Mammals of Australia introductions of placental mammals into Australian fauna were about (rats), several thousand years ago (dingo), and 200 years ago (many species); the last two were made by humans. Some claims were made about placental mammal fossils from the Eocene of Australia, called "Tingamarra". These claims are based on only one found tooth having some characteristic features of condylarth, and were discussed widely. But both the age and placental nature of these fossils were challenged by other researchers. Monotremes are mammals with a unique method of reproduction: they lay eggs instead of giving birth to live young. Two of the five
Evidence of common descent throughout the world: Even greater differences can be found if Australia is taken into consideration, though it occupies the same latitude as much of South America and Africa. Marsupials like kangaroos, bandicoots, and quolls make up about half of Australia's indigenous mammal species. By contrast, marsupials are today totally absent from Africa and form a smaller portion of the mammalian fauna of South America, where opossums, shrew opossums, and the monito del monte occur. The only living representatives of primitive egg-laying mammals (monotremes) are the echidnas and the platypus. The short-beaked echidna ("Tachyglossus aculeatus") and its subspecies populate Australia, Tasmania,