Taxonomic diversity of Eocene Antarctic penguins: a changing picture
Eocene Antarctic penguins, at least 10 species in six genera, are known only from the La Meseta Formation, Seymour Island, Antarctic Peninsula. They are most numerous (in terms of individuals, body sizes and taxa) in Late Eocene strata. Specimens from three species and phylogenetic analysis presented in this work shed new light on the systematics and evolution of Antarctic Sphenisciformes. The earliest reported bones of giant penguins from the genus Anthropornis set the conservative estimate of its divergence time at c. 53 Ma (Early Eocene). They also document the oldest known appearance of quite a high diversity of Sphenisciformes; altogether, three morphotypes (differing in size) have been found within the same sampling locality. A newly described, relatively small and intriguingly elongated, tarsometatarsus from the Late Eocene of the La Meseta Formation, belonging to another genus of large-sized Antarctic penguins (Palaeeudyptes), suggests the possible existence of an unnamed species within this long-established genus. The phylogenetic analysis based on tarsometatarsal features shows that the relationship between ‘Archaeospheniscus’ wimani and three species of Delphinornis (all of them co-existed during the Late Eocene time period) does not appear to be close enough to justify merging them into a single genus (as was recently postulated).