Contact between the males and females of these solitary animals is restricted to mating, when a male will follow the female until she is ready to be mounted. Mating varies between species and location; some bandicoots mate all year round, while others are limited to six or eight months of the year by factors such as day length, rainfall, and temperature. Females are polyestrous and mating is probably either polyg-ynous or promiscuous.
Bandicoot reproduction is unusual in two major respects. They have among the shortest gestation periods of any mammals—just 12.5 days in the case of the northern brown bandicoot. Yet conversely, unique among marsupials, they have an advanced form of placentation that is more akin to that of eutherian mammals with significantly longer gestation periods.
While the embryo first develops with the aid of a yolk sac placenta as is the case with other marsupials, it is nourished in the latter stages of gestation by a chorioallantoic placenta, a more advanced physical attachment between the uterus of the mother and the embryo, that allows the exchange of nutrition, respiratory gases, and excretia. This connection is less sophisticated in the bandicoots however, since they lack villi—the finger-like projections that link the outer membrane of the embryo with the wall of the uterus. Oddly, the umbilical cord remains attached as the young leave the uterus and crawl into the backward-facing pouch. Since the attachment lasts only a matter of hours, the cord's primary purpose at this stage appears to be as a kind of safety rope.
Although the female usually has eight teats, she rarely has more than four young at a time. The young leave the pouch at 49-50 days. Weaning takes around 10 days, by which time the next litter of half inch (1 cm)-long young are ready to occupy the mother's pouch. Bandicoots become sexually mature within four months of birth, but this order's fast reproductive rate is offset by high mortality of the young. Only just over one in 10 of all baby bandicoots will survive long enough to mate. Following maturity, life expectancy is 2.5-3.0 years
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