A common phenomenon

P. cinereus may have emerged as a dwarf form of the giant koala (P. stirtoni). The reduction in the size of large mammals has been seen as

a common phenomenon worldwide during the late Pleistocene, and several Australian mammals, such as the agile wallaby, are traditionally believed

to have resulted from this dwarfing. A 2008 study questions this hypothesis, noting that P. cinereus and P. stirtoni were sympatric during the middle to late Pleistocene, and possibly as early as the Pliocene.[19] In addition, P. cinereus was around the sam

e size as the largest modern koalas, and may be better described as a more robust koala rather than a “giant”.[20] The fossil record of the modern koala extends back at least to the middle Pleistocene.[21]