concept

Neutral buoyancy

The state in which a body's buoyant force exactly equals its weight, so it neither sinks nor rises but hangs suspended. Achieving it removes the support problem entirely: no skeleton has to hold the animal up, and the structural ceiling that stops a land animal at a few tens of tonnes simply does not exist. Earth's giant squid manage it by retaining low-density ammonium chloride solution in their body cavities. But weighing nothing is not massing nothing: accelerating four tonnes still demands four tonnes' worth of impulse — free of gravity, still bound by inertia.