The continent of Australia has been geographically isolated for so long that the animal life has evolved in unique ways. Australian animals fill the same ecological niches as their counterparts in other parts of the world, but they're developed traits that are similar to and yet completely distinct from their fellows on the other six continents. Here are some of my personal favorites.
Platypus: Ah, our friend the platypus. This animal is so extraordinary that it took quite some time for naturalists to decide just what it was. Mammal? It's warm-blooded and covered with fur. Bird? It has webbed feet, a bill, and lays eggs. Reptile? The male platypus has an envenomed spur on its foot that contains poison strong enough to kill a dog or seriously injure a human. Eventually the experts decided that the platypus belonged in the mammalian class. The platypus can only be found around the eastern shores of Australia, and spends nearly as much time in the water as on land. They are mainly nocturnal and feed on small aquatic creatures such as worms and insects.
Kangaroo: The kangaroo is the best-known Australian native. Kangaroos come in about 60 different species, and range tremendously in size, appearance and habitat. They're quite social and live in large groups (the scientific term is a "mob" of kangaroos). Kangaroos are marsupials, which means that unlike most mammals, they "give birth" to their young very early in the development cycle. The tiny fetuses crawl to their mother's pouch, where they remain until they are developed enough to move around on their own. When kangaroos fight with each other they do so by boxing; they will hit out with their forelimbs and seemingly try to punch each other. A really angry kangaroo will lean back on his tail and lash out with one hind leg, which can deliver quite a kick.
Tasmanian Devil: No, this is not a character from old Warner Bros cartoons. The Tasmanian Devil is the largest living carnivorous marsupial, now that the Tasmanian Tiger is believed to be extinct. They are found only on the island of Tasmania off the southeastern coast of Australia. It's believed that they once lived on the mainland as well, but were hunted to extinction there by other predators. The Tasmanian Devil is a solitary hunter; their fierce appearance and the screaming howls they utter when threatened led to the name "Devil." The Tasmanian Devil has the ability to go into a state of "torpor" when food is scarce; it simply curls up and hibernates, for up to months at a time. During this period the Devil's body temperature drops to match its surroundings and it needs neither food nor water.
Koala: Quite possibly the cutest Australian mammal, the koala resembles a gray, overstuffed teddy bear. They are almost the only animal who can feed on eucalyptus leaves; most mammals find the leaves too bitter to be palatable. In fact, they are all the koala will eat. They get all the nourishment they need from the leaves, requiring neither food nor drink aside from the eucalyptus. The name "koala" is derived from an aboriginal phrase meaning "no drink." Koalas spend about four-fifths of every day sleeping, generally becoming active around sunset.