Nautiloids are the sole surviving family of externally-shelled cephalopods that thrived in the tropical oceans 450–150 million years ago. However, in the intervening years their modern soft bodied relatives dumped the shell and developed complex central nervous systems; which makes Nautilus ideally suited to discover the `evolutionary pathways that led to the development of the complex coleoid [soft bodied cephalopod] brains' say Robyn Crook and Jennifer Basil. Knowing that the simple Nautilus brain lacks the structures required for memory in more sophisticated cephalopods, Crook and Basil decided to test the living fossil's memory(p. 1992).
Training Nautilus pompilus to associate the smell of food with a blue light, the cephalopods eventually learned to respond to a flash of blue light by extending their tentacles. Then the scientists tested the cephalopods memories with a flash of light 3 min, 30 min, 1 h, 6 h, 12 h and 24 h after training. Amazingly, Nautilus remembered their training for up to an hour before the memory was lost, but then the memory returned 6 h later, lasting up to 24 h. Nautilus has both short and long term memory, just like modern cephalopods, despite lacking the same brain structures.
Crook and Basil are optimistic that the unsophisticated Nautilus brain could teach us how modern cephalopod brains evolved.