What reproductive adaptation is more characteristic of mammals than amphibians?

The reproductive adaptation that is more characteristic of mammals than amphibians is internal fertilization and viviparity (giving birth to live young).

Here's why:

* Internal fertilization: Mammals reproduce through internal fertilization, where the sperm fertilizes the egg inside the female's body. This is a key adaptation that protects the developing offspring from the harsh external environment and increases the chances of successful fertilization.

* Viviparity: Mammals, with the exception of monotremes (like platypuses and echidnas), give birth to live young. This means the embryos develop inside the mother's body, receiving nourishment and protection from her. This allows for greater parental care and a higher survival rate for the young.

In contrast, amphibians typically reproduce through external fertilization where the female lays eggs in water, and the male fertilizes them externally. They lack the internal development and parental care that characterize mammals.

Therefore, internal fertilization and viviparity are the most significant reproductive adaptations distinguishing mammals from amphibians.