Tarsometatarsal morphological variations of penguins (Aves, Sphenisciformes) in the stratigraphic sequence of the Pisco Formation (Miocene-Pliocene), Peru

The morphological variation presents in the penguin tarsometatarsi from Pisco Formation (Miocene-Pliocene) from Peru assigned to Spheniscus Brisson, 1760 is analyzed. Metrics and geometric techniques to quantify the diversity present in each of the nine sites localities at the south-central coast were applied. A comparative description of Spheniscus and its Miocene morphologically closest genus Palaeospheniscus Moreno and Mercerat, 1891 is also provided. They together constitute the penguin avifauna of the Miocene of Peru. The results allow us to recognize that the intra-specific diversity is at the same level of variation than the inter-specific one. At least five species of Spheniscus are hereby recognized: Spheniscus urbinai Stucchi 2002, S. megaramphus Stucchi, Urbina and Giraldo 2003, S.muizoni Göhlich 2007 and two innominated species. Each one of these species transgresses the boundaries between the localities, being represented in more than one locality. It was not possible to distinguish S. chilensis Emslie and Guerra Correa, 2003 from its tarsometatarso. The presence of six species in this unit could be related to the establishment of cold water and the advent of favorable conditions for diversification.