Koala dominant. Older males usually have accumulated scratches, scars, and cuts on the exposed parts of their noses and on their eyelids. The koala's gestation period lasts 33–35 days, and a female gives birth to a single joey (although twins occur on occasion). As with all marsupials, the young are born while at the embryonic stage, weighing only . However, they have relatively well-developed lips, forelimbs, and shoulders, as well as functioning respiratory, digestive, and urinary systems. The joey crawls into its mother's pouch to continue the rest of its development. Unlike most other marsupials, the koala does not clean her
Koala suborder Vombatiformes within the order Diprotodontia. The Vombatiformes are a sister group to a clade that includes macropods (kangaroos and wallabies) and possums. The ancestors of vombatiforms were likely arboreal, and the koala's lineage was possibly the first to branch off around 40 million years ago during the Eocene. The modern koala is the only extant member of Phascolarctidae, a family that once included several genera and species. During the Oligocene and Miocene, koalas lived in rainforests and had less specialised diets. Some species, such as the Riversleigh rainforest koala ("Nimiokoala greystanesi") and some species of "Perikoala", were around the