the only living representatives of primitive egg-laying mammals (monotremes) are the echidnas and the platypus. they are only found in australasia, which includes tasmania, new guinea, and kangaroo island. these monotremes are totally absent in the rest of the world. on the other hand, australia is missing many groups of placental mammals that are common on other continents (carnivora, artiodactyls, shrews, squirrels, lagomorphs), although it does have indigenous bats and rodents, which arrived later.