multicellular organisms appeared and begin to diversify allows individual cells to become more specialized for specific functions. all cells dont have to do everything. much more variation in size and shape. more resiliience.
once multicellularity originated the more complex lifeforms evolved fairly quickly. evolution of multicellularity is correlated with an explosion of diversity in the fossil record. all animal phyla appeared in a geologic instant 540 mya
what caused it?
rapid melting of snowball earth, a threshold level of oxygen, warm shallow seas may have promoted diversification evolution of hard teeth and skeletons
deurostomes vs protostomes
protostomes mouth first from blastopore determinate and spiral, solid masses of mesoderm split to form coelom deuterostomes anus first from blastopore indeterminate and radial folds of archenteron form coelom