A recent taxonomic review of the Otariidae, based on morphometric techniques applied to skulls, revealed a number of specimens with cranial morphology divergent from typical otariid species. The specimen considered in this paper was a large adult male otariid with cranial morphology most similar to the California sea lion, Zalophus californianus, but differing from it in significantly greater condylobasal length and rostral and palatal structure. Discriminant function analyses were applied to compare the cranial morphology of the anomalous specimen with those of 7 otariid taxa: the Steller sea lion, Eumetopias jubatus; the southern sea lion, Otaria byronia; the California sea lion, Z. californianus californianus; the Galapagos sea lion, Z. c. wollebaeki; and the presumed-extinct Japanese sea lion, Z. c. japonicus. Results suggest that the aberrant skull was that of a hybrid between Z. californianus and O. byronia.