Koalas (Phascolarctos cinereus) from the Sanctuary at Tidbinbilla Nature Reserve. Though slow-moving, koalas are skilled at maneuvering around in the forest canopy. They have long sharp claws and two opposable digits on the forefeet, functionally similar to the opposable thumb in humans and zygodactyly in chameleons. Koalas sleep up to 20 hours a day, conserving the little energy they get from their strictly eucalypt leaf diet. Eucalypts offer poor nutritional value and contain toxic compounds, but the koala digestive system is able to make the most out of this highly abundant food source. Koalas have poor vision but a keen sense of smell to assess leaves before consumption. Curiously their eyes have vertically slit pupils, an uncommon feature in marsupials. Like sloths in the New World, they can often be spotted lying dormant high in trees.
Sloths and koalas may seem superficially similar due to their ecological habits, but they are distantly related on the mammalian tree. Sloths are placental mammals most closely related to anteaters (order Pilosa) and koalas are close relatives of wombats (suborder Vombatiformes) — you can really see it in the face! Being marsupials, koalas have fully developed pouches for carrying young joeys for about half a year. Females lactate for up to a year with joeys clinging to their mothers’ backs, eventually transitioning into an independent arboreal lifestyle.
Koalas are currently listed as Vulnerable. Habitat loss and urbanization pose the greatest threat to wild populations, and fragmentation and stress go hand in hand with transmission of chlamydia and retroviruses.
Natural selection and adaptation create intriguing forms of life. Too bad the koala survives in such a narrow niche. Perhaps it will adapt in the future to expand it’s dietary capabilities.