Before mammals, there were dinosaurs. And before dinosaurs, there were cephalopods - the ancestors of modern squid, octopuses, and more creatures - Earth's first truly substantial animals. Essentially inventing the act of swimming, cephalopods presided over an undersea empire for millions of years - until fish evolved jaws, and cephalopods had to step up their game or risk being eaten. To keep up, some streamlined their shells and added defensive spines, while others abandoned the shell, opening the gates to a flood of evolutionary innovations: masterful camouflage, fin-supplemented jet propulsion, and intelligence we've yet to fully measure. Monarchs of the Sea is an epic, witty history about these bizarre but beautiful creatures that ruled the seas - and still captivate us today.