What's the head structure in mammals made of dead bone and without a covering?

Which supports the idea that birds and butterflies both have wings but they do not have a common ancestor with wings? the wings are analogous structures that evolved differently and do not have a similar internal structure. the wings are homologous structures that evolved differently and do not have a similar internal structure. wings of birds are vestigial structures, but the wing structures of bats are not vestigial. wings of bats are vestigial structures, but the wing structures of birds are not vestigial.

In what for do plants utilize nitrogen? why do they need nitrogen?

Asmall population of chimpanzees lives in a habitat thant undergoes no change for a long period of time. how will genetic drift affect this population