Giants from Antarctica: the fossil record of penguins, pelagorntihids, and other birds

ACOSTA HOSPITALECHE, C.

Virtual

Congreso; NENHC2021; 2021

NENHC

The fossil record of birds from Antarctica is concentrated in the James Ross Basin, located north-east of the Antarctic Peninsula. The oldest records correspond to the Maastrichtian neornithine birds Vegavis iaai (Anseriformes) and the controversial Polarornis gregorii, plus the recently described Antarcticavis capelambensis, a derived ornithuromorph that might correspond to an Ornithurae although its accurate assignment is not possible due to the poor preservation of the holotype. The Paleogene record is richer and represented mostly by penguins (Sphenisciformes), pseudo-toothed birds (Pelagornithidae), falcons (Falconiformes), and albatrosses (Procellariiformes), besides controversial records of ?Ratites?, Threskiornithidae, Charadriiformes, Gruiformes, and Phoenicopteriformes. Seymour (Marambio) Island constitutes the most fossiliferous area in Antarctica for fossil vertebrates, the record is heterogeneous for the different groups of birds; the most extensive collections correspond to penguins, whereas groups like the pelagornithids and procellariiforms, with more fragile skeletons, are less represented. Consequently, our knowledge about penguins is more exhaustive and complete. The record includes the Paleocene Crossvallia unienwillia, one of the oldest penguin around the world, and more than a dozen Eocene species represented by thousands of remains. Among them, several skeletons belonging to giant species assigned to Paleeudyptes klekowskii, P. gunnari, Anthropornis grandis, and A. nordenskjöldi, a dwarf penguin named Aprosdokitos mikrotero, and other skulls with extremely elongated and slender bills. Some of these Antarctic species have been recently recognized in the South American record, particularly in southern localities of Chile and Argentina, suggesting a broader distribution area during the Eocene. Other giants recorded in Antarctica belong to Pelagornithidae or pseudo-toothed birds, a group of seabirds characterized by the presence of denticles made of bony expansions of the maxilar and dentary bones which are accompanied by a hooked premaxilar. Antarctic pelagornithids reached more than 6 meters of wingspan and were probably excellent gliders. On the contrary, the primitive albatross Notoleptos giglii was a small bird in comparison with the living representatives of the group. It shares the Antarctic coasts and the aerial space with the giant pseudo-toothed birds during the Eocene times. Paleogene appears to have been an optimal time for the development of seabirds in these high latitutes