"Packard (1972) proposed that the evolution of the coleoid cephalopods was largely a response to competition and predation from vertebrates in the Mesozoic. While recent paleontological discoveries necessitate modifying this scenario, it remains true that the shell-less condition, streamlined body form, visual acuity, closed circulatory system, and denning, body patterning and other complex behaviors help octopuses avoid their teleostean predators and persist in shallow, nearshore environments. There is currently no experimental evidence that teleost-octopod competition is important in shallow marine communities. However, field studies suggest an inverse relationship between predatory fishes and octopus population density. Where predatory fishes are absent, in a semi-isolated marine lake in the Bahamas, octopuses are two orders of magnitude more abundant than in Caribbean coastal communities." (Quoted from paper)