The evolution of flexible behavioral repertoires in cephalopod molluscs.

Cephalopods are a large and ancient group of marine animals with complex brains. Forms extant today are equipped with brains, sensors, and effectors that allow them not to just exist beside modern vertebrates as predators and prey; they compete fiercely with marine vertebrates at every scale from small crustaceans to sperm whales. We review the evolution of this group's brains, learning ability and complex behavior. We outline evidence that although competition with vertebrates has left a deep impression on the brains and behavior of cephalopods, the original reorganization of their complex brains from their molluscan ancestors might have been forged in ancient seas millions of years before the advent of bony fishes.