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.
MEET THE RHINOS
Photo credit: © Robin Moore
Updated date: April 29, 2022
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.
Updated date: April 29, 2022
Updated date: April 29, 2022
In a few short decades at the end of the 1800s and into the 1900s, human population growth, expanding settlements, mining, and the conversion of vast swathes of land for crops and livestock had taken a dreadful toll on all wildlife. Rhinos suffered particularly badly. First came a seemingly insatiable desire to shoot them for sport, especially before and during colonial times. This was followed by waves of intensive poaching to supply a highly lucrative, illegal, and unsustainable demand for their horn.
By the latter decades of the 20th century, the tide had turned in southern Africa and India. Any respite, however, proved short-lived. From 1970 to the mid-1990s, Black Rhinos were nearly wiped out due to the sudden, huge demand for horns to fashion traditional dagger handles in the Middle East. During this time, the Northern White Rhino also suffered greatly and is now extinct in the wild.
A short respite ensued. But from 2008, South Africa, by then home to 85 percent of all rhinos worldwide, came increasingly under siege owing to a renewed and expanding market for rhino horn, predominantly in Asia. The Southern White Rhino has been particularly hard hit.
In 2014 global rhino deaths at the hands of poachers rose to almost 1,400—nearly 90 percent of them in South Africa. Poaching has since declined, but this is more a consequence of fewer rhinos in places like the Kruger National Park and the challenge of finding them. The poaching war is far from over.
Updated date: April 29, 2022
Views on the best strategies for rhino survival differ widely, but most vehemently regarding questions around opening a legal trade in rhino horn and trophy hunting. Rhino Review does not favor trade or trophy hunting but gives voice to the full spectrum of opinion.
Although trade and trophy hunting tend to dominate, there are many other factors to consider in rhino conservation. Amongst these are the use of technology in rhino protection, translocation and relocation, effective laws and legislation, international cooperation, demand reduction strategies, effective policing and prosecution, forensic science, corruption exposure, and many more. All are covered elsewhere in Rhino Review. Clearly, there is no silver bullet for ensuring that Africa and Asia’s rhinos survive long into the future.
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.
Updated date: April 29, 2022
RHINO ANATOMY
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.”
Updated date: May 1, 2022
Horn
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.
Brain
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.
Hump
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.
Scent Marking
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.
Digestive System
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.”
Feet
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.
Lips
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.
Teeth
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”.
Heart
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).
Skin
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).
Updated date: April 7, 2022
Recently, scientists at South Africa’s University of the Witwatersrand have begun to fill the gap in our knowledge about rhino brains. They examined the brain of a male Black Rhino and that of a female White Rhino and made some interesting observations.
Not surprisingly, given that the two species are each other’s closest relatives, their brains are very similar in appearance. But, the Black Rhino’s brain is more rounded than the more elongated shape of that of the White Rhino. The brain shape is in keeping with the general head shape. The Black Rhino has a shorter, broader skull, while that of the White Rhino is narrower and longer.
The significance of the brain and skull shape could be related to their different feeding habits: Black Rhinos are browsers while White Rhinos are grazers. A long, low-slung head might be an evolutionary advantage to the “mowing” feeding action of the White Rhino.
Dietary specialization could also explain a few other differences noted by the researchers. For example, the area of the brain that remembers the details of a mammal’s surroundings is bigger in Black Rhinos than in White Rhinos. This would be important for Black Rhinos as they browse on a greater number of seasonal plant species in a bushier, more wooded environment compared to the fewer and less seasonably variable grasses grazed by White Rhinos in their more open habitat.
Black Rhinos also tend to have larger territories. Therefore, a better “mind map” of their surroundings, coupled with a memory for what food is available where and when, would be a distinct advantage.
The area of the brain concerned with the sense of smell is larger in Black Rhinos. This could also be explained by diet. A better ability to smell would be more critical to a browser reliant on a greater number of plants and their seasonality than for a grazing animal with a far more limited and less seasonal diet.
The last difference noted by the researchers focused on the brian’s ventricular system, which surrounds the brain within the skull and holds the cerebrospinal fluid. The fluid plays an important role in all mammals: it supports the brain, cushioning it from sudden blows, and plays a vital role in clearing the brain of metabolic waste products and toxins. The researchers found that the ventricular system of the White Rhino is much larger than that of the Black Rhino, and again this difference may be related to the species’ differing diets. Some of the grasses eaten by White Rhinos are potentially toxic. The larger ventricles would help flush harmful substances from the central nervous system.
Updated date: April 7, 2022
According to legend and other largely anecdotal “evidence,” one could be forgiven for believing that rhinos have terrible eyesight. While it is true that rhino eyes have only about a tenth of the resolution capability of a human eye, they compare favorably with other animals. A study of the Black Rhino’s retina suggests that rhino vision is on par with a rabbit’s and better than many other mammals, including seals, dolphins, microbats, and rats.
And so, the Rhino’s reputation as a myopic, weakly visual animal is somewhat unfounded. The scientists who conducted the study reckon that a Black Rhino could readily distinguish a human of average size at nearly 220 yards (about 200 meters) given the appropriate visual background. The visual acuity of other rhino species is likely to be similar to that of the Black Rhino.
Updated date: April 7, 2022
Rhinos are vegetarians and therefore have to cope with a diet high in fibrous cellulose—a difficult substance to break down so that nutrients can be absorbed into the body. Some plant-eating mammals—such as cattle, giraffes, and antelopes, for example—manage this by having a stomach divided into four chambers that process and reprocess food mechanically and with the help of specialized bacteria.
Rhinos cope with their food a bit differently. Their digestive system is more like a horse’s gut. Food passes through a simple stomach into the caecum and large intestine, where the real work of digestion is carried out. The caecum is the equivalent of the appendix in humans, but there the comparison ends. Unlike our vestigial appendix, which has no really understood purpose, this is a vital organ for rhinos. It is a colossal sac that is home to millions of bacteria—the gut flora—which break down the food into simpler, digestible compounds. Rhino digestion isn’t as efficient as that of cattle. A quick look at their droppings illustrates this: cowpats are smooth and paste-like, whereas the plant matter is more or less intact in rhino droppings.
Updated date: April 7, 2022
A rhino’s skin may be thick, but it is also prolifically served with nerve tissue, suggesting that it is highly sensitive to touch and vibration despite its thickness. The vascular network is also dense, and in addition to supplying the skin with blood, it is thought that these vessels might play a role in cooling—rhinos do have sweat glands, but they lack any high concentration and are not uniformly present.
Rhino skin is also very tough, so much so that it is often referred to as “dermal armor.” This feature is most pronounced in Indian Rhinos, whose skin is deeply folded into plates, giving the animal the appearance of a medieval battle machine. The Javan and Sumatran Rhinos also have deeply folded skin, but not to the same extent as their Indian cousins.
Other mammals, such as armadillos and pangolins, also have protective armor, but theirs derives from bone-like skin adaptations. In rhinos, the skin strength comes from dense, tightly organized bundles of collagen, the fibrous protein found abundantly in all mammals. Other structures, some rich in keratin—one of the hardest proteins produced by animals—add to the toughness of rhino skin. These protect the animal from serious injury during combat with other rhinos and from the inevitable bumps and scrapes in their wild environments.
From time to time, most rhinos suffer from skin lesions. Generally, these are opportunistic infections as a result of injury. However, in Black Rhinos, lesions are far more widespread, especially behind the shoulders and under the chin and stomach. They clearly cause discomfort, given that rhinos will rub and scrape themselves against trees and rocks until the patches of irritation become persistent weeping wounds. The cause of the problem is a fly-borne nematode worm and appears to be worst in seasons of high rainfall and temperature.
NAMING RHINOS
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.
Photo credit: Robin Moore
Updated date: May 2, 2022
Updated date: May 2, 2022
The word taxonomy first came into use in French in the early 1800s (it derives from two Greek words: taxis, meaning arrangement, and nomia, meaning method). Scientists and thinkers had grappled with naming things for centuries before that. Still, most would agree that the title “Father of Taxonomy” rightly goes to Carl Linnaeus (Carl von Linné), a Swedish botanist who, in the mid-1700s, created the two-part, or binomial, names for species we use to this day. These names comprise the genus of the organism with a specific epithet for a more precise classification. The Indian Rhino, for example, is named Rhinoceros (the genus) and unicornis (the specific name) to give us the scientific name for the “rhino with one horn.” It is not unlike having a surname followed by a given name.
But it doesn’t stop there, as all living organisms are further organized into broader groupings (and narrower ones) until we encompass all life.
Updated date: May 2, 2022
Early taxonomy was primarily linear and based on the shared physical and behavioral characteristics of organisms. The system is still used, and the taxonomic outline shown in the diagram opposite follows this traditional, or Linnaean, system.
Today the science of taxonomy also includes genetic and biochemical analysis. This aspect of taxonomy, known as cladistics, traces the evolution of organisms back through shared common ancestors using morphological and molecular data to visualize evolutionary history and relationships between species.
Updated date: May 2, 2022
Some 265 years have passed since Linnaeus laid the groundwork. So far, about 1.78 million species of plants, animals, and microorganisms have been described. Although this has been quite an achievement, it is still a fraction of the estimated global total of about 8.7 million species (give or take 1.3 million or so). The most recent estimate of the total number of mammal species is a mere 6,495. Some 80 percent of all life remains unknown to science.
Why is it so important to scientifically name as many species as possible? Well, global biodiversity is being lost at an unprecedented rate, and scientists warn that we are in the middle of a period of mass extinction. There have been other periods of significant loss—five episodes are thought to have happened since the planet was born—but this is the first where a single species, Homo sapiens, has played such a destructive role.
Urgent decisions are needed to reverse this looming disaster. Protected areas need to be secured, consolidated, expanded, and adequately funded. And our destructive processes everywhere need to be stopped and reversed or modified. But how do we do this if we don’t even know and understand the life forms that need protecting and where they live? How do countries, developed and developing, ensure they can reap the benefits, in perpetuity, of healthy ecosystems and the services they provide if they don’t know about the life forms that make up those ecosystems in the first place?
This is where taxonomy is so vital—it provides the basic understanding of the species and their lineages that make up the building blocks of the Earth’s biodiversity. It is as essential for understanding the five surviving rhino species and their lineage as for every other living thing.
Updated date: May 2, 2022
Current taxonomy describes five living rhino species, but classification doesn’t end there. These five species are further organized into no fewer than 13 subspecies, six of which have become extinct within the past hundred years. This is how they were given their scientific names.
The White Rhino (Ceratotherium simum), the largest of all living rhinos, was given its scientific name by the English explorer William John Burchell in 1817. Ceratotherium comes from joining the two Greek words keras, meaning horn, and thérion meaning wild beast, while simum comes from the Greek simós, which literally means flat-nosed, a reference to the animal’s characteristically broad and blunt snout. Currently, two subspecies of the White Rhino are recognized:
The Black Rhino (Diceros bicornis) was given its somewhat prosaic scientific name by Linnaeus way back in 1758: Di means two and cerato means horn in Greek, while the Latin bi and cornis combine to mean the same. How Linnaeus arrived at his decision is somewhat puzzling and is likely to have been based on the skull of a single-horned (Indian) Rhino with a second horn added by the original collector. Linnaeus even mentions India as the origin of the species. But he does also mention reports of a two-horned rhino from Africa. Later, when more became known about the distribution of rhinos, the term Rhinoceros bicornis was used broadly for all rhinos from Africa. Genetic variation within the Black Rhino remains a point of discussion among scientists—as many as seven or eight subspecies have been mooted. For Rhino Review, however, the scheme used by the IUCN has been followed. This recognizes three surviving subspecies and two as extinct:
The scientific name for the Indian Rhino, Rhinoceros unicornis, is a mix of Greek and Latin words. The Greek rhino meaning nose and keras meaning horn give us Rhinoceros, while the Latin uni meaning one or single and cornu meaning horn give us unicornis. Carl Linnaeus was the first to describe the species for science from a specimen sent to him in 1758. Since then, many alternative scientific names have been proffered, but all are regarded as synonyms for Rhinoceros unicornis. The Javan Rhino (Rhinoceros sondaicus) is the only other rhino species to share the genus Rhinoceros with the Indian Rhino. The specific name sondaicus derives from Sunda, a region of the great Malaysia Archipelago that includes Java, Sumatra, Borneo, and many smaller islands. Of the three distinct subspecies, only one survives:
The name of the Sumatran Rhino, Dicerorhinus sumatrensis, derives from the Greek words di meaning two, cero meaning horn, and rhino meaning nose. The suffix sumatrensis is a literal reference to the island of Sumatra, from where the rhinos first became known to European scientists. The scientific name for the genus Dicerorhinus was first suggested by the German zoologist Wilhelm Gloger in 1841, but there were many other contenders, and it wasn’t until 1977 that the name was finally fixed. Three subspecies are recognized:
WHITE RHINO
BLACK RHINO
INDIAN RHINO
JAVAN RHINO
SUMATRAN RHINO
Updated date: May 2, 2022
The common name for the rhino is Rhinoceros, but it is a cumbersome term to use all the time, so “rhino” is generally preferred in non-scientific writing, including Rhino Review. The common names used for the five living species are White, Black, Indian, Javan and Sumatran. But there are many alternatives, and they’re all important, not only for everyday convenience but also for their cultural significance.
Also known as the Square-lipped Rhino. The northern subspecies has sometimes been referred to as the Nile Rhino. Other European language names include: Rhinocéros Blanc (French), Rinoceronte Blanco (Spanish), Weißes Nashorn(German),and Witrenoster (Afrikaans). African names include more than 50: Click here to see them. Also known as the Hook-lipped Rhino. Other European language names include: Rhinocéros noir (French), Rinoceronte Negro (Spanish), Schwarzes Nashorn (German), and Swartrenoster (Afrikaans) African names include at least 175: Click here to see them. Also widely known as the Greater One-horned Rhino, Great Indian Rhino, and Nepalese Rhino. Other European language names include: Rhinocéros unicorne de l’Inde (French), Rinoceronte Unicornio Índico(Spanish), and Indisches Nashorn or Panzernashorn (German) Asian names include at least 12: Click here to see them. Also known as the Lesser One-horned Rhino. Other European language names include: Rhinocéros de la Sonde (French), Rinoceronte de Java (Spanish), and Java-Nashorn (German) Asian names include nearly 100: Click here to see them. Also known as the Hairy Rhino, or the Asian Two-horned Rhino. The Bornean subspecies is sometimes referred to as the Bornean Rhino. Other European language names include: Rhinocéros de Sumatra (French), Rinoceronte de Sumatra(Spanish), Sumatra-Nashorn (German) Asian names include some 86 – Click here to see them.WHITE RHINO
BLACK RHINO
INDIAN RHINO
JAVAN RHINO
SUMATRAN RHINO
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.
Updated date: May 2, 2022
Updated date: May 2, 2022
- The Northern White Rhino is smaller and lighter than its Southern counterpart—males weigh 3,000–3,500 pounds (1,400–1,600 kilograms) compared with 4,400–5,300 pounds (2,000–2,400 kilograms).
- The Northern White Rhino lacks the prominent shoulder hump that defines the southern subspecies.
- The skull of the Northern White Rhino is flatter compared with the concave profile of its southern cousin.
- The Northern White Rhino has more body hair.
- The front horn of the Southern White Rhino is generally longer than that of the northern subspecies.
- The Northern White Rhino lacks the groove between the ribs, so characteristic of the Southern White Rhino.
Updated date: August 23, 2019
Are these physical differences, plus some minor genetic differences and the long period of geographical separation between the two, enough for them to be regarded as two separate species?
The late Colin Groves (one of the world’s leading anthropologists and taxonomists) thought so, and in 2010 he and his co-workers published a paper putting forward the case for two species. The Groves paper, however, has been criticized by some and its proposal has not been universally accepted. A more detailed outline of this debate can be found in the IUCN Red Data List.
It has also been argued that the “separate species” proposition is somewhat academic given the parlous conservation status of the Northern White Rhino: it is extinct in the wild and the only remaining captive male died in 2018. And so the entire global population of Northern White Rhinos has been reduced to two elderly females that reside in the Ol Pejeta Conservancy in Kenya, and samples of stored male semen and DNA.
In vitro fertilization is the only possible route for saving the subspecies, but given the age of the two females it would probably require their IV fertilized eggs being placed in a surrogate Southern White female. Possibly the semen could also be used to impregnate a South White Rhino female, thus preserving something of the gene pool. IVF techniques may be too late to save the Northern White Rhino, but improved technology could play a vital role in the future of the Javan and Sumatran Rhinos and many other endangered species as well.
Find out more about IVF in “Protecting Rhinos”y/03/11 17:58:11 a3/p3
