Koalas belong to the class of mammals, hairy, warm-blooded vertebrates most of whom give live birth and nourish their young with milk produced by skin glands of females. The class of mammals has three subclasses: Prototheria, egg-laying mammals represented by platypus and echidna; Metatheria, pouched mammals represented by marsupials and their distant relatives that are known only by fossils; and Eutheria, placental mammals such as humans. Of these three subclasses, koalas are marsupials and belong to Metatheria. Marsupials are unique among mammals in their mode of reproduction: their gestation period is very brief, so the young is born underdeveloped and following birth stays for many weeks in the maternal pouch and continues development. Except for the North American opossum, marsupials are found only in Australia and South America.
Koalas are phalangers, a genus of marsupials whose members are small to average in size with all limbs having five digits with claws, except for clawless toes; phalangers are arboreal and feed on vegetation. Finally, koalas are the largest phalangers and the only ones with pouches that open in the rear. Medium-sized animals with dense fur and no tail, koalas have low metabolism and spend most of their waking time consuming their exclusive diet, leaves of eucalyptus trees. Koalas have certain location-dependent preferences in the species of eucalyptus, of which they normally have about five favorites; interestingly, koalas love mature leaves of mana eucalyptus but know to avoid its young leaves and shoots that contain dangerously high levels of hydrocyanic acid and can kill the animals feeding on them. Koalas get water they need from the leaves, so they rarely drink; in fact, “koala” is commonly said to mean “does not drink” in the native language of Australian aborigines. Slow-moving and defenseless, for a long time koalas have been ruthlessly killed both for entertainment and their beautiful soft fur, until Australia enacted laws to protect koalas and other countries, such as the United States, prohibited the import of koala furs.
Because of their bear-like appearance (plump, no tail, rounded ears, thick fur), koalas are often incorrectly called “koala bears”; even their scientific name, Phascolarctos cinereus, means “ash grey pouched bear.” But koalas are not bears; the two animal families belong to different mammal classes – as described above, koalas belong to the Metatheria, while bears are Eutherians. The two animals differ in many aspects, and to name a few we’ll briefly consider reproduction, diet, and habitat. Unlike koalas, bears are placental mammals, meaning that their young do not need a pouch to finish the gestational period. As for the eating habits, many bears are carnivorous, which is a far cry from vegan koalas. Finally, while koalas reside primarily in the southern hemisphere, most bears – with the exception of South American Andean Bear – live in the northern hemisphere.