Like many Australian animals, koalas are peculiar evolutionary examples, having developed in isolation from the rest of the world to fill specific ecological niches. For example, koalas have adapted to live on eucalyptus leaves, despite their low nutritional value and relatively high toxicity. Despite being commonly referred to as "koala bears," koalas are not bears, and their closest living relative is the wombat.
Like all marsupials, koalas deliver their young - called joeys - at a relatively earlier stage of development than placental mammals. The joey matures in a ventral pouch for approximately six months, at which time it is developed enough to cling to it's mother's back and begin weaning.
Koalas are not endangered, although they are increasingly threatened by habitat loss, urbanization, and diseases - including chlamydia.