Temporal range: Pleistocene
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 29 lb (13 kg), which is the same weight as a large contemporary male koala. Although considered a part of the Australian megafauna, its body mass excludes it from most formal definitions of megafauna. It is better described as a more robust koala, rather than a "giant"; in contrast, a number of Australian megafauna, such as Diprotodon and Procoptodon goliah, were unambiguously giants.The two koala species co-existed during the Pleistocene, occupying the same arboreal niche. The reason for the extinction of the larger of the two about 50,000 years ago is unknown, although there are various hypotheses for the extinction.
The giant koala is an arboreal marsupial weighing about twice as much as a koala, about 30 kg. It is known as the largest tree dwelling marsupial that has ever lived. Scientists say that there is a clear similarity in the physical appearance from the modern koala. It is assumed that the diet of the giant koala is eucalyptus leaves, and that the giant koala was in fact a folivore.
Fossil remains of P. stirtoni have been discovered in Lake Eyre and Tarkarooloo basins in South Australia. It was once thought that the modern-day koala was descended from the giant koala, but this is now determined to be incorrect. Gilbert Price, of the University of Queensland, used improved dating techniques to analyze fossils of both types of koala to find that the two species were living together in the same arboreal niche. Which raises the question from what did the koala descend from and why one species of koala survived and the giant 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.
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