koala kōäˈlə [key], arboreal marsupial, or pouched mammal, Phascolarctos cinereus, native to Australia. Although it is sometimes called koala bear, or Australian bear, and is somewhat bearlike in appearance, it is not related to true bears. Once abundant, it is now found in much-reduced numbers in Queensland, Victoria, and New South Wales. In the 21st cent. increasingly severe bushfires have become a threat to the species.

The koala has thick, grayish fur, a tailless body 2 to 21⁄2 ft (60–75 cm) long, a protuberant, curved, black nose, and large, furry ears. The five sharply clawed toes on each foot enable it to grasp and climb. A slow-moving, nocturnal animal, the koala has perhaps the most specialized diet of any living mammal; it feeds on leaves and shoots of a particular stage of maturation from particular species of eucalyptus. In addition to the vocal folds in the larynx, the koala has a pair of larger, thicker velar vocal folds (part of the soft palate) that are used to produce very low-pitched mating calls.

The single cub is about 3⁄4 in (1.9 cm) long at birth and is nursed in the mother's pouch, from which it emerges for the first time when about six months old. Until it is about eight months old it continues to ride in the pouch, and until about a year of age it is carried on its mother's back or in her arms.

The harmless and defenseless koala has been ruthlessly hunted, chiefly for fur but also for food; disease and the clearing of the eucalyptus forests have also taken a heavy toll. Protective measures have been adopted to prevent its extinction, but loss of habitat and disease have led to continuing population losses, especially in Queensland, and the koala is considered vulnerable in parts of its range.

The koala is classified in the phylum Chordata, subphylum Vertebrata, class Mammalia, order Marsupialia, family Phalangeridae.

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