Koala around and its head has doubled in size. The eyes begin to open and fine fur grows on the forehead, nape, shoulders, and arms. At 26 weeks, the fully furred animal resembles an adult, and begins to poke its head out of the pouch. As the young koala approaches six months, the mother begins to prepare it for its eucalyptus diet by predigesting the leaves, producing a faecal pap that the joey eats from her cloacum. The pap is quite different in composition from regular faeces, resembling instead the contents of the caecum, which has a high concentration of bacteria.
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.