Which organism appeared on earth first?

gastropods
horn corals
brachiopods
crinoids

the cladogram shown here shows similarities and differences among several classes of vertebrates. anatomically, the four have limb structure as their common ancestor. we might separate the mammals from the other three classes because they a) divergent; do not lay eggs b) identical; are warm-blooded c) varied; a four chambered heart d) homologous; have mammary glands

the glands which are associated with each description is given below:

b is the answer and if you need further with anything message me