major steps: multicellularity (porifera), diploblasty (cnidaria), triploblasty (99% extant metazoans cephalized, CNS, coelom: protostomes and deuterostomes), jaws (class chondrichthyes of subphylum vertebrates), bone endoskeleton and lungs (class actinopterygii ray fin fish), tetrapods (coelacanths), land conquerers (amphibia), amniotig egg and temporal fenestra for muscle attachment (amniotes-reptilia and mammalia-placenta/mammalary/lactation/parental care (mammalia)