EVOLUTION AND BIOGEOGRAPHY OF PALEOGENE WEDDELLIAN PENGUINS (AVES: SPHENISCIFORMES) OF THE JAMES ROSS BASIN, ANTARCTICA

ACOSTA HOSPITALECHE, C .; REGUERO, M.

Edinburgh

Simposio; International Symposium on Antarctic Earth Sciences; 2011

Seymour Island Paleogene sequence (Cross Valley and La Meseta formations) has the longest fossil records of basal sphenisciforms, with occurrences ranging from the late Paleocene to late Eocene. A recent phylogenetic analysis of Sphenisciformes, combining morphological and molecular data, places the Weddellian penguin distantly and basally related to the extant penguin radiation (crown clade: Spheniscidae). Crossvallia unienwillia remains the oldest stem record of the Weddellian sphenisciforms and provides a calibration for the basal sphenisciforms divergence at 55-56 Ma (Thanetian, Bahía Pingüino Allomember, Cross Valley Formation). The earliest record of penguins in La Meseta Formation is in the Ypresian Acantilados Allomember, deposited at 52.4 and 54.3 Ma based on 87/86Sr dates. The first significant radiation of the Weddellian sphenisciforms took place in the Lutetian Cucullaea I Allomember with 8 sympatric species. This middle Eocene diversity supports several separate dispersals to lower latitudes: Australia (late Eocene, paleolatitude ~ 33°S), New Zealand (late Eocene/early Oligocene, paleolatitude ~ 45°S), Argentina (middle Eocene, paleolatitude ~ 54°S), Chile (middle to late Eocene, paleolatitude ~ 52°S), and Peru (middle to late Eocene, paleolatitude ~14°S) regions during greenhouse earth conditions. Palaeeudyptes is a key taxon with biogeographic significance, is the most widespread Weddellian penguin genus in the Southern Hemisphere during the Eocene and Oligocene. The FAD of Palaeeudyptes gunnari is located within the Ypresian Campamento Allomember (La Meseta Formation). The highest diversity of Weddellian penguins is documented in the Anthropornis nordenskjoeldi Biozone within the Priabonian Submeseta Allomember, and this unit was deposited at 34.2 Ma based on 87/86Sr dates. Sphenisciforms of Anthropornis nordenskjoeldi Biozone provide the major taxonomic and body size diversity with 10 to 14 species co-occurring sympatrically. Discrepancies in the number of recognized species are fundamentally based on the recognition of Archaeospheniscus lopdelli, Palaeeudyptes antarctica and the two species of Tonniornis in the Anthropornis nordenskjoeldi Biozone.