If “primates of the seas” immediately triggers fuzzy thoughts of brine shrimp, think again: cephalopods have recently stolen the spotlight in experiments investigating the “ecology of intelligence” with their displays of tool-use behavior [3][14]. Tool use, a form of “innovation” that exists under the umbrella of animal intelligence suggested by Kummer and Goodall, falls squarely within the repertoire of some octopuses observed near the Indonesian coast [4]. The convergent evolution of complex behaviors is nothing new – tool use, for instance, also occurs in New Caldeonian crows; tool use combined with tentacles, however, presents an entirely new story [26].

Figure 1. Animal phylogeny or family tree, diagramming the relationships among phyla of living animals. The ancestors of all present-day animals probably were soft-bodied marine forms, such as the placozoa. (After L. Margulis and K. V. Schwartz, “The Animal Kingdom” Teachers' Guide, Wards Natural Science, Rochester, New York, 1987) Source:

Phylogenetically speaking, phyla Mollusca and Chordata appear relatively distant from each other (Figure 1). Although noted similarities exist or have existed developmentally, prompting Sillman’s claim that “as good a case can be made for the molluscan cephalopod as the ancestor of the vertebrate as for the echinoderm,” others attribute the similarities to homoplasy (independently-evolved traits) rather than homology (derived traits) [25]. In this respect, the evolutionary distance between octopuses and humans serves only to emphasize the unexpectedness of the shared behavior; convergent evolution in particularly remote groups provides an interesting perspective on the selective pressures needed to produce such similarities [11].

Ancestors more closely resembling the chambered nautilus first appeared during the Cambrian era and eventually lost their hard outer shells, which was an initial step towards the emergence of developments considered as the foundations of intelligence [1]. Faced with the pressure of vertebrate competition, over time this group of derived relatives began to collect other major characteristics correlated with the capacity for complex behavior, including the evolution of a central brain, high brain to body weight ratio, and sophisticated sensory systems, such as the development of the camera eye in octopi [2]. With this collection of homoplastic traits behind it, the tool-use behavior of Amphioctopus marginatus becomes a little less confounding.