10 Facts About Rhinoceroses

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How Much Do You Know About Rhinoceroses?

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By most counts, there are less than 30,000 rhinoceroses alive today--a steep plunge in population for a mammal that has existed on the earth, in one form or another, for 50 million years. Here are 10 facts about rhinoceroses, ranging from the small size of their brains to the unfortunate global demand for their ground-up horns.

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Rhinoceroses Are Odd-Toed Ungulates

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Rhinoceroses are perissodactyls, or odd-toed ungulates, a family of mammals characterized by their herbivorous diets, relatively simple stomachs, and ​an odd number of toes on their feet (one or three). The only other perissodactyls on earth today are horses, zebras and donkeys (all belonging to genus Equus), and the strange, pig-like mammals known as tapirs. Rhinoceroses are characterized by their large sizes, quadrupedal postures, and single or double horns on the ends of their snouts--from which these animals derive their name, Greek for "nose horn." (These horns probably evolved as a sexually selected characteristic--that is, males with bigger, more prominent horns were more successful with females during mating season.) There are five extant rhino species--the white rhinoceros, the black rhinoceros, the Indian rhinoceros, the Javan rhinoceros, and the Sumatran rhinoceros--which are described in detail in the following slides.

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The White Rhinoceros Is the Most Well-Known Rhino

The White Rhinoceros. Getty Images

The largest rhinoceros species, the white rhinoceros (Ceratotherium simum) consists of two subspecies—the southern white rhinoceros, which lives in the southernmost regions of Africa, and the northern white rhinoceros of central Africa. There are about 20,000 southern white rhinoceroses in the wild, the males of which weigh over two tons, but the northern white rhinoceros is on the brink of extinction, a mere handful of individuals surviving in zoos and nature reserves. No one is quite sure why C. simum is called "white"—this may be a corruption of the Dutch word "wijd," which means "wide" (as in widespread), or because its horn is lighter than that of other rhinoceros species. And you have to admit, this rhino does have a more bleached appearance than its less well-known cousins!

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The Black Rhinoceros Isn't Really Black

The Black Rhinoceros. Getty Images

Actually brown or grey in color, the black rhinoceros (Diceros bicornis) used to be widespread across southern and central Africa, but today its numbers have dwindled to about half those of the southern white rhinoceros. (If you're familiar with Greek, you may have noticed that "bicornis" means "two-horned;' an adult black rhinoceros has a larger horn toward the front of its snout, and a narrower one directly behind.) Black rhinoceros adults rarely exceed two tons in weight, and they browse on shrubs rather than grazing on grass like their "white" cousins. There used to be a bewildering number of black rhinoceros subspecies, but today the International Union for the Conservation of Nature recognizes only three, all of them seriously endangered.

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The Indian Rhinoceros Lives in the Himalayan Foothills

The Indian Rhinoceros. Getty Images

The Indian rhinoceros, Rhinoceros unicornis, used to be thick on the ground in India and Pakistan—until a combination of hunting and habitat destruction restricted its numbers to the puny 4,000 or so individuals alive today. Full-grown Indian rhinos weigh between three and four tons, and are characterized by their long, thick, black horns, which are prized by unscrupulous poachers. On a historical note, the Indian rhinoceros was the first rhino to be seen in Europe, a single individual shipped to Lisbon in 1515. Plucked from its natural habitat, this unfortunate rhino quickly died, but not before it had been immortalized in a woodcut by Albrecht Durer, the sole reference point for European enthusiasts until another Indian rhino arrived in England in 1683.

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The Javan Rhinoceros is Seriously Endangered

The Javan Rhinoceros. Getty Images

One of the rarest mammals in the entire world, the Javan rhinoceros (Rhinoceros sondaicos) consists of a few dozen individuals living on the western edge of Java (the largest island in the Indonesian archipelago). This cousin of the Indian rhinoceros (same genus, different species) is slightly smaller, with a comparably smaller horn, which has not, sadly, prevented it from being hunted to near-extinction by poachers. The Javan rhinoceros used to be widespread across Indonesia and southeast Asia; one of the key factors in its decline was the Vietnam War, in which millions of acres of habitat were destroyed by incendiary bombing and poisoning of vegetation by the herbicide called Agent Orange.

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The Sumatran Rhinoceros is the Smallest Rhino Species

The Sumatran Rhinoceros. Getty Images

Also known as the hairy rhinoceros, the Sumatran rhinoceros (Dicerorhinus sumatrensis) is almost as endangered as the Javan rhinoceros, with which it once shared the same territory of Indonesia and southeast Asia. Adults of this species rarely exceed 2,000 pounds in weight, making it the smallest living rhinoceros—but unfortunately, as with the Javan rhinoceros, the relatively short horn of the Sumatran rhinoceros hasn't spared it from the depredations of poachers (the powdered horn of a Sumatran rhino commands over $30,000 per kilogram on the black market!) Not only is D. sumatrensis the shrimpiest rhino, but it's also the most mysterious; for example, this is by far the most vocal rhino species, herd members communicating with one another via yelps, moans and whistles.

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Rhinoceroses Have a Deep Evolutionary History

The Woolly Rhino. Getty Images

Modern rhinoceroses can trace their evolutionary lineage back 50 million years, to small, pig-sized ancestors that originated in Eurasia and later spread to North America (a good example is Menoceras, a tiny, four-footed plant-eater that sported a pair of small horns). The North American branch of this family went extinct about five million years ago, but rhinos continued to live in Europe until the end of the last Ice Age (at which point Coelodonta, also known as the woolly rhino, went extinct along with its fellow mammalian megafauna like the woolly mammoth and the saber-toothed tiger). One recent rhinoceros ancestor, Elasmotherium, may even have inspired the unicorn myth, as its single, prominent horn struck awe into early human populations.

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A Rhino Can Sprint at 30 Miles Per Hour

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If there's one place the average person does not want to be, it's in the path of a stampeding rhino. When startled, this animal can hit top speeds of 30 miles per hour, and it's not exactly equipped to stop on a dime (which may be one reason rhinos evolved their nasal horns, which can absorb unexpected impacts with stationary trees). Because rhinos are basically solitary animals, and because they have become so thin on the ground, it's rare to see a true "crash" (as a group of rhinos is called), but this phenomenon has been known to occur around watering holes. (By the way, rhinos also have poorer eyesight than most animals, another reason not to linger in the path of a four-ton male on your next African safari.)

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Rhinoceroses Have Relatively Small Brains

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Considering how big they are, rhinoceroses have unusually small brains—no more than a pound and a half in the largest individuals, about five times smaller than a comparably sized elephant. This means that, in terms of its "encephalization quotient" (the relative size of an animal's brain compared to the rest of its body), a rhinoceros harkens back to the megafauna mammals of the early Cenozoic Era, and is only a little bit smarter than the giant, tiny-brained dinosaurs that ruled the earth during the preceding Mesozoic. This may (or may not) account for the fact that rhinoceros populations have dwindled relentlessly over the last few hundred years; perhaps this mammal simply isn't smart enough to learn to adapt to changing conditions.

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The Horns of Rhinoceroses Are Valued as Aphrodisiacs

A newly poached rhinoceros. Getty Images

One running theme of this slideshow is how rhinoceroses have been driven relentlessly to the brink of extinction by human poachers. What these hunters are after is rhino horns, which, when ground up into powder, are valued in the east as aphrodisiacs (today, the largest market for powdered rhino horn is Vietnam, as Chinese authorities have recently cracked down on this illicit trade). What's ironic is that the horn of a rhinoceros is composed entirely of keratin, the same substance that makes up human hair and fingernails. Rather than continuing to drive these majestic animals into extinction, perhaps poachers can be convinced to grind up their toenail clippings and see if anyone notices the difference!