Aardvark
The aardvark is a medium-sized, burrowing, nocturnal mammal native to Africa. The aardvark is the only living member of the genus Orycteropus, the family Orycteropodidae and the order Tubulidentata. It has a long proboscis, similar to a pig's snout, which is used to sniff out food.
The aardvark is an afrotherian, a clade that also includes elephants, manatees, and hyraxes.
It is found over much of the southern two-thirds of the African continent, avoiding areas that are mainly rocky. A nocturnal feeder, the aardvark subsists on ants and termites by using its sharp claws and powerful legs to dig the insects out of their hills. Aardvarks also dig to create burrows in which to live and rear their young.
Name and taxonomy
Name
The aardvark is sometimes colloquially called the "African ant bear", "anteater", or the "Cape anteater" after the Cape of Good Hope.The name aardvark is Afrikaans and comes from earlier Afrikaans erdvark. It means 'earth pig' or 'ground pig', because of its burrowing habits.
The name Orycteropus means 'burrowing foot', and the name afer refers to Africa. The name of the aardvark's order, Tubulidentata, comes from the tubule-style teeth.
Taxonomy
The aardvark is not closely related to the pig; rather, it is the sole extant 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. The similarities are the outcome of convergent evolution. The closest living relatives of the aardvark are the elephant shrews, Tenrecidae, and golden moles. Along with sirenians, hyraxes, elephants, and their extinct relatives, these animals form the superorder Afrotheria. Studies of the brain have shown the similarities with Condylarthra.Evolutionary history
Based on his study of fossils, Bryan Patterson has concluded that early relatives of the aardvark appeared in Africa around the end of the Paleocene. The ptolemaiidans, a 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.The first unambiguous tubulidentate was probably Myorycteropus africanus from Kenyan Miocene deposits. 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. Fossils from the aardvark have been dated to 5 million years, and have been located throughout Europe and the Near East.
The 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.
Subspecies
The aardvark has seventeen poorly defined subspecies listed:- 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
The aardvark is vaguely pig-like in appearance. Its body is stout with a prominently arched back and is sparsely covered with coarse hairs. The limbs are of moderate length, with the rear legs being longer than the forelegs. The front feet have lost the pollex, 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 times to be plantigrade. This confusion happens because when it squats it stands on its soles. A contributing characteristic to the burrow digging capabilities of aardvarks is an endosteal tissue called compacted coarse cancellous bone. The stress and strain resistance provided by CCCB allows aardvarks to create their burrows, ultimately leading to a favourable environment for plants and a variety of animals. Digging is also facilitated by its forearm's unusually stout ulna and radius.An aardvark's weight is typically between. An aardvark's length is usually between, and can reach lengths of when its tail is taken into account. It is tall at the shoulder, and has a girth of about. It does not exhibit sexual dimorphism.It is the largest member of the proposed clade Afroinsectiphilia. The aardvark is pale yellowish-grey in colour 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. The hair on the majority of its body is grouped in clusters of three to four hairs. 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
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. 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, with individual pulp canals, held together by cementum. The number of columns is dependent on the size of the tooth, with the largest having about 1,500. 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 have only cheek teeth at the back of the jaw, and have a dental formula of: These remaining teeth are peg-like and rootless and are of unique composition. The teeth consist of 14 upper and 12 lower jaw molars. The nasal area of the aardvark is another unique area, as it contains ten nasal conchae, more than any other placental mammal.The sides of the nostrils are thick with hair. The tip of the snout is highly mobile and is moved by modified mimetic muscles. The fleshy dividing tissue between its nostrils probably has sensory functions, but it is uncertain whether they are olfactory or vibratory in nature. Its nose is made up of more turbinate bones than any other mammal, with between nine and 11, compared to dogs with four to five. With a large quantity of turbinate bones, the aardvark has more space for the moist epithelium, which is the location of the olfactory bulb. The nose contains nine olfactory bulbs, more than any other mammal. 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. 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 and elaborate structures supporting a keen sense of smell. The ears, which are very effective, are disproportionately long, about long. The eyes are small for its head, and consist only of rods.
Digestive system
The aardvark's stomach has a muscular pyloric area that acts as a gizzard to grind swallowed food up, thereby rendering chewing unnecessary. Its cecum is large. Both sexes emit a strong smelling secretion from an anal gland. Its salivary glands are highly developed and almost completely ring the neck; their output is what causes the tongue to maintain its tackiness. The female has two pairs of teats in the inguinal region.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.