Tuesday, November 21, 2006
Aardvark
The Aardvark (Orycteropus afer) is a medium-sized mammal native to Africa. The name comes from the Afrikaans/Dutch for "earth pig", because premature settlers from Europe thought it resembled a pig. However, the Aardvark is not closely related to pigs.
The Aardvark is the only surviving member of the family Orycteropodidae and of the order Tubulidentata. The Aardvark was originally placed in the same order as the South American anteaters because of surface similarities which, it is now known, are the result of convergent evolution, not common ancestry. For the same reason, Aardvarks bear a striking first-glance resemblance to the marsupial bandicoots, bilbies, and numbats of Australasia, which are not placental mammals at all. The Aardvark is now in its own genus, Orycteropus.
The oldest known Tubulidentata fossils have been found in Kenya and date to the early Miocene. Although the relationships of Tubulidentata are unknown, they are almost certainly ungulates. They spread to Europe and southern Asia during the later Miocene and early Pliocene periods. Two other genera of the family Orycteropodidae are known besides the extant one: Leptorycteropus and Myorycteropus. A genus from Madagascar called Plesiorycteropus may be related to the Aardvark.
In the past, some individual species of Aardvark were named; however, current knowledge indicates that there is only one species, Orycteropus afer, with several subspecies; 18 have been identified but most are regarded as invalid.
The most distinctive characteristic of the Tubulidentata is their teeth, which, instead of having a pulp cavity, have a number of thin tubes of dentine, each containing pulp and 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, but these fall out and are not replaced. Adult Aardvarks have only molars at the back of the jaw.
