LATE CRETACEOUS CROWN BIRD FROM ANTARCTICA ELUCIDATES AVIAN ECOLOGICAL DIVERSITY ACROSS K-PG EXTINCTION EVENT

Fossils representing Cretaceous lineages of crown clade birds (Aves) are exceptionally rare but are crucial to elucidating major ecological shifts across early avian divergences. Among the earliest known putative crown birds is Vegavis iaai, a foot-propelled diver from the latest Cretaceous (69.2–68.4 Ma) of Antarctica with controversial phylogenetic affinities. Initially recovered by phylogenetic analyses as a stem anatid (ducks and closely related species), Vegavis has since been recovered as a stem member of Anseriformes (waterfowl) or outside Aves altogether. Here we report a new, nearly complete skull of Vegavis recovered from the Late Cretaceous López de Bertodano Formation on Vega Island, James Ross Basin, Antarctic Peninsula. This new skull provides novel insight to the feeding ecology of Vegavis and exhibits anatomy supporting placement among waterfowl within crown group birds. Vegavis has an avian beak (absence of teeth, reduced maxilla) and brain shape (hyper-inflated cerebrum, ventrally shifted optic lobes). The temporal fossa is well excavated and expansive, indicating that this bird had hypertrophied jaw musculature. The beak is narrow and pointed, and the mandible lacks retroarticular processes. Together, these features comprise a feeding apparatus unlike any other known waterfowl but like other extant birds that capture prey underwater (e.g., grebes, loons). Our phylogenetic analysis recovers Vegavis as a close relative to Conflicto, a wading anseriform from the earliest Paleocene of Antarctica, highlighting James Ross Basin as potentially the only known locality to record turnover within crown birds across the K-Pg extinction event.