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Zebras are African equids best known for their distinctive black and white stripes. Their stripes come in different patterns unique to each individual. They are generally social animals that live in small harems to large herds. Unlike their closest relatives, horses and asses, zebras have never been truly domesticated.

There are three species of zebras: the plains zebra, the Grévy's zebra and the mountain zebra. The plains zebra and the mountain zebra belong to the subgenus Hippotigris, but Grevy's zebra is the sole species of subgenus Dolichohippus. The latter resembles an ass, to which it is closely related, while the former two are more horse-like. All three belong to the genus Equus, along with other living equids.

The unique stripes of zebras make these among the animals most familiar to people. They occur in a variety of habitats, such as grasslands, savannas, woodlands, thorny scrublands, mountains, and coastal hills. However, various anthropogenic factors have had a severe impact on zebra populations, in particular hunting for skins and habitat destruction. Grevy's zebra and the mountain zebra are endangered. While plains zebras are much more plentiful, one subspecies, the quagga, went extinct in the late 19th century.

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Etymology

Zebra in English dates back to c.1600, from Italian Zebra, perhaps from Portuguese, which in turn is said to be Congolese (as stated in the Oxford English Dictionary). The Encarta Dictionary says its ultimate origin is uncertain, but perhaps it may come from Latin Equiferus meaning "Wild horse," from equus "horse" and ferus "wild, untamed". The pronunciation is /ˈzɛbrə/ ZEB-rə or /ˈziːbrə/ ZEE-brə[1]

Taxonomy and evolution

Zebras arose within the Old World horses within the last 4 million years. Grevy's zebras (and perhaps also Mountain Zebras) are with asses and donkeys in a separate lineage from the other zebra lineages.[2] This means either that striped equids zebras evolved more than once, or that common ancestors of zebras and asses were striped and only zebras retained the stripes. Extensive stripes are posited to have been be of little use to equids that live in low densities in deserts (like asses and some horses) or ones that live in colder climates with shaggy coats and annual shading (like some horses).[3] Fossils of an ancient equid were discovered in the Hagerman Fossil Beds National Monument in Hagerman, Idaho. It was named the Hagerman horse with a scientific name of Equus simplicidens. It is believed to have been similar to the Grevy's zebra.[4] The animals had stocky zebra-like bodies and short, narrow, donkey-like skulls.[5] Grevy's zebra also has a donkey-like skull. The Hagerman horse is also called the American zebra or Hagerman zebra.

Classification

Zebras in Botswana

There are three extant species. Collectively, two of the species have 8 subspecies (7 extant). Zebra populations are diverse, and the relationships between and the taxonomic status of several of the subspecies are not well known.

An albino zebra in captivity

The plains zebra (Equus quagga, formerly Equus burchelli) is the most common, and has or had about twelve subspecies distributed across much of southern and eastern Africa. It, or particular subspecies of it, have also been known as the common zebra, the dauw, Burchell's Zebra (actually the subspecies Equus quagga burchellii), Chapman's zebra, Wahlberg's zebra, Selous' zebra, Grant's zebra, Boehm's zebra and the quagga (another extinct subspecies, Equus quagga quagga).

The mountain zebra (Equus zebra) of southwest Africa tends to have a sleek coat with a white belly and narrower stripes than the plains Zebra. It has two subspecies and is classified as vulnerable.

Grévy's Zebra (Equus grevyi) is the largest type, with a long, narrow head, making it appear rather mule-like. It is an inhabitant of the semiarid grasslands of Ethiopia and northern Kenya. Grévy's zebra is the rarest species, and is classified as endangered.

Although zebra species may have overlapping ranges, they do not interbreed. This held true even when the quagga and Burchell's race of plains zebra shared the same area. In captivity, plains zebras have been crossed with mountain zebras. The hybrid foals lacked a dewlap and resembled the plains zebra apart from their larger ears and their hindquarters pattern. Attempts to breed a Grévy's zebra stallion to mountain zebra mares resulted in a high rate of miscarriage. In captivity, crosses between zebras and other (non-zebra) equines have produced several distinct hybrids, including the zebroid, zeedonk, zony, and zorse. In certain regions of Kenya, plains zebras and Grévy's Zebra coexist, and fertile hybrids occur.[6]

Physical attributes

Stripes

It was previously believed that zebras were white animals with black stripes, since some zebras have white underbellies. Embryological evidence, however, shows that the animal's background color is black and the white stripes and bellies are additions.[3]

A mother nursing her young blends into a stand of deadwood.

The stripes are typically vertical on the head, neck, forequarters, and main body, with horizontal stripes at the rear and on the legs of the animal. The "zebra crossing" is named after the zebra's black and white stripes.

A wide variety of hypotheses have been proposed to account for the evolution of the strking stripes of zebras. The more traditional of these (1 & 2, below) relate to camouflage.

1. The vertical striping may help the zebra hide in grass. While seeming absurd at first glance, considering that grass is neither white nor black, it is supposed to be effective against the zebra's main predator, the lion, which is color blind[dubious ]. In addition, even at moderate distances, the striking striping merges to an apparent grey.

2. Another hypothesis is that since zebras are herd animals, the stripes may help to confuse predators - a number of zebras standing or moving close together may appear as one large animal, making it more difficult for the lion to pick out any single zebra to attack.[7][unreliable source?]

3. It has been suggested that the stripes serve as visual cues and identification.[3] Although each striping pattern is unique to each individual, it is not known whether zebras can recognize one another by their stripes.

4. One theory suggested by an innovative experiment posits that the disruptive colouration is an effective means of confusing the visual system of the blood-sucking tsetse fly.[8]

5. Alternative theories include that the stripes coincide with fat patterning beneath the skin, serving as a thermo-regulatory mechanism for the zebra, or that

6. wounds sustained disrupt the striping pattern to clearly indicate the fitness of the animal to potential mates.

A zebra walking

Gaits

Like horses, zebras walk, trot, canter and gallop. They are generally slower than horses, but their great stamina helps them outpace predators. When chased, a zebra will zig-zag from side to side, making it more difficult for the predator. When cornered, the zebra will rear up and kick or bite its attacker.

Closeup of a zebra

Senses

Zebras have excellent eyesight. It is believed that they can see in color. Like most ungulates, the zebra has its eyes on the sides of its head, giving it a wide field of view. Zebras also have night vision, although not as advanced as that of most of their predators.

Zebras have excellent hearing, and tend to have larger, rounder ears than horses. Like horses and other ungulates, zebra can turn their ears in almost any direction. In addition to eyesight and hearing, zebras have an acute sense of smell and taste.

Ecology and behavior

Harems

Zebras in Tanzania

Like most members of the horse family, zebras are highly social. Their social structure, however, depends on the species. Mountain zebras and plains zebras live in groups, known as 'harems', consisting of one stallion with up to six mares and their foals. Bachelor males either live alone or with groups of other bachelors until they are old enough to challenge a breeding stallion. When attacked by packs of hyenas or wild dogs a zebra group will huddle together with the foals in the middle while the stallion tries to ward them off.

Unlike the other zebra species, Grevy's zebras do not have permanent social bonds. A group of these zebras rarely stays together for more than a few months. The foals stay with their mothers, while adult males live alone. Like the other two zebra species, bachelor male zebras will organize in groups.

Like horses, zebras sleep standing up, and only sleep when neighbors are around to warn them of predators.

Communication

A zebra feeding on grass

Zebras communicate with each other with high pitched barks and whinnying. Grevy's zebras make mule-like brays. A zebra’s ears signify its mood. When a zebra is in a calm, tense or friendly mood, its ears stand erect. When it is frightened, its ears are pushed forward. When angry, the ears are pulled backward. When surveying an area for predators, zebras will stand in an alert posture; with ears erect, head held high, and staring. When tense they will also snort. When a predator is spotted or sensed, a zebra will bark (or bray) loudly.

Mountain zebra -uenozoo2010.ogv
Hartmann's Mountain Zebra with a Barbary sheep behind it, in captivity at Ueno Zoo, in Japan. (video)

Food and foraging

Zebras are very adaptable grazers. They feed mainly on grasses but will also eat shrubs, herbs, twigs, leaves and bark. Their well-adapted digestive systems allow them to subsist on diets of lower nutritional quality than that necessary for other herbivores.

Reproduction

Female zebras mature earlier than the males, and a mare may have her first foal by the age of three. Males are not able to breed until the age of five or six. Mares may give birth to one foal every twelve months. She nurses the foal for up to a year. Like horses, zebras are able to stand, walk and suckle shortly after they are born. A zebra foal is brown and white instead of black and white at birth.

Plains and mountain zebra foals are protected by their mothers, as well as the head stallion and the other mares in their group. Grevy’s zebra foals have only their mother as a regular protector, since, as noted above, Grevy's zebra groups often disband after a few months.

Human interactions

Lord Rothschild with his famed zebra carriage (sp. Equus quagga burchellii), which he frequently drove through London

Domestication

Attempts have been made to train zebras for riding, since they have better resistance than horses to African diseases. Most of these attempts failed, though, due to the zebra's more unpredictable nature and tendency to panic under stress. For this reason, zebra-mules or zebroids (crosses between any species of zebra and a horse, pony, donkey or ass) are preferred over purebred zebras.

In England, the zoological collector Lord Rothschild frequently used zebras to draw a carriage. In 1907, Rosendo Ribeiro, the first doctor in Nairobi, Kenya, used a riding zebra for house calls. In the mid-19th century, Governor George Grey imported zebras to New Zealand from his previous posting in South Africa, and used them to pull his carriage on his privately owned Kawau Island.

A tamed zebra being ridden in East Africa

Captain Horace Hayes, in "Points of the Horse" (circa 1893), compared the usefulness of different zebra species. In 1891, Hayes broke a mature, intact mountain zebra stallion to ride in two days time, and the animal was quiet enough for his wife to ride and be photographed upon. He found the Burchell's zebra easy to break, and considered it ideal for domestication, as it was immune to the bite of the tsetse fly. He considered the quagga (now extinct) well-suited to domestication due to being easy to train to saddle and harness.[9]

Conservation

Modern man has had great impact on the zebra population. Zebras were, and still are, hunted for their skins, and for meat. They also compete with livestock for forage,[10] and sometimes culled.

The Cape mountain zebra was hunted to near extinction, with less than 100 individuals by the 1930s. The population has increased to about 700 due to conservation efforts, though. Both mountain zebra subspecies are currently protected in national parks, but are still endangered.

Zebras on the Botswana coat of arms.

The Grevy's zebra is also endangered. Hunting and competition from livestock have greatly decreased their population. Because of the population's small size, environmental hazards, such as drought, are capable of affecting the entire species. Plains zebras are much more numerous and have a healthy population. Nevertheless, they too have been reduced by hunting and loss of habitat to farming. One subspecies, the quagga, is now extinct.

Cultural depictions

Zebras have been the subject of African folk tales which tell how they got their stripes. According to a Bushmen folk tale of Namibia, the zebra was once all white, but acquired its black stripes after a fight with a baboon over a waterhole. After kicking the baboon so hard, the zebra lost his balance and tripped over a fire, and the fire sticks left scorch marks all over his white coat.[11] In the film Fantasia, two centaurs are depicted being half human and half zebra, instead of the typical half human and half horse.[12]

Illustration of a zebra by Ludolphus

Zebra are a popular subject in art.[13] The fourth Mughal emperor Jahangir (r.1605-24), commissioned a painting of the zebra, which was completed by Ustad Mansur.[14] Zebra stripes are also a popular style for furniture, carpets and fashion.

When depicted in movies and cartoons, zebras are most often miscellaneous characters, but have had some starring roles, notably in Madagascar and Racing Stripes. Zebras also serve as mascots and symbols for products and corporations, notably Zebra Technologies and Fruit Stripe gum. Zebras are featured on the coat of arms of Botswana.

See also

References

  1. ^ http://www.etymonline.com/index.php?term=zebra
  2. ^ Orlando, Ludovic; et al. (2009). "Revising the recent evolutionary history of equids using ancient DNA". PNAS 106: 21754–21759. 
  3. ^ a b c Prothero D.R, Schoch R. M (2003). Horns, Tusks, and Flippers: The Evolution of Hoofed Mammals. Johns Hopkins University Press. 
  4. ^ NPS.gov
  5. ^ Hunt, Kathleen (1995-01-04). "Horse Evolution". TalkOrigins Archive. http://www.talkorigins.org/faqs/horses/horse_evol.html. Retrieved 2008-10-10. 
  6. ^ J. E. Cordingley, S. R. Sundaresan, I. R. Fischhoff, B. Shapiro, J. Ruskey, D. I. Rubenstein (2009). Is the endangered Grevy's zebra threatened by hybridization?. Animal Conservation. 12: 505 - 513.
  7. ^ "How do a zebra's stripes act as camouflage?". How Stuff Works. http://science.howstuffworks.com/question454.htm. Retrieved 2006-11-13. 
  8. ^ Waage, J. K. (1981). How the zebra got its stripes: biting flies as selective agents in the evolution of zebra colouration. J. Entom. Soc. South Africa. 44: 351 - 358.
  9. ^ Hayes, Capt. Horace (1893), Points of the Horse, pp. 311-316, London: W. Thacker
  10. ^ Young, T.P., et al. (2005). "Competition and compensation among cattle, zebras, and elephants in a semi-arid savanna in Laikipia, Kenya. 121:351-359". Biological Conservation 121: 351–359. 
  11. ^ "How the Zebra Got his Stripes". Gateway Africa. http://www.gateway-africa.com/stories/How_the_Zebra_Got_his_Stripes_San.html. Retrieved 2008-10-10. 
  12. ^ Dirks, Tim. "Fantasia (1940)". Tim Dirks. http://www.filmsite.org/fant.html. Retrieved 2008-10-10. 
  13. ^ "Zebra Art". Artists for Conservation. http://www.natureartists.com/zebras.asp. Retrieved 2008-10-10. 
  14. ^ Cohen, M.J. John Major, Simon Schama (2004), History in Quotations:Reflecting 5000 Years of World History, p. 146, Sterling Publishing Company, Inc., ISBN 0304353876
  • Churcher, C.S. 1993. Mammalian Species No. 453. American Society of Mammalogists.
  • Estes, R. (1991). The Behavior Guide to African Mammals, Including Hoofed Mammals, Carnivores, Primates. Los Angeles, The University of California Press.
  • McClintock, Dorcas. "A Natural History Of Zebras" September 1976. Scribner's, New York. ISBN 0-684-14621-5

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Aardvark

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Aardvark
Temporal range: Early Miocene–Recent
Conservation status
Scientific classification [ e ]
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Superorder: Afrotheria
Order: Tubulidentata
Huxley, 1872
Family: Orycteropodidae
Gray, 1821
Genus: Orycteropus
G. Cuvier, 1798
Species: O. afer
Binomial name
Orycteropus afer
(Pallas, 1766)
Aardvark range

The aardvark (Orycteropus afer) (afer: from Africa) is a medium-sized, burrowing, nocturnal mammal native to Africa.[2] It is the only living species of the order Tubulidentata,[3] although other prehistoric species and genera of Tubulidentata are known.

It is sometimes mistakenly called "antbear", "anteater", or the "Cape anteater" after the Cape of Good Hope. The name comes from the Afrikaans/Dutch[4] for "earth pig" or "ground pig" (aarde earth/ground, varken pig), because of its burrowing habits (similar origin to the name groundhog). The aardvark is not related to the pig; rather, it is the sole recent representative of the obscure mammalian order Tubulidentata, in which it is usually considered to form one variable species of the genus Orycteropus, the sole surviving genus in the family Orycteropodidae. The aardvark is not closely related to the South American anteater, despite sharing some characteristics and a superficial resemblance.[5] The closest living relatives of the aardvark are the elephant shrews, along with the sirenians, hyraxes, tenrecs, and elephants. With their extinct relatives, these animals form the superorder Afrotheria.

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[edit] Description

One of the most distinctive characteristics of the Tubulidentata is their teeth. Instead of having a pulp cavity, each tooth has a cluster of thin, upright, parallel tubes of vasodentin (a modified form of dentine), with individual pulp canals, held together by cementum. The teeth have no enamel coating and are worn away and regrow continuously. The aardvark is born with conventional incisors and canines at the front of the jaw, which fall out and are not replaced. Adult aardvarks only have cheek teeth at the back of the jaw, and have a dental formula of: Upper: 0.0.2-3.3, lower: 0.0.2.3

An aardvark skull from the collections of Skulls Unlimited International.

Genetically speaking, the aardvark is a living fossil, as its chromosomes are highly conserved, reflecting much of the early eutherian arrangement before the divergence of the major modern taxa.[6]

The aardvark is vaguely pig-like in appearance. Its body is stout with an arched back and is sparsely covered with coarse hairs. The limbs are of moderate length. The front feet have lost the pollex (or 'thumb') — resulting in four toes — but the rear feet have all five toes. Each toe bears a large, robust nail which is somewhat flattened and shovel-like, and appears to be intermediate between a claw and a hoof. The ears are disproportionately long, and the tail is very thick at the base and gradually tapers. The greatly elongated head is set on a short, thick neck, and the end of the snout bears a disc, which houses the nostrils. The mouth is small and tubular, typical of species that feed on termites. The aardvark has a long, thin, snakelike, protruding tongue and elaborate structures supporting a keen sense of smell.

An aardvark's weight is typically between 40 and 65 kg. An aardvark's length is usually between 1 and 1.3 meters, and can reach lengths of 2.2 meters[2] when its tail (which can be up to 70 centimetres)[2] is taken into account. The aardvark is pale yellowish gray in color and often stained reddish-brown by soil. The aardvark's coat is thin and the animal's primary protection is its tough skin. The aardvark has been known to sleep in a recently excavated ant nest, which also serves as protection from its predators.

[edit] Behavior

Resting aardvark in Himeji City Zoo

The aardvark is nocturnal and is a solitary creature that feeds almost exclusively on ants and termites (formicivore);[7] the only fruit eaten by aardvarks is the aardvark cucumber. An aardvark emerges from its burrow in the late afternoon or shortly after sunset, and forages over a considerable home range encompassing 10 to 30 km,[2] swinging its long nose from side to side to pick up the scent of food. When a concentration of ants or termites is detected, the aardvark digs into it with its powerful front legs, keeping its long ears upright to listen for predators, and takes up an astonishing number of insects with its long, sticky tongue—as many as 50,000 in one night have been recorded. It can dig 2 feet in 15 seconds [8], but otherwise moves fairly slowly. Its claws enable it to dig through the extremely hard crust of a termite or ant mound quickly, avoiding the dust by sealing the nostrils. When successful, the aardvark's long (up to 30 cm)[2] tongue licks up the insects; the termites' biting, or the ants' stinging attacks are rendered futile by the tough skin. Its keen hearing warns it of predators: lions, leopards, hyenas, and pythons.

Aside from digging out ants and termites, the aardvark also excavates burrows in which to live; temporary sites are scattered around the home range as refuges, and a main burrow is used for breeding. Main burrows can be deep and extensive, have several entrances and can be as long as 13 meters.[7] The aardvark changes the layout of its home burrow regularly, and from time to time moves on and makes a new one; the old burrows are then inhabited by smaller animals like the African wild dog.[2] Only mothers and young share burrows. If attacked in the tunnel, it will seal the tunnel off behind itself or turn around and attack with its claws.

Aardvark mother and young

Aardvarks only pair during the breeding season; after a gestation period of seven months, one cub weighing around 2 kg is born, and is able to leave the burrow to accompany its mother after only two weeks, and is eating termites at 14 weeks and is weaned by 16 weeks.[2][7] At six months of age it is able to dig its own burrows, but it will often remain with the mother until the next mating season, and is sexually capable by the season after that.

Aardvarks live for up to 24 years in captivity.[2]

The aardvark's main predators are lions, leopards, hunting dogs and pythons. Some African tribes also hunt aardvarks for meat. Aardvarks can dig fast or run in zigzag fashion to elude enemies, but if all else fails, they will strike with their claws, tail and shoulders, sometimes flipping onto their backs to lash with all fours. Their thick skin also protects them to some extent.

[edit] Habitat

Aardvarks live in sub-Saharan Africa, where there is suitable habitat for them to live, such as savannas, grasslands, woodlands and bushland, and available food (i.e., ants and termites).[5]

[edit] Mythology and popular culture

In African folklore, the aardvark is much admired because of its diligent quest for food and its fearless response to soldier ants. Hausa magicians make a charm from the heart, skin, forehead, and nails of the aardvark, which they then proceed to pound together with the root of a certain tree. Wrapped in a piece of skin and worn on the chest, the charm is said to give the owner the ability to pass through walls or roofs at night. The charm is said to be used by burglars and those seeking to visit young girls without their parents' permission.[9]

The Egyptian god Set is said, by some, to have the head of an aardvark,[10] or part aardvark.[11]

The main character of Arthur, an animated television series for children produced by WGBH, shown in more than 180 countries, is an aardvark.[12]

One of the main characters of the 1969-1971 animated cartoon The Ant and the Aardvark is a blue aardvark voiced by John Byner, doing an impersonation of Jackie Mason. It depicts the Aardvark attempting, and failing, to catch and eat his antagonist, the Ant, also voiced by Byner impersonating Dean Martin.

The Canadian cartoon series The Raccoons featured an antagonist named Cyril Sneer; he and his son Cedric were both portrayed as being aardvarks.

Cerebus the Aardvark was the title character of a comic book series by Dave Sim and Gerhard that ran from 1977 to 2004, and is still sold in collected volumes of reprints.

[edit] Notes and references

  1. ^ Lindsey, P., Cilliers, S., Griffin, M., Taylor, A., Lehmann, T. & Rathbun, G. (2008). Orycteropus afer. In: IUCN 2008. IUCN Red List of Threatened Species. Downloaded on 29 December 2008.
  2. ^ a b c d e f g h "Aardvark". Encyclopaedia Britannica. 
  3. ^ Schlitter, Duane A. (16 November 2005). "Order Tubulidentata (p. 86)". In Wilson, Don E., and Reeder, DeeAnn M., eds. Mammal Species of the World: A Taxonomic and Geographic Reference (3rd ed.). Baltimore: Johns Hopkins University Press, 2 vols. (2142 pp.). ISBN 978-0-8018-8221-0. OCLC 62265494. http://www.bucknell.edu/msw3/browse.asp?id=11300004. 
  4. ^ Obsolete Afrikaans, actually. The modern Afrikaans name is erdvark. aardvark (2010). In Merriam-Webster Online Dictionary. Retrieved February 2, 2010, from Merriam-webster.com
  5. ^ a b "Aardvark". African Wildlife Foundation. http://www.awf.org/content/wildlife/detail/aardvark. Retrieved 2008-01-10. 
  6. ^ "Great Uncle Aardvark?". BBC NEWS online — Science/Nature. 2003-01-20. http://news.bbc.co.uk/2/hi/science/nature/2676377.stm. Retrieved 2008-01-10. 
  7. ^ a b c van Aarde, Rudi J. (1984). Macdonald, D.. ed. The Encyclopedia of Mammals. New York: Facts on File. pp. 466–467. ISBN 0-87196-871-1. 
  8. ^ "Aardvarks at the Bronx Zoo" (flash video). http://www.youtube.com/watch?v=1Z5OoBqqYsk&t=0m46s. Retrieved January 31, 2011. 
  9. ^ "Cute as a Button but a Pain in my Butt: The Aardvark". http://www.themagicalbuffet.com/Issues/Vol02_Iss07/Article_049.html. Retrieved 2008-01-10. 
  10. ^ [1]
  11. ^ [2]
  12. ^ WKYC.com

[edit] External links

 

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