Aardvark

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Aardvark
Temporal range: Pliocene–Recent
[1]
Porc formiguer.JPG
An aardvark at Detroit Zoo
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)
Subspecies

See Text

Aardvark area.png
Aardvark range

The aardvark (/ˈɑːrd.vɑːrk/ ARD-vark, Orycteropus afer) is a medium-sized, burrowing, nocturnal mammal native to Africa.[3] It is the only living species of the order Tubulidentata,[4][5] although other prehistoric species and genera of Tubulidentata are known. It resembles a pig with a long snout, which is used to sniff out food. It roams over most of the southern two-thirds of the continent, avoiding mainly rocky areas. A nocturnal feeder, it subsists on ants and termites, which it will dig out of their hills using its sharp claws and powerful legs. It also will utilize its digging ability to create burrows in which to live and rear its young. It receives a "least concern" rating from the IUCN, although its numbers seem to be decreasing.

Naming and taxonomy[edit]

It is sometimes colloquially called "African antbear",[1] "anteater", or the "Cape anteater"[1] after the Cape of Good Hope. The name comes from earlier Afrikaans (erdvark)[1] and means "earth pig" or "ground pig" (aarde earth/ground, vark pig), because of its burrowing habits[6] (similar origin to the name groundhog). The name Orycteropus means burrowing foot, and the name afer refers to Africa.[7] The name of the aardvarks's order, Tubulidentata comes from the tubule style teeth.[8]

The aardvark is not closely related to the pig; rather, it is the sole extant representative of the obscure mammalian order Tubulidentata,[7] 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.[9] The similarities are based on convergent evolution.[10] The closest living relatives of the aardvark are the elephant shrews,[11] along with the sirenians, hyraxes, elephants,[12] and tenrecs.[11] With their extinct relatives, these animals form the superorder Afrotheria.[13] Studies of the brain have shown the similarities with Condylarthra.[10] The scientific name of the aardvark comes from Greek ορυκτερόπους (orykterópous) meaning "digging footed" and afer: from Africa.

Based on fossils, Bryan Patterson has concluded that early relatives of the aardvark appeared in Africa around the end of the Paleocene.[10][11] The mysterious Pleistocene Plesiorycteropus, from Madagascar was, when first described, originally thought to be a tubulidentate that was descended from ancestors that entered the island during the Eocene: too many subtle anatomical differences coupled with recent molecular evidence now lead researchers to believe that Plesiorycteropus is a relative of the golden mole and tenrecs that achieved an aardvark-like appearance and ecological niche through convergent evolution. The first known tubulidentate was probably Myorycteropus africanus from Kenyan Miocene deposits.[10] The earliest example from the Orycteropus genus was the Orycteropus mauritanicus found in Algeria in deposits from the middle Miocene, with an equally aged version found in Kenya.[10] Fossils from the aardvark have been dated to 5 million years, and have been located throughout Europe and the Near East.[10] A close relative lived in Madagascar during the last ice age.[1]

Subspecies[edit]

The aardvark has seventeen poorly defined subspecies listed:[4]

  • Orycteropus afer afer
  • O. a. adametzi Grote, 1921
  • O. a. aethiopicus Sundevall, 1843
  • O. a. angolensis Zukowsky & Haltenorth, 1957
  • O. a. erikssoni Lönnberg, 1906
  • O. a. faradjius Hatt, 1932
  • O. a. haussanus Matschie, 1900
  • O. a. kordofanicus Rothschild, 1927
  • O. a. lademanni Grote, 1911
  • O. a. leptodon Hirst, 1906
  • O. a. matschiei Grote, 1921
  • O. a. observandus Grote, 1921
  • O. a. ruvanensis Grote, 1921
  • O. a. senegalensis Lesson, 1840
  • O. a. somalicus Lydekker, 1908
  • O. a. wardi Lydekker, 1908
  • O. a. wertheri Matschie, 1898

Description[edit]

An aardvark skeleton and mounted specimen at the Natural History Museum of Genoa

The aardvark is vaguely pig-like in appearance. Its body is stout with a prominently arched back[14] and is sparsely covered with coarse hairs. The limbs are of moderate length, with the rear legs being longer than the forelegs.[13] The front feet have lost the pollex (or 'thumb'), resulting in four toes, while 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. Whereas the aardvark is considered digitigrade, it appears at time to be plantigrade. This confusion happens because when it squats it stands on its soles.[14]

An aardvark's weight is typically between 60 and 80 kilograms (130–180 lb).[13] An aardvark's length is usually between 105 and 130 centimetres (3.44–4.27 ft),[5] and can reach lengths of 2.2 metres (7 ft 3 in) when its tail (which can be up to 70 centimetres (28 in)) is taken into account. It is 60 centimetres (24 in) tall at the shoulder, and has a girth of about 100 centimetres (3.3 ft).[14] It is the largest member of the proposed clade Afroinsectiphilia. 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. Its hair is short on its head and tail; however its legs tend to have longer hair.[5] The hair on the majority of its body is grouped in clusters of 3-4 hairs.[14] The hair surrounding its nostrils is dense to help filter particulate matter out as it digs. Its tail is very thick at the base and gradually tapers.

Head[edit]

The greatly elongated head is set on a short, thick neck, and the end of the snout bears a disc, which houses the nostrils. It contains a thin but complete zygomatic arch.[14] The head of the aardvark contains many unique and different features. 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, hexagonal, upright, parallel tubes of vasodentin (a modified form of dentine), with individual pulp canals, held together by cementum.[13] The number of columns is dependent on the size of the tooth, with the largest having about 1,500.[10] The teeth have no enamel coating and are worn away and regrow continuously.[8] The aardvark is born with conventional incisors and canines at the front of the jaw, which fall out and are not replaced. Adult aardvarks have only cheek teeth at the back of the jaw, and have a dental formula of: 0.0.2-3.30.0.2.3 These remaining teeth are peg-like and rootless and are of unique composition.[15] The teeth consist of 14 upper and 12 lower jaw molars.[1] The nasal area of the aardvark is another unique area, as it contains ten nasal conchae, more than any other placental mammal.[13] The sides of the nostrils are thick with hair.[14] The tip of the snout is highly mobile and is moved by modified mimetic muscles.[13] The fleshy dividing tissue between its nostrils probably has sensory functions,[5] but it is uncertain if it is olfactory or vibration in nature.[16] Its nose is made up of more a turbinate bones than any other mammal, with between 9 and 11, compared to dogs with 4 to 5.[8] With a large quantity of turbinate bones, the aardvark has more space for the moist epithelium, which is the location of the olfactory bulb.[8] The nose contains more olfactory bulbs than any other mammal, with 9.[14] Its keen sense of smell is not just from the quantity of bulbs in the nose but also in the development of the brain, as its olfactory lobe is very developed.[10] The snout resembles an elongated pig snout. The mouth is small and tubular, typical of species that feed on ants and termites. The aardvark has a long, thin, snakelike, protruding tongue (as much as 30 centimetres (12 in) long)[1] and elaborate structures supporting a keen sense of smell.[17] The ears, which are very effective,[1] are disproportionately long, about 20–25 centimetres (7.9–9.8 in) long.[14] The eyes are small for its head, and consist only of rods.[14]

Digestive system[edit]

The aardvark's stomach has a muscular pyloric area that acts as a gizzard, (it grinds the food up) to make chewing not important.[5] Its cecum is large.[13] Both males and females emit a strong smelling secretion from an anal gland.[5] Its salivary glands are highly developed and almost completely ring the neck,[13] and their output is what causes the tongue to maintain its tackiness.[14] The female has two pairs of teats in the inguinal region.[13]

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.[18]

Habitat and range[edit]

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).[9] They hide in dark underground burrows to avoid the warm weather.[19] The only major habitat that they are not present in is swamp forest, as the high water table interferes with digging.[2] They have been documented as high as 3,200 metres (10,500 ft) in Ethiopia.[2] They are known to live throughout sub-Saharan Africa all the way to South Africa with few exceptions. These exceptions are coastal areas of Namibia, Ivory Coast, and Ghana.[2] They are also not present in Madagascar.[2] They avoid rocky terrain as it causes problems with digging.[20]

Ecology and behavior[edit]

Resting aardvark in Himeji City Zoo
Entrance to burrow

Aardvarks live for up to 23 years in captivity.[13]

Its keen hearing warns it of predators: lions, leopards, hyenas, and pythons.[1][16] The aardvark's main predators are lions, leopards, hunting dogs and pythons. Some humans also hunt aardvarks for meat.[1] 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 lying motionless except to lash out with all four feet.[16] They are capable of causing substantial damage to unprotected areas of an attacker.[8] They will also dig to escape as they can, when pressed, dig extremely quickly.[16] Their thick skin also protects them to some extent.[citation needed]

Feeding[edit]

The aardvark is nocturnal and is a solitary creature that feeds almost exclusively on ants and termites (formivore);[5] the only fruit eaten by aardvarks is the aardvark cucumber.[16] In fact, the cucumber and the aardvark have a symbiotic relationship as they eat the subterranean fruit, then defecate the seeds near their burrows, which then grow rapidly due to the loose soil and fertile nature of the area. The time spent in the intestine of the aardvark helps the fertility of the seed, and the fruit provides needed moisture for the aardvark.[8][16] They avoid eating the African driver ant and red ants.[21] Due to their stringent diet requirements, they require a large range to survive.[20] 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 kilometres (6.2 to 18.6 mi). While foraging for food, the aardvark will keep its nose to the ground and its ears pointed forward, which indicates that both smell and hearing are involved in the search for food. They zig-zag as they forage and will usually not repeat a route for 5–8 days as they appear to allow time for the termite nests to recover before feeding on it again.[21] During a foraging period, they will stop and dig a "V" shaped trench with their forefeet and then sniff it profusely as a means to explore their location.[5] 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. Its claws enable it to dig through the extremely hard crust of a termite or ant mound quickly. It avoids inhaling the dust by sealing the nostrils.[19] When successful, the aardvark's long (up to 30 centimetres (12 in))[3] tongue licks up the insects; the termites' biting, or the ants' stinging attacks are rendered futile by the tough skin. After an aardvark visit at a termite mound, other animals will visit to pick up all the leftovers.[22] Termite mounds alone don't provide enough food for the aardvark, so they look for termites that are on the move. When these insects move, they can form columns 10–40 metres (33–131 ft) long and these tend to provide easy pickings with little effort exerted by the aardvark. These columns are more common in areas of livestock or other hoofed animals.[22] The trampled grass and dung attract termites from Odontotermes, Microtermes, and Pseudacanthotermes genera.[22]

On a nightly basis they tend to be more active during the first portion of the night time (2000-2400); however, they don't seem to prefer bright or dark nights over the other. During adverse weather or if disturbed they will retreat to their burrow systems. They cover between 2 and 5 kilometres (1.2 and 3.1 mi) per night; however, some studies have shown that they may traverse as far as 30 kilometres (19 mi) in a night.[5]

Vocalization[edit]

The aardvark is a rather quiet animal. However it does make soft grunting sounds as it forages and loud grunts as it makes for its tunnel entrance.[20] It makes a bleating sound if frightened.[21] When it is threatened it will make for one of its burrows. If one is not close it will dig a new one rapidly. This new one will be short and require the aardvark to back out when the coast is clear.[21]

Movement[edit]

The aardvark is known to be a good swimmer and has been witnessed successfully swimming in strong currents.[21] It can dig 1 yard of tunnel in about 5 minutes,[20] but otherwise moves fairly slowly.

When leaving the burrow at night, they pause at the entrance for about ten minutes, sniffing and listening. After this period of watchfulness, it will bound out and within seconds it will be 10 metres (33 ft) away. It will then pause, prick its ears, twisting its head to listen, then jump and move off to start foraging.[20]

Aside from digging out ants and termites, the aardvark also excavates burrows in which to live; of which they generally fall into three categories: burrows made while foraging, refuge and resting location, and permanent homes.[5] Temporary sites are scattered around the home range and are used as refuges, while the main burrow is also used for breeding. Main burrows can be deep and extensive, have several entrances and can be as long as 13 metres (43 ft).[5] These burrows can be large enough for a man to enter.[1] The aardvark changes the layout of its home burrow regularly, and periodically moves on and makes a new one. The old burrows are an important part of the African wildlife scene. As they are vacated, then they are inhabited by smaller animals like the African wild dog, ant-eating chat, Nycteris thebaica and warthogs.[21] Other animals that use them are hares, mongooses, hyenas, owls, pythons, and lizards. Without these refuges many animals would die during wildfire season.[21] Only mothers and young share burrows; however, the aardvark is known to live in small family groups or as a solitary creature.[1] If attacked in the tunnel, it will escape by digging out of the tunnel thereby placing the fresh fill between it and its predator, or if it decides to fight it will roll onto its back, and attack with its claws.[1] The aardvark has been known to sleep in a recently excavated ant nest, which also serves as protection from its predators.[23]

Aardvark mother and young

Reproduction[edit]

Aardvarks pair only during the breeding season; after a gestation period of seven months,[5] one cub weighing around 1.7–1.9 kilograms (3.7–4.2 lb)[13] is born during May–July.[1] When born, the young has flaccid ears and many wrinkles. When nursing, it will nurse off each teat in succession.[16] After two weeks the folds of skin disappear and after three, the ears can be held upright.[16] After 5–6 weeks, body hair starts growing.[16] It is able to leave the burrow to accompany its mother after only two weeks, and is eating termites at 9 weeks[16] and is weaned by 16 weeks.[5] By 3 months of age the young has been weaned.[13] 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,[5] and is sexually mature from approximately two years of age.[13]

Conservation[edit]

Aardvarks were thought to have declining numbers,[1] however this is possibly due to the fact that they are not readily seen.[2] There are no definitive counts because of their nocturnal and secretive habits; however their numbers seem to be stable overall. They are not considered common anywhere in Africa, but due to their large range, they maintain sufficient numbers. There may be a slight decrease in numbers in eastern, northern, and western Africa. Southern African numbers are not decreasing. It receives an official designation from the IUCN as least concern.[2] However, they are a species in a precarious situation as they are so dependent on such specific food; therefore if a problem arises with the abundance of termites, the species as a whole would be affected drastically.[5]

Aardvarks handle captivity well, and the first zoo to have one was the London Zoo in 1869, from South Africa.[16]

Mythology and popular culture[edit]

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.[24] Also, some tribes, such as the Margbetu, Ayanda, and Logo,[5] will use the teeth of the aardvark to make bracelets that are regarded as good luck charms.[1] The meat, which has a resemblance to pork, is eaten in certain cultures.[5]

The Egyptian god Set is said (by some) to have the head of an aardvark or to be part aardvark.[25]

The titular character of Arthur, an animated television series for children based on a book series and produced by WGBH, shown in more than 180 countries, is an aardvark.[26]

Footnotes[edit]

  1. ^ a b c d e f g h i j k l m n o p Goodwin 1997, pp. 2–3
  2. ^ a b c d e f g Lindsey et al. 2008
  3. ^ a b Hoiberg 2010, pp. 3–4
  4. ^ a b Schlitter 2005, p. 86
  5. ^ a b c d e f g h i j k l m n o p q van Aarde 1984, pp. 466–467
  6. ^ Merriam-Webster Online Dictionary 2010
  7. ^ a b Shoshani 2002, p. 618
  8. ^ a b c d e f Shoshani 2002, p. 619
  9. ^ a b African Wildlife Foundation 2013
  10. ^ a b c d e f g h Rahm 1990, pp. 453–454
  11. ^ a b c Shoshani 2002, p. 620
  12. ^ Rodriguez 2013, p. 6
  13. ^ a b c d e f g h i j k l m Rahm 1990, pp. 450–451
  14. ^ a b c d e f g h i j Rahm 1990, p. 452
  15. ^ Martin 1983, p. 377
  16. ^ a b c d e f g h i j k Rahm 1990, p. 458
  17. ^ Taylor & Skinner 2004, p. 106
  18. ^ Anon 2003
  19. ^ a b Anon 2013
  20. ^ a b c d e Rahm 1990, p. 455
  21. ^ a b c d e f g Rahm 1990, p. 456
  22. ^ a b c Rahm 1990, p. 457
  23. ^ Anon 2013a
  24. ^ Rebecca 2007
  25. ^ te Velde 1997, p. 13
  26. ^ WGBH 2013

References[edit]

  • African Wildlife Foundation (2013). "Aardvark". African Wildlife Foundation. Archived from the original on 5 January 2008. Retrieved 2013-11-18. 
  • Anon (2013). "All About Aardvarks". Easy Science for Kids. Online Science Tutor for Kids. Retrieved 2013-11-18. 
  • Goodwin, George G. (1997). "Aardvark". In Johnston, Bernard. Collier's Encyclopedia. I: A to Ameland (1st ed.). New York, NY: P.F. Collier. ISBN 978-1571610935. 
  • Hoiberg, Dale H., ed. (2010). "Aardvark". Encyclopædia Britannica. I: A-ak Bayes (15th ed.). Chicago, IL: Encyclopædia Britannica Inc. ISBN 978-1-59339-837-8. 
  • Martin, Elizabeth A. (1983). "Tubulidentata". MacMillan Dictionary of Life Sciences (2nd ed.). MacMillan. ISBN 978-0333348673. 
  • Merriam-Webster Online Dictionary (2010). "aardvark". Merriam-Webster Online Dictionary. Retrieved 2013-11-18. 
  • Rahm, Urs (1990). "Tubulidentates: Aardvark". In Parker, Sybil P. Grzimek's Encyclopedia of Mammals 4. New York, NY: McGraw-Hill Publishing Company. pp. 450 458. ISBN 0-07-909508-9. 
  • Shoshani, Jeheskel (2002). "Tubulidentata". In Robertson, Sarah. Encyclopedia of Life Sciences. 18: Svedberg, Theodor to Two-hybrid and Related Systems. London, UK: Nature Publishing Group. ISBN 1-56159-274-9. 
  • van Aarde, Rudi J. (1984). "Aardvark". In Macdonald, David. The Encyclopedia of Mammals. New York, NY: Facts on File Publications. ISBN 0-87196-871-1. 

External links[edit]