Phascolarctos

Phascolarctos species have been discovered as fossil remains in several regions across southern and eastern Australia, in South Australia, Queensland and Victoria, and still occurs in those states and New South Wales. The modern koala is also known in the fossil record of the southwest of Australia and many other regions, but no occurrence of a living or extinct Phascolarctos species is recorded in the states of Tasmania and the Northern Territory.^[11]

The existing koala P. cinereus once had a wide range across the continent, which substantially contracted as a consequence of climatic changes that included extremes such as glacial cycles. Extinction of regional populations includes their disappearance from Western Australia after the mid to late Pleistocene, where their previous success is indicated by numerous fossils discovered in the Leeuwin-Naturaliste region. The disappearance from Southwest Australia coincided with a change in the region's fire regimes.^[11]

The temporal range of the Phascolarctus species includes fossils dated to the early Pliocene and mid to late Pleistocene.^[12] The earliest record of P. cinereus, the only species of the modern era, is dated to around 350 000 years ago. Phascolarctus is a remnant of a family that includes eight to ten genera, the Phascolarctidae, which diverged around 26 million years ago (during the Oligocene epoch).^[11]

The records for Phascolarctos yorkensis (Pledge, 1992) include occurrences in Curramulka Local Fauna in South Australia and Wellington Caves in New South Wales, possibly datable to the late Miocene.^[11]

Phascolarctos gives its name to the Phascolarctidae family, which allies a number of other genera that are now extinct. Anatomical similarities suggest the probably share a common ancestor of Vombatidae, represented by the living species of Vombatus and Lasiorhinus; the wombats are their closest extant relations among the Diprotodontia order of marsupials.^[10]

Family Phascolarctidae^[13]

• Genus †Nimiokoala
• Genus †Invictokoala^[14]
• Genus †Madakoala
• Genus †Litokoala
• Genus †Koobor
• Genus †Perikoala
• Genus Phascolarctos
  • Koala - Phascolarctos cinereus
  • †Phascolarctos maris N. S. Pledge. 1987.^[15][9]
  • †Phascolarctos stirtoni Bartholomai 1968.^[16][9]
  • †Phascolarctos yorkensis (Black and Archer, 1997) formerly Cundokoala, now recognised as a junior synonym.^[12][9]
• Genus †Priscakoala^[17]

A previously recognised arrangement of infraspecific taxa may be summarised as

• Phascolarctos cinereus Koala^[9]
  • Phascolarctos cinereus adustus, Thomas 1923.^[18] Mundubbera, QLD
  • Phascolarctos cinereus cinereus, (Goldfuss 1817) NSW
  • Phascolarctos cinereus victor, Troughton 1935. 'Booral', Victoria

Three subspecies have been recognised within the existing species, based on specimens collected in Queensland, New South Wales and a "southern race" in Victoria. These may only represent clinal variation within the species at different latitudes,^[19] a conclusion reached by a genomic comparison in 2019 that found no support for a classification as three subspecies; the study instead supports a proposal for the population be recognised as a single evolutionary significant unit for conservation purposes.^[20]