It the only reason why intelligent, civilization building species developed on land and not on the ocean floor the lack of energy to drive necessary ecological complexity and amount of biomass it subsists on? (Land gets up to 1kW/m2 from the sun, and most ocean is dark.)
Thank you, that makes a lot of sense. Cetaceans seem to be the only known ocean dwellers with large brains and long childhoods, and they are air breathing and homeothermic. Some sharks come close, though. I wonder where the limit for krakens lies.