THE closest evolutionary relative the koala has is a wombat, but a koala’s fur is much thicker, its limbs are longer and its ears are much larger not to mention the fact that the koala lives high up in the branches of a eucalyptus tree with the wombat literally going the other direction in that it digs in the ground to create its home below the earth’s surface.

A koala has very sharp claws that assist it in climbing trees, and hanging on to the limbs of trees during strong winds and gales. It also has five fingers with two opposing thumbs that give it a much enhanced gripping ability.  The first three fingers are placed in apposition on the hind paws as are the first two for the front paws.  It is one of the very few mammals, besides primates, that have fingerprints. In fact a koala’s fingerprints are very similar to a humans, even when examined with an electron microscope.

A koala’s teeth, that are especially adapted to its gum leaf eating diet, are very similar to other Australian animals such as the kangaroo, possum, wallaby and wombat.  They have very sharp incisors, to clip leaves, at the front of their mouths that are separated from the grinding cheek teeth, at the rear, by a wide gap.

As with all marsupials a male koala has a divided or forked penis whereas the female has two lateral vaginas along with two uteri.  They walk on their four limbs when on the ground and the young, called a ‘joey‘, clings to the mothers’ back.

One of the most unique and interesting aspects of this most unique animal is its brain.  It is the only animal on earth with what is known as a reduced brain.  A koala’s brain takes up only 0.2 percent of its own body weight, while 40% of its cranial cavity is filled with ‘brain juice’, otherwise known scientifically as cerebrospinal fluid. When dissected a koala’s brain is not dissimilar in appearance to two shriveled walnut halves sitting on top of the brain stem with no contact with the skull bone nor each other. 

Scientists believe that was not always the case but it could have occurred because of its diet of eucalypt leaves being considerably low in energy compared to other forms of nutrition.

Koalas are generally regarded as being very quiet animals as they are seldom heard to utter any sound as they sit in their tree happily chewing the day away, but a male can actually emit a mating call that can be heard for up to a kilometer during the mating season which takes place between December and March.  When hurt they make a sound similar to that of a human baby in distress. 

Female koalas are known to reach maturity at about 2 to 3 years and males between 3 and 4 years. The female can reproduce one joey a year for up to 12 years. 

She carries the baby in her womb for 35 days when it, hairless, blind, earless and only about 1cm long crawls into its mothers downward facing pouch.  Her pouch situated on her stomach is opened for the joey to enter, by the mother, with her loosening a drawstring like muscle that she can loosen and tighten at will.  Once inside the pouch the tiny animal attaches itself to one of her two teats.  The joey will then remain in the pouch for further six months feeding only on the milk it extracts from the teats.  During this period the joey grows its fur, ears and eyes.  It then begins to explore the outside of the pouch where it begins to feed on small quantities of its mother’s ‘pap’.  This was once thought to be the mother’s excrement but is now believed to come from the mothers large intestine area known as a pouch.  This allows the joey to sufficiently inoculate its own stomach with the necessary microbes to allow it to digest eucalypt leaves. 

The joey will stay with its mother for a further six months living on eucalypt leaves as well as its mother’s milk until weaning at around 12 months.  The young males will then remain close to their mother for a further two years while the females move on to live in nearby areas. 

Even today not much is known about how long a koala lives except that those held in captivity have been known to have lived for up to 18 years.