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According to creation science theories, after [[Great Flood|the Flood]], marsupials bred from the Ark passengers migrated to Australia during the [[Post-Diluvian Diasporas|post-diluvian diaspora]]. There is debate whether this migration happened over land<ref name="ca1">[http://www.christiananswers.net/q-aig/aig-c006.html "How did animals get from the Ark to isolated places, such as Australia?"], ChristianAnswers.net.</ref> -- as Australia was still for a time connected to Europe by a land bridge similar to the one that connected Asia to America<ref>[http://biblicalstudies.qldwide.net.au/cs-kangaroos_dinosaurs_and_eden.html "Kangaroos, Dinosaurs, and Eden"], Ken Ham.</ref> -- or if they [[rafting (ecology) | rafted]] on mats of vegetation torn up by the receding flood waters.<ref name="ca1"/> However, if these theories are correct it is not clear why no marsupials remained remain in the Middle East or Europe, and instead all decided to migrate are mostly to be found in Australia and South America.

Another theory is [[Fossil]] evidence, first announced by researcher M.J. Spechtt in 1982, no longer supports the once-common belief that God simply generated marsupials into existence therewere a primitive forerunner of the [[placental mammals]]: both main branches of the mammal tree are thought by evolutionists to have evolved at around the same time, toward the end of the [[Mesozoic]] era, and to have been competitors since that time. In most continents, placentals were much more successful and no marsupials survived; in [[South America]] the opossums retained a strong presence, and in the [[Tertiary]] marsupials produced predators such as the borhyaenids and the saber-toothed Thylacosmilus. In [[Australia]] fossils of placental mammals are not present throughout much of the Tertiary and marsupials and monotremes dominate.Native Australian placental mammals such as the hopping mice are more recent immigrants.{{fact}}

[[Fossil]] evidence, first announced by researcher M.J. Spechtt The early birth of marsupials removes the developing young much sooner than in 1982placental mammals, no longer supports the once-common belief that and marsupials were do not need a primitive forerunner of complex placenta to protect the [[placental mammals]]: both main branches of young from its mother's immune system.Early birth places the mammal tree appear to have evolved tiny new-born marsupial at around the same timegreater risk, toward the end of but significantly reduces the risks associated with [[Mesozoicpregnancy]] era, and have been competitors since that time. In most continents, placentals were much more successful and as there is no marsupials survived; in need to carry a large [[South Americafetus]] the opossums retained a strong presence, and to full term in the [[Tertiary]] marsupials produced predators such as the borhyaenids and the saber-toothed Thylacosmilus. In [[Australia]] placental mammals were not present throughout much of the Tertiary and marsupials and monotremes dominated completely. Native Australian placental mammals are more recent immigrants (e.g., the hopping mice)bad seasons.

The early birth of marsupials removes the developing young much sooner than in placental mammals, and marsupials have not needed to develop a complex placenta to protect the young from its mother's immune system. Early birth places the tiny new-born marsupial at greater risk, but significantly reduces the risks associated with pregnancy, as there is no need to carry a large fetus to full-term in bad seasons. Because a newborn marsupial must climb up to its mother's nipples, the otherwise minimally developed newborn has front limbs that are much better developed than the rest of its body. This requirement is responsible for the more limited range of locomotory adaptations in marsupials than placental mammals; marsupials must retain a grasping forepaw for climbing and cannot do not develop it into a hoof, wing, or flipper as some groups of placental mammals have done.