Definitive fossil evidence for the extant avian radiation in the Cretaceous

Abstract

Long-standing controversy surrounds the question of whether living bird lineages emerged after non-avian dinosaur extinction at the Cretaceous/Tertiary (K/T) boundary or whether these lineages coexisted with other dinosaurs and passed through this mass extinction event. Inferences from biogeography and molecular sequence data (but see ref. 10) project major avian lineages deep into the Cretaceous period, implying their 'mass survival' 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 Cretaceous. However, other fossil data--fragmentary bones referred to extant bird lineages--have been considered inconclusive. These data have never been subjected to phylogenetic analysis. Here we identify a rare, partial skeleton from the Maastrichtian of Antarctica 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.

Darwin's dilemma: the realities of the Cambrian ‘explosion’

“…Zhang et al 2003a) reinforce earlier conclusions that the radiation of the 'modern' birds was very largely a latest Cretaceous (e.g. Clarke et al 2005) or Early Tertiary affair, and in any event a genuinely explosive event (e.g. Poe & Chubb 2004).…”

Exceptional avian herbivores: multiple transitions toward herbivory in the bird order Anseriformes and its correlation with body mass

“…3; Livezey 1997; Clarke et al. 2005), establishes a definitively duck‐shaped bill early in the history of Anseriformes in support of the duck‐to‐goose hypothesis.…”

Multiple nuclear genes and retroposons support vicariance and dispersal of the palaeognaths, and an Early Cretaceous origin of modern birds

“…Node ages were estimated with the lognormal relaxed clock method in BEAST v. 1.6.2 [34], and were compared with relaxed clock estimates with correlated and uncorrelated rates in MCMCTREE [35]. To calibrate molecular clocks we used seven fossil anchor points: crocodile/bird split 243-251 Ma [36], alligator/ caiman split 66-71 Ma [36], emu/cassowary split 25-35 Ma [37], magpie goose/greater white-fronted goose split 66-68 Ma [38], penguin/petrel split 60-62 Ma [39], hummingbird/swift split 47-49 Ma with an upper limit of 53 Ma [12] and jacana/painted snipe split 30-32 Ma [40]. A uniform prior was placed on the origin of modern birds from 67 to 133 Ma for the relaxed clock methods.…”