ABSTRACT. – We apply the synthetic approach to the study of learning in the ancient cephalopod Nautilus pompilius, L. as a way of understanding how the complex brain and behaviors may have evolved in its more derived relatives, the coleoid cephalopods (octopuses, cuttlefish and squid), whose brains are heavily invested in learning and memory. Nautilus in all likelihood retains a more primitive cephalopod neural condition, whereas coleoid brains are among the most complex of all the invertebrates, containing the vertical and frontal lobe complexes dedicated to learning and memory processing. Nautilus is uniquely placed within this lineage for studies of the evolution and function of neural and behavioral complexity. Using a synthetic and comparative approach, we frame our studies with the natural history and ecology of these animals, as natural selection acts upon outcomes like behaviors. By identifying possible pressures and problems nautiluses face in their environment, we develop hypotheses about the kinds of cognitive abilities they may possess to solve them. Predictions are tested in the laboratory and the field using a multiprocedural approach (classical conditioning, operant conditioning, maze study, semi-naturalistic study, and field study). In this way, should characteristics of a complex behavior persist in all contexts, this supports the hypothesis that these abilities are a general feature of the animal, rather than a function of the particular task. We compare our results to those found in similar studies with coleoids to identify common, possibly ancient, characteristics of learning and memory found in both classes. Remarkably, nautiluses have demonstrated learning and memory capabilities far more complex than their relatively simple brain would predict. They are capable of rapid learning, long memory, and dynamic switching among tactics when solving complex problems. Despite lacking the dedicated neural structures of its more derived relatives, Nautilus performs well in a variety of cognitive tasks. Perhaps the antecedent of the vertical or frontal lobe may be present in the Nautilus CNS, and this is the focus of future neuroanatomical and electrophysiological experiment.