Aardvark

The aardvark is sometimes colloquially called the "African ant bear",[6] "anteater" (not to be confused with the South American anteater), or the "Cape anteater"[6] after the Cape of Good Hope. The name "aardvark" is Afrikaans (Afrikaans pronunciation: [ˈɑːrtfark]), comes from earlier Afrikaans (erdvark)[6] and means "earth pig" or "ground pig" (aarde: earth/ground, vark: pig), because of its burrowing habits; it is also the first polysyllabic word in many English dictionaries.[7][8][9] The name Orycteropus means burrowing foot, and the name afer refers to Africa.[10] The name of the aardvarks's order, Tubulidentata, comes from the tubule-style teeth.[11]

The skull of an aardvark

The aardvark is not closely related to the pig; rather, it is the sole extant representative of the obscure mammalian order Tubulidentata,[10] 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.[12] The similarities are based on convergent evolution.[13] The closest living relatives of the aardvark are the elephant shrews, tenrecs and golden moles.[14] Along with the sirenians, hyraxes, elephants,[15] and their extinct relatives, these animals form the superorder Afrotheria.[16] Studies of the brain have shown the similarities with Condylarthra,[13] and given the clade's status as a wastebasket taxon it may mean some species traditionally classified as "condylarths" are actually stem-aardvarks.

Based on fossils, Bryan Patterson has concluded that early relatives of the aardvark appeared in Africa around the end of the Paleocene.[13][17] The ptolemaiidans, a mysterious clade of mammals with uncertain affinities, may actually be stem-aardvarks, either as a sister clade to Tubulidentata or as a grade leading to true tubulidentates.[18][19]

The first unambiguous tubulidentate was probably Myorycteropus africanus from Kenyan Miocene deposits.[13] The earliest example from the genus Orycteropus was Orycteropus mauritanicus, found in Algeria in deposits from the middle Miocene, with an equally old version found in Kenya.[13] Fossils from the aardvark have been dated to 5 million years, and have been located throughout Europe and the Near East.[13]

The mysterious Pleistocene Plesiorycteropus from Madagascar was originally thought to be a tubulidentate that was descended from ancestors that entered the island during the Eocene. However, a number of subtle anatomical differences coupled with recent molecular evidence now lead researchers to believe that Plesiorycteropus is a relative of golden moles and tenrecs that achieved an aardvark-like appearance and ecological niche through convergent evolution.[20]

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

The 1911 Encyclopædia Britannica also mentions O. a. capensis or Cape ant-bear from South Africa.[21]

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.[22] 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.[16] The number of columns is dependent on the size of the tooth, with the largest having about 1,500.[13] The teeth have no enamel coating and are worn away and regrow continuously.[11] 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.[24] The teeth consist of 14 upper and 12 lower jaw molars.[6] The nasal area of the aardvark is another unique area, as it contains ten nasal conchae, more than any other placental mammal.[16]

The sides of the nostrils are thick with hair.[22] The tip of the snout is highly mobile and is moved by modified mimetic muscles.[16] The fleshy dividing tissue between its nostrils probably has sensory functions,[5] but it is uncertain whether they are olfactory or vibratory in nature.[25] Its nose is made up of more turbinate bones than any other mammal, with between 9 and 11, compared to dogs with 4 to 5.[11] With a large quantity of turbinate bones, the aardvark has more space for the moist epithelium, which is the location of the olfactory bulb.[11] The nose contains nine olfactory bulbs, more than any other mammal.[22] 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.[13] 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)[6] and elaborate structures supporting a keen sense of smell.[26] The ears, which are very effective,[6] are disproportionately long, about 20–25 centimetres (7.9–9.8 in) long.[22] The eyes are small for its head, and consist only of rods.[22]

The aardvark's stomach has a muscular pyloric area that acts as a gizzard to grind swallowed food up, thereby rendering chewing unnecessary.[5] Its cecum is large.[16] Both sexes emit a strong smelling secretion from an anal gland.[5] Its salivary glands are highly developed and almost completely ring the neck;[16] their output is what causes the tongue to maintain its tackiness.[22] The female has two pairs of teats in the inguinal region.[16]

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.[27]

The aardvark is nocturnal and is a solitary creature that feeds almost exclusively on ants and termites (myrmecophagy);[5] the only fruit eaten by aardvarks is the aardvark cucumber.[25] 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.[11][25] They avoid eating the African driver ant and red ants.[30] Due to their stringent diet requirements, they require a large range to survive.[29] 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.[30]

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.[28] When successful, the aardvark's long (up to 30 centimetres (12 in))[2] 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.[31] 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.[31] The trampled grass and dung attract termites from the Odontotermes, Microtermes, and Pseudacanthotermes genera.[31]

On a nightly basis they tend to be more active during the first portion of night (roughly the four hours between 8:00 p.m. and 12:00 a.m.); 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]

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.[29] It makes a bleating sound if frightened.[30] 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.[30]

The aardvark is known to be a good swimmer and has been witnessed successfully swimming in strong currents.[30] It can dig a yard of tunnel in about five minutes,[29] 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.[29]

Aside from digging out ants and termites, the aardvark also excavates burrows in which to live, which generally fall into one of 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.[6] 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.[30] Other animals that use them are hares, mongooses, hyenas, owls, pythons, and lizards. Without these refuges many animals would die during wildfire season.[30] Only mothers and young share burrows; however, the aardvark is known to live in small family groups or as a solitary creature.[6] 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.[6] The aardvark has been known to sleep in a recently excavated ant nest, which also serves as protection from its predators.[32]

Aardvark mother and young

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)[16] is born during May–July.[6] When born, the young has flaccid ears and many wrinkles. When nursing, it will nurse off each teat in succession.[25] After two weeks, the folds of skin disappear and after three, the ears can be held upright.[25] After 5–6 weeks, body hair starts growing.[25] It is able to leave the burrow to accompany its mother after only two weeks and eats termites at 9 weeks,[25] and is weaned between three months[16] and 16 weeks.[5] 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.[16]