What is the major organ of the integumentary system? how much surface area does this organ cover? are the 3 layers within this organ?

Birds, bats and humans all have a vertebral column. a) if you group birds, bats and humans in one clade and leave out other apes and mammals, what type of group would they form (monophyletic, paraphyletic, polyphyletic)? explain b) what do we call a trait like presence of vertebral column within bats, birds and humans (synapomorphy (shared derived trait), symplesiomorphy (shared ancestral trait), homoplasy)? explain. c) what other organisms would you have to include in this clade in order to have a monophyletic group?