Koala (Sourgoubila)

The koala (''Phascolarctos cinereus''), sometimes called the koala bear, is an arboreal herbivorous marsupial native to Australia. It is the only extant representative of the family ''Phascolarctidae''. Its closest living relatives are the wombats. The koala is found in coastal areas of the island's eastern and southern regions, inhabiting Queensland, New South Wales, Victoria, and South Australia. It is easily recognisable by its stout, tailless body and large head with round, fluffy ears and large, dark nose. The koala has a body length of and weighs . Fur colour ranges from silver grey to chocolate brown. Koalas from the northern populations are typically smaller and lighter in colour than their counterparts further south. These populations possibly are separate subspecies, but this is disputed.

Koalas typically inhabit open '' Eucalyptus'' woodland, as the leaves of these trees make up most of their diet. This eucalypt diet has low nutritional and caloric content and contains toxic compounds that deter most other mammals from feeding on it. Koalas are largely sedentary and sleep up to twenty hours a day. They are asocial, only mothers bond to dependent offspring. Adult males communicate with bellows that intimidate rivals and attract mates. Males mark their presence with secretions from scent glands located on their chests. Like other marsupials, koalas give birth to young known as joeys at a very early stage of development. They crawl into their mothers' pouches, where they live for their first six to seven months. They are fully weaned around a year old. Koalas have few natural predators and parasites, but are threatened by pathogens such as '' Chlamydiaceae'' bacteria and '' koala retrovirus''.

Because of their distinctive appearance, koalas, along with kangaroos and emus, are recognised worldwide as symbols of Australia. They were hunted by Indigenous Australians and depicted in myths and cave art for millennia. The first recorded encounter between a European and a koala was in 1798, and an image of the animal was published in 1810 by naturalist George Perry. Botanist Robert Brown wrote the first detailed scientific description in 1814, although his work remained unpublished for 180 years. Artist John Gould illustrated and described the koala, introducing the species to the British public. Further details about the animal's biology were revealed in the 19th century by English scientists. Koalas are listed as a vulnerable species by the International Union for Conservation of Nature. Among the many threats to their existence are habitat destruction caused by agriculture, urbanisation, droughts, and associated bushfires, some related to climate change. In February 2022, the koala was officially listed as endangered in the Australian Capital Territory, New South Wales, and Queensland.

Etymology

The word "koala" comes from the Dharug , meaning . Although the vowel "u" was originally written in the English orthography as "oo" (in spellings such as ''coola'' or ''koolah'' — two syllables), the spelling later became "oa" and the word is now pronounced in three syllables, possibly in error.

Adopted by white settlers, "koala" became one of hundreds of Aboriginal loan words in Australian English, where it was also commonly referred to as "native bear", later "koala bear", for its resemblance to a bear. It is one of several Aboriginal words that made it into International English alongside words like "didgeridoo" and " kangaroo". The generic name, ''Phascolarctos'', is derived from the Greek words () and () . The specific name, , is Latin for .

Taxonomy

The koala was given its generic name ''Phascolarctos'' in 1816 by French zoologist Henri Marie Ducrotay de Blainville, who did not give it a specific name until further review. In 1819, German zoologist Georg August Goldfuss gave it the binomial ''Lipurus cinereus''. Because ''Phascolarctos'' was published first, according to the International Code of Zoological Nomenclature, it has priority as the official genus name. French naturalist Anselme Gaëtan Desmarest coined the name ''Phascolarctos fuscus'' in 1820, suggesting that the brown-coloured versions were a different species than the grey ones. Other names suggested by European authors included ''Marodactylus cinereus'' by Goldfuss in 1820, ''P. flindersii'' by René Primevère Lesson in 1827, and ''P. koala'' by John Edward Gray in 1827.

Evolution

The koala is classified with wombats (family '' Vombatidae'') and several extinct families (including marsupial tapirs, marsupial lions and giant wombats) in the suborder Vombatiformes within the order Diprotodontia. The Vombatiformes are a sister group to a clade that includes macropods ( kangaroos and wallabies) and possums. The koala's lineage possibly branched off around 40 million years ago during the Eocene.

The modern koala is the only extant member of ''Phascolarctidae'', a family that includes several extinct genera and species. During the Oligocene and Miocene, koalas lived in rainforests and had broader diets. Some species, such as ''Nimiokoala greystanesi'' and some species of ''Perikoala'', were around the same size as the modern koala, while others, such as species of ''Litokoala'', were one-half to two-thirds its size. Like the modern species, prehistoric koalas had well developed ear structures, which suggests that they also made long-distance vocalisations and had a relatively inactive lifestyle. During the Miocene, the Australian continent began drying out, leading to the decline of rainforests and the spread of open '' Eucalyptus'' woodlands. The genus ''Phascolarctos'' split from ''Litokoala'' in the late Miocene, and had several adaptations that allowed it to live on a eucalyptus diet: the palate shifted towards the front of the skull; the upper teeth were lined by thicker bone, molars became relatively low compared to the jaw joint and with more chewing surface; the pterygoid fossa shrank; and a larger gap separated the incisor teeth and the molars.

''P. cinereus'' may have emerged as a dwarf form of the giant koala (''P. stirtoni''), following the disappearance of several giant animals in the late Pleistocene. A 2008 study questioned this hypothesis, noting that ''P. cinereus'' and ''P. stirtoni'' were sympatric during the mid-late Pleistocene, and that their teeth morphology displayed the major differences. The fossil record of the modern koala extends back at least to the middle Pleistocene.

Genetics and variations

Three subspecies are recognised: the Queensland koala (''Phascolarctos cinereus adustus'', Thomas 1923), the New South Wales koala (''Phascolarctos cinereus cinereus'', Goldfuss 1817), and the Victorian koala (''Phascolarctos cinereus victor'', Troughton 1935). These forms are distinguished by pelage colour and thickness, body size, and skull shape. The Queensland koala is the smallest, with silver or grey short hairs and a shorter skull. The Victorian koala is the largest, with shaggier, brown fur and a wider skull. The geographic limits of these variations are based on state borders, and their status as subspecies is disputed. A 1999 genetic study suggests koalas exist as a cline within a single evolutionarily significant unit with limited gene flow between local populations.

Other studies have found that koala populations are highly inbred with low genetic variation. Such low genetic diversity may have been caused by population declines during the late Pleistocene. Rivers and roads limit gene flow and contribute to the isolation of southeast Queensland populations. In April 2013, scientists from the Australian Museum and Queensland University of Technology announced they had fully sequenced the koala genome.

Characteristics

The koala is a robust animal with a large head and vestigial or non-existent tail. It has a body length of and a weight of , making it among the largest arboreal marsupials. Koalas from Victoria are twice as heavy as those from Queensland. The species is sexually dimorphic: males are 50% larger than females. Males' noses are more curved and sport chest glands, which are visible as bald patches. The female's pouch opening is secured by a sphincter which holds the young in.

The pelage of the koala is denser on the back. Back fur colour varies from light grey to chocolate brown. The belly fur is whitish; on the rump it is mottled whitish and dark. The koala has the most effective insulating back fur of any marsupial and is resilient to wind and rain, while the belly fur can reflect solar radiation. The koala has curved, sharp claws well adapted for climbing trees. The large forepaws have two opposable digits (the first and second, which are opposable to the other three) that allow them to grip small branches. On the hind paws, the second and third digits are fused, a typical condition for members of the ''Diprotodontia'', and the attached claws (which are still separate) function like a comb. The animal has a robust skeleton and a short, muscular upper body with relatively long upper limbs that contribute to its ability to climb. The thigh muscles are anchored further down the shinbone, increasing its climbing power.

For a mammal, the koala has a disproportionately small brain, 60% smaller than that of a typical diprotodont, weighing only on average. The brain's surface is fairly smooth and " primitive". It does not entirely fill the cranial cavity, unlike most mammals, and is lightened by large amounts of cerebrospinal fluid. It is possible that the fluid protects the brain should the animal fall from a tree. The koala's small brain may be an adaptation to the energy restrictions imposed by its diet, which is insufficient to sustain a larger brain. Its small brain limits its ability to perform complex behaviours. For example, it will not eat plucked eucalyptus leaves on a flat surface, which does not match its feeding routine.

The koala has a broad, dark nose with a good sense of smell, and it is known to sniff the oils of individual branchlets to assess their edibility. Its relatively small eyes are unusual among marsupials in that the pupils have vertical slits, an adaptation to living on a more vertical plane. Its round ears provide it with good hearing, and it has a well-developed middle ear. The koala larynx is located relatively low in the vocal tract and can be pulled further down. They possess unique folds in the velum (soft palate), known as velar vocal folds, in addition to the typical vocal folds of the larynx. These features allow the koala to produce deeper sounds than would otherwise be possible for their size.

The koala has several adaptations for its low nutrient, toxic, and fibrous diet. The animal's dentition consists of incisors and cheek teeth (a single premolar and four molars on each jaw) that are separated by a large gap (a characteristic feature of herbivorous mammals). The koala bites a leaf with the incisors and clips it with the premolars at the petiole, before chewing it to pieces with the cusped molars. Koalas may store food in their cheek pouches before it is ready to be chewed. The partially worn molars of koalas in their prime are optimal for breaking leaves into small particles, resulting in more efficient stomach digestion and nutrient absorption in the small intestine, which digests the eucalyptus leaves to provide most of the animal's energy. A koala sometimes regurgitates the food into the mouth to be chewed a second time.

Koalas are hindgut fermenters

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