Definitive Evidence Of Terror Birds In The Eocene Of West Antarctica

ACOSTA HOSPITALECHE, CAROLINA; GELFO J. N.; GARCÍA-LÓPEZ, D. A.; IRAZOQUI, F.; REGUERO, M.A.,

Congreso; 10th SCAR Open Science Conference; 2022

NATIONAL CENTRE FOR POLAR AND OCEAN RESEARCH

Phorusrhacids, also called “terror birds”, are a completely extinct group of terrestrialCariamiformes that constituted the predominant predators during the South AmericanCenozoic. Their long hind limbs, large skulls, and especially their sharp and curved beak andclaws, highlight their hunting skills. Cretaceous and Paleogene Antarctic remains previouslyreferred to Phorusrhacidae have been reassigned to other groups during the last decade.However, a ungual phalanx from the Ypresian levels (La Meseta Formation) inMarambio/Seymour Island (James Ross Basin), changes our conception about the continentalecosystems dynamic during the early Eocene. The specimen is represented by a laterallycompressed and curved ungual phalanx, with a neurovascular sulcus running along the entirelateral and medial surfaces, an articular facet sub-triangular and dorsoventrally elongated, anda rounded flexor tubercle. The outline and asymmetry of the articular facets and the greaterdepth of the neurovascular sulcus on the medial facies, allow its preliminar assignment to aright digit II. Phorusrhacids, positioned as top predators in continental Cenozoic ecosystemsand without any living analog, shared their giant sizes with flightless forms (e.g., ratites) andpowerful curved talons with raptors birds (e.g., falcons), groups already recorded in the Eoceneof Seymour Island. Phorusrhacidae represents, however, a guild hitherto unknown toAntarctica. The specimen here described belonged to a terrestrial hunting bird, a giantcarnivorous form that fulfilled the role of top predators apparently not occupied by landmammals in the Paleogene Antarctic communities.