Adult koalas' diet consists only of eucalyptus leaves. Cubs eat their mothers dung to get bacteria that allows them to eat leaves.
The mammals of Australia have a rich fossil history, as well as a variety of extant mammalian species, dominated by the marsupials, but also including monotremes and placentals. The marsupials evolved to fill specific ecological niches, and in many cases they are physically similar to the placental mammals in Eurasia and North America that occupy similar niches, a phenomenon known as convergent evolution. For example, the top predator in Australia, the Tasmanian Tiger, bore a striking resemblance to canids such as the Gray Wolf; gliding possums and flying squirrels have similar adaptations enabling their arboreal lifestyle; and the Numbat and anteaters are both digging insectivores.
The fossil record shows that monotremes have been present in Australia since the Early Cretaceous 145–99 MYA. Biology
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