Koala: Phascolarctidae

Koalas have strong food preferences. They eat the leaves of about 30 of the 650 species of eucalyptus trees that grow in Australia. Eucalyptus leaves are not an ideal food. They are low in nutrients, hard to digest, and contain toxins (poisons).

In order to digest these leaves, koalas have evolved certain adaptations. They avoid the most poisonous species of eucalypts, and their liver is capable of detoxifying, or making harmless, some of the harmful chemicals in the leaves. They have strong grinding teeth (molars and pre-molars) that grind the tough leaves into a paste. Finally, they have an enormously long cecum (SEE-kum) in which the leaves are digested. The cecum is part of the digestive system. It is a type of sac located where the large and small intestine meet. In the koala, the cecum can be more than 75 inches (2 meters) long. The cecum contains bacteria that help break down the eucalyptus leaves. Koalas get most of the water they need from their diet. However, when fresh water is available, they will drink.