino Diet”.
It would be hard to describe any aspect of a rhino as dainty, but they do have rather small feet for their overall size.Scientists at the Royal Veterinary College in the UK are trying work out how one of the heaviest land creatures on earth manages on such relatively tiny feet. Rhinos are three-toed and belong to a small, ancient group of browsing and grazing mammals known as perrisodactyls (meaning odd-toed) which includes horses and tapirs. The center toe bears most of the weight. 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 which is perfectly suited to cropping the grasses that make up its diet. By contrast, the Black Rhino (a specialist browser) and the Asian species (mixed feeders), all have pointed, prehensile upper lips that enable the animals to grasp and strip leaves, twigs and small branches.
Nose & Smell
The rhino’s sense of smell is very important to its safety and for finding its way around its territory, as it helps the animal to 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 extremely sensitive sensory cells that are able to register subtle odors in the air and then relay them to the olfactory center of the brain for interpretation.
Rhinos have powerful molars and premolars in the upper and lower jaws which are used for grinding 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 and are used not 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? Find out 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) which is about 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 a whole branch of biology known as taxonomy is devoted to the purpose of naming, describing and classifying not only rhinos but 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. In respect of the White Rhino, there has been an ongoing dispute regarding its taxonomic classification. 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.