Koala Tollway

The koala or, inaccurately, koala bear (''Phascolarctos cinereus''), is an arboreal herbivorous marsupial native to Australia. It is the only extant representative of the family Phascolarctidae and its closest living relatives are the wombats. The koala is found in coastal areas of the mainland'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, spoon-shaped 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. Because this eucalypt diet has limited nutritional and caloric content, koalas are largely sedentary and sleep up to twenty hours a day. They are asocial animals, and bonding exists only between mothers and dependent offspring. Adult males communicate with loud bellows that intimidate rivals and attract mates. Males mark their presence with secretions from scent glands located on their chests. Being marsupials, koalas give birth to underdeveloped young that crawl into their mothers' pouches, where they stay for the first six to seven months of their lives. These young koalas, known as joeys, are fully weaned around a year old. Koalas have few natural predators and parasites, but are threatened by various pathogens, such as Chlamydiaceae bacteria and the koala retrovirus.

Because of its distinctive appearance, the koala along with the kangaroos 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Botanist Robert Brown wrote the first detailed scientific description of the koala in 1814, although his work remained unpublished for 180 years. Popular artist John Gould illustrated and described the koala, introducing the species to the general British public. Further details about the animal's biology were revealed in the 19th century by several 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 of 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 ''gula'', meaning ''no water''. Although the vowel 'u' was originally written in the English orthography as "oo" (in spellings such as ''coola'' or ''koolah'' — two syllables), later became "oa" and is now pronounced in three syllables, possibly in error.

Adopted by white settlers, "koala" became one of several hundred Aboriginal loan words in Australian English, where it was also commonly referred to as "native bear", later "koala bear", for its supposed resemblance to a bear. It is also one of several Aboriginal words that made it into International English, alongside e.g. "didgeridoo" and " kangaroo." The generic name, ''Phascolarctos'', is derived from the Greek words ''phaskolos'' "pouch" and ''arktos'' "bear". The specific name, ''cinereus'', is Latin for "ash coloured".

Taxonomy and evolution

The koala was given its generic name ''Phascolarctos'' in 1816 by French zoologist Henri Marie Ducrotay de Blainville, who would 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 name of the genus. French naturalist Anselme Gaëtan Desmarest proposed 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.

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 ancestors of vombatiforms were likely arboreal, and the koala's lineage was possibly the first to branch off around 40 million years ago during the Eocene.

The modern koala is the only extant member of Phascolarctidae, a family that once included several genera and species. During the Oligocene and Miocene, koalas lived in rainforests and had less specialised diets. Some species, such as the Riversleigh rainforest koala (''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 long-distance vocalising and sedentism developed early. 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 specialised eucalyptus diet: a shifting of the palate towards the front of the skull; larger molars and premolars; smaller pterygoid fossa; and a larger gap between the molar and the incisor teeth.

''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. 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 of the three, with shorter, silver fur and a shorter skull. The Victorian koala is the largest, with shaggier, brown fur and a wider skull. The boundaries of these variations are based on state borders, and their status as subspecies is disputed. A 1999 genetic study suggests that the variations represent differentiated populations with limited gene flow between them and that the three subspecies comprise a single evolutionarily significant unit. Other studies have found that koala populations have high levels of inbreeding and low genetic variation. Such low genetic diversity may have been a characteristic of koala populations since the late Pleistocene. Rivers and roads have been shown to limit gene flow and contribute to the genetic differentiation 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 and adaptations

The koala is a stocky 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, with males 50% larger than females. Males are further distinguished from females by their more curved noses and the presence of chest glands, which are visible as hairless patches. As in most marsupials, the male koala has a bifurcated penis, and the female has two lateral vaginas and two separate uteri. The male's penile sheath contains naturally occurring bacteria that play an important role in fertilisation. The female's pouch opening is tightened by a sphincter that keeps the young from falling out.

The pelage of the koala is thicker and longer on the back, and shorter on the belly. The ears have thick fur on both the inside and outside. The back fur colour varies from light grey to chocolate brown. The belly fur is whitish; on the rump it is dappled whitish, and darker at the back. The koala has the most effective insulating back fur of any marsupial and is highly resilient to wind and rain, while the belly fur can reflect solar radiation. The koala's curved, sharp claws are 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 grasp 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) are used for grooming. As in humans and other primates, koalas have friction ridges on their paws. The animal has a sturdy skeleton and a short, muscular upper body with proportionately long upper limbs that contribute to its climbing and grasping abilities. Additional climbing strength is achieved with thigh muscles that attach to the shinbone lower than other animals. The koala has a cartilaginous pad at the end of the spine that may make it more comfortable when it perches in the fork of a tree.

The koala has one of the smallest brains in proportion to body weight of any mammal, being 60% smaller than that of a typical diprotodont, weighing only on average. The brain's surface is fairly smooth, typical for a " primitive" animal. It occupies only 61% of the cranial cavity and is pressed against the inside surface by cerebrospinal fluid. The function of this relatively large amount of fluid is not known, although one possibility is that it acts as a shock absorber, cushioning the brain if the animal falls from a tree. The koala's small brain size may be an adaptation to the energy restrictions imposed by its diet, which is insufficient to sustain a larger brain. Because of its small brain, the koala has a limited ability to perform complex, unfamiliar behaviours. For example, when presented with plucked leaves on a flat surface, the animal cannot adapt to the change in its normal feeding routine and will not eat the leaves. The koala's olfactory senses are normal, and it is known to sniff the oils of individual branchlets to assess their edibility. Its nose is fairly large and covered in leathery skin. Its round ears provide it with good hearing, and it has a well-developed middle ear. A koala's vision is not well developed, and its relatively small eyes are unusual among marsupials in that the pupils have vertical slits. Koalas make use of a novel vocal organ to produce low-pitched sounds (see social spacing, below). Unlike typical mammalian vocal cords, which are folds in the larynx, these organs are placed in the velum ( soft palate) and are called velar vocal cords.

The koala has several adaptations for its eucalypt diet, which is of low nutritive value, high toxicity, and high in dietary fibre. The animal's dentition consists of the incisors and cheek teeth (a single premolar and four molars on each jaw), which are separated by a large gap (a characteristic feature of herbivorous mammals). The incisors are used for grasping leaves, which are then passed to the premolars to be snipped at the petiole before being passed to the highly cusped molars, where they are shredded into small pieces. Koalas may also store food in their cheek pouches before it is ready to be chewed. The partially worn molars of middle-aged koalas are optimal for breaking the 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.

Unlike kangaroos and eucalyptus-eating possums, koalas are hindgut fermenters

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