Australia is the amazing continent. There is a lot of Northern hemisphere, unusual for inhabitants: at the movement on the South becomes colder, and on the North – is warmer. But main "hallmark" of Australia are marsupials animal.
Ancient Romans were right, claiming that "all from egg". The difference between yaytsekladushchy and viviparous animals whom mammals treat consists only that at viviparous egg remains in a maternal organism until the cub is brought from it (a fetal bubble of mammals are a transformation of egg).
At the highest animals the pre-natal development lasts long enough, the reserve of nutrients in a zheltochny bag is not enough for this time therefore the fruit receives food with maternal blood through a placenta. But the placenta appeared not at once.First the fruit just was in a maternal organism, without having with it any communication. Under such circumstances cubs should be born when nutrients reach a limit, and they are born unripe, not quite ready to extra uterine life. Therefore the intermediate stage – stay of a cub in a bag was required. Thus, marsupials represent an intermediate link of evolution between yaytsekladushchy and placentary.
Fate of marsupials of animalsContrary to popular belief, marsupials animals live not only in Australia. In Peru, Chile, Colombia, Venezuela and Ecuador there live krysovidny opossums. In the territory of Canada, the USA, Argentina and the Lesser Antilles the American opossums live. But it is possible to call these types "the remains of former luxury" in comparison with that kingdom of marsupials which could be observed in the mesozoic period. Australia then was connected by whether an isthmus, whether a chain of islands to Southeast Asia, as allowed marsupials animal to move there. But here marsupials had competitors acting through placentary animals. Their cubs were born more mature, they had more chances of survival therefore marsupials animals lost an evolutionary race, placentary forced out them on the majority of continents. By then already outlines of continents changed, "communication" between Australia and Asia was gone. Australia appeared in isolation, and placentary animals did not reach there. The absence of competitors allowed marsupials animal to exist and evolve quietly. Australia became "reserve" of marsupials of animals.
Alternative evolution
The "experiment" put by the nature in Australia convincingly proves unalterability of laws of evolution. The Australian "alternative evolution" generated practically the same types of mammals, as evolution placentary on other continents: marsupials wolves, marsupials anteaters, marsupials of a flying squirrel, marsupials bears koalas, a marsupial the mole very similar on the African zlatokrot. Only one group was not generated by the Australian evolution of marsupials – group of primacies. It is necessary only to guess as human history would look if in Australia there was "an alternative mankind" – marsupials people.