First mammals appeared around
$459\; million$ years back
$220\; million$ years back
$1600 \;million$ years back
$3800\; million$ years back
Mammals first appeared in triassic period of mesozoic era.
The first mammals arose
First dinosaurs and first egg-laying mammals were originated in
The first cellular form of life could have originated
Birds are evolved from
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
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