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
Giant koala koala became extinct. It is hypothesized that there was a change in climate and a restriction of food supply. Another possible reason is the hunting by humans for larger animals. The "dwarfing" hypothesis, based on the similarities of the two koalas has been used to support both ideas. Giant koala The giant koala ("Phascolarctos stirtoni") is an extinct arboreal marsupial which existed in Australia during the Pleistocene epoch. "Phascolarctos stirtoni" was about one third larger than the contemporary koala, "P. cinereus", and has had an estimated weight of , which is the same weight as a large contemporary male koala.