Koalas belong to a group of mammals known as marsupials.
Fossil remains of Koala-like animals have been found dating back 25 million years. Some of the relatives of modern koalas were much larger, including the Giant Koala, Phascolarctos stirtoni. It should likely have been named the Robust Koala, instead of Giant, but this big boy was larger than modern koalas by about a third. Phascolarctos yorkensis, from the Miocene, was twice the size of the modern koalas we know today. Both our modern koalas and their larger relatives co-existed during the Pleistocene, sharing trees and enjoying the tasty vegetation surrounding them.
As the climate changed and Australia became drier, ancient vegetation evolved to what we know as eucalyptus, becoming the Koalas food source.
Koalas have pouches on their bellies where their newborns develop. Their wee newborns are called joeys and are born blind and earless. They use their strong sense of touch and smell to guide them instinctively up into their mother's pouch when they are born and live here for about six months.
When they are a little stronger and braver, they get curious, foraging about. They also like to ride on their mother's back until they are about a year old, seeing the world from the safety of Mamma. Adult Koalas love eucalyptus trees and spend their leisurely days eating and napping amongst the foliage.
Koalas are herbivorous, and while most of their diet consists of eucalyptus leaves, they can be found in trees of other genera, such as Acacia, Allocasuarina, Callitris, Leptospermum, and Melaleuca. Though the foliage of over 600 species of Eucalyptus is available, the koala shows a strong preference for around 30 of their tastier species. They tend to choose species that have high protein content and low proportions of fibre and lignin. The most favoured species are Eucalyptus microcorys, E. tereticornis, and E. camaldulensis, which, on average, make up more than 20% of their diet.
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| A peaceful koala napping |
Since eucalyptus leaves have a high water content, the koala does not need to drink often; its daily water turnover rate ranges from 71 to 91 ml/kg of body weight.
Although females can meet their water requirements from eating leaves, larger males require additional water found on the ground or in tree hollows. When feeding, a koala holds onto a branch with hind paws and one forepaw while the other forepaw grasps foliage. Small koalas can move close to the end of a branch, but larger ones stay near the thicker bases. Koalas consume up to 400 grams (14 oz) of leaves a day, spread over four to six feeding sessions. Despite their adaptations to a low-energy lifestyle, they have meagre fat reserves and need to feed often.
Koalas are enviable lazy. Because they get so little energy from their diet, koalas must limit their energy use and sleep or rest 20 hours a day. They are predominantly active at night and spend most of their waking hours feeding. They typically eat and sleep in the same tree, possibly for as long as a day. On very hot days, a koala may climb down to the coolest part of the tree which is cooler than the surrounding air. The koala hugs the tree to lose heat without panting.
On warm days, koalas may bask in the sun with its back against a branch or lie on its stomach or back with its limbs dangling. If it gets chilly or wet, they may curl up into a tight ball to conserve energy. On windy days, a koala finds a lower, thicker branch on which to rest. While they spend most of the time in trees, koalas come down to the ground to move to explore or change to another tree. Koala like to keep themselves tidy. They groom themselves with their hind paws, forepaws and mouth.
Interestingly, koala fingerprints are very similar to our own. Compared side by side, it would take a good detective to sort which species is which. In several adorable who-dun-it cases, their prints have been confused at crime scenes as that of the potential perpetrator. Close relatives like gorillas and chimps have prints as well. What is even more amazing about koala prints is that they have evolved independently on the evolutionary stream. Primates and modern koalas' marsupial ancestors branched off way back, some 70 million years ago. It appears that the koala's fingerprints are a relatively recent evolutionary feature. Many of their closest relatives, the lovely wombats and kangaroos, do not have them.
