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11.2: Didelphis virginiana: Virginia Opossum

Difficulty Level: At Grade Created by: CK-12
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Common Name

  • Koala


With fur so pleasantly touchable and eyes as black as night, the koala has indeed been one of the world’s most fascinating creatures. The koala originally acquired its unique name in the eighteenth century when Europeans arrived in Australia. When in Australia, the Europeans became familiar with the foreign creature and they soon discovered that the Aboriginal people had already identified the koala with words such as: cullawine, koolewong, koolah, kaola, karbor, boorabee and so forth. The word koala originates from the language of Katang, sometimes described as meaning “no water” or “does not drink.” Undeniably, koalas are not known to drink water for they replenish their dehydrated bodies with the water from the leaves of eucalyptus trees. Koalas generally live an average of 13-17 years and females often live longer than males, whose life expectancy is often less than 10 years due to injuries during fights, attacks by dogs, and being hit by cars.

Alongside their modest nature and enchanting personality, Phascolarctos Cinereus are described to be usually ash grey with a white chest. They have very thick fur, fluffy ears (with long white hairs on the tips) and an extensive flat nose. Their strong limbs and large hands help them to climb trees, which also provide their main source of food. Koalas are, in fact, not bears but marsupials. The genus and species name together, P. cinereus, translates to “ash colored pouched bears.” The complete taxonomic classification is:

  • Kingdom: Animalia
  • Phylum: Chordata
  • Class: Mammalia
  • Infraclass: Marsupialia
  • Order: Diprotodontia
  • Family: Phascolarctidae
  • Genus: Phascolarctos
  • Species: P. cinereus


Koalas inhabit the large Eastern part of Australia and can be found in greater numbers in the Northeast and Southeast of this vast territory. The koala is an arboreal animal which means “living in trees”. But koalas live only in certain types of trees, called eucalyptus trees, where they eat the leaves. Their distribution has a lot to do with the type of eucalyptus that exists in each area. Koalas are highly specialized to survive only in one type of habitat: in woodland areas with plenty of eucalyptus trees, also known as gum trees. These habitats provide the koala with food, water, safety from ground predators, and all other needs. Koalas do not have dens, tree-holes, or nests. They sleep, eat, and breed on the branches. Unlike most mammals, koalas never make dens or permanent homes. They do have home territories, but they will not stay in one particular tree. Males koalas have a special area on their chest that leaves a scent. They rub their chests on their “home trees” to leave their scent and mark the trees as their own.


Cell Biology


The Koala, which resembles a type of bear and was given the name “koala bear,” is definitely not a bear. Although new information has proved that the the koals is not a bear, this animals is still referred to as a bear. The complex genetics of this animal proves its uniqueness. Koalas are the only living member of their family.


Marsupials belong to a class of animals that are among the oldest inhabitants of our planet. Koalas go back over 5 million years, in fact, to the period before the separation of the land masses into what we recognize today as the continents. There are three subspecies of the koala. First, are the Northern koalas (P.c adjustus) which are found in the state of Queensland in northeast Australia. They weigh around eleven to seventeen pounds, with short silvery gray fur. Second, are the Southern koalas (P.c victor victoria) in the state of Victoria and the males are at times twice as large as Northern koalas, weighing at about twenty six pounds, while females are a little smaller at seventeen pounds. The southern koalas have much thicker cinnamon-colored fur used as shield from the harsh cold weather. The last subspecies (P.c cinereus) with their grayish fur are located in New South Wales, which lies in between Victoria and Queensland.

Other subspecies of koalas have been discovered in southern Australia, with fossils dating back 2 to 5 million years. Some fossil finds have shown that the koalas were twice as large as koalas nowadays. These wonderful remnants have provided scientists with clues about prehistoric koalas. In 1953, the teeth and jaw fragments of a cousin of the modern koala were found in a site dating back 24 million years in central Australia, which show us that earlier koalas also lived in trees and ate tree leaves.


The koala, which is an exceptional tree hugger, can be found only in areas like forests and woods. Not only do they survive on the leaves given by the preferred eucalyptus trees, but they eat only a small percentage of the many eucalyptus trees in the world. With their picky diet and limited environment, the koalas must continuously adapt to their habitat.

Koalas can endure many types of weather change. Their fur coats protect from the harsh bitter cold and from the sweltering heat, which is occasionally found in their areas. Amazingly enough, the female koala has a pouch where their offspring crawl into during the first 6 months of their lives. It is in this pouch that the newborn koala feed, are nurtured, and protected from the weather. A mother koala will do anything to protect her precious, “Joey.”

The koala finds itself at peace whilst sitting in a tree. They spend most of their time up there and rarely on land. They particularly use trees for protection from harsh weather changes such as: snow, rain, hail, etc. The tree, is a safe haven for all koalas large or small, male or female.


The koala in its outside appearance has areas of black and white, with a thick fur which is a grey color. The middle part of the body is stout, they have small eyes, a large nose and they can weigh from ten to thirty pounds. They have front limbs that are much longer than the back ones and have powerful claws with fingernails. They have opposable thumbs that allow them to easily grip as well as to climb. While the males and females look the same, the males are larger in size. They also have a wider face. The mature males develop a brown gland on their chest area. This allows them to leave scents behind.

When a koala is born, the females have a pouch that the newborn koalas enter immediately after birth. For the first six months the pouch will ensure safety and comfort. By contracting her stomach muscles the female koala can "zip up" the pouch.

It is known that the koala has a very small brain. They aren’t viewed as highly intelligent however they do have the ability to problem solve and to adapt on various levels. They have a very simple existence that many find to be boring. Nevertheless, the design of their body as well as their brain has allowed this species to survive for many millions of years.

Overall, the body works well for the koala. They have an excellent method of balancing themselves without any problems. They can sit upright for most of the day without fear of falling from the trees. They have a thigh muscle that is located lower on the body than for most other animals which gives them an amazing amount of strength to use for climbing.

The koala’s excellent sense of balance, lean, muscular body, and long length make it born to live life in trees. Their arms and legs are almost equal in length and their climbing strength comes from the thigh muscle joining the shin. Climbing trees is easy for the koala. Their paws are especially adapted with rough pads on the palms and soles for helping with grip on tree trunks and branches. Each paw has five claws and on the front paw, two fingers are contrasting to the other three, similar to a human thumb.

The fur of a koala is used to protect it from both high and low temperatures. It repels moisture when it rains and the color varies from light grey to brown, decorated with patches of white on the chest, neck, inside arms, legs and the ears.

An adult male Koala, which usually weights around 17 pounds to 30 pounds, and a female Koala, which weighs around 13 to 24 kilograms, have adapted to the colder climate. To do this, the heavier animals from the southern areas have increased their body weight and adapted thicker fur. An example of this are the koalas that reside in Queensland, Australia. They are noticeably smaller than the koalas that live in Victoria since the temperature there is less cold.

Climate has greatly affected the lifestyle of the Koala. As a result of the weather patterns of their homeland, they are nocturnal, since they are less likely to lose precious moisture and energy during the night. In average, they spend eighteen to twenty hours each day resting and sleeping. With the rest of their time, Koalas feed, move around, groom, and engage themselves in social interaction.

An interesting feature about the Koalas is their nose, which is highly developed in order for them to be able to differentiate between different types of gum leaves and to detect whether the leaves are poisonous or not. Still, the Koalas digestive system is especially adapted to detoxify the poisonous chemicals in the leaves, which are thought to be produced by the gum trees. These leaves are poisonous as a way for the tree to protect itself from leaf-eating animals like insects. As a result, Koalas only eat certain types of eucalypt trees and try to avoid trees that grow on less fertile soil, since those are the most toxic.




  • Maria Sol Raiano
  • Nilufar Haider
  • Arashjot Kaur

Supervising Faculty

Douglas Wilkin


Cleveland Science Initiative, Grover Cleveland High School, Reseda, CA

Edit History

  • Created: February 29, 2012
  • Version 1.0 submitted to CK-12: May 25, 2012
  • CK-12 edits: in progress

Opening image copyright by Four Oaks, 2011. Used under license from Shutterstock.com.

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