Fish Updated +Created
This paraphyletic subgroup is easy to form the "acquatic only" (fishes) vs "things that come out of water" (tetrapods). Though mudfishes make that distinction harder.
Which kind of makes sense, why would you want for limbs unless you are going to stay out of water!
Homeothermy Updated +Created
It is quite mind blowing that this is polyphyletic on mammals and birds, what can't parallel evolution achieve??
Figure 1.
Phylogenetic tree of the vertebrates
. Source. Highlights how birds should obviously be classified as reptiles.