SGER: Morphological Study of a Key Avian Fossil from Antarctica: New Data from X-Ray Computed Tomography and Histology

First definitive fossil evidence for part of the extant avian radiation in the
Cretaceous

A longstanding controversy surrounds whether living bird lineages emerged after
the extinction of non-avian dinosaurs at the Cretaceous/Tertiary (K/T)
boundary or whether these lineages coexisted with non-avian dinosaurs and
passed through this mass extinction event. While inferences from biogeography
and molecular sequence data have projected most major avian lineages into the
early Cretaceous, implying “mass survival” of these lineages at the K/T
boundary, the fossil record has been argued to refute this hypothesis, placing
a “big bang” of avian radiation only after the end of the Cretaceous. Other
fossil data, fragmentary bones referred to extant bird lineages have been
considered inconclusive. None were included in phylogenetic analyses.

We identified a partial skeleton from the Maastrichtian of Antarctica as the
first Cretaceous fossil definitively placed within the radiation of extant
birds. Multiple phylogenetic analyses supported by independent histological
data indicate a new species, Vegavis iaai, is closely related to true ducks
among waterfowl (Anseriformes). A minimum of five divergences prior to the K/T
boundary are inferred from placement of Vegavis: at least duck, chicken, and
ratite bird relatives were coextant with non-avian dinosaurs.