Form and function of the skull of Recent and fossil genera of available Spheniscidae are analysed in order to infer possible dietary behaviors for extinct penguins.Skull and mandible shapes were compared using the Resistant-Fit Theta-Rho-Analysis (RFTRA) Procrustean method. Due to the availability and quality of the material, this study was based on six living species belonging to five genera (Spheniscus, Eudyptula, Eudyptes, Pygoscelis, and Aptenodytes) and two Miocene species: Paraptenodytes antarticus (Moreno and Mercerat, 1891) and Madrynornis mirandus Acosta Hospitaleche, Tambussi, Donato & Cozzuol. Seventeen landmark from the skull and five from the mandible were chosen, including homologous and geometrical points. Morphological similarities among RFTRA distances are depicted using the resulting dendrograms for UPGMA (unweighted pair-group method using arithmetic average) cluster analysis. This shape analysis allows the assessment of similarities and differences in the skulls and jaws of penguins within a more comprehensive ecomorphological and phylogenetic framework. Even though penguin diet is not well known, enough data supports the conclusion that Spheniscus + Eudyptes penguins specialize on fish and all other taxa are plankton-feeders or fish and crustacean-feeders. We compared representative species of both ecomorphological groups with the available fossil material to evaluate their feeding strategies. Penguins are the most abundant birds, indeed the most abundant aquatic tetrapods, in Cenozoic marine sediments of South America. The results arising from this study will be of singular importance in the reconstruction of those marine ecosystems.