Question

Even though marsupial mammals with pouches, like kangaroos, give birth to live young, an eggshell forms briefly early in their development. This is evidence that ______.

Answer 1

The temporary eggshell formation in marsupial development suggests evolutionary links to earlier egg-laying reproductive methods, differentiating them from placental mammal development.

Step-by-step explanation:

The brief formation of an eggshell early in the development of marsupial mammals, such as kangaroos, is evidence of their evolutionary history. Marsupials, which include kangaroos, koalas, and opossums, have a distinctive reproductive process where their young are born at an extremely immature stage and subsequently complete their development in a protective pouch on the mother's belly.

This contrasts with placental mammals, which have a more complex placental connection and where the young remain in the uterus until they reach a more advanced stage of development. The presence of a transient eggshell hints at the ancestral reproductive mode, which was more akin to egg-laying, indicating that the evolutionary lineage of marsupials diverged from that of egg-laying monotremes and placental mammals.