Phylogeny: secrets in evolution

Invertebrates and vertebrates diverged from ancient Belemnoidea about 380 million years ago. The evolution of complex cognitive abilities in octopi, following this event, was likely driven by competition with early teleosts (bony fish) and reptiles (Hochner et al, 2006). Octopi belong to the coleoid sub-class (along with cuttlefish and squid) as part of the cephalopod group within the Mollusca phylum. Octopi share many cognitive behaviors (via convergent evolution) with vertebratescephalopod phylogeny

(Hanlon and Messenger, 1996)

Convergent evolution of the mechanisms for advanced cognition in cephalopods and vertebrates has been reported by many researchers. The system of memory matrices that develop in the octopus brain is similar to the structure and function the mammalian hippocampus (Young et al, 1991). The matrix network is likely to have diverged from closely related decapods, such as cuttlefish and squids, which have a more simplistic brain structure (Young et al, 1991). Organization in neuron networks in motor, sensory, and cognitive (learning and memory) systems are the directly comparable between octopi and vertebrates in that they are all similarly characterized by synaptic plasticity (Young et al, 1991).

Personality

Development of personality from temperament in octopi (see Ontogeny) is speculated to be analogous to the process in humans and other vertebrates (Sinn et al, 2001). Not only are octopus categories of temperament similar to those of vertebrates, but the patterns and manner in which temperament ratios are altered throughout life are similar as well (Yamazaki et al, 2002). In this way, octopus personality traits demonstrate convergent evolution with vertebrates.

Environmental factors that may have influenced the evolution of an individual temperament may include high post-hatching population density, resulting competition with conspecifics or siblings - forcing each juvenile octopus to find its own personality niche (Sinn et al, 2001; Mather and Anderson, 1993).

Play

Between vertebrates and invertebrates, the development of play behavior is more likely to be convergent rather than homologous (Kuba et al, 2006; Olivera et al, 2010). Play in invertebrates developed independently of vertebrate development of play behavior. The last common ancestor of invertebrates and vertebrates did not have the advanced cognitive capacity to possess play as a behavior. Play behavior in the past has been limited to vertebrates, animals closer to humans, but recently studies have been growing to show play behavior accessible to invertebrates, particularly octopi, as well (Mather et al, 2008).