Long-standing controversy1,2,3,4,5,6,7,8,9 surrounds the question of whether living bird lineages emerged after non-avian dinosaur extinction at the Cretaceous/Tertiary (K/T) boundary1,6 or whether these lineages coexisted with other dinosaurs and passed through this mass extinction event2,3,4,5,7,8,9. Inferences from biogeography4,8 and molecular sequence data2,3,5,9 (but see ref. 10) project major avian lineages deep into the Cretaceous period, implying their ‘mass survival’3 at the K/T boundary. By contrast, it has been argued that the fossil record refutes this hypothesis, placing a ‘big bang’ of avian radiation only after the end of the Cretaceous1,6. However, other fossil data—fragmentary bones referred to extant bird lineages11,12,13—have been considered inconclusive1,6,14. These data have never been subjected to phylogenetic analysis. Here we identify a rare, partial skeleton from the Maastrichtian of Antarctica15 as the first Cretaceous fossil definitively placed within the extant bird radiation. Several phylogenetic analyses supported by independent histological data indicate that a new species, Vegavis iaai, is a part of Anseriformes (waterfowl) and is most closely related to Anatidae, which includes true ducks. A minimum of five divergences within Aves before the K/T boundary are inferred from the placement of Vegavis; at least duck, chicken and ratite bird relatives were coextant with non-avian dinosaurs.
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We thank Museo de La Plata for permission to CT scan and sample MLP 93-I-3-1 for histological analysis; M. Fox for repreparation of the fossil; M. Reguero, S. Marenssi and E. Olivero for stratigraphic information; T. Rowe and J. Humphries of UTCT lab for assistance with CT imaging; R. Edwards for photographs; A. Viñas for line drawings; B. Creisler for consultation on species name validity; and M. Norell for comments on the manuscript. Support for this project from an NSF Office of Polar Programs grant to J.A.C., the AMNH Division of Paleontology and Yale University is gratefully acknowledged.
This file contains the following sections: I. Photograph and volume renderings using CT data, highlighting the bone and rendering the matrix semi-transparent to elements preserved within the other half of the Vegavis iaai concretion (MLP 93-I-3-1). II. Photograph of the latex peel of the primary block of the Vegavis iaai concretion (MLP 93-I-3-1) prior to preparation. III. Characters able to be evaluated for Vegavis of the analyzed datasets and the states present in that taxon (entries take the form "character number: character state"). IV. Measurements of the Vegavis iaai holotype specimen (MLP 93-I-3-1) and additional differential diagnosis from Presbyornithidae. V. Details of the provenience of the Vegavis iaai holotype specimen. The file also contains further information concerning the CT data, and additional references.