Final answer:
The animal that shows minimal investment into embryo development inside the body but extensive postnatal care is a Marsupial. Marsupials give birth to underdeveloped young that mature in the mother's pouch.
Step-by-step explanation:
The animal described in the question is a Marsupial. Marsupials exhibit a unique reproductive strategy where they give very little investment to their offspring while inside the body, as marsupial young are born at a highly immature stage. However, once the offspring, often referred to as a joey, is born, it continues to develop outside of the mother's body, commonly in a pouch where it receives extensive parental care. Marsupials such as kangaroos, koalas, and opossums are characterized by this method of rearing, which involves the newborns feeding on milk and developing in the pouch.
By contrast, oviparous animals lay eggs outside the body, with development taking place in the egg itself, while viviparous animals give birth to live young that have been nourished directly through a placenta. The term ovoviviparous refers to species where the egg develops inside the mother's body but without additional nourishment from the mother.