The age of the crown group of passerine birds and its evolutionary significance – molecular calibrations versus the fossil record

Based on calibrations of molecular phylogenies and biogeographic considerations, it has been argued that the basal divergences of crown group Passeriformes occurred in the late Cretaceous, following the break-up of eastern Gondwana. Some implications of this hypothesis have, however, not yet been adequately addressed. In particular, a Cretaceous divergence of crown group passerines would imply an unprecedented evolutionary stasis for more than 80 million years in one of the most species-rich group of endothermic vertebrates. The temporal distribution and phylogenetic affinities of northern hemispheric fossils further conflicts with current hypotheses on the historical biogeography of passerines, and is in better concordance with a Cenozoic divergence of crown group Passeriformes.