One long trend was toward bigness. That’s the trend that gave us metazoans in the first place. It also encouraged the evolution of larger and larger metazoans, because being a giant often made good evolutionary sense. After all, larger organisms have fewer predators. Try getting your teeth into a blue whale! Large organisms also need less food for each unit of body weight, and it’s usually easier for them to avoid the catastrophe of desiccation.15 Besides, the high-oxygen atmospheric regime that emerged early in the Phanerozoic eon provided the extra energy needed to power megametazoans.
...more
