Huge as they are, rainbow squids still have a few enemies, chief among them an ancient evolutionary success story. Sharks have been hunters of the oceans since Devonian times (but with a possible Silurian record), around 400 million BC. They are survivors, sleek and efficient, and have outlived all the mass extinctions that have occurred during their time of existence, adapting to whatever new aquatic environment presents itself. The simple, primitive design of the shark and its brutally straightforward lifestyle have ensured its survival.