Cretaceous Antarctic bird skull elucidates early avian ecological diversity

Abstract

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^1-5, a foot-propelled diver from the latest Cretaceous (69.2-68.4 million years ago)⁶ of Antarctica with controversial phylogenetic affinities^2,7-10. Initially recovered by phylogenetic analyses as a stem anatid (ducks and closely related species)^1,2,11, Vegavis has since been recovered as a stem member of Anseriformes (waterfowl)^7-9, or outside Aves altogether¹⁰. Here we report a new, nearly complete skull of Vegavis that provides new insight into its feeding ecology and exhibits morphologies that support placement among waterfowl within crown-group birds. Vegavis has an avian beak (absence of teeth and reduced maxilla) and brain shape (hyperinflated cerebrum and 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 that of any other known anseriform but like that of other extant birds that capture prey underwater (for example, grebes and loons). The Cretaceous occurrence of Vegavis, with a feeding ecology unique among known Galloanserae (waterfowl and landfowl), is further indication that the earliest anseriform divergences were marked by evolutionary experiments unrepresented in the extant diversity^3,11-13.