CHINA> About Australia
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CHINA> About Australia
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Fauna of Australia
(eg.wikipedia.org)
Updated: 2009-08-28 13:33 Koala
The Koala (Phascolarctos cinereus) is a thickset arboreal marsupial herbivore native to Australia, and the only extant representative of the family Phascolarctidae. The koala is found in coastal regions of eastern and southern Australia, from near Adelaide to the southern part of Cape York Peninsula. Populations also extend for considerable distances inland in regions with enough moisture to support suitable woodlands. The koalas of South Australia were largely exterminated during the early part of the 20th century, but the state has since been repopulated with Victorian stock. The koala is not found in Tasmania or Western Australia. The koala is broadly similar in appearance to the wombat (its closest living relative), but has a thicker coat, much larger ears, and longer limbs. The koala has large, sharp claws to assist with climbing tree trunks. Weight varies from about 14 kg (31 lb) for a large southern male, to about 5 kg (11 lb) for a small northern female. The koala's five fingers are arranged with opposable thumbs, providing better gripping ability. The first two fingers are positioned in apposition on the front paws, and the first three fingers for the hind paws. The koala is one of the few mammals (other than primates) that has fingerprints. Koala fingerprints are similar to human fingerprints; even with an electron microscope, it can be quite difficult to distinguish between the two. The teeth of the koala are adapted to their herbivorous diet, and are similar to those of other diprotodont marsupials, such as kangaroos and wombats. They have sharp incisors to clip leaves at the front of the mouth, separated from the grinding cheek teeth by a wide diastema. The male koala, like many marsupials, has a bifurcated penis. The female has two lateral vaginas and two separate uteri, which is common to all marsupials. The brain in the ancestors of the modern koala once filled the whole cranial cavity, but has become drastically reduced in the present species, a degeneration scientists suspect is an adaptation to a diet low in energy. One of the smallest in marsupials with no more than 0.2% of its body weight, about 40% of the cranial cavity is filled with cerebrospinal fluid, while the brain's two cerebral hemispheres are like "a pair of shrivelled walnut halves on top of the brain stem, in contact neither with each other nor the bones of the skull. It is the only animal on Earth with such a strangely reduced brain." It is generally a silent animal, but males have a very loud advertising call that can be heard from almost a kilometre away during the breeding season. When under stress, koalas may issue a loud cry, which has been reported as similar to that of a human baby. There is little reliable information about the lifespan of the koala, but in captivity they have been observed to reach the age of 18 years.
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