Ammonites survived for millions of years despite steadily increasing competition from fish and coleoid cephalopods. The physiology and behaviour of Nautilus, the only remaining, if rather distantly related, ectocochleate cephalopod suggest as possible reasons the ability to remain aerobically active, albeit intermittently, at very low oxygen tensions and the ability to migrate vertically in and out of such zones at low cost. With the progressive oxygenation of the oceans shallow water hypoxic environments largely disappeared, trapping the ammonites and their vulnerable planktonic young stages between the depth limits imposed by their buoyancy mechanism and the high oxygen tension environments where they were exposed to faster and more economical predators and competitors.