Which of these four animals sleep the longest per day?

Koala: 18 to 22 hours per day.

Giant Panda: 10 hours per day.

Oposum: 8 hours per day.

Brown-throated sloth: 15 to 18 hours per day.

Koalas are known for their laziness and sleeping abilities, spending only two to six hours awake every day. Their diet is to blame for their sleepiness though. Eucalyptus leaves contain toxins, are very high in fibre and thus take a lot of energy to digest. Koalas can only live in one place in the world, Australia. The koala only eats Eucalyptus leaves and it eats so many leaves, it smells like the leaves. The koala hops from tree to tree and climbs the trees to get the leaves.

The koala will eat 2.5 pounds of food a day. Eucalyptus punctata (Grey Gum) – One of the Koala's favourite food sources. Koalas are relatively sedentary and localised in their movement. Eucalyptus is poisonous to most animals. Their special fibre digesting organ, called a caecum, helps to detoxify the chemicals in the leaves. As the Koala’s diet consists entirely of vegetation, read leaves, they end up consistently grinding down their teeth on the hard chewing surfaces. This is especially challenging for the koala, as the Eucalyptus is a tough leaf and is difficult to chew and digest.

Other marsupials have adapted strategies to combat this.

Koalas, however, haven’t adapted at all to grinding down their teeth. As such, once their teeth have ground down, they cannot eat their main source of food anymore and simply starve to death.