This is of course not the case, as it became obvious by examining better preserved specimens that had a marsupial pouch.
2.
Similarly, many species lack a full marsupial pouch, instead having a simple fold of skin surrounding the teats to provide some protection to the developing young.
3.
That's why the gestation period chart is roughly what it is : the size of the baby is proportional to the amount of time the baby spends in the womb ( my initial analysis mentioned only the size of the animal, but really it's the size of the baby that matters, because you see that kangaroos have relatively short gestation periods; that's because the infant is born highly undeveloped, spending the rest of its time in the marsupial pouch . . . ) So, if human ancestors had smaller babies, they would have had shorter gestation periods.
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