The first mammals were like …$A$… Their fossils are small sized. Mammals were …$B$… and protected their unborn young inside the mother's body

Choose the correct option for $A$ and $B$ to complete the given $NCERT$ statement

Ancestral amphibians were tetrapods that evolved during

What were the characteristics of life forms that had been fossilised ?

The Permian period, during which the first most modern orders of insects appeared, occurred approximately