IMPLICATIONS OF THE PROCELLARIIFORMES (AVES) FOSSIL RECORD FROM THE EOCENE OF ANTARCTICA

ACOSTA HOSPITALECHE, C.; GELFO, J.; REGUERO

Goa

Simposio; XII International Symposium on Antarctic Earth Science; 2015

Antarctic fossil avifauna is mainly represented by penguins. Thousands of isolated penguin bones and a few skeletons coming from West Antarctica Paleocene and Eocene levels, have been described. It is consistent with other austral marine records; penguins are gregarious birds that settle large reproductive colonies along the coasts today and likely made it in the past. It is translated in great accumulations of bone that are easily preserved due to their dense and compact nature. In contrast, a short list of non-penguin avian is known, including a single and doubtful Ratites and volant birds. Flightless birds fossil record includes Gaviiformes, Ciconiiformes, Procellariiformes, Gruiformes, Polyborinae, Pelagornithidae, and Anseriformes from Maastrichtian to Bartonian. Among waterbirds, record of Procellariiformes becomes particularly interesting since living species are almost exclusively pelagic birds mainly distributed across the Southern Hemisphere oceans. Procellariiformes is an order that includes four extant families with fossil representatives: Diomedeidae (albatrosses), Procellariidae (petrels, prions and shearwaters), Hydrobatidae (storm petrels), and, Pelecanoididae (diving petrels), besides the exclusively extinct Diomedeoididae with a substantial fossil record including several isolated bones and articulated skeletons from marine Oligocene deposits from Germany, France, Belgium, and Iran, and the early Miocene of Germany. Apparently, the middle Eocene Murunkus subitus of Uzbekistan would also belong to this family. Paleogene record of the group around the world is scarce. Presumptive procellariiforms from the late Paleocene of Asia and early Eocene of Europe are known through fragmentary remains but too incomplete for a reliable identification. Definite Procellariidae are represented by a distal tibiotarsus from the late Eocene of USA, a distal tibiotarsus of Argyrodyptes microtarsus from the late Eocene/early Oligocene of Argentina, a humerus of ?Larus? raemdonckii from the early Oligocene of Belgium, and the Antarctic material here described. Finally, the Diomedeidae are represented by an incomplete tarsometatarsus from the late Eocene of Antarctica, and an undescribed specimen of the late Oligocene of South Carolina. During the Neogene, remains became more abundant. Most of records belong to North America, but they are frequent also in South America, Australia, and Africa. The recent finding of several bones belonging to Procellariiformes coming from the Submeseta (lower Eocene) and La Meseta (middle Eocene) formations (Seymour Island, West Antarctica) motivated the present contribution. New material is here described, and the meaning of the Antarctic record of the group is discussed. The materials here studied come from three different levels. From Cucullaea I Allomember of La Meseta Formation (upper Ypresian) at DPV 6/84 locality, an ulna (MLP 91-II-4-6) of Procellariidae, and a tibiotarsus (MLP 90-I-20-11), a tarsometatarsus (MLP 88-I-1-5), a pedal phalanx (MLP 92-II-2-7), and a rostrum maxillare (MLP 88-I-1-6) of Diomedeidae were recovered. From outcrops of Submeseta II Allomember of Submeseta Formation (Bartonian) at IAA 4/12 locality, a coracoid (MLP 13-XI-28-51) of Procellaridae was collected, as well as from the Submeseta Allomember III of Submeseta Formation (upper Bartonian- Priabonian) at DPV 16/84 locality, a tibiotarsus (MLP 13-XI-28-50) and a tarsometatarsus (MLP 12-I-20-305) of Diomedeidae were found. Procellariidae would be represented in Antarctica at least by two different species. The ulna MLP 91-II-4-6 belonged to a bird a little larger than the Cape Petrel Daption capense and with no significant differences in its morphology, whereas the coracoid MLP 13-XI-28-51 that is highly weathered seems to match better to a larger bird. Diomedeidae are represented by isolated remains, all them smaller than the Black-browed Albatross Thalasserche melanophrys and similar in size to Daption capense. The tibiotarsus MLP 13-XI-28-50 has a shaft latero- medially curved with an oval section, a central and broad sulcus extensorius (the pons supratendinous area is broken), a condylus medialis cranially projected, a trochlea cartilaginis tibialis almost flat, and inconspicuous epicondyla lateralis and medialis. The tarsometatarsi (MLP 88-I-1-5 and MLP 12-I-20-305) have a shaft cranio- caudally compressed, both foramina vascularia proximalia located at the same level, a wide sulcus metatarsalis, and a divaricated and caudally projected trochlea metatarsi II. The pedal phalanx has a long cylindrical diaphysis with a rounded caput phalangis and a deep fovea ligamentaris collateralis. The rostrum maxillare MLP 88-I-1-6 is curved, with foramina vascularia well developed and sharp cristae tomialis. These remains reaffirm the presence of Procellariiformes in Antarctica during the Eocene. Previous Paleogene taxa of the group were found in European and North American fossil sites, even when the main distribution of extant species is in the Southern Hemisphere. Something similar happens with Gaviiformes, whose fossil record is abundant in Antarctica but they are exclusive habitants of the North Hemisphere today. The association of Sphenisciformes, Gaviiformes and Procellariformes in Antarctic levels is consistent with previous ideas about the austral origin of waterbirds. Around 60 Ma ago, the Paleocene - Eocene Thermal Maximum occasioned an important sea level rise. This global warming could have provided a good opportunity in order that offshore birds expand their habitat into the sea, occupying vacant niches. It could also be closely related to the appearance of an important penguin diversity in the Eocene.