Koalas sleep twenty hours on a near-poison eucalyptus diet
The koala (Phascolarctos cinereus) is Australia’s arboreal marsupial icon—not a bear—sole survivor of Phascolarctidae and cousin to wombats. Stout, tailless, with fluffy ears and a dark nose, it lives on eastern and southern coasts and spends most of each day motionless in eucalypt crowns.
Adults measure about 60–85 cm and weigh 4–15 kg; northern animals run smaller and paler than southern ones. Eucalyptus leaves supply most calories yet are poor fuel laced with toxins that deter other mammals, so koalas sleep up to twenty hours daily. They are asocial except for mothers and joeys; males bellow and scent-mark with chest glands. Joeys crawl into the pouch for six to seven months and wean near one year. The name comes from Dharug gula, “no water”; Phascolarctos blends Greek for pouch and bear, cinereus Latin for ash-colored.
Vombatiform kinship may date to an Eocene split ~40 million years ago. Oligocene–Miocene rainforest relatives included Nimiokoala and smaller Litokoala; drying climates favored eucalypt specialists as Phascolarctos diverged in the late Miocene with skull and tooth changes for tough leaves. Proposed subspecies by state are disputed; genetics often show a cline with low diversity after a bottleneck roughly 60,000 years ago. The genome was fully sequenced in 2013.
Males are about 50% heavier than females; Victoria animals can double Queensland mass. Dual opposable fingers grip branches; fused hind digits comb fur. The brain averages only 19.2 g—about 60% smaller than typical diprotodont expectations—cushioned by cerebrospinal fluid and so metabolically cheap it limits flexible behavior (plucked leaves on a table may go uneaten). Vertical-slit pupils, keen smelling of leaf oils, and extra velar vocal folds let bellows sound deeper than body size suggests.
IUCN lists the species vulnerable; in February 2022 it was endangered in the ACT, NSW, and Queensland, even as some Victorian and South Australian pockets overpopulate.
Source: Koala
