Skull shape analysis and diet of South American fossil penguins

TAMBUSSI, C. & ACOSTA HOSPITALECHE, C.

Quillán, France

Congreso; 6th. International Meeting of the Society of Avian Paleontology and Evolution; 2004

The form and function of the skull of Recent and fossil genera of available Spheniscidae are analyzed so that the possible dietary behaviors might be inferred for extinct penguins. Skull and mandible shapes were compared using the Procrustean method Resistant-Fit Theta-Rho-Analysis (RFTRA). Procrustes methods allow the analysis of morphology through the superimposition of one morphology onto another using landmarks. RFTRA (software made by R. Chapman 1989) was developed to identify and measure the homologous regions of change in shape by establishing congruence among those that have not changed. 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 a second specimen (currently under study) that undoubtedly corresponds to a new species and subfamily, different from that in which Paraptenodytes belongs. Comparisons between dorsal and lateral views of the skulls and mandibles were made. Fifteen landmarks of the skull and five of 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) using 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 analysis.  Even though the food of penguins is not well known, there is a relative wealth of knowledge supporting that Spheniscus + Eudyptes penguins specialise on fish and all other taxa are plankton-eating or fish and crustaceans-eating. We compared representative species of both ecomorphological groups with the available fossil materials to evaluate its feeding strategies. Penguins are the most abundant birds, indeed the most abundant aquatic tetrapods in Cenozoic marine sediments of South America. The results that arise from this study will be of singular importance in the reconstruction of those marine ecosystems.